From embryos to larvae: seven-month-long paternal care by male Japanese giant salamander

Parental care is remarkably diverse in its modes both within and across taxa. Within amphibians, various pre- and post-hatching care behaviours have been described in frogs. In contrast, the current knowledge about salamander parental care is largely limited to pre- hatching attendance by females. In particular, post-hatching parental care by male salamanders have never been described and analysed in detail. A recent study revealed various modes of pre- hatching care provided by male Japanese giant salamanders (Andrias japonicus). Their hatched larvae are known to stay in the nest with the father (i.e. den master) for several months before dispersal, which led to the hypothesis that den masters continue providing care for hatchlings. To test this hypothesis, we videotaped and analysed post-hatching behaviours of two male A. japonicus that remained in the nests with hatchlings in situ. We also developed and tested several predictions regarding the post-hatching care behaviours in comparison to the pre- hatching behaviours. While one male abandoned the nest, the other male remained in the nest and provided care until the larvae dispersed in the following spring. The comparative analyses on three parental care behaviours (tail fanning, agitating/checking and hygienic filial cannibalism) between pre- and post-hatching care suggest their flexible and condition-dependent nature. Furthermore, the comparison in larval mortality and potential predators between the attended and abandoned nest revealed the crucial role of a den master in improving offspring survivorship. Our observations also disclosed the possibility of leech infection posing a serious threat to larval giant salamanders. The life-history traits associated with the evolution of such prolonged post-hatching paternal care in salamanders are fully aquatic life cycle, external fertilization and stream habitat. The rare combination of these traits is unique to the family Cryptobranchidae which consists of the three imperiled and secretive giant salamanders.