The Chelidonura tsurugensis-sandrana (Gastropoda: Cephalaspidea) species complex: Do reproductive decisions maintain colour polymorphism?

Abstract

Cephalaspid gastropod molluscs are increasingly being utilized in studies of tradeoffs associated with conflicts in simultaneous hermaphroditic reproduction. Chelidonura sandrana exhibits a wide range of colour forms, from black to yellow-spotted or marked with white. One of these colour morphs was described as Chelidonura tsurugensis Baba & Abe, 1959, while others have been accepted as natural variation within C. sandrana Rudman, 1973. Previous work has mostly assumed (1) that colour forms represent the same species and (2) that reproductive behaviour does not differ among colour forms. Mating behaviour between three co-occurring colour forms (simplified to 'black', 'yellow' and 'white') of the Chelidonura tsurugensis-sandrana species complex was investigated to test the above assumptions. Individuals of each colour form were crossed with individuals of the same form, and then with each of the two other colour forms, and with additional species as controls. Mating frequency, duration and an individuals role of sperm donor or receiver were recorded. The results show that there was no evidence for positive assortative mating with respect to colour form. Instead, at least one colour form was shown to mate significantly more often, and for longer, with individuals of colour forms other than its own. There was no evidence for trading of intromissions or intromission duration among colour forms. Although all three colour forms readily mate and behave like a single biological species, the questionable identity of C. tsurugensis prevents synonymization of C. sandrana with this species. Conservatively, we suggest that until a systematic revision of Chelidonura is carried out, the application of the name C. tsurugensis should be restricted to Japan, and elsewhere the yellow-spotted colour form should be referred to as C. sandrana. © 2011 The Author.