The role of adult fiddler crab environmental acoustic cues and chemical cues in stimulating molting of field-caught megalopae

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In mid-Atlantic estuaries, three fiddler crab species, Uca pugilator, Uca pugnax and Uca minax, co-occur, with their adults occupying different habitat types distinguished by salinity and sediment size. Some evidence exists that selective settlement is responsible for this separation but the mechanism is largely unknown. We tested the hypothesis that field-caught megalopae would be stimulated to molt in the presence of adult species-specific environmental acoustic cues and conspecific chemical cues. We placed megalopae in seawater with and without adult chemical cues, exposed them to one of three sound treatments for 8 days, and recorded the time each megalopa took to metamorphose. Time to molt was unaffected by sound treatment either alone or in combination with chemical cues. In the absence of adult chemical cues, very few megalopae molted regardless of the sound treatment. Molting in the presence of habitat sound and chemical cues varied by species. Many U. pugilator molted in all sound and odor combinations, including the no odor and no sound treatment, and molted sooner in conspecific and congeneric odors. U. pugnax was stimulated to molt by chemical cues from either U. pugilator or U. pugnax, but molting was similar across sound treatments. Lastly, due to the small number of U. minax in the experiment, no statistical analyses or conclusions could be made. Our results do not support the hypothesis that sound stimulates molting of fiddler crab megalopae, but provide additional evidence that chemical odors from adults act as molting cues.