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1.
We tested the prediction of the sensory drive hypothesis using four allopatric populations of the lizard Anolis cristatellus from two distinct environments (i.e., mesic and xeric conditions). For each population, we measured habitat light characteristics and quantified signal design by measuring the spectral and total reflectance and transmittance of the dewlap. We used these data to calculate dewlap detectability using an empirically based model of signal detection probability. We found that populations from mesic and xeric conditions occupy two distinct habitats with respect to light intensity and spectral quality and that dewlap design has diverged between populations in a way that increases signal detectability in each habitat. The major difference in dewlap design was in total reflectance and transmittance, making dewlaps from xeric habitats darker and dewlaps from mesic habitats brighter. Furthermore, dewlap detection decreased significantly when a dewlap from a xeric habitat is detected under the spectral conditions of a mesic habitat. The converse is true for a dewlap from a mesic habitat. We propose that sensory drive has promoted divergence in dewlap design in distinct habitat light conditions, and we discuss the possibility that selection might promote early stages of reproductive isolation as a by-product of selection on dewlap design to distinct habitat light conditions.  相似文献   

2.
 The evolutionary relationship between visual system response and visual signal design was investigated in four species of anoline lizards which occupy distinctly different habitats. Anoles display with motion patterns of a colorful throat fan called the dewlap. We assessed signal visibility by recording evoked potentials from the optic tectum in response to a moving stimulus flag (a dewlap-like stimulus), and, in one species, by testing behavioral response. The motion pattern, intensity and spectral quality of the stimulus flag, and the background against which it was viewed, were independently manipulated. In all cases, high-velocity motion patterns with a high percentage of brightness contrast between stimulus and background produced the greatest response. Differences in spectral quality between stimulus and background (color contrast) had no effect on tectal responses, but did influence the behaviorally measured detection probability. Using habitat light data we estimated the visibility of the dewlap of each species in different natural habitats. Each species' dewlap was highly visible in its own habitat, but some were much less visible in the habitats of some other species. Habitat light conditions and visual system response properties appear to have constrained the evolution of dewlap design, in at least some of the species. Accepted: May 1998  相似文献   

3.
Terrestrial habitats exhibit a variety of light environments. If species exhibit evolutionary adaptations of their visual system or signals to habitat light conditions, then these conditions can directly influence the structure of communities. We evaluated habitat light characteristics and visual-signal design in a pair of sympatric species of lizards: Anolis cooki and Anolis cristatellus. We found that each species occupies a distinct microhabitat with respect to light intensity and spectral quality. We measured the relative retinal spectral sensitivity and found significant differences between the species that correlate with differences in habitat spectral quality. We measured the spectral reflectance of the dewlaps (colourful throat fans used in communication), and found that the A. cooki dewlap reflects little ultraviolet (UV), while that of A. cristatellus reflects strongly in the UV. For both species downwelling light (irradiance) is rich in UV. However the background light (radiance) is rich in UV for A. cooki, but low in UV for A. cristatellus. Thus, the dewlap of each species creates a high contrast with the background in the UV. Our findings strongly suggest that these two species are partitioning their habitat through specializations of the visual system and signal design to microhabitat light conditions.  相似文献   

4.
Whether general patterns of signal evolution can be explained by selection for signal efficacy (detectability) has yet to be established. To establish the importance of signal efficacy requires evidence that both signals and their detectability to receivers have evolved in response to habitat shifts in a predictable fashion. Here, we test whether habitat structure has predictable effects on the evolution of male and female display coloration in 21 lineages of African dwarf chameleon (Bradypodion), based on a phylogenetic comparative analysis. We used quantitative measures of display coloration and estimated signal detectability as the contrast of those colors among body regions or against the background vegetation as perceived by the chameleon visual system. Both male and female display colors varied predictably with different aspects of habitat structure. In several (but not all) instances, habitat-associated shifts in display coloration resulted in habitat-associated variation in detectability. While males exhibit a remarkable variety of colors and patterns, female display coloration is highly conserved, consisting in all populations of contrasting dark and light elements. This color pattern may maximize detectability across all habitat types, potentially explaining female conservatism. Overall, our results support the view that selection for signal efficacy plays an important role in the evolution of animal signals.  相似文献   

5.
Sexual ornamentation needs to be conspicuous to be effective in attracting potential mates and defending territories and indeed, a multitude of ways exists to achieve this. Two principal mechanisms for increasing conspicuousness are to increase the ornament's colour or brightness contrast against the background and to increase the size of the ornament. We assessed the relationship between the colour and size of the dewlap, a large extendible throat‐fan, across a range of species of gliding lizards (Agamidae; genus Draco) from Malaysia and the Philippines. We found a negative relationship across species between colour contrast against the background and dewlap size in males, but not in females, suggesting that males of different species use increasing colour contrast and dewlap size as alternative strategies for effective communication. Male dewlap size also increases with increasing sexual size dimorphism, and dewlap colour and brightness contrast increase with increasing sexual dichromatism in colour and brightness, respectively, suggesting that sexual selection may act on both dewlap size and colour. We further found evidence that relative predation intensity, as measured from predator attacks on models placed in the field, may play a role in the choice of strategy (high chromatic contrast or large dewlap area) a species employs. More broadly, these results highlight that each component in a signal (such as colour or size) may be influenced by different selection pressures and that by assessing components individually, we can gain a greater understanding of the evolution of signal diversity.  相似文献   

6.
Male ornaments have been the subject of numerous studies on sexual selection and communication, although female ornaments have garnered substantially less study, even though female ornaments are well developed in some species. The factors that have propelled the evolution of elaborate ornaments in females are poorly understood but may include genetic correlations between the sexes, social selection, sensory drive or species recognition. We used simulation‐based comparative methods and a newly estimated phylogeny to test these four hypotheses to explain female ornamentation within the diverse neotropical lizard genus Anolis. We found support for the sensory drive hypothesis and the social selection hypothesis; the female dewlap was larger in species that use more arboreal habitats, as well as in species where the sexes were less dimorphic. We did not find support for the genetic correlation hypothesis or the species recognition hypothesis. We propose that the size of the female dewlap may evolve in response to sensory drive differentially affecting species in different habitats, as well as social selection such as male mate choice or intrasexual competition for territory among females. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 191–201.  相似文献   

7.
The existence of elaborate ornamental structures in males is often assumed to reflect the outcome of female mate choice for showy males. However, female mate choice appears weak in many iguanian lizards, but males still exhibit an array of ornament‐like structures around the throat. We performed a phylogenetic comparative study to assess whether these structures have originated in response to male–male competition or the need for improved signal efficiency in visually difficult environments. We found little evidence for the influence of male–male competition. Instead, forest species were more likely to exhibit colourful throat appendages than species living in open habitats, suggesting selection for signal efficiency. On at least three independent occasions, throat ornamentation has become further elaborated into a large, conspicuously coloured moving dewlap. Although the function of the dewlap is convergent, the underlying hyoid apparatus has evolved very differently, revealing the same adaptive outcome has been achieved through multiple evolutionary trajectories. More generally, our findings highlight that extravagant, ornament‐like morphology can evolve in males without the direct influence of female mate choice and that failure to consider alternative hypotheses for the evolution of these structures can obscure the true origins of signal diversity among closely related taxa.  相似文献   

8.
Animal signalling systems are extremely diverse as they are under different, often conflicting, selective pressures. A classic textbook example of a diverse signal is the anoline dewlap. Both at the inter‐ and intraspecific levels, dewlap size, colour, shape and pattern vary extensively. Here, we attempt to elucidate the various factors explaining the diversity in dewlap size and pattern among seven Anolis sagrei populations from different islands in the Bahamas. The seven islands differ in the surface area, number and kind of predators, sexual size dimorphism and Anolis species composition. In addition, we investigate whether selective pressures acting on dewlap design differ between males and females. Whereas dewlap pattern appears to serve a role in species recognition in both sexes, our data suggest that relative dewlap size is under natural and/or sexual selection. We find evidence for the role of the dewlap as a pursuit‐deterrence signal in both males and females as relative dewlap size is larger on islands where A. sagrei occurs sympatrically with predatory Leiocephalus lizards. Additionally, in males relatively large dewlaps seem to be selected for in a sexual context, whereas in females natural selection, for instance by other predators than Leiocephalus lizards, appears to constrain relative dewlap size.  相似文献   

9.
Animals communicate using a variety of signals that differ dramatically among and within species. The astonishing dewlap diversity in anoles has attracted considerable attention in this respect. Yet, the evolutionary processes behind it remain elusive and have mostly been explored for males only. Here, we considered Anolis sagrei males and females to study signal divergence among populations. First, we assessed the degree of variation in dewlap design (size, pattern and colour) and displays by comparing 17 populations distributed across the Caribbean. Second, we assessed whether the observed dewlap diversity is associated with variation in climate‐related environmental conditions. Results showed that populations differed in all dewlap characteristics, with the exception of display rate in females. We further found that males and females occurring in ‘xeric’ environments had a higher proportion of solid dewlaps with higher UV reflectance. In addition, lizards inhabiting ‘mesic’ environments had primarily marginal dewlaps showing high reflectance in red. For dewlap display, a correlation with environment was only observed in males. Our study provides evidence for a strong relationship between signal design and prevailing environmental conditions, which may result from differential selection on signal efficacy. Moreover, our study highlights the importance of including females when studying dewlaps in an evolutionary context.  相似文献   

10.
The expression of male secondary sexual traits can be dynamic, changing size, shape, color, or structure over the course of different seasons. However, the factors underlying such changes are poorly understood. In male Anolis carolinensis lizards, a morphological secondary sexual signal called the dewlap changes size seasonally within individuals. Here, we test the hypothesis that seasonal changes in male dewlap size are driven by increased use and extension of the dewlap in spring and summer, when males are breeding, relative to the winter and fall. We captured male green anole lizards prior to the onset of breeding and constrained the dewlap in half of them such that it could not be extended. We then measured dewlap area in the spring, summer, and winter, and dewlap skin and belly skin elasticity in summer and winter. Dewlaps in unconstrained males increase in area from spring to summer and then shrink in the winter, whereas the dewlaps of constrained males consistently shrink from spring to winter. Dewlap skin is significantly more elastic than belly skin, and skin overall is more elastic in the summer relative to winter. These results show that seasonal changes in dewlap size are a function of skin elasticity and display frequency, and suggest that the mechanical properties of signaling structures can have important implications for signal evolution and design.  相似文献   

11.
Caribbean Anolis lizards are often cited as a textbook example of adaptive radiation. Similar morphologies (ecomorphs) have originated in similar ecological settings on different large islands in the West Indies. However, relatively little is known about one of the morphologically most specialized and divergent ecomorphs: the twig anoles. Here, we investigate aspects of morphology, dewlap size, locomotor and bite performance, structural habitat and diet of the poorly known twig anole, Anolis sheplani from Hispaniola. Few observations have previously been made of this species in its natural habitat, and few quantitative data on its natural history are available. A. sheplani is an extreme twig anole with respect to its morphology, performance capacities, and ecological niche. Males and females of this species do not differ from each other in body dimensions, performance or habitat use, but males do have a bigger dewlap than females. We present data for 25 individuals and compare them with data for other Greater Antillean anoles. It becomes apparent that twig anoles constitute a large component of the morphological, functional, and ecological diversity of Anolis lizards. Small twig anoles such as A. sheplani appear to be pushing the boundaries of morphospace and are thus crucial in our understanding of the evolution of phenotypic diversity.  相似文献   

12.
When a population experiences relaxation of selective pressures due to reduced predation or competition, it may undergo ecological release. Ecological release often manifests as increased niche breadth and trait variation, as individuals have the opportunity to exploit a wider variety of resources. At the recently‐colonized White Sands dune formation in New Mexico, lizards from white sand habitat have fewer predators and competitors than their dark soil counterparts, and show evidence of ecological release compared to dark soil lizards. To determine whether the dynamics of ecological release also play out over an even finer habitat gradient, we studied southwestern fence lizards in the center of the White Sands dune formation and the narrow ecotone between White Sands and the surrounding dark soil habitats. We predicted that lizards from the central dunes would exhibit ecological release in terms of broadened resource use compared to lizards from the ecotone. We first conducted avian surveys in both the central dunes and ecotone habitats to measure abundance, richness and diversity of avian species that could act as lizard predators. Next, we measured microhabitat‐scale resource use by comparing perch selection of lizards in both habitats. Finally, we measured landscape‐scale resource use by quantifying home range sizes and daily distances traveled by lizards in both habitats. We found that central dunes lizards used a greater diversity of perch types, and had greater variation in both home range size and daily distances traveled, than ecotone lizards. There were fewer predatory bird species in the central dunes than on the ecotone, and there was a tendency for fewer predation events in the central dunes than on the ecotone. Our results demonstrate that ecological release is detectable over a fine habitat gradient, such as between the center of a recently‐colonized habitat and its ecotone with the surrounding ecosystem.  相似文献   

13.
Density‐dependent habitat selection has been used to predict and explain patterns of abundance of species between habitats. Thermal quality, a density‐independent component of habitat suitability, is often the most important factor for habitat selection in ectotherms which comprise the vast majority of animal species. Ectotherms may reach high densities such that individual fitness is reduced in a habitat due to increased competition for finite resources. Therefore, density and thermal quality may present conflicting information about which habitat will provide the highest fitness reward and ectotherm habitat selection may be density‐independent. Using ornate tree lizards Urosaurus ornatus at 10 sites each straddling two adjacent habitats (wash and upland), we tested the hypothesis that habitat selection is density‐dependent even when thermal quality differs between habitats. We first tested that fitness proxies decline with density in each habitat, indicating density‐dependent effects on habitat suitability. We also confirmed that the two habitats vary in suitability (quantified by food abundance and thermal quality). Next, we tested the predictions that habitat selection depends on density with isodar analyses and that fitness proxies are equal in the two habitats within a site. We found that monthly survival rates decreased with density, and that the wash habitat had more prey and higher thermal quality than the upland habitat. Lizards preferred the habitat with more food and higher thermal quality, lizard densities in the two habitats were positively correlated, and fitness proxies of lizards did not differ between habitats. These patterns are consistent with density‐dependent habitat selection, despite differences in thermal quality between habitats. We expect that density‐dependent habitat selection is widespread in terrestrial ectotherms when densities are high and temperatures are close to their optimal performance range. In areas where thermal quality is low, however, we expect that depletable resources, such as food, become less limiting because assimilating resources is more difficult.  相似文献   

14.
Adaptations that facilitate the reception of long‐range signals under challenging conditions are expected to generate signal diversity when species communicate in different habitats. Although we have a general understanding of how individual communicating animals cope with conditions influencing signal detection, the extent to which plasticity and evolutionary changes in signal characteristics contribute to interspecific differences in signaling behavior is unclear. We quantified the visual displays of free‐living lizards and environmental variables known to influence display detection for multiple species from two separate island radiations. We found evidence of both adaptive evolution and adaptive plasticity in display characteristics as a function of environmental conditions, but plasticity accounted for most of the observed differences in display behavior across species. At the same time, prominent differences between the two island radiations existed in aspects of signaling behavior, unrelated to the environment. Past evolutionary events have therefore played an important role in shaping the way lizards adjust their signals to challenges in present‐day environments. In addition to showing how plasticity contributes to interspecific differences in communication signals, our findings suggest the vagaries of evolution can in itself lead to signal variation between species.  相似文献   

15.
The extensive wing pattern diversity observed among sympatric unpalatable mimetic butterflies is difficult to explain. Diversity is a paradox because selection by predators is expected to drive local species to use the same aposematic patterns. Habitat segregation among mimicry complexes has been suggested as a hypothesis to explain how diversity could be maintained. However, very few studies have tested this hypothesis. To test whether mimicry complexes are associated with particular habitats, I sampled a diverse assemblage of ithomiine butterflies from eastern Ecuador comprising nine discrete mimicry complexes. Butterflies were sampled in four habitats varying along a gradient of succession. A total of 43 species and 902 individuals were sampled. Ithomiine species richness and abundance were lowest in open habitats, and habitat preferences were documented for many species. Mimicry complexes exhibited significant habitat differences supporting the role of habitat segregation in maintaining mimetic diversity. However, there was obvious overlap among mimicry complexes, particularly involving the two numerically dominant patterns at the site. The pattern of segregation appears to be driven by common species, with relatively little evidence that the distribution of rarer species matches that of the more abundant species. Thus, habitat segregation is likely to play a role in the evolution of mimetic diversity as a result of segregated abundant model species, but the effect is probably weak and other factors are also important.  相似文献   

16.
Many features of species' biology, including life history, physiology, morphology, and ecology are tightly linked to body size. Investigation into the causes of size divergence is therefore critical to understanding the factors shaping phenotypic diversity within clades. In this study, we examined size evolution in monitor lizards (Varanus), a clade that includes the largest extant lizard species, the Komodo dragon (V. komodoensis), as well as diminutive species that are nearly four orders of magnitude smaller in adult body mass. We demonstrate that the remarkable body size disparity of this clade is a consequence of different selective demands imposed by three major habitat use patterns-arboreality, terrestriality, and rock-dwelling. We reconstructed phylogenetic relationships and ancestral habitat use and applied model selection to determine that the best-fitting evolutionary models for species' adult size are those that infer oppositely directed adaptive evolution associated with terrestriality and rock-dwelling, with terrestrial lineages evolving extremely large size and rock-dwellers becoming very small. We also show that habitat use affects the evolution of several ecologically important morphological traits independently of body size divergence. These results suggest that habitat use exerts a strong, multidimensional influence on the evolution of morphological size and shape disparity in monitor lizards.  相似文献   

17.
Aim Explanations of biogeographic diversity patterns have emphasized the role of large‐scale processes that determine species pools, whereas explanations of local patterns have not. We address the hypothesis that local diversity patterns are also primarily dependent on the size of the available species pools, which are expected to be large when the particular habitat type has been evolutionary more abundant, or in unproductive habitats due to shorter generation time and hence higher diversification rates. Location The Canary Islands. Methods We determined the geographic distribution and habitat requirements of all native vascular plant species in the Canary Islands. Species pools for each habitat type on particular islands were further split into two categories according to origin: either originating due to local diversification or due to natural immigration. The dependence of historical diversification and diversification rate on habitat type, area, age, altitude and distance to the mainland was tested with general linear mixed models weighed according to the Akaike information criterion. Results The largest portion of the local variation in plant species diversity was attributed to the historic (pre‐human) habitat area, although island age was also important. The diversification rate was higher in unproductive habitats of coastal scrub and summit vegetation. Main conclusion Our study supports the species pool hypothesis, demonstrating that natural local patterns of species diversity in different habitats mirror the abundance of those particular habitats in evolutionary history. It also supports the community‐level birth rate hypothesis, claiming that stressful conditions result in higher diversification rates. We conclude that much of the observed local variation in plant diversity can be attributed to the differing sizes of species pools evolved under particular habitat conditions, and that historic parameters are far more important determinants of local diversity than suggested by ecological theory.  相似文献   

18.
The pattern of reproductive character displacement (RCD)—in which traits associated with reproductive isolation are more different where two species occur together than where they occur in isolation—is frequently attributed to reinforcement, a process during which natural selection acting against maladaptive mating events leads to enhanced prezygotic isolation between species or incipient species. One of the first studies of RCD to include molecular genetic data was described 40 years ago in a complex of Haitian trunk anole lizards using a small number of allozyme loci. In this example, Anolis caudalis appears to experience divergence in the color and pattern of an extensible throat fan, or dewlap, in areas of contact with closely related species at the northern and southern limits of its range. However, this case study has been largely overlooked for decades; meanwhile, explanations for geographic variation in dewlap color and pattern have focused primarily on adaptation to local signalling environments. We reinvestigate this example using amplified fragment length polymorphism (AFLP) genome scans, mtDNA sequence data, information on dewlap phenotypes and GIS data on environmental variation to test the hypothesis of RCD generated by reinforcement in Haitian trunk anoles. Together, our phenotypic and genetic results are consistent with RCD at the southern and northern limits of the range of A. caudalis. We evaluate the evidence for reinforcement as the explanation for RCD in Haitian trunk anoles, consider alternative explanations and provide suggestions for future work on the relationship between dewlap variation and speciation in Haitian trunk anoles.  相似文献   

19.
Ecology and signal evolution in lizards   总被引:1,自引:0,他引:1  
Current models of signal evolution explain diversity by invoking a variety of social, perceptual and environmental factors. Social systems and spacing patterns determine the active space of signals and their function. Receiver sensory systems and habitat characteristics interact to constrain signal design. These factors are traditionally implicated in promoting directional evolutionary change, leading to increases or decreases in signal complexity. We examine macro-evolutionary trends in signal design, as reflected by display modifier repertoire size, for 124 species of iguanian lizards to identify the importance of ecological factors in display evolution. Possessing a small home range, being arboreal and feeding on moving prey are all correlated with the evolution of large repertoires. However, living in closed habitats is associated with increased evolutionary change in repertoire size, producing greater signal diversity. Ecological factors can thus act either directionally or to promote evolutionary lability.   © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 127–148.  相似文献   

20.
A phylogenetic test for adaptive convergence in rock-dwelling lizards   总被引:1,自引:0,他引:1  
Phenotypic similarity of species occupying similar habitats has long been taken as strong evidence of adaptation, but this approach implicitly assumes that similarity is evolutionarily derived. However, even derived similarities may not represent convergent adaptation if the similarities did not evolve as a result of the same selection pressures; an alternative possibility is that the similar features evolved for different reasons, but subsequently allowed the species to occupy the same habitat, in which case the convergent evolution of the same feature by species occupying similar habitats would be the result of exaptation. Many lizard lineages have evolved to occupy vertical rock surfaces, a habitat that places strong functional and ecological demands on lizards. We examined four clades in which species that use vertical rock surfaces exhibit long hindlimbs and flattened bodies. Morphological change on the phylogenetic branches leading to the rock-dwelling species in the four clades differed from change on other branches of the phylogeny; evolutionary transitions to rock-dwelling generally were associated with increases in limb length and decreases in head depth. Examination of particular characters revealed several different patterns of evolutionary change. Rock-dwelling lizards exhibited similarities in head depth as a result of both adaptation and exaptation. Moreover, even though rock-dwelling species generally had longer limbs than their close relatives, clade-level differences in limb length led to an overall lack of difference between rock- and non-rock-dwelling lizards. These results indicate that evolutionary change in the same direction in independent lineages does not necessarily produce convergence, and that the existence of similar advantageous structures among species independently occupying the same environment may not indicate adaptation.  相似文献   

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