Аннотация:We have performed an integrative analysis of Asiatic salamanders of the genus
Hynobius (Family Hynobiidae) from Japan and Taiwan, using available information
about their biogeography, chromosome numbers, life history, and larval morphology
to try to understand their evolutionary relationships. Hynobius species fall into two
broad groups on the basis of life history, chromosome number, and larval morphology:
1) Pond-type larvae, with a diploid number of 2n = 56 chromosomes, and interdigital
membranes (IMs) that form during early limb development, and 2) stream-type larvae
with 2n = 58 chromosomes, and vestigial IMs (vIMs). According to current
cytogenetic theory in amphibians, karyotypes with 2n = 58 chromosomes, as found in
stream-type larvae, are thought to be plesiomorphic relative to those with 2n = 56
chromosomes, as found in pond-type larvae. This is supported by the fact that the
majority of outgroups to Hynobius within the Family Hynobiidae have chromosome
numbers greater than 58 (40 – 78, mean = 60). Considering their biogeographical
distribution, and using the hynobiid genus Salamandrella (2n = 62, pond-type larvae
with fully formed IM) as an outgroup, we conclude that the common ancestor of
Hynobius species had a relatively high chromosome number (2n = 58), pond-type
larvae, and well-developed IMs. Thus, the genus Hynobius is characterized by mosaic
evolution, in which the vIMs of species with stream-type larvae are clearly derived
relative to the well-developed IMs of those with pond-type larvae, despite the fact
that the former species have retained more plesiomorphic karyotypes. Overall, we are
convinced that well-developed IMs, characteristic of pond-type larvae, constitute a
synapomorphy for the Cryptobranchoidea. This suggests that the common ancestor of
hynobiids, and even of cryptobranchoids, must have had well-developed IMs and
possibly therefore pond-type larvae, and that stream-type larvae must have evolved
several times independently.