Highly Complex Mitochondrial Dna Genealogy in an Endemic Japanese Subterranean Breeding Brown FrogRana Tagoi(Amphibia, Anura, Ranidae)

Abstract

The endemic Japanese frog Rana tagoi is unique among Holarctic brown frogs in that it breeds in small subterranean streams. Using mitochondrial 16S ribosomal RNA and NADH dehydrogenase subunit 1 genes, we investigated genealogical relationships among geographic samples of this species together with its relative R. sakuraii, which is also a unique stream breeder. These two species together form a monophyletic group, within which both are reciprocally paraphyletic. Rana tagoi is divided into two major clades (Clade A and B) that are composed of 14 genetic groups. Rana sakuraii is included in Clade A and split into two genetic groups, one of which forms a clade (Subclade A-2) with sympatric R. tagoi. This species-level paraphyly appears to be caused by incomplete taxonomy, in addition to introgressive hybridization and/or incomplete lineage sorting. Rana tagoi strongly differs from other Japanese anurans in its geographic pattern of genetic differentiation, most probably in relation to its unique reproductive habits. Taxonomically, R. tagoi surely includes many cryptic species.

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

“…1, 2). It is noteworthy that the latter eastern subclade was included in a clade with R. tagoi specimens from populations P1, P2, and P6, consistent with Eto et al [2012]. R. tagoi specimens from western Japan (P7 and P8) were placed in the Shikoku and Kyushu islands clade: this clade is distinct from the clade including R. sakuraii and R. tagoi specimens from populations P1-3 and P1, P2, and P6, which were located in and near Tokyo, respectively.…”

“…Thus, we hypothesize that the XY sex chromosomes of R. sakuraii specimens from the eastern sub-clade were established by interspecies hybridization via the introduction of R. tagoi chromosome 7. Our mitochondrial gene sequence analysis and that of Eto et al [2012] provide evidence of regional interspecies hybridization between these species -the R. sakuraii eastern sub-clade is completely included in the larger clade together with R. tagoi in P1-3. This hypothesis indicates that the inversion had already occurred in chromosome 7 in R. tagoi before hybridization but not on the Y chromosome itself of the R. sakuraii specimens from the eastern sub-clade (Fig.…”

“…Evolution of the sex chromosomes in R. sakuraii and R. tagoi. Colors of circles and outlines indicate nuclear and mitochondrial genomes, respectively: R. sakuraii is shown in green and R. tagoi in red based on this study and on Eto et al [2012]. The dotted arrow indicates introgression of subtelocentric chromosome 7 and transfer of mitochondria from R. tagoi to R. sakuraii in Tokyo and nearby location.…”

“…7). It may be due to coupling with the high rate of speciation in the restricted lineages of this species complex, because taxonomic description of several more cryptic species is suggested on the basis of the genetic differentiation [Eto et al, 2012].…”

“…The sister species, R. sakuraii, breeds deep beneath the water surface in mountain streams and is therefore referred to as the stream brown frog [Matsui and Matsui, 1990]. Mitochondrial sequence investigation has identified several major clades within the Tago species complex, and the existence of several cryptic species is predicted [Eto et al, 2012]. This reflects a high speciation rate within this species complex.…”