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One of the main goals of sex allocation theory is understanding sex ratio evolution. However, theoretical studies predicting sex ratios in species with unusual sexual systems, such as protandric simultaneous (PS) hermaphroditism, are rare. In PS hermaphrodites, juveniles Wrst develop into functional males that mature into simultaneous hermaphrodites later in life. Here, we report on the sex ratio (males/males + hermaphrodites) in the PS hermaphroditic shrimp Exhippolysmata oplophoroides. A 2-year study demonstrated that hermaphrodites dominated the population in two diVerent bays. This skewed sex ratio may be explained by limited encounter rates among conspeciWcs. In agreement with this idea, the density of shrimps was extremely low (•1 shrimp km ¡2 ) at the two study sites. Size at sex phase change and sex ratios remained relatively stable through time at the two bays. The stability of these parameters might be explained by the rather steady population structure of this species during the study period. A review of sex ratios in PS hermaphroditic shrimps (Lysmata and Exhippolysmata) revealed considerable variation; some species have male-and others hermaphroditeskewed sex ratios. The conditions explaining inter-and intra-speciWc sex ratio variation in protandric simultaneous hermaphroditic species remain to be addressed.Communicated by F. Bulleri.

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ABSTRACT

The occurrence of species of hermit crabs and their ecological distribution in soft bottoms off Ubatuba, São Paulo, Brazil were analyzed. To better understand the distribution of the species in relation to environmental factors, the similarity and speciesdiversity indexes were calculated. Paguroideans were sampled monthly from January through December 2000. The trawls were made with two otter-trawl nets at 13 different sites, at depths of 2-40 m. Water temperature, salinity, sediment texture, and organic matter content were measured. Gastropod shells occupied by hermit crabs were also assessed. A total of 1,238 specimens was collected, belonging to the families Diogenidae and Paguridae, comprising seven genera and thirteen species. The most abundant hermit crab species were Dardanus insignis (761 specimens) and Loxopagurus loxochelis (351 specimens). Phimochirus holthuisi is newly reported from the São Paulo coast. The highest diversity index was found for the shallower sites near rocky shores. The results of the grouping analysis for sites and species indicated three distinct groups for sites, and four groups for species. This suggests that the occurrence of these anomurans is associated with the environmental and biotic factors analyzed.