Paedomorphosis in the Ezo salamander (Hynobius retardatus) rediscovered after almost 90 years

Hisanori Okamiya,Ryohei Sugime,Yoshihiro Inoue,Chiharu Furusawa,Osamu Kishida

doi:10.1186/s40851-021-00183-x

Abstract

Although paedomorphosis is widespread across salamander families, only two species have ever been documented to exhibit paedomorphosis in Hynobiidae. One of these two exceptional species is Hynobius retardatus in which paedomorphosis was first reported in 1924, in specimens from Lake Kuttara in Hokkaido. This population became extinct after the last observation in 1932; since then, no paedomorphs of this species have been reported anywhere. Here, we report the rediscovery of paedomorphs of this species. Three paedomorph-like male salamanders were collected from a pond in the south Hokkaido in December 2020 and April 2021; in size, these specimens were similar to metamorphosed adults but they still displayed larval features such as external gills and a well-developed caudal fin. An artificial fertilization experiment demonstrated that they were sexually compatible with metamorphosed females, thus, confirming them to be paedomorphs. Future efforts to find additional paedomorphs in this and other populations are required to assess the prevalence of paedomorphosis in H. retardatus and to improve understanding of the ecology and evolution of paedomorphisis in Urodela.

Highlights

Paedomorphosis, defined as the retention of larval features while attaining sexual maturity, has long been of great interest in the fields of developmental biology and evolutionary ecology [1, 2], because it is a representative case of heterochronic development as a mechanism of phenotypic diversification [1, 3]
Around 100 years ago paedomorphosis was reported in H. retardatus inhabiting Lake Kuttara, a small volcanic lake in Hokkaido [11]; specimens collected from the bottom of the lake were sexually mature but exhibited aquatic larval morphology [11, 12]
In PC2, the paedomorph-like males were significantly discriminated only from the metamorphosed female (Fig. S3b), but the relative basal tail width (RBTAW), which had the strongest loading on PC2, of the paedomorph-like males was not much different from that of the metamorphosed females (Fig. S4)

Summary

Introduction

Paedomorphosis, defined as the retention of larval features while attaining sexual maturity, has long been of great interest in the fields of developmental biology and evolutionary ecology [1, 2], because it is a representative case of heterochronic development as a mechanism of phenotypic diversification [1, 3]. Around 100 years ago paedomorphosis was reported in H. retardatus inhabiting Lake Kuttara, a small volcanic lake in Hokkaido [11]; specimens collected from the bottom of the lake were sexually mature but exhibited aquatic larval morphology (e.g., external gills and well-developed caudal fins) [11, 12]. This paedomorphic population had disappeared after the last observation in 1932 (i.e., exact year of the extinction was unknown), apparently eliminated by introduced salmonid fish, and no paedomorphic individuals have ever been reported from other localities [14,15,16]. We report the rediscovery of paedomorphic individuals of H. retardatus after almost 90 years

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Results

Discussion

Conclusion