Francis R C, Barlow G W
Department of Integrative Biology, University of California, Berkeley 94720.
Proc Natl Acad Sci U S A. 1993 Nov 15;90(22):10673-5. doi: 10.1073/pnas.90.22.10673.
Sexual differentiation in teleost fishes is characteristically labile. The most dramatic form of sexual lability is postmaturational sex change, which is common among teleosts although rare or absent in other vertebrate taxa. In many cases this process is regulated by social cues, particularly dominance interactions. Here we show that in the Midas cichlid, Cichlasoma citrinellum, these same sorts of social interactions affect much earlier stages of sexual differentiation. In this species, males are larger than females. By manipulating relative size in juveniles, we show that this sex-based size difference does not arise from endogenous factors associated with sex. Rather, sex is determined by relative size as a juvenile. We argue that this mode of sex determination, which may be common among teleosts, is a heterochronic variant of postmaturational sex change, one in which some individuals are deflected from a default female trajectory before maturation, as a result of social signals. The size-advantage model, which specifies the optimal size for sex change in hermaphroditic species, can be extended to account for the decision whether to mature as a male or a female in the Midas cichlid.
硬骨鱼类的性别分化通常不稳定。性别不稳定最显著的形式是成熟后的性逆转，这在硬骨鱼类中很常见，而在其他脊椎动物类群中则很少见或不存在。在许多情况下，这个过程受社会线索调控，特别是支配性相互作用。在此我们表明，在迈达斯丽鱼（Cichlasoma citrinellum）中，同样类型的社会相互作用会影响性别分化的更早阶段。在这个物种中，雄性比雌性大。通过操纵幼鱼的相对大小，我们发现这种基于性别的大小差异并非源于与性别相关的内在因素。相反，性别是由幼鱼期的相对大小决定的。我们认为，这种性别决定模式可能在硬骨鱼类中很常见，它是成熟后性逆转的一种异时变体，即由于社会信号，一些个体在成熟前偏离了默认的雌性发育轨迹。雌雄同体物种中性逆转的最佳大小的大小优势模型，可以扩展到解释迈达斯丽鱼中是成熟为雄性还是雌性的决定。
