Latitudinal and climatic variation in body size and dorsal scale counts in Sceloporus lizards:a phylogenetic perspective

Squamates often follow an inverse Bergmann's rule, with larger-bodied animals occurring in warmer areas or at lower latitudes. The size of dorsal scales in lizards has also been proposed to vary along climatic gradients, with species in warmer areas exhibiting larger scales, putatively to reduce heat load. We tested for these patterns in the diverse and widespread lizard genus Sceloporus. Among 106 species or populations, body size was associated positively with maximum temperature (consistent with the inverse of Bergmann's rule) and aridity, but did not covary with latitude. Scale size (inferred from the inverse relation with numbers of scales) was positively related to body size. Controlling for body size via multiple regression, scale size was associated negatively with latitude (best predictor), positively with minimum temperature, and negatively with aridity (similar results were obtained using scores from a principal components analysis of latitude and climatic indicators). Thus, lizards with larger scales are not necessarily found in areas with higher temperatures. Univariate analyses indicated phylogenetic signal for body size, scale counts, latitude, and all climate indicators. In all cases, phylogenetic regression models fit the data significantly better than nonphylogenetic models; thus, residuals for log(10) number of dorsal scale rows exhibited phylogenetic signal.     

The relationship between sexual size dimorphism and habitat use in Greater Antillean Anolis lizards

Abstract.— Sexual size dimorphism (SSD) is the evolutionary result of selection operating differently on the body sizes of males and females. Anolis lizard species of the Greater Antilles have been classified into ecomorph classes, largely on the basis of their structural habitat (perch height and diameter). We show that the major ecomorph classes differ in degree of SSD. At least two SSD classes are supported: high SSD (trunk-crown, trunk-ground) and low SSD (trunk, crown-giant, grass-bush, twig). Differences cannot be attributed to an allometric increase of SSD with body size or to a phylogenetic effect. A third explanation, that selective pressures on male and/or female body size vary among habitat types, is examined by evaluating expectations from the major relevant kinds of selective pressures. Although no one kind of selective pressure produces expectations consistent with all of the information, competition with respect to structural habitat and sexual selection pressures are more likely possibilities than competition with respect to prey size or optimal feeding pressures. The existence of habitat-specific sexual dimorphism suggests that adaptation of Anolis species to their environment is more complex than previously appreciated.     

Evolutionary correlations among morphology, habitat use and clinging performance in Caribbean Anolis lizards

A central issue in evolutionary biology concerns whether morphology, performance and habitat use have coevolved. We investigated evolutionary relationships among the size of the subdigital toepad, clinging ability and perch height in 12 species of Caribbean Anolis lizard. Specifically, we predicted that: (1) because larger anole species tend to perch high in the canopy, both toepad area and clinging ability should scale with positive allometry to enable small and large lizards to possess approximately similar ratios of both variables relative to mass; (2) anole species with relatively larger toepads (i.e. size-adjusted) should be relatively better clingers compared with species with relatively small toepads; (3) species that perch high in the canopy should possess relatively large clinging abilities (either on an absolute or a size-adjusted basis). Our first hypothesis was refuted, as both toepad area and clinging ability scaled close to isometry (0.67) relative to mass, indicating that large lizard species have low ratios of clinging ability to mass compared with small lizard species. However, our second and third predictions were confirmed. Anole species with relatively larger toepads were relatively better clingers compared with species with relatively smaller toepads. Anole species that perched high in the canopy (either on an absolute scale or relative to size) tended to have relatively larger toepads and greater clinging capacities compared with species that perched lower in the canopy. These data provide indirect comparative evidence that the evolution of increased toepad size in some anole species is adaptive, by facilitating the occupation of perches high in the canopy.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 389–398.     

Enemy at the gates: Rapid defensive trait diversification in an adaptive radiation of lizards

Adaptive radiation (AR), the product of rapid diversification of an ancestral species into novel adaptive zones, has become pivotal in our understanding of biodiversity. Although it has widely been accepted that predators may drive the process of AR by creating ecological opportunity (e.g., enemy‐free space), the role of predators as selective agents in defensive trait diversification remains controversial. Using phylogenetic comparative methods, we provide evidence for an “early burst” in the diversification of antipredator phenotypes in Cordylinae, a relatively small AR of morphologically diverse southern African lizards. The evolution of body armor appears to have been initially rapid, but slowed down over time, consistent with the ecological niche‐filling model. We suggest that the observed “early burst” pattern could be attributed to shifts in vulnerability to different types of predators (i.e., aerial versus terrestrial) associated with thermal habitat partitioning. These results provide empirical evidence supporting the hypothesis that predators or the interaction therewith might be key components of ecological opportunity, although the way in which predators influence morphological diversification requires further study.     

Adaptive radiation versus intraspecific differentiation: morphological variation in Caribbean Anolis lizards

Lizards in the genus Anolis have experienced adaptive radiation in the Greater Antilles, producing a suite of species morphologically adapted to use different parts of the environment. In the Lesser Antilles, adaptive radiation has not occurred, but on some islands, interpopulational variation is high and represents adaptation to different habitats. We compared the extent of morphological differentiation among Greater Antillean habitat specialists with that exhibited among populations of two species, Anolis marmoratus and A. oculatus, from the Lesser Antillean islands of Guadeloupe and Dominica. Although extensive, intraspecific divergence in the Lesser Antilles is substantially less in magnitude than the differences among habitat specialists in the Greater Antilles. All populations of A. marmoratus are most similar to Greater Antillean trunk‐crown habitat specialists, but populations of A. oculatus differ in their affinities: some are similar to trunk‐crown anoles, but others are more similar to trunk‐ground habitat specialists.     

Phenotypic integration between claw and toepad traits promotes microhabitat specialization in the Anolis adaptive radiation

The performance of an organism in its environment frequently depends more on its composite phenotype than on individual phenotypic traits. Thus, understanding environmental adaptation requires investigating patterns of covariation across functionally related traits. The replicated adaptive radiations of Greater Antillean Anolis lizards are characterized by ecological and morphological convergence, thus, providing an opportunity to examine the role of multiple phenotypes in microhabitat adaptation. Here, we examine integrated claw and toepad morphological evolution in relation to habitat partitioning across the adaptive radiations of Greater Antillean anoles. Based on analysis of 428 specimens from 57 species, we found that different aspects of claw morphology were associated with different perch dimensions, with claw height positively associated with perch diameter and claw curvature positively associated with perch height. Patterns of integration also varied across claw and toepad traits, likely driven by correlative selection for performance on smoother and rougher substrates. Finally, rates of evolution differed between claw and toepad traits, with claw length evolving faster than all other traits despite having no predicted functional importance. Our results highlight the multivariate nature of phenotypic adaptation and suggest that phenotypic integration across Greater Antillean anoles is driven by fine‐scale correlative selection based on structural habitat specialization.     

Claw morphometrics in monitor lizards: Variable substrate and habitat use correlate to shape diversity within a predator guild

Numerous studies investigate morphology in the context of habitat, and lizards have received particular attention. Substrate usage is often reflected in the morphology of characters associated with locomotion, and, as a result, claws have become well‐studied ecomorphological traits linking the two. The Kimberley predator guild of Western Australia consists of 10 sympatric varanid species. The purpose of this study was to quantify claw size and shape in the guild using geometric morphometrics, and determine whether these features correlated with substrate use and habitat. Each species was assigned a Habitat/substrate group based on the substrate their claws interact with in their respective habitat. Claw morphometrics were derived for both wild caught and preserved specimens from museum collections, using a 2D semilandmark analysis. Claw shape significantly separated based on Habitat/substrate group. Varanus gouldii and Varanus panoptes claws were associated with sprinting and extensive digging. Varanus mertensi claws were for shallow excavation. The remaining species’ claws reflected specialization for some form of climbing, and differed based on substrate compliance. Varanus glauerti was best adapted for climbing rough sandstone, whereas Varanus scalaris and Varanus tristis had claws ideal for puncturing wood. Phylogenetic signal also significantly influenced claw shape, with Habitat/substrate group limited to certain clades. Positive size allometry allowed for claws to cope with mass increases, and shape allometry reflected a potential size limit on climbing. Claw morphology may facilitate niche separation within this trophic guild, especially when considered with body size. As these varanids are generalist predators, morphological traits associated with locomotion may be more reliable candidates for detecting niche partitioning than those associated directly with diet.     

Physiological evolution during adaptive radiation: A test of the island effect in Anolis lizards

Phenotypic evolution is often exceptionally rapid on islands, resulting in numerous, ecologically diverse species. Although adaptive radiation proceeds along various phenotypic axes, the island effect of faster evolution has been mostly tested with regard to morphology. Here, we leveraged the physiological diversity and species richness of Anolis lizards to examine the evolutionary dynamics of three key traits: heat tolerance, body temperature, and cold tolerance. Contrary to expectation, we discovered slower heat tolerance evolution on islands. Additionally, island species evolve toward higher optimal body temperatures than mainland species. Higher optima and slower evolution in upper physiological limits are consistent with the Bogert effect, or evolutionary inertia due to thermoregulation. Correspondingly, body temperature is higher and more stable on islands than on the American mainland, despite similarity in thermal environments. Greater thermoregulation on islands may occur due to ecological release from competitors and predators compared to mainland environments. By reducing the costs of thermoregulation, ecological opportunity on islands may actually stymie, rather than hasten, physiological evolution. Our results emphasize that physiological diversity is an important axis of ecological differentiation in the adaptive radiation of anoles, and that behavior can impart distinct macroevolutionary footprints on physiological diversity on islands and continents.     

Environmental correlates of phenotypic evolution in ecologically diverse Liolaemus lizards

Evolutionary correlations between phenotypic and environmental traits characterize adaptive radiations. However, the lizard genus Liolaemus, one of the most ecologically diverse terrestrial vertebrate radiations on earth, has so far shown limited or mixed evidence of adaptive diversification in phenotype. Restricted use of comprehensive environmental data, incomplete taxonomic representation and not considering phylogenetic uncertainty may have led to contradictory evidence. We compiled a 26‐taxon dataset for the Liolaemus gracilis species group, representing much of the ecological diversity represented within Liolaemus and used environmental data to characterize how environments occupied by species'' relate to phenotypic evolution. Our analyses, explicitly accounting for phylogenetic uncertainty, suggest diversification in phenotypic traits toward the present, with body shape evolution rapidly evolving in this group. Body shape evolution correlates with the occupation of different structural habitats indicated by vegetation axes suggesting species have adapted for maximal locomotory performance in these habitats. Our results also imply that the effects of phylogenetic uncertainty and model misspecification may be more extensive on univariate, relative to multivariate analyses of evolutionary correlations, which is an important consideration in analyzing data from rapidly radiating adaptive radiations.     

Nowhere to run: the role of habitat openness and refuge use in defining patterns of morphological and performance evolution in tropical lizards

For species from open habitats with little cover and few refugia, selection should favour morphologies that enhance performance at tasks that enable rapid movement across open areas. Similarly, selection should also favour traits that enable rapid access and movement within suitable refugia. This study examined the relationship between habitat openness, refuge use, morphology and performance of 19 species representing 23 populations of tropical Lygosomine skink. Species from this group occupy a wide array of habitats from open forest and open rocky intertidal zones to high‐altitude heaths and dense, closed forests. Species that occupied open habitats were faster at sprinting, climbing and had better cling ability than species from more cluttered, closed habitats. In addition, species from habitats that used rock crevices as refuges had enhanced sprinting ability. This study shows the importance of both habitat openness and refuge type in the evolution of both the morphology and performance in lizards.     

Exploiting genomic resources in studies of speciation and adaptive radiation of lizards in the genus Anolis

Lizards in the genus Anolis have radiated extensively within and among islands in the Caribbean. Here, I provide a prospectus for identifying genes underlying adaptive phenotypic traits in anoles. First I review patterns of diversification in Anolis and the important morphological axes along which divergence occurs. Then I discuss two features of anole diversification, the repeated, convergent evolution of ecomorphs, and phenotypic divergence among populations within species, that provide opportunities to identify genes underlying adaptive phenotypic variation. While small clutch size and difficulty with captive rearing currently limit the utility of quantitative trait locus analyses, comparative analyses of gene expression, and population genomic approaches are promising.     

Testing the island effect in adaptive radiation: rates and patterns of morphological diversification in Caribbean and mainland Anolis lizards

Many of the classic examples of adaptive radiation, including Caribbean Anolis lizards, are found on islands. However, Anolis also exhibits substantial species richness and ecomorphological disparity on mainland Central and South America. We compared patterns and rates of morphological evolution to investigate whether, in fact, island Anolis are exceptionally diverse relative to their mainland counterparts. Quite the contrary, we found that rates and extent of diversification were comparable--Anolis adaptive radiation is not an island phenomenon. However, mainland and Caribbean anoles occupy different parts of morphological space; in independent colonizations of both island and mainland habitats, island anoles have evolved shorter limbs and better-developed toe pads. These patterns suggest that the two areas are on different evolutionary trajectories. The ecological causes of these differences are unknown, but may relate to differences in predation or competition among mainland and island communities.     

Intraspecific variation in Anolis sagrei mirrors the adaptive radiation of Greater Antillean anoles

Anolis lizards of the Greater Antilles represent one of the classic examples of vertebrate adaptive radiation. The same morphological types ('ecomorphs') have evolved repeatedly in response to similar ecological pressures on different islands. We tested whether patterns of within species diversification were congruent with between species patterns and the processes leading to the adaptive radiation of Greater Antillean anoles by measuring variation in performance-related morphological characters in the brown anole, Anolis sagrei . We measured morphological and genetic variation in two different habitat types on each of five islands in the Bahamas. We estimated population structure and rates of gene flow within and among islands using eight microsatellite markers. Intraspecific variation in performance-related morphological characters was similar to the pattern of interspecific variation that characterizes the adaptive radiation of this group in the Greater Antilles. For example, limb length was correlated with perch diameter within A. sagrei as has also been shown among species of anole. Morphological divergence in traits has occurred despite relatively high levels of gene flow both within and among islands. These results are discussed in the context of the divergence-with-gene-flow model of speciation. The results provide important intraspecific evidence that the diversification of anoles has been shaped by natural selection and show how ecologically-based selection pressures explain diversification at both the population and species levels.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 189–199.     

Convergent body flattening in a clade of tropical rock-using lizards (Scincidae: Lygosominae)

The repeated occurrence of similar morphologies in organisms from similar habitats provides good evidence of convergent selection, and convergent patterns of evolutionary change. In lizards, a flattened morphology has often been noted; however, whether this trait is convergent in specific habitats has never been tested using phylogenetic methods. The present study examined patterns of morphological convergence in 18 species of tropical Lygosomine skinks from three broad habitat categories (generalist, leaf litter-dwelling, and rock-using species). In general, although there where relatively few morphological differences of species from different habitats, phylogenetic analyses revealed that rock-using species have consistently and repeatedly evolved a dorsoventrally flattened head and body. The adaptive basis of this flattened morphology is consistent with both biomechanical predictions of performance (e.g. climbing locomotion) and ecology (e.g. use of rock crevices, camouflage) of species that occupy rocky habitats.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 399–411.     

Lizard habitat partitioning on islands: the interaction of local and landscape scales

Aim This study addresses how species resolve environmental differences into biological habitats at multiple, interacting spatial scales. How do patterns of local habitat use change along an elevation gradient? How do patterns of local habitat partitioning interact with partitioning at a landscape scale? Location Northern and southern Lesser Antilles islands, West Indies. Methods We document how Anolis Daudin, 1802 lizards partition habitat locally at sites along a landscape‐scale elevation gradient. We examine habitat partitioning both with and without interspecific interactions in the predominately flat northern Lesser Antilles islands and in the more mountainous southern islands. Results Anoles partition local habitat along perch‐height and microclimate axes. Northern‐group sympatric anoles partition local habitat by perch height and have overlapping distributions at the landscape scale. Southern‐group sympatric anoles partition local habitat by microclimate and specialize in particular habitats at the landscape scale. In both the northern and southern groups, species use different perch heights and microclimates only in areas of species overlap along the elevation gradient. Main conclusions We demonstrate the interaction between local‐ and landscape‐scale habitat partitioning. In the case of microclimate partitioning, the interaction results from the use of thermal physiology to partition habitat at multiple scales. This interaction prompts the question of whether habitat partitioning developed ‘local‐out’ or ‘landscape‐in’. We pose this dichotomy and present a framework for its resolution.     

Water loss in Anolis lizards: evidence for acclimation and intraspecific differences along a habitat gradieNT

• 1.1. Rates of evaporative water loss (EWL) were measured in Anolis roquet and A. marmoratus each from three localities which varied in conditions of aridity.
• 2.2. There were significant interpopulational differences in rates of EWL for both species which correlated with habitat aridity.
• 3.3. Rates of EWL were significantly lower in A. roquet after 6 weeks acclimation to more xeric conditions, populational differences were still evident.
• 4.4. Acclimational effects on rates of EWL were 2 to 3 times greater than populational differences.

     

Contrasting global‐scale evolutionary radiations: phylogeny,diversification, and morphological evolution in the major clades of iguanian lizards

Parallel evolutionary radiations in adjacent locations have been documented in many systems, but typically at limited geographical scales. Here, we compare patterns of evolutionary radiation at the global scale in iguanian lizards, the dominant clade of lizards. We generated a new time‐calibrated phylogeny including 153 iguanian species (based on mitochondrial and nuclear data) and obtained data on morphology and microhabitats. We then compared patterns of species diversification, morphological disparity, and ecomorphological relationships in the predominantly Old World and New World clades (Acrodonta and Pleurodonta, respectively), focusing on the early portions of these radiations. Acrodonts show relatively constant rates of species diversification and disparity over time. In contrast, pleurodonts show an early burst of species diversification and less‐than‐expected morphological disparity early in their history, and slowing diversification and increasing disparity more recently. Analyses including all species (with MEDUSA) suggest accelerated diversification rates in certain clades within both Acrodonta and Pleurodonta, which strongly influences present‐day diversity patterns. We also find substantial differences in ecomorphological relationships between these clades. Our results demonstrate that sister clades in different global regions can undergo very different patterns of evolutionary radiation over similar time frames. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Vitellogenin diversity in tropical lizards (Anolis pulchellus): identification and partial characterization.

1. Three size-classes of vitellogenin polypeptides were detected by electrophoretic and radiolabeling techniques in 32Pi-labeled plasma of vitellogenic female lizards but not in male animals. Based on their apparent Mr, the polypeptides were designated as VTG-226-201K, VTG-169-153K and VTG-116-123K. 2. Structural differences were found between VTG-169-153K and VTG-116K by partial proteolysis with S. aureus V8 protease and radiolabeling techniques. 3. Autoradiography of a 3-10% native gradient gel revealed three different species of VTG in 32Pi-labeled plasma of stimulated males: VTG-I (Mr = 850,000), VTG-II (Mr = 750,000) and VTG-III (Mr = 610,000). By 2D PAGE, it was shown that VTG-169K and VTG-116K are components of VTG-I, while VTG-153K and VTG-116K comprise VTG-III. These results suggest an oligomeric structure for native VTG. 4. Amino acid analysis, 32Pi incorporation, electrophoretical behavior and Mr estimation demonstrated homology between VTG-116K and the S1-lipovitellin from the lizard egg. 5. These results strongly indicate an unusual multiplicity of VTG forms in tropical lizards when compared to other egg-laying vertebrates.