Systematics and evolution of the Australian knob-tail geckos (Nephrurus, Carphodactylidae, Gekkota): plesiomorphic grades and biome shifts through the Miocene

Clades that predate the origin of biomes that they inhabit provide unique opportunities to examine both when major environmental transitions occurred, and how lineages adapted to these changes. The isolated island continent Australia has undergone a profound environmental transition through the Miocene, from relatively mesic to predominantly arid; however, we have much to learn about both the timing of this change, and how organisms may have responded to it. The family Carphodactylidae is an ancient Gondwanan group of geckos that occurs across all major Australian biomes. A multilocus (ND2, Rag-1, c-mos) phylogenetic and dating analysis of the most ecologically diverse clade within this group, the genus Nephrurus (sensuBauer, 1990) reveals that two of three morphological taxa historically recognized (the 'spiny knob-tails' and 'Underwoodisaurus') are relatively species depauperate, pleisomorphic basal grades that diversified through the late Oligocene and early Miocene, and are now absent from most of the arid biome. Based on their deep divergence and morphological distinctiveness we recognize two lineages (milii and sphyrurus) as monotypic genera, the later of which is named herein (Uvidicolus nov. gen). In contrast, a third morphological group, the 'smooth knob-tails,' is a monophyletic group of five exclusively arid zone burrowing species that has radiated relatively recently (mid-Miocene). Our phylogeny indicates that successful colonization of this novel and challenging biome by Nephrurus correlates with an initial shift to terrestriality and adaptation to at least seasonally arid conditions around the early Miocene, and the eventual evolution and subsequent mid-Miocene radiation of a lineage specialized for burrowing.     

A phylogenetic approach to total evaporative water loss in mammals

Abstract Maintaining appropriate water balance is a constant challenge for terrestrial mammals, and this problem can be exacerbated in desiccating environments. It has been proposed that natural selection has provided desert-dwelling mammals physiological mechanisms to reduce rates of total evaporative water loss. In this study, we evaluated the relationship between total evaporative water loss and body mass in mammals by using a recent phylogenetic hypothesis. We compared total evaporative water loss in 80 species of arid-zone mammals to that in 56 species that inhabit mesic regions, ranging in size from 4 g to 3,500 kg, to test the hypothesis that mammals from arid environments have lower rates of total evaporative water loss than mammals from mesic environments once phylogeny is taken into account. We found that arid species had lower rates of total evaporative water loss than mesic species when using a dichotomous variable to describe habitat (arid or mesic). We also found that total evaporative water loss was negatively correlated with the average maximum and minimum environmental temperature as well as the maximum vapor pressure deficit of the environment. Annual precipitation and the variable Q (a measure of habitat aridity) were positively correlated with total evaporative water loss. These results support the hypothesis that desert-dwelling mammals have lower rates of total evaporative water loss than mesic species after controlling for body mass and evolutionary relatedness regardless of whether categorical or continuous variables are used to describe habitat.     

Digest: The evolutionary relationship between environment and size in Australian rodents

Biome shifts are thought to be relatively rare, but some clades shift among starkly different environments with relative ease. What causes these shifts, and how do they shape phenotypic evolution? Roycroft et al. found that biome shifts in the Pseudomys Division of murid rodents were repeatedly accompanied by body size evolution in accordance with Bergmann's rule, suggesting adaptive evolution in response to changing climate conditions.     

Radiation of the Australian flora: what can comparisons of molecular phylogenies across multiple taxa tell us about the evolution of diversity in present-day communities?

The Australian fossil record shows that from ca. 25 Myr ago, the aseasonal-wet biome (rainforest and wet heath) gave way to the unique Australian sclerophyll biomes dominated by eucalypts, acacias and casuarinas. This transition coincided with tectonic isolation of Australia, leading to cooler, drier, more seasonal climates. From 3 Myr ago, aridification caused rapid opening of the central Australian arid zone. Molecular phylogenies with dated nodes have provided new perspectives on how these events could have affected the evolution of the Australian flora. During the Mid-Cenozoic (25-10 Myr ago) period of climatic change, there were rapid radiations in sclerophyll taxa, such as Banksia, eucalypts, pea-flowered legumes and Allocasuarina. At the same time, taxa restricted to the aseasonal-wet biome (Nothofagus, Podocarpaceae and Araucariaceae) did not radiate or were depleted by extinction. During the Pliocene aridification, two Eremean biome taxa (Lepidium and Chenopodiaceae) radiated rapidly after dispersing into Australia from overseas. It is clear that the biomes have different histories. Lineages in the aseasonal-wet biome are species poor, with sister taxa that are species rich, either outside Australia or in the sclerophyll biomes. In conjunction with the fossil record, this indicates depletion of the Australian aseasonal-wet biome from the Mid-Cenozoic. In the sclerophyll biomes, there have been multiple exchanges between the southwest and southeast, rather than single large endemic radiations after a vicariance event. There is need for rigorous molecular phylogenetic studies so that additional questions can be addressed, such as how interactions between biomes may have driven the speciation process during radiations. New studies should include the hitherto neglected monsoonal tropics.     

Body size and extinction risk in Australian mammals: An information‐theoretic approach

The critical weight range (CWR) hypothesis for Australian mammals states that extinctions and declines have been concentrated in species with body mass between 35 g and 5.5 kg. The biological basis for this hypothesis is that species of intermediate size are disproportionately impacted by introduced predators. The CWR hypothesis has received support from several statistical studies over the past decade, although the evidence is weaker or non‐existent for certain groups such as mesic‐zone mammals and arboreal mammals. In this study, we employ an information‐theoretic model selection approach to gain further insights into the relationship between body mass and extinction risk in Australian mammals. We find evidence, consistent with the CWR hypothesis, that extinction risk peaks at intermediate body masses for marsupials, rodents and ground‐dwelling species, but not for arboreal species. In contrast to previous studies, we find that the CWR describes extinction patterns in the mesic zone as well as the arid zone. In the mesic zone, there is also a weaker tendency for large species above the CWR to be more vulnerable, consistent with extinction patterns on other continents. We find that a more biological plausible Gaussian distribution consistently fits the data better than the polynomial models that have been used in previous studies. Our results justify conservation programmes targeted at species within the CWR across Australia.     

DIVERSIFICATION AND PERSISTENCE AT THE ARID–MONSOONAL INTERFACE: AUSTRALIA‐WIDE BIOGEOGRAPHY OF THE BYNOE'S GECKO (HETERONOTIA BINOEI; GEKKONIDAE)

Late Neogene aridification in the Southern Hemisphere caused contractions of mesic biota to refugia, similar to the patterns established by glaciation in the Northern Hemisphere, but these episodes also opened up new adaptive zones that spurred range expansion and diversification in arid‐adapted lineages. To understand these dynamics, we present a multilocus (nine nuclear introns, one mitochondrial gene) phylogeographic analysis of the Bynoe's gecko (Heteronotia binoei), a widely distributed complex spanning the tropical monsoon, coastal woodland, and arid zone biomes in Australia. Bayesian phylogenetic analyses, estimates of divergence times, and demographic inferences revealed episodes of diversification in the Pliocene, especially in the tropical monsoon biome, and range expansions in the Pleistocene. Ancestral habitat reconstructions strongly support recent and independent invasions into the arid zone. Our study demonstrates the varied responses to aridification in Australia, including localized persistence of lineages in the tropical monsoonal biome, and repeated invasion of and expansion through newly available arid‐zone habitats. These patterns are consistent with those found in other arid environments in the Southern Hemisphere, including the South African succulent karoo and the Chilean lowlands, and highlight the diverse modes of diversification and persistence of Earth's biota during the glacial cycles of the Pliocene and Pleistocene.     

The phylogeny and biogeography of Hakea (Proteaceae) reveals the role of biome shifts in a continental plant radiation

The frequency of evolutionary biome shifts during diversification has important implications for our ability to explain geographic patterns of plant diversity. Recent studies present several examples of biome shifts, but whether frequencies of biome shifts closely reflect geographic proximity or environmental similarity of biomes remains poorly known. We explore this question by using phylogenomic methods to estimate the phylogeny of Hakea, a diverse Australian genus occupying a wide range of biomes. Model‐based estimation of ancestral regions indicates that Hakea began diversifying in the Mediterranean biome of southern Australia in the Middle Eocene–Early Oligocene, and dispersed repeatedly into other biomes across the continent. We infer around 47 shifts between biomes. Frequencies of shifts between pairs of biomes are usually similar to those expected from their geographic connectedness or climatic similarity, but in some cases are substantially higher or lower than expected, perhaps reflecting how readily key physiological traits can be modified to adapt lineages to new environments. The history of frequent biome‐shifting is reflected in the structure of present‐day assemblages, which tend to be more phylogenetically diverse than null‐model expectations. The case of Hakea demonstrates that the radiation of large plant clades across wide geographic areas need not be constrained by dispersal limitation or conserved adaptations to particular environments.     

Space versus phylogeny: disentangling phylogenetic and spatial signals in comparative data

Variation in traits across species or populations is the outcome of both environmental and historical factors. Trait variation is therefore a function of both the phylogenetic and spatial context of species. Here we introduce a method that, within a single framework, estimates the relative roles of spatial and phylogenetic variations in comparative data. The approach requires traits measured across phylogenetic units, e.g. species, the spatial occurrences of those units and a phylogeny connecting them. The method modifies the expected variance of phylogenetically independent contrasts to include both spatial and phylogenetic effects. We illustrate this approach by analysing cross-species variation in body mass, geographical range size and species-typical environmental temperature in three orders of mammals (carnivores, artiodactyls and primates). These species attributes contain highly disparate levels of phylogenetic and spatial signals, with the strongest phylogenetic autocorrelation in body size and spatial dependence in environmental temperatures and geographical range size showing mixed effects. The proposed method successfully captures these differences and in its simplest form estimates a single parameter that quantifies the relative effects of space and phylogeny. We discuss how the method may be extended to explore a range of models of evolution and spatial dependence.     

The role of phylogeny and ecology in shaping morphology in 21 genera and 127 species of Australo‐Papuan myobatrachid frogs

Body shape is predicted to differ among species for functional reasons and in relation to environmental niche and phylogenetic history. We quantified morphological differences in shape and size among 98.5% of the 129 species and all 21 genera of the Australo‐Papuan endemic myobatrachid frogs to test the hypothesis that habitat type predicts body shape in this radiation. We tested this hypothesis in a phylogenetic context at two taxonomic levels: across the entire radiation and within the four largest genera. Thirty‐four external measurements were taken on 623 museum specimens representing 127 species. Data for seven key environmental variables relevant to anurans were assembled for all Australian‐distributed species based on species' distributions and 131,306 locality records. The Australo‐Papuan myobatrachid radiation showed high diversity in adult body size, ranging from minute (15 mm snout–vent length) to very large species (92 mm), and shape, particularly sin relative limb length. Five main morphological and environmental summary variables displayed strong phylogenetic signal. There was no clear relationship between body size and environmental niche, and this result persisted following phylogenetic correction. For most species, there was a better match between environment/habitat and body shape, but this relationship did not persist following phylogenetic correction. At a broad level, species fell into three broad groups based on environmental niche and body shape: 1) species in wet habitats with relatively long limbs, 2) species in arid environments with relatively short limbs (many of which are forward or backward burrowers) and 3) habitat generalist species with a conservative body shape. However, these patterns were not repeated within the four largest genera ? Crinia, Limnodynastes, Pseudophryne and Uperoleia. Each of these genera displayed a highly conservative anuran body shape, yet individual species were distributed across the full spectrum of Australian environments. Our results suggest that phylogenetic legacy is important in the evolution of body size and shape in Australian anurans, but also that the conservative body plan of many frogs works well in a wide variety of habitats.     

Integrating phylogeny,environment and space to explore variation in macroecological traits of Viperidae and Elapidae (Squamata: Serpentes)

We used eigenvector mapping in space and phylogeny to investigate the relationships among space, phylogeny and environment on body size and range size variation across two groups of venomous snakes – Viperidae and Elapidae – from the New World. Data on species geographic range sizes, maximum body sizes and phylogenetic relationships were compiled from the available literature. The distributional data were also used to calculate the latitudinal and longitudinal midpoint and the environmental centroids for each species. The eigenvectors extracted from the pair wise spatial and phylogenetic distance matrices were integrated with environmental variables into a method of variation partitioning where the variation in each trait was quantitatively attributed to ‘pure’ and/or shared effects of phylogeny, environment and space. Our results showed that variation in body size was predominantly determined by phylogeny in both groups of snakes. For Viperidae, we found that pure ‘effects’ of phylogeny were the strongest, indicating that most of the body size evolution that was phylogenetically determined in this group occurred independently of environment and geographical proximity. Regarding range sizes, pure phylogenetic influences were very low in both groups, whereas the largest single fraction of explained variation corresponded to overlapped influences of the three sets of predictors, especially for Elapidae. Along with this, we found evidence that niche conservatism is an important processes underlying variation in body size and range size in both groups of snakes.     

Mass turnover and recovery dynamics of a diverse Australian continental radiation

Trends in global and local climate history have been linked to observed macroevolutionary patterns across a variety of organisms. These climatic pressures may unilaterally or asymmetrically influence the evolutionary trajectory of clades. To test and compare signatures of changing global (Eocene‐Oligocene boundary cooling) and continental (Miocene aridification) environments on a continental fauna, we investigated the macroevolutionary dynamics of one of Australia's most diverse endemic radiations, pygopodoid geckos. We generated a time‐calibrated phylogeny (>90% taxon coverage) to test whether (i) asymmetrical pygopodoid tree shape may be the result of mass turnover deep in the group's history, and (ii) how Miocene aridification shaped trends in biome assemblages. We find evidence of mass turnover in pygopodoids following the isolation of the Australian continental plate ～30 million years ago, and in contrast, gradual aridification is linked to elevated speciation rates in the young arid zone. Surprisingly, our results suggest that invasion of arid habitats was not an evolutionary end point. Instead, arid Australia has acted as a source for diversity, with repeated outward dispersals having facilitated diversification of this group. This pattern contrasts trends in richness and distribution of other Australian vertebrates, illustrating the profound effects historical biome changes have on macroevolutionary patterns.     

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.     

Primary productivity can affect mammalian body size frequency distributions

Frequency distributions of mammal body sizes in large‐scale assemblages have often been found to show a positive skew. In an attempt to explain this pattern, a model has been put forward which incorporates energetic constraints on fitness and thereby predicts optimal body sizes corresponding to the mode of the distribution. A key assumption of the model is that energy is unlimited. However, if energy is limited, the input of energy into a herbivorous mammal community should influence the shape of the frequency distribution. Thus, I propose that increases in primary productivity will decrease the variation of body size and increase the mean body size in a distribution. So, in low‐productivity environments we should see a predominance of small‐sized species, but with a great variation of body sizes due to limitations of resources (energy). I tested this hypothesis using the herbivorous mammal fauna (rodents, bats and marsupials) in seven biomes of Australia. Because herbivorous marsupials generally are fairly large‐bodied while rodents and bats are small‐sized and because marsupials also have a different mode of reproduction from placental mammals, the hypothesis was also tested on placental mammals and marsupials separately. There was no clear mode for the entire assemblage in any biome, but as primary productivity increased, the variation of body masses decreased and the mean body mass of the distribution increased. Body mass distributions of both placental mammals and marsupials displayed clear modes. Placental mammals also showed an increase in mean body mass. The variation in body mass of marsupials was highest for the intermediately productive biomes. Primary productivity does seem to have some effect on mammalian body mass in this case, but the results here need to be complemented with studies of other assemblages before any general conclusions can be drawn. It is also important to distinguish which taxa are affected in a heterogeneous assemblage like the Australian herbivorous mammal fauna.     

Thermoregulatory patterns of two sympatric rodents: Otomys unisulcatus and Parotomys brantsii

1. The adaptations to an arid environment in two closely related rodent species were investigated. 2. The rate of oxygen consumption (VO2), body temperature (Tb), evaporative water loss and minimal conductance in Otomys unisulcatus and Parotomys brantsii were determined under controlled conditions at ambient temperatures (Ta), ranging from 11-31 C. 3. Physiological features atypical of desert-adapted rodents include a basal metabolic rate higher than predicted by body mass, the low "lower critical temperature" and symptoms of heat stress at 31 degrees C. 4. The low Tb and wide thermoneutral zone recorded for both species are characteristic of desert rodent species. 5. These species' physiological abilities reflect their mesic phylogeny and we suggest that behaviour must play an important role in their survival in semi-arid areas.     

Convergent evolution across the Australian continent: ecotype diversification drives morphological convergence in two distantly related clades of Australian frogs

Animals from different clades but subject to similar environments often evolve similar body shapes and physiological adaptations due to convergent evolution, but this has been rarely tested at the transcontinental level and across entire classes of animal. Australia's biome diversity, isolation and aridification history provide excellent opportunities for comparative analyses on broad‐scale macroevolutionary patterns. We collected morphological and environmental data on eighty‐four (98%) Australian hylid frog species and categorized them into ecotypes. Using a phylogenetic framework, we tested the hypothesis that frogs from the same ecotype display similar body shape patterns: (i) across all the Australian hylids, and (ii) through comparison with a similar previous study on 127 (97%) Australian myobatrachid species. Body size and shape variation did not follow a strong phylogenetic pattern and was not tightly correlated with environment, but there was a stronger association between morphotype and ecotype. Both arboreal and aquatic frogs had long limbs, whereas limbs of fossorial species were shorter. Other terrestrial species were convergent on the more typical frog body shape. We quantified the strength of morphological convergence at two levels: (i) between fossorial myobatrachid and hylid frogs, and (ii) in each ecomorph within the hylids. We found strong convergence within ecotypes, especially in fossorial species. Ecotypes were also reflected in physiological adaptations: both arboreal and cocooned fossorial frogs tend to have higher rates of evaporative water loss. Our results illustrate how adaptation to different ecological niches plays a crucial role in morphological evolution, boosting phenotypic diversity within a clade. Despite phylogenetic conservatism, morphological adaptation to repeatedly emerging new environments can erase the signature of ancestral morphotypes, resulting in phenotypic diversification and convergence both within and between diverse clades.     

Low bird diversity in the Fynbos plant diversity hotspot: Quaternary legacies in the current distributions of passerine birds

The Fynbos Biome or Cape Floristic Region is well‐known for its plant diversity. This diversity does not seem to carry over at higher trophic levels, and in particular in birds. Here, we analyzed the passerine bird assemblages of the Fynbos Biome at the quarter degree resolution with occupancy models and citizen science data. Multivariate analysis of distribution summary metrics revealed a gradient of specialist to generalist species, in which range‐restricted, specialist species responded positively to increases in number of competing species and included ancient lineages. Wide‐ranging, generalist species exhibited stronger affinities for the arid Karoo Biomes than for the other neighboring biome (Albany Thicket) and for the other mesic biomes in South Africa. Both results are explained by the Quaternary legacy hypothesis: the combined effects of habitat filtering, isolation by distance, and limited in situ diversification, acting throughout the Quaternary, and caused by the contrasting winter‐rainfall regime of the region and the low phylogenetic diversity and original adaptations of the plant assemblages.     

Pioneering polyploids: the impact of whole-genome duplication on biome shifting in New Zealand Coprosma (Rubiaceae) and Veronica (Plantaginaceae)

The role of whole-genome duplication (WGD) in facilitating shifts into novel biomes remains unknown. Focusing on two diverse woody plant groups in New Zealand, Coprosma (Rubiaceae) and Veronica (Plantaginaceae), we investigate how biome occupancy varies with ploidy level, and test the hypothesis that WGD increases the rate of biome shifting. Ploidy levels and biome occupancy (forest, open and alpine) were determined for indigenous species in both clades. The distribution of low-ploidy (Coprosma: 2x, Veronica: 6x) versus high-ploidy (Coprosma: 4–10x, Veronica: 12–18x) species across biomes was tested statistically. Estimation of the phylogenetic history of biome occupancy and WGD was performed using time-calibrated phylogenies and the R package BioGeoBEARS. Trait-dependent dispersal models were implemented to determine support for an increased rate of biome shifting among high-ploidy lineages. We find support for a greater than random portion of high-ploidy species occupying multiple biomes. We also find strong support for high-ploidy lineages showing a three- to eightfold increase in the rate of biome shifts. These results suggest that WGD promotes ecological expansion into new biomes.     

Biome stability predicts population structure of a southern African aridland bird species

Environments are heterogeneous in space and time, and the permeability of landscape and climatic barriers to gene flow may change over time. When barriers are present, they may start populations down the path toward speciation, but if they become permeable before the process of speciation is complete, populations may once more merge. In Southern Africa, aridland biomes play a central role in structuring the organization of biodiversity. These biomes were subject to substantial restructuring during Plio‐Pleistocene climatic fluctuations, and the imprint of this changing environment should leave genetic signatures on the species living there. Here, we investigate the role of adjacent aridland biome boundaries in structuring the genetic diversity within a widespread generalist bird, the Cape Robin‐chat (Cossypha caffra). We find evidence supporting a central role for aridland biomes in structuring populations across Southern Africa. Our findings support a scenario wherein populations were isolated in different biome refugia, due to separation by the exceptionally arid Nama Karoo biome. This biome barrier may have arisen through a combination of habitat instability and environmental unsuitability, and was highly unstable throughout the Plio‐Pleistocene. However, we also recovered a pattern of extensive contemporary gene flow and admixture across the Nama Karoo, potentially driven by the establishment of homesteads over the past 200 years. Thus, the barrier has become permeable, and populations are currently merging. This represents an instance where initial formation of a barrier to gene flow enabled population differentiation, with subsequent gene flow and the merging of populations after the barrier became permeable.     

Range size-abundance relationships in Australian passerines

Aim To investigate the relationship between geographical range size and abundance (population density) in Australian passerines. Location Australia (including Tasmania). Methods We analysed the relationship between range size and local abundance for 272 species of Australian passerines, across the whole order and within families. We measured abundance as mean and maximum abundance, and used a phylogenetic generalized least‐squares regression method within a maximum‐likelihood framework to control for effects of phylogeny. We also analysed the relationship within seven different habitat types. Results There was no correlation between range size and abundance for the whole set of species across all habitats. Analyses within families revealed some strong correlations but showed no consistent pattern. Likewise we found little evidence for any relationship or conflicting patterns in different habitats, except that woodland/forest habitat species exhibit a negative correlation between mean abundance and range size, whilst species in urban habitats exhibit a significant positive relationship between maximum abundance and range size. Despite the general lack of correlation, the raw data plots of range size and abundance in this study occupied a triangular space, with narrowly distributed species exhibiting a greater variation in abundances than widely distributed species. However, using a null model analysis, we demonstrate that this was due to a statistical artefact generated by the frequency distributions for the individual variables. Conclusions We find no evidence for a positive range size‐abundance relationship among Australian passerines. This absence of a relationship cannot be explained by any conflicting effects introduced by comparing across different habitats, nor is it explained by the fact that large proportions of Australia are arid. We speculate that the considerable isolation and evolutionary age of Australian passerines may be an explanatory factor.     

Stripes,jewels and spines: further investigations into the evolution of defensive strategies in a chemically defended gecko radiation (Strophurus,Diplodactylidae)

The geckos in the genus Strophurus (Diplodactylidae) are one of only two squamate lineages with specialized caudal defensive glands. Many species in this genus also have distinctive caudal ornamentation combined with bright and/or contrasting colour pattern elements on the iris, tail and especially the lining of the mouth that are hypothesized to be adaptations for specialized (e.g. deimatic) defensive functions. We present the first multilocus, phylogenetic analysis of the biogeography and evolution of all recognized taxa of Strophurus. Contrary to previous phenotypic and ecological assessments, our phylogenetic analyses delineate four divergent lineages. Three lineages are relatively small (snout‐vent length [SVL] 40–60 mm), species‐poor (<5 recognized taxa), cryptically coloured (either striped or spotted) and lack precloacal pores (a secondary sexual trait) and putative deimatic elements. In contrast, the remaining lineage is comparatively species rich (at least 14 taxa), attains a larger body size (SVL 60–90 mm), possesses precloacal pores and shows extensive variation in caudal ornamentation and often bright and/or contrasting eye, tail and mouth colouration. The three less diverse lineages have smaller distributions and tend to be associated with spinifex (e.g. Triodia) hummock grasses or rocks, whereas the fourth lineage is much more widespread (including multiple biomes) and consistently reported to utilize more exposed diurnal microhabitats on shrubs and trees. Biogeographical analyses also indicate that – in contrast to many other Australian radiations – the arid biome is the ancestral area of occupation for Strophurus, with multiple inferred shifts into surrounding sclerophyll and monsoon biomes. This study emphasizes that – independent of caudal defensive glands – it appears to be a shift in microhabitat use that correlates with the accumulation of bright and contrasting colouration elements, secondary sexual characters and the widest geographic distribution.