Global diversity of lizards in freshwater (Reptilia: Lacertilia)

No lizards are strictly aquatic, but at least 73 species in 11 different families can be considered to regularly utilize freshwater habitats. There are no aquatic lizards in the Nearctic or Palearctic regions, whereas the Neotropics, Southeast Asia, and the Indo-Australian Archipelago support the greatest diversity of freshwater forms, particularly in the families Gymnophthalmidae, Scincidae and Varanidae. A number of larger aquatic lizards are harvested for food and for the reptile skin trade and several are CITES listed. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment     

Maternal body-volume as a constraint on reproductive output in lizards: evidence from the evolution of viviparity

A few species of squamate reptiles contain both oviparous (egg-laying) and viviparous (live-bearing) populations, and thus offer exceptional opportunities to test adaptationist hypotheses on the determinants of reproductive output. We focus on the hypothesis that maternal body-volume constrains reproductive output in squamate reptiles. If females are “full” of eggs, what happens when viviparity evolves within a lineage? Eggs increase in volume and mass during development, primarily due to the uptake of water, so how can they be accommodated within the mother's abdomen? We predict that the resultant increase in relative clutch mass (RCM) will be lessened by (1) a decrease in reproductive output (by reducing the number or size of offspring), and/or (2) an increase in maternal body-volume (via modifications of size or shape of adult females). Our comparisons of conspecific oviparous and viviparous lizards (Lerista bougainvillii) confirm that live-bearers carry heavier clutches (in both absolute and relative terms) and show the predicted shifts in body size and shape of reproductive females. However, offspring size and number were unaffected by the evolution of viviparity, and the shifts in maternal morphology were too small to fully offset the increase in clutch mass. Thus, RCMs increased by 50%, indicating that viviparous females produced clutches which more completely filled the space available in the abdominal cavity. We conclude that maternal body-volume does play a role in determining reproductive output, but that the observed clutch masses may be optimized, rather than maximized, with respect to the abdominal space available.     

Life-history evolution in Australian snakes: a path analysis

I recently attempted to investigate interspecific patterns in ecological traits of Australian snakes using univariate statistical techniques (Shine 1994), but high intercorrelations among variables (especially with mean adult body size) made it difficult to interpret the observed patterns. In the present paper, I attempt to tease apart causal factors using multivariate (path) analysis on the same data set (103 species, based on dissection of >22000 museum specimens). Two separate path analyses were conducted: one that treated each species as an independent unit (and thus, ignored phylogeny) and the other based on independent phylogenetic contrasts. Path coefficients from the two types of analyses were similar in magnitude, and highly correlated with each other, suggesting that most interspecific patterns among traits may reflect functional association rather than phylogenetic conservatism. Path analysis showed that indirect effects of one variable upon another (i.e., mediated via other traits) were often stronger than direct effects. Thus, even when two variables appeared to be uncorrelated in the univariate analysis, this apparent lack of relationship sometimes masked strong but conflicting indirect effects. For example, a tradeoff between clutch size and offspring size tends to mask the direct effect of mean adult body size on clutch size. Path analysis may also suggest original causal hypotheses. For example, interspecific allometry of sexual size dimorphism (as seen in Australian snakes, and many other animal groups) may result from a strong effect of another allometrically-tied trait (offspring size) on growth trajectories of females.     

Thermal sensitivity of growth rate in hatchling Sceloporus lizards: environmental,behavioral and genetic aspects

Summary To investigate the physiological, behavioral, and genetic contributions to growth rate, we studied the thermal sensitivity of growth rate in hatchlings of the iguanid lizards Sceloporus occidentalis and S. graciosus in the laboratory. We used a cycling thermal regime patterned after thermal environments found in nature. Growth rates increased with duration of access to radiant heat. Thus, variation in the thermal environment can cause phenotypic variation in growth rate and hence body size. The two species differed in both the magnitude and thermal sensitivity of growth rate, and these differences were associated with differences in behavioral thermoregulation. Thus, growth is determined interactively by both behavior and physiology. We found evidence of among-family variation in the growth rates of S. occidentalis, suggesting that growth rate has the genetic potential to evolve. In S. occidentalis, both growth rate and egg size affected body size of hatchlings at several weeks of age. In turn, hatchling size may affect fitness: for example, larger S. occidentalis hatchlings had higher sprint speeds and may therefore be more adept at capturing prey or evading predators. Our results demonstrate that growth rate has genetic, behavioral, and physiological components, and that the resulting effects on body size may have important consequences for ecological performance e.g., sprint speed.     

Lygosomine phylogeny and the origins of Australian scincid lizards

Aim Australian scincid lizards represent three distinct groups within the cosmopolitan clade Lygosominae, the Egernia, Eugongylus and Sphenomorphus groups. This paper presents a time‐calibrated phylogeny for Lygosominae that provides the necessary temporal framework for assessing the contributions of immigration from Asia and of Gondwanan inheritance in the derivation of the Australian scincid fauna. Location Australasia, Asia, Africa. Methods Phylogenetic relationships and divergence times were inferred from novel BDNF, c‐mos and PTPN12 sequences (2408 aligned sites). Results Lygosomine monophyly is well supported, and there is strong support for monophyly of the Egernia, Eugongylus and Sphenomorphus groups. A sister‐group relationship of Tribolonotus (distributed in Melanesia and the Papuan Region) and the Egernia group is strongly supported in both Bayesian and maximum likelihood analyses. Australian representatives of the Sphenomorphus group compose a significantly supported clade estimated to have originated c. 25 Ma. An age of c. 18 Ma is inferred for a strongly supported clade comprising Australian representatives of the Egernia group; this clade diverged from Corucia zebrata (confined to the Solomon Islands) c. 25 Ma and from Tribolonotus c. 54 Ma. A well‐supported clade including all Australian Eugongylus group taxa sampled is estimated to have arisen c. 20 Ma. Main conclusions The Australian Sphenomorphus group is nested within the more inclusive Sphenomorphus group (distributed primarily in Asia and Australasia), suggesting comparatively recent descent from a colonizing Asian ancestor; the divergence times inferred here indicate that colonization occurred during the mid Cenozoic, subsequent to the rifting of Australia from Antarctica. An Oligocene origin of the extant Eugongylus group fauna of Australasia (the basal members of which are distributed in the Southwest Pacific) indicates that Eugongylus group lygosomines also dispersed to Australia relatively recently. The Egernia group diverged from Tribolonotus in the Early Eocene; however, extant Egernia group lygosomines originated only during the Late Oligocene, implying extensive pruning of stem taxa (i.e. extinction). As a result, inferences of the timing of dispersal into Australia are associated with substantial uncertainty, although independent palaeontological evidence suggests that the Egernia group entered Australia prior to the Oligocene, immediately after (or perhaps before) the separation of Australia and Antarctica.     

Phylogeographic analysis detects congruent biogeographic patterns between a woodland agamid and Australian wet tropics taxa despite disparate evolutionary trajectories

Aim To test the congruence of phylogeographic patterns and processes between a woodland agamid lizard (Diporiphora australis) and well‐studied Australian wet tropics fauna. Specifically, to determine whether the biogeographic history of D. australis is more consistent with a history of vicariance, which is common in wet tropics fauna, or with a history of dispersal with expansion, which would be expected for species occupying woodland habitats that expanded with the increasingly drier conditions in eastern Australia during the Miocene–Pleistocene. Location North‐eastern Australia. Methods Field‐collected and museum tissue samples from across the entire distribution of D. australis were used to compile a comprehensive phylo‐geographic dataset based on c. 1400 bp of mitochondrial DNA (mtDNA), incorporating the ND2 protein‐coding gene. We used phylogenetic methods to assess biogeographic patterns within D. australis and relaxed molecular clock analyses were conducted to estimate divergence times. Hierarchical Shimodaira–Hasegawa tests were used to test alternative topologies representing vicariant, dispersal and mixed dispersal/vicariant biogeographic hypotheses. Phylogenetic analyses were combined with phylogeographic analyses to gain an insight into the evolutionary processes operating within D. australis. Results Phylogenetic analyses identified six major mtDNA clades within D. australis, with phylogeographic patterns closely matching those seen in many wet tropics taxa. Congruent phylogeographic breaks were observed across the Black Mountain Corridor, Burdekin and St Lawrence Gaps. Divergence amongst clades was found to decrease in a north–south direction, with a trend of increasing population expansion in the south. Main conclusions While phylogeographic patterns in D australis reflect those seen in many rain forest fauna of the wet tropics, the evolutionary processes underlying these patterns appear to be very different. Our results support a history of sequential colonization of D. australis from north to south across major biogeographic barriers from the late Miocene–Pleistocene. These patterns are most likely in response to expanding woodland habitats. Our results strengthen the data available for this iconic region in Australia by exploring the understudied woodland habitats. In addition, our study shows the importance of thorough investigations of not only the biogeographic patterns displayed by species but also the evolutionary processes underlying such patterns.     

Evolution of thermal physiology and growth rate between populations of the western fence lizard (Sceloporus occidentalis)

Summary Hatchling Sceloporus occidentalis from northern populations (central Oregon) grow more slowly than hatchlings from southern populations (southern California) in nature. In this study, I determine whether this difference in growth rate results from differences in thermal environment and/or in thermoregulatory behavior. To determine the degree to which the thermal environment affects growth rate among populations, I reared hatchings from the northern and southern populations in a cycling thermal regime in one of three experimental treatments differing in access to radiant heat (6, 9, or 12 h radiant heat; remainder of 24 h at 15°C). I also measured the body temperature that each individual voluntarily selected over the course of the daily activity cycle. Growth rate varied positively with duration of access to radiant heat. Within the three treatments, individual growth rate was positively correlated with body temperature. Moreover, the difference in growth rate between the northern and southern populations was due in part to differences in behavior — individuals from northern populations selected lower body temperatures. I found that significant variation in body temperature was associated with family membership, suggesting that thermal physiology has a genetic basis. Moreover, growth rate was correlated with body temperature among families in each population suggesting a genetic correlation underlies the phenotypic correlations. Thus, genetically based variation in thermal physiology contributes to differences in growth rate among individuals within a population as well as to differences among populations.     

Evolution of cranial shape in a continental‐scale evolutionary radiation of Australian lizards

A defining character of adaptive radiations is the evolution of a diversity of morphological forms that are associated with the use of different habitats, following the invasion of vacant niches. Island adaptive radiations have been thoroughly investigated but continental scale radiations are more poorly understood. Here, we use 52 species of Australian agamid lizards and their Asian relatives as a model group, and employ three‐dimensional geometric morphometrics to characterize cranial morphology and investigate whether variation in cranial shape reflects patterns expected from the ecological process of adaptive radiation. Phylogenetic affinity, evolutionary allometry, and ecological life habit all play major roles in the evolution of cranial shape in the sampled lizards. We find a significant association between cranial shapes and life habit. Our results are in line with the expectations of an adaptive radiation, and this is the first time detailed geometric morphometric analyses have been used to understand the selective forces that drove an adaptive radiation at a continental scale.     

Nest predators and the evolution of avian reproductive strategies: a comparison of Australian and New Zealand birds

Summary Nest predation has been considered an important factor in the evolution of avian life histories: smaller clutches and shorter incubation and nestling periods are expected where nest predation has significant effects on reproductive success. Unlike the Australian avifauna, terrestrial New Zealand birds have evolved in the absence of reptilian and mammalian predators. Here we compare the reproductive strategies of terrestrial native New Zealand birds with those of their Australian sister taxa. In 11 of 14 comparisons, New Zealand birds were larger than their Australian relatives, but we did not find any significant differences in reproductive tactics between the two regions, a result inconsistent with the nest predation hypothesis. We discuss several reasons why this may be so. One possibility is that selection imposed on avian life history tactics by mammalian predators following the arrival of humans in New Zealand has led to strategies similar to those adopted in Australia.     

A comparison of low temperature tolerance traits between closely related aphids from the tropics, temperate zone, and Arctic

The survival of aphids exposed to low temperatures is strongly influenced by their ability to move within and between plants and to survive exposure to potentially lethal low temperatures. Little is known about the physiological and behavioural limitations on aphid movement at low temperatures or how they may relate to lethal temperature thresholds. These questions are addressed here through an analysis of the thermal ecology of three closely related aphid species: Myzus persicae, a ubiquitous temperate zone pest, Myzus polaris, an arctic species, and Myzus ornatus, a sub-tropical species. Lower lethal temperatures (LLT₅₀) of aphids reared at 15 °C were similar for M. persicae and M. polaris (range: −12.7 to −13.9 °C), but significantly higher for M. ornatus (−6.6 °C). The temperature thresholds for activity and chill coma increased with rearing temperature (10, 15, 20, and 25 °C) for all clones. For M. polaris and M. ornatus the slopes of these relationships were approximately parallel; by contrast, for M. persicae the difference in slopes meant that the difference between the temperatures at which aphids cease walking and enter coma increased by approximately 0.5 °C per 1 °C increase in rearing temperature. The data suggest that all three species have the potential to increase population sizes and expand their ranges if low temperature limitation is relaxed.     

Life history strategies and psychopathology: the faster the life strategies,the more symptoms of psychopathology

There is little extant empirical literature examining the associations between life history strategies and symptoms of psychopathology. The current study (N = 138) investigated the associations between life history strategies, symptoms of psychopathology, aggression, incidence of self-harm behaviour, and attachment (perceived parental support) in sample drawn from the general population and community mental health service providers. The results from the study indicate those with a faster life strategy report greater levels of aggression and symptoms of psychopathology. Further, perceptions of poorer parental support were associated with a faster life history strategy. Implications for life history theory, conceptualising psychopathology, and future research directions are discussed.     

Ant- and termite-eating in Australian mammals and lizards: a comparison

Abstract Relative abundance is one factor that influences selection of prey by insectivorous mammals and lizards. Ants and termites are extremely abundant over most of inland Australia. Their patterns of abundance are also broadly similar across climatic gradients, being most and least abundant in seasonally arid (tropic and sub-tropic) and temperate mesic regions, respectively. All else being equal (e. g. mechanisms of prey defence, palat-ability, availability), animals that eat many termites should also eat many (adult) ants. The present study asks three questions: (i) What is the diversity of specialized ant-eaters (>50% volume)?; (ii) Does specialization vary with climate?; and (iii) Are ants and termites eaten in broadly similar proportions (using an earlier study on termites). Of the mammals, only the echidna (Tachyglossus aculeatus) in mesic regions, and probably the marsupial mole (Notoryctes typhlops) in the arid zone and the striped possum (Dactylopsila trivirgata) in mesic regions are ant-specialized. Ant-specialization in mammals shows no pattern with regard to climate. Of the lizards, only four agamid lizards are ant-specialized: Moloch horridus (arid, semi-arid), Ctenophorus fordi (arid, semi-arid), Ctenophorus isolepis (arid) and Ctenophorus maculatus (arid). Specialization on ants by lizards is greatest in the arid zone (4 spp.); no lizard species were found to be ant-specialists in mesic regions. In the arid and semi-arid zone, two mammals each specialize on termites and one on ants; in mesic regions, two mammals specialize on ants and one on termites. Specialized insectivorous mammals thus demonstrate no marked preference for either termites or ants. Lizards, in contrast, are markedly termite-specialized (4 ant-specialist spp., 16 termite-specialist spp.), and specialization is greatest in the arid zone (16 spp.). Greater specialization on termites than on (adult) ants in lizards is explained with reference to differences in prey defence and palatability between ants and termites. Consumption of ant brood (eggs, larvae, pupae) appears to be associated with a fossorial foraging mode (the marsupial mole N. typhlops; spp. of Aprasia lizards; spp. of blindsnakes Ramphotyphlops).     

Biogeography of the Australian monsoon tropics

Aim This paper reviews the biogeography of the Australian monsoon tropical biome to highlight general patterns in the distribution of a range of organisms and their environmental correlates and evolutionary history, as well as to identify knowledge gaps. Location Northern Australia, Australian Monsoon Tropics (AMT). The AMT is defined by areas that receive more than 85% of rainfall between November and April. Methods Literature is summarized, including the origin of the monsoon climate, present‐day environment, biota and habitat types, and phylogenetic and geographical relationships of selected organisms. Results Some species are widespread throughout the AMT while others are narrow‐range endemics. Such contrasting distributions correspond to present‐day climates, hydrologies (particularly floodplains), geological features (such as sandstone plateaux), fire regimes, and vegetation types (ranging from rain forest to savanna). Biogeographical and phylogenetic studies of terrestrial plants (e.g. eucalypts) and animals (vertebrates and invertebrates) suggest that distinct bioregions within the AMT reflect the aggregated effects of landscape and environmental history, although more research is required to determine and refine the boundaries of biogeographical zones within the AMT. Phylogenetic analyses of aquatic organisms (fishes and prawns) suggest histories of associations with drainage systems, dispersal barriers, links to New Guinea, and the existence of Lake Carpentaria, now submerged by the Gulf of Carpentaria. Complex adaptations to the landscape and climate in the AMT are illustrated by a number of species. Main conclusions The Australian monsoon is a component of a single global climate system, characterized by a dominant equator‐spanning Hadley cell. Evidence of hot, seasonally moist climates dates back to the Late Eocene, implying that certain endemic elements of the AMT biota have a long history. Vicariant differentiation is inferred to have separated the Kimberley and Arnhem Land bioregions from Cape York Peninsula/northern Queensland. Such older patterns are overlaid by younger events, including dispersal from Southeast Asia, and range expansions and contractions. Future palaeoecological and phylogenetic investigations will illuminate the evolution of the AMT biome. Understanding the biogeography of the AMT is essential to provide a framework for ecological studies and the sustainable development of the region.     

The phylogeny of varanoid lizards and the affinities of snakes

Evidence that platynotan squamates (living varanoid lizards, snakes and their fossil relatives) are monophyletic is presented. Evolutionary relationships within this group are then ascertained through a cladistic analysis of 144 osteological characters. Mosasauroids (aigialosaurs and mosasaurs), a group of large marine lizards, are identified as the nearest relatives of snakes, thus resolving the long-standing problem of snake affinities. The mosasauroid–snake clade (Pythonomorpha) is corroborated by 40 derived characters, including recumbent replacement teeth, thecodonty, four or fewer premaxillary teeth, supratemporal–prootic contact, free mandibular tips, crista circumfenestralis, straight vertical splenio-angular joint, loss of posterior ramus of the coronoid, reduced basipterygoid processes, reduced interpterygoid vacuity, zygosphene–zygantral articulations, and absence of epiphyses on the axial skeleton and skull. After mosasauroids, the next closest relatives of snakes are varanids (Varanus, Saniwa and Saniwides) and lanthanotids (Lanthanotus and Cherminotus). Derived features uniting varanids and lanthanotids include nine cervical vertebrae and three or fewer pairs of sternal ribs. The varanid–lanthanotid–pythonomorph clade, here termed Thecoglossa, is supported by features such as the anteriorly positioned basal tubera, and the loss of the second epibranchial. Successive outgroups to thecoglossans are Telmasaurus, an unresolved polytomy (Estesia, Gobidermatidae and Helodermatidae), Paravaranus and Proplatynota. The ''necrosaurs'' are demonstrated to be an artificial (polyphyletic) assemblage of primitive platynotans that are not particularly closely related to each other.Snakes are presumed to have evolved from small, limbless, burrowing lizards and the inability of previous analyses to resolve the affinities of snakes has been attributed to extensive convergence among the numerous lineages of such lizards. The present study contradicts this claim, demonstrating that the problem is due instead to omission of critical fossil taxa. No modern phylogenetic analysis of squamate relationships has simultaneously included both mosasauroids and snakes: previous studies have therefore failed to identify the mosasauroid–snake association and the suite of derived characters supporting it. Mosasauroids are large aquatic animals with well-developed appendages, and none of the derived characters uniting mosasauroids and snakes is obviously correlated with miniaturization, limb reduction or fossoriality. Recognition that mosasauroids, followed by varanids and lanthanotids, are the nearest relatives of snakes will also facilitate studies of relationships within snakes, which until now have been hampered by uncertainty over the most appropriate (closely-related) lizard outgroups.     

Life-history constraints on the success of the many small eggs reproductive strategy

The reproductive strategy of most fishes is to produce a large number of tiny eggs, leading to a huge difference between egg size and asymptotic body size. The viability of this strategy is examined by calculating the life-time reproductive success R₀ as a function of the asymptotic body size. A simple criterion for the optimality of producing small eggs is found, depending on the rate of predation relative to the specific rate of consumption. Secondly it is shown that the success of the reproductive strategy is increasing with asymptotic body size. Finally the existence of both upper and lower limits on the allowed asymptotic sizes is demonstrated. A metabolic upper limit to asymptotic body size for all higher animals is derived.     

Ecological constraints on the evolutionary association between field and preferred temperatures in Tropidurinae lizards

Ectothermic body temperatures affect organismal performances and presumably fitness, and are strongly influenced by the thermal environment. Therefore, the processes of colonization of novel thermal habitats by lizards might involve changes in thermal preferences, performance curves (reaction norms) and field activity temperatures. According to theory based on optimality analysis, diverse aspects of the thermal biology of vertebrate ectotherms should co-evolve as to maximize performance at the temperature range more often experienced by animals in the field. One corollary of this premise is that derived lizard clades that experienced a significant shift in thermal ecology, in comparison with the ancestral condition, should prefer and select temperatures in a thermal gradient similar to those experienced in nature. Here we report an analysis of the premise stated before. Specifically, we verify whether or not Tropidurinae species from three major Brazilian habitats (the Rainforests, the semi-arid Caatingas and the Cerrados, a Savannah-like biome) differ in thermal ecology and thermoregulatory behavior. The Caatinga is believed to be the ancestral habitat of this sub-family, and differences are expected because species from semi-arid habitats usually exhibit high body temperatures for lizards, whereas forest specialists might be thermoconformers and active at low temperatures. We also compared selected temperatures in the laboratory by species from the two open habitats (Caatingas and Cerrados). Data were analyzed using both conventional and phylogenetic analysis tools. Although species from Caatingas exhibited higher activity temperatures in nature than those from Cerrados, mean selected temperatures were similar between ecological groups. Phylogenetic analyses confirmed these findings and evidenced large␣evolutionary divergence in field activity temperatures between sister species from different␣open habitats without coupled divergence in selected temperatures. Therefore, thermoregulatory behavior and ecological parameters did not evolve similarly during the colonization of contrasting open habitats by Tropidurinae.     

Correlates of active body temperatures and microhabitat occupation in nine species of central Australian agamid lizards

Body temperatures of active lizards and their correspondence with microhabitat occupation were studied for nine species of agamid lizards in the central Australian arid zone. Thermoregulatory behaviour was also documented using several measures, such as the use of shade and perch height. The effects of thermal environment on lizard habitat occupation were hypothesized to be significant, because desert regions experience daily and seasonal extremes of temperature that are well in excess of a lizard’s preferred temperature range. All species, except Ctenophorus isolepis and Diporiphora winneckei, were found to have body temperatures that corresponded closely to ground and surface temperatures. Thermoregulatory behaviour was also found to be important throughout a lizard’s daily activity; all study species, other than Ctenophorus isolepis, were found to increase their perch height in the middle of the day. Ctenophorus isolepis was shown to be a strictly terrestrial species that uses the shade of spinifex in its thermoregulatory behaviour. Species exhibited a non‐random selection of microhabitats and a preference for a particular set of thermal and structural factors. In this study, it was shown that structural factors were particularly important in microhabitat occupation. Thermal factors accounted for a smaller proportion of variance in microhabitat occupation, but still played a considerable role in the microhabitat use in central Australian agamids.     

Population ecology and life history of the diurnal skink Morethia boulengeri in arid Australia

Summary The life history and population ecology of the skink Morethia boulengeri were studied from September 1985 to May 1987 in populations in a riverine woodland habitat and at an abandoned homestead in Kinchega National Park. The population dynamics and life histories of the two populations were remarkably similar. Yearly mortality (including emigration) ranged from 0.84–0.89. The yearly emigration rate was 0.01–0.03. Size-and body-condition-dependent mortality could be demonstrated for the population in riverine woodland. Average spring time densities were similar in both study sites but varied between years and ranged from 421-1823 individuals/ha. M. boulengeri females laid on average 2.8 eggs per clutch and usually produced three clutches per year. Egg mass was significantly correlated with female snout-vent-length, but relative clutch mass and egg size were not. All surviving juveniles reproduced for the first time in their first year. Some activity occurred throughout the year. Preferred body temperatures decreased in the cooler months. The data fit demographic models of life history evolution.     

Geographic variation in hybridization and ecological differentiation between three syntopic,morphologically similar species of montane lizards

To understand factors shaping species boundaries in closely related taxa, a powerful approach is to compare levels of genetic admixture at multiple points of contact and determine how this relates to intrinsic and extrinsic factors, such as genetic, morphological and ecological differentiation. In the Australian Alps, the threatened alpine bog skink Pseudemoia cryodroma co‐occurs with two morphologically and ecologically similar congeners, P. entrecasteauxii and P. pagenstecheri, and all three species are suspected to hybridize. We predicted that the frequency of hybridization should be negatively correlated with genetic divergence, morphological differentiation and microhabitat separation. We tested this hypothesis using a mitochondrial locus, 13 microsatellite loci, morphological and microhabitat data and compared results across three geographically isolated sites. Despite strong genetic structure between species, we detected hybridization between all species pairs, including evidence of backcrossed individuals at the two sites where all three species are syntopic. Hybridization frequencies were not consistently associated with genetic, morphological or ecological differentiation. Furthermore, P. entrecasteauxii and P. pagenstecheri only hybridized at the two sites where they are syntopic with P. cryodroma, but not at the largest site where P. cryodroma was not recorded, suggesting that P. cryodroma may serve as a bridging species. This study reveals the complex dynamics within a three species hybrid zone and provides a baseline for assessing the impact of climate change and anthropogenic habitat modification on future hybridization frequencies.