, Volume 103, Issue 3, pp 349-358

Planktotrophic larval development is associated with a restricted geographic range in Lasaea, a genus of brooding, hermaphroditic bivalves

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Abstract

Members of the intertidal, near-cosmopolitan mollusc genus Lasaea brood their young either to a planktotrophic veliger or crawl-away juvenile stage of development. Developmental mode can be reliably inferred from brood masses and from prodissoconch structure. I have conducted a global developmental survey of this genus based mainly on examination of hundreds of museum lots. With one exception, Lasaea species with a planktotrophic larval development were restricted to the western Pacific. Congeners that lack planktotrophic larvae were found on all continents apart from Antarctica, and also on a large number of oceanic islands. These results indicate that (1) Lasaea “species” releasing crawl-away juveniles have a markedly greater collective geographic range than congeners with planktotrophic larvae; (2) pelagic larvae are not necessary for long-distance dispersal in this genus; (3) rafting has played a key role in the evolutionary success of the genus Lasaea; (4) cross-fertilizing Lasaea species with feeding larvae are less successful in utilizing chance rafting events to colonize new areas than are congeners lacking these traits.

Communicated by M. G. Hadfield, Honolulu