Effect of social environment on sexual differentiation in the highly gregarious red cherry shrimp (Neocaridina davidi)

Studies on social control of functional sex in crustaceans are scarce and focused on hermaphroditic species. Hence, the objective of this study was to determine whether adult sex ratio affects juvenile sexual differentiation in a gonochoristic caridean shrimp, Neocaridina davidi (Bouvier 1904). We tested two alternative hypotheses: (1) that undifferentiated juveniles become males when reared in the presence of adult females and vice versa; and (2) that the presence of adult males affects juvenile sexual differentiation through androgenic gland secretions. Newly hatched juveniles were maintained with adult males or adult females during a 50-day period, after which they were sexed. In both treatments, juvenile sex ratios showed no deviations from the expected 1:1 relationship. This suggests that adult sex ratio is not a selective force determining juvenile phenotypic sex, even though mating opportunities may be null for juveniles differentiating into the sex of surrounding adults. The 1:1 sex ratio observed in broods reared with adult males and adult females also suggests that the potential chemical cues released by adults have neither masculinizing nor feminizing effects on undifferentiated juveniles. Present results reject our initial hypotheses and are consistent with a strong genetic basis of juvenile sexual differentiation in caridean shrimps.

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