Meeting Abstract
Reproduction is associated with significant sex-specific costs. To accommodate these costs and maximize reproductive success, many animal species have evolved a flexible sexual strategy – functional sex change. Theory predicts that transitions between sexes should occur when the fitness payoff of maintaining the current sex is exceeded by the fitness of switching to the opposite sex. In this study we sought to examine sex-specific costs of reproduction in a sex-changing vertebrate, the mangrove rivulus fish (Kryptolebias marmoratus). Rivulus are androdioecious; populations consist of self-fertilizing hermaphrodites and males. Hermaphrodites transition into males as they age or when exposed to elevated ambient temperatures. We generated 40 male-hermaphrodite pairs and quantified baseline steroid hormone levels, behavioral traits (aggression and risk-taking), metabolic rates, and anatomical traits (organ masses). We found significant differences in anatomical, physiological, and behavioral traits between the sexes. Hermaphrodites had larger gonadosomatic indices, higher maximum metabolic rates, were more aggressive, and were more risk-aversive relative to males. Males had greater body masses, possessed considerable fat stores, and had higher androgen and estrogen levels relative to hermaphrodites. Our findings suggest that hermaphrodites invest more heavily in gonadal tissue than males, maintain elevated metabolic rates, and sacrifice somatic growth to accommodate this investment. Our study provides support for future research investigating how external conditions (e.g. ambient temperature) influence internal conditions (e.g. metabolism), the impact that changes in internal conditions have on reproductive investment and, ultimately, how these changes dictate the point of transition between sexes.
