Why be choosy? Temporal changes in larval sensitivity to several naturally-occurring metamorphic inducers in the opisthobranch Haminaea callidegenita

In the opisthobranch Haminaea callidegenita Gibson & Chia, time of metamorphic competence varies among sibling larvae over a 2-wk period. Intra-clutch variation in onset of competence occurs in constant presence of inducer and is independent of larval feeding, as these are lecithotrophic larvae. All larvae become competent and metamorphose successfully This suggests that intra-clutch variability in time of competence may be adaptive in providing flexibility to the larval period, rather than reflecting the slow development of a few ''inferior'' larvae. Competence occurs throughout both the encapsulated and free-swimming larval phases. As a result, both dispersive larvae and nondispersive juveniles are simultaneously released at hatching, an unusual mode of development termed poecilogony. Hatched veligers are characterized by (1) an initially high rate of metamorphic competence which rapidly decreases with increasing time hatched, (2) a decrease in larval ''choosiness'', or an increase in sensitivity to various substrata, and (3) the ability for ''spontaneous'' metamorphosis occurring in absence of known cue. Competent larvae initially metamorphose rapidly in response to a naturally-occurring inducer found in egg mass jelly and to excess potassium, then gradually become sensitive to certain other substrata [the seagrass Zostera marina L., and the filamentous green alga Chaetamorpha linum (O.F. Miiller)]. Older larvae are not simply becoming indiscriminate in responding to these other substrata, as evidenced by their lack of response to biofilmed sediment. This pattern of increasing sensitivity may result in short-range dispersal of most hatched veligers (possibly within or near the large estuarine system inhabited by parents) and longer-range dispersal of a few siblings, thus maintaining the potential for mixing within and exchange among populations.