ABSTRACT
Around 88% of sh species are gonochorists, whilst the remaining 12%, comprising 27 out of 448 teleost families, are hermaphrodites: most of them protogynous and the others simultaneous hermaphrodites or protandrous (Patzner, 2008; for a review see de Mitcheson and Liu, 2008). In gobies, the most common sexual pattern is gonochorism. Protogynous hermaphroditism, including bi-directional sex change, also occurs (Patzner, 2008; reviewed by de Mitcheson and Liu, 2008). is last is di cult to prove as exemplified by Lythrypnus dalli, for which both simultaneous (Fishelson 1989; St. Mary, 1993) and protogynous hermaphroditism have been proposed (Reavis and Grober, 1999; Drilling and Grober, 2005). However, recent studies have demonstrated both female-to-male and maleto female sex change in known individuals (Rodgers et al., 2005; Lorenzi et al., 2006). In gobies, functional hermaphroditism has been reported for species of the genera Coryphopterus (Robertson and Justines, 1982; Cole and Robertson, 1988; Cole and Shapiro, 1990, 1992), Eviota (Cole, 1990), Paragobiodon (Cole, 1990, Kuwamura et al., 1994), Gobiodon (Cole, 1990; Nakashima et al., 1996; Munday et al., 1998; Cole and Hoese, 2001), Priolepis (Cole, 1990; Sunobe and Nakazono, 1999), Trimma (Cole, 1990; Sunobe and Nakazono, 1993; Kobayashi et al., 2005), Lythrypnus (Cole, 1988; St Mary, 1993, 1996, 1998, 2000), and in Tigrigobius multifasciatus (Robertson and Justines, 1982). is last species represents an exception. Within the genus Tigrigobius and the whole Gobiosoma group to which the genus belongs hermaphroditism has been documented only in T. multifasciatus (Cole, 2008), while for all the other studied species hermaphroditism is widespread in the genus. Con rming sex change in gobiid shes has been problematic because of the great variability in testicular and ovarian tissue presence and organization both before and during sex change (Cole, 1990). In Coryphopterus species, testicular tissue, in the form of small cysts of spermatocytes, appears within the ovarian stroma only during sex change and subsequently replaces all ovarian tissue. In contrast, in Trimma unisquamis presumptive testicular tissue is commonly present along the ovary wall during the female phase, hence long before sex change occurs and, in Paragobiodon hipoliti, the gonad comprises both testicular and ovarian tissues that are topographically separated and appear to be active simultaneously for some period of time before sex change is completed (Cole, 1990). Within the genus Lythrypnus, individuals, varying from pure female to pure male, present both gonadal tissues (St Mary, 1993, 2000). In addition, the testes of protogynous gobies do not always reflect the preceding ovarian morphology as occurs, for
instance, in wrasses and parrot sh (de Mitcheson and Liu, 2008). Indeed, in these species the ovarian cavity disappears soon a er sex change and sperm are not collected by peripheral sperm sinuses but typically exit the body via a newly formed anastomosing network of tubules lined with spermatogenic cysts (Cole, 1983, 1990; Cole and Robertson, 1988). A morphological feature, associated with the gonads, that has proved a useful criterion for the diagnosis of hermaphroditism in this family is the presence of the ‘precursive accessory gonadal structures’ (pAGSs) (Cole 1988, 1990; Cole and Robertson, 1988; Cole and Shapiro, 1990). pAGSs have been detected in conjunction with the ovaries of functional females in protogynous species. During sex change these structures develop into a pair of secretory organs, lateral to the sperm duct and hence correspond to the SDG. Precursive SDG structures have also been described in immature females of functionally gonochoric species and all the gonochoric species presenting precursive SDG structures belong to phylogenetic groups in which functional hermaphroditism is reported, therefore suggesting hermaphroditism as the ancestral status of the group (Cole, 2008). e observed di erences in gonadal morphology among hermaphrodite gobies has been argued follow phylogenetic lines (Cole, 1990; St. Mary, 1998). In contrast, the occurrence of functional hermaphroditism in this family and the type of hermaphorditism exhibited, i.e., protogyny rather than bi-directional sex change, appear to be linked to the life history traits of the species and represent adaptive responses to the social-ecological context individuals experience (Munday et al., 2006; Herler et al., this volume).
