The life history fitness of F-1 hybrids of the microcrustaceans Daphnia pulex and Daphnia pulicaria (Crustacea, Anomopoda)

Negative interaction between alleles that arise independently in diverging populations (i.e., Dobzhansky-Muller incompatibilities) can cause reduction of fitness in their hybrids. However, heterosis in hybrids can emerge if hybridization breaks down detrimental epistatic interaction within parental lineages. In this study, we examined the life history fitness of the interspecific F(1)s of two recently diverged microcrustacean species, Daphnia pulex and D. pulicaria, as well as intraspecific crosses of D. pulex. We identified heterosis in two of five life history traits in the interspecific F(1)s. According to theories that heterosis can transiently emerge in early speciation, the observation of heterosis in these life history traits suggests that there are no major genetic incompatibilities between these two species affecting these traits and that D. pulex and D. pulicaria are at an early stage of speciation.