A Histocompatibility Analysis of Inheritance in the Unisexual Fish Poeciliopsis 2 monacha-lucida

Poeciliopsis 2 monacha-lucida is a triploid unisexual fish species which reproduces by gynogenesis. Spleen grafts between genetic lines descendent from single, wild-caught females demonstrated that natural populations are comprised of several histocompatibility clones. Histoincompatible clones are characterized by acute allograft reactions. Grafts within genetic lines, i.e. mother to daughter, daughter to mother and between sibs were all accepted as were grafts between histocompatible lines. Inheritance in P. 2 monacha-lucida is strictly clonal. Certain pairs of lines are characterized by unidirectional histocompatibility; i.e., a graft from line A to B is accepted, but the reciprocal graft, line B to A, is rejected. This suggests one clone was derived from the other perhaps by a mutation, a rare gametic fusion or a rare recombinational event. P. 2 monacha-lucida is like another gynogenetic unisexual fish Poecilia formosa in that both species are polyclonal (Kallman, 1962b). These two gynogenetic fishes are a contrast to the thelytokous unisexual lizard Cnemidophorus tesselatus in that populations of the latter usually consist of a single clone (Maslin, 1967). Several factors must affect the clonal structure of natural populations. Selection can act to perpetuate or eliminate clones, whereas stochastic factors always reduce the number of clones. New clones can arise by mutation, rare sexual events such as gametic fusion and recombination, deletion and recurring hybridization between parental species. The preliminary nature of the studies reported to date preclude conclusive judgements as to which factors are most important. It is clearly possible, however, that mutation is not the sole source of new clones and that selection plays some role in main