Origin of sex chromosomes in six groups of Rana rugosa frogs inferred from a sex-linked DNA marker

Understanding the genetic sex-determining mechanism in Hyla eximia treefrog inferred from H-Y antigen

Genetic sex-determining mechanisms have been extensively elucidated in mammals; however, the sex chromosomes, sex-determining genes, and gene regulatory networks involved in sex differentiation remain poorly understood in amphibians. In this study, we investigated the sex-determining mechanism in the Hyla eximia treefrog based on karyotypic analysis and identification of H-Y antigen, a sex-linked peptide that is present in the gonads of the heterogametic sex (XY or ZW) in all vertebrates. Results show a diploid chromosome number 2n = 24 with homomorphic sex chromosomes. The heterogametic sex, ZW-female, were hypothesized based on H-Y antigen mRNA expression in female gonads (24,ZZ/24,ZW). The treefrog H-Y peptide exhibited a high percentage of identity with other vertebrate sequences uploaded to GenBank database. To obtain gene expression profiles, we also obtained the coding sequence of the housekeeping Actb gene. High H-Y antigen expression levels were further confirmed in ovaries using real-time polymerase chain reaction (RT-PCR) during non-breeding season, we noted a decrease in the expression of the H-Y antigen during breeding season. This study provides evidence that sex hormones might suppress H-Y antigen expression in the gonads of heterogametic females 24,ZW during the breeding season. These findings suggest that H-Y gene expression is a well-suited model for studying heterogametic sex by comparing the male and female gonads.

Diversity, distribution and molecular species delimitation in frogs and toads from the Eastern Palaearctic

Biodiversity analyses can greatly benefit from coherent species delimitation schemes and up-to-date distribution data. In this article, we have made the daring attempt to delimit and map described and undescribed lineages of anuran amphibians in the Eastern Palaearctic (EP) region in its broad sense. Through a literature review, we have evaluated the species status considering reproductive isolation and genetic divergence, combined with an extensive occurrence dataset (nearly 85k localities). Altogether 274 native species from 46 genera and ten families were retrieved, plus eight additional species introduced from other realms. Independent hotspots of species richness were concentrated in southern Tibet (Medog County), the circum-Sichuan Basin region, Taiwan, the Korean Peninsula and the main Japanese islands. Phylogeographic breaks responsible for recent in situ speciation events were shared around the Sichuan Mountains, across Honshu and between the Ryukyu Island groups, but not across shallow water bodies like the Yellow Sea and the Taiwan Strait. Anuran compositions suggested to restrict the zoogeographical limits of the EP to East Asia. In a rapidly evolving field, our study provides a checkpoint to appreciate patterns of species diversity in the EP under a single, spatially explicit, species delimitation framework that integrates phylogeographic data in taxonomic research.

Sex Differentiation in Amphibians: Effect of Temperature and Its Influence on Sex Reversal

The role of environmental factors in sexual differentiation in amphibians is not new. The effect of hormones or hormone-like compounds is widely demonstrated. However, the effect of temperature has traditionally been regarded as something anecdotal that occurs in extreme situations and not as a factor to be considered. The data currently available reveal a different situation. Sexual differentiation in some amphibian species can be altered even by small changes in temperature. On the other hand, although not proven, it is possible that temperature is related to the appearance of sex-reversed individuals in natural populations under conditions unrelated to environmental contaminants. According to this, temperature, through sex reversal (phenotypic sex opposed to genetic sex), could play an important role in the turnover of sex-determining genes and in the maintenance of homomorphic sex chromosomes in this group. Accordingly, and given the expected increase in global temperatures, growth and sexual differentiation in amphibians could easily be affected, altering the sex ratio in natural populations and posing major conservation challenges for a group in worldwide decline. It is therefore particularly urgent to understand the mechanism by which temperature affects sexual differentiation in amphibians.

Testis Development and Differentiation in Amphibians

Sex is determined genetically in amphibians; however, little is known about the sex chromosomes, testis-determining genes, and the genes involved in testis differentiation in this class. Certain inherent characteristics of the species of this group, like the homomorphic sex chromosomes, the high diversity of the sex-determining mechanisms, or the existence of polyploids, may hinder the design of experiments when studying how the gonads can differentiate. Even so, other features, like their external development or the possibility of inducing sex reversal by external treatments, can be helpful. This review summarizes the current knowledge on amphibian sex determination, gonadal development, and testis differentiation. The analysis of this information, compared with the information available for other vertebrate groups, allows us to identify the evolutionarily conserved and divergent pathways involved in testis differentiation. Overall, the data confirm the previous observations in other vertebrates-the morphology of the adult testis is similar across different groups; however, the male-determining signal and the genetic networks involved in testis differentiation are not evolutionarily conserved.

Taxonomic identity of four groups of Glandirana rugosa (Anura, Ranidae) in Japan revealed by the complete mitochondrial genome sequence analysis

The Japanese Glandirana rugosa phylogenetically consists of four groups. However, the taxonomic identity of these groups still remains unclear. We determined the complete mitogenome sequences of the four groups of G. rugosa. The mitogenomes were 17,394–17,781 bp in length. The phylogenetic analysis clearly showed that the genus Glandirana is monophyletic and that the four groups of G. rugosa are separated into two clusters: one cluster represents G. rugosa, the other cluster may represent a different species.

Novel genetic sex markers reveal high frequency of sex reversal in wild populations of the agile frog (Rana dalmatina) associated with anthropogenic land use

Populations of ectothermic vertebrates are vulnerable to environmental pollution and climate change because certain chemicals and extreme temperatures can cause sex reversal during early ontogeny (i.e. genetically female individuals develop male phenotype or vice versa), which may distort population sex ratios. However, we have troublingly little information on sex reversals in natural populations, due to unavailability of genetic sex markers. Here, we developed a genetic sexing method based on sex-linked single nucleotide polymorphism loci to study the prevalence and fitness consequences of sex reversal in agile frogs (Rana dalmatina). Out of 125 juveniles raised in laboratory without exposure to sex-reversing stimuli, 6 showed male phenotype but female genotype according to our markers. These individuals exhibited several signs of poor physiological condition, suggesting stress-induced sex reversal and inferior fitness prospects. Among 162 adults from 11 wild populations in North-Central Hungary, 20% of phenotypic males had female genotype according to our markers. These individuals occurred more frequently in areas of anthropogenic land use; this association was attributable to agriculture and less strongly to urban land use. Female-to-male sex-reversed adults had similar body mass as normal males. We recorded no events of male-to-female sex reversal either in the laboratory or in the wild. These results support recent suspicions that sex reversal is widespread in nature, and suggest that human-induced environmental changes may contribute to its pervasiveness. Furthermore, our findings indicate that sex reversal is associated with stress and poor health in early life, but sex-reversed individuals surviving to adulthood may participate in breeding.

A Phylogenetically Distinct Group of Glandirana rugosa Found in Kyushu, Japan

The Japanese wrinkled frog Glandirana rugosa is separated into five genetically different groups. One group in western Japan is further divided into three subgroups, found in Kyushu, Shikoku, and western Honshu. We collected G. rugosa frogs at 39 sites in Kyushu and determined nucleotide sequences of the mitochondrial 12S and 16S rRNA genes for phylogenetic analysis. Unexpectedly, we found a group of frogs in southeastern Kyushu that did not cluster with any of the pre-existing five groups of G. rugosa on the phylogenetic trees. The frogs in the new group and G. rugosa in Kyushu were externally similar, but there were a few significant differences in morphological features between the two populations. In addition, we observed significant differences in the frogs' calls . Thus, the group of the frogs in southeastern Kyushu may represent a new candidate species in the genus Glandirana. We discuss the possibility of a new species.