Article

The function of zebra stripes

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  • Institute for Disease Modeling
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Abstract

Despite over a century of interest, the function of zebra stripes has never been examined systematically. Here we match variation in striping of equid species and subspecies to geographic range overlap of environmental variables in multifactor models controlling for phylogeny to simultaneously test the five major explanations for this infamous colouration. For subspecies, there are significant associations between our proxy for tabanid biting fly annoyance and most striping measures (facial and neck stripe number, flank and rump striping, leg stripe intensity and shadow striping), and between belly stripe number and tsetse fly distribution, several of which are replicated at the species level. Conversely, there is no consistent support for camouflage, predator avoidance, heat management or social interaction hypotheses. Susceptibility to ectoparasite attack is discussed in relation to short coat hair, disease transmission and blood loss. A solution to the riddle of zebra stripes, discussed by Wallace and Darwin, is at hand.

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... In ectoparasites, host choice can be affected by several characteristics such as for instance host chemical cues (Dallas and Foré 2013) or morphological characteristics (Caro et al. 2014). The parasite's individual experience (Vantaux et al. 2014) and the abiotic environment such as the season of the year can also play a role (Burkett-Cadena et al. 2012). ...
... Increasing evidence in both lab and wild parasite populations suggests plasticity in host choice in ectoparasites. For instance, it has been shown that host morphology and physiology influence host choice (Caro et al. 2014;Christe et al. 2007) as well as the parasite's previous feeding experience and its microbiome (Benelli 2020;Takken and Verhulst 2013 ...
... Several other characteristics might affect parasite success once physical contact has been established. For instance, attachment and feeding success in ticks and other ectoparasites may be influenced by host integumentary properties such as for instance skin thickness, feather/fur density and length, or the level of keratinization and vascularization (Caro et al. 2014;Marufu et al. 2011). Thus, hosts with a weaker integumentary layout might be more sensitive to parasites thus partially explaining individual differences in host quality. ...
... Although the arguments go back many decades, there is a vigorous current debate in which two groups of authors (Caro et al. 2014;Caro and Stankowich 2015;Larison et al. 2015aLarison et al. , 2015bCaro 2016) are trying to explain the evolution of zebra stripes by relating, throughout their range in Africa, the degree to which they are striped to a range of independent variables and from this, to draw some conclusions about the function of the stripes. A third group of authors Blaho et al. 2012Blaho et al. , 2013 investigated the sensory preferences of tabanid flies to stripes, spots and a range of odours, from which they have drawn a number of conclusions about the advantages to zebras of being striped, as a means of avoiding the nuisance of biting flies. ...
... A recent analysis by Caro et al. (2014) sets out to examine the relationship between the intensity of striping of zebras and other equids, and a number of independent variables, including those that might represent each in turn of the major hypotheses. Their analysis leads them to conclude that stripes have evolved as a mechanism to deter biting flies, an explanation first tested by Waage (1981), for tsetse flies only. ...
... Their analysis leads them to conclude that stripes have evolved as a mechanism to deter biting flies, an explanation first tested by Waage (1981), for tsetse flies only. At the same time as Caro et al. (2014) were examining data from Africa, another group Egri et al. 2012), studying the behaviour of tabanid flies in response to differently coloured artificial surfaces, concluded that black and white stripes were a deterrent to tabanids, and that this would confer advantages for zebras. Thus, coming at the problem from two completely different angles, these two groups of authors converged on the same conclusion, namely that zebra's stripes deter biting flies. ...
Article
The temperatures of black and white stripes on two zebras and a zebra hide were measured, throughout separate sunny days in Kenya. There is a 12–15oC difference between living zebras’ stripe temperatures throughout the middle seven daytime hours. The hide temperatures reach 16oC higher than the living zebras. Like all equids, zebras sweat to keep cool. Movement of sweat away from the skin is accelerated by the recently discovered surfactant equid protein latherin, a vital component of cooling in racehorses. Latherin decreases the surface tension of the sweat, facilitating evaporative cooling at the hair tips. We suggest that the abrupt temperature difference between the stripes causes chaotic air movement above the hair surface, thus enhancing evaporative heat dissipation. This cooling mechanism explains the lower temperatures of living zebra stripes than those of the inanimate hide. We observed that the black stripes can be separately erected, while the white remain flat. This may further refine the mechanism. There is an ongoing debate about the function of zebra stripes, recently focussed on the fact that stripes deter biting flies. The data and observations in this paper suggest that the primary function of the stripes may be thermoregulation and a secondary benefit, fly-deterrence.
... These stripes are usually located vertically on the neck and body, and they are effective in hiding zebras from predators as well as an inhibitory agent against biting flies. Specifications and descriptions of their conditions are as follows: They have a body length of 210-300 cm with a tail long 38-75 cm, 110-160 cm shoulder height, and weigh 175-450 kg [48]. The zebra is a heavy animal whose long and slender legs help the animal run at high speeds if necessary. ...
... The zebras' first strategy against predators is to escape in a zigzag motion pattern. However, sometimes by gathering, they try to confuse or frighten the predator [48]. ...
... In the second phase, simulations of the zebra's defense strategy against predator attacks are employed to update the position of population members of ZOA in the search space. The main predators of zebras are lions; however, they are threatened by cheetahs, leopards, wild dogs, brown hyenas, VOLUME 10, 2022 and spotted hyenas [48]. Crocodiles are another predator of zebras when they approach water [52]. ...
Article
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In this paper, a new bio-inspired metaheuristic algorithm called Zebra Optimization Algorithm (ZOA) is developed; its fundamental inspiration is the behavior of zebras in nature. ZOA simulates the foraging behavior of zebras and their defense strategy against predators’ attacks. The ZOA steps are described and then mathematically modeled. ZOA performance in optimization is evaluated on sixty-eight benchmark functions, including unimodal, high-dimensional multimodal, fixed-dimensional multimodal, CEC2015, and CEC2017. The results obtained from ZOA are compared with the performance of nine well-known algorithms. The simulation results show that ZOA can solve optimization problems by creating a suitable balance between exploration and exploitation and has a superior performance compared to nine competitor algorithms. ZOA’s ability to solve real-world problems has been tested on four engineering design problems, namely, tension/compression spring, welded beam, speed reducer, and pressure vessel. The optimization results show that ZOA is an effective optimizer in determining the values of the design variables of these problems compared to the nine competitor algorithms.
... Instead, there is an emerging consensus among biologists that the primary function of contrasting black and white stripes on the three species of zebras is to thwart attack from tabanids, and possibly glossinids, stomoxys and other biting muscoids based on laboratory and field experiments with striped materials [3,[9][10][11][12] and on comparative evidence [13]. In Africa where zebras live, tabanids carry diseases fatal to zebras including trypanosomiasis, equine infectious anemia, African horse sickness and equine influenza [14] and zebras are particularly susceptible to infection because their thin pelage allows biting flies to probe successfully with their mouthparts [13]. ...
... Instead, there is an emerging consensus among biologists that the primary function of contrasting black and white stripes on the three species of zebras is to thwart attack from tabanids, and possibly glossinids, stomoxys and other biting muscoids based on laboratory and field experiments with striped materials [3,[9][10][11][12] and on comparative evidence [13]. In Africa where zebras live, tabanids carry diseases fatal to zebras including trypanosomiasis, equine infectious anemia, African horse sickness and equine influenza [14] and zebras are particularly susceptible to infection because their thin pelage allows biting flies to probe successfully with their mouthparts [13]. The exact mechanism by which stripes prevent flies from obtaining a blood meal is less well understood, however. ...
... Compared to horses, flies approached zebras more quickly in terms of speed (median 13 Focusing to the 0.5 s period prior to actually contacting equids' coats, we noticed that tabanids approaching zebras failed to decelerate in a controlled fashion towards the end of their flight trajectories whereas they steadily decelerated before landing or touching horse pelage (t = 3.30; df = 61.3; p = 0.0016 taking individual fly into account; Fig 3). ...
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Averting attack by biting flies is increasingly regarded as the evolutionary driver of zebra stripes, although the precise mechanism by which stripes ameliorate attack by ectoparasites is unknown. We examined the behaviour of tabanids (horse flies) in the vicinity of captive plains zebras and uniformly coloured domestic horses living on a horse farm in Britain. Observations showed that fewer tabanids landed on zebras than on horses per unit time, although rates of tabanid circling around or briefly touching zebra and horse pelage did not differ. In an experiment in which horses sequentially wore cloth coats of different colours, those wearing a striped pattern suffered far lower rates of tabanid touching and landing on coats than the same horses wearing black or white, yet there were no differences in attack rates to their naked heads. In separate, detailed video analyses, tabanids approached zebras faster and failed to decelerate before contacting zebras, and proportionately more tabanids simply touched rather than landed on zebra pelage in comparison to horses. Taken together, these findings indicate that, up close, striped surfaces prevented flies from making a controlled landing but did not influence tabanid behaviour at a distance. To counteract flies, zebras swished their tails and ran away from fly nuisance whereas horses showed higher rates of skin twitching. As a consequence of zebras’ striping, very few tabanids successfully landed on zebras and, as a result of zebras’ changeable behaviour, few stayed a long time, or probed for blood.
... Our finding that stripe width did not alter fly repulsion also addresses proposed explanations for the variation in stripe width between different parts of the zebra body. In all zebra species, stripes are the narrowest on the face and legs 17,41 . This has been suggested to align with the anti-parasite function of zebra stripes, as flies will often take flight from vegetation and cruise close to the ground, encountering the legs or face of a grazing zebra before other parts of the body [41][42][43] . ...
... In all zebra species, stripes are the narrowest on the face and legs 17,41 . This has been suggested to align with the anti-parasite function of zebra stripes, as flies will often take flight from vegetation and cruise close to the ground, encountering the legs or face of a grazing zebra before other parts of the body [41][42][43] . But if narrower stripes are not better at deflecting biting flies, why are stripes narrowest in these regions of the body? ...
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The best-supported hypothesis for why zebras have stripes is that stripes repel biting flies. While this effect is well-established, the mechanism behind it remains elusive. Myriad hypotheses have been suggested, but few experiments have helped narrow the field of possible explanations. In addition, the complex visual features of real zebra pelage and the natural range of stripe widths have been largely left out of experimental designs. In paired-choice field experiments in a Kenyan savannah, we found that hungry Stomoxys flies released in an enclosure strongly preferred to land on uniform tan impala pelts over striped zebra pelts but exhibited no preference between the pelts of the zebra species with the widest stripes and the narrowest stripes. Our findings confirm that zebra stripes repel biting flies under naturalistic conditions and do so at close range (suggesting that several of the mechanisms hypothesized to operate at a distance are unnecessary for the fly-repulsion effect) but indicate that interspecific variation in stripe width is associated with selection pressures other than biting flies.
... Both findings contradict theory 9 mentioned above. According to Caro et al. 47 , Caro and Stankowich 48 and Caro 6 , the most important selection factor in the evolution of zebra stripes is the defence against tabanids, which results support theory 7. Kojima et al. 49 showed that black cows painted with white stripes imitating zebra stripes minimally attract blood-sucking stable flies (Stomoxys calcitrans), horn flies (Haematobia irritans) and tabanids (Tabanus sapporoensis). This observation also supports theory 7. Currently, the most thoroughly proven evolutionary advantage of zebra stripes and other striped/spotted coat patterns is the visual unattractiveness to biting flies, especially horseflies and tsetse flies 6,26,27,[31][32][33]40,41,49 . ...
... How do our results relate to previous studies showing that horseflies prefer warmer temperatures, because it helps them evade host responses? It is an observational and experimental fact that horseflies prefer sunlit homogeneous dark hosts against sunlit hosts with bright or heterogeneous (striped/spotted) coat patterns 6,[32][33][34][35]40,41,47,54 . Tabanids avoid striped/spotted hosts, and usually do not land to seek for blood vessels on dark stripes/spots despite of their higher temperature in sunshine. ...
Article
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Multiple hypotheses have been proposed for possible functions of zebra stripes. The most thoroughly experimentally supported advantage of zebra stripes is their visual unattractiveness to horseflies (tabanids) and tsetse flies. We propose here a plausible hypothesis why biting horseflies avoid host animals with striped pelages: in sunshine the temperature gradients of the skin above the slightly warmer blood vessels are difficult to distinguish from the temperature gradients induced by the hairs at the borderlines of warmer black and cooler white stripes. To test this hypothesis, we performed a field experiment with tabanids walking on a host-imitating grey test target with vessel-mimicking thin black stripes which were slightly warmer than their grey surroundings in sunshine, while under shady conditions both areas had practically the same temperature as demonstrated by thermography. We found that horseflies spend more time walking on thin black stripes than surrounding grey areas as expected by chance, but only when the substrate is sunlit. This is because the black stripes are warmer than the surrounding grey areas in the sun, but not in the shade. This is consistent with the flies’ well-documented attraction to warmer temperatures and provides indirect support for the proposed hypothesis. The frequent false vessel locations at the numerous black–white borderlines, the subsequent painful bitings with unsuccessful blood-sucking attempts and the host’s fly-repellent reactions enhance considerably the chance that horseflies cannot evade host responses and are swatted by them. To eliminate this risk, a good evolutionary strategy was the avoidance of striped (and spotted) host animals.
... Little is known about the precise cues used by horseflies to visually segment their scene into host versus background and how this may feed into their in-flight decisions (but see [22][23][24]). However, it remains likely that at distances greater than 2 m from a zebra, black and white stripes fall below the resolving power of the tabanid eye (based on an estimated ommatidial acceptance angle (Δρ) of 1°(MJ How 2019, unpublished data) and an average stripe width of 35 mm [25]; figure 1c i ). Tabanids seeking a bloodmeal from a zebra will initially be attracted to a grey host from a distance because the angular spatial frequency of the stripes will be higher than the cut-off angular spatial frequency of the modulation transfer function of the flies' visual system (determined by Δρ). ...
... Before concluding, we want to emphasize that stripes are only one way by which zebras reduce successful probing for blood by biting flies. Others include behavioural means including frequent swishing of tails and running away from tabanid annoyance [13] and zebra skin odour deterring tsetse flies from landing [32], suggesting that there are severe selection pressures for African Equidae to avoid biting fly attack [25]. ...
Article
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Of all hypotheses advanced for why zebras have stripes, avoidance of biting fly attack receives by far the most support, yet the mechanisms by which stripes thwart landings are not yet understood. A logical and popular hypothesis is that stripes interfere with optic flow patterns needed by flying insects to execute controlled landings. This could occur through disrupting the radial symmetry of optic flow via the aperture effect (i.e. generation of false motion cues by straight edges), or through spatio-temporal aliasing (i.e. misregistration of repeated features) of evenly spaced stripes. By recording and reconstructing tabanid fly behaviour around horses wearing differently patterned rugs, we could tease out these hypotheses using realistic target stimuli. We found that flies avoided landing on, flew faster near, and did not approach as close to striped and checked rugs compared to grey. Our observations that flies avoided checked patterns in a similar way to stripes refutes the hypothesis that stripes disrupt optic flow via the aperture effect, which critically demands parallel striped patterns. Our data narrow the menu of fly-equid visual interactions that form the basis for the extraordinary colouration of zebras.
... Zebras constitute important non-preferred hosts of tsetse flies [17][18][19]. Previous studies have argued that the striped coats of zebra might play a role in their avoidance by tsetse flies [24,25]. However, the allomonal basis for this avoidance is not understood. ...
... Previous research has shown that zebras, although present in tsetse habitat, are usually avoided by these flies [17][18][19]. A previously proposed hypothesis for this avoidance suggests that the polarization effects of the striped pelage of zebras is the driving component of the observed avoidance [24]. However, the stripes of this ungulate is visible to tsetse flies only at a distance of about 5-10 m and beyond this distance, zebras appear uniformly grey to these flies [36]. ...
Article
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Background: African trypanosomosis, primarily transmitted by tsetse flies, remains a serious public health and economic challenge in sub-Saharan Africa. Interventions employing natural repellents from non-preferred hosts of tsetse flies represent a promising management approach. Although zebras have been identified as non-preferred hosts of tsetse flies, the basis for this repellency is poorly understood. We hypothesized that zebra skin odors contribute to their avoidance by tsetse flies. Methodology/principal findings: We evaluated the effect of crude zebra skin odors on catches of wild savannah tsetse flies (Glossina pallidipes Austen, 1903) using unbaited Ngu traps compared to the traps baited with two known tsetse fly management chemicals; a repellent blend derived from waterbuck odor, WRC (comprising geranylacetone, guaiacol, pentanoic acid and δ-octalactone), and an attractant comprising cow urine and acetone, in a series of Latin square-designed experiments. Coupled gas chromatography-electroantennographic detection (GC/EAD) and GC-mass spectrometry (GC/MS) analyses of zebra skin odors identified seven electrophysiologically-active components; 6-methyl-5-hepten-2-one, acetophenone, geranylacetone, heptanal, octanal, nonanal and decanal, which were tested in blends and singly for repellency to tsetse flies when combined with Ngu traps baited with cow urine and acetone in field trials. The crude zebra skin odors and a seven-component blend of the EAD-active components, formulated in their natural ratio of occurrence in zebra skin odor, significantly reduced catches of G. pallidipesby 66.7% and 48.9% respectively, and compared favorably with the repellency of WRC (58.1%- 59.2%). Repellency of the seven-component blend was attributed to the presence of the three ketones 6-methyl-5-hepten-2-one, acetophenone and geranylacetone, which when in a blend caused a 62.7% reduction in trap catch of G. pallidipes. Conclusions/significance: Our findings reveal fundamental insights into tsetse fly ecology and the allomonal effect of zebra skin odor, and potential integration of the three-component ketone blend into the management toolkit for tsetse and African trypanosomosis control.
... Pigmentation patterns such as the stripes of zebras, patches of giraffes, and petal spots of many flowers have fascinated biologists and mathematicians for centuries. These patterns often function as visual cues in mate choice and interspecies communications, adapting organisms to their environments and potentially contributing to reproductive isolation among species [1][2][3][4]. Unlike previously well-characterized pigmentation patterns in insect wings and some flowers that are spatially organized by coinciding expression domains of regulatory genes that serve as position-specific signals [5][6][7][8][9][10][11], our understanding of how dispersed pigmentation patterns emerge in concert with or entirely untethered from such positional information is primarily theoretical [12][13][14][15]. The reaction-diffusion (RD) model, initially proposed by Turing [16] and then independently developed and elaborated by Gierer and Meinhardt [17][18][19] and further extended by others [12,[20][21][22], postulates that local activation of pattern differentiation factors combined with long-range inhibition of the activity of those factors can produce defined, regularly spaced, tissue-level spot and stripe patterns. ...
Article
Many organisms exhibit visually striking spotted or striped pigmentation patterns. Developmental models predict that such spatial patterns can form when a local autocatalytic feedback loop and a long-range inhibitory feedback loop interact. At its simplest, this self-organizing network only requires one self-activating activator that also activates a repressor, which inhibits the activator and diffuses to neighboring cells. However, the molecular activators and inhibitors fully fitting this versatile model remain elusive in pigmentation systems. Here, we characterize an R2R3-MYB activator and an R3-MYB repressor in monkeyflowers (Mimulus). Through experimental perturbation and mathematical modeling, we demonstrate that the properties of these two proteins correspond to an activator-inhibitor pair in a two-component, reaction-diffusion system, explaining the formation of dispersed anthocyanin spots in monkeyflower petals. Notably, disrupting this pattern impacts pollinator visitation. Thus, subtle changes in simple activator-inhibitor systems are likely essential contributors to the evolution of the remarkable diversity of pigmentation patterns in flowers.
... In those reports, various genetic factors that contribute to pigmentary phenotypic differences in larval and adult bodies have been identified, including numerous pleiotropic factors, the sex-linked gene tan, the HOX genes abd-A and Abd-B, and Spatzle3 [10][11][12]. Although the formation mechanisms underlying the formation of stripe patterns of a variety of organisms have been studied, including zebrafish, zebra, rodents, and insects [13][14][15][16], the mechanism underlying the regulation of the metabolites for producing multiple stripe and spot patterns is largely unknown. ...
Article
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The complex stripes and patterns of insects play key roles in behavior and ecology. However, the fine-scale regulation mechanisms underlying pigment formation and morphological divergence remain largely unelucidated. Here we demonstrated that imaginal disc growth factor (IDGF) maintains cuticle structure and controls melanization in spot pattern formation of Bombyx mori. Moreover, our knockout experiments showed that IDGF is suggested to impact the expression levels of the ecdysone inducible transcription factor E75A and pleiotropic factors apt-like and Toll8/spz3, to further control the melanin metabolism. Furthermore, the untargeted metabolomics analyses revealed that BmIDGF significantly affected critical metabolites involved in phenylalanine, beta-alanine, purine, and tyrosine metabolism pathways. Our findings highlighted not only the universal function of IDGF to the maintenance of normal cuticle structure but also an underexplored space in the gene function affecting melanin formation. Therefore, this study furthers our understanding of insect pigment metabolism and melanin pattern polymorphisms.
... In addition, the secretion of hippopotami (called red sweat) is an oily substance which protects against transdermal water loss 18 . Despite being blood hosts, hippopotami have no apparent protection method from insect biting, such as a long pelage or a coat patterning like zebras [19][20][21][22] . Therefore, we predicted that this exudate may provide protection against mosquitoes. ...
Article
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Mosquito legs have a unique highly water-repellent surface structure. While being beneficial to mosquitoes, the water-repellence of the tarsi enhances the wettability of hydrophobic substances such as oils. This high wettability induces strong attraction forces on a mosquito’s legs (up to 87% of the mosquito’s weight) towards the oil. We studied the landing behaviour of mosquitoes on oil-coated surfaces and observed that the mosquito contact time was reduced compared to that on hydrophilic-liquid-coated surfaces, suggesting that the oil coating induces an escape response. The observed escape behaviour occurred consistently with several hydrophobic liquids, including silicone oil, which is used globally in personal care products. As the repellent effect is similar to multiple hydrophobic substances, it is likely to be mechanically stimulated owing to the physical properties of the hydrophobic liquids and not due to chemical interactions. On human skin, the contact time was sufficiently short to prevent mosquitoes from starting to blood-feed. The secretion of Hippopotamus amphibius, which has physical properties similar to those of low-viscosity silicone oil, also triggered an escape response, suggesting that it acts as a natural mosquito repellent. Our results are beneficial to develop new, safe, and effective mosquito-repellent technologies.
... The wing patterns of butterflies have proven to be a uniquely tractable system for research at the interface of evolution and development (Nijhout, 1991;Beldade and Brakefield, 2002;Jiggins, 2017). Unlike the stripes of zebras (Jonathan, 1977;Caro et al., 2014) or the networks of spots found on the coats of leopards (Allen et al., 2011), butterfly color patterns are composed of a limited number of homologous characters that are comparable to better known systems of homologs, such as the bones of pentadactyl limbs (Wagner, 2014). A theoretical archetype known as the nymphalid groundplan (NGP) (Nijhout, 1991) allows for the identification of these homologous characters within and across species, making it possible to precisely describe the results of experiments designed to interfere with pattern development (Monteiro et al., 2006;Martin and Reed, 2014;Mazo-Vargas et al., 2017), and identify large-scale trends in pattern evolution (Monteiro, 2008). ...
Article
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The nymphalid groundplan (NGP) has proven to be extraordinarily useful in the study of butterfly color patterns because it allows for the identification of homologous elements across species. It has long been thought that the NGP is broadly applicable to all Lepidoptera, implying that the characters which make-up butterfly color patterns are homologous to those found in the moths. However, this conjecture remains mostly untested. We analyzed the wing patterns of the hyper-diverse arctiid tiger moths, which are represented worldwide by approximately 11,000 species, and found that the color patterns of these animals can be parsed into a limited toolkit of homologous characters. Some of the pattern elements identified, such as the basal and central symmetry system, are present on the NGP, but their morphology is often quite different from what is seen in the butterflies. The border ocelli of the NGP appear to be absent altogether in the Arctiidae, and conversely, two distal pattern element we term the “van Bemmelen” and “terminal” bands are present in the color patterns of many arctiids, but are not represented on the NGP. In light of the observed differences, we derive a new theoretical groundplan based on the original NGP that we refer to as the “arctiid archetype.” This model provides a comprehensive framework for understanding how the wing patterns of these animals develop, and yields novel insight into their evolutionary history.
... A case in point is the fact that we only discovered the reason for zebras having stripes in 2014. 1 White and black stripes are certainly not good camouflage in the African savannah. It turns out that tsetse flies and horse flies (the vector of various equid diseases) avoid black-and-white striped surfaces. ...
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... A great number of hypotheses have been proposed to explain the diversity in patterns and colours in the animal kingdom, and biologists continue to debate the adaptive significance of pigmentation and markings. For example, the function of the black and white stripes of zebra has long been debated, with many popular hypotheses not withstanding analysis 1 . Some phenomena have received a lot of attention: it is well-established that camouflage plays an important role in disguising animals both from predator and prey 2 . ...
Article
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There are many hypotheses explaining the diversity of colours and patterns found in nature, but they are often difficult to examine empirically. Recent studies show the dark upperside of gliding birds’ wings could reduce drag by decreasing the density of surrounding air. It may therefore be expected that species with darker wings have less efficient morphology than their paler counterparts. I conducted an analysis of the Larinae (gulls), which exhibit extreme variation in wing (mantle and wingtip) melanization, to test whether wing loading is a predictor of wing darkness. I found that, for each standard deviation increase in wing loading, mantle darkness is predicted to increase by 1.2 shades on the Kodak grey scale. Wing loading is also positively related to the proportion of black on wingtips. Furthermore, heavier species have lower aspect ratio wings, suggesting that dark wings have evolved to improve the trade-off between maneuverability and long distance flight. An analysis of gull wing colour and loading indicates an evolutionary trade-off between dark wings and flight capability.
... Among these hypotheses, several studies now indicate that preventing attack by biting flies is the function of zebra stripes. For example, Caro et al. [2] showed that a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 the phylogenetic distribution of body stripes is associated with tabanid fly distributions at the species and subspecies level. Additionally, Egri et al. [3] experimentally showed that tabanids avoid landing on black-and-white surfaces, such as trays, boards, balls, and buckets. ...
Article
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Experimental and comparative studies suggest that the striped coats of zebras can prevent biting fly attacks. Biting flies are serious pests of livestock that cause economic losses in animal production. We hypothesized that cows painted with black and white stripes on their body could avoid biting fly attacks and show fewer fly-repelling behaviors. Six Japanese Black cows were assigned to treatments using a 3 × 3 Latin-square design. The treatments were black-and-white painted stripes, black painted stripes, and no stripes (all-black body surface). Recorded fly-repelling behaviors were head throw, ear beat, leg stamp, skin twitch, and tail flick. Photo images of the right side of each cow were taken using a commercial digital camera after every observation and biting flies on the body and each leg were counted from the photo images. Here we show that the numbers of biting flies on Japanese Black cows painted with black-and-white stripes were significantly lower than those on non-painted cows and cows painted only with black stripes. The frequencies of fly-repelling behaviors in cows painted with black-and-white stripes were also lower than those in the non-painted and black-striped cows. These results thus suggest that painting black-and-white stripes on livestock such as cattle can prevent biting fly attacks and provide an alternative method of defending livestock against biting flies without using pesticides in animal production, thereby proposing a solution for the problem of pesticide resistance in the environment.
... On the selected effects (SE) version of Wright's account (e.g., Millikan 1989, Neander 1991, requirement (a) is spelled out in terms of natural selection. For example, "the function of zebra stripes is to avoid biting flies" (Izzo et al. 2014) means that zebras have stripes because they ward off biting flies -there was selection for zebra stripes in the past because they conferred an advantage in environments with biting flies -and that avoiding biting flies is a consequence of zebra's having stripes. ...
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I examine the use of the term function in Aldo Leopold's land ethic, invoked as: 1) the healthy functioning of the land community, which is dependent on 2) the maintenance of the characteristic functions of populations that are parts of the land community. The latter can be understood as referring to interactions between species that are the products of coevolution (such as parasite-host, predator-prey, etc.), and thus, in terms of the “selected effect” account of function. The performance of these functions under certain conditions maintain what Leopold took to be the healthy functioning of a land community.
... A higher predisposition to develop cutaneous habronematidosis has been suggested for grey or diluted coat equines (Pusterla et al., 2003;Caro et al., 2014), such as the Andalusian donkey. However, neither breed, sex nor age different predilections seems to exist in horses (Reed et al., 2009), and no statistically proven information has been reported for donkeys up to the date. ...
Thesis
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Tools allowing to understand the evolution of donkey populations in time, the future trends that these populations describe, and the factors conditioning such trends, become invaluably critical when aiming at preserving and later recovering such populations from their endangerment status. Basing on the characteristic lack of information regarding the genealogical background of donkey populations and taking a particular breed as an example, it is possible to infer a model to assess the genetic and demographical structure of other international endangered donkey populations. Then, we can plot selection strategies to implement once such populations have reached the sufficient number of individuals, and are supported by solid enough structures. Microsatellite-tested pedigree analyses were carried out to study the genetic diversity, structure and historical evolution of the Andalusian donkey breed since the 1980s. Despite mean inbreeding was low, highly inbred animals were present. The effective population size based on individual inbreeding rate was about half when based on individual coancestry rate. Nei's distances and equivalent subpopulations number indicated differentiated farms in a highly structured population. Although genetic diversity loss since the founder generations could be considered small, intraherd breeding policies and the excessive contribution of few ancestors to the gene pool could lead to narrower pedigree bottlenecks. Long average generation intervals could be considered when reducing inbreeding. Wright's fixation statistics indicated slight inbreeding between farms. Pedigree shallowness suggested applying new breeding strategies to reliably estimate descriptive parameters and control the negative effects of inbreeding, which could indeed, mean the key to preserve such valuable animal resources avoiding the extinction they potentially head towards. Diversity studies render especially important in donkeys as they reveal the genetic background in the populations and the starting point for making decisions on whether to apply conservation or breeding plans in this functionally misallocated species. Once genetic diversity parameters are balanced, finding new niches for donkeys becomes potentially the most relevant aim to approach in the midterm future for the species. Selection strategies in donkeys are approached from three different perspectives; donkey-assisted therapy and therapeutic riding, fertility and disease resistance, not only as a way to widen the functional spectrum of opportunities of donkeys but also to lengthen their useful lives, and improve their life quality and welfare. Studying the specific genetic background behind functional traits enables quantifying the degree in which such features pass from jacks and jennies onto the new foal generations. As a genetic term, environment means all influences other than inherited factors. Controlling the environmental factors conditioning the expression of certain functional features help to build animal models shedding light in the genetic fraction involved in such functional traits. The functional performance of 300 microsatellite-assisted parentage tested donkeys was studied using REML and Gibbs sampling Bayesian methods for the obtention of genetic parameters and breeding values using BLUP methodology. The first functional niche for which donkeys may be well-suited is linked to their special psychological nature and physical characteristics as facilitators of learning processes and for the development of key life skills and confidence building for a wide spectrum of vulnerable people. Therapeutic riding and asinotherapy take advantage of the physical and psychological interaction between donkeys and patients given the potential application of donkey's characteristics and abilities for the treatment of specific human disorders. The selection of donkeys when the breeding criteria is their suitability for equine-assisted therapies was implemented following two different approaches; the selection for coping styles and cognitive processes and the selection for gaits and kinetics. Aiming at developing suitable models seeking the consolidation of equine assisted-therapy breeding criteria, we studied 29 factors that may potentially influence several cognitive processes in donkeys. These factors not only affect donkeys' short-term behaviour but may also determine their long-term cognitive skills from birth. Thus, animal behaviour becomes a useful tool to obtain past, present or predict information from the situation of a certain animal in a particular area. Operant conditioning and Qualitative Behavioural Assessment (QBA) synergism can provide valuable information about animals' extinction/learning and emotional status. All noncognitive animal inherent features significantly affected four variables (P<0.001), although some were not linearly correlated. On the other hand, the effect power of meteorological factors ranged from 7.9% for the birth season on learning (P<0.05) to 38.8% for birth moon phase on mood (P<0.001). Psychometric testing enables quantifying animal cognitive capabilities and their genetic background. Among these cognitive capabilities, the study of problem-solving coping styles achieves a special relevance as it brings together the need genetically select donkeys displaying a neutral reaction during training, given its implication with handler/rider safety and trainability. Heritabilities for coping style traits were moderate, 0.18 to 0.21. Phenotypic correlations between intensity and mood/emotion or response type were -0.21 and -0.25, respectively. Genetic correlations between the same variables were -0.46 and -0.53, respectively. Phenotypic and genetic correlations between mood/emotion and response type were 0.92 and 0.95, respectively. Principal components and Bayesian analyses were used to compute the variation in cognitive capabilities explained by 13 cognitive processes and their genetic parameters, respectively. Heritabilities ranged 0.06 to 0.38 suggesting the same patterns previously reported for humans and other animal species. By contrast, when considering the selection for therapeutic riding, gaits' heritability estimates ranged from 0.53 to 0.67 for walk and trot, respectively. Genetic correlations ranged from 0.28 to 0.42, for walk/trot and amble/trot, respectively. Our results suggest that gait genetic lines could be developed. Among other breeding criteria, disease resistance and reproduction offer two functional niches to consider given their relationship with donkey life quality and welfare. Breeding programs selecting for disease resistance could address food safety and quality issues in products such as donkey milk, and may be perceived to be more humane. Cutaneous habronematidosis (CH) is a highly prevalent parasitic seasonally recurrent skin disease causes distress and relapsing wounds to the animals. CH hypersensibility heritability was 0.0346. Genetic parameters and breeding values for functional traits enable planning strategies for endangered donkey breed preservation and breeding what may turn into a measure to improve animal welfare indirectly.Multiple births in equids are dangerous situations that compromise the life of the dam and offspring. However, embryo collection techniques take advantage of individuals whose multiple ovulations allow flushing more fertilized embryos from the oviduct. Heritabilities ranged from 0.18 to 0.24. Genetic and phenotypic correlations ranged from 0.496 to 0.846 and 0.206 to 0.607, respectively.
... Animal color patterns play critical roles in animal survival, adaptation, intra-and interspecific communication, and speciation (1)(2)(3)(4)(5)(6). Traditionally, and reasonably, biologists have used animal coloration as an important key to identification of a species (7,8). ...
Article
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Animals exhibit a fascinating variety of skin patterns, but mechanisms underlying this diversity remain largely unknown, particularly for complex and camouflaged colorations. A mathematical model predicts that intricate color patterns can be formed by “pattern blending” between simple motifs via hybridization. Here, I analyzed the skin patterns of 18,114 fish species and found strong mechanistic associations between camouflaged labyrinthine patterns and simple spot motifs, showing remarkable consistency with the pattern blending hypothesis. Genomic analyses confirmed that the coloring on multiple labyrinthine fish species has originated from pattern blending by hybridization, and phylogenetic comparative analyses have further substantiated the pattern blending hypothesis in multiple major fish lineages. These findings provide a plausible mechanistic explanation for the characteristic diversity of animal markings and suggest a novel evolutionary process of complex and camouflaged colorations by means of pattern blending.
... Recently, Horváth et al. [30] demonstrated that horseflies need polarization vision for host detection, because polarized light helps horseflies select sunlit dark host animals from the dark patches of the visual environment. However, the thorough studies of Caro et al. [64], Caro & Stankowich [65], Caro [25] and Melin et al. [66] showed that polarization of host-reflected light is not the only factor affecting horsefly behaviour during host detection. ...
Article
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Bodypainting is widespread in African, Australian and Papua New Guinean indigenous communities. Many bodypaintings use white or bright yellow/grey/beige stripes on brown skin. Where the majority of people using bodypainting presently live, blood-sucking horseflies are abundant, and they frequently attack the naked brown regions of the human body surface with the risk of transmitting the pathogens of dangerous diseases. Since horseflies are deterred by the black and white stripes of zebras, we hypothesized that white-striped paintings on dark brown human bodies have a similar effect. In a field experiment in Hungary, we tested this hypothesis. We show that the attractiveness to horseflies of a dark brown human body model significantly decreases, if it is painted with the white stripes that are used in bodypaintings. Our brown human model was 10 times more attractive to horseflies than the white-striped brown model, and a beige model, which was used as a control, attracted two times more horseflies than the striped brown model. Thus, white-striped bodypaintings, such as those used by African and Australian people, may serve to deter horseflies, which is an advantageous byproduct of these bodypaintings that could lead to reduced irritation and disease transmission by these blood-sucking insects.
... Of the various traits showing spatial specific differences in the skin, mammalian pigment patterns are one of the most fascinating, due to their visual accessibility, diversity, and obvious relevance from an adaptive perspective (1,2). The general appearance of pigment patterns allows a simple classification (3) as either stochastic, such as the variegated and patchy nature of a calico cat (4), or organized, as in regularly spaced stripes in a tabby cat (5,6), or the unique facial appearances that characterize closely related species of African monkeys (7). ...
Article
Mammalian periodic pigment patterns, such as spots and stripes, have long interested mathematicians and biologists because they arise from nonrandom developmental processes that are programmed to be spatially constrained, and can therefore be used as a model to understand how organized morphological structures develop. Despite such interest, the developmental and molecular processes underlying their formation remain poorly understood. Here, we argue that Arvicanthines, a clade of African rodents that naturally evolved a remarkable array of coat patterns, represent a tractable model system in which to dissect the mechanistic basis of pigment pattern formation. Indeed, we review recent insights into the process of stripe formation that were obtained using an Arvicanthine species, the African striped mouse (Rhabdomys pumilio), and discuss how these rodents can be used to probe deeply into our understanding of the factors that specify and implement positional information in the skin. By combining naturally evolved pigment pattern variation in rodents with classic and novel experimental approaches, we can substantially advance our understanding of the processes by which spatial patterns of cell differentiation are established during embryogenesis, a fundamental question in developmental biology. This article is protected by copyright. All rights reserved.
... Specifically for striped black and white patterns, known functions vary from crypsis (e.g. disruptive camouflage, countershading, etc.) to warning signals and can interfere with a predator's ability to attack a prey through a dazzling effect (Feltwell, 2016;Izzo et al., 2014;Stevens et al., 2008). Aside from aposematism, the complex M. histrionica egg color pattern may thus have alternative adaptive functions, and future studies should look into those in this species as well as in taxa with similar egg coloration such as Eurydema spp. ...
Thesis
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How can immobile life stages such as eggs protect themselves against physical and biological threats? One protective adaptation that has evolved to help them survive is egg coloration. In this thesis, I begin by reviewing the studies looking at the adaptive insect egg coloration and distinguish what is known based on scientific evidence versus untested hypotheses. I then move on to testing whether the eggs of the Harlequin cabbage bug are chemically defended, in an attempt to link glucosinolate sequestration to possible aposematic egg coloration. I argue that the nymphs are not only chemically defended, but also use tonic immobility as an alternative antipredation strategy until sufficient compound sequestration is achieved. Finally, I assess the selective pressures behind the evolution of egg color polymorphism in the Spined soldier bug. I demonstrate that frequency-dependent predation is necessary to select for approximately equal frequencies of the two main morphs observed in nature.
... It is now believed to be (in part) the result of an evolutionary advantage to avoid the biting of tsetse flies. Studies have shown that tsetse flies and other obligate blood-feeding flies, are less likely to land on black and white striped surfaces than on uniform ones (Caro et al., 2014). Blood-brain barrier Attempts to deliver drugs to the brain for treatment of sleeping sickness, using an anti-trypanosome dye named trypan-blue, led to the discovery of the blood brain barrier (Bentivoglio and Kristensson, 2014). ...
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Sleeping sickness is caused by a eukaryotic unicellular parasite known to infect wild animals, cattle, and humans. It causes a fatal disease that disrupts many rhythmic physiological processes, including daily rhythms of hormonal secretion, temperature regulation, and sleep, all of which are under circadian (24-h) control. In this review, we summarize research on sleeping sickness parasite biology and the impact it has on host health. We also consider the possible evolutionary advantages of sleep and circadian deregulation for the parasite.
... In insects, integumentary melanins also play an immunoprotective role, which has also been suggested in vertebrates (Mackintosh 2001), given that melanocytes participate in the skin immune response (Wankowicz-Kalinska et al. 2003). Additionally, some colorations confer antiparasitic protection in vertebrates by attracting fewer parasites (Blahó et al. 2013;Caro et al. 2014). Environments rich in ectoparasites may not only promote the evolution of external barriers but also the evolution of internal mechanisms of immune responses and behavioral adaptations (Owen et al. 2010). ...
Article
Melanin is the most widespread pigment in organisms. Melanin-based coloration has been repeatedly observed to be associated with the same traits and in the same direction in different vertebrate and insect species. However, whether any factors that are common to different taxa account for the repeated evolution of melanin-phenotype associations remains unclear. We propose to approach this question from the perspective of convergent and parallel evolution to clarify to what extent different species have evolved the same associations owing to a shared genetic basis and being subjected to similar selective pressures. Our current understanding of the genetic basis of melanin-phenotype associations allows for both convergent and parallel evolution, but this understanding is still limited. Further research is needed to clarify the generality and interdependencies of the different proposed mechanisms (supergenes, pleiotropy based on hormones or neural crest cells). The general ecological scenarios whereby melanin-based coloration is under selection, protection from UV radiation, thermoregulation in cold environments or as a signal of social status, offer a good opportunity to study how melanin-phenotype associations evolve. Reviewing these scenarios shows that some traits associated with melanin-based coloration might be selected together with coloration by also favoring adaptation, but that other associated traits might impede adaptation, which may be indicative of genetic constraints. We therefore encourage further research on the relative role of selection and genetic constraints in shaping multiple melanin-phenotype associations. Placed into a phylogenetic context, this will help clarify to what extent these associations result from convergent or parallel evolutionary processes and why melanin-phenotype associations are so common across the tree of life.
... Table 2 e.g. Waage, 1981;Gibson, 1992;Ruxton, 2002;Caro, et al., 2014;Horváth et al., 2018Sasaki 2001 , 5 Barrass 1960Brady & Shereni 1988 ...
Article
The role of zebra stripes is considered to be defensing from blood sucking by insects, such as tsetse flies and tabanid flies, those perform actively host-seeking flight. Aedes albopictus is opportunistically blood sucker, so, the reaction to zebra stripes may be different from such flies. Thus, we investigated the reaction of A. albopictus to the rugs of three color patterns, black, white, and zebra stripes. During the sunny days on August and September, 2019 with three different times in a day (morning, daytime, and evening), we counted the number of mosquitoes landed on the rugs on human decoy at a park in Tokyo. Significant difference (p<0.05) was found in the total number of mosquitoes landed on the three types of rugs, while no significant difference (p>0.05) was found in the numbers of mosquitoes landed on the rugs at each observation time. The number of A. albopictus which landed on the black-colored rug was two times more than that of a mosquito flying around the face of human decoy, while those on the rugs of white color and zebra stripes were a half and only 3% of those flying around the face of human decoy, respectively. The lured A. albopictus landed smoothly on the black rug, but the landings were not smooth on the zebra-striped rug. It was revealed that A. albopictus avoids zebra stripes as same as tsetse flies and tabanid flies.
... Specifically for striped black and white patterns, known functions vary from crypsis (e.g. disruptive camouflage, countershading, etc.) to warning signals and can interfere with a predator's ability to attack a prey through a dazzling effect (Stevens et al. 2008;Izzo et al. 2014;Feltwell 2016). Aside from aposematism, the complex M. histrionica egg color pattern may thus have alternative adaptive functions, and future studies should look into those in this species as well as in taxa with similar egg coloration such as Eurydema spp. ...
Article
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Antipredation strategies contribute to the lifetime reproductive success of organisms, particularly in more vulnerable life stages that look to survive until reproduction. In insects, eggs and larval stages are often immobile or unable to rapidly flee and hide from predators. Understanding what alternative antipredation strategies they use, but also how these change over development time, is required to fully appreciate how species adapt to biotic threats. Murgantia histrionica is a stink bug, conspicuously colored from egg to adult, known to sequester defensive glucosinolates from its cruciferous hosts as adults. We sought to assess whether this chemical defense is also present in its eggs and early nymphal instars and quantified how it fluctuates among life stages. In parallel, we looked at an alternative antipredation strategy, described for the first time in this species: tonic immobility (i.e., death feigning). We also qualitatively investigated ultraviolet reflectance in eggs and adults as a proxy of conspicuousness against UV-absorbing leaves. Our results show that the eggs are significantly more chemically defended than the first two but not third mobile life stages, yet compound concentrations do not statistically differ across nymphal instars. Tonic immobility is favored by hatchlings, but less so by subsequent instars. Eggs also had obvious ultraviolet reflectance, suggesting that they would contrast against a leaf substrate and, considering their chemical load, that they may be aposematic. We argue that there are two possible interpretations of our results. One is that, throughout ontogeny, tonic immobility is a useful defensive strategy until adequate chemical protection is achieved over an extended feeding period. The other is that both aposematism and tonic immobility are used by this species, but variation in strategy use throughout ontogeny is decoupled.
... The high contrast, conspicuous patterns seen on animals such as zebras have attracted a range of evolutionary explanations, including camouflage, thermoregulation, communication, and the avoidance of biting flies [1][2][3][4][5][6][7]. One hypothesis that has received attention in recent years is the 'motion dazzle' hypothesis, which proposes that these patterns may act to cause confusion when the animal is in motion, causing illusions in the visual system of the viewer that may lead to misjudgements of speed and direction [8]. ...
Article
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The motion dazzle hypothesis posits that high contrast geometric patterns can cause difficulties in tracking a moving target and has been argued to explain the patterning of animals such as zebras. Research to date has only tested a small number of patterns, offering equivocal support for the hypothesis. Here, we take a genetic programming approach to allow patterns to evolve based on their fitness (time taken to capture) and thus find the optimal strategy for providing protection when moving. Our ‘Dazzle Bug’ citizen science game tested over 1.5 million targets in a touch screen game at a popular visitor attraction. Surprisingly, we found that targets lost pattern elements during evolution and became closely background matching. Modelling results suggested that targets with lower motion energy were harder to catch. Our results indicate that low contrast, featureless targets offer the greatest protection against capture when in motion, challenging the motion dazzle hypothesis.
... Il a également été montré que le camouflage sert à la fois pour éloigner les prédateurs mais également les parasites (Caro et al, 2014). En milieu naturel la seiche a la possibilité de passer d'une texture lisse à rugueuse à l'aide des papilles rendant difficile l'adhésion d'organismes parasites sur la peau de son manteau. ...
Thesis
En France la seiche commune Sepia officinalis est élevée en eau claire alors qu’elle a évolué dans un environnement naturel où la turbidité de l’eau varie saisonnièrement et quotidiennement. Cette thèse tente de voir si l’élevage dans des conditions proches du milieu naturel (i.e turbides) ne permet pas d’améliorer les conditions de vie des seiches en laboratoire. Nous avons démontré que la préférence pour le milieu turbide est âge dépendante : les jeunes seiches préfèrent l’eau claire et les plus âgées l’eau turbide. Le comportement prédateur des seiches n’est pas modifié en milieu turbide sauf pour le groupe élevé en turbidité forte où le comportement prédateur est moins performant en eau turbide. Les seiches adaptent leur camouflage à la turbidité de l’eau de leur environnent. L’environnement d’élevage joue probablement sur la façon dont les seiches perçoivent la turbidité. La turbidité impacte également l’ensablement, un comportement défensif pourtant peu dépendant des stimuli visuels. Nous avons également montré un effet de l’expérience individuelle et du milieu d’élevage sur l’adaptation à la turbidité. A l’âge de 7 jours les seiches élevées dans une eau turbide développent des capacités visuelles supérieures en eau claire (sensibilité à la polarisation) et en eau turbide (contraste d’intensité). Nos résultats préliminaires semblent suggérer que la seiche utilise préférentiellement la modalité olfactive en eau turbide. La couleur de l’œuf, le site de ponte et le milieu d’élevage influencent les capacités visuelles de seiches juvéniles et conditionnent leur sensibilité et leur adaptation à la turbidité. Chez une espèce d’eau claire, Sepia pharaonis la turbidité influence les capacités visuelles mais les individus semblent limités dans les réponses adaptatives qu’ils peuvent produire pour se camoufler dans un milieu turbide. L’ensemble de nos résultats montrent que la turbidité du milieu, lorsqu’elle est modérée, est un élément d’enrichissement qui pourrait être utilisée afin d’améliorer les conditions d’élevage de la seiche commune.
... The physical characteristics of the skin and coat are important factors in the vulnerability of ungulates to flies (Caro et al. 2014, Kynkaanniemi et al. 2014, Scasta & Smith 2019. Bison spp. ...
Article
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Flies (Diptera) damage ungulates far beyond the injury of their bite wounds: they are vectors of diseases and cause ungulates to lose foraging opportunities due to avoidance behaviour. We can use the behavioural and physiological responses of bison Bison spp. (Artiodactyla: Bovidae), caribou/reindeer Rangifer tarandus (Artiodactyla: Cervidae), and moose/elk Alces alces (Artiodactyla: Cervidae) to assess the impacts of flies on these ungulates. Ungulates rely on morphological and physiological resistance to flies at low intensities of exposure. However, as fly exposure increases, ungulates begin to react with behavioural avoidance in addition to increasing their physiological response. Rangifer tarandus are highly sensitive to flies and respond quickly to their presence by avoidance behaviours that incur fitness costs through reduced body mass. Alces alces are less reactive to fly exposure, enduring the presence of flies and maintaining a low loss of fitness, sometimes dying from the cumulative effects of exposure. Bison spp. may use a facultative strategy that depends upon the prevalence of flies and associated diseases in their environment. Among these strategies, variables such as the type of fly bite, presence and degree of infection, and heritability of resistance affect individual host survival. Relationships between flies and ungulates can integrate multiple scales of organisation in the ecosystem to reflect system stability. Climate change is predicted to alter the species composition and seasonal phenology of flies and the associated effects of wounding and vector‐borne disease on ungulate populations that are central to the functions of Arctic and temperate ecosystems in the Northern Hemisphere. Ungulates resist flies initially by morphological barriers of skin and hair, and later by physiological processes of healing and immunity. The cost of repairing skin increases with damage to the body surface, but the costs of immune response vary widely with the fly and the associated diseases. Avoidance of flies reduces the uncertainty of responding to an infection but confers a cost in lost foraging opportunities. Rangifer tarandus (silhouettes on left with dashed line) avoid flies, while Alces alces (silhouette on right with solid line) do not avoid flies and live a mostly solitary life, leaving the Alces alces to rely on physical resistance followed by physiological response. Bison spp. (middle silhouettes) may use a facultative strategy in between the strategies of Rangifer tarandus and Alces alces, which depends upon the prevalence of flies in their environment.
... However, our results clearly demonstrate that there are no descending air streams above sunlit white stripes, and www.nature.com/scientificreports/ the assumed convective eddies, composed of a series of adjacent upwelling and downwelling air streams, do not form above sunlit zebra stripes. It is well known that zebra-striped coats do not attract tsetse flies 18,19 and horseflies 1,20 with respect to a homogeneous dark fur, and this is the most widely accepted hypothesis for zebra striping nowadays [21][22][23] . Cobb and Cobb 7 suggested that the air next to the zebras' skin may be sufficiently unstable to deter (biting) flies from landing. ...
Article
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There is a long-lasting debate about the possible functions of zebra stripes. According to one hypothesis, periodical convective air eddies form over sunlit zebra stripes which cool the body. However, the formation of such eddies has not been experimentally studied. Using schlieren imaging in the laboratory, we found: downwelling air streams do not form above the white stripes of light-heated smooth or hairy striped surfaces. The influence of stripes on the air stream formation (facilitating upwelling streams and hindering horizontal stream drift) is negligible higher than 1–2 cm above the surface. In calm weather, upwelling air streams might form above sunlit zebra stripes, however they are blown off by the weakest wind, or even by the slowest movement of the zebra. These results forcefully contradict the thermoregulation hypothesis involving air eddies.
... One of the difficulties with studying conspicuous coloration in this Class (Caro 2013) has been overcoming an informal consensus that black-and-white pelage is associated with noxious anal secretions (Macdonald et al. 2017;Fisher and Stankowich 2018). Nonetheless, we know this is not true: zebras (Equus spp.) are striped to avoid biting flies (Caro et al. 2014), giant pandas match their backgrounds (Caro et al. 2017a;Nokelainen et al. unpubl. ms.), and in those species that are aposematic, Norwegian lemmings' (Lemmus lemmus) contrasting pelage signals pugnacity (Andersson 2015), and the masks of slow lorises (Nycticebus spp.) advertise venomous bites (Nekaris et al. 2019) rather than noxiousness. ...
Article
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Aposematic coloration is traditionally considered to signal unpalatability or toxicity. In mammals, most research has focused on just one form of defense, namely noxious anal secretions, and its black‐and‐white advertisement as exemplified by skunks. The original formulation of aposematism, however, encompassed a broader range of morphological, physiological, and behavioral defenses, and there are many mammal species with black‐and‐white contrasting patterns that do not have noxious adaptations. Here, using Bayesian phylogenetic models and data from 1,726 terrestrial non‐volant mammals we find that two aspects of conspicuous coloration, black‐and‐white coloration patterns on the head and body, advertise defenses that are morphological (spines, large body size), behavioral (pugnacity), and physiological (anal secretions), as well as being involved with sexual signalling and environmental factors linked to crypsis. Within Carnivora, defensive anal secretions are associated with complex black‐and‐white head patterns and longitudinal black‐and‐white body striping; in primates larger‐bodied species exhibit irregular patches of black‐and‐white pelage; and in rodents, pugnacity is linked to sharp countershading and irregular blocks of white and black pelage. We show that black‐and‐white coloration in mammals is multifunctional, that it serves to warn predators of several defenses other than noxious anal secretions, and that aposematism in mammals is not restricted to carnivores. This article is protected by copyright. All rights reserved
... e function of zebras' stripe is hypothecated four categories: a cryptic form probably matching a woodland background and disrupting predatory attack, reducing thermal load, having a social function and avoiding biting y attack (e.g. Cloudsley-ompson, 1984;Kingdon, 1984;Mcleod, 1987;Morris, 1990;Louw, 1993;Ruxton, 2002;Ljeto et al., 2007;Stevens and Merilaita, 2009;Caro et al., 2014;How and Zanker, 2014;Larison et al., 2015;Ireland and Ruxton, 2017). Recently, the disrupting predatory attack theory is negated (Melin et al., 2016) and the reducing thermal load theory is also negated by Horváth et al., (2018). ...
Article
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The role of zebra stripes has so far been described in four categories: camouflage and visual disturbance, reduced body temperature rise, social function, and avoidance of blood-sucking insects. Although there are various studies that prove this, a few are from the viewpoint of entomology. Therefore, we verified whether zebra stripes would avoid blood-sucking flies by trapping method at Toga, Toyama, Japan, using the Nzi trap (with attractant) made black, white and zebra-patterned cotton cloth. As a result, the zebra-striped Nzi traps and white ones could not significantly (p<0.01) attract and capture Tabanus iyoensis than the black ones, and significant difference between the zebra-striped and white ones were not recognized (p>0.05).
... Allomonal volatile emissions may explain the absence in tsetse flies of bloodmeals from zebra [28] and waterbuck [13,29], both of which are present in Shimba Hills (Kenya Wildlife Service KWS 2021, www.kws.go.ke/content/shimba-hills-national-reserve, assessed on 3 November 2021). However, skin coloration patterns in zebra are believed to confuse tsetse flies and discourage vector attacks [30][31][32]. Even though we did not detect bloodmeals of zebra, waterbuck, and several other animal species (e.g., giraffe and monitor lizard) previously shown to be fed on by tsetse flies [3], bloodmeal host diversity in tsetse flies was high in Shimba Hills in comparison to reports from some similar ecologies, for example, the Kafue National Park Zambia and Hurungwe Game Reserve Zimbabwe [33]. ...
Article
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Trypanosomes are endemic and retard cattle health in Shimba Hills, Kenya. Wildlife in the area act as reservoirs of the parasites. However, wild animal species that harbor and expose cattle to tsetse-borne trypanosomes are not well known in Shimba Hills. Using xeno-monitoring surveillance to investigate wild animal reservoirs and sources of trypanosomes in Shimba Hills, we screened 696 trypanosome-infected and uninfected tsetse flies for vertebrate DNA using multiple-gene PCR-High Resolution Melting analysis and amplicon sequencing. Results revealed that tsetse flies fed on 13 mammalian species, preferentially Phacochoerus africanus (warthogs) (17.39%, 95% CI: 14.56–20.21) and Bos taurus (cattle) (11.35%, 95% CI: 8.99–13.71). Some tsetse flies showed positive cases of bloodmeals from multiple hosts (3.45%, 95% CI: 2.09–4.81), including warthog and cattle (0.57%, 95% CI: 0.01–1.14). Importantly, tsetse flies that took bloodmeals from warthog had significant risk of infections with Trypanosoma vivax (5.79%, 95% CI: 1.57–10.00), T. congolense (7.44%, 95% CI: 2.70–12.18), and T. brucei sl (2.48%, 95% CI: −0.33–5.29). These findings implicate warthogs as important reservoirs of tsetse-borne trypanosomes affecting cattle in Shimba Hills and provide valuable epidemiological insights to underpin the parasites targeted management in Nagana vector control programs in the area.
Article
Quaggas were beautiful pony-sized zebras in southern Africa that had fewer stripes on their bodies and legs, and a browner body coloration than other zebras. Indigenous people hunted quaggas, portrayed them in rock art, and told stories about them. Settlers used quaggas to pull wagons and to protect livestock against predators. Taken to Europe, they were admired, exhibited, harnessed to carriages, illustrated by famous artists and written about by scientists. Excessive hunting led to quaggas' extinction in the 1880s but DNA from museum specimens showed rebreeding was feasible and now zebras resembling quaggas live in their former habitats. This rebreeding is compared with other de-extinction and rewilding ventures and its appropriateness discussed against the backdrop of conservation challenges—including those facing other zebras. In an Anthropocene of species extinction, climate change and habitat loss which organisms and habitats should be saved, and should attempts be made to restore extinct species?
Book
Cambridge Core - Philosophy of Science - What Biological Functions Are and Why They Matter - by Justin Garson
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There are many hypotheses explaining the diversity of colours and patterns found in nature, but they are often difficult to examine empirically. Recent studies show the dark upperside of the wings of gliding birds could reduce drag by decreasing the density of surrounding air. It may therefore be expected that species with darker wings have less efficient wing morphology than their paler counterparts. I conducted a phylogenetic comparative analysis of the Larinae (gulls) to test whether wing loading is a predictor of wing darkness. I found that, for each standard deviation increase in wing loading, wing darkness is predicted to increase by 1.2 shades on the Kodak grey scale. Wing darkness is also negatively correlated with the distance from the equator of species’ breeding and resident ranges. Furthermore, heavier species have lower aspect ratio wings, suggesting that dark wings have evolved to improve the trade-off between maneuverability and long distance flight.
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Living in groups provides benefits but incurs costs such as attracting disease vectors. For example, synanthropic flies associate with human settlements, and higher fly densities increase pathogen transmission. We investigated whether such associations also exist in highly mobile non‐human primate groups (NHP). We studied flies in a group of wild sooty mangabeys (Cercocebus atys atys) and three communities of wild chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire. We observed markedly higher fly densities within both mangabey and chimpanzee groups. Using a mark‐recapture experiment, we showed that flies stayed with the sooty mangabey group for up to 12 days and for up to 1.3 km. We also tested mangabey associated flies for pathogens infecting mangabeys in this ecosystem, Bacillus cereus biovar anthracis (Bcbva), causing sylvatic anthrax, and Treponema pallidum pertenue, causing yaws. Flies contained treponemal (6/103) and Bcbva (7/103) DNA. We cultured Bcbva from all PCR‐positive flies, confirming bacterial viability and suggesting that this bacterium might be transmitted and disseminated by flies. Whole genome sequences of Bcbva isolates revealed a diversity of Bcbva, likely derived from several sources. We conclude that flies actively track mangabeys and carry infectious bacterial pathogens; these associations represent an understudied cost of sociality and potentially expose many social animals to a diversity of pathogens.
Chapter
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Debates concerning the units and levels of selection have persisted for over fifty years. One major question in this literature is whether units and levels of selection are genuine, in the sense that they are objective features of the world, or merely reflect the interests and goals of an observer. Scientists and philosophers have proposed a range of answers to this question. This Element introduces this literature and proposes a novel contribution. It defends a realist stance and offers a way of delineating genuine levels of selection by invoking the notion of a functional unit.
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The horses of Shackleford Banks, NC, United States are harassed by many species of biting flies. Apart from being a nuisance, their bites can lead to blood loss and transmit disease. As a result, these horses tend to avoid areas where fly abundances are high. Like other free-ranging horse populations, environmental factors such as low wind speeds and high temperatures increase fly loads per horse. Similarly, coat color matters since darker horses attract more flies than lighter ones, especially on hot sunny days. Many horse populations reduce per capita fly loads by living in large groups or by bunching tightly together. Shackleford horses do so, too, but also use wind speed differences among habitats to modulate fly numbers. By adopting a systematic pattern of moving between habitats such that they only visit a habitat when wind speed is high enough to keep fly harassment to a tolerable level, they can avoid being bitten while continuing to forage. Typically, they begin the day foraging on the salt marshes where fly abundance is inherently low and are lowered further by faint early morning breezes. Later in the morning, horses move to grassy patches (swales) when increasing wind speed reduces fly landings there to levels found on the marshes. Later still, when wind speeds peak, horses begin foraging among the sand dunes. At this point wind speeds are high enough so that horses using any habitat will be minimally harassed by flies, thus enabling them to freely choose where to feed based on which habitat meets particular dietary needs for protein, energy and nutrients on any particular day. Hence, Shackleford horses follow the breeze to solve a challenging dilemma of maintaining a high nutritional plane without succumbing to fly harassment. Other free-ranging horses populations appear to have a more limited “either-or” choice of “bite or be bitten,” thus limiting their decision-making options.
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The motion dazzle hypothesis posits that high contrast geometric patterns can cause difficulties in tracking a moving target, and has been argued to explain the patterning of animals such as zebras. Research to date has only tested a small number of patterns, offering equivocal support for the hypothesis. Here, we take a genetic programming approach to allow patterns to evolve based on their fitness (time taken to capture) and thus find the optimal strategy for providing protection when moving. Our “Dazzle Bug” citizen science game tested over 1.5 million targets in a touch screen game at a popular visitor attraction. Surprisingly, we found that targets lost pattern elements during evolution and became closely background matching. Modelling results suggested that targets with lower motion energy were harder to catch. Our results indicate that low contrast, featureless targets offer the greatest protection against capture when in motion, challenging the motion dazzle hypothesis.
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Animals display extensive diversity in motifs adorning their coat, yet these patterns have reproducible orientation and periodicity within species or groups. Morphological variation has been traditionally used to dissect the genetic basis of evolutionary change, while pattern conservation and stability in both mathematical and organismal models has served to identify core developmental events. Two patterning theories, namely instruction and self-organisation, emerged from this work. Combined, they provide an appealing explanation for how natural patterns form and evolve, but in vivo factors underlying these mechanisms remain elusive. By bridging developmental biology and mathematics, novel frameworks recently allowed breakthroughs in our understanding of pattern establishment, unveiling how patterning strategies combine in space and time, or the importance of tissue morphogenesis in generating positional information. Adding results from surveys of natural variation to these empirical-modelling dialogues improves model inference, analysis, and in vivo testing. In this evo-devo-numerical synthesis, mathematical models have to reproduce not only given stable patterns but also the dynamics of their emergence, and the extent of inter-species variation in these dynamics through minimal parameter change. This integrative approach can help in disentangling molecular, cellular and mechanical interaction during pattern establishment.
Chapter
Animals display a tremendous diversity of patterns – from pigmentation markings to segmented body parts, which result from the establishment of discrete domains within developing organs through the integration of positional information. How such pattern-forming processes underlie the apparent complexity and diversity of natural patterns has long puzzled mathematicians and developmental biologists alike. Here, attention is focused on the patterning of skin characters (i.e., pigments and cutaneous appendages) which historically have been studied in genetics and evolutionary biology, to summarize the current understanding of the source, molecular nature, and mode of action of positional molecules and thus, more generally, of the genetic and morphogenetic bases of the formation and evolution of natural patterns.
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Zebras’ stripes cannot protect them from predators, Darwin concluded, and current consensus tends to support his view 1,2 . In principle, stripes could support crypsis or aposematism, could dazzle, confuse or disrupt predators’ perception 3–8 , yet no such effects are manifest in predator-prey interactions 9–11 . Instead, narrow stripes covering zebras’ head, neck, limbs and flanks are an effective deterrent to tabanids ¹² , vectors for equine disease 13,14 . Accordingly, while other potential benefits, e.g., thermoregulation 15,16 and intraspecific communication ¹⁷ , cannot be excluded, zebra stripes likely evolved primarily to deter parasites 18–20 . Rump stripes, however, do not fit this, or any extant view. Typically horizontal and broader in sub-species with width variation, they are ill-suited to crypsis or parasite-deterrence ¹² and vary with hyaena threat ¹⁸ , perhaps shaped by an additional selective pressure. We observed that rump (and rear-flank) stripes remain highly conspicuous when viewed in motion or at distance, while other stripes do not. To study this striking effect, we filtered images of zebra to simulate acuity limitations in lion and hyaena photopic and mesopic vision. For mountain zebra and plains zebra without shadow striping, rump stripes were the most conspicuous image regions according to computational salience models, corroborated by human observers’ judgements of maximally attention-capturing image locations, which were strongly biased toward the rear. By hijacking exogenous attention mechanisms to force predator attention to the rear, salient rump stripes confer benefits to zebra, estimated here in pursuit simulations. Benefits of rump stripe salience may counteract anti-parasite benefits and costs of conspicuity to shape rump and shadow stripe variation. 1 Highlights Zebra stripes likely evolved to deter biting flies, but rump stripes are ill-suited to this. Rump-stripes remain highly conspicuous when viewed at distance or in motion. Computational models and human observers’ judge rump stripes are most salient stripes. Salient rump stripes drive predator attention to rear, hindering capture by predators. Observe this striking effect in moving zebra at: viscog.psychol.cam.ac.uk/resources-and-downloads
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Tim Caro introduces why zebras are striped.
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Mosquito host utilization is a key factor in the transmission of vector-borne pathogens given that it greatly influences host-vector contact rates. Blood-feeding patterns of mosquitoes are not random, as some mosquitoes feed on particular species and/or individuals more than expected by chance. Mosquitoes use a number of cues including visual, olfactory, acoustic, and thermal stimuli emitted by vertebrate hosts to locate and identify their blood meal sources. Thus, differences in the quality/intensity of the released cues may drive host selection by mosquitoes at both inter-and intra-specific levels. Such patterns of host selection by mosquitoes in space and time can be structured by factors related to mosquitoes (e.g. innate host preference, behavioural plasticity), to hosts (e.g. emission of host-seeking cues, host availability) or to both (e.g. pathogen infection). In this study, we review current evidence, from phenomena to mechanisms, of how these factors influence host utilization by mosquitoes. We also review the methodologies commonly used in this research field and identify the major challenges for future studies. To bridge the knowledge gaps, we propose improvements to strengthen traditional approaches and the use of a functional trait-based approach to infer mosquito host utilization in natural communities.
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Several hypotheses tried to explain the advantages of zebra stripes. According to the most recent explanation, since the borderlines of sunlit white and black stripes can hamper thermal vessel detection by blood-seeking female horseflies, striped host animals are unattractive to these parasites which prefer hosts with an homogeneous coat, on which the temperature gradients above blood vessels can be detected more easily. This hypothesis has been tested in a field experiment with horseflies walking on a grey barrel with thin black stripes which were slightly warmer than their grey surroundings in sunshine, while in shade both areas had practically the same temperature. To eliminate the multiple (optical and thermal) cues of this test target, we repeated this experiment with improved test surfaces: we attracted horseflies by water- or host-imitating homogeneous black test surfaces, beneath which a heatable wire ran. When heated, this invisible and mechanically impalpable wire imitated thermally the slightly warmer subsurface blood vessels, otherwise it was thermally imperceptible. We measured the times spent by landed and walking horseflies on the test surface parts with and without underlying heated or unheated wire. We found that walking female and male horseflies had no preference for any (wired or wireless) area of the water-imitating horizontal plane test surface on the ground, independent of the temperature (heated or unheated) of the underlying wire. These horseflies looked for water, rather than a host. On the other hand, in the case of host-imitating test surfaces, female horseflies preferred the thin surface regions above the wire only if it was heated and thus warmer than its surroundings. This behaviour can be explained exclusively with the higher temperature of the wire given the lack of other sensorial cues. Our results prove the thermal vessel recognition of female horseflies and support the idea that sunlit zebra stripes impede the thermal detection of a host‘s vessels by blood-seeking horseflies, the consequence of which is the visual (non-thermal) unattractiveness of zebras to horseflies.
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The diversity of mammalian coat colors, and their potential adaptive significance, have long fascinated scientists as well as the general public. The recent decades have seen substantial improvement in our understanding of their genetic bases and evolutionary relevance, revealing novel insights into the complex interplay of forces that influence these phenotypes. At the same time, many aspects remain poorly known, hampering a comprehensive understanding of these phenomena. Here we review the current state of this field and indicate topics that should be the focus of additional research. We devote particular attention to two aspects of mammalian pigmentation, melanism and pattern formation, highlighting recent advances and outstanding challenges, and proposing novel syntheses of available information. For both specific areas, and for pigmentation in general, we attempt to lay out recommendations for establishing novel model systems and integrated research programs that target the genetics and evolution of these phenotypes throughout the Mammalia. Expected final online publication date for the Annual Review of Animal Biosciences, Volume 9 is February 16, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Preferred associate (nearest neighbour) and mutual grooming relationships among mares, in an isolated family band of free-ranging horses (Equus caballus), were studied, and the structural and functional differences between these two relationships were examined. The frequent partners accompanying the mare were not the same in both these relationships (p < 0.05) and mares changed their partners during the study period between 1988-1990. Individual horses of similar rank tended to remain closer together in both winter and summer. Aggressive-submissive behaviour was so infrequent during spring that rank determinations could not be made; however, in fall, although rank could be determined, rank was not correlated with nearest neighbour. Three subgroups, based on preferred associate relationships in summer, fall and winter, directly reflected the age and social rank of the mares in the group. Individual horses of higher rank tended to have many partners in winter, while individuals of lower rank had fewer. There was no significant correlation between the frequency of mutual grooming and individual rank. The mutual grooming relationship was strongly influenced by seasonal changes as the relative amount of grazing time per day increased. Thus, the frequency of mutual grooming was lowest in winter and highest in summer. The mutual grooming relationship was based on the bonds between individual horses, which were little influenced by social rank. Lower ranking individuals tended to have a greater variety of grooming partners in summer.
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The horses of Shackelford Banks, North Carolina, USA, are heavily parasitized by intestinal worms and harassed by dipterans, and although both types influence behavior only internal parasites affect bodily condition and the structuring of horse society. Thirteen species of internal parasites were identified, but only 4 of 13 groups contain them all and even within groups differences among individuals are large. Among individuals ova emissions vary ranging from 50 to 76,875 eggs per gram. The most important environmental factors influencing egg production are season and a group's location on the island, presumably because of salinity and soil differences and their effects on ova survival. Of the social and life history factors, age, and group size, but neither reproductive state nor dominance status are important. The fitness consequences of internal parasitism may be large since the number emitted is negatively correlated with next year's bodily condition. Biting fly burdens are also affected by a variety of environmental factors. In general, horses are covered with more flies on sunny days, when winds are moderately brisk, when occupying dunes, and around mid-day. In contrast to endoparasites, fly burden is affected by reproductive condition and dominance status and tends to decrease as groups increase in size. Since groups do not grow very large, nor do females attempt to bring groups together, the negative effects of endoparasites appear to overide those associated with ectoparasites. Consequently, endoparasites appear to exert a stronger influence on social structure, even though ectoparasites seem to play a stronger role in shaping details of behavior.
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1. Gridded climatologies have become an indispensable component of bioclimatic modelling, with a range of applications spanning conservation and pest management. Such globally conformal data sets of historical and future scenario climate surfaces are required to model species potential ranges under current and future climate scenarios. 2. We developed a set of interpolated climate surfaces at 10′ and 30′ resolution for global land areas excluding Antarctica. Input data for the baseline climatology were gathered from the WorldClim and CRU CL1·0 and CL2·0 data sets. A set of future climate scenarios were generated at 10′ resolution. For each of the historical and future scenario data sets, the full set of 35 Bioclim variables was generated. Climate variables (including relative humidity at 0900 and 1500 hours) were also generated in CLIMEX format. The Köppen–Geiger climate classification scheme was applied to the 10′ hybrid climatology as a tool for visualizing climatic patterns and as an aid for specifying absence or background data for correlative modelling applications. 3. We tested the data set using a correlative model (MaxEnt) addressing conservation biology concerns for a rare Australian shrub, and a mechanistic niche model (CLIMEX) to map climate suitability for two invasive species. In all cases, the underlying climatology appeared to behave in a robust manner. 4. This global climate data set has the advantage over the WorldClim data set of including humidity data and an additional 16 Bioclim variables. Compared with the CRU CL2·0 data set, the hybrid 10′ data set includes improved precipitation estimates as well as projected climate for two global climate models running relevant greenhouse gas emission scenarios. 5. For many bioclimatic modelling purposes, there is an operational attraction to having a globally conformal historical climatology and future climate scenarios for the assessments of potential climate change impacts. Our data set is known as ‘CliMond’ and is available for free download from http://www.climond.org.
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2007: Zebra stripes as an amplifier of individ-ual quality? — Ann. Zool. Fennici 44: 368–376. Amplifiers belong to a class of signals that alone do not indicate an individual's qual-ity, but through design they improve the receiver's ability to assess pre-existing cues and signals. Amplifiers are cost free to produce and maintain, but may yield disadvan-tages to the individuals that are compelled to reveal their inferior quality. We suggest that zebra stripes, combined with the movement and proximity of other individuals with the same pattern, might function as an amplifier of the individual's escape poten-tial. As a zebra flock is set in motion by predators, stripes may facilitate ascertainment of the quality of the moving individuals (i.e., their escape potential) relative to other individuals in the flock. We tested whether the suggested relationship between stripes such as that of the zebra and quality ascertainment might occur by constructing anima-tions involving 5 moving objects, with one object moving differently from the others. A test panel was asked to identify the deviant object in 4 animations, each of the 4 ani-mations having objects with a different color pattern (striped, black, gradient and spot-ted). This study lends support to the hypothesis as behaviorally deviant objects were easiest observed in "flocks" of zebra striped objects. Thus, zebra stripes may make odd individuals more visible rather than making them less distinguishable.
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Resting time in red deer (Cervus elaphus) was shown to be more than twice as long on days when harassment by head flies (Hydrotaea irritans) was considered severe compared with days when fly harassment was estimated as low. Avoidance reactions in the deer decreased as soon as the deer reclined and became stabilized at a level corresponding to approximately 50% of the initial response frequency. The present observations do not give any clear indications as to whether it is the head flies per se or climatic factors that are the primary cause of reduced locomotory behaviour in the deer. It is concluded, however, that due to a causal relationship between the appearance of flies and certain types of weather, and because lying down has a relieving effect, inactivity may be an important part of the strategy used by red deer to cope with head fly harassment.
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The characteristic striped appearance of zebras has provoked much speculation about its function and why the pattern has evolved, but experimental evidence is scarce. Here, we demonstrate that a zebra-striped horse model attracts far fewer horseflies (tabanids) than either homogeneous black, brown, grey or white equivalents. Such biting flies are prevalent across Africa and have considerable fitness impact on potential mammalian hosts. Besides brightness, one of the likely mechanisms underlying this protection is the polarization of reflected light from the host animal. We show that the attractiveness of striped patterns to tabanids is also reduced if only polarization modulations (parallel stripes with alternating orthogonal directions of polarization) occur in horizontal or vertical homogeneous grey surfaces. Tabanids have been shown to respond strongly to linearly polarized light, and we demonstrate here that the light and dark stripes of a zebra's coat reflect very different polarizations of light in a way that disrupts the attractiveness to tabanids. We show that the attractiveness to tabanids decreases with decreasing stripe width, and that stripes below a certain size are effective in not attracting tabanids. Further, we demonstrate that the stripe widths of zebra coats fall in a range where the striped pattern is most disruptive to tabanids. The striped coat patterns of several other large mammals may also function in reducing exposure to tabanids by similar mechanisms of differential brightness and polarization of reflected light. This work provides an experimentally supported explanation for the underlying mechanism leading to the selective advantage of a black-and-white striped coat pattern.
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Stable flies, Stomoxys calcitrans (L.), are among the most damaging arthropod pests of cattle worldwide. The last estimate of their economic impact on United States cattle production was published 20 yr ago and placed losses at $608 million. Subsequently, several studies of effects of stable flies on beef cattle weight gain and feed efficiency have been published, and stable flies have become increasingly recognized as pests of cattle on pasture and range. We analyzed published studies and developed yield-loss functions to relate stable fly infestation levels to cattle productivity, and then estimated the economic impact of stable flies on cattle production in the United States. Four industry sectors were considered: dairy, cow-calf, pastured stockers, and feeder cattle. In studies reporting stable fly infestation levels of individual herds, median annual per animal production losses were estimated to be 139 kg of milk for dairy cows, and 6, 26, and 9 kg body weight for preweanling calves, pastured stockers, and feeder cattle, respectively. The 200,000 stable flies emerging from an average sized winter hay feeding site reduce annual milk production of 50 dairy cows by an estimated 890 kg and weight gain of 50 preweanling calves, stockers, or feeder cattle by 58, 680, or 84 kg. In 2009 dollars, the value of these losses would be $254, $132, $1,279, or $154, respectively. Using cattle inventories and average prices for 2005-2009, and median monthly infestation levels, national losses are estimated to be $360 million for dairy cattle, $358 million for cow-calf herds, $1,268 million for pastured cattle, and $226 million for cattle on feed, for a total impact to U.S. cattle industries of $2,211 million per year. Excluded from these estimates are effects of stable flies on feed conversion efficiency, animal breeding success, and effects of infested cattle on pasture and water quality. Additional research on the effects of stable flies on high-production dairy cows and nursing beef calves is needed to increase the reliability of the estimates.
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Camouflage patterns that hinder detection and/or recognition by antagonists are widely studied in both human and animal contexts. Patterns of contrasting stripes that purportedly degrade an observer's ability to judge the speed and direction of moving prey ('motion dazzle') are, however, rarely investigated. This is despite motion dazzle having been fundamental to the appearance of warships in both world wars and often postulated as the selective agent leading to repeated patterns on many animals (such as zebra and many fish, snake, and invertebrate species). Such patterns often appear conspicuous, suggesting that protection while moving by motion dazzle might impair camouflage when stationary. However, the relationship between motion dazzle and camouflage is unclear because disruptive camouflage relies on high-contrast markings. In this study, we used a computer game with human subjects detecting and capturing either moving or stationary targets with different patterns, in order to provide the first empirical exploration of the interaction of these two protective coloration mechanisms. Moving targets with stripes were caught significantly less often and missed more often than targets with camouflage patterns. However, when stationary, targets with camouflage markings were captured less often and caused more false detections than those with striped patterns, which were readily detected. Our study provides the clearest evidence to date that some patterns inhibit the capture of moving targets, but that camouflage and motion dazzle are not complementary strategies. Therefore, the specific coloration that evolves in animals will depend on how the life history and ontogeny of each species influence the trade-off between the costs and benefits of motion dazzle and camouflage.
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Movement is the enemy of camouflage: most attempts at concealment are disrupted by motion of the target. Faced with this problem, navies in both World Wars in the twentieth century painted their warships with high contrast geometric patterns: so-called "dazzle camouflage". Rather than attempting to hide individual units, it was claimed that this patterning would disrupt the perception of their range, heading, size, shape and speed, and hence reduce losses from, in particular, torpedo attacks by submarines. Similar arguments had been advanced earlier for biological camouflage. Whilst there are good reasons to believe that most of these perceptual distortions may have occurred, there is no evidence for the last claim: changing perceived speed. Here we show that dazzle patterns can distort speed perception, and that this effect is greatest at high speeds. The effect should obtain in predators launching ballistic attacks against rapidly moving prey, or modern, low-tech battlefields where handheld weapons are fired from short ranges against moving vehicles. In the latter case, we demonstrate that in a typical situation involving an RPG7 attack on a Land Rover the reduction in perceived speed is sufficient to make the grenade miss where it was aimed by about a metre, which could be the difference between survival or not for the occupants of the vehicle.
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To test the generality of adaptive explanations for coat coloration in even-toed ungulates, we examined the literature for hypotheses that have been proposed for color patterns exhibited by this taxon, and we derived a series of predictions from each hypothesis. Next, we collected information on the color, behavioral, and ecological characteristics of 200 species of even-toed ungulates and coded this in binary format. We then applied chi-square or Fisher's Exact probability tests that pitted presence of a color trait against presence of an ecological or behavioral variable for cervids, bovids, and all artiodactyls. Finally, we reanalyzed the data by using concentrated-changes tests and a composite molecular and taxonomic phylogeny. Hinging our findings on whether associations persisted after controlling for shared ancestry, we found strong support for hypotheses suggesting even-toed ungulates turn lighter in winter to aid in concealment or perhaps thermoregulation, striped coats in adults and spotted pelage in young act as camouflage, side bands and dark faces assist in communication, and dark pelage coloration is most common in species living in the tropics (Gloger's rule). Whereas white faces, dark legs, white legs, dark tails, and white tails did not appear to assist in communication alone, legs and tails that were either dark or white (i.e., conspicuous) did seem to be linked with communication. There was moderate support for hypotheses that countershading aids concealment, that white faces are a thermoregulatory device, and that white rumps are used in intraspecific communication. There was weak support for spots in adults and stripes in young providing camouflage and for dark leg markings being a form of disruptive coloration. We found little or no evidence that overall coat color serves as background matching, that side bands are disruptive coloration devices, or that white rumps help in thermoregulation. Concealment appears the principal force driving the evolution of coloration in ungulates with communication, and then thermoregulation, playing less of a role. Copyright 2003.
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Genetic data from extant donkeys (Equus asinus) have revealed two distinct mitochondrial DNA haplogroups, suggestive of two separate domestication events in northeast Africa about 5000 years ago. Without distinct phylogeographic structure in domestic donkey haplogroups and with little information on the genetic makeup of the ancestral African wild ass, however, it has been difficult to identify wild ancestors and geographical origins for the domestic mitochondrial clades. Our analysis of ancient archaeological and historic museum samples provides the first genetic information on the historic Nubian wild ass (Equus africanus africanus), Somali wild ass (Equus africanus somaliensis) and ancient donkey. The results demonstrate that the Nubian wild ass was an ancestor of the first donkey haplogroup. In contrast, the Somali wild ass has considerable mitochondrial divergence from the Nubian wild ass and domestic donkeys. These findings resolve the long-standing issue of the role of the Nubian wild ass in the domestication of the donkey, but raise new questions regarding the second ancestor for the donkey. Our results illustrate the complexity of animal domestication, and have conservation implications for critically endangered Nubian and Somali wild ass.
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White horses frequently suffer from malign skin cancer and visual deficiencies owing to their high sensitivity to the ultraviolet solar radiation. Furthermore, in the wild, white horses suffer a larger predation risk than dark individuals because they can more easily be detected. In spite of their greater vulnerability, white horses have been highly appreciated for centuries owing to their natural rarity. Here, we show that blood-sucking tabanid flies, known to transmit disease agents to mammals, are less attracted to white than dark horses. We also demonstrate that tabanids use reflected polarized light from the coat as a signal to find a host. The attraction of tabanids to mainly black and brown fur coats is explained by positive polarotaxis. As the host's colour determines its attractiveness to tabanids, this parameter has a strong influence on the parasite load of the host. Although we have studied only the tabanid-horse interaction, our results can probably be extrapolated to other host animals of polarotactic tabanids, as the reflection-polarization characteristics of the host's body surface are physically the same, and thus not species-dependent.
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The problems of existence, uniqueness and location of maximum likelihood estimates in log linear models have received special attention in the literature (Haberman, 1974, Chapter 2; Wedderburn, 1976; Silvapulle, 1981). For multinomial logistic regression models, we prove existence theorems by considering the possible patterns of data points, which fall into three mutually exclusive and exhaustive categories: complete separation, quasicomplete separation and overlap. Our results suggest general rules for identifying infinite parameter estimates in log linear models for frequency tables.
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The transformation of wild animals into domestic ones available for human nutrition was a key prerequisite for modern human societies. However, no other domestic species has had such a substantial impact on the warfare, transportation, and communication capabilities of human societies as the horse. Here, we show that the analysis of ancient DNA targeting nuclear genes responsible for coat coloration allows us to shed light on the timing and place of horse domestication. We conclude that it is unlikely that horse domestication substantially predates the occurrence of coat color variation, which was found to begin around the third millennium before the common era.
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Alighting of horse flies (Diptera: Tabanidae) and non-biting muscids (Diptera: Muscidae) was studied at Khartoum, Sudan, using black cylindrical models mimicking a goat, calf and cow. Flies were intercepted by attaching electrocution grids or clear adhesive film to models. Alighting sites and defensive behaviour were also documented on hosts through observation. Female Tabanus sufis (Jennicke), T. taeniola (Palisot) and Atylotus agrestis (Wiedemann) were the main tabanids captured. Muscids landed in equal numbers on all sizes of models. They had a strong preference for the upper portions of both models and hosts. Landings of T. taeniola and A. agrestis increased with model size, but not so for T. sufis. T. taeniola and A. agrestis scarcely alighted on the legs of models whereas 60-78% of T. sufis did so. Landings of T. sufis on artificial legs did not vary with model size. Landings of all tabanids on the lower and upper portions of a model increased with model size. For both hosts and models, most tabanids (88-98%) alighted on the lower half and legs. Most muscids (63-89%) alighted on the upper half. Landing of tabanids on the cow was 34.9 and 69.3 times greater than that on the calf and goat, respectively. These results are discussed in relation to strategies for the control of blood-sucking flies associated with farm animals using either insecticide-treated live baits or their mimics.
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Individual recognition is considered a complex process and, although it is believed to be widespread across animal taxa, the cognitive mechanisms underlying this ability are poorly understood. An essential feature of individual recognition in humans is that it is cross-modal, allowing the matching of current sensory cues to identity with stored information about that specific individual from other modalities. Here, we use a cross-modal expectancy violation paradigm to provide a clear and systematic demonstration of cross-modal individual recognition in a nonhuman animal: the domestic horse. Subjects watched a herd member being led past them before the individual went of view, and a call from that or a different associate was played from a loudspeaker positioned close to the point of disappearance. When horses were shown one associate and then the call of a different associate was played, they responded more quickly and looked significantly longer in the direction of the call than when the call matched the herd member just seen, an indication that the incongruent combination violated their expectations. Thus, horses appear to possess a cross-modal representation of known individuals containing unique auditory and visual/olfactory information. Our paradigm could provide a powerful way to study individual recognition across a wide range of species.
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Many traits in animals reduce the rate of attack from visually hunting predators, including camouflage, warning signals and mimicry. In addition, some animal markings may reduce the likelihood that an attack ends in successful capture. These might include dazzle markings, high-contrast patterns that make the estimation of speed and trajectory difficult. However, until now, no study has experimentally tested whether some markings may achieve such an effect. We developed a computer 'game' where human 'predators' have to capture computer-generated prey moving across a background. In two experiments, we find that although uniform camouflaged targets were among the hardest to capture, so were a range of high-contrast conspicuous patterns, such as bands and zigzags. Prey were also more difficult to capture against more heterogeneous than uniform backgrounds, and at faster speeds of movement. As such, we find the first experimental evidence that conspicuous patterns, similar to those found in a wide range of real animals, make the capture of moving prey more challenging. Various anti-predator markings may work prey during motion, and some animals may combine such dazzle patterns with other functions, such as camouflage, thermoregulation, sexual and warning signals.
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Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes. [Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN].
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Species and subspecies of zebras are examined using traditional (pelage and craniometric) taxonomic methods, including multivariate analysis. Mountain Zebras are split into two species, Equus zebra and Equus hartmannae, because they differ absolutely (100%); Burchell's or plains zebras, however, are placed in Equus quagga because there are no absolute differences. The subspecies of Equus quagga are revised; six subspecies are recognisable. E. zebra, E. hartmannae and E. grevyi are monotypic.
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Horse flies (Tabanidae) on and around feral ponies in harem groups were counted at Assateague Island National Seashore, Maryland, U.S.A., between June and August 1985. Harem stallions attracted the most flies; adult mares showed intermediate fly numbers, while few flies landed on foals under any circumstances. The use of thermal and chemical cues by flies selecting a host may have helped create this disparity. When flies were abundant, ponies reduced spacing within the group. Ponies in larger groups suffered from fewer flies than ponies in smaller groups. There was, however, no evidence that ponies merged into larger groups in response to fly harassment, suggesting that biting flies play little role in structuring pony social organization.
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Abstract A field study in Zimbabwe of Glossina pallidipes Austen and G. morsitans morsitans Westwood supported Waage's (1981) hypothesis that the striped pattern of zebras may protect them from being bitten by blood-sucking flies. In addition, the results suggest that the orientation of the stripes may be crucially important for the unattractiveness of zebras. The relative attractiveness of five different stationary targets (black, white, grey, vertically-striped and horizontally-striped; stripe width = 5 cm) were each tested on their own and in pairs of all combinations, with artificial host odour (CO2 plus acetone) always present. Electric nets were used to catch flies as they attempted to land on or circle the targets. The results were similar for the two species of tsetse. When tested on their own, grey and vertically-striped targets caught similar numbers of flies and both caught significantly fewer than black or white targets (c. 36% as many). Horizontally-striped targets caught <10% as many flies as any other single target. Although there was no significant difference between the attractiveness of grey and vertically striped targets when they were presented together, when paired with the other targets, grey was as attractive as black or white, but the vertically-striped target was significantly less attractive than black or white (P < 0.001). In other words, a difference between grey and vertical stripes was found only in their attractiveness in relation to other targets. The horizontally-striped target, however, always caught the fewest flies, regardless of whether it was presented alone or alongside another target.
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ABSTRACT The literature addressing evolutionary reasons for the striped patterns of zebra coats is reviewed here. Possible mechanisms, and the evidence for and against them, are discussed. These mechanisms span four general themes: protection from predators; social functions; thermoregulation; and protection from tsetse flies. The last is the only hypothesis that has been tested experimentally, and the results of these tests are inconclusive. Additionally or alternatively, although stripes apparently increase zebra visibility in daylight, it is at least plausible that they provide effective cryptic protection from predators in poor light, although critical testing has not been attempted. Other related evolutionary questions are raised and suggestions made for future research.
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Blood-sucking insects transmit many of the most debilitating diseases to man including malaria, sleeping sickness, filariasis, dengue, typhus and plague. Additionally these insects cause major economic losses in agriculture by direct damage to livestock. This new edition of The Biology of Blood-Sucking in Insects has been fully updated since it was first published in 1991. It provides a unique, topic-led commentary on the biological aspects that are common to blood-sucking insects. This account focuses on the biological adaptations that clearly suit the blood-sucking habit and further discusses host-insect interactions and the transmission of parasites by blood-sucking insects. It also outlines the medical, social and economic impact of blood-sucking insects. The final chapter is designed as a useful quick-reference section. Written in a clear, concise fashion and well illustrated throughout, the text will be of direct interest to advanced undergraduate and postgraduate students of medical and veterinary entomology and parasitology.
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The old primary classification of the Tabanidae, based on the presence or absence of hind tibia1 spurs, has been replaced by one based primarily on the genitalia of both sexes, but supported by a significant, though not complete, correlation with external characters. The early stages, so far as known, support the new arrangement. The following subfamilies and tribes are recognized: Pangoniinae Scepsidinae Chrysopinae Tabaninue Pangoniini Bouvieromyiini Diachlorini Scionini Chrysopini Haematopotini Philolichini Rhinomyzini Tabanini Distribution of the family is world-wide, but can be divided into three main sections. More primitive groups are predominantly southern, occurring in some or all of South America, southern Africa, Australia, and New Zealand, with occasional northern extensions, and, in one case (Pangoniini), an extensive Holarctic arc. More specialized groups show two patterns. Southern regional radiations have occurred in South America and Africa, with extensions respectively into the Nearctic and Oriental-Australasian regions. Northern radiation of Chrysopini,Haematopotini, and Tabanini has resulted in a radial distribution like that of the eutherian mammals.
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In the current resurgence of interest in the biological basis of animal behavior and social organization, the ideas and questions pursued by Charles Darwin remain fresh and insightful. This is especially true of The Descent of Man and Selection in Relation to Sex, Darwin's second most important work. This edition is a facsimile reprint of the first printing of the first edition (1871), not previously available in paperback. The work is divided into two parts. Part One marshals behavioral and morphological evidence to argue that humans evolved from other animals. Darwin shoes that human mental and emotional capacities, far from making human beings unique, are evidence of an animal origin and evolutionary development. Part Two is an extended discussion of the differences between the sexes of many species and how they arose as a result of selection. Here Darwin lays the foundation for much contemporary research by arguing that many characteristics of animals have evolved not in response to the selective pressures exerted by their physical and biological environment, but rather to confer an advantage in sexual competition. These two themes are drawn together in two final chapters on the role of sexual selection in humans. In their Introduction, Professors Bonner and May discuss the place of The Descent in its own time and relation to current work in biology and other disciplines.
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Ten species of Tabanus, five of Chrysops, and one of Atylotus are recorded from the Churchill, Manitoba, area. Of these, Tabanus itasca Philip, Tabanus sp. (new?), and Atylotus ohioensis (Hine) represent new records. It is established that Tabanidae in this region overwinter in the larval stage and that most species have at least a three-year life cycle. Problems in taxonomy are discussed. Methods of rearing the immature stages, of collecting adults emerging in the field, of estimating larval and adult populations, and of correlating adult activity and weather conditions are described, and the results are presented. Larvae of the tipulid Prionocera dimidiata (Lw.) are reported as predators of larvae of Chrysops spp. The emergence of the chalcid parasite Diglochis occidentalis (Ashm.) from pupae of Tabanus and Chrysops spp. reared from the larval stage is recorded.
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During the summer of 1957, experiments to determine the effect of biting f1y control on weight gain in beef cattle were conducted in Centre County, Pennsylvania. Insecticide-repellent formulations were applied daily to a herd of Aberdeen Angus by means of an electric-eye-controlled sprayer at the rate of approximately 75 ml. per animal. A water-base spray containing N, N-diethyl-m-toluamide and methoxychlor provided effective protection against biting flies, which included the horn fly, Siphona irritans (L.), the stable fly, Stomoxys calcitrans (L.), and a negligible number of a horse fly, Tabanus quinquevittata (Wied.). Equally satisfactory results were achieved with an oil base spray containing 2,3,4,5-bis (∆2 butylene)-tetrahydrofurfural, pyrethrins, N-octyl bicycloheptene dicarboximide and piperonyl butoxide. Both formulations were much more effective against the horn fly than against the stable fly, when data for each species were treated separately. After 8 weeks of treatment, none of the cattle was adversely affected. The favorable effect of biting fly control was demonstrated by the greater weight gain of the treated animals as compared with that of the untreated. As a result of treatments, the mean gain in weight of the treated group was found to surpass that of the untreated group by approximately one-half to two-thirds of a pound per animal per day. Statistical analyses indicated that the difference in weight gain between the two groups was significant. The cost of spray material was, in average, one cent a day for each animal.
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Adult female horse flies (Tabanus spp. L.) were collected hourly in modified Malaise traps. Regression analyses of numbers of flies collected and the values of various meteorological factors in the ranges observed indicated which factors influenced activity. From greater to lesser influence, these factors were: barometric pressure, temperature, evaporation and evaporation change per hour, total sky radiation change per hour, total sky radiation and wind velocity change per hour, and relative humidity and temperature change per hour. The influence of these factors upon activity of the 6 most abundant species was also determined. Prediction equations are presented and the traps described.
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The landing preferences of fed males of Glossina morsitans morsitans Westwood and Stomoxys calcitrans (L.) were measured under constant conditions in a two-choice situation. Pairs of black-and-white landing targets were presented on the grey walls of an arena ca 60 cm in diameter. In a simple choice of blackness vs whiteness, G. m. morsitans showed a ninefold greater preference for black; S. calcitrans displayed no preference. G. m. morsitans landed twice as frequently on a 15×30-cm vertical black stripe as on a horizontal one, but S. calcitrans preferred the horizontal one. Comparisons between a vertical stripe (or a horizontal one) and similar stripes sloping at various angles indicated that at about 50° G. m. morsitans distinguished the sloping stripe from the vertical (or the horizontal), but did not well distinguish slopes closer to the vertical (or horizontal). Tests with multiple vertical stripe patterns indicated that G. m. morsitans did not significantly distinguish between a single 15-cm stripe and two- or three-striped targets of the same total black area, but landed significantly less frequently on targets of four or five stripes, implying an angular, behavioural visual ‘resolution' of roughly 17°; S. calcitrans responded similarly. Both species showed a marked preference for landing near the edge of the black on all targets, with G. m. morsitans strongly biassed to the black side of an interface.
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Lions Panthera leo are generally thought to prey on medium to large ungulates. Knowledge of which species are actually preferred and which are avoided is lacking, however, as is an understanding of why such preference or avoidance may arise. An analysis of 32 studies over 48 different spatial locations or temporal periods throughout the distribution of the lion shows that it preferentially preys upon species within a weight range of 190–550 kg. The most preferred weight of lion prey is 350 kg. The mean mass of significantly preferred prey species is 290 kg and of all preferred species is 201 kg. Gemsbok, buffalo, wildebeest, giraffe and zebra are significantly preferred. Species outside the preferred weight range are generally avoided. Species within the preferred weight range that are not significantly preferred (such as roan, sable and eland) generally have features that reduce predation either morphologically (e.g. sable horns), ecologically (e.g. roan and sable occurring at low density), or behaviourally (e.g. the large herd size and increased vigilance of eland). Warthog are below the preferred weight range yet are taken in accordance with their availability and this is probably due to their sympatry with lion, their relatively slow evasion speed and their lower level of vigilance. Plots of prey preference against prey body mass follows a bell curve with a right skew that, we argue, is caused by collective hunting by lions of larger-bodied prey. Our methods can be use