Experimental Evidence of Food‐Independent Larval Development in Endemic Jamaican Freshwater‐Breeding Crabs

Abstract

In an experimental study, we compared reproductive and developmental traits of endemic sesarmid crabs from Jamaica living in landlocked limnic or terrestrial habitats. Laboratory rearing and behavioral observations showed that the larval development of Sesarma windsor, Sesarma dolphinum (both from freshwater brooks), and Metopaulias depressus (the bromeliad crab) invariably consists of two nonfeeding zoeal stages and a facultatively lecithotrophic megalopa. In a quantitative study of life-history processes characterizing this developmental mode, we provide for S. windsor first data of biomass and elemental composition (dry mass, W; carbon, hydrogen, nitrogen, collectively, CHN) during development from the egg through successive larval stages. These data show that larval independence of food is based on an enhanced female energy allocation in reproduction, reflected in unusually large egg size (1.45-1.70 mm), as well as high contents of C and H (about 60% and 9%, respectively) and high C : N ratios (7.6-8.4) in eggs and early larvae. During zoeal development, about 6% of initial W and 9% of N but 13% each of C and H were lost; similar losses occurred during megalopal development in continued absence of food. These patterns reflect the metabolic utilization of stored organic matter, with preferential degradation of lipid reserves. Fed megalopae gained greater amounts of W and N as compared with C and H (increments of 37% and 38% vs. 25% and 19%, respectively), indicating preferential investment of nutritional energy in proteins required for the formation of new tissues and organs, while generally decreasing proportions of CHN within total W suggested an increasing mineralization of the exoskeleton. Although survival and molt * Corresponding author; e-mail: kanger@awi-bremerhaven.de. cycle duration of the megalopa stage were not affected by absence of food, significant effects were found in the size of firststage juvenile crabs, indicating a trade-off between nutritional flexibility in the last larval stage and postmetamorphic fitness. Similar patterns of development and biomass in M. depressus as well as preliminary data obtained for S. dolphinum and Sesarma fossarum suggest that reproductive and developmental traits may be similar in all endemic Jamaican sesarmids. These traits are interpreted as life-history adaptations to development in landlocked habitats, probably playing a key role during adaptive radiation. Physiological and Biochemical Zoology

Adaptive traits in ecology, reproduction and early life history of Sesarma meridies, an endemic stream crab from Jamaica

“…The latter assumption was confirmed in recent life-history studies on the endemic Jamaican crabs Sesarma windsor, S. dolphinum, S. fossarum, and Metopaulias depressus (Anger 2005;Anger and Schubart 2005). All of these species show an abbreviated larval development in freshwater, consistently comprising two non-feeding zoeal stages and a facultatively lecithotrophic megalopa.…”

“…Extended hatching patterns have been observed not only in other endemic Jamaican sesarmids (S. windsor, S. fossarum: Anger 2005;Anger and Schubart 2005), but also in various further Decapoda with large eggs and an abbreviated larval development, for example, lithodid crabs and campylonotid shrimps (Thatje et al , 2004. In marine species, such patterns were interpreted as an adaptive trait that may reduce pelagic predation on unusually large and visible larvae drifting in the water column.…”

“…Hartnoll 1964;Reimer et al 1998;Diesel et al 2000;Anger 2005;Anger and Schubart 2005). This is several times larger than the egg size commonly known from estuarine and coastal marine species of grapsoid crabs, and it is typically associated with an abbreviated and at least partially food-independent mode of larval development (Rabalais and Gore 1985;Anger 1995Anger , 2001).…”

“…In contrast to the evolutionarily much older crayfish and potamoid crabs, which reveal a direct development from the egg to an adult-like juvenile stage, the life cycles of the endemic Jamaican sesarmids comprise -at least in all species where this aspect has been studied -free-living larval stages, which develop in freshwater (Anger and Schuh 1992;Anger 2005;Anger and Schubart 2005). Because this phase is by origin marine planktonic, the larvae face both physical (namely osmotic) and nutritional stress in environments with low ion concentrations and poor or unpredictable plankton production.…”

Ongoing Phenotypic and Genotypic Diversification in Adaptively Radiated Freshwater Crabs from Jamaica

“…These shrimps have a marine larval development which allows dispersal among the Caribbean islands (Reuschel and Schubart, submitted). In contrast, the freshwater crabs have a direct (Pseudothelphusidae) or an abbreviated larval development (Sesarmidae) (Hartnoll 1964;Chace and Hobbs 1969;Schubart et al 2000;Anger and Schubart 2005;González-Gordillo et al 2010). This allows for independent evolution and radiations on the different islands.…”