Sex allocation in a simultaneous hermaphrodite, the blue-banded goby (Lythrypnus dalli): the effects of body size and behavioral gender and the consequences for reproduction

Although species with both male and female sexual functionsare often dichotomized into simultaneous and sequential hermaphrodites,many simultaneous hermaphrodites also exhibit sequential changesin sex allocation. In a field experiment using one such species,the gobiid fish, Lythrypnus dalli, female-biased individualsreallocated to male function in relation to their relative bodysize: consistent with the sizeadvantage hypothesis, large femaleswere more likely to reallocate and large fish had the highestspawningrates. Individuals, despite internal allocation to bothsexual functions, adopted only one behavioral gender. Behavioralmales had higher reproductive rates than behavioral females,and laboratory experiments showed that females preferred tomate with large males. Behavioral males grew more rapidly anddid notdiffer from behavioral females in survivorship. In addition,individuals who adopted male behavior but did not receive eggsin their nests maintained high levels of female tissue, whereasmales that received eggs did not. Laboratory experiments showedthat, unlike most hermaphroditic animals, L. dalli canchangeallocation either from ‘female’ to ‘male’or from ‘male’ to ‘female’. Thus, L.dalli shares haracteristics of both sequential and simultaneoushermaphrodites. Simultaneous hermaphroditism maybe maintained,in this species, to facilitate rapid sex change from femaleto male and to retain flexibility o that unsuccessful malescan revert to reproduction as females.