Gonadal Development and Sexual Allocation in Mangrove Killifish, Rivulus marmoratus (Pisces: Atherinomorpha)

Gonadal morphology in the self-fertilizing mangrove killifish, Kryptolebias marmoratus

“…Oocytes of PN were observed in most ovarian regions but tended to decrease in the anterior part of the gonad. We found oocytes at various stages of maturation throughout the gonad, as has been reported in previous studies (Soto et al, 1992;Cole and Noakes, 1997;Sakakura and Noakes, 2000). From 10 specimens for which we had all cross sections, yolk vesicle stage oocytes (2.4 oocytes in average) were observed in 61-80 % of ovarian regions, whereas Y1 (2.7) and Y2 (2.4) oocytes were found in 41-60 % of ovarian regions.…”

“…They were euthanized with 400 ppm of MS222 and then fixed in Bouin's fixative. We processed all preserved specimens for histological study by dehydrating and embedding in paraffin following the procedure of Cole and Noakes (1997). We made transverse sections serially at 5-7 µm through the entire body cavity (about 2000 sections per fish), mounted sections on glass slides, and then stained them with hematoxylin and eosin.…”

Phenotypic differences between the sexes in the sexually plastic mangrove rivulus fish (Kryptolebias marmoratus)

“…Maintaining ovarian tissue has negative impacts on individual survival, growth, immunocompetence and future reproductive efforts (Bergeron et al, 2011;. Hermaphroditic rivulus must maintain both ovarian and testicular tissues while males only need to maintain testicular tissue (Cole and Noakes, 1997;Sakakura et al, 2006). Our findings suggest that higher maximum metabolic rates in hermaphrodites might support energetically expensive activities (e.g.…”

“…Males are rare in natural populations (<3%), with the exception of some Belize populations in which males reach frequencies above 20% (Turner et al, 2006). Males are categorized either as primary, where embryos develop as males, or secondary, where an adult hermaphrodite transitions to male (Cole and Noakes, 1997;Harrington, 1974). Temperature is one known trigger of primary and secondary male development, although the precise mechanisms remain unknown (Harrington, 1974;Turner et al, 2006).…”

“…The ovotestis is also about twice as large as the male testis. Thus, hermaphrodites have the energetically expensive task of maintaining larger, more complex gonads (both ovarian and testicular tissues) relative to males, which maintain small, less complex gonads (testicular tissue only; Cole and Noakes, 1997;Sakakura et al, 2006). We thus predicted that maintaining both ovarian and testicular tissues should require hermaphrodites to have elevated metabolic rates compared with males.…”