Sympatric Australian Lasaea species (Mollusca: Bivalvia) differ in their ploidy levels, reproductive modes and developmental modes

The cosmopolitan marine bivalve genus Lasaea is predominantly composed of highly polyploid asexual lineages with one exception: the diploid, sexual Australian species L. australis. Two undescribed, direct‐developing congeners co‐occur with the indirect‐developing L. australis on the rocky intertidal of southeastern Australia. One of these, L. colmani sp. nov., is also diploid and sexual. The other direct‐developing congener is an asexual polyploid composed of a variety of clonal lineages. All three sympatric Australian Lasaea congeners are morphologically distinguishable, although prodissoconch distinctions are required to separate large polyploid clams from equivalently‐sized L. australis. Similarities in mitochondrial gene sequence and in shell morphology suggest that L. australis and the Australian sympatric polyploid clones share an exclusive common ancestor despite differing in developmental mode, ploidy and reproductive mode. However, detailed karyological analyses failed to identify a chromosome set morphologically similar to that of L. australis among the sympatric Australian polypoid complement. We propose that generation of the polyploid Australian clones (presumably by hybridization) was followed by radical karyological rearrangement.