Colour varieties as sibling species in the polychromatic ophiuroid Amphipholis squamata (Echinodermata): evidence from inheritance of body colour and luminescence characters

Abstract

Individuals of Amphipholis squamata from two colour varieties (beige and black) that differ strongly in luminescence performance, were collected from the field and raised in aquaria through three subsequent generations. The ophiuroid is a brooding species and a simultaneous hermaphrodite. Progeny from mature isolated adults and from pairs of adults of the same or of different colour varieties were scored for their characters of body colour and luminescence. Both characters change with age of the individual and reach maximal expression in the adult, the body colour being more marked and the luminescence production more intense and faster. Nevertheless, juveniles of the beige and the black variety were already clearly distinct in body colour and luminescence performance. Also, although body colour became diminished over the three generations in captivity, all progeny, from juvenile to adult, displayed the same characters of body colour and luminescence as the brooding parent. This was confirmed by observation from field-collected individuals whose brooded juveniles were always of the variety of the brooding parent. During rearing, no intermediate variety occurred that would indicate cross-fertilization between varieties. Thus, individuals could have reproduced by cross-fertilization when together with another individual if only of the same variety, or by self-fertilization when alone. Therefore, our results imply that body colour and luminescence characters are genetically determined, and that the beige and the black varieties are distinct sibling species, genetically different and isolated for reproduction.