MIXED-SPECIES SHOALS AND THE MAINTENANCE OF A SEXUAL-ASEXUAL MATING SYSTEM IN MOLLIES

The mating system of the sexual-asexual complex of sailfin mollies, Po ecilia latipinna, and Amazon mollies, P. formosa, depends on the close proximity of individuals in aggregations or shoals because P. formosa is gynogenetic (that is, sperm only initiate embryogenesis but do not contribute genetic material) and must be inseminated by male P. latip inna. Furthermore, female P. latipinna copy the mate choice of female P. formosa with the result that male P. latipinna become more attracti ve to conspecific females when they mate with P. formosa. Mate copying of heterospecifics has not been reported in other systems, and in mol lies it could result from the inability of females to discriminate spe cies. In experiments both P. formosa and P. latipinna females preferre d to associate with a conspecific than a heterospecific, but preferred a larger heterospecific group to a smaller conspecific one. Females c an thus discriminate between conspecific and heterospecific females, s o that heterospecific mate copying is not a result of mistaken identit y. Females preferred to associate with conspecifics, but this preferen ce was overridden by preference for larger groups although the thresho ld differed between the two species. (C) 1996 The Association for the Study of Animal Behaviour