Food storage and carrion feeding in the fiddler crab Uca lactea

Abstract

Food hoarding is an adaptive strategy that enhances survival and reproductive success in food-scarce environments. It has been assumed that food hoarders, especially vertebrates, have the ability to cache food based on their current requirements and expected reproductive success. The present study provides empirical evidence that food storage in aquatic invertebrates is dependent on the availability of food and semilunar intertidal rhythms. The white-clawed fiddler crab Uca lactea, which inhabits food-scarce sandy mudflats, usually feeds on organic materials in sediment and occasionally on animal carrion, including conspecifics. This food is brought by the fiddler crabs into their burrows, presumably to be consumed during flood tides or heavy rains when the crabs cannot emerge to feed at the surface. When food was supplemented in the sediment every other day, females tended to store food-enriched sediment into their burrows. This behavior peaked around spring tides, when females were reproductively most active (i.e. mate-searching and mating). These results suggest that females may increase their reproductive effort by storing food.KEY WORDS: Caching · Crustaceans · Deposit-feeder · Fiddler crab · Food availability · Food hoarding Resale or republication not permitted without written consent of the publisherAquat Biol 10: [33][34][35][36][37][38][39] 2010 that female U. vocans scraped up surface mud and carried it into their burrows, perhaps because it contained a higher concentration of food.In the present study, carrion-feeding and foodstorage behavior of Uca lactea is described for the first time. To determine whether sediment storage is foodhoarding behavior, we tested whether crabs stored sediment more frequently when food was supplemented on the sediment. We also examined whether there were differences in storage behavior between sexes. Additionally, because feeding activity has been related to tidal rhythms in fiddler crabs (Kim et al. 2004a), as well as in other animals (e.g. Meyer-Rochow & Brown 1998), storing frequencies were observed in relation to semilunar cycles and reproductive rhythms. MATERIALS AND METHODSNatural history of the study species. There are approximately 100 species of fiddler crabs in the world, most of which live on intertidal sand or mudflats (Crane 1975). Individual fiddler crabs dig burrows in the sediment as shelter against predation or harsh environmental conditions (Crane 1975). The burrows (~30 to 50 cm in depth) also function as incubation chambers (Christy & Schober 1994). The crabs are not active during flood tides or heavy rain when their habitat is covered by water. When tides recede, they come out of their burrows and feed on the surface. Males use a single small cheliped for feeding and the other enlarged claw only for fighting or attracting females. In contrast, females have 2 small chelipeds and use both for feeding, fighting, and defense.Uca lactea have 2 mating modes. In burrow mating, males build courtship structures (semidomes) at their burrows (Kim...

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