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Sexual differences in color and color change in wood frogs
Canadian Journal of Zoology
Abstract
An observer-free method of color classification was used to determine whether wood frogs, Rana sylvatica, exhibit sexual differences in color and color change. Males and females captured from breeding aggregations differed significantly in color: females reflected a greater amount of long-wavelength (yellow–red) light and less short-wavelength (blue–green) light than males. The color difference was not just a result of differences in the state of physiological color change at the time of capture but persisted for a month after capture. Males and females also differed in their color-change responses to black and white backgrounds: both sexes changed in brightness, but only males changed in the relative amount of light reflected at different wavelengths. Wood frog color may function in predator avoidance through crypsis. There was a good match between frogs and some of the leaves from the leaf litter surrounding the breeding ponds. Hypotheses for the development of sexual differences in wood frog color include sexual differences in availability of pigment and pigment precursors, morphological color change, and evolutionary response to different selection pressures.
... Therefore, in this study, we investigated numerous hypotheses considering the role of proximate and ultimate mechanisms behind the maintenance of intraspecific color variation, in both intra-and interspecific ecological contexts. Using the wood frog (Rana sylvatica), a species that presents remarkable intraspecific color variation and sexual dimorphism (Banta 1914, Martof and Humphries 1959, King and King 1991, Lambert et al. 2017), we first describe color variation in our study populations. Variation provides clues about potential signaling functions. ...
... Across their geographic range, wood frogs have been described as having regional morphotypes that differ not only in morphology (i.e., relative leg length), but also in body coloration and patterning, with background colors ranging from a tan or chestnut brown to a dark brown (Martof and Humphries 1959). They also exhibit considerable color variation within populations (King andKing 1991, Lambert et al. 2017; D. Goedert, personal observation; Appendix S1: Fig. S1) that has been partially explained by sexual dimorphism, with males expressing darker and yellower coloration, and females being lighter and redder than males (Banta 1914, King and King 1991, Lambert et al. 2017. Sexual dichromatism in wood frogs has been proposed as a mechanism for sexual recognition, with anecdotal evidence that lighter-colored, redder females are more readily recognized by males than are darker colored females when entering breeding aggregations (Banta 1914). ...
... Across their geographic range, wood frogs have been described as having regional morphotypes that differ not only in morphology (i.e., relative leg length), but also in body coloration and patterning, with background colors ranging from a tan or chestnut brown to a dark brown (Martof and Humphries 1959). They also exhibit considerable color variation within populations (King andKing 1991, Lambert et al. 2017; D. Goedert, personal observation; Appendix S1: Fig. S1) that has been partially explained by sexual dimorphism, with males expressing darker and yellower coloration, and females being lighter and redder than males (Banta 1914, King and King 1991, Lambert et al. 2017. Sexual dichromatism in wood frogs has been proposed as a mechanism for sexual recognition, with anecdotal evidence that lighter-colored, redder females are more readily recognized by males than are darker colored females when entering breeding aggregations (Banta 1914). ...
Animal coloration is a multifaceted trait with many ecological roles and related to a variety of developmental and physiological processes. Consequently, coloration is often subject to a variety of selective pressures, leading to the evolutionary maintenance of variation. In this study, we investigated hypotheses related to the maintenance of dorsal color variation in wood frogs (Rana sylvatica). First, we tested for multimodality, and whether color correlates with body size or condition or varies by sex or age class. We combined behavioral trials with visual modeling to test for sex recognition. We also considered visual models for predators and tested for an interaction between discriminability indexes (JND) of color channel (chromatic vs. achromatic) and predator type (birds vs. snakes), as well as for a within individual trade‐off between the JND of chromatic and achromatic coloration. Finally, we tested for disruptive viability selection on color using predation trials, and for antagonistic directional selection between viability selection and reproductive investment of females. We found that wood frogs present continuous color variation that does not correlate with body size or condition, but that changes with age. Wood frogs present subtle sexual dichromatism, but we found no evidence for a role of color in sex recognition. Instead, we discuss the possibility that sex differences might, at least in part, have a demographic explanation. Predator visual models indicated that wood frogs cannot solely rely on dorsal coloration for camouflage. Moreover, different predators might present selective pressures in different color channels, while individuals’ achromatic and chromatic coloration trade‐off in JND. Therefore, different selective pressures caused by different predators might interact with ontogenetic changes and developmental/physiological trade‐offs to maintain color variation. We found no relationship between color and survival or reproductive investment, suggesting further work is required to fully understand selection on color. Our results highlight the importance of understanding evolutionary trade‐offs and developmental/physiological constraints in combination with one another, and suggest the potential for an interaction between these proximate and ultimate mechanisms in the evolutionary maintenance of variation. These results likely extend beyond color expression in amphibians, and exemplify a more general process for such evolutionary outcomes.
... Ostrofsky (1993), Maerz et al. (2005aMaerz et al. ( , b, 2010, Ard on and Pringle (2008) Litter inputs increase physical refuge space and mediate both visual and chemical communication between predators and prey. Richardson (1992), King and King (1991), Brown et al. (2002) Plastic phenotypic responses to litter inputs include changes in consumer development time, growth rate, reproductive output, sexual traits, and metamorphic appendages. Shorter hydroperiod induces both faster and slower litter decay rates, likely dependent on litter quality. ...
... However, dark water might also serve as a visual indicator of high resource abundance, which can attract ovipositing insects that act as predators in their aquatic stage (Williams et al. 2007). In turn, some prey can mimic the color of litter in wetlands to avoid predation (King and King 1991). As the quality or quantity of litter inputs changes within a wetland system, such subtle effects are likely to alter the diversity and composition of food webs and ecosystem function. ...
The input of senescent terrestrial leaf litter into soil and aquatic ecosystems is one of the most massive cyclic subsidies on Earth, particularly within forested ecosystems. For freshwater systems embedded within forests, litter inputs provide a vital source of energy and nutrients that allows greater production than in situ resources can provide. In return, freshwater food webs can provide an enormous amount of material to the terrestrial landscape through biotic respiration, photosynthesis, and organism emergence. Most research concerning this important aquatic‐terrestrial link has focused on lotic ecosystems (i.e., streams and rivers); far less attention has been given to its role in lentic systems (i.e., wetlands and lakes). A focus on small forested wetlands is particularly important, as these systems account for a disproportionate amount of global carbon flux relative to their spatial coverage, and the decomposition of leaf litter is a major contributor. Here, we review six themes: (1) the evidence for the role of leaf litter inputs as an ecologically important subsidy in forested wetlands; (2) the bottom‐up effects of quantitative and qualitative variation in litter inputs; (3) how diversity in litter mixtures can alter ecological functioning; (4) evidence for top‐down consequences of litter inputs through toxic effects on predators and parasites, and the alteration of predator–prey interactions; (5) the relevance of our review to other research fields by considering the role of litter inputs relative to other types of subsidies and environmental gradients (e.g., temperature, canopy cover, and hydrology); and (6) the interaction of litter subsidies with anthropogenic disturbances. We conclude by highlighting several high‐priority research questions and providing suggestions for future research on the role of litter subsidies in freshwater ecosystems.
... Interestingly, sexual dichromatism is absent at time 15 March (time point 4), immediately after overwintering, but is present both in the fall before overwintering and again in late spring after breeding typically occurs in wild populations. Given that breeding Wood Frogs are known to be sexually dichromatic (Banta 1914;King and King 1991), this result suggests that the seasonal onset of dichromatism occurs in a relatively short window of time (days or weeks) in the spring when Wood Frogs emerge from overwintering but before they enter ponds to breed. This result also indicates that 4 d of increasing temperature following hibernation was insufficient to elicit the spring onset of sexual dichromatism. ...
... First, sexual dichromatism might represent sexspecific selection to avoid predation. Prior work found that adult female Wood Frog coloration matches terrestrial forest leaf litter better than adult male coloration (King and King 1991). This likely helps females avoid depredation during terrestrial movements. ...
Some species exhibit sex-specific color differences (sexual dichromatism) that are considered important for reproduction. The developmental timing of sexual dichromatism is largely unknown, particularly in amphibians, and is important for informing our basic understanding of sex-specific divergence in the physiology, anatomy, and ecology of species more broadly. Using a controlled laboratory environment, we explored the onset of sexual dichromatism in Wood Frogs (Rana sylvatica), a species in which adult females typically appear redder than males. We photographed juvenile Wood Frogs approximately every two months for one year and quantified coloration (hue, saturation, brightness). Our results show that Wood Frog hue becomes sexually dichromatic before their first winter, with yellower hues in males and redder hues in females. Hue differences persist throughout the following spring and summer, with the exception of immediately after emergence from overwintering when both sexes are dramatically less bright. Male and female Wood Frogs typically do not join breeding aggregations until their first and second year, respectively; our results therefore indicate that sexual dichromatism is established soon after metamorphosis and substantially before first breeding attempts. We also noted seasonal fluctuations in hue and luminance, both of which increased during the first fall, decreased during winter, and increased again during the second spring and summer. These fluctuations suggest that color plays a role not only in sexual signaling but also in terrestrial camouflage. Future work should explore the ecological and evolutionary relevance of the early onset of sexual dichromatism and the function of seasonal variation in frog coloration.
... Colors include light tan to dark brown, olive, green, gray, and pink. Females may be lighter in color than males (Seale 1982, King andKing 1991). A study in Indiana revealed that wood frogs are capable of changing color to match the substrate on which they are found (King and King 1991); this characteristic likely occurs throughout the range of the frog. ...
... Females may be lighter in color than males (Seale 1982, King andKing 1991). A study in Indiana revealed that wood frogs are capable of changing color to match the substrate on which they are found (King and King 1991); this characteristic likely occurs throughout the range of the frog. A black or dark brown mask extends from the tip of the nose across the eye ending just past the tympanum, and a white jaw stripe is present below the mask. ...
ACKNOWLEDGMENTS The authors would,like to acknowledge,the help of the many,people who,contributed time and answered questions during our review of the literature. AUTHORS’ BIOGRAPHIES Dr. Erin Muths is a Zoologist with the U.S. Geological Survey – Fort Collins Science Center. She has been studying amphibians,in Colorado and the Rocky Mountain Region for the last 10 years. Her research focuses on demographics of boreal toads, wood frogs and chorus frogs and methods research. She is a principle investigator for the USDOI Amphibian Research and Monitoring Initiative and is an Associate Editor for the Northwestern Naturalist. Dr. Muths earned a B.S. in Wildlife Ecology from the University of Wisconsin, Madison (1986); a M.S. in Biology (Systematics and Ecology) from Kansas State University (1990) and a Ph.D. in Zoology from the University of Queensland, Brisbane, QLD, Australia (1997). Suzanne Rittmann has been a field biologist for both the USGS and Colorado Division of Wildlife. Her work began in 2000 and focused on health,evaluations of amphibians,in Rocky,Mountain National Park and population monitoring of Boreal toads (Bufo boreas boreas) in both Rocky Mountain National Park and the mountains of Clear Creek county, Colorado. She earned her B.S. in Biology from Lewis and Clark College (1991) in Portland, Oregon. Dr. Jason T.Irwin is an ecophysiologist interested in cold tolerance, especially freeze tolerance in ectotherms. He has worked,on the physiology and evolution of the wood,frog and its relatives to identify the pathways,by which freeze tolerance may have evolved in the brown-frog group. He is currently an assistant professor in the Department of Biological Sciences at Central Washington University.
... This is true not only for H. regilla but also for anurans in general. In anuran amphibians, color change may be used for avoiding predators (crypsis) in addition to water balance and (or) thermoregulation (Hoppe 1979; King and King 1991; King et al. 1994). It is likely that the most important aspect of color change is to increase cryptic value (Kats and Van Dragt 1986), but the relative importance of color change to hydro-and thermo-regulation is still unclear. ...
... Therefore, it is important to study the simple and interactive responses of color components in the context of wholeanimal color change for a clear understanding of the ecological significance of color change. Traditionally, human observation (e.g., Edgren 1954; Iga and Bagnara 1975; Kats and Van Dragt 1986) and reflectance spectrophotometry (e.g., Nielsen 1980; King and King 1991; King et al. 1994; Wente and Phillips 2003) have been the two methods employed in color change studies. Digital imagery overcomes the subjectivity of human observation and the invasiveness of reflectance spectrophotometry (Nielsen 1978a, 1978b; Zuk and Decruyenaere 1994) and is a reliable method (e.g., Villafuerte and Negro 1998; Gerald et al. 2001;). ...
A number of environmental variables have been identified as affecting anuran color, but rarely have the interactions between these variables been investigated. In attempt to elucidate the function of color change, we conducted a within-subject, full factorial experiment designed to determine the simple and interactive effects of background, temperature, and light intensity on the rate of color change in the Pacific tree frog (Hyla regilla Baird and Girard, 1852). Color was investigated holistically, as well as by decomposing it into its constituent parts (hue, chroma, and lightness), using digital photography. The rate of color change was faster on the green versus the brown background, at 10 versus 25 degreesC, and at low versus high light intensity. There was also a significant effect of the interaction between background color and temperature on the rate of color change. We found increased rates of hue, chroma, lightness, and color change with increasing initial hue, chroma, lightness, and color distances between the Pacific tree frog and its background, respectively. In addition, initial color distance covaried with changes in environmental variables. After controlling for initial color distance, and thus the effects of background matching, background color and temperature still showed a significant interaction for their effects on rate of color change. These results suggest that crypsis (i.e., background matching) is not the only function of physiological color change in H. regilla. Physiological color change may also be used to hydro- and (or) thermo-regulate.
... Boana prasina (Burmeister, 1856), B. dentei (Bokermann, 1967), Bokermannohyla circumdata (Cope, 1871), B. alvarengai (Bokermann, 1956), Dryophytes japonicus (Günther, 1859), Pseudacris regilla (Baird and Girard, 1852), Scinax fuscomarginatus (Lutz, 1925), S. hayii (Barbour, 1909) and S. ruber (Laurenti, 1768 and Phyllomedusidae Phasmahyla cochranae (Bokermann, 1966), P. guttata (Lutz, 1924), P. exilis (Cruz, 1980), P. jandaia (Bokermann and Sazima, 1978), Pithecopus azureus (Cope, 1862), P. megacephalus (Miranda-Ribeiro, 1926) and P. rohdei (Mertens, 1926) (Stegen et al., 2004;Toledo and Haddad, 2009;Choi and Jang, 2014;Machado et al., 2015;Pedroso-Santos et al., 2019;Mendonça et al., 2020). For anurans in general, this phenomenon is related to mechanisms to avoid predation, thermoregulation, and reproductive activities (Hoppe, 1979;King and King, 1991;King et al., 1994;Toledo and Haddad, 2009). ...
Os anuros possuem uma ampla variedade de mecanismos antipredadores relacionados à coloração como aposematismo, mimetismo, camuflagem, coloração disruptiva e polifenismo. Neste estudo, relatamos o primeiro registro de polifenismo dinâmico para o cambo (P. bicolor) e para o gênero Phyllomedusa. Nosso registro sugere que o polifenismo apresentado por P. bicolor pode estar relacionado à sua estratégia de camuflagem, uma vez que os dois indivíduos mudaram rapidamente de cor para se adaptar a uma situação ambiental diferente (iluminação) no microhabitat, ao mesmo tempo em que apresentavam o mecanismo antipredador de “agachamento abaixo".
... There is also growing evidence of the important structural effects of vegetation on community interactions and evolutionary responses to predation among amphibians (King & King, 1991;Walls, 1995;Relyea, 2002;Ghioca-Robrecht, Smith & Densmore, 2009;Purrenhage & Boone, 2009;Hossie & Murray, 2010;Costa & Kishida, 2015). Although amphibian communities have a rich history as model systems in community ecology (Werner, 1994;Wilbur, 1997), there has been remarkably little intentional integration of plants as constituents of those communities. ...
Descriptions of amphibian habitat, both aquatic and terrestrial, often include plants as characteristics but seldom is it understood whether and how those plants affect amphibian ecology. Understanding how plants affect amphibian populations
is needed to develop strategies to combat declines of some amphibian populations. Using a systematic approach, we reviewed and synthesized available literature on the effects of plants on pond-breeding amphibians during the aquatic and terrestrial stages of their life cycle. Our review highlights that plant communities can strongly influence the distribution, abundance, and performance of amphibians in multiple direct and indirect ways. We found three broad themes of plants’ influence on amphibians: plants can affect amphibians through effects on abiotic conditions including the thermal, hydric, and chemical aspects of an amphibian’s environment; plants can have large effects on aquatic life stages through effects on resource quality and abundance; and plants can modify the nature and strength of interspecific interactions between amphibians and other species – notably predators. We synthesized insights gained from the literature to
discuss how plant community management fits within efforts to manage amphibian populations and to guide future research efforts. While some topical areas are well researched, we found a general lack of mechanistic and trait-based work which is needed to advance our understanding of the drivers through which plants influence amphibian ecology. Our literature review reveals the substantial role that plants can have on amphibian ecology and the need for integrating plant and amphibian ecology to improve research and management outcomes for amphibians.
... This explanation is not necessarily applicable to amphibians; many larvae in wetlands are darkly colored and probably camouflaged from terrestrial predators by the dark colors. In addition, some tadpoles are capable of darkening skin colors in response to their environment (King and King, 1991). This possibility certainly warrants further investigation, particularly because it could alter aquatic-terrestrial linkages. ...
Breeding organisms rely on numerous environmental cues to determine optimal sites for oviposition. Site selection is often associated with factors that increase fitness, and the identification of these factors can help conservation efforts. For amphibians that breed in wetlands, the quality of terrestrial subsidies (e.g., leaf litter) can strongly influence larval survival and development by altering water chemistry and available nutrients. In this study, we examined the preference of breeding Gray Treefrogs (Hyla versicolor) for wetlands containing litter species of varying chemical quality. Based on previous studies of larval survival, we hypothesized that treefrogs would oviposit more eggs into wetland mesocosms containing litter with high nutrient concentrations and low phenolic concentrations. To test our hypothesis, we counted the number of eggs oviposited by treefrogs in artificial wetland mesocosms containing either Red Maple (Acer rubrum), Black Oak (Quercus velutina), or Eastern Hemlock (Tsuga canadensis) litter. We conducted this study over two breeding seasons. Counter to our hypothesis, we found that treefrogs preferred to oviposit in mesocosms containing maple litter, which contains high levels of both nutrients and phenolic acids. We discuss possible explanations for this result, including the possible anti-parasitic effects of phenolic acids. This is the first study demonstrating that breeding amphibians can differentiate between wetlands containing leaf litter species of differing chemistry. Given global declines in amphibian species concurrent with widespread changes in forest composition, our results emphasize the importance of considering leaf litter quality in wetland management and conservation efforts.
... Polyphenism has been documented in several species of anurans of the family Hylidae, such as Bokermannohyla circumdata, B. alvarengai, Dryophytes japonicus, Hyliola regilla, Scinax fuscomarginatus and S. hayii; and the Phyllomedusidae Phasmahyla cochranae, P. guttata, P. jandaia, (Stegen et al., 2004;Toledo and Haddad, 2009;Choi and Jang, 2014;Machado et al., 2015). In general, this phenomenon, in anurans, has been related with anti-predator mechanism and thermoregulation (Hoppe, 1979;King and King, 1991;King et al., 1994). In this note, we report for the first time polyphenism displayed by two hylids in the eastern Amazon region: Boana dentei (Bokermann, 1967) and Scinax ruber (Laurenti, 1768). ...
Polyphenism has been well documented in anurans as an anti-predator mechanism. Herein, we report two cases of this defensive behaviour in Boana dentei and Scinax ruber in Amapá State, eastern Amazon, Brazil. Both species changed colour when exposed to different microhabitats. Our field observations suggest that this phenomenon is important for anurans to avoid potential predators.
... Polyphenism has been documented in several species of anurans of the family Hylidae, such as Bokermannohyla circumdata, B. alvarengai, Dryophytes japonicus, Hyliola regilla, Scinax fuscomarginatus and S. hayii; and the Phyllomedusidae Phasmahyla cochranae, P. guttata, P. jandaia, (Stegen et al., 2004;Toledo and Haddad, 2009;Choi and Jang, 2014;Machado et al., 2015). In general, this phenomenon, in anurans, has been related with anti-predator mechanism and thermoregulation (Hoppe, 1979;King and King, 1991;King et al., 1994). In this note, we report for the first time polyphenism displayed by two hylids in the eastern Amazon region: Boana dentei (Bokermann, 1967) and Scinax ruber (Laurenti, 1768). ...
Polyphenism has been well documented in anurans as an anti-predator mechanism. Herein, we report two cases of
this defensive behaviour in Boana dentei and Scinax ruber in Amapá State, eastern Amazon, Brazil. Both species changed
colour when exposed to different microhabitats. Our field observations suggest that this phenomenon is important for anurans
to avoid potential predators.
... Metachrosis, the rapid change of color, has been observed in many ectotherms, particularly herpetofauna (Rahn 1942;King et al. 1994;Tanaka 2005;Stuart-Fox and Moussali 2008). Metachrosis is used in lizards for thermoregulation (Velasco and Tattersall 2008;Clusella-Trullas et al. 2009;Krohn and Rosenblum 2016); in anoles, frogs, and boas in response to changing photoperiod regimes (Rahn and Rosendale 1941;McAlpine 1983;Camargo et al. 1999;Wente and Phillips 2003;Stegen et al. 2004;Boback and Siefferman 2010); in anoles and frogs for camouflage (Kleinholz 1936(Kleinholz , 1938King and King 1991;Stegen et al. 2004); and in chameleons and anoles for social signaling (Greenberg 2002(Greenberg , 2003Yang and Wilczynski 2003;Stuart-Fox and Moussalli 2008). The ability to change color in response to environmental stimuli could have profound consequences for an individual's fitness. ...
Metachrosis, or color change, in reptiles is used for thermoregulation, crypsis, and many other purposes. The mechanism and function of metachrosis remain unknown for many species, however, especially snakes. Anecdotal observations suggest that some snake species,
including rattlesnakes, undergo varying degrees of color change when captured and confined. A possible explanation for this color change is the increase in plasma levels of the primary stress hormone, corticosterone (CORT). In this study, we implanted Southern Pacific Rattlesnakes (Crotalus helleri) with either CORT or sham silastic implants and photographed them under standardized lighting in a curtained box at the time of implant and 2 and 4 wk postimplant. We quantified light value (brightness or darkness) of the dark and light bands of the subjects’ tails and examined the relationships of these variables to baseline CORT levels (CORT level at time of capture) as well as CORT levels after 1 h of acute confinement stress. CORT-treated snakes had higher baseline CORT than control snakes, but treatment had no direct effect on color. Regardless of
treatment group, baseline CORT was positively correlated with lighter light bands, but had no relationship with the dark bands. Additionally, the magnitude of the CORT increase during acute stress was related to greater increase in contrast between light and dark bands. Defensive behavior was negatively correlated with contrast. We discuss potential reasons for the relationship between stress, defensive behavior, and color change.
... Changes in both colour and luminance are important for camouflage (Choi and Jang, 2014;King et al., 1994;King and King, 1991;Stevens et al., 2014a,b;Vroonen et al., 2012); even small changes (e.g. <2% increase in reflectance) can ultimately improve the level of background matching of an animal to its natural habitat (Stevens et al., 2013). ...
Animals may improve camouflage by both dynamic colour change and local evolutionary adaptation of colour but we have little understanding of their relative importance in colour-changing species. We tested for differences in colour change in response to background colour and light intensity in two populations of central bearded dragon lizards (Pogona vitticeps) representing the extremes in body coloration and geographical range. We found that bearded dragons change colour in response to various backgrounds and that colour change is affected by illumination intensity. Within-individual colour change was similar in magnitude in the two populations but varied between backgrounds. However, at the endpoints of colour change, each population showed greater similarity to backgrounds that were representative of the local habitat compared with the other population, indicating local adaptation to visual backgrounds. Our results suggest that even in species that change colour, both phenotypic plasticity and geographic divergence of coloration may contribute to improved camouflage.
... (metachrosis) in response to changing light levels and background colours, which may also make them less conspicuous to predators (Duellman, 1970, Iga and Bagnara, 1975, King and King, 1991). One such group of frogs that display this ability are the hylids. ...
The ecology of the Buton macaque (Macaca ochreata brunnescens) is poorly understood, and its status and habitat preferences have not been previously investigated. The aim of this study was to determine the population density and population size of the Buton macaque in the forests of central Buton. The habitat requirements of the species were also investigated. Data collected indicate a population density of 14.9 Buton macaques/km2, and a current population size of 3,752 within the protected forests of central Buton. This is likely to be viable in the long- term. No habitat preferences could be identified, although the current habitat appears adequate.
Howler monkeys (Alouatta spp.) were studied in Honduras with the aim of identifying the species present and characterising its activity patterns. There is dispute over the identity of the howler monkey species occurring in Honduras, but morphological and behavioural data presented here indicate that the species present in the Cusuco National Park, Honduras, is A. palliata. A new, molecular, species identification technique using non-invasively collected DNA samples extracted from faeces was also employed, although this was unsuccessful. Differences were observed between the activity budgets of male and female howler monkeys, which could be explained by their different social roles. However, the sample size of the study was relatively small.
The eye morphology of the tree frogs Agalychnis calcarifer and A. craspedopus, is unusual within the genus Agalychnis. The iris of these two species displays apparent metachrosis (colour change) as the eye opens, a phenomenon which is unreported in amphibians. This study uses a new technique involving digital image analysis to quantitatively assess this process, and to determine the mechanism by which it occurs. Observations suggest that the visible colour of the iris is modulated by revealing different areas of the iris as opposed to redistributing pigment. The eye morphology of A. calcarifer and A. craspedopus was also described in relation to other Agalychnis frogs. The advantages and limitations of digital image analysis as a morphometric tool are discussed.
... Although several studies have attempted to quantify crypsis of animals living in visually varying habitats (Norris & Lowe, 1964;Endler, 1984;Morey, 1990;Harris & Weatherall, 1991;King, 1992King, , 1993Kiltie, 1992;Belk & Smith, 1996;Westmoreland & Kiltie, 1996;King & King, 1991), optimization of crypsis in heterogeneous habitats has received surprisingly little theoretical attention. In homogeneous habitats the probability of detection can be decreased simply by increasing the degree of crypsis against that background. ...
... Consequently, it tends to be background- specific. Although several studies have attempted to quantify crypsis of animals living in visually varying habitats (Norris & Lowe, 1964; Endler, 1984; Morey, 1990; Harris & Weatherall, 1991; King, 1992, 1993; Kiltie, 1992; Belk & Smith, 1996; Westmoreland & Kiltie, 1996; King & King, 1991), optimization of crypsis in heterogeneous habitats has received surprisingly little theoretical attention. In homogeneous habitats the probability of detection can be decreased simply by increasing the degree of crypsis against that background. ...
We present a theoretical approach to the optimization of crypsis in heterogeneous habitats. Our model habitat consists of two different microhabitats, and the optimal combination of crypsis in the microhabitats is supposed to maximize the probability of escaping detection by a predator. The probability of escaping detection for a prey is a function of: (i) degree of crypsis, (ii) probability of occurrence in the microhabitats and (iii) probability of encountering a predator in the microhabitats. Because crypsis is background-specific there is a trade-off between crypsis in two visually different microhabitats. Depending on the nature of the trade-off, the optimal coloration is either a compromise between the requirements of the differing microhabitats or entirely adapted to only one of them. An increased risk of predation in one of the microhabitats favours increased crypsis in that microhabitat. Because the trade-off constrains possible optimal solutions, it is not possible to predict the optimal coloration only from factors (i)–(iii). However, habitat choice may fundamentally change the situation. If minimizing predation risk does not incur any costs, the prey should exclusively prefer the microhabitat where it has a lower probability of encountering a predator and better crypsis. The implications of these results for variation in cryptic coloration and polymorphism are discussed.
... The phenomenon of dynamic colour change in animals could be essential for many reasons, such as camouflage to avoid predators (Camargo et al., 1999;Stevens and Merilaita, 2009;Stuart-Fox and Moussalli, 2009), thermoregulation (Norris, 1967;Tattersall et al., 2006) and sexual selectionto stand out and attract mates Moussalli, 2008, 2009;Chen et al., 2012). Although there have been numerous studies on the function of colour change in amphibians (Edgren, 1954;Nielsen, 1978aNielsen, ,b, 1979Nielsen, , 1980Kats and Vandragt, 1986;King and King, 1991;King et al., 1994;Wente and Phillips, 2003;Stegen et al., 2004;Tattersall et al., 2006), only a few of these have focussed on this in the context of rapid changes (a change within minutes) for social signalling and breeding. Dynamic sexual dichromatism (reversible colour change during breeding) has been observed in approximately 31 anuran species and due to the ephemeral nature of colour change this number may increase as species are studied in more detail (Bell and Zamudio, 2012). ...
... Although several studies have attempted to quantify crypsis of animals living in visually varying habitats (Norris & Lowe, 1964;Endler, 1984;Morey, 1990;Harris & Weatherall, 1991;King, 1992King, , 1993Kiltie, 1992;Belk & Smith, 1996;Westmoreland & Kiltie, 1996;King & King, 1991), optimization of crypsis in heterogeneous habitats has received surprisingly little theoretical attention. In homogeneous habitats the probability of detection can be decreased simply by increasing the degree of crypsis against that background. ...
We present a theoretical approach to the optimization of crypsis in heterogeneous habitats. Our model habitat consists of two different microhabitats, and the optimal combination of crypsis in the microhabitats is supposed to maximize the probability of escaping detection by a predator. The probability of escaping detection for a prey is a function of: (i)degree of crypsis, (ii) probability of occurrence in the microhabitats and (iii) probability of encountering a predator in the microhabitats. Because crypsis is background-specific there is a trade-off between crypsis in two visually different microhabitats. Depending on the nature of the trade-off, the optimal coloration is either a compromise between the requirements of the differing microhabitats or entirely adapted to only one of them. An increased risk of predation in one of the microhabitats favours increased crypsis in that microhabitat. Because the trade-off constrains possible optimal solutions, it is not possible to predict the optimal coloration only from factors (i)-(iii). However, habitat choice may fundamentally change the situation. If minimizing predation risk does not incur any costs, the prey should exclusively prefer the microhabitat where it has a lower probability of encountering a predator and better crypsis. The implications of these results for variation in cryptic coloration and polymorphism are discussed.
Color change serves many antipredator functions and may allow animals to better match environments or disrupt outlines to prevent detection. Rapid color change could potentially provide camouflage to animals that frequently move among microhabitats. Determining the adaptiveness of whole-animal rapid color changes in natural habitats with respect to predator visual systems would greatly broaden our fundamental understanding of the evolution of rapid color change. We tested whether whole-body color change provides water anoles (Anolis aquaticus) with camouflage against avian predators and whether these rapid changes allow them to shift between environment matching and edge disruption. We manipulated A. aquaticus placement in natural microhabitats and used digital image analysis to quantify color matching, pattern matching, and edge disruption produced by microhabitat-induced color change. Color change reduced lizard detectability to predators in microhabitat-specific ways. Environment matching was favored when lizards were in solid-colored microhabitats, regardless of exposure to predators. Edge disruption was instead induced by high exposure and varied by body region. We provide the first evidence that rapid color change permits a tetrapod to flexibly employ the most optimal camouflaging strategy by form (e.g., color matching vs. edge disruption) to minimize detection in the eyes of its predators.
In an effort to better understand the function of physiological color change in anurans, we measured color change responses of the green treefrog, Hyla cinerea, to background brightness and temperature. We used our results to compare color and color change responses of males and females and to test two hypotheses for the function of physiological color change in anurans: (1) that color change serves to prevent detection by visual predators, and (2) that color change functions in thermoregulation or water balance. We found that (1) males are generally darker than females but the sexes exhibit similar color change responses, (2) treefrogs become lighter on brighter backgrounds, (3) treefrogs become lighter at higher temperatures, and (4) there is a background-by-temperature interaction such that color change responses to one variable depend on the level of the other. Our results suggest that color change may function both in predator avoidance and in thermoregulation or water balance. However, further investigations of color change responses to differently hued backgrounds, of the magnitude and biological significance of color-induced changes in body temperature and rates of evaporative water loss, and of color change in free-ranging animals are needed.
Blue‐spotted individuals are found in many populations of the slow worm (Anguis fragilis) throughout Europe. The frequency of occurrence of this colour morph was studied in eight populations from a mountainous territory of northeastern Italy (Tarvisio Forest, Carnic Alps, 750–1600 m a.s.l.). Blue‐spotted individuals were very rare (0.8% of the total sample; n = 744). However, the population inhabiting the town of Tarvisio presented a significantly higher proportion of blue‐spotted individuals than did the other sampled populations. All the blue‐spotted individuals were adult males of large size (average SVL = 173.5 ± 6.8 mm), with heavy body (average body mass = 41 ± 6 g), while the sole blue‐spotted animal captured in Valais was subadult. The presence of blue‐spotted animals within a population was apparently not correlated with habitat type, altitude and latitude, but was positively correlated with increase of longitude from Greenwich (Spearman's r = 0.73, n = 8, P = 0.038). A predation experiment with model slow worms demonstrated that the blue‐spotted individuals suffered higher risks of predation than normal coloured ones. Taking into account the result of this experiment, and considering that (1) the frequency of occurrence of the blue‐spotted males within populations was inversely correlated with the proportion of individuals with broken tails (Spearman's r = ‐ 0.91, n = 8, P = 0.002), and that (2) higher frequencies of broken tails may mean higher risks of prédation for natural lizard populations, we conclude that blue‐spotted individuals should be rare in the areas where the density of potential predators is high. It is also suggested that the blue‐spotted colouration may be intrasexually selected for augmenting the individual success of male slow worms in sexual contexts.
In amphibians solar basking far from water sources is relatively uncommon since the highly permeable amphibian skin does not represent a significant barrier to the accompanying risk of losing water by evaporation. A South American frog, Bokermannohyla alvarengai (Bokermann 1956), however, spends a significant amount of the day exposed to full sun and relatively high temperatures. The means by which this frog copes with potentially high rates of evaporative water loss and high body temperatures are unknown. Thus, in this study, skin colour changes, body surface temperature, and evaporative water loss rates were examined under a mixture of field and laboratory conditions to ascertain whether changes in skin reflectivity play an important role in this animal's thermal and hydric balance. Field data demonstrated a tight correlation between the lightness of skin colour and frog temperature, with lighter frogs being captured possessing higher body temperatures. Laboratory experiments supported this relationship, revealing that frogs kept in the dark or at lower temperatures (20 degrees C) had darker skin colours, whereas frogs kept in the light or higher temperatures (30 degrees C) had skin colours of a lighter hue. Light exhibited a stronger influence on skin colour than temperature alone, suggesting that colour change is triggered by the increase in incident solar energy and in anticipation of changes in body temperature. This conclusion is corroborated by the observation that cold, darkly coloured frogs placed in the sun rapidly became lighter in colour during the initial warming up period (over the first 5 min), after which they warmed up more slowly and underwent a further, albeit slower, lightening of skin colour. Surprisingly, despite its natural disposition to bask in the sun, this species does not possess a ;waterproof' skin, since its rates of evaporative water loss were not dissimilar from many hylid species that live in arboreal or semi-aquatic environments. The natural history of B. alvarengai is largely unknown and, therefore, it is likely that the herein reported colour change and basking behaviour represent a complex interaction between thermoregulation and water balance with other ecologically relevant functions, such as crypsis.
On the basis of field and laboratory studies, I found that the habitat selected by Rana sylvatica in the non-breeding season is one combining a forest canopy and small ponds. Frogs face the water and sit at the edge of the bank on flat, recently submerged litter. They follow the receding water-line as the ponds dry up and move under the loose leaf-litter of the forest floor when the water is gone. Within the range of field conditions, more frogs are active at high temperatures and relative humidities than at lower ones. They are sedentary and even during "activity" periods are motionless unless they see a prey item or are disturbed. The typical escape behavior is to dive in a pond and either become concealed in submerged litter or surface some distance away.
Western North American races of the gopher snake Pituophis melanoleucus share aspects of coloration, pattern and defense behavior with the sympatric rattlesnake Crotalus viridis, and have been suggested to be Batesian mimics. Strong geographic variation in appearance and behavior occurs in Pituophis; in southwestern California the adjacent races P. m. annectens and P. m. catenifer appear to be "poor" and "good" mimics of C. v. helleri and C. v. oreganus, respectively. Resemblance corresponds to convergence in habitat utilization: analysis of background matching shows that coastal Pituophis and Crotalus are cryptic in different microhabitats, whereas inland populations are cryptic in a shared shortgrass environment. Phenotypic similarity may thus be due to convergence on a common cryptic pattern rather than or in addition to selection for mimicry. Geographic variation in intensity of defense behavior provides evidence for the latter view; Pituophis populations that are dissimilar to C. viridis or occur outside its range seldom display an active defense (except as juveniles), whereas those occurring in close association with C. viridis defend vigorously. The importance of mimicry thus varies geographically as a secondary result of selection for cryptic coloration.
A full understanding of a biological system requires parallel consideration of both the form and the function of that system. This basic approach, the essence of post-Darwinian biology, has been widely applied to the morphology and physiology of animals and in recent years to some aspects of their behavior, notably by Niko Tinbergen and his students (Baerends et al. 1976). Rather little use of this dual approach has been made in the analysis of the causal mechanisms underlying behavior, however, although McFarland (1976) has shown how such an approach can lead to a better understanding of the mechanisms determining the precise order in which behavior patterns occur. It is the purpose of this paper to show how an understanding of the causation of courtship behavior in the smooth newt, Triturus vulgaris, which has been the subject of extensive experimental analysis, can be enhanced by a consideration of various functional aspects of the behavior.
The variation in mating success of male wood frogs, Rana sylvatica, was studied in natural populations and laboratory mate-choice experiments using males of varying ages, body sizes and geographic origins. The results of both laboratory and field experiments suggest that male-male competition was responsible for the greater mating success of the larger males. Older males did not have greater mating success when size was controlled. Males showed a strong preference for larger females and ignored very small females. Most matings were not significantly assortative. In those rare cases where assortative mating was observed, it resulted from male competition, male choice, and the relative abundance of each sex as opposed to female choice of a preferred body size. Substantial among-pond and within-year variation in sex ratios and age composition of breeding populations was observed. Such variation may have been important in determining the pattern of mate choice observed and the variation in male reproductive success.
The tremendous advances in electronic data processing are likely to result in revolutionary changes in the theories and practices of taxonomy. The process of classification is being removed from speculations regarding the origin of the taxa being classified. A natural classification is one whose taxa share the largest number of properties and which is most useful for a wide range of purposes. The principles of numerical taxonomy are stated briefly and illustrated by means of diagrammatic examples. The relative roles of the taxonomist and computer are discussed and estimates given of computer time and costs involved in numerical taxonomic work. The numerical taxonomic work done in botany so far is discussed and the paper concludes with a brief mention of several problems of numerical taxonomy with regard to botanical work. These are: scarcity of characters, correlations between cytogenetic work and phenetic similarities, and problems raised by hybridization.
A series of simple heat-transfer models (termed the basic, conduction, physiological, and wet-skin models) is derived to examine a large number of behavioral and physiological mechanisms that are used by terrestrial ectotherms to control body temperature (Tb; table 1). The models reaffirm two generalizations: (1) in environments where solar radiation is available, behavioral mechanisms may provide a range of Tb's that is many times greater than the range in Tb's that results from physiological adjustments; and (2) among behavioral mechanisms, the times of seasonal and daily activity appear to be the most critical in determining Tb. Furthermore, microhabitat selection is more important than postural adjustments for controlling Tb. The models calculate Tb as the sum of air temperature (Ta) and the body-air temperature difference (Td). The direct effects of body size are expressed as functions of Td. Many behavioral mechanisms can then be expressed as some fraction of Td. The models (eqs. 3, 6, 8, 11), in combination with table 2 and the Smithsonian tables (List 1966), allow one to quickly estimate the effects of many environmental variables and behavioral and physiological mechanisms on Tb.
Measurements have been made of the spectral reflectance of the dorsal skin of living tree frogs, Hyla cinerea.
The colors assumed by the frogs when placed on backgounds of different col-ors varied with respect to both dominant wavelength (565–580 nm), purity (42–58%) and lightness (2–19%).
A certain adaptation to the lightness of the background took place, whereas adaptation to hue and purity seems almost negligible.
On the basis of reflection measurements of single chromatophores and chro-matophore associationa, a model is proposed for the color generation in the chromatophores, assuming an absorption of short-wave light in the xantho-phores, a reflection of short-and medium-wave light (blue, green) from the iridophores, and almost total absorption of all light in the melanophores, and a uniform, but subtotal, reflection of light of all wavelenghts from the connective tissue.
It is suggested that the states of dispersion of the three types of chro-matophores may be related to simple parameters which can be calculated from the reflectance spectra. Using these parameters it was found that mela-nophores, xanthophores and iridophores all play an active part in the color change, and an explanation is presented on how the observed frog colors are generated by means of changes in the chromatophores.
The three types of chromatophores probably are able to react independently of each other, thus indicating that the unihumoral theory fails to explain the color changes in Hyla cinerea.
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.
In studies of animal colouration it is no longer necessary to rely on subjective assessments of colour and conspicuousness, nor on methods which rely upon human vision. This is important because animals vary greatly in colour vision and colour is context-dependent. New methods make it practical to measure the colour spectrum of pattern elements (patches) of animals and their visual backgrounds for the conditions under which patch spectra reach the conspecific's, predator's or prey's eyes. These methods can be used in both terrestrial and aquatic habitats. A patch's colour is dependent not only upon its reflectance spectrum, but also upon the ambient light spectrum, the transmission properties of air or water, and the veiling light spectrum. These factors change with time of day, weather, season and microhabitat, so colours must be measured under the conditions prevalent when colour patterns are normally used. Methods of measuring, classifying and comparing colours are presented, as well as techniques for assessing the conspicuousness of colour patterns as a whole. Some implications of the effect of environmental light and vision are also discussed.
Mating behaviour of woodfrogs was investigated in a woodland pond in southeastern Michigan. Males became sexually mature one year before females and outnumbered females by 5.6 to 1 at the breeding site. Males employed searching behaviour to obtain mates. Yearly male mating success varied from 0 to 2 matings, and larger males had a greater probability of mating than smaller males. The mating season lasted less than 10 days. Most egg masses were deposited in 1 m2 of a 256-m2 pond. Experimental introduction of egg masses to the breeding site indicated that presence of eggs was sufficient to stimulate egg deposition. The influence of selection for synchronous sexual receptivity in females, communal egg deposition, and delayed female sexual maturation on male mating behaviour and variation in male mating success is discussed.
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Biology of amphibians Progressive background matching in moths, and a quantitative measure of crypsis On the measurement and classification of colour in studies of animal colour patterns
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The method of sex recognition in the wood frog, Rana sylvatica
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