Experimental evidence of food-independent larval development in endemic Jamaican freshwater-breeding crabs

kanger [ at ] awi-bremerhaven.de


In an experimental study, we compared reproductive and developmental traits of endemic sesarmid crabs from Jamaica living in land-locked limnic or terrestrial habitats. Laboratory rearing and behavioural observations showed that the larval development of Sesarma windsor, S. dolpinum (both from freshwater brooks), and Metopaulias depressus (the bromeliad crab) invariably consists of two non-feeding 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 to C and H (increments of 37-38% 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 moult-cycle duration of the megalopa stage were not affected by absence of food, significant effects were found in the size of first-stage 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 S. 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 land-locked habitats, probably playing a key role during adaptive radiation.

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Anger, K. and Schubart, C. D. (2005): Experimental evidence of food-independent larval development in endemic Jamaican freshwater-breeding crabs , Physiological and Biochemical Zoology, 78 (2), pp. 246-258 .

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