Histocompatibility analysis of clonal diversity in unisexual hybrids of the killifishes Fundulus heteroclitus and Fundulus diaphanus

Hybrids of the killifishes Fundulus diaphanus and Fundulus heteroclitus, found at two sites on the Atlantic coast of Nova Scotia, are unisexual diploid gynogens. Because there seemed to be many opportunities for the sexual progenitor species to hybridize and form new clones at these sites, we initially had expected that clonal diversity might be high among the hybrids. However, examination of their histocompatibility genomes, via inter-individual scale grafting, provides evidence, albeit not conclusive, that most of the hybrids at the two sites, which are separated by 125 km, comprise a single clone. Grafts made among F. diaphanus were rejected within an average of 16-20 days, establishing that sufficient diversity exists within the histocompatibility genomes of these fish to permit their immune systems to reject foreign melanophores. Grafts made from F. diaphanus to the hybrids were also rejected, within an average of 17-26 days, demonstrating that the hybrids possessed competent immune systems. Grafts made between hybrids were nearly always accepted. Those few that appeared to be rejected were usually accepted when regrafted. Melanophores carried on the graft remained visible for the duration of the study (90-180 days) or, if they slowly disappeared, they did so at a rate comparable with that of autograft scales.