Reproductive investment in Brachyura

The costs of reproduction in brachyurans are reviewed. In both sexes a number of aspects of reproductive behaviour and physiology can result in higher mortality and/or slower growth. Mortality can be increased by the greater exposure or the reduced mobility of the crabs: these are illustrated by selected examples, but there is a dearth of quantitative data. Slower growth can result from reduced feeding, or the diversion of resources to reproduction. These have been better quantified. The investment by females in egg production is examined in detail. In free living crabs investment per brood in dry weight terms ranges from 3-21%, with a mean of about 11%. This investment is constrained by body morphology. However, in commensal/ parasitic crabs the value rises to 60-90%: reasons for this are discussed. Many crabs produce more than one brood per year, and annual investment rises with brood number, though with some trade off. For temperate free living species annual investment ranges from 6-64%, with a mean of 22%. However tropical species produce more broods, and annual investment can reach 250%. In both temperate and tropical regimes there is a higher annual investment by commensal/parasitic species, of up to 470%. Priorities for future research are outlined.