SEX RATIO ANALYSIS IN ERIPHIA GONAGRA (DECAPODA, XANTHIDAE) João Marcos de Góes 1 Adilson Fransozo' ABSTRACT The sex ratio ofEriphia gonagra (Fabricius, 1781) by estimating the proportions of both sexes within a population was determined and discussed with other brachyuran species. Crabs were monthly collected from January to December of 1993, 1994, 1996 and 1997 at a rocky shore of Praia Grande, Ubatuba, São Paulo, Brazil. Sex ratio was 0.86:1 in 1993; 1.08:1 in 1994 and, 0.90:1 in 1996 and 1997. In each year, significam differences among months or size classes were absent in most cases (p>0.05). This may be an outcome of unbiased sampling, which is expected in data drawn from populations inhabiting discrete areas such as rocky shores. It is suggested that overall sex ratio for brachyurans tends to 1:1. Departures from this ratio may be related to certain sampling procedures and to selecting inadequate sampling areas. KEYWORDS. Sex ratio, Eriphia, Brachyura, Xanthidae. INTRODUCTION Some authors reported that sex ratio is genetically controlled in several species (Crew, 1937; Mayr, 1939). In studies regarding population dynamics, sex ratio has been estimated by comparing the proportion of males and females in samples obtained from a given population (Haley, 1979). Kolman (1960) presents a model in which the mechanism described by Fisher ( 1 930) regarding natural selection of sex ratio is quantified and further extended. This shows how sex ratio is adjusted to balance parental costs of producing males and females, a mechanism that may affect the sex ratio average but not its variance. Therefore, sex ratio is generally about 1:1 in animais with sexual reproduction. According to Wilson & Pianka (1963), this pattern is favored by natural selection but alterations usually emerge after a period of parental care. Wenner ( 1 972) described four patterns of sex ratio Variation as a function of size in marine crustaceans and provided some possible explanations for the "anomalous pattern" based on sexual reversion, sex-related longevity, migratory patterns, mortality and growth rate. 1. Departamento de Zoologia, Institutode Biociéncias, Universidade Estadual Paulista. CEP 18618-000, Botucatu, SP, Brasil. Iheringia, Sér. Zool., Porto Alegre, (88): 151-157, 31 de maio de 2000
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