Prolactin-based “Water-drive Theory” in Migratory Salamanders: Some Disprovable Data

Abstract

To reconsider a classic theory that prolactin induces water-drive behavior in migratory salamanders (i.e., prolactin-based water-drive theory), I showed, with a brief review of past references, some disprovable data on the basis of “migratory activity type” and “mucus secretion” in the hynobiid salamanders, Hynobius hidamontanus and Salamandrella keyserlingii. This theory could not explain fall immigrations toward terrestrial hibernacula unrelated to mating in S. keyserlingii. Likewise, literature review indicated that it also could not explain breeding immigrations toward dry pond basins in Ambystoma opacum and toward terrestrial nest-sites adjacent to the water in Tylototriton (Echinotriton) andersoni. Mucus that was secreted from dermal mucous glands, a target organ for prolactin, was absent on the skin of both fall-nonbreeding and spring-breeding immigrants of S. keyserlingii. In the context of existence of ecological and physiological examples against the prolactin-based water-drive theory, which have been so far neglected in endocrinological studies, it is conclusively necessary to determine plasma prolactin concentrations in salamanders just before entering the water.