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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.

Sex chromosome turnover is the transition between sex chromosomes and autosomes. Although many cases have been reported in poikilothermic vertebrates, their evolutionary causes and genetic mechanisms remain unclear. In this study, we report multiple transitions between the Y chromosome and autosome in the Japanese Tago's brown frog complex. Using chromosome banding and molecular analyses (sex-linked and autosomal single nucleotide polymorphisms, SNPs, from the nuclear genome), we investigated the frogs of geographic populations ranging from northern to southern Japan of two species, Rana tagoi and Rana sakuraii (2n = 26). Particularly, the Chiba populations of East Japan and Akita populations of North Japan in R. tagoi have been, for the first time, investigated here. As a result, we identified three different sex chromosomes, namely chromosomes 3, 7, and 13, in the populations of the two species. Furthermore, we found that the transition between the Y chromosome (chromosome 7) and autosome was repeated through hybridization between two or three different populations belonging to the two species, followed by restricted chromosome introgression. These dynamic sex chromosome turnovers represent the first such findings in vertebrates and imply that speciation associated with inter- or intraspecific hybridization plays an important role in sex chromosome turnover in frogs. [ABSTRACT FROM AUTHOR]

Chromosome rearrangements are often implicated with genomic divergence and are proposed to be associated with species evolution. Rearrangements alter the genomic structure and interfere with homologous recombination by isolating a portion of the genome. Integration of multiplatform next-generation DNA sequencing technologies has enabled putative identification of chromosome rearrangements in many taxa; however, integrating these data sets with cytogenetics is still uncommon beyond model genetic organisms. Therefore, to achieve the ultimate goal for the genomic classification of eukaryotic organisms, physical chromosome mapping remains critical. The ridge-tailed goannas (Varanus acanthurus BOULENGER) are a group of dwarf monitor lizards comprised of several species found throughout northern Australia. These lizards exhibit extreme divergence at both the genic and chromosomal levels. The chromosome polymorphisms are widespread extending across much of their distribution, raising the question if these polymorphisms are homologous within the V. acanthurus complex. We used a combined genomic and cytogenetic approach to test for homology across divergent populations with morphologically similar chromosome rearrangements. We showed that more than one chromosome pair was involved with the widespread rearrangements. This finding provides evidence to support de novo chromosome rearrangements have occurred within populations. These chromosome rearrangements are characterized by fixed allele differences originating in the vicinity of the centromeric region. We then compared this region with several other assembled genomes of reptiles, chicken, and the platypus. We demonstrated that the synteny of genes in Reptilia remains conserved despite centromere repositioning across these taxa. [ABSTRACT FROM AUTHOR]

Sex determination in animals is amazingly plastic. Vertebrates display contrasting strategies ranging from complete genetic control of sex (genotypic sex determination) to environmentally determined sex (for example, temperature-dependent sex determination) (1). Phylogenetic analyses suggest frequent evolutionary transitions between genotypic and temperature-dependent sex determination in environmentally sensitive lineages, including reptiles (2). These transitions are thought to involve a genotypic system becoming sensitive to temperature, with sex determined by gene-environment interactions (3). Most mechanistic models of transitions invoke a role for sex reversal (3-5). Sex reversal has not yet been demonstrated in nature for any amniote, although it occurs in fish (6) and rarely in amphibians (7,8). Here we make the first report of reptile sex reversal in the wild, in the Australian bearded dragon (Pogona vitticeps), and use sex-reversed animals to experimentally induce a rapid transition from genotypic to temperature-dependent sex determination. Controlled mating of normal males to sex-reversed females produces viable and fertile offspring whose phenotypic sex is determined solely by temperature (temperature-dependent sex determination). The W sex chromosome is eliminated from this lineage in the first generation. The instantaneous creation of a lineage of ZZ temperature-sensitive animals reveals a novel, climate-induced pathway for the rapid transition between genetic and temperature-dependent sex determination, and adds to concern about adaptation to rapid global climate change., Sex determination is the regulatory process that initiates differentiation of the gonads in the early embryo to form either testes or ovaries. Very many reptiles have temperature-dependent sex determination (TSD), [...]