Abstract
The growth and reproduction investment of the young of the year (0+) of the squat lobster Munida gregaria in San Jorge Gulf, Argentina, were analysed. Moult cycle and size frequency distribution were studied in monthly field samples. Experiments to determine moult increments and intermoult duration were conducted. Sexual maturity, fecundity and reproductive output were analysed in field samples. In addition, maturity experiments in laboratory cultures were conducted. After settlement (November), juveniles showed fast growth until winter (July) and growth restarted in September-October. At the beginning of the mating period (early June), males 0+ exhibited mature gonads, whereas females 0+ only showed previtellogenic oocytes. Experimental data showed that females with developed gonads had smaller-size increments in the previous moult. Fecundity and reproductive output were significantly lower in females 0+ than in older females. The early life history of M. gregaria in San Jorge Gulf differs from that of southern populations as those of Beagle Channel and Strait of Magellan due to faster growth and early reproductive investment. Our results suggest that females 0+ of M. gregaria have two investment strategies: early maturity with low fecundity and delayed maturity with higher future fecundity.
Highlights
Growth and reproduction are antagonist processes that play a central role in the life history of species
Moult activity was higher during summer and early autumn, while at the end of winter (August-September) most squat lobsters were in intermoult
Growth rate, size and age at maturity, and fecundity are important life-history traits (Kozlowski 1991, Ramírez Llodra 2002). These traits are related to energy allocation strategies and are the basis of the differences between different life history and population dynamics (Heino and Kaitala 1999, Ramírez Llodra 2002)
Summary
Growth and reproduction are antagonist processes that play a central role in the life history of species. The different ways in which resources are allocated to growth and reproduction form the basis of the different life-history strategies in marine invertebrates (Ramírez Llodra 2002). In decapod species with determinate growth (e.g. Majoidea), resource allocation to growth and reproduction is temporarily separated, whereas decapod species with indeterminate growth experience a life-history trade-off in resource allocation between reproduction and growth throughout their lives. In both growth models, size and age at maturity play a pivotal role in the life cycle of species because selection pressures change drastically. Age at maturity is an allocation decision that results from the balance between costs and benefits of starting reproduction investment at this age (Stearns 1992, Ramírez Llodra 2002)
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