Meeting Abstract
In most vertebrates, sex is determined chromosomally; however, a number of teleosts rely exclusively on environmental cues. In the highly social, bi-directionally sex changing fish, Lythrypnus dalli, social status regulates sexual phenotype. While the control of adult sex change is well understood, this is the first investigation of sexual development and differentiation in juveniles. We first analyzed gonad and genital papilla morphology in wild-caught juveniles of different sizes and developmental stages. Second, we lab-reared juveniles together in social groups to test whether social status regulates sexual development, as in adults. Hematoxylin and eosin staining of the gonad revealed the presence of both sperm and egg in nearly all field-caught juveniles, demonstrating that the early gonad is bipotential and differentiates over time. Adult genital papilla morphology is a reliable indicator of gonadal sex, and most field-caught juveniles had either female-typical or ambiguous papillae. In lab social groups, juveniles formed a hierarchical social structure similar to adults. All dominant juveniles developed a male-typical papilla and a primarily male gonad, indicating social regulation of sexual development. On the reef, juveniles were observed in local social environments of varying complexities. The rarity of male juveniles in the field supports a primarily subordinate social role for juveniles. Together, these data demonstrate the fundamental importance of early-life social cues in regulating sexual development, which will have a long-term impact on fitness.
