Hatching rhythms in Uca pugilator (Decapoda:Brachyura)

Abstract

Gravid female Uca pugilator (Bosc) maintained in conditions of 14h L: 10h D light regime and constant temperature without simulated tides showed a significant positive correlation between time of hatch and time of the nighttime high tide. Light: Dark experiments showed no entrainment by LD cues. Larval hatching was delayed until dark when high tide occurred between 1900 and 2130 hrs. Hatch time was a positive linear function of the time of the nighttime high tide when high tide occurred after 2130 hrs. Time of hatch was delayed by the light period on days lacking a nighttime high tide. Experiments conducted under constant light (LL) and temperature, without simulated tides, indicated a persistent free-running rhythm of approximately 25 h 03 min, suggesting an endogenous timer. Rhythmic larval release on the nighttime high tide may be adaptive as a predator-avoidance mechanism for adult gravid females.