Poecilogony in the caenogastropod Calyptraea lichen (Mollusca: Gastropoda)

Abstract. In marine invertebrates, polymorphism and polyphenism in mode of development are known as “poecilogony. ” Understanding the environmental correlates of poecilogony and the developmental mechanisms that produce it could contribute to a better understand-ing of evolutionary transitions in mode of development. However, poecilogony is rare in marine invertebrates, with only ten recognized, well-documented cases. Five examples occur in sacoglossan gastropods, and five occur in spionid polychaetes. Here, we document the eleventh case, and the first in a caenogastropod mollusc. Females of Calyptraea lichen collected in the field or reared in the laboratory often produce broods of planktotrophic larvae. They can also be collected with mixed broods, in which each capsule contains plank-totrophic larvae, nurse embryos, and adelphophagic embryos. Adelphophages eat the nurse embryos and hatch as short-lived lecithotrophic larvae, or even as juveniles. Mitochondrial COI and 16S DNA sequences for females with different types of broods differ by less than 0.5%, supporting conspecific status. Some females collected in the field with mixed broods subsequently produced planktotrophic broods, demonstrating that females can produce two different kinds of broods. Calyptraea lichen is therefore polyphenic in two ways: mode of development can vary among embryos within a capsule, and females can change the types of broods they produce. Additional key words: adelphophagy, Calyptraeidae, polyphenism, mode of development, plasticity Alternative phenotypes, the expression of more than one discrete phenotype either during the life-time of an individual or among individuals of the same species, are thought to play a major role in generating biological diversity (West-Eberhard 2003; Schwander & Leimar 2011). Evolutionary transi-tions between different genetically fixed discrete monomorphic states may occur by passage through transitional stages that could include polypheni