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 chromosome evolution from a heteromorphic to a homomorphic system by inter-population hybridization in a frog

Sex chromosomes generally evolve from a homomorphic to heteromorphic state. Once a heteromorphic system is established, the sex chromosome system may remain stable for an extended period. Here, we show the opposite case of sex chromosome evolution from a heteromorphic to a homomorphic system in the Japanese frog Glandirana rugosa. One geographic group, Neo-ZW, has ZZ-ZW type heteromorphic sex chromosomes. We found that its western edge populations, which are geographically close to another West-Japan group with homomorphic sex chromosomes of XX-XY type, showed homozygous genotypes of sex-linked genes in both sexes. Karyologically, no heteromorphic sex chromosomes were identified. Sex-reversal experiments revealed that the males were heterogametic in sex determination. In addition, we identified another similar population around at the southwestern edge of the Neo-ZW group in the Kii Peninsula: the frogs had homomorphic sex chromosomes under male heterogamety, while shared mitochondrial haplotypes with the XY group, which is located in the east and bears heteromorphic sex chromosomes. In conclusion, our study revealed that the heteromorphic sex chromosome systems independently reversed back to or turned over to a homomorphic system around each of the western and southwestern edges of the Neo-ZW group through hybridization with the West-Japan group bearing homomorphic sex chromosomes. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)'.

Antimicrobial Property and Mode of Action of the Skin Peptides of the Sado Wrinkled Frog, Glandirana susurra, against Animal and Plant Pathogens

The Sado wrinkled frog Glandirana susurra has recently been classified as a new frog species endemic to Sado Island, Japan. In this study, we cloned 12 cDNAs encoding the biosynthetic precursors for brevinin-2SSa–2SSd, esculentin-2SSa, ranatuerin-2SSa, brevinin-1SSa–1SSd, granuliberin-SSa, and bradykinin-SSa from the skin of G. susurra. Among these antimicrobial peptides, we focused on brevinin-2SSb, ranatuerin-2SSa, and granuliberin-SSa, using their synthetic replicates to examine their activities against different reference strains of pathogenic microorganisms that infect animals and plants. In broth microdilution assays, brevinin-2SSb displayed antimicrobial activities against animal pathogens Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, and Candida albicans and plant pathogens Xanthomonas oryzae pv. oryzae, Clavibacter michiganensis subsp. michiganensis, and Pyricularia oryzae. Ranatuerin-2SSa and granuliberin-SSa were active against C. albicans and C. michiganensis subsp. michiganensis, and granuliberin-SSa also was active against the other plant pathogenic microbes. Scanning electron microscopic observations demonstrated that brevinin-2SSb, ranatuerin-2SSa, and granuliberin-SSa induced morphological abnormalities on the cell surface in a wide range of the reference pathogens. To assess the bacterial-endotoxin-binding ability of the peptides, we developed an enzyme-linked endotoxin-binding assay system and demonstrated that brevinin-2SSb and ranatuerin-2SSa both exhibited high affinity to lipopolysaccharide and moderate affinity to lipoteichoic acid.

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

Each vertebrate species, as a general rule, has either the XX/XY or ZZ/ZW chromosomes by which sex is determined. However, the Japanese Rana (R.) rugosa frog is an exception, possessing both sex-determining combinations within one species, varying with region of origin. We collected R. rugosa frogs from 104 sites around Japan and South Korea and determined the nucleotide sequences of the mitochondrial 12S ribosomal RNA gene. Based on the sequences, R. rugosa frogs were divided into four groups from Japan and one from South Korea. The ZZ/ZW type is reportedly derived from the XX/XY type, although recently a new ZZ/ZW type of R. rugosa was reported. However, it still remains unclear from where the sex chromosomes in the five groups of this species were derived. In this study, we successfully isolated a sex-linked DNA maker and used it to classify R. rugosa frogs into several groupings. From the DNA marker as well as from nucleotide analysis of the promoter region of the androgen receptor (AR) gene, we identified another female heterogametic group, designated, West-Central. The sex chromosomes in the West-Central originated from the West and Central groups. The results indicate that a sex-linked DNA marker is a verifiable tool to determine the origin of the sex chromosomes in R. rugosa frogs in which the sex-determining system has changed, during two independent events, from the male to female heterogamety.