Evolutionary biology of Hynobius
Preface
Edited by Masafumi Matsui
The hynobiid small salamanders of the genus Hynobius represent a uniquely interesting lineage in the Japanese fauna. Studies of these salamanders can be traced back more than 120 years to articles in Zoological Magazine, Tokyo, the antecedent of Zoological Science (Ikeda, 1891), but recent years have seen a renaissance of comparative studies of these tailed amphibians, as reflected in this collection of papers published in the last two decades in this journal.
The family Hynobiidae, including Hynobius, is now unambiguously considered as the most primitive from results of molecular phylogenetic studies. This view, however, has long been advocated from its primitive mode of reproduction, i.e., external fertilization, unlike most other tailed amphibians. This reproductive property allows the comparison of mechanisms of in situ fertilization with tailless amphibians.
Hynobius shows a unique pattern of distribution restricted to East Asia, and its high species diversity on the Japanese Archipelago, including small islands peripheral to main islands, has been famous. Yet new species are still being found and occurrence of many cryptic species have been detected. Pattern of species diversity in this genus offers a good opportunity to estimate the geo-history of the East Asian region, regarding which accurate geological information remains incomplete. At the transition stage from water to land, amphibians are famous for the large amount of DNA in their genomes, and this is most conspicuous in Hynobius. Known correlation of karyotypic and ecological properties of the genus also provides important key to understand genome evolution in primitive amphibians.
Finally, moderately high fecundity and long larval life in some members of Hynobius enable the study of morphological and ecological plasticity with respect to prey-predation relationships including kin selection. Making use of simpler surrounding ecological properties than those for members inhabiting more southern regions, this complex, yet evolutionarily very interesting problem has been effectively studied in the northernmost member, Hynobius retardatus.
As a member of the advisory board of Zoological Science, I am happy to see an increasing number of papers on evolutionary biology of salamanders in this unique genus being submitted to the journal.