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The life history of insular gecarcinid crabs is divided into a marine larval and an adult phase, adapted to the terrestrial environment. As adults, individuals migrate seasonally to locations near the sea, engaging in reproductive behaviors. Therefore, identifying breeding and recruitment areas is crucial for the conservation of insular gecarcinids, especially for those endangered, such as Johngarthia lagostoma (H. Milne Edwards, 1837). We used sex ratio and sexual dimorphism analyses (body and cheliped size) as well as records of juveniles and adults to describe the population structure of J. lagostoma in the Trindade Island, Brazil. During the reproductive period, several population parameters were compared among sites with different altitudes, comprising two beaches (Andradas and Tartarugas) and two hills (Príncipe, 136 m; and Desejado, 612 m). Overall, males predominated in the population and invested more in body and cheliped growth than females. However, at Andradas Beach, it was observed a similar frequency of adult males and females as well as a small difference in the body size between the sexes. In comparison, the smallest crabs were found at Príncipe Hill. The analyzed population presented a predominance of adults, especially at Andradas Beach (93.1%). Compared to the other sites sampled, Príncipe Hill showed the highest abundance of juveniles (males: 22.2%; females: 40.8%). Thus, Andradas Beach was considered a reproductive site, while Príncipe Hill had the highest density of juveniles, which makes them priority areas for the conservation of J. lagostoma in Trindade Island. [ABSTRACT FROM AUTHOR]

We analyzed the social structure, sexual dimorphism and relative growth in the burrowing shrimp Callichirus seilacheri from the tropical eastern Pacific. To this end, 456 individuals of C. seilacheri were collected during monthly sampling from December 2011 to November 2012. No shrimp pairs or burrows inhabited by more than one shrimp were detected during the study period. Males were significantly smaller than females, denoting sexual dimorphism with respect to body size. In many juvenile males and females, the size of the right and left claws was the same, whereas in others the largest cheliped was located on the right or left side. Analysis of allometric growth between cheliped carpus length and cephalothorax length revealed an isometric relationship in juveniles of both sexes and adult females and positive allometric growth in adult males. The adjustment of the above relationship by the Somerton's method, denoted the existence of two main phases of growth related to sexual maturity, with transition points between juvenile and adult phase at 12.3 mm and 12.0 mm of body size for males and females, respectively. The observations on social structure, sexual dimorphism and relative growth of C. seilacheri argued that this species is polygamous. Furthermore, the high frequency of solitary females found brooding embryos suggested that males might roam among galleries in search of receptive females. [ABSTRACT FROM AUTHOR]