A REEVALUATION OF THE RED-QUEEN MODEL FOR THE MAINTENANCE OF SEX IN ACLONAL-SEXUAL FISH COMPLEX (POECILIIDAE, POECILIOPSIS)

The validity of the assumptions of the Red Queen model for the mainten ance of sexual reproduction was reassessed using life-history data col lected from clonal and sexual fish in the genus Poeciliopsis. A previo us study using these strains (one sexual, two clonal) indicated that s ex might be maintained by coevolutionary processes outlined in the Red Queen model. However, the previous study did not test the assumption that parasitism negatively affects the host's fitness. The current stu dy was undertaken to address this issue, as well as to reevaluate the assumptions of the Red Queen model in this complex. Data on size, fecu ndity, and parasitic intensity were collected from fish from seven Mex ican pools. Parasitic intensity was highest for one clone, but intensi ty was not correlated with clonal frequency, as assumed by the Red Que en model. Variance in parasitic intensity was not reduced in the clona l strains relative to the sexual strain, and intensity was not correla ted with fecundity. These data, combined with aspects of the parasite' s biology, indicate that the Red Queen model is unlikely to maintain s ex in this clonal-sexual complex.