A molecular study of phylogenetic relationships and evolution of antipredator strategies in Australian Diplodactylus geckos, subgenus Strophurus

Variation in density, but not morphology, of cutaneous sensilla among body regions in nine species of Australian geckos

Skin sense organs, i.e., cutaneous sensilla, are a well-known feature of the integument of squamate reptiles, and particularly geckos. They vary widely in morphology among species, and are thought to be mechanosensitive, associated with prey capture and handling, tail autotomy, and placement of the adhesive toepads in pad-bearing species. Some authors suggest that they may also sense abiotic environmental features, such as temperature, or humidity. Here, we describe the morphology and distribution of cutaneous sensilla among body regions of nine Australian gecko species, in four genera. We hypothesised that if sensilla morphology was distinct, or sensilla density high, around the mouth, on the tail, and on extremities, sensilla were likely used for these direct tactile functions. We found that sensilla morphology was uniform among body regions within species, but varied among species, while sensilla densities varied among species and body regions. In gecko species studied, sensilla density was highest on the labials and the dorsal tail scales, and low on the feet, head and body, providing strong support for the hypothesis that sensilla serve tactile mechanoreceptive functions for prey capture and handling and for predator avoidance, but not for toepad placement. We suggest sensilla density may be explained by mechanoreception, whereas structure may be influenced by other factors.

Defensive spray by a semiaquatic osmylid larva (Insecta: Neuroptera) for both aquatic and terrestrial predators

Chemical secretions are an effective means by which insects can deter potential enemies. Several terrestrial insects spray these liquids directionally toward enemies, but little is known about spraying behavior in aquatic and semiaquatic insects. The larvae of Osmylus hyalinatus (Neuroptera: Osmylidae) are semiaquatic, inhabiting the edges of small streams and ponds where they encounter multiple enemies on land and in water. The larvae of this osmylid sprayed a hyaline liquid from the anal opening if disturbed in either air and water, although the spray appeared slightly viscous in water. The liquid was stored in the posterior half of the hindgut and sprayed directionally toward an artificial stimulus. Spraying allowed the larvae to escape biting by ants, and to repel them in 90% of encounters. Spraying caused the regurgitation of 71% and 60% of all larvae swallowed by terrestrial frogs and aquatic newts, respectively. Aquatic fishfly larvae released 30% of captured larvae due to spraying. Most of the larvae that repelled ants or were regurgitated by amphibians survived, but those released by fishfly larvae were killed by heavy biting with the mandibles. This is the first report of effective liquid spraying by insects in water, and also within the order Neuroptera.

Ecological associations among epidermal microstructure and scale characteristics of Australian geckos (Squamata: Carphodactylidae and Diplodactylidae)

A first step in examining factors influencing trait evolution is demonstrating associations between traits and environmental factors. Scale microstructure is a well-studied feature of squamate reptiles (Squamata), including geckos, but few studies examine ecology the of microstructures, and those focus mainly on toe pads. In this study, the ecomorphology of cutaneous microstructures on the dorsum was described for eight Australian species of carphodactylid (Squamata: Carphodactylidae) and 19 diplodactylid (Squamata: Diplodactylidae) geckos. We examined scale dimensions, spinule and cutaneous sensilla (CS) morphology, using scanning electron microscopy, and described associations of these traits with microhabitat selection (arboreal, saxicoline or terrestrial) and relative humidity of each species' habitat (xeric, mesic or humid). We used a phylogenetic flexible discriminant analysis (pFDA) to describe relationships among all traits and then a modeling approach to examine each trait individually. Our analysis showed that terrestrial species tended to have long spinules and CS with more bristles, saxicoline species larger diameter CS and arboreal species tended to have large granule scales and small intergranule scales. There was high overlap in cutaneous microstructural morphology among species from xeric and mesic environments, whereas species from humid environments had large diameter CS and few bristles. Significant associations between epidermal morphology and environmental humidity and habitat suggest that epidermal microstructures have evolved in response to environmental variables. In summary, long spinules, which aid self-cleaning in terrestrial geckos, are consistent with greater exposure to dirt and debris in this habitat. Long spinules were not clearly correlated to environmental humidity. Finally, more complex CS (larger diameter with more bristles) may facilitate better perception of environmental variation in geckos living in drier habitats.

Key innovations and island colonization as engines of evolutionary diversification: a comparative test with the Australasian diplodactyloid geckos

The acquisition of key innovations and the invasion of new areas constitute two major processes that facilitate ecological opportunity and subsequent evolutionary diversification. Using a major lizard radiation as a model, the Australasian diplodactyloid geckos, we explored the effects of two key innovations (adhesive toepads and a snake-like phenotype) and the invasion of new environments (island colonization) in promoting the evolution of phenotypic and species diversity. We found no evidence that toepads had significantly increased evolutionary diversification, which challenges the common assumption that the evolution of toepads has been responsible for the extensive radiation of geckos. In contrast, a snakelike phenotype was associated with increased rates of body size evolution and, to a lesser extent, species diversification. However, the clearest impact on evolutionary diversification has been the colonization of New Zealand and New Caledonia, which were associated with increased rates of both body size evolution and species diversification. This highlights that colonizing new environments can drive adaptive diversification in conjunction or independently of the evolution of a key innovation. Studies wishing to confirm the putative link between a key innovation and subsequent evolutionary diversification must therefore show that it has been the acquisition of an innovation specifically, not the colonization of new areas more generally, that has prompted diversification.

A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes

BACKGROUND

The extant squamates (>9400 known species of lizards and snakes) are one of the most diverse and conspicuous radiations of terrestrial vertebrates, but no studies have attempted to reconstruct a phylogeny for the group with large-scale taxon sampling. Such an estimate is invaluable for comparative evolutionary studies, and to address their classification. Here, we present the first large-scale phylogenetic estimate for Squamata.

RESULTS

The estimated phylogeny contains 4161 species, representing all currently recognized families and subfamilies. The analysis is based on up to 12896 base pairs of sequence data per species (average = 2497 bp) from 12 genes, including seven nuclear loci (BDNF, c-mos, NT3, PDC, R35, RAG-1, and RAG-2), and five mitochondrial genes (12S, 16S, cytochrome b, ND2, and ND4). The tree provides important confirmation for recent estimates of higher-level squamate phylogeny based on molecular data (but with more limited taxon sampling), estimates that are very different from previous morphology-based hypotheses. The tree also includes many relationships that differ from previous molecular estimates and many that differ from traditional taxonomy.

CONCLUSIONS

We present a new large-scale phylogeny of squamate reptiles that should be a valuable resource for future comparative studies. We also present a revised classification of squamates at the family and subfamily level to bring the taxonomy more in line with the new phylogenetic hypothesis. This classification includes new, resurrected, and modified subfamilies within gymnophthalmid and scincid lizards, and boid, colubrid, and lamprophiid snakes.

Sequestered defensive toxins in tetrapod vertebrates: principles, patterns, and prospects for future studies

Chemical defenses are widespread among animals, and the compounds involved may be either synthesized from nontoxic precursors or sequestered from an environmental source. Defensive sequestration has been studied extensively among invertebrates, but relatively few examples have been documented among vertebrates. Nonetheless, the number of described cases of defensive sequestration in tetrapod vertebrates has increased recently and includes diverse lineages of amphibians and reptiles (including birds). The best-known examples involve poison frogs, but other examples include natricine snakes that sequester toxins from amphibians and two genera of insectivorous birds. Commonalities among these diverse taxa include the combination of consuming toxic prey and exhibiting some form of passive defense, such as aposematism, mimicry, or presumptive death-feigning. Some species exhibit passive sequestration, in which dietary toxins simply require an extended period of time to clear from the tissues, whereas other taxa exhibit morphological or physiological specializations that enhance the uptake, storage, and/or delivery of exogenous toxins. It remains uncertain whether any sequestered toxins of tetrapods bioaccumulate across multiple trophic levels, but multitrophic accumulation seems especially likely in cases involving consumption of phytophagous or mycophagous invertebrates and perhaps consumption of poison frogs by snakes. We predict that additional examples of defensive toxin sequestration in amphibians and reptiles will be revealed by collaborations between field biologists and natural product chemists. Candidates for future investigation include specialized predators on mites, social insects, slugs, and toxic amphibians. Comprehensive studies of the ecological, evolutionary, behavioral, and regulatory aspects of sequestration will require teams of ecologists, systematists, ethologists, physiologists, molecular biologists, and chemists. The widespread occurrence of sequestered defenses has important implications for the ecology, evolution, and conservation of amphibians and reptiles.

Molecular phylogenetics of the arboreal Australian gecko genus Oedura Gray 1842 (Gekkota: Diplodactylidae): another plesiomorphic grade?

The family Diplodactylidae is the most ecologically diverse and geographically widespread radiation of geckos within Australasia. Herein we present a first comprehensive phylogenetic analysis of relationships of diplodactylid geckos currently assigned to the genus Oedura, a group of relatively generalised arboreal Australian geckos. Maximum Likelihood, bayesian and Maximum Parsimony analyses of a combination of over two and a half kilobases of nuclear (PDC, Rag-1) and mitochondrial (ND2, ND4, tRNA) sequence data all identified four distinctive lineages within Oedura s.l. Based on their deep divergences and a suite of diagnostic morphological characters we recognise each of these four lineages as genera, two of which are monotypic and newly described herein. Our molecular data also suggest that Oedura s.l. is not monophyletic, but is instead a plesiomorphic grade restricted to islands of rocky or forested habitat around coastal and central Australia. In contrast, combined analysis of all data suggests the Australian arid zone is dominated by a single comparatively derived and relatively species rich clade including most other genera of Australian Diplodactylidae. Additional data are required to properly resolve basal divergence events within the Diplodactylidae, however the emerging pattern of relationships and divergence is consistent with the hypothesis that monsoonal and temperate lineages are ancestral to the arid zone fauna, but also indicate that arid zone lineages and radiations are relatively old, and potentially date back to the mid Miocene or earlier.

Species interactions mediate phylogenetic community structure in a hyperdiverse lizard assemblage from arid Australia

Evolutionary history can exert a profound influence on ecological communities, but few generalities have emerged concerning the relationships among phylogeny, community membership, and niche evolution. We compared phylogenetic community structure and niche evolution in three lizard clades (Ctenotus skinks, agamids, and diplodactyline geckos) from arid Australia. We surveyed lizard communities at 32 sites in the northwestern Great Victoria Desert and generated complete species-level molecular phylogenies for regional representatives of the three clades. We document a striking pattern of phylogenetic evenness within local communities for all groups: pairwise correlations in species abundance across sites are negatively related to phylogenetic similarity. By modeling site suitability on the basis of species' habitat preferences, we demonstrate that phylogenetic evenness generally persists even after controlling for habitat filtering among species. This phylogenetic evenness is coupled with evolutionary lability of habitat-associated traits, to the extent that closely related species are more divergent in habitat use than distantly related species. In contrast, lizard diets are phylogenetically conserved, and pairwise dietary overlap between species is negatively related to phylogenetic distance in two of the three clades. Our results suggest that contemporary and historical species interactions have led to similar patterns of community structure across multiple clades in one of the world's most diverse lizard communities.

Genetic diversity and biogeographic history inform future conservation management strategies for the rare sunset frog (Spicospina flammocaerulea)

Outlining the distribution of genetic variation, patterns of gene flow and clarifying the biogeographic processes underlying population history are critical components of a comprehensive conservation strategy for endangered or vulnerable species. We provide this information for the vulnerable sunset frog (Spicospina flammocaerulea) using a comprehensive genetic dataset (ND2) with samples from 17 of 22 geographic localities where this species has been found. From genetic, biogeographic and coalescent-based analyses, we document the existing genetic variation, likely movement patterns and explore the biogeographic history of S. flammocaerulea. While catchment-based genetic variation is well documented in other high-rainfall taxa in south-western Australia, a much more complex scenario including dispersal across ridge lines between catchments better explains the distribution of genetic variation and observed patterns of gene flow in S. flammocaerulea. The population history of S. flammocaerulea is strongly indicative of recent population contraction and expansion, which may be related to late Pleistocene climate fluctuations. This suggests that this species can adapt or move in response to fluctuating climates provided suitable habitats or expansion areas are available. However, like many other endemic taxa with limited geographic ranges in south-western Australia, the potential to shift distributions is hampered by being land-locked within an agricultural landscape, limiting management options in the face of climate change.

Birth of a biome: insights into the assembly and maintenance of the Australian arid zone biota

The integration of phylogenetics, phylogeography and palaeoenvironmental studies is providing major insights into the historical forces that have shaped the Earth's biomes. Yet our present view is biased towards arctic and temperate/tropical forest regions, with very little focus on the extensive arid regions of the planet. The Australian arid zone is one of the largest desert landform systems in the world, with a unique, diverse and relatively well-studied biota. With foci on palaeoenvironmental and molecular data, we here review what is known about the assembly and maintenance of this biome in the context of its physical history, and in comparison with other mesic biomes. Aridification of Australia began in the Mid-Miocene, around 15 million years, but fully arid landforms in central Australia appeared much later, around 1-4 million years. Dated molecular phylogenies of diverse taxa show the deepest divergences of arid-adapted taxa from the Mid-Miocene, consistent with the onset of desiccation. There is evidence of arid-adapted taxa evolving from mesic-adapted ancestors, and also of speciation within the arid zone. There is no evidence for an increase in speciation rate during the Pleistocene, and most arid-zone species lineages date to the Pliocene or earlier. The last 0.8 million years have seen major fluctuations of the arid zone, with large areas covered by mobile sand dunes during glacial maxima. Some large, vagile taxa show patterns of recent expansion and migration throughout the arid zone, in parallel with the ice sheet-imposed range shifts in Northern Hemisphere taxa. Yet other taxa show high lineage diversity and strong phylogeographical structure, indicating persistence in multiple localised refugia over several glacial maxima. Similar to the Northern Hemisphere, Pleistocene range shifts have produced suture zones, creating the opportunity for diversification and speciation through hybridisation, polyploidy and parthenogenesis. This review highlights the opportunities that development of arid conditions provides for rapid and diverse evolutionary radiations, and re-enforces the emerging view that Pleistocene environmental change can have diverse impacts on genetic structure and diversity in different biomes. There is a clear need for more detailed and targeted phylogeographical studies of Australia's arid biota and we suggest a framework and a set of a priori hypotheses by which to proceed.

Phylogenetic relationships of the heath dragons (Rankinia adelaidensis and R. parviceps) from the south-western Australian biodiversity hotspot

Although the south-western Australian region is recognised as a global biodiversity hotspot, there are still significant gaps in our understanding of the biodiversity of this region. We present a phylogenetic study of the heath dragons (Rankinia adelaidensis and R. parviceps) from this region, incorporating a 1612-bp section of mtDNA and two nuclear introns, Gapdh (~244 bp) and Enol (~330 bp). In addition, we present a generic-level analysis of three gene regions (mtDNA, Gapdh, BDNF), which provides clear evidence that Rankinia adelaidensis and R. parviceps are not closely related to Rankinia diemensis from eastern Australia. Instead, the heath dragons are strongly supported as forming a clade with the genus Ctenophorus. In addition, we find that there are significant levels of haplotype divergence between currently recognised subspecies of the heath dragons (R. a. adelaidensis, R. a. chapmani, R. p. parviceps, R. p. butleri). We suggest that the genetic divergences between subspecies result from geographic isolation in allopatry owing to habitat preferences, followed by drift and/or selection. On the basis of these deep divergences and consistent morphological differences between subspecies, we recommend elevating all taxa to full species, and provide a taxonomic revision of the genera Rankinia and Ctenophorus.

Phylogenetic analysis of the scaling of wet and dry biological fibrillar adhesives

Fibrillar, or "hairy," adhesives have evolved multiple times independently within arthropods and reptiles. These adhesives exhibit highly desirable properties for dynamic attachment, including orientation dependence, wear resistance, and self-cleaning. Our understanding of how these properties are related to their fibrillar structure is limited, although theoretical models from the literature have generated useful hypotheses. We survey the morphology of 81 species with fibrillar adhesives to test the hypothesis that packing density of contact elements should increase with body size, whereas the size of the contact elements should decrease. We test this hypothesis in a phylogenetic context to avoid treating historically related species as statistically independent data points. We find that fiber morphology is better predicted by evolutionary history and adhesive mechanism than by body size. As we attempt to identify which morphological parameters are most responsible for the performance of fibrillar adhesives, it will be important to take advantage of the natural variation in morphology and the potentially suboptimal outcomes it encompasses, rather than assuming evolution to be an inherently optimizing process.

Impact of Plio-Pleistocene arid cycling on the population history of a southwestern Australian frog

Southwestern Australia is regarded as a global biodiversity hotspot. The region contains a high number of endemic species, ranging from Gondwanan relicts to much more recently evolved plant and animal species. Myobatrachid frogs are diverse in southwestern Australia, and while we know they have speciated in situ in the southwest, we know little about the temporal and geographical patterning of speciation events. Crinia georgiana is an ideal subject to test hypotheses concerning the effect of climatic history on southwestern Australian anurans, as it is an old lineage with a broad distribution covering the entire region. We compiled an extensive phylogeographical data set based on 1085 bp of the mitochondrial gene ND2 for 68 individuals from 18 sites across the species' range. Two major genetic clades were identified which were largely confined to the high rainfall and southeast coastal biogeographical zones, respectively. The clades appear to have diverged around the Plio-Pleistocene border (1.26-1.72 million years ago), concordant with increasing intensity and frequency of arid climate cycles. Subsequent phylogeographical structure appears to have developed primarily during the Pleistocene climatic fluctuations that also have been integral in generating species diversity in the endemic southwestern Australian flora. Phylogeographical analyses identified several dispersal routes, possible refugial areas within the range of the species and also regions of secondary contact. Dispersal routes identified may now be closed to the species because of habitat destruction and salinity problems in inland regions, posing concerns about the evolutionary potential of the species in light of predicted climate change.

Comparative phylogeography of three skink species (Oligosoma moco, O. smithi, O. suteri; Reptilia: Scincidae) in northeastern New Zealand

Sea-level fluctuations during the Pliocene and Pleistocene have shaped the landscape of the Northland region of New Zealand. We examined the comparative phylogeography of three skink species (Oligosoma moco, O. smithi, O. suteri) in northeastern New Zealand in order to investigate the impact of the historical processes that have prevailed since the Pliocene on the Northland fauna. O. moco, O. smithi and O. suteri have similar distributions across northeastern New Zealand, frequently occurring in sympatry. We obtained sequence data from across the entire range of each species, targeting the ND2 mitochondrial gene. Using Neighbor-Joining, Maximum likelihood and Bayesian methods, our analysis revealed contrasting phylogeographic patterns in each species. We found substantial phylogeographic structure within O. moco, with three distinct clades identified. Similarly, deep phylogeographic divergence was evident within O. smithi, with three distinct clades present. Clade 1 included O. smithi populations from the Three Kings Islands and the western coastline of Northland, while Clade 2 encompassed the remainder of the range. However, since Clade 3 corresponded to a described species (O. microlepis), O. smithi might represent a species complex. In both O. moco and O. smithi, divergences among clades are estimated to have occurred in the Pliocene, with divergences within clades occurring during the Pleistocene. In contrast, genetic divergence among O. suteri populations was extremely limited and indicative of more recent divergences during the Pleistocene. The lack of phylogeographic structure in O. suteri might be a consequence of its oviparous reproductive mode, which restricted its distribution to warm northern refugia during glacial maxima. Differences in the ecology and biology of each species might have produced contrasting responses to the same historical processes, and ultimately diverse phylogeographic patterns. Our study reveals an absence of consistent and concordant phylogeographic patterns in the Northland biota, even within the same taxonomic group.

Biogeography and speciation of a direct developing frog from the coastal arid zone of Western Australia

Within the southwestern Australian biodiversity hotspot, the Shark Bay region displays high levels of plant and animal endemism, particularly in the herpetofauna. The region has been subjected to dramatic climatic fluctuations and has been geologically active from the Late Miocene to the present. The myobatrachid frog Arenophryne rotunda, a Shark Bay endemic, provides an ideal opportunity to examine the relative effects of fluctuating climates and geological activity on the biota of Shark Bay. A comprehensive phylogeographic analysis of A. rotunda, based on data comprising 1154 bp of the mitochondrial gene ND2, is presented. My results demonstrate a major genetic break that divides this species at the northern edge of the Victorian Plateau into northern and southern species lineages, dating to the Late Miocene, with a further division of the southern species lineage across the Murchison Gorge dating to the Plio-Pleistocene border. Both of these periods are related to prominent geological activity and climatic shifts in the Shark Bay region. Interpretation of phylogeographic results point to the prominent role of fluctuating Pleistocene climates and associated coastal landscape evolution in the generation of phylogeographic structure within the distinct A. rotunda species lineages. Similar processes have been invoked to explain the diversity of other Shark Bay biota.

Phylogenetic relationships in the lizard genus Diplodactylus Gray and resurrection of Lucasium Wermuth (Gekkota, Diplodactylidae)

Diplodactylid geckos offer a model system for investigating the biogeographic history of Australia and adaptive radiations in the arid zone, but there is considerable uncertainty in the systematics of several key genera. We used sequence data from mitochondrial DNA to carry out a comprehensive analysis of phylogenetic relationships of geckos in the genus Diplodactylus. Parsimony and Bayesian analyses were highly concordant and allocated all species to one of two monophyletic clades, one comprising the species placed in the vittatus and conspicillatus species groups, the other comprising species placed in the stenodactylus and steindachneri species groups, plus D. byrnei, formerly in the vittatus group. The distinctness of these two clades is supported by external morphology of the digits, body and limb proportions, and osteology of the bones in the orbital region, and we use these characters to formally define the two clades as genera. We revive and expand the genus Lucasium for D. byrnei, D. steindachneri and the stenodactylus group, with the other species staying in a redefined Diplodactylus. The monotypic Rhynchoedura is distinct from Lucasium, although the Bayesian mtDNA analysis (but not parsimony) gives some support for a sister-group relationship between Lucasium and Rhynchoedura. Molecular data suggest that each of these clades represents a distinct radiation into semiarid and arid terrestrial habitats during the mid-Tertiary, well before the hypothesised Pliocene onset of major aridification.

Molecular phylogeny and phylogeography of the Australian Diplodactylus stenodactylus (Gekkota; Reptilia) species-group based on mitochondrial and nuclear genes reveals an ancient split between Pilbara and non-Pilbara D. stenodactylus

There is a paucity of research on intra-specific morphological and genetic diversity in Australian arid-zone reptiles, and a number of Australian reptile species have for many years been regarded as "species complexes" that classical morphological analyses could not resolve. We conducted a phylogenetic and phylogeographic study of a widespread species group of Australian geckonid lizards to address two main aims. First, based on a large mitochondrial and nuclear gene data set, we have generated the first molecular phylogeny for the Diplodactylus stenodactylus species group (D. alboguttatus, D. damaeus, D. maini, and D. squarrosus, D. stenodactylus) and multiple outgroups to examine the evolutionary relationships among these arid-zone species and phylogenetic patterns within some species. The edited alignment of 41 individuals comprises 2485 characters (1163 ND2+tRNAs; 490 16s; 832 RAG-1), and of these 717 (29%) were variable and parsimony informative (568 ND2+tRNAs; 89 16s; 60 RAG-1). This broad-scale, multi-gene phylogeny has supported previous conjectures on the higher-level phylogenetic relationships among members of the D. stenodactylus species-group based on morphology, but also has uncovered hidden diversity within the group with two new species identified. Analysis at this broad level has identified patterns associated with the distribution of the D. stenodactylus species group that appear to be influenced by environmental processes operating at large geographic scales. Two major clades within the species group were associated with broad differences in habitat types, with one group largely restricted to the temperate zone of the Southwest Province and another largely restricted to central and northern Western Australia north of Kalgoorlie, in line with the Eremaean Province of the Eremaean Zone and the Northern Province of the Tropical Zone. Second, we have assembled phylogeographic data based on a mitochondrial gene (ND2+tRNAs) for five species (Rhynchoedura ornata, Diplodactylus maini, D. pulcher, D. squarrosus, D. stenodactylus) where larger sampling is available, with particular focus on D. stenodactylus, which is distributed both in the iconic but little-known Pilbara area of endemism in north-western Australia as well as in other parts of the Australian arid zone. The edited alignment of 95 individuals comprises 1142 characters and of these 601 (53%) are variable and parsimony informative. We found significant intra-specific genetic variation in all five species, highlighting the need for large-scale screening of cryptic species, with sampling specifically targeted at determining the geographic limits of such taxa. In particular, within D. stenodactylus, a deep and ancient phylogenetic split distinguishes populations in the Pilbara region from non-Pilbara populations. This split may be the result of broad differences in underlying geological substrate, with the Pilbara clade generally preferring harder soils and the non-Pilbara clade adapted to sand.

Deep history impacts present-day ecology and biodiversity

Lizards and snakes putatively arose between the early Jurassic and late Triassic; they diversified worldwide and now occupy many different ecological niches, making them ideal for testing theories on the origin of ecological traits. We propose and test the "deep history hypothesis," which claims that differences in ecological traits among species arose early in evolutionary history of major clades, and that present-day assemblages are structured largely because of ancient, preexisting differences. We combine phylogenetic data with ecological data collected over nearly 40 years to reconstruct the evolution of dietary shifts in squamate reptiles. Data on diets of 184 lizard species in 12 families from 4 continents reveal significant dietary shifts at 6 major divergence points, reducing variation by 79.8%. The most striking dietary divergence (27.6%) occurred in the late Triassic, when Iguania and Scleroglossa split. These two clades occupy different regions of dietary niche space. Acquisition of chemical prey discrimination, jaw prehension, and wide foraging provided scleroglossans access to sedentary and hidden prey that are unavailable to iguanians. This cladogenic event may have profoundly influenced subsequent evolutionary history and diversification. We suggest the hypothesis that ancient events in squamate cladogenesis, rather than present-day competition, caused dietary shifts in major clades such that some lizard clades gained access to new resources, which in turn led to much of the biodiversity observed today.