Meeting Abstract

S8.3  Thursday, Jan. 6  Roles of oxygen and tidal cycle for embryonic incubation and hatching ISHIMATSU, Atsushi*; GRAHAM, Jeffrey B; Nagasaki Univ., Nagasaki, Japan; Univ. of California, San Diego a-ishima@nagasaki-u.ac.jp

Reproduction on mudflats requires that eggs are protected from different environmental challenges during development and hatch when environmental conditions are favorable for juvenile survival. Mudskippers are air-breathing, amphibious gobies, and one of few vertebrates that reside on mudflats.　They lay their eggs in mud burrows containing extremely　hypoxic water.　Mudskipper burrows can be located at a high intertidal level where water covers burrow openings only at high water spring tide. We found that the Japanese mudskipper Periophthalmus modestus deposits its eggs on the walls of an air-filled chamber within its burrow. To ensure adequate oxygen for egg development, the burrow-guarding male mudskipper deposits mouthfuls of fresh air into the egg chamber during each low tide, a behaviour that can be upregulated by egg chamber hypoxia. When egg development is complete, the male removes the egg-chamber air and releases it outside the burrow on a nocturnal rising tide. This floods the egg chamber and induces egg hatching. Because P. modestus eggs only have a 5–6 day window for hatching competence, the male’s initial selection of burrow position within the intertidal zone and the timing of spawning in its burrow relative to the tidal cycle are important factors in hatching success. This is particularly crucial for those burrows in high intertidal zone, which remain emerged during neap tide. Thus, P. modestus has developed a reproductive strategy that allows it to nurture eggs in this severe habitat rather than migrating away from the mudflat. This requires that mudskipper eggs be specialized to develop in air and that the air-breathing capacity of the egg-guarding male be integrated in a complex behavioural repertoire that includes egg guarding, ferrying air to and from the egg chamber, and sensing oxygen levels therein, all in concert with the tidal cycle.