A complex sexual cycle in sandy beaches: the reproductive strategy of Emerita brasiliensis (Decapoda: Anomura)

Abstract

Reproductive tactics displayed by the mole crab Emerita brasiliensis that inhabits Atlantic beaches of South America are reported. The analysis of external sexual characters and reproductive organs disclosed seven developmental forms: megalopae, neotenic males, early females, juveniles, males, females (ovigerous or not) and intersex individuals. Precocious acquisition of gonopores in females, production of spermatophores in neotenic males and presence of juveniles and intersex individuals are reported for the first time for this species. Sex ratios were biased towards male forms in summer, whereas the opposite trend was observed in autumn. The occurrence of different forms within a single population, coupled with a marked temporal variability in its abundance, suggest a high complexity in the sexual life cycle of the mole crab. This involves two different pathways: (a) short, where megalopae moult into neotenic (mature) males or early females; and (b) long, following a sequence of moults involving several stages (zoeas, megalopae, juveniles and adults).

Crustacean larvae distribution in the coastal upwelling zone off Central Chile

“…Larvae are released in the intertidal zone and although highest concentrations of Stage I were found close to shore, high offshore advection was evident even for this first stage. The annual bimodal spawning pattern of E. analoga in late summer (this study) and also in winter (Contreras et al 1999) differs from the unimodal pattern of larval release of E. brasiliensis from the Atlantic coast at approximately the same latitude (Delgado & Defeo, 2006). Since closely related species from the same habitat tend to develop convergent strategies when faced to similar environmental pressures, we proposed that the oceanographic setting (seasonal upwelling dynamics) in south central Chile influences the timing of E. analoga larval release.…”

Heterochronic phenotypic plasticity with lack of genetic differentiation in the southeastern Pacific squat lobster Pleuroncodes monodon

“…For example, there is paedomorphic plasticity in the carapace hingements and inner marginal carapace area of ostracods (Ozawa and Ishii 2008). Similar to the kind of heterochrony that may be occurring in P. monodon, some other species of Crustacea show variations in the timing of appearance and rates of character development, which occur at different stages in abbreviated larval development, such as euphausiids, brachyurans, and anomurans (Makarov and Maslennikov 1981;Clark 2005;Delgado and Defeo 2006). Particularly for the anomuran mole crab, Emerita brasiliensis, Delgado and Defeo (2006) state ''The principal benefit to early maturation is demographic: sexually mature neotenic males are most likely to succeed since they have less chance of dying before maturation.''…”

“…Heterochronic phenotypic variation has been reported for several species. For crustaceans it has been associated with an abbreviated larval development (Makarov and Maslennikov 1981;Clark 2005;Delgado and Defeo 2006;Kavanagh et al 2006;Ozawa and Ishii 2008). In some species, heterochronic plasticity translates into the existence of more than one form of adult, but without genetic differentiation between forms.…”

Effects of morphodynamic and estuarine gradients on the demography and distribution of a sandy beach mole crab: implications for source–sink habitat dynamics

“…Intermediate larval stages increase offshore distance, and approach the coast again during later planktonic stages (Veloso & Valentin 1993). The sedentary phase includes juveniles, which are derived from the megalopa stage that settles on to the beach, and different developmental stages leading to adulthood (Delgado & Defeo 2006.…”

“…Intermediate larval stages increase offshore distance, and approach the coast again during later planktonic stages (Veloso & Valentin 1993). The sedentary phase includes juveniles, which are derived from the megalopa stage that settles on to the beach, and different developmental stages leading to adulthood (Delgado & Defeo 2006.Preliminary observations showed that the species also inhabits estuarine beaches affected by the estuarine gradient generated by the Rio de la Plata. However, the simultaneous role of morphodynamics and estuarine gradients in modeling large-scale demographic patterns has not been assessed.…”