Novel Sexual Patterns in Two Simultaneously Hermaphroditic Gobies, Lythrypnus dalli and Lythrypnus zebra

Abstract

The gobiid species Lythrypnus dalli and L. zebra are simultaneous hermaphrodites and are also known to provide male parental care. This combination of traits has not previously been reported, and the internal sex allocation patterns of these two species contrast with the patterns typically seen in simultaneous hermaphrodites. Examination of gonadal tissue suggests that L. dalli populations consist of females, female-biased hermaphrodites, and males, whereas populations of L. zebra are comprised of female-biased hermaphrodites, male-biased hermaphrodites, and a small number of females. These are the first examples of fish populations that include both pure females and female-biased hermaphrodites. In addition, L. zebra is so far unique among simultaneous hermaphrodites in that male-biased hermaphrodites rather than pure males coexist with female-biased hermaphrodites. The Lythrypnus system poses an interesting challenge to sex allocation theory. Theory predicts that, when the benefits of male parental care are high relative to egg production and male success is dependent on large size, separate sexes or a protogynous pattern of sequential hermaphroditism should be favored. The results of the present study suggest that the key to understanding the occurrence of simultaneous hermaphroditism in species with male parental care may lie in factors that limit the success of nesting males or favor rapid transitions between male and female function.