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

Abstract 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 inter-specific F1 hybrids of two recently diverged microcrustacean species Daphnia pulex and D. pulicaria as well as intra-specific F1 hybrids of D. pulex. We identified heterosis in four out of five life-history traits in the inter-specific F1 hybrids. The observation of heterosis in these life-history traits suggests that there are no major genetic incompatibilities between these two species affecting these traits. This also suggests that D. pulex and D. pulicaria are at the early stage of speciation where heterosis can still occur.