Australian lizards are outstanding models for reproductive biology research

Australian lizards are a diverse group distributed across the continent and inhabiting a wide range of environments. Together, they exhibit a remarkable diversity of reproductive morphologies, physiologies, and behaviours that is broadly representative of vertebrates in general. Many reproductive traits exhibited by Australian lizards have evolved independently in multiple lizard lineages, including sociality, complex signalling and mating systems, viviparity, and temperature-dependent sex determination. Australian lizards are thus outstanding model organisms for testing hypotheses about how reproductive traits function and evolve, and they provide an important basis of comparison with other animals that exhibit similar traits. We review how research on Australian lizard reproduction has contributed to answering broader evolutionary and ecological questions that apply to animals in general. We focus on reproductive traits, processes, and strategies that are important areas of current research, including behaviours and signalling involved in courtship; mechanisms involved in mating, egg production, and sperm competition; nesting and gestation; sex determination; and finally, birth in viviparous species. We use our review to identify important questions that emerge from an understanding of this body of research when considered holistically. Finally, we identify additional research questions within each topic that Australian lizards are well suited for reproductive biologists to address.

Selection outweighs drift at a fine scale: Lack of MHC differentiation within a family living lizard across geographically close but disconnected rocky outcrops

The highly polymorphic genes of the major histocompatibility complex (MHC) are involved in disease resistance, mate choice and kin recognition. Therefore, they are widely used markers for investigating adaptive variation. Although selection is the key driver, gene flow and genetic drift also influence adaptive genetic variation, sometimes in opposing ways and with consequences for adaptive potential. To further understand the processes that generate MHC variation, it is helpful to compare variation at the MHC with that at neutral genetic loci. Differences in MHC and neutral genetic variation are useful for inferring the relative influence of selection, gene flow and drift on MHC variation. To date, such investigations have usually been undertaken at a broad spatial scale. Yet, evolutionary and ecological processes can occur at a fine spatial scale, particularly in small or fragmented populations. We investigated spatial patterns of MHC variation among three geographically close, naturally discrete, sampling sites of Egernia stokesii, an Australian lizard. The MHC of E. stokesii has recently been characterized, and there is evidence for historical selection on the MHC. We found E. stokesii MHC weakly differentiated among sites compared to microsatellites, suggesting selection, acting similarly at each site, has outweighed any effects of low gene flow or of genetic drift on E. stokesii MHC variation. Our findings demonstrate the strength of selection in shaping patterns of MHC variation or consistency at a fine spatial scale.

Life-history characteristics of the yakka skink, Egernia rugosa, indicate long-term social structure

One lineage of squamates, the Egernia group, has received particular study due to stable aggregations identified in many of the species. Egernia rugosa is a large, terrestrial, viviparous skink and has been reported living communally. To investigate whether this species lives in social aggregations, we examined life-history characteristics in one population within the Mulga Lands bioregion of south-west Queensland. We found this skink used both active and inactive rabbit burrows. Parturition occurred in January/February and took several days to complete, with a mean litter size of 2.4 and a mean snout–vent length (SVL) of 84.5 mm. Six subadult age cohorts were identified. Juveniles took at least five years to reach sexual maturity and lizards had a life expectancy of >12 years. Lizards were found clustered in aggregations of up to 21 individuals (mean = 7.21) of multiple ages. An average of 50% (range = 31–67%) of all individuals within each of the age cohorts were located at their original location for two or more seasons. Dispersal was recorded for older subadult lizards. These characteristics support the hypothesis that E. rugosa aggregations comprise long-term family units; however, genetic analysis would be needed to confirm kin-based associations.