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Comparative analysis of primary defences in spiders (Araneae)
Abstract
1. Being frequent prey of many predators, including especially wasps and birds, spiders have evolved a variety of defence mechanisms. Here I studied patterns of passive defences, namely anachoresis, crypsis, masquerade, aposematism and Batesian mimicry, in spiders. 2. Using published information pertaining more than 1,000 spider species, the phylogenetic pattern of different passive defences (i.e. defences that decrease the risk of the risk of an encounter with the predator) were investigated. Furthermore, I studied the effect of foraging guild, geographical distribution, and diel activity on the frequency of defences as these determine the predators diversity, presence and perception. 3. I found that crypsis (backgorund matching) combined with anachoresis (hiding) was the most frequent defence confined mainly to families/genera at the base of the tree. Aposematism (warning colouration) and Batesian mimicry (imitation of noxious/dangerous model) were found in taxa that branched later in the tree, and masquerade (imitation of inedible objects) was confined to families at intermediate positions of the tree. Aposematism and Batesian mimicry were restricted to a few lineages. 4. Masquerade was used particularly by web-building species with nocturnal activity. Aposematism was rare but mainly used by web-building diurnal species. Batesian mimicry was frequently observed in cursorial species with diurnal activity. Cryptic species were more common in temperate zones, wherease aposematic and mimetic species were more common in the tropics. 5. Here I show that the evolution of passive defences in spiders was influenced by ecology of species. Then I discuss the evolutionary significance of the particularly defences. This article is protected by copyright. All rights reserved.
... The first barrier a predator has to overcome is detection or recognition of the spider as prey. Different forms of crypsis and masquerade are the most common visual defensive strategies in spiders (Pekár 2014). Crypsis or visual camouflage is achieved through body (Araneidae) has in its web decorations made of debris that misdirect the predator's attack away from the actual spider location. ...
... When disturbed, the spider drops from its web and changes from a conspicuous yellow to a dark colouration that matches the ground substrate (Hawes 2017). Orb weavers' secondary defences include not only dropping to the ground but also changing sides on the web and web vibration/flexing to avoid capture (Pekár 2014;Gawryszewski 2017). ...
... Even when aposematism has been linked to honest signalling of prey's unprofitability, animals advertise many other types of defences (Caro and Ruxton 2019). Spiders with aposematic colouration have contrasting colours (black/white, black/red, black/yellow) and obvious defences (Pekár 2014). Those defences might include large fangs, spines, urticating hairs, or potent venom (Gawryszewski 2017). ...
Many animals use visual traits as a predator defence. Understanding these visual traits from the perspective of predators is critical in generating new insights about predator–prey interactions. In this paper, we propose a novel framework to support the study of strategies that exploit the visual system of predators. With spiders as our model taxon, we contextualise these strategies using two orthogonal axes. The first axis represents strategies using different degrees of conspicuousness to avoid detection or recognition of the spider and deter predator attacks. The second axis represents the degree of honesty of the visual signal. We explore these issues with reference to the three main vision parameters: spectral sensitivity, visual acuity, and temporal resolution, as well as recent tools to study it, including multispectral digital imaging.
... A common and taxonomically widespread kind of passive defence is crypsis (Ruxton et al., 2004). In some species, it is the primary type of passive defences against visually oriented predators (Johnsen, 2014;Pek ar, 2014). A cryptic organism can present a disruptive coloration pattern, such as bands or other markings that break up the outline of its body when seen by a predator (Tso, Lin & Yang, 2004;Cuthill et al., 2005). ...
... Another kind of passive defence, masquerade, is a process that is considered different from crypsis (Skelhorn et al., 2010;Pek ar, 2014). In this defensive strategy, species have evolved morphologies that allow them to be mistaken for inedible objects that are common in their environment. ...
... In this defensive strategy, species have evolved morphologies that allow them to be mistaken for inedible objects that are common in their environment. These species masquerade as twigs, leaves, stones, bird droppings and other things (Skelhorn et al., 2011;Liu et al., 2014;Pek ar, 2014). Therefore, the function of masquerade is to lead the predator to misclassify and not to preclude detection as in crypsis (Skelhorn et al., 2010). ...
... Jumping spider species are also highly specialized in different microhabitats (Cumming & Wesolowska 2004). Taken together, this variation in receiver visual systems and background appearance could explain the considerable interspecific variation in jumping spider appearance (Nelson et al., 2005;Pekár, 2014), making it an ideal system in which to investigate camouflage evolution. ...
... Moreover, jumping spiders have a wide variation in body coloration that plays a role in intraspecific communication (Lim & Li, 2013) and sexual selection (Maddison & McMahon, 2000;Masta & Maddison, 2002;Painting et al., 2016). Nevertheless, there is a lack of empirical evidence of visual camouflage perceived by potential prey and predators in different microhabitats, even though it has been suggested that this coloration acts as a passive defence mechanism that results in a variety of camouflage strategies in this spider family (Pekár, 2014). Likewise, there are no studies that have previously assessed the importance of body marks and patterns in concealment of body or crypsis in jumping spiders. ...
... We found evidence that the studied spider species have both colour and pattern traits that maximize camouflage against their associated microhabitat backgrounds relative to one another. Our findings support the statement that body coloration in spiders reflects a camouflage strategy against a specific habitat (Oxford & Gillespie, 1998), and the coloration strategies differed between species (Pekár, 2014). ...
Camouflage is used by prey to avoid detection by predators, and by predators to remain unseen by their prey. Effective camouflage can be achieved through background matching, where an animal matches the colours and patterns of the background or through disruptive coloration, where high-contrast markings disrupt the viewer’s ability to detect the animal’s shape. We used digital images to measure the body colour of two jumping spiders, Anasaitis sp. and Ilargus sp., and the substrate in which they were found (vegetation and leaf litter, respectively), in order to investigate their camouflage strategies. We evaluated the chromatic and achromatic contrast and the body patterns of spiders and both substrates modelling the perception of a bird (Cyanistes caeruleus) and a fly (Drosophila melanogaster) as potential predator and prey. Both Anasaitis sp. and Ilargus sp. were a good colour match to leaf litter in fly and avian vision; however, Ilargus sp. was a worse colour match to foliage than Anasaitis sp. Compared with its background, Anasaitis sp. also had far higher contrast stripes than Ilargus sp. We suggest that Anasaitis sp. is adopting a disruptive coloration, generalist strategy, whereas Ilargus sp. is adopting a background-matching strategy.
... Masquerade, the resemblance to uninteresting objects, is a fascinating product of natural selection that deceives predators or helps gain access to prey (Skelhorn et al. 2010). Better known in insects, plants, birds, and fish (Nel et al. 2008), masquerade in arachnids involves only a handful of spider genera with phenotypes that resemble flowers, dead twigs, plant detritus, buds, bark, or bird droppings (Foelix 2011;Liu et al. 2014;Pekar 2014). However, genuine leaf masquerade has not been known in arachnids. ...
... True masquerade is rare in spiders being described in only about 100 of the 45,945 known species of spiders (Pekar 2014;World Spider Catalog 2016). In spiders, masquerade is mostly confined to the family Araneidae, with spider resemblance to twigs, debris, fruits, or bird droppings (Liu et al. 2014;Pekar 2014), and as we report here, leaves. ...
... True masquerade is rare in spiders being described in only about 100 of the 45,945 known species of spiders (Pekar 2014;World Spider Catalog 2016). In spiders, masquerade is mostly confined to the family Araneidae, with spider resemblance to twigs, debris, fruits, or bird droppings (Liu et al. 2014;Pekar 2014), and as we report here, leaves. Thomisid genera resemble flowers and plant detritus, Deinopis idae) mimic plant detritus, whereas Caerostris and some other Poltys (Araneidae) mimic plant buds or bark (Grasshoff 1984;Smith 2006;Gregorič et al. 2015b). ...
Leaf masquerade-an animal resembling leaves that are inedible for predators or innocuous for prey-is well known in insects but less so in arachnids. We report a case of a striking morphological and behavioral adaptation that can be labeled as leaf masquerade in an undescribed spider species (Poltys C.L. Koch, 1843, Araneidae) from southwest China. The female abdomen has anatomical analogues of a leaf pedicel and venation, and its color is both green and brown, thus resembling both live and dry leaves. The spider camouflages itself with pulled dead leaves among live ones. This novel natural history in a spider adds an arachnid model to the growing literature on animal masquerade.
... Specifically, fitness is calculated as the product of prey surviving to reproduction and their fecundity if they do survive: (Santos et al., 2003), and conspicuous coloration is correlated with large body size (Hagman & Forsman, 2003). Correlations between defences are also commonly studied as indicators of signal honesty in aposematism (e.g., mush- (Pekár, 2014) and millipedes (Rodriguez et al., 2018) warning colouration only evolves after chemical defence. Recently, where b is the mean fecundity of surviving prey before paying for any defences. ...
... Latitudinal gradients in multiple defences are one aspect of this last question where some progress has been made. A comparative analysis of primary defences in spiders revealed that the relative frequency of species using crypsis increases with latitude, but frequency of species using Batesian mimicry decreases (Pekár, 2014). ...
Prey seldom rely on a single type of antipredator defence, often using multiple defences to avoid predation. In many cases, selection in different contexts may favour the evolution of multiple defences in a prey. However, a prey may use multiple defences to protect itself during a single predator encounter. Such "defence portfolios" that defend prey against a single instance of predation are distributed across and within successive stages of the predation sequence (encounter, detection, identification, approach (attack), subjugation and consumption). We contend that at present, our understanding of defence portfolio evolution is incomplete, and seen from the fragmentary perspective of specific sensory systems (e.g., visual) or specific types of defences (especially aposematism). In this review, we aim to build a comprehensive framework for conceptualizing the evolution of multiple prey defences, beginning with hypotheses for the evolution of multiple defences in general, and defence portfolios in particular. We then examine idealized models of resource trade-offs and functional interactions between traits, along with evidence supporting them. We find that defence portfolios are constrained by resource allocation to other aspects of life history, as well as functional incompatibilities between different defences. We also find that selection is likely to favour combinations of defences that have synergistic effects on predator behaviour and prey survival. Next, we examine specific aspects of prey ecology, genetics and development, and predator cognition that modify the predictions of current hypotheses or introduce competing hypotheses. We outline schema for gathering data on the distribution of prey defences across species and geography, determining how multiple defences are produced, and testing the proximate mechanisms by which multiple prey defences impact predator behaviour. Adopting these approaches will strengthen our understanding of multiple defensive strategies.
... A comparative study (Pekár 2014a) focusing on passive defences (anachoresis, background matching, camouflage, warning displays, and Batesian mimicry) in more than 1,000 (out of almost 50 000) spider species revealed that background matching combined with anachoresis (hiding) was the most frequent type of defence. Warning displays and Batesian mimicry were restricted to a few lineages. ...
... How aposematic coloration evolved in arachnids has not been investigated. Contrasting coloration probably evolved from cryptic phenotypes (Pekár 2014a). Aposematism could arise, however, only if the arachnid was unpalatable. ...
Arachnida represent a hyperdiverse group of terrestrial arthropods. Although arachnids are mostly predators, they often fall prey to other predators. Here, the diversity of enemies and the defences of arachnids which are used against their predators is reviewed. The main predators of arachnids are other arachnids, followed by insects, mammals and birds. Almost all types of defences has evolved in this class, but countershading, and elusiveness await to be discovered in Arachnida. Overall, empirical evidence is rare but has slowly been accumulating over the last decade. Anachoresis is used most frequently across all orders; only in Acari, Araneae, Opiliones, and Solifugae it is rivalled by background matching, and Batesian mimicry. The number of different types of defences used by an order is positively correlated with the number of predatory groups preying on it. The major gaps are identified and future avenues for investigation – cases which deserve special attention because these may reveal completely new phenomena – are proposed. It is concluded that this group offers a very diverse array of defences which has not been sufficiently studied; thus, this review aims to stimulate further research.
... As large females need more moults to reach maturation, the time spent on foraging on the web is longer and therefore the risks imposed by predators are also higher for females than males. The modified abdomen and twig or leaf camouflaging, as a type of passive defence, presumably to increase survival rates (Pekár 2014), likely better protects large females. Alternatively, although small-sized males are considered to have higher climbing and rappelling ability when searching for mates (Moya-Laraño et al. 2002;Grossi and Canals 2015;but, see Quiñones-Lebrón et al. 2019), this may not be relevant to male Poltys dwarfs. ...
... Also, rejecting the hypothesis ofSmith (2005), Araneus is not the sister clade of Cyphalonotus. Finally, although our analyses do not confirm Poltyeae precisely as proposed bySimon (1895), these do recover a sister relationship between Cyphalonotus and Poltys, confirming a hypothesis from the hand-patched phylogeny ofPekár (2014). Future classification efforts should likely classify this clade as Poltynae. ...
Cyphalonotus is a poorly studied Old World araneid spider genus of which the phylogenetic proximity remains unknown due to the paucity of morphological and molecular data. We test the phylogenetic placement and the taxonomic composition of Cyphalonotus and place the male and female size variation of Cyphalonotus and related genera in an evolutionary context. Our collection and field observations from Taiwan and China facilitate description of a new and a known species, and original sequence data enable species delimitation and phylogenetic analyses. The phylogenetic results reject all four classification hypotheses from the literature and instead recover a well-supported clade comprising Cyphalonotus + Poltys. We review the male and female size variation in Cyphalonotus, Poltys and related genera. These data reveal that all known species of Poltys are extremely sexually size dimorphic (eSSD = females over twice the size of males) reaching values exceeding 10-fold differences, whereas Cyphalonotus and other genera in phylogenetic proximity are relatively sexually monomorphic (SSD < 2.0). This confirms an independent origin of eSSD in Poltys, one of multiple convergent evolutionary outcomes in orbweb spiders.
... The prey animal can exhibit various threatening displays or anti-predator defensive behaviour. Such defence mechanisms can be divided into two major groups: primary (or passive) and secondary (or active) (Cloudsley-Thompson, 1995;Pekár, 2014). Passive defensive behavioural mechanisms include anachoresis, crypsis, masquerade, aposematism, and mimicry, while active defences include fleeing, dropping, and death-feigning (thanatosis). ...
... A variety of passive defences has been described in spiders. For example, anachoresis, mimicry, and crypsis were observed for the species of Lycosidae, Zodariidae, Corinnidae, Salticidae, and Thomisidae, while dropping and death-feigning are known in some web-building species (Cloudsley-Thompson, 1995;Cutler, 1991;Nelson & Jackson, 2012;Pekár, 2014). ...
It has become increasingly popular to observe animal behaviour by video recording done by amateur naturalists. Here we report the first observed defensive behaviour of a male of Lachesana blackwalli (O. Pickard-Cambridge, 1872) (Araneae, Zodariidae) based on a video recorded by a non-specialist observer. The spider was encountered during a night walk, then it was disturbed by the observer, and its defensive behaviour was recorded. As the spider was disturbed by the observer, it displayed several conspicuous defensive responses such as death-feigning, lunging, and scaring. The main observed response was feigning death. This is the first documented defensive behaviour for L. blackwalli.
... Araneid spiders, such as Gasteracantha, Micrathena, Macracantha and Thelacantha, which have hard integuments and spines, stay in the centre of their webs during the day and are predated by diurnal and visually oriented groups (Levi, 1978;P ekar, 2014;Ra ska, 2020), may actually be signalling distastefulness to predators. Although studies of aposematism are more commonly associated with chemical than morphological defences, the latter is a possible route for the evolution of aposematism and it is a reliable signal for predators (Speed & Ruxton, 2005). ...
... Unlike other orb-web spiders, experimental evidence suggests that conspicuous colours of G. cancriformis do not increase their foraging success (Gawryszewski & Motta, 2012). Alternatively, conspicuous colours in this species may be a warning signal against predators (Edmunds & Edmunds, 1983;Gawryszewski & Motta, 2012;P ekar, 2014) because spiders of the genus Gasteracantha possess sharp spines and a hard abdomen (Edmunds & Edmunds, 1983). Furthermore, mud-dauber wasps (Sceliphron laetum) avoid providing Gasteracantha prey to the initial instars in their nests, possibly due to the spines and difficult-to-digest hard integument of Gasteracantha spp. ...
Conspicuous colours in animals are usually explained by mate attraction, predator avoidance and prey attraction. Predators may lure prey by mimicking food or other resources. Alternatively, some animals avoid predation by visually signalling unpalatability to predators. The evolution of a signal is affected by receiver processing mechanisms. Therefore, variation in sensory systems may explain the evolution of colour polymorphism of conspicuous species. We aimed to investigate the role of receivers in the evolution and maintenance of colour conspicuousness and polymorphism in Gasteracantha cancriformis (Araneidae). We tested two hypotheses: (1) conspicuous coloration is a prey lure strategy; (2) conspicuous coloration is a warning signal to predators. Furthermore, we identified the taxonomic order of prey captured and the type of predator (avian versus arthropod). To assess the role of prey, we conducted a field experiment in which webs were assigned to one of four treatments: yellow, red or black spider models, or no model. For each treatment, we counted the number of prey trapped on the webs and calculated the damaged area of the webs. To assess the role of predators, we conducted a second field experiment in which we attached yellow, red and black models to trees using nylon thread and observed the number of attack markings on each model. Our results did not corroborate the prey attraction hypothesis. In the predation experiment, black models had more attack markings, indicating that yellow and red models were less preferred. This suggests that spider coloration may play a role in predator avoidance. Colour polymorphism in this species is possibly a multifunctional attribute, where some morphs benefit from aposematism, whereas others may have alternative fitness advantages. Nonadaptive explanations should also be considered in future experiments of the evolution and maintenance of colour polymorphisms
... This variation in foraging behaviour suggests that jumping spiders behave according to a background-matching strategy (Robledo-Ospina et al. 2017). Background-matching, or crypsis, is the most common anti-predator strategy in spiders (Pekár 2014). Spiders using this strategy have been shown to be less detectable by predators (Théry and Casas 2002, Defrize et al. 2010, Rubi et al. 2019. ...
... This finding is in line with results from a meta-analysis by Verdolin (2006), which revealed that habitat characteristics elicit stronger behavioural adjustments in prey organisms than cues of live predators; albeit most of the data included in this analysis is based on rodents and vegetation cover (Verdolin 2006). Since crypsis is the most common passive defence in spiders (Pekár 2014), habitat characteristics should help to predict spatial variation of predation risk. Although birds are key predators of cursorial hunting spiders (Gunnarsson and Wiklander 2015), individuals in our tests responded to simulated bird overflights only by starting to forage later and by spending more time under the hide. ...
One of the strongest determinants of behavioural variation is the tradeoff between resource gain and safety. Although classical theory predicts optimal foraging under risk, empirical studies report large unexplained variation in behaviour. Intrinsic individual differences in risk‐taking behaviour might contribute to this variation. By repeatedly exposing individuals of a small mesopredator to different experimental landscapes of risks and resources, we tested 1) whether individuals adjust their foraging behaviour according to predictions of the general tradeoff between energy gain and predation avoidance and 2) whether individuals differ consistently and predictably from each other in how they solve this tradeoff. Wild‐caught individuals (n = 42) of the jumping spider Marpissa muscosa, were subjected to repeated release and open‐field tests to quantify among‐individual variation in boldness and activity. Subsequently, individuals were tested in four foraging tests that differed in risk level (white/dark background colour) and risk variation (constant risk/variable risk simulated by bird dummy overflights) and contained inaccessible but visually perceivable food patches. When exposed to a white background, individuals reduced some aspects of movement and foraging intensity, suggesting that the degree of camouflage serves as a proxy of perceived risk in these predators. Short pulses of acute predation risk, simulated by bird overflights, had only small effects on aspects of foraging behaviour. Notably, a significant part of variation in foraging was due to among‐individual differences across risk landscapes that are linked to consistent individual variation in activity, forming a behavioural syndrome. Our results demonstrate the importance of among‐individual differences in behaviour of animals that forage under different levels of perceived risk. Since these differences likely affect food–web dynamics and have fitness consequences, future studies should explore the mechanisms that maintain the observed variation in natural populations.
... Since mobility often breaks camouflage (Ioannou & Krause, 2009;Hall et al., 2013), compared to day-resting prey, day activity may promote the evolution of other protective strategies in prey, such as those based on striking coloration. For instance, in spiders and lepidopterans, the evolution of defences involving striking colorations, that is aposematism or mimicry, is associated with diurnal activity and crypsis (backgroundmatching or masquerade) with nocturnality (Merilaita & Tullberg, 2005;Pek ar, 2014). Therefore, we hypothesize that (ii) the evolution of striped patterns and colourful tails is more likely in diurnal rather than in nocturnal lizards. ...
... Defensive colours might be ineffective against visual predators during nocturnal conditions. Since the effectiveness of cryptic coloration is known to be deteriorated by movement (Ioannou & Krause, 2009;Hall et al., 2013), diurnally active animals may be forced to rely on other protective strategies involving bright colours (Merilaita & Tullberg, 2005;Hawlena et al., 2006;Pek ar, 2014). Our results indicate that both stripes and colourful tails are associated with the diurnal activity (Fig. 2b,d), supporting the idea that striking colorations are more likely to evolve in diurnally active animals as a result of constraints imposed on other defensive strategies (e.g. ...
Understanding the functions of animal coloration has been a long‐standing question in evolutionary biology. For example, the widespread occurrence of striking longitudinal stripes and colourful tails in lizards begs for an explanation. Experiments have suggested that colourful tails can deflect attacks towards the tail (the ‘deflection’ hypothesis), which is sacrificable in most lizards, thereby increasing the chance of escape. Studies also suggest that in moving lizards, longitudinal body stripes can redirect predators’ strikes towards the tail through the ‘motion dazzle’ effect. Despite these experimental studies, the ecological factors associated with the evolution of such striking colourations remain unexplored. Here, we investigated if predictions from motion dazzle and attack deflection could explain the widespread occurrence of these striking marks using comparative methods and information on eco‐physiological variables (caudal autotomy, diel activity, microhabitat, and body temperature) potentially linked to their functioning. We found both longitudinal stripes and colourful tails are associated with diurnal activity and with the ability to lose the tail. Compared to stripeless species, striped species are more likely to be ground‐dwelling and have higher body temperature, emphasizing the connection of stripes to mobility and rapid escape strategy. Colourful tails and stripes have evolved multiple times in a correlated fashion, suggesting that their functions may be linked. Overall, our results together with previous experimental studies support the notion that stripes and colourful tails in lizards may have protective functions based on deflective and motion dazzle effects.
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... Orb-web spiders use secondary defence strategies such as dropping to the ground, changing sides on the web, and/or web vibration/flexing to avoid capture (Cloudsley-Thompson 1995, Pekár 2014, Gawryszewski 2017. Web-flexing occurs when the rapid extension-retraction of the spider legs cause motion along the web's short axis, also perceived as moving backwards and forward (Tolbert 1975). ...
Some visual antipredator strategies involve the rapid movement of highly contrasting body patterns to frighten or confuse the predator. Bright body colouration, however, can also be detected by potential predators and used as a cue. Among spiders , Argiope spp. are usually brightly coloured but they are not a common item in the diet of araneophagic wasps. When disturbed, Argiope executes a web-flexing behaviour in which they move rapidly and may be perceived as if they move backwards and towards an observer in front of the web. We studied the mechanisms underlying web-flexing behaviour as a defensive strategy. Using multispectral images and high-speed videos with deep-learning-based tracking techniques, we evaluated body colouration, body pattern, and spider kinematics from the perspective of a potential wasp predator. We show that the spider's abdomen is conspicuous, with a disruptive colouration pattern. We found that the body outline of spiders with web decorations was harder to detect when compared to spiders without decorations. The abdomen was also the body part that moved fastest, and its motion was composed mainly of translational (vertical) vectors in the potential predator's optical flow. In addition, with high contrast colouration, the spider's movement might be perceived as a sudden change in body size (looming effect) as perceived by the predator. These effects alongside the other visual cues may confuse potential wasp predators by breaking the spider body outline and affecting the wasp's flight manoeuvre, thereby deterring the wasp from executing the final attack.
... For shelter-building spider species, capturing prey involves leaving the shelter, which may increase the risk of exposure to predators (Manicom et al. 2008). Therefore, spiders can adopt foraging strategies to minimize the exposure time outside the shelter in periods of higher activity of their predators (Scharf et al. 2011;Pekár 2014). Most predators are visually oriented and diurnal, such as birds (Gunnarsson and Wiklander 2015), lizards (Spiller and Schoener, 1988), hunting wasps from the Crabronidae family, specialized in capturing spiders (Moura et al. 2019), as well as other spider species (Moura et al. 2016;Meira et al. 2021). ...
Optimal foraging and individual specialization theories suggest that different properties of the interaction between prey and predators determine foraging strategies. However, none of them consider how the nutritional status of the predators and the risk of being attacked by other predators can affect the option for these strategies. Some spider species can build webs as dynamic traps to capture prey and perform behaviors that optimize capture efficiency while adopting strategies to minimize their exposure to predators, such as building a shelter. In this sense, the risk of predation during foraging and the nutritional status of spiders may be important factors mediating predator-prey interactions, because capturing prey involves leaving the shelter, which may contribute to an increased risk of exposure to predators lurking close to the web. In this study, we evaluated the hypotheses that individuals of the shelter-building spider Metazygia laticeps (Araneidae) with poor nutritional status (i) are more exposed to predators during foraging and (ii) invest more in web structures to capture prey. Nutritional status was unrelated to exposure to predation. However, M. laticeps individuals left the shelter faster at night than during the day, regardless of their nutritional status, probably to reduce exposure to visually oriented predators. In addition, individuals with poor nutritional status did not show higher investment in webs when compared to well-nourished spiders. Nutritional status, therefore, was not a determining factor modulating investment in web foraging structures by M. laticeps .
... Instead, they usually sit and wait motionless on a flower, leaf, bark or branch for prey to arrive (Morse, 2007;Vieira et al., 2017). Crab spiders employ a broad range of colour-based defences known in animals such as crypsis, masquerade and mimicry (Cloudsley-Thompson, 1995;Pekár, 2014). The crab spider genus Phrynarachne is an often-cited example of a bird dropping masquerade that serves a protective function (Cott, 1940;Edmunds, 1974; Figure 1). ...
Selection imposed by visually-hunting predators has driven the evolution of colour-based antipredator defence strategies such as crypsis, masquerade, mimicry and aposematism. Individuals of many animals are generally considered to rely on a single type of defence strategy, but individuals of some species use multiple colour-based defences. Many animals switch between colour-based defences against visually-hunting predators during ontogeny. However, why this occurs remains poorly understood.
The crab spider Phrynarachne ceylonica is an often-cited example of a bird dropping masquerade. It has recently been demonstrated that P. ceylonica crab spiders gain protection from their predators by being misidentified as bird droppings by their predators. P. ceylonica females show an ontogenetic shift in colour defences: early instars possess a dark and cryptic form, while at later instars and as adults, the spiders resemble bird droppings. We hypothesised that this shift may be driven by differential changes in predation risk of two defence strategies with increasing body size due to ontogeny.
We tested this hypothesis by presenting naïve domestic chicks with 3D printed artificial spiders of two different sizes (small, large) and two colours (dark, bird dropping-like), and determined if larger bird dropping-like spiders are more readily found and attacked than cryptic forms by chicks. We found that small cryptic spiders were more difficult to detect than small bird dropping masquerading spiders, but large cryptic spiders were attacked much more quickly and more frequently than large bird dropping masquerading spiders.
Increasing predation pressure on larger, cryptic spiders during ontogeny suggests that switching to bird dropping masquerade may be a more effective defence as spiders increase in size. We thus conclude that the ontogenetic shift from crypsis to masquerade is adaptive.
... The cases of myrmecomorphy are scattered across the spider phylogeny usually with one or two genera in most families except for the families Corinnidae and Salticidae where multiple genera are myrmecomorphic (Pekár, 2014b). Detailed comparative analysis of the evolution of myrmecomorphic traits in these families showed independent origin in a number of genera (Pekár, 2014a). ...
Aim
The evolution and maintenance of accurate Batesian mimicry has been explained by several hypotheses built upon relaxed selection. However, selection can be influenced by ecological factors, such as habitat type or geographical distribution, which have not been considered.
Location
Worldwide.
Taxon
Araneae.
Methods
I gathered data on body size, geographical area of distribution (temperate, subtropical, tropical), and habitat stratification (ground, low vegetation, bush, tree) from literature on more than 400 ant-mimicking (myrmecomorphic) spider species from 18 spider families. I ranked them into four accuracy levels based on morphology, from poor inaccurate mimics to very accurate ones. I used regression to study the effect of body size, distribution, and habitat on mimetic accuracy while controlling for phylogeny.
Results
Mimetic accuracy increased with spider body size but differently depending on habitat type. On the ground and in low vegetation, smaller species were inaccurate; whereas on shrubs and trees even smaller species were accurate. Accuracy increased from temperate to tropical locations, again differently depending on habitat. In the temperate zone, only species occurring on bushes were accurate, but in the tropical zone even ground-living species were accurate.
Main conclusions
Higher accuracy at lower latitudes is likely due to stronger predation pressure from visually hunting predators. Lower accuracy in species occurring near the ground is presumably due to predation pressure by non-visually hunting predators. Inaccurate myrmecomorphy in spiders appears to be further driven by smaller body size due to lower profitability to predators; and higher latitude due to increased occurrence of generalist predators.
... However, this hypothesis must be properly tested and this type of temporal influence on prey size (daytime and nighttime) is a novelty in this study. The general tendency to nocturnal foraging by orb-web spiders is usually thought as a consequence of the high selective pressure from diurnal, visually oriented predators (e.g., Pekár, 2014;Xavier et al., 2018). Nevertheless, the foraging requirements and limitations may also affect these temporal patterns. ...
Orb-webs show diversity in several traits, including silk types, architecture, physical properties, locale, and period of exposition. The investigation of how they determine the identity of intercepted prey is important to functional ecology and to the evaluation of trophic niche partitioning within communities. However, the influence of several of these variables on the composition of intercepted insects remains to be determined. In this study, we evaluated the effects of web architectural traits, height, and daily periods of exposition on the interception of different insects in terms of sizes, masses, and taxa. We conducted observations of prey intercepted by the orb webs of 16 sympatric spider species and artificial webs. We found that all orb webs mainly intercepted small and light insects, sharing the most abundant insect families found in the study area. However, spiders that show nocturnal activity, more radii in their webs, large and high webs captured heavier insects. Other orb-web traits, such as the density of capture threads did not influence the kind of intercepted insects. We discuss why some variables affected prey interceptions in terms of mass. Finally, we discuss the implications of these influential variables to functional ecology, niche differentiation, and how behavioral assessments can complete this investigation in future studies.
... A single database that accommodates all trait data would enable scientists to investigate spiders more effectively and to perform large-scale comparative analyses (23)(24)(25)(26)(27)(28)(29). ...
Spiders are a highly diversified group of arthropods and play an important role in terrestrial ecosystems as ubiquitous predators, which makes them a suitable group to test a variety of eco-evolutionary hypotheses. For this purpose, knowledge of a diverse range of species traits is required. Until now, data on spider traits have been scattered across thousands of publications produced for over two centuries and written in diverse languages. To facilitate access to such data, we developed an online database for archiving and accessing spider traits at a global scale. The database has been designed to accommodate a great variety of traits (e.g. ecological, behavioural and morphological) measured at individual, species or higher taxonomic levels. Records are accompanied by extensive metadata (e.g. location and method). The database is curated by an expert team, regularly updated and open to any user. A future goal of the growing database is to include all published and unpublished data on spider traits provided by experts worldwide and to facilitate broad cross-taxon assays in functional ecology and comparative biology.
Database URL: https://spidertraits.sci.muni.cz/
... Masquerading is practised by many spiders (Peká r 2014), but only the protective hypothesis has been experimentally tested to date (Liu et al. 2014;Zhang et al. 2015;Xavier et al. 2018). The sitand-wait crab spider genus Phrynarachne (Araneae, Thomisidae) is an often-cited example of BD masquerade and widely accepted that BD resemblance functions as protective masquerade (Cott 1940;Edmunds 1974;Peká r 2014). It is hypothesized that Phrynarachne spiders resemble BDs (see Figure 1A) to also evade recognition and lure insects as prey, because BDs are a food source for some insects such as flies, however, their role as aggressive mimics is yet to be tested (Jacobson 1921;Mascord 1980;Ono 1988;Zhu and Song 2006;Quicke 2017). ...
In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic bird droppings in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders, therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among bird droppings, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans in particular were attracted to bird droppings at a higher rate than to spiders, other dipterans and hymenopterans were attracted to bird droppings at a similar rate as spiders. Both spiders and bird droppings attracted insects at a significantly higher rate than did control leaves. As predicted, prey were attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and bird droppings can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured by spiders may misidentify them as bird droppings, and bird dropping masquerading may serve as aggressive mimicry in addition to predator avoidance in P. ceylonica.
... Masquerading is practised by many spiders (Peká r 2014), but only the protective hypothesis has been experimentally tested to date (Liu et al. 2014;Zhang et al. 2015;Xavier et al. 2018). The sitand-wait crab spider genus Phrynarachne (Araneae, Thomisidae) is an often-cited example of BD masquerade and widely accepted that BD resemblance functions as protective masquerade (Cott 1940;Edmunds 1974;Peká r 2014). It is hypothesized that Phrynarachne spiders resemble BDs (see Figure 1A) to also evade recognition and lure insects as prey, because BDs are a food source for some insects such as flies, however, their role as aggressive mimics is yet to be tested (Jacobson 1921;Mascord 1980;Ono 1988;Zhu and Song 2006;Quicke 2017). ...
In aggressive mimicry, a predator accesses prey by mimicking the appearance and/or behavior of a harmless or beneficial model in order to avoid being correctly identified by its prey. The crab spider genus Phrynarachne is often cited as a textbook example of masquerading as bird droppings in order to avoid predation. However, Phrynarachne spiders may also aggressively mimic bird droppings in order to deceive potential prey. To date, there is no experimental evidence to support aggressive mimicry in masquerading crab spiders, therefore, we performed a field survey, a manipulative field experiment, and visual modeling to test this hypothesis using Phrynarachne ceylonica. We compared prey-attraction rates among bird droppings, spiders, and control empty leaves in the field. We found that although all prey combined and agromyzid dipterans in particular were attracted to bird droppings at a higher rate than to spiders, other dipterans and hymenopterans were attracted to bird droppings at a similar rate as spiders. Both spiders and bird droppings attracted insects at a significantly higher rate than did control leaves. As predicted, prey were attracted to experimentally blackened or whitened spiders significantly less frequently than to unmanipulated spiders. Finally, visual modeling suggested that spiders and bird droppings can be detected by dipterans and hymenopterans against background leaves, but they are indistinguishable from each other. Taken together, our results suggest that insects lured
... 'an aposematic frog'), whereas in reality they may utilize several different strategies sequentially or simultaneously (Caro, 2005;Ruxton et al., 2018). While the presence of several protective coloration mechanisms could indicate Batesian mimicry was more common in cursorial species and less common in burrowing species Pekár (2014) Biological Reviews (2020) 000-000 © 2020 Cambridge Philosophical Society that they have evolved in response to common environmental features, both a priori predictions and comparative tests are still underdeveloped. We make two recommendations: antipredator defence research should document cooccurring defence strategies in related species, for example in lepidopterans or anurans, recording whether they are used at the same time in the predatory sequence, at different times during ontogeny, and in response to the same predators. ...
The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life-history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small-scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self-shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad-scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.
... In agreement with these statements, in the present research, some diurnal wandering spiders, such as ambushers (i.e., philodromids) and stalkers (i.e., salticids), were significantly affected by the intensity of spraying, while no significant effect was found on web builders (i.e., theridiids, areaneids, and linyphiids). Philodromids usually adopt a cryptic defense behavior that is of little use against the physical or toxic effects of pesticides [82], while salticids, being strictly diurnal [83], have a higher chance of being impacted by spraying than crepuscular or nocturnal species. In relation to the guilds less susceptible to pesticides, Pekár [74] observed that some araneids survived against broad-spectrum insecticides by hiding under leaves when they are out of their webs. ...
Spiders are key predatory arthropods that are negatively affected by spraying pesticides in orchards. The aim of this research was to determine the structure of the community of spiders in pear orchards and the impact of the intensity of spraying. The study was carried out over three years in four pear orchards in southern Spain; two of them were conducted by ourselves with no or low-intensity spraying of insecticides, and two under the criteria of technicians (conventional). Spiders were sampled on pear trees by the beating method. The orchards hosted a rich community of spiders belonging to 13 different families and 51 genera. However, the genera Philodromus, Oxyopes, Cheiracanthium, Icius, and Neoscona accounted for 72% of the captures. Spiders were more abundant and had a higher richness of genera in the low-intensity spraying than in conventional orchards. Philodromidae, Salticidae, and Cheiracanthiidae experienced a significant population reduction in conventional orchards, while Araneidae, Linyphiidae, and Thomisidae were not significantly affected by the intensity of spraying. The wandering hunting mode could explain the negative impact on Philodromidae, Salticidae, and Cheiracanthiidae but does not explain the lack of effect on Oxyopidae and Thomisidae. No significant effect was found on any family of web builders.
... Several ant-mimicking arthropods, such as spiders, co-occur with their ant models (Cushing 1997). In fact, ants are the most frequent mimetic models for spiders (Pekár 2014). This is because ants have very similar morphology (e.g., the absence of wings), occupy similar habitats, are often superabundant compared to spider mimics, and are unpalatable for many predators (McIver & Stonedahl 1993, Jackson & Nelson 2012. ...
In visual Batesian mimicry, the mimic acquires protection from predators by imitating visual signals of the model. It has not been known whether the occurrence of mimics among models is a result of selection by predators or an active choice by the mimics. Here, the occurrence of an ant-like spider, Micaria sociabilis Kulczyński, 1897, which occurs on tree trunks and visually imitates arboricolous Liometopum microcephalum (Panzer, 1798) ants, was studied. The fauna of arboricolous ant species was surveyed together with six tree characteristics in order to find which variables determined the occurrence and abundance of M. sociabilis. It was found that M. sociabilis occurred exclusively on trees where L. microcephalum ants occurred. The effect of any tree variable was not significant. The abundance of M. sociabilis increased positively with the abundance of L. microcephalum. Then, experiments using an olfactometer and Y-maze with volatile and contact cues obtained from the two most abundant ant species, L. microcephalum and Lasius fuliginosus (Latreille, 1798), were performed to find whether Micaria preferred any cue. Micaria sociabilis did not respond to volatile cues obtained from the gaster of the two ant species. In contrast, it avoided contact cues from L. fuliginosus and was attracted to contact cues from L. microcephalum ants and its gaster extract in hexane. The results thus show that M. sociabilis associates exclusively with L. microcephalum and is attracted to contact cues from this ant while avoiding cues from the competing ant. This study reveals that Batesian mimics may use kairomones to associate with visual models.
... Spider-hunting wasps are usually confronted with cognitive and physical challenges when capturing many prey taxa, because spiders can use several different defensive strategies to avoid predation, such as the use of shelters (Moura et al., 2016), protective web resources (Gonzaga & Vasconcellos-Neto, 2005), camouflage (Xavier et al., 2018), and mimicry (Pekár, 2014). In addition, spiders present a wide range of size, habitat choice, foraging strategy (sit-and-wait or wandering), web inclination in web-building species, and sociality level (aggregated or solitary) (Purcell et al., 2012;Viera & Gonzaga, 2017). ...
Abstract. 1. Sister taxa that coexist in the same space and time often face competition due to the use of similar resources. However, some closely related species can adopt fine-grained specialization in resource use to coexist. In this study, we investigated niche overlap between three sympatric spider-hunting wasp species of the genus Trypoxylon (Hymenoptera: Crabronidae) known to nest in three of the habitats found in the study area.
2. First, we estimated the co-occurrence of these wasp species in the three habitats as a proxy for potential competition. Then, we tested the following hypotheses: (1) niche partitioning is seem more often between species that co-occur in a habitat, while there is niche overlap between species nesting in distinct habitats (prey specialization hypothesis); and (2) wasp species capture prey according to their size (physical constraint hypothesis).
3. We found two pairs of wasp species consistently nesting in the same habitat. Niche partitioning based on prey taxa occurred regardless of the habitat preference. We also found that the differences in the size of wasps were reflective of distinctions in the size of their prey.
4. Our findings were consistent over the years, showing that the significance of specialization in foraging activities and physical constraints during prey capture can play key roles in the coexistence of sympatric species. We discuss distinctions in the foraging strategies of these wasps and potential mechanisms driving the evolution in prey specialization, with insights for future studies.
... (d) Best camouflage-Shared by many species. In the course of their evolution, many spider species have developed mimicry impressively (Pekar, 2014), and thus it is almost impossible to decide upon the best mimetic species. Spiders are able to mimic inanimate objects (masquerading mimicry), unpalatable or undesirable food in the eyes of their predators (Batesian mimicry), some of the habitat features in which they dwell (crypsis) or even specific pheromones produced by their prey (see "Most creative hunting strategies"). ...
Organismal biology has been steadily losing fashion in both formal education and scientific research. Simultaneous with this is an observable decrease in the connection between humans, their environment, and the organisms with which they share the planet. Nonetheless, we propose that organismal biology can facilitate scientific observation, discovery, research, and engagement, especially when the organisms of focus are ubiquitous and charismatic animals such as spiders. Despite being often feared, spiders are mysterious and intriguing, offering a useful foundation for the effective teaching and learning of scientific concepts and processes. In order to provide an entryway for teachers and students-as well as scientists themselves-into the biology of spiders, we compiled a list of 99 record breaking achievements by spiders (the "Spider World Records"). We chose a world-record style format, as this is known to be an effective way to intrigue readers of all ages. We highlighted, for example, the largest and smallest spiders, the largest prey eaten, the fastest runners, the highest fliers, the species with the longest sperm, the most venomous species, and many more. We hope that our compilation will inspire science educators to embrace the biology of spiders as a resource that engages students in science learning. By making these achievements accessible to non-arachnologists and arachnologists alike, we suggest that they could be used: (i) by educators to draw in students for science education, (ii) to highlight gaps in current organismal knowledge, and (iii) to suggest novel avenues for future research efforts. Our contribution is not meant to be comprehensive, but aims to raise public awareness on spiders, while also providing an initial database of their record breaking achievements.
... In arachnids, aposematism has been proposed as the function of certain color patterns in venomous spiders (Brandley et al. 2016); these patterns include the colors yellow or red and appear to have originated relatively recently (Pekár 2014). In ixodid ticks, background color patterns consist of various shades of brown, or even orangish hues (Ixodes Latreille), while colorful ornamentation is rare. ...
Among the hard ticks (Acari: Ixodidae), many species in the section Metastriata have intricate ornamentation on the scutum that is often used as a taxonomic character. However, the biological function(s) of this ornamentation remains unknown. Here, we summarize the main functions of color patterns recognized in the animal kingdom—thermoregulation, aposematism, camouflage, aggregation, mate recognition, and sexual signaling—and evaluate the potential of each of these to explain ornamentation in hard ticks. We also note the challenges and uncertainties involved in interpreting ornamentation in ticks as well as potential approaches for future research.
... Among spiders, Batesian mimicry has been identified in more than 400 species, mainly within the families Salticidae and Corinnidae. In these groups, ant mimicry (or myrmecomorphy) is by far the most common form of Batesian mimicry (Pekár 2014a). Ant-mimicking spiders are ideal candidates to investigate the efficacy of Batesian mimicry, given their morphological, phylogenetic and ecological diversity (Ceccarelli and Crozier 2007;Ceccarelli 2008;Pekár et al. 2011;Nelson 2012;Nelson and Jackson 2012;Pekár 2014a, b). ...
The use of ultraviolet (UV) cues for intra- and inter-specific communication is common in many animal species. Still, the role of UV signals under some predator-prey contexts, such as Batesian mimicry, is not clear. Batesian mimicry is a defensive strategy by which a palatable species (the mimic) resembles an unpalatable or noxious species (the model) to avoid predation. This strategy has evolved independently in many different taxa that are predated by species capable of UV perception. Moreover, there is considerable variation in how accurately Batesian mimics resemble their models across species. Our aim was to investigate how UV colour contributed to mimetic accuracy using several ant-mimicking spider species as a case study. We measured the reflectance spectrum (300–700 nm) for several species of mimics and models, and we tested whether they differ in visible and UV colour. We modelled whether two different predators could discriminate between mimics and models using colour information. We found that generally, ant-mimicking spiders differed significantly from their ant models in UV colour and that information from the visible range of light cannot be extrapolated into the UV. Our modelling suggested that wasps should be able to discriminate between mimics and models combining information from visible and the UV light, whereas birds may not discriminate between them. Thus, we show that UV colour can influence mimic accuracy and we discuss its potential role in Batesian mimicry. We conclude that colour, especially in the UV range, should be taken into account when measuring mimetic accuracy.
... Early medical reports of human envenomation by Redback spiders often involved external toilets, and bites often occurred on the genitalia or buttocks. As indoor plumbing increased, the incidences of bites shifted from these sensitive areas to the limbs, as bites occur when people reach under objects where the spider is hiding or when people put on clothing, gloves, or shoes harboring the spider (Vetter and Visscher 1998;Pekár 2014). Several deaths have been attributed to Redback spider bites in Australia, but there have been no deaths since the introduction of an antivenom. ...
Considering the fear that spiders can generate in humans, examining human–spider interactions in urban settings may at first glance appear odd. However, human–spider interactions, which occur quite frequently in urban settings, do not necessarily have to be negative; they can, in some cases, foster respect and tolerance (sometimes through avoidance). When one considers how global transformations, invasive species, urbanization, and adaptation will impact human–spider interactions, a review of the literature pertaining to these encounters is timely. We begin this discussion by describing spiders and providing an overview of some of their positive and negative impacts. Challenges regarding species identification and envenoming are also discussed. After the role of biological, psychological, and social aspects in human–spider interactions are re-examined, we provide future options aimed at organizing broad-scale public programs for five specific target groups: 1) the general public, 2) health professionals, 3) educators, 4) naturalists, and 5) researchers. In the conclusion, we provide potential management and educational strategies aimed at increasing our knowledge and tolerance of these animals in urban settings.
... One may logically expect female spiders to respond to such sex-specific challenges though adaptive morphological changes that contribute to sexual shape, as well as size dimorphism. Spiders offer numerous such examples (Fig. 1), their abdominal morphological modifications presumably enhancing female survival, e.g. through leaf-or twig-mimicry (Poltys, Deinopis, Arachnura) or spinal adornments (Micrathena, Gasteracantha, Poltys and others) (Elgar and Jebb 1999;Pekár 2014). These highly modified female spider morphologies may be accompanied by extreme SSD, but comparative research has never tested for a direct connection between SSD and SShD. ...
Many organisms are sexually dimorphic, reflecting sex-specific selection pressures. But although sexual dimorphism may consist of different variables from size to shape and physiology, most research emphasizes a single aspect of sexual dimorphism, notably size, without specifying its components and their relationship. Among terrestrial animals, spiders exhibit most extreme sex-specific differences in size and abdominal shape, and therefore represent ideal models to address this question. Here, we dissect sexual dimorphism in spiders at two phylogenetic hierarchical levels. At the species level, we employ comparative phylogenetic tests to explore the association between sexual shape dimorphism (SShD) and sexual size dimorphism (SSD) in the orbweb clade Argiopinae. At the genus level, we then explore such patterns on a phylogeny of orb weavers (Araneoidea). Female argiopines had more diverse abdominal morphotypes than the males and the abdominal shape evolution was only poorly correlated between the sexes. Phylogenetic and comparative data suggested that evolution of SShD in argiopines was related to geographic history, but that sexually shape monomorphic cases arose through selection for male size, perhaps acting against fe-cundity selection. While in argiopines there was no clear association between SShD and SSD, we detected a significant correlation in all orb weavers at the genus level. The shape and the size components of sexual dimorphism may thus respond independently to selection pressures, but at certain phylogenetic levels SSD may be a prerequisite for SShD. Research on other animal groups is needed to establish whether the here detected patterns on spiders are general.
Some wasp species use spiders as food resources, overcoming several anti-predator barriers that are exerted by spiders. Tromatobia ichneumonid wasps are spider egg predators that usually attack Araneidae species, although there are few records of predation on Clubionidae, Philodromidae, Linyphiidae, Tetragnathidae,
and Theridiidae spiders. Here, we describe the interaction between Tromatobia sp. and Chrysso compressa, a subsocial theridiid spider that exhibits extended maternal care, in the Atlantic Forest of southeastern Brazil. We observed that the larva of Tromatobia sp. develop inside the egg sacs of C. compressa, preying on the entire egg mass and building cocoons that change the color and morphology of the egg sacs. Despite these structural modifications, we registered an adult female of C. compressa guarding and caring for the cocoons (attacked egg sac) of the predators as if they were offspring (non-attacked egg sac). To the best of our knowledge, this study represents the first record of Tromatobia preying on Chrysso eggs.
During a recent investigation of ant-mimicking arthropods in Costa Rica, two new species of salticid spiders were discovered. Here, I provide descriptions of the two species, Myrmapana costaricaensis sp. nov. and Corcovetella galianoae sp. nov. The former species has two forms; the dark form resembles Neoponera ants, while the light form resembles Pseudomyrmex ants. Corcovetella galianoae resembles Camponotus ants.
Spiders are diverse, predatory arthropods that have inhabited Earth for around 400 million years. They are well known for their complex venom systems that are used to overpower their prey. Spider venoms contain many proteins and pep-tides with highly specific and potent activities suitable for biomedical or agrochemical applications, but the key role of venoms as an evolutionary innovation is often overlooked, even though this has enabled spiders to emerge as one of the most successful animal lineages. In this review, we discuss these neglected biological aspects of spider venoms. We focus on the morphology of spider venom systems, their major components, biochemical and chemical plasticity, as well as ecological and evolutionary trends. We argue that the effectiveness of spider venoms is due to their unprecedented complexity, with diverse components working synergistically to increase the overall potency. The analysis of spider venoms is difficult to standardize because they are dynamic systems, fine-tuned and modified by factors such as sex, life-history stage and biological role. Finally, we summarize the mechanisms that drive spider venom evolution and highlight the need for genome-based studies to reconstruct the evolutionary history and physiological networks of spider venom compounds with more certainty.
Lures are deceptive strategies that exploit sensory biases in prey, usually mimicking a prey’s mate or food item. Several predators exploit plant–pollinator systems, where visual signals are an essential part of interspecific interactions. Many diurnal, and even nocturnal, orb-web spiders present conspicuous body coloration or bright color patches. These bright colors are regarded as color-based lures that exploit biases present in insect visual systems, possibly mimicking flower colors. The prey attraction hypothesis was proposed more than 20 years ago to explain orb-web spider coloration. Although most data gathered so far has corroborated the predictions of the prey attraction hypothesis, there are several studies that refute these predictions. We conducted a multilevel phylogenetic meta-analysis to assess the magnitude of the effect of conspicuous orb-web spider body coloration on prey attraction. We found a positive effect in favor of the prey attraction hypothesis; however, there was substantial heterogeneity between studies. Experimental designs comparing conspicuous spiders to painted spiders or empty webs did not explain between-studies heterogeneity. The lack of theoretical explanation behind the prey attraction hypothesis makes it challenging to address which components influence prey attraction. Future studies could evaluate whether color is part of a multicomponent signal and test alternative hypotheses for the evolution of spider colors, such as predator avoidance and thermoregulation.
Despite being widely known as a diverse group of predators, spiders are also a regular prey item of several vertebrate and invertebrate predators. Some of these organisms (e.g., wasp species and araneophagic spiders) are spider-hunting specialists. A number of morphological structures and behaviours in spiders have been proposed to be anti-predator adaptations. They comprise strategies such as background matching, disruptive patterns, web decorations, mimicry, masquerading, aposematism, urticating bristles, spines, retreats, barrier webs, group living, and dropping from webs. In this chapter, spider anti-predator strategies are presented, and the correlational and causal evidence of anti-predator adaptations are critically discussed in light of potential costs and benefits they may entail. Studies involving Neotropical species are presented to illustrate most strategies.
Although spiders are common inhabitants of tree cavities, factors that drive their community structure in these microhabitats are little known. Here we investigated whether bark type, season, intraguild predation (IGP) among spiders, and presence of vertebrate predators can influence the spider community structure in tree cavities. We examined spider abundance and the taxonomic and functional composition of spiders in nest-boxes within two mixed forest stands in central Slovakia in 2012–2013. In total, 1211 spiders belonging to 31 species were sampled from 60 nest-boxes at two sites over three seasons. Spider abundance peaked in autumn as spiders sought wintering sites. Guilds and taxonomic composition changed seasonally with spring and autumn communities dominated by ‘‘Other hunters’’ (Anyphaenidae, Clubionidae, Philodromidae) while during summer the community was dominated by ‘‘Sheet web weavers’’ (Linyphiidae). The guild and taxonomic turnover may be partly explained by the interaction between spiders’ phenology and IGP exerted by winter-active spiders on smaller spiders from autumn until spring. Bark type influenced the guild composition as dominance of ‘‘Space web weavers’’ was higher in trees with rough bark than in trees with smooth bark. The rough bark also reduced the intensity of IGP by Anyphaena accentuata (Sundevall, 1833) on philodromids. The presence of insectivorous birds reduced the abundance of spiders by 67%. The presence of bird predators altered the guild composition as they affected mostly the web spiders. The results show that the biotic interactions and abiotic factors interactively determined the spider community structure in the nest-boxes depending on spiders’ functional traits.
Batesian mimicry, in which a palatable organism resembles an unpalatable model, is widespread among taxa. Batesian mimics can be classified based on their level of accuracy (inaccurate or accurate). Using data on defensive strategies in more than 1000 species of spiders I investigated whether inaccurate myrmecomorphy is ancestral to accurate myrmecomorphy. I classified 233 myrmecomorphic species into four accuracy levels based on morphology, from poor inaccurate mimics to very accurate ones. I found that myrmecomorphy has evolved independently in 16 families and 85 genera. On the family-level phylogeny, the occurrence of myrmecomorphy is confined mainly to families branching later on the tree, from the RTA clade. On the generic-level phylogenies in Corinnidae and Salticidae, myrmecomorphy is not only of derived origin. Estimated ancestral state was non-mimetic in Salticidae and poor inaccurate myrmecomorphy in Corinnidae. Thus, inaccurate myrmecomorphic spider mimics seem rather ancestral to accurate but additional analysis on species-level phylogenies is needed to support this conclusion. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, ●●, ●●–●●.
As species evolve along a phylogenetic tree, we expect closely related species to retain some phenotypic similarities due to their shared evolutionary histories. The amount of expected similarity depends both on the hierarchical phylogenetic structure, and on the specific magnitude and types of evolutionary changes that accumulate during each generation. In this study, we show how models of microevolutionary change can be translated into the resulting macroevolutionary patterns. We illustrate how the structure of phenotypic covariances expected in interspecific measurements can be derived, and how this structure depends on the microevolutionary forces guiding phenotypic change at each generation. We then explore the covariance structure expected from several simple macroevolutionary models of phenotypic evolution, including various combinations of random genetic drift, directional selection, stabilizing selection, and environmental change, as well as models of punctuated or burst-like evolution. We find that stabilizing selection leads to patterns of exponential decrease of between species covariance with phylogenetic distance. This is different from the usual linear patterns of decrease assumed in most comparative and systematic methods. Nevertheless, linear patterns of decrease can result from many processes in addition to random genetic drift, such as directional and fluctuating selection as well as modes of punctuated change. Our framework can be used to develop methods for (1) phylogenetic reconstruction; (2) inference of the evolutionary process from comparative data; and (3) conducting or evaluating statistical analyses of comparative data while taking phylogenetic history into account.
Myrmecomorphs are arthropods that have evolved a morphological resemblance to ants. Myrmecophiles are arthropods that live in or near ant nests and are considered true symbionts. The literature and natural history information about spider myrmecomorphs and myrmecophiles are reviewed. Myrmecomorphy in spiders is generally considered a type of Batesian mimicry in which spiders are gaining protection from predators through their resemblance to aggressive or unpalatable ants. Selection pressure from spider predators and eggsac parasites may trigger greater integration into ant colonies among myrmecophilic spiders. /// Los mirmecomorfos son artrópodos que han evolucionado desarrollando una semejanza morfológica a las hormigas. Los Myrmecófilos son artrópodos que viven dentro o cerca de nidos de hormigas y se consideran verdaderos simbiontes. Ha sido evaluado la literatura e información de historia natural acerca de las arañas mirmecomorfas y mirmecófilas. El myrmecomorfismo en las arañas es generalmente considerado un tipo de mimetismo Batesiano en el cual las arañas están protegiéndose de sus depredadores a través de su semejanza con hormigas agresivas o no apetecibles. La presión de selección de los depredadores de arañas y de parásitos de su saco ovopositor pueden inducir una mayor integración de las arañas mirmecófílas hacia las colonias de hormigas.
Egg sacs of25 species of spiders in 14 families were found to contain immatures of Mantisp a viridis in northwestern South Carolina, bringing the total spider taxa associated with this species to at least 2 9 species in15 families . Thirty-one of the 124 M. viridis infested egg sacs had two or more mantispids in them . However, only three of these sacs produced two or more adult mantispids, with two sacs producing two adult s each and the third sac producing four adults .
An apparent outbreak of Hymenoepimecis sp., a heretofore unknown ectoparasite of the giant orb weaver, Nephila clavipes is documented in Panama during 1984-1985. Parasitism was highest (25-30%) among intermediate-sized, juvenile female spiders. During the second year the wasps became less discriminating in selecting host spiders. Female wasps were significantly larger than males, and the size of the wasp ectoparasite was positively correlated with the size of the host spider. Although intermediate-sized females that had males in their webs were less likely to be parasitized than such females without males, results from an insectary experi.ment showed that male spiders did not prevent an established wasp larva from killing its host.
Biotic interactions are believed to play a role in the origin and maintenance of species diversity, and multiple hypotheses link the latitudinal diversity gradient to a presumed gradient in the importance of biotic interactions. Here we address whether biotic interactions are more important at low latitudes, finding support for this hypothesis from a wide range of interactions. Some of the best-supported examples are higher herbivory and insect predation in the tropics, and predominantly tropical mutualisms such as cleaning symbioses and ant-plant interactions. For studies that included tropical regions, biotic interactions were never more important at high latitudes. Although our results support the hypothesis that biotic interactions are more important in the tropics, additional research is needed, including latitudinal comparisons of rates of molecular evolution for genes involved in biotic interactions, estimates of gradients in interaction strength, and phylogenetic comparisons of the traits that med...
DNA sequence data from four gene regions (28S, 18S, 16S-ND1, and CO1) were gathered from 65 jumping spider (sal-ticid) taxa to supplement previously gathered molecular data for the family's phylogeny. The additional taxa are mostly from Australasia and other regions of the Old World. Bayesian and parsimony analyses support a clade, here called the Astioida, representing a large proportion of the Australasian fauna. Included in the Astioida are, for example, the robust-bodied Simaetha and Mopsus, the flattened bark-dweller Holoplatys, the delicate foliage-dweller Tauala, the antlike Myrmarachne and the litter-dwelling Neon. One astioid, Rhondes neocaledonicus, is returned to that genus from its placement in Hasarius. Another newly supported clade, the Aelurilloida, includes the aelurillines, the freyines, and the Bacelarella group of genera. Other newly delimited clades are the Philaeus group (Philaeus, Mogrus, Carrhotus and oth-ers), the Leptorchesteae (Leporchestes, Yllenus and Paramarpissa) and the Hasarieae (Hasarius, Habrocestum and Chi-nattus). These results concur with previous discoveries (e.g., Amycoida, Marpissoida) in suggesting that salticid clades are largely restricted to continental regions.
We present the first cladistic analysis focused at the tribal and subfamily level of the orb-weaving spider family Araneidae. The data matrix of 82 characters scored for 57 arancid genera of 6 subfamilies and 19 tribes (and 13 genera from 8 outgroup families) resulted in 16 slightly different, most parsimonious trees. Successive weighting corroborated 62 of the 66 informative nodes on these cladograms; one is recommended as the ‘working’ araneid phylogcny. The sister group of Araneidae is all other Araneoidea. Araneidae comprises two major clades: the subfamily Araneinae, and the ‘argiopoid’ clade, which includes all other subfamilies and most tribes (((Gasteracanthinae, Caerostreae), (((Micratheninae, Xylcthreae), Eruyosaccus), (Eurycorminae, Arciinae)), Cyrlarachninae), ((Argiopinae, Cyrtophorinae), Arachnureae)). Cyrtarachneae and Mastophoreae are united in a new subfamily, Cyr-tarachninae. The spiny orb-weavers alone (Gasteracanthinae and Micratheninae) are not monophyletic. The mimetid subfamily Arciinae and the ‘tetragnathid’ genus Zygiella are araneids, but .Nephila (and other tetragnathids) are not. On the preferred tree, web decorations (stabilimenta) evolved 9 times within 15 genera, and were lost once. The use of silk to subdue prey evolved once in cribellate and four times in ecribillate orb weavers. Sexual size dimorphism evolved once in nephilines, twice in araneids, and reverted to monomorphism five times. Evolution in other genitalic and somatic characters is also assessed; behavioral and spinneret features arc most consistent (male genitalia, leg and prosomal features least consistent) on the phylogeny.
Orb-weaving spiders rely on sticky capture threads to retain prey long enough to be located and attacked. The evolution of viscid silk is associated with the high diversity of araneoid orb-weaving spiders, in part because it is cheaper to produce than the primitive dry cribellate fibrous adhesive used by deinopoid orb-weaving spiders. Unlike cribellate threads, viscid glue contributes little to the tensile strength of the capture spiral it decorates. However, viscid silk utilizes a unique suspension bridge mechanism, absent in cribellate silk, which increases total stickiness by recruiting the adhesion of multiple glue droplets. Here, we analyze the relationship between stickiness of viscid silk and various biomechanical and architectural features of webs that may influence its evolution, across a sample of 17 ecribellate orb-weaving species. The force required to break capture spiral fibers is the single most important factor explaining about 90% of the variation in stickiness among orb spiders. Stickiness increases linearly with capture spiral strength, but with a significant safety factor because stickiness is always less than the force required to break the silk. Our results thus indicate that evolutionary changes in the stickiness of the capture spiral are largely constrained by the strength of the fiber the glue is placed on rather than by the chemistry of the glue itself. This implies that orb webs function optimally when threads are able to detach and adhere repeatedly to struggling prey.
The Hawaiian happy face spider (Theridion grallator Simon, 1900), named for a remarkable abdominal colour pattern resembling a smiling face, has served as a model organism for understanding the generation of genetic diversity. Theridion grallator is one of 11 endemic Hawaiian species of the genus reported to date. Asserting the origin of island endemics informs on the evolutionary context of diversification, and how diversity has arisen on the islands. Studies on the genus Theridion in Hawaii, as elsewhere, have long been hampered by its large size (> 600 species) and poor definition. Here we report results of phylogenetic analyses based on DNA sequences of five genes conducted on five diverse species of Hawaiian Theridion, along with the most intensive sampling of Theridiinae analysed to date. Results indicate that the Hawaiian Islands were colonised by two independent Theridiinae lineages, one of which originated in the Americas. Both lineages have undergone local diversification in the archipelago and have convergently evolved similar bizarre morphs. Our findings confirm para- or polyphyletic status of the largest Theridiinae genera: Theridion, Achaearanea and Chrysso. Convergent simplification of the palpal organ has occurred in the Hawaiian Islands and in two continental lineages. The results confirm the convergent evolution of social behaviour and web structure, both already documented within the Theridiidae. Greater understanding of phylogenetic relationships within the Theridiinae is key to understanding of behavioural and morphological evolution in this highly diverse group.
What to attack is one of the most basic decisions predators must make, and these decisions are reliant upon the predator's sensory and cognitive capacity. Active choice of spiders as preferred prey, or araneophagy, has evolved in several distantly related spider families, including jumping spiders (Salticidae), but has never been demonstrated in ant-like jumping spiders. We used prey-choice tests with motionless lures to investigate prey-choice behaviour in Myrmarachne melanotarsa, an East African ant-like salticid that normally lives in aggregations and often associates with other spider species. We show that M. melanotarsa chooses spiders as prey in preference to insects and, furthermore, discriminates between different types of spiders. Myrmarachne melanotarsa's preferred prey were juvenile hersiliids and its second most preferred were other salticids. To date, all documented examples of araneophagic salticids have been from the basal subfamily Spartaeinae. Myrmarachne melanotarsa is the first non-spartaeine and also the first ant-like salticid for which araneophagy has been demonstrated.
Butterflies that hibernate exhibit particularly efficient defence against predation. A first line of defence is crypsis, and
most hibernating butterflies are leaf mimics. When discovered, some species have a second line of defence; the peacock, I. io, when attacked by a predator flicks its wings open exposing large eyespots and performs an intimidating threat display. Here
we test the hypothesis that butterflies relying solely on leaf mimicking and butterflies with an intimidating wing pattern,
when attacked, exhibit different behavioural suites—because leaf mimicking is best implemented by immobility, whereas intimidating
coloration is best implemented by intimidating behaviour. In laboratory experiments blue tits, Parus caeruleus, were allowed 40min to attack single individuals of three species of butterfly: one relying solely on crypsis, the comma,
Polygonia c-album; one relying on intimidating wing pattern in addition to crypsis, the peacock; and one intermediate species, the small tortoiseshell
Aglais urticae. The results are in accordance with expectations and demonstrate that: (1) birds take longer to discover the leaf mimicking
species, the comma, than the tortoiseshell and the peacock; (2) the comma remained motionless throughout experimental trials
but small tortoiseshells and peacocks flicked their wings when attacked; (3) the most intimidating butterfly, the peacock,
started flicking its wings at a greater distance from the attacking bird than the small tortoiseshell; and (4) the intimidating
pattern and behaviour of peacocks was effective—when discovered, all peacocks survived interactions with blue tits, whereas
only 22% of commas and 8% of small tortoiseshells survived.
The book discusses the diversity of mechanisms by which prey can avoid or survive attacks by predators, both from ecological and evolutionary perspectives. There is a particular focus on sensory mechanisms by which prey can avoid being detected, avoid being identified, signal (perhaps sometimes dishonestly) to predators that they are defended or unpalatable. The book is divided into three sections. The first considers detection avoidance through, for example, background matching, disruptive patterning, countershading and counterillumination, or transparency and reflective silvering. The second section considers avoiding or surviving an attack if detection and identification by the predator has already taken place (i.e., secondary defences). The key mechanism of this section is aposematism: signals that warn the predator that a particular prey type is defended. One particularly interesting aspect of this is the sharing of the same signal by more than one defended species (the phenomenon of Mullerian mimicry). The final section considers deception of predators. This may involve an undefended prey mimicking a defended species (Batesian mimicry), or signals that deflect predator’s attention or signals that startle predators. The book provides the first comprehensive survey of adaptive coloration in a predator-prey context in thirty years.
Theories of ecological diversification make predictions about the timing and ordering of character state changes through history. These theories are testable by "reconstructing" ancestor states using phylogenetic trees and measurements of contemporary species. Here we use maximum likelihood to estimate and evaluate the accuracy of ancestor reconstructions. We present likelihoods of discrete ancestor states and derive probability distributions for continuous ancestral traits. The methods are applied to several examples: diets of ancestral Darwin's finches; origin of inquilinism in gall wasps; microhabitat partitioning and body size evolution in scrubwrens; digestive enzyme evolution in artiodactyl mammals; origin of a sexually selected male trait, the sword, in platies and swordtails; and evolution of specialization in Anolis lizards. When changes between discrete character states are rare, the maximum-likelihood results are similar to parsimony estimates. In this case the accuracy of estimates is often high, with the exception of some nodes deep in the tree. If change is frequent then reconstructions are highly uncertain, especially of distant ancestors. Ancestor states for continuous traits are typically highly uncertain. We conclude that measures of uncertainty are useful and should always be provided, despite simplistic assumptions about the probabilistic models that underlie them. If uncertainty is too high, reconstruction should be abandoned in favor of approaches that fit different models of trait evolution to species data and phylogenetic trees, taking into account the range of ancestor states permitted by the data.
A common predator of spiders at Legon, Ghana, is the wasp Pison xanthopus, 96% of whose prey were salticids. Comparison of salticids in wasp cells with those found on nearby vegetation shows that fewer ant mimics (Myrmarachne spp.) are taken than one would expect if wasps were capturing salticids in proportion to their occurrence, but also that some individual wasps specialize in capturing Myrmarachne. Implications for the search image hypothesis are discussed. -from Author
We present the first cladistic analysis focused at the tribal and subfamily level of the orb-weaving spider family Araneidae. The data matrix of 82 characters scored for 57 araneid genera of 6 subfamilies and 19 tribes (and 13 genera from 8 outgroup families) resulted in 16 slightly different, most parsimonious trees. Successive weighting corroborated 62 of the 66 informative nodes on these cladograms; one is recommended as the ‘working’ araneid phylogeny. The sister group of Araneidae is all other Araneoidea. Araneidae comprises two major clades: the subfamily Araneinae, and the ‘argiopoid’ clade, which includes all other subfamilies and most tribes (((Gasteracanthinae, Caerostreae), (((Micratheninae, Xylethreae),Encyosaccus), (Eurycorminae, Arciinae)), Cyrtarachninae), ((Argiopinae, Cyrtophorinae), Arachnureae)). Cyrtarachneae and Mastophoreae are united in a new subfamily, Cyrtarachninae. The spiny orb-weavers alone (Gasteracanthinae and Micratheninae) are not monophyletic. The mimetid subfamily Arciinae and the ‘tetragnathid’ genusZygiellaare araneids, butNephila(and other tetragnathids) are not. On the preferred tree, web decorations (stabilimenta) evolved 9 times within 15 genera, and were lost once. The use of silk to subdue prey evolved once in cribellate and four times in ecribillate orb weavers. Sexual size dimorphism evolved once in nephilines, twice in araneids, and reverted to monomorphism five times. Evolution in other genitalic and somatic characters is also assessed; behavioral and spinneret features are most consistent (male genitalia, leg and prosomal features least consistent) on the phylogeny.
Inferences about the evolution of defensive strategies in tiger beetles (genus Cicindela) have been contentious, largely due to the lack of a phylogenetic hypothesis for the group. We used a dataset that includes measures of chemical defense, habitat association, and body coloration for a representative sample of North American Cicindela (Pearson et al. 1988) to reassess, within a phylogenetic context, the problem of covariation in defensive strategies. We reconstructed a phylogenetic hypothesis from mtDNA for a total of 44 Cicindela and seven outgroup taxa using 1896 base pairs from three segments of the mitochondrial genome. Characters involved in predator deterrence and escape were optimized onto this phylogeny. Although most taxa producing large amounts of benzaldehyde fall into two monophyletic clades, numerous changes in the level of benzaldehyde secretion across the genus suggest that this parameter is poorly conserved phylogenetically. In contrast to previous studies, we also found little support for correlated character changes in benzaldehyde secretion and habitat type, a presumed indicator of the selective regime. Aposematic coloration of the abdomen was restricted to a single monophyletic group of taxa producing large amounts of benzaldehyde. Bright iridescent coloration, implicated in predator evasion during flight, was only loosely correlated with the phylogenetic affinities of taxa and appears to be part of a defensive strategy not usually acting in combination with chemical defenses. Our study of character covariation clarifies earlier analyses of the adaptive significance of benzaldehyde defense, which were inconclusive without a phylogenetic hypothesis.
The biology of a primitive salticid spider, Portia fimbriata (Doleschall), is described from observations in a Queensland rain-forest and the laboratory. Locomotory specializations enable the spiders to move about readily on webs; and all stages of life history are associated with webs, both alien and two types they build themselves. The more flimsy Type 1 webs are used as resting sites similar to the nests employed by more familiar jumping spiders. Type 2 webs are more substantial structures in which the spider moults, mates, oviposits, broods its eggs and remains for as long as 48 days. The predatory strategy of Portia includes the use of distinct alternative tactics in the pursuit of varied types of prey. Most of these tactics are ones not usually associated with salticids. Portia invaded diverse types of webs without difficulty, including adhesive and non-adhesive, cribellate and ecribellate, and two-and three-dimensional ones. Once in the web, Portia produced vibratory stimuli by specialized but varied movements of the legs and palps. Web spiders responded to these in a manner more appropriate for a potential prey item or a conspecific in its web than a potential predator. Sometimes vibrations lured the spider to the waiting Portia. Other times, localized movements were elicited which assisted Portia in remaining orientated toward the spider as it stalked across the web. Outside webs, Portia stalked other species of salticids, moving in a very slow and “mechanical” fashion and arresting forward motion whenever faced by the prey. Evidently, the salticids did not recognize Portia as another salticid and a potential predator. Although Portia pursued insects, they pursued spiders more readily, persistently and successfully. Portia captured insects outside webs, on their own webs and on the webs of other species. Those on their own webs adhered temporarily to the silk. In webs of other spiders, insects were sometimes taken directly from the chelicerae of the host. Also, their own webs assisted Portia in capturing other spiders. Eggs of spiders were fed upon both on and off webs. Different attack tactics tended to be employed with different types of prey: web spiders, lunge; salticids, swoop; insects, pick-up. Egg-cases were opened by means of specialized movements involving the chelicerae and the eggs were raked toward the mouth with the legs. Most prey were seized after the attack, but sometimes they were stabbed with fangs and ran several centimetres before immobilized. Portia maintained its orientation, then walked to the stabbed prey and fed. Vision of the prey seemed to be of major importance for most aspects of predatory behaviour. In the rain-forest habitat, webs of Portia, pisaurids, pholcids, and theridiids are often contiguous and facilitate the tactic of web-invasion. It is proposed that the pervasive use of webs by Portia is a primary character conserved from ancestral salticids, and that in the evolution of the family, invasion of contiguous webs could have led to selection for a sophisticated visual system that assisted in the localization of their residents. The developed visual system could then have allowed vagrant predation en route to more distant webs, and finally emancipation from dependence on webs altogether.
This study presents a new phylogeny of erigonine spiders with emphasis on genera from the Neotropics. Thirty-nine exemplar taxa representing mostly Neotropical genera were added to a global sample of 31 erigonine and 12 outgroup exemplar taxa analyzed in a previous study. These 82 taxa were coded for 176 (172 informative) mostly morphological characters. Eighty-one characters were identical to or modified from the 73 (67 informative) characters included in a previous study; the remaining 95 characters are new. The complete data set includes 70 erigonine exemplars representing 65 genera, seven nonerigonine linyphiid exemplars, and five exemplars representing four araneoid families in the outgroup. Cladistic analysis resulted in a single most parsimonious tree (L =904, CI = 0.23, RI = 0.58; uninformative characters excluded: L = 900, CI = 0.23). This paper explores the implications of the new topology for the evolution of several characters of interest in erigonine evolution. The phylogeny implies that the desmitracheate condition is a synapomorphy of erigonines, with a reversal to the haplotracheate condition in one large clade within Erigoninae. We infer that the loss of the paracymbium in Neotropical erigonines occurred twice and may have progressed by different evolutionary pathways. Our phylogeny differs markedly from the previous cladistic hypothesis of erigonine relationships. We investigate how the addition of characters and taxa (alone and together) have altered the earlier hypothesis of erigonine phylogeny. We conclude that topological changes from the previous study to the current one are largely the result of adding and modifying characters, not adding taxa. Continuous Jackknife Function (CJF) analysis predicts that the inclusion of additional character data will continue to imply changes in the relationships among taxa in our analysis.
Theories of ecological diversification make predictions about the timing and ordering of character state changes through history. These theories are testable by "reconstructing" ancestor states using phylogenetic trees and measurements of contemporary species. Here we use maximum likelihood to estimate and evaluate the accuracy of ancestor reconstructions. We present likelihoods of discrete ancestor states and derive probability distributions for continuous ancestral traits. The methods are applied to several examples: diets of ancestral Darwin's finches; origin of inquilinism in gall wasps; microhabitat partitioning and body size evolution in scrubwrens; digestive enzyme evolution in artiodactyl mammals; origin of a sexually selected male trait, the sword, in platies and swordtails; and evolution of specialization in Anolis lizards. When changes between discrete character states are rare, the maximum likelihood results are similar to parsimony estimates. In this case the accuracy of estimates is often high, with the exception of some nodes deep in the tree. If change is frequent then reconstructions are highly uncertain, especially of distant ancestors. Ancestor states for continuous traits are typically highly uncertain. We conclude that measures of uncertainty are useful and should always be provided, despite simplistic assumptions about the probabilistic models that underlie them. If uncertainty is too high, reconstruction should be abandoned in favor of approaches that fit different models of trait evolution to species data and phylogenetic trees, taking into account the range of ancestor states permitted by the data.
A phylogenetic analysis of five sequenced genes (28S, 16S, EF1-α , CO1, ND1) from 81 genera of jumping spiders (Salticidae) and five outgroups supports the monophyly of the Dendryphantinae and Euophryinae and refines the concepts of the Plexippinae and Pelleninae. The clade that excludes lyssomanines and spartaeines and contains the bulk of salticid species is formally named as the Salticoida. The previously proposed clade delimited by an embolus articulated and separated from the tegulum by a developed distal hematodocha (as opposed to fused immovably to the tegulum) is rejected, suggesting the 'free embolus' evolved independently several times. Three major clades are discovered, the Marpissoida (including Dendryphantinae, Marpissinae and smaller groups such as synagelines), the Plexippoida (plexippines plus pellenines) and the Amycoida (including Amycinae, Sitticinae, Hyetusseae, Hurieae, Synemosyninae). The amycoids form a large neotropical radiation from which only a single known group (Sitticus and Attulus) has reached the Old World. The marpissoids also constitute a major New World group with relatively few species in the Old World. In contrast, the Plexippoida is predominantly an Old World group (except for the spectacular radiation of Habronattus in North America), as is the Heliophaninae. These results suggest that much of salticid diversification occurred after the separation of the continents of the Old World and New World.
HISTORICAL ecology contains various examples of how predators introduced onto islands by man have apparently exterminated native prey species1–6. Conversely, a pioneering experiment7 showed an increase in number of species with predator presence. Subsequent experiments have shown both increases and decreases in prey diversity8–10. Here we investigate how predator introduction affects one aspect of prey diversity (number of species or species richness), and prey abundance. We ran a seven-year experiment on an entirely natural system of small islands, using the commonest local lizard as the predator and web spiders as prey. Lizard introduction caused rapid and devastating effects on spider diversity and abundance: within two years, islands onto which lizards had been introduced became almost identical to islands with natural lizard populations. The proportion of species becoming extinct was 12.6 times higher on lizard-introduction' islands than on islands without lizards. Locally common and rare species were both reduced by the introduction of lizards, but nearly all of the latter became permanently extinct.
The first quantitative phylogenetic analysis of three sequenced genes (16S rRNA, cytochrome c oxidase subunit I, histone 3) of 25 genera of crab spiders and 11 outgroups supports the monophyly of Thomisidae. Four lineages within Thomisidae are recovered. They are informally named here as the Borboropactus clade, Epidius clade, Stephanopis clade and the Thomisus clade, pending detailed morphology based cladistic work. The Thomisus clade is recovered as a strongly supported monophyletic group with a minimal genetic divergence. Philodromidae previously widely considered a subfamily of Thomisidae do not group within thomisids and is excluded from Thomisidae. However, Aphantochilinae previously generally considered as a separate family falls within the Thomisus clade and is included in Thomisidae. The recently proposed new family Borboropactidae is rejected, as it is paraphyletic.
© The Willi Hennig Society 2008.
This paper studies the phylogeny of the spider families Liocranidae and Corinnidae as they have been delimited to date, using an exemplar approach. In the analysis, 40 species belonging to 24 liocranid and 14 corinnid genera are scored for 157 morphological characters. The genera Clubiona (Clubionidae) and Gnaphosa (Gnaphosidae) are used as outgroups. Under implied weighting, a single fittest tree is found. This hypothesis seriously challenges the presently prevailing classification of the former Clubionidae sensu lato. The subfamily Phrurolithinae (Liocranidae) turns out to be the sister group of Trachelinae and is transferred to Corinnidae. In the interest of taxonomic stability, no radical rearrangement of the families constituting Clubionidae sensu lato is proposed, as it is felt that the present results should first be further corroborated by additional, more elaborate analyses on an even larger data set.
Jan Bosselaers, ‘Dochterland’, R. novarumlaan 2, B-2340 Beerse, Belgium. E-mail: hortipes@dochterland.org
Rudy Jocqué, Musée Royal de l’Afrique Centrale, B-3080 Tervuren, Belgium. E-mail: jocque@africamuseum.be
There have been many different and conflicting definitions of mimicry. Some of the definitions of mimicry include crypsis and others do not. Each definition includes different groups of phenomena and uses different criteria to distinguish mimetic from non-mimetic phenomena. The confusion is eliminated by a consideration of the criteria of all definitions. This shows that there are in fact three major criteria dividing six phenomona, rather than a single dichotomy between mimicry and crypsis (Table 2). The criteria are defined by the results of a mistake in discrimination between the model and mimìc: (a) the mistake does or does not depend upon relationship between mimic and background; (b) the mistake has or has no effect on the population dynamics or evolution of the model and (c) the mistake affects dynamics or evolution of one or of many models. The main reason for the contusion about mimicry and crypsis is that each author's definition includes differing and partially overlapping subsets of the six classes: crypsis; masquerade; Batesism; Müllerism; polymorphism and convergence.
A method is presented for quantitative estimation of the degree of crypsis of species seen by visual predators against known backgrounds. It is based upon a comparison between transects taken across animal and background colour patterns. The method was applied to day-resting moths in deciduous forest in New Jersey. Each species is found for two to four weeks at characteristic dates, and there is a constant turnover of species. In both moths and backgrounds there is a regular change in the colour pattern parameters from winter through spring to early summer. Moths are on average more cryptic at their normal dates than they would be if present earlier or later in the year. Species with known resting sites are on average more cryptic on their resting sites than other background habitats. Species that rest on more than one background habitat are less cryptic on their preferred habitats than are specialists. Species that rest under leaves and are not visible from above are not very cryptic. Specific v. general resemblance, disruptive coloration, and factors affecting ‘aspect diversity’ are discussed. The new method of estimating crypsis is useful for studies of crypsis as well as in sexual selection. It is necessary to know much about the resting sites and behaviour of moths, as well as other functions of colour patterns, to understand colour pattern evolution.
The monophyly of Tetragnathidae including the species composition of the family (e.g., Are Nephila and their relatives part of this lineage?), the phylogenetic relationships of its various lineages, and the exact placement of Tetragnathidae within Araneoidea have been three recalcitrant problems in spider systematics. Most studies on tetragnathid phylogeny have focused on morphological and behavioral data, but little molecular work has been published to date. To address these issues we combine previous morphological and behavioral data with novel molecular data including nuclear ribosomal RNA genes 18S and 28S, mitochondrial ribosomal RNA genes 12S and 16S and protein-coding genes from the mitochondrion [cytochrome c oxidase subunit I (COI)] and from the nucleus (histone H3), totaling ca. 6.3 kb of sequence data per taxon. These data were analyzed using direct optimization and static homology using both parsimony and Bayesian methods. Our results indicate monophyly of Tetragnathidae, Tetragnathinae, Leucauginae, the “Nanometa clade” and the subfamily Metainae, which, with the exception of the later subfamily, received high nodal support. Morphological synapomorphies that support these clades are also discussed. The position of tetragnathids with respect to the rest of the araneoid spiders remains largely unresolved but tetragnathids and nephilids were never recovered as sister taxa. The combined dataset suggests that Nephilidae is sister to Araneidae; furthermore, the sister group of Nephila is the clade composed by Herennia plus Nephilengys and this pattern has clear implications for understanding the comparative biology of the group. Tetragnathidae is most likely sister to some members of the “reduced piriform clade” and nephilids constitute the most-basal lineage of araneids.
It is widely assumed that high resource specificity predisposes lineages toward greater likelihood of extinction and lower likelihood of diversification than more generalized lineages. This suggests that host range evolution in parasitic organisms should proceed from generalist to specialist, and specialist lineages should be found at the ‘tips’ of phylogenies. To test these hypotheses, parsimony and maximum likelihood methods were used to reconstruct the evolution of host range on a phylogeny of parasitoid flies in the family Tachinidae. In contrast to predictions, most reconstructions indicated that generalists were repeatedly derived from specialist lineages and tended to occupy terminal branches of the phylogeny. These results are critically examined with respect to hypotheses concerning the evolution of specialization, the inherent difficulties in inferring host ranges, our knowledge of tachinid-host associations, and the methodological problems associated with ancestral character state reconstruction. Both parsimony and likelihood reconstructions are shown to provide misleading results and it is argued that independent evidence, in addition to phylogenetic trees, is needed to inform models of the evolution of host range and the evolutionary consequences of specialization.
This study infers the higher-level cladistic relationships of linyphiid spiders from five genes (mitochondrial CO1, 16S; nuclear 28S, 18S, histone H3) and morphological data. In total, the character matrix includes 47 taxa: 35 linyphiids representing the currently used subfamilies of Linyphiidae (Stemonyphantinae, Mynogleninae, Erigoninae, and Linyphiinae (Micronetini plus Linyphiini)) and 12 outgroup species representing nine araneoid families (Pimoidae, Theridiidae, Nesticidae, Synotaxidae, Cyatholipidae, Mysmenidae, Theridiosomatidae, Tetragnathidae, and Araneidae). The morphological characters include those used in recent studies of linyphiid phylogenetics, covering both genitalic and somatic morphology. Different sequence alignments and analytical methods produce different cladistic hypotheses. Lack of congruence among different analyses is, in part, due to the shifting placement of Labulla, Pityohyphantes, Notholepthyphantes, and Pocobletus. Almost all combined analyses agree on the monophyly of linyphioids, Pimoidae, Linyphiidae, Erigoninae, Mynogleninae, as well as Stemonyphantes as a basal lineage within Linyphiidae. Our results suggest independent origins of the desmitracheate tracheal system in micronetines and erigonines, and that erigonines were primitively haplotracheate. Cephalothoracic glandular specializations of erigonines and mynoglenines apparently evolved independently. Subocular sulci of mynoglenines and lateral sulci (e.g. Bathyphantes) evolved independently but glandular pores in the prosoma proliferated once. The contribution of different character partitions and their sensitivity to changes in traditional analytical parameters is explored and quantified. © The Willi Hennig Society 2009.
When threatened, the black widow spider, Latrodectus hesperus, emits an adhesive, viscous web, pulls the strand from its spinnerets with its fourth pair of legs, and spreads its appendages. This behavior positions the web over the delicate abdomen, increases the area of protection, and enables the spider to place the web onto the offender, if necessary.
In laboratory interactions, the viscous web protected black widows from mice (Peromyscus spp.). Mature female spiders, which had their spinnerets blocked and hence could not discharge the viscid silk, escaped less often than did black widows that were not experimentally altered.
The viscid silk is palatable to mice and it appears that the deterrent effect of the web is due solely to mechanical irritation.
The defensive behavior is elicited most often from mature females, which may suffer greater predation than other age groups. Males lose the ability to produce the defensive web at maturity and may shift their energy resources totally into reproductive effort.
The ability to change body coloration is widely used in the context of visual camouflage to hide from predators or prey. Although experimental evidence from human vision shows that background and prey eye colours may trigger adaptive colour change in crab spiders, no study has addressed this hypothesis in the perceptual colour space of either predator or prey. I simultaneously tested the effects of reflected light and prey eye colours on background matching of female crab spiders, Misumena vatia. Using spectror- adiometric measurements and modelling of perceptual colour space of the most frequent prey, I tested whether individual spiders were able to match white and yellow light reflected by artificial backgrounds when fed either white- or red-eyed fruit flies, Drosophila melanogaster. The colour of light reflected by the visual background triggered adaptive camouflage as seen by Hymenopteran prey. In addition, there was a significant effect of prey eye colour within each light colour experiment, with spiders fed white- eyed flies better matching light reflected by the white background, and spiders fed red-eyed flies better matching the yellow reflected light. However, only spiders exposed to yellow reflected light and fed red- eyed flies could approach the colour detection threshold calculated for Hymenoptera. These results provide insights into how colour change is triggered in crab spiders, and indicate that ommochrome pigments in- gested with prey eyes not only are used by crab spiders to adjust their adaptive coloration, but also may indicate the hunting ability of females to potential mates