Unique Behavioral Strategies Adopted by Gravid Ghost Crab Ocypode gaudichaudii to Overcome Dehydration Stress while Minimizing Predation Risks.

Abstract

Semi-terrestrial crabs require continual access to water to maintain life-sustaining processes such as circulation and feeding. When they emerge from their burrows during low tide to forage, they face the problem of dehydration as they leave the dampness of their burrows. While foraging above ground, water uptake is elicited through capillary action via the hydrophilic setae near the base of the crab's body. Extruded eggs that are borne on the abdominal flap of females tend to obstruct the contact of the setae with the wet sediment. The behavioral adaptations that enable the gravid female painted ghost crab, Ocypode gaudichaudii, to overcome dehydration stress and minimize predation risks at a sandy shore in Playa Venao, Panama were studied using field observations. Comparison of the morphometric measurements of setal tufts between 30 male and 30 female crabs was made to determine if there were morphological adaptations. Analysis of the water uptake behavior from video footage showed that gravid crabs spent a longer duration on water uptake than crabs that did not carry eggs. For the first time, masquerading behavior of a gravid O. gaudichaudii was observed, in which the crab minimized predatory detection by freezing its movement next to a stone enroute to the lower shore during the day. There was no sexual dimorphism in the length and width of the setal tufts between the male and female adult crabs. The results of this study provide the first evidence that the water-uptake behavior in gravid O. gaudichaudii is dependent on behavioral adaptations, as setal tuft morphology does not differ between the sexes.