Growth and differentiation during delayed metamorphosis of feeding gastropod larvae: signatures of ancestry and innovation |
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Authors: | Maryna P Lesoway Louise R Page |
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Institution: | (1) Department of Biology, University of Victoria, V8W 3N5 Victoria, BC, Canada |
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Abstract: | Extent of larval growth among marine invertebrates has potentially profound implications for performance by benthic recruits
because body size influences many biological processes. Among gastropods, feeding larvae often attain larger size at metamorphic
competence than non-feeding larvae of basal gastropod clades. Delay of metamorphosis can further influence size at recruitment
if larvae continue to grow during the delay. Some caenogastopod larvae grow during delayed metamorphosis, but opisthobranch
larvae do not. Data on larval growth of neritimorph gastropods are needed to help determine which of these growth patterns
for planktotrophic gastropod larvae is more derived. We cultured planktotrophic larvae from all three major gastropod clades
with feeding larvae through delays of metamorphosis of 3–10 weeks. Larvae of the caenogastropod Euspira lewisii and the euthyneurans Haminoea vesicula (Opisthobranchia) and Siphonaria denticulata (Pulmonata) conformed to previously described growth patterns for their respective major clades. Furthermore, the caenogastropod
continued to lengthen the prototroch (ciliary band for swimming and feeding) and to differentiate prospective post-metamorphic
structures (gill filaments and radular teeth) during delayed metamorphosis. Larvae of the neritimorph Nerita atramentosa arrested shell growth during delayed metamorphosis but the radula continued to elongate, a pattern most similar to that of
non-feeding larvae of Haliotis, a vetigastropod genus. Character mapping on a phylogenetic hypothesis suggests that large larval size and capacity for continued
growth during delayed metamorphosis, as exhibited by some caenogastropods, is a derived innovation among feeding gastropod
larvae. This novelty may have facilitated post-metamorphic evolution of predatory feeding using a long proboscis. |
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