Gonadal steroid hormone patterns in saddleback wrasses are paralleled by differences in gonadal ultrastructure and steroid hormone synthetic capacity. Females exhibited greater gonadal E2 synthetic capacity than advanced sex changers in vitro when stimulated by salmon gonadotropin, while terminal phase males showed greater 11KT synthesis than females in vitro with advanced sex changers being intermediate . A follow up study compared terminal phase males with female-mimic initial phase males . Initial phase males are externally indistinguishable from females except for the genital papilla. This external similarity is likely important for success in ‘sneaker' mating tactics (a topic I return to in section 3). Initial phase male saddleback wrasses show both lower plasma levels and lower production of 11KT by the testes in vitro than terminal phase males.
Consistent with almost every other intercourse switching variety, highest degrees of E
Stoplight parrotfish (Sparisoma viride) exhibit a similar pattern of sexual phenotype differentiation characterized by diandric protogyny with colorful and territorial terminal phase males and initial phase males that are very similar to females in external morphology. As with saddleback wrasses, terminal phase male stoplight parrotfish exhibit higher 11KT levels than females or initial phase males while females exhibit the highest E2 levels [16,17]. Cardwell and Liley were also able to sample fish undergoing natural female-to-male sex change and found elevations in plasma 11KT and decreases in E2 in these transitional individuals. Initial phase males undergoing only color change during development into terminal phase males showed increases in 11KT consistent with a role in development of the terminal phase male phenotype. The pattern of higher E2 levels in females and higher 11KT in males is also seen in gobies such as the blackeye goby Coryphopterus nicholsi and a variety of grouper species [1,7,68,102,103].
In agreement with the findings described for protogynous species and despite the reversed direction of sex change, the protandrous anemonefish Amphiprion melanopus displays higher levels of 11KT in males and higher levels of E2 in females ( Figure 3 ; [46,47]). Testosterone levels are also higher in female A. melanopus, but this is likely explained by T's role as a biosynthetic precursor to E2. Gobies able to exhibit serial, bi-directional sex change are especially interesting in this context as they maintain both ovarian and testicular tissue in the adult gonad with only one type being active at a time [e.g., 87]. 2 are observed when gobies are functioning as females [96,105]. By contrast, Lorenzi and coworkers examined excreted 11KT in the bluebanded goby Lythrypnus dalli and found no difference between individuals functioning as males versus females, a finding consistent with the lack of differences across functional sexes in whole-body 11KT levels in the bidirectionally sex changing Gobiodon erythrospilus [98, both L. dalli and G. erythrospilus are very small bodied, precluding plasma measurements]. The lack of sex differences in 11KT levels may be related to their ability of serial, bidirectional sex change and/or their relative lack of external sexual dimorphism. Recall that initial phase male saddleback wrasses and stoplight parrotfish also lack male secondary sexual characters and have low 11KT levels, a feature generally consistent with other examples of teleost alternative male phenotypes and gonochoristic teleosts that do not display pronounced sexual dimorphism [10,11]. This relation between 11KT levels and the display of secondary sexual characters was also strongly supported in studies of the wrasse Pseudolabrus sieboldi, where shifts from the female-typical to terminal phase-male typical coloration of the anal fin were closely correlated to serum levels of 11KT [but not E2, 119].