FLEXIBILITY IN TIMING OF THE METAMORPHIC MOLT BY FIDDLER-CRAB MEGALOPAE UCA-PUGILATOR

The larvae of many invertebrate taxa can delay metamorphosis for considerable periods of time in the absence of specific stimuli for settlement. This study tested the hypothesis that the duration of the megalopal stage of fiddler crabs can be adjusted by several days depending on the availability of some habitat components. The hypothesis that megalopae can delay the metamorphic molt was tested by comparing the proportion of individuals molting to the first crab instar in aquaria containing only filtered seawater to that in aquaria with mud, sand, and/or an adult crab, near the predicted time of molting. The hypothesis that molting can be advanced was tested by comparing the proportion of sibling larvae molting at intervals throughout the megalopal stage in aquaria containing only filtered seawater or seawater plus an adult crab, mud, and sand. Megalopae delayed molting unless 2 stimuli were present: an adult crab and sediment, either mud or sand. The metamorphic molt was advanced in the presence of both these cues, although contact with the sediment by the adult crab appears necessary for maximal effect. Flexibility in timing of molting and the requirement for more than one cue can increase the chance that megalopae settle and molt to the first crab instar in appropriate adult habitats.