Karyotypes of Rana tagoi Okada with diploid number 28 in the Chausu Mountains of the Minamishinshu district of Nagano Prefecture, Japan (Anura: Ranidae)

Evolution of Sex Chromosome Heteromorphy in Geographic Populations of the Japanese Tago's Brown Frog Complex

The sex chromosomes of most anuran amphibians are characterized by homomorphy in both sexes, and evolution to heteromorphy rarely occurs at the species or geographic population level. Here, we report sex chromosome heteromorphy in geographic populations of the Japanese Tago's brown frog complex (2n = 26), comprising Rana sakuraii and R. tagoi. The sex chromosomes of R. sakuraii from the populations in western Japan were homomorphic in both sexes, whereas chromosome 7 from the populations in eastern Japan were heteromorphic in males. Chromosome 7 of R. tagoi, which is distributed close to R. sakuraii in eastern Japan, was highly similar in morphology to the Y chromosome of R. sakuraii. Based on this and on mitochondrial gene sequence analysis, we hypothesize that in the R. sakuraii populations from eastern Japan the XY heteromorphic sex chromosome system was established by the introduction of chromosome 7 from R. tagoi via interspecies hybridization. In contrast, chromosome 13 of R. tagoi from the 2 large islands in western Japan, Shikoku and Kyushu, showed a heteromorphic pattern of constitutive heterochromatin distribution in males, while this pattern was homomorphic in females. Our study reveals that sex chromosome heteromorphy evolved independently at the geographic lineage level in this species complex.

Evidence from the primary structures of dermal antimicrobial peptides that Rana tagoi okiensis and Rana tagoi tagoi (Ranidae) are not conspecific subspecies

Morphological evidence and data from comparisons of nucleotide sequences of mitochondrial genes demonstrate considerable intraspecies variation among populations of the Japanese brown frog Rana tagoi Okada 1928 (Tago's brown frog). Five peptides with antimicrobial activity were isolated from an extract of the skins of specimens of Rana tagoi okiensis collected on the Oki Islands, Japan. Determination of their primary structures demonstrated that two peptides belong to the ranatuerin-2 family, two peptides to the temporin family, and one peptide to the brevinin-1 family. Ranatuerin-2 peptides were not previously identified in the skin of specimens of R. t. tagoi collected in Chiba Prefecture, Japan and the structures of the temporin peptides from R. t. okiensis (temporin-TOa: FLPILGKLLSGFL.NH(2) and temporin-TOb: FLPILGKLLSGLL.NH(2)) are different from temporin-TGa (FLPILGKLLSGIL.NH(2)) isolated from R. t. tagoi. Similarly, the acyclic C-terminally alpha-amidated brevinin-1 peptide from R. t. okiensis (Brevinin-1TOa, GIGSILGVIAKGLPTLISWIKNR.NH(2)) shows three amino acid substitutions (Gly(1)-->Ala, Val(8)-->Ala, Ile(9)-->Leu) compared to the ortholog from R. t. tagoi. In addition, bradykinin, identical to the mammalian peptide, is present in high concentration in the skin of R. t. okiensis but not R. t. tagoi. The data provide evidence to support the proposal that R. t. tagoi and R. t. okiensis should be regarded as separate species (R. tagoi and R. okiensis) rather than conspecific subspecies.

Unusual primitive heteromorphic ZZ/ZW sex chromosomes in Proceratophrys boiei (Anura, Cycloramphidae, Alsodinae), with description of C-Band interpopulational polymorphism

We performed cytogenetic analyses on specimens from three population samples of Proceratophrys boiei from southeastern and northeastern Brazil. We stained chromosomes of mitotic and meiotic cells with Giemsa, C-banding and Ag-NOR methods. All specimens of P. boiei presented a karyotype with a full chromosome complement of 2n=22, metacentric and submetacentric. We observed the secondary constriction within the short arm of pair 8, which was in the same position of the nucleolus organizer region (NOR). NOR heteromorphism was observed within two specimens from the municipality of Mata de São João (northeastern Bahia State). The C-banding evidenced an unusual heterochromatic pattern in the genome of P. boiei. In the southern most population samples (São Paulo State), we observed large blocks of heterochromatin in the centromeric regions of all chromosomes, whereas the northernmost samples (Bahia State) presented a small amount of constitutive heterochromatin. We suppose that this geographic variation in heterochromatin quantities could be due to heterochromatinization of some chromosome regions in the genome of the São Paulo samples. Furthermore, females from São Paulo presented, within chromosome pair 1 from C-banded karyotypes, one homologous chromosome almost heterochromatic, whereas males had heterochromatin restricted to the centromeric region. This unusual heterochromatic arrangement led us to assume that P. boiei owns a ZZ/ZW type of sexual determination system. This finding is very important, as this is the first record of ZZ/ZW sex chromosomes within Cycloramphidae. We believe that the cytogenetic differences found between southeastern and northeastern Brazilian population samples of P. boiei strongly supports the existence of a species complex under the name P. boiei, and the requirement of taxonomic and systematic reviews by morphological, bioacoustical, molecular, and cytogenetic data could define this taxonomic issue in the future.