Abstract

Phenotypic plasticity in response to food availability results in either the achievement of larval metamorphic competence or exposing larvae to a reduced probability for survival. Larvae of the temperate aspidochirote sea cucumber, Australostichopus mollis fed the diatom Chaetoceros muelleri grew best in 3000 cells ml - 1 day - 1 , reaching a maximum length of 896 ± 22.8 μm by day 12 (mean ± SE). When shape was quantified independent of growth and size larvae were consistently shorter and wider in 300 but became longer and narrower in 3000 cells ml - 1 day - 1 . They were also consistently shorter and narrower in 6000 than those in 600 cells ml - 1 day - 1 , which became longer and wider. In both 300 and 6000 gut shape did not change whereas in 600 and 3000 cells ml - 1 day - 1 the gut became more oval shaped. By day 12 most in 3000 cells ml - 1 day - 1 were late auricularia whereas development was delayed in other feeding regimes. Although by day 18 in all feeding regimes larvae had 2 hyaline spheres in the posterior folds of the ciliated band, only those fed 600 and 3000 cells ml - 1 day - 1 had more. Of the surviving larvae in these feeding regimes, most were competent, undergoing, or likely to complete metamorphosis. Phenotypic plasticity or a change in shape allows larvae to moderate growth and form in response to food availability but it may also act as a selection mechanism in determining the contribution of larvae to subsequent generations by delaying development.

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