Daphnia galeata and D. dentifera are geographically and ecologically separated whereas their hybrids occur in intermediate habitats: a survey of 44 Chinese lakes

The idea that hybridization promotes range expansion has received recent attention, but support from field studies is limited. We hypothesized that in the cladoceran waterflea Daphnia, parental species are geographically and ecologically separated, whereas hybrids occupy intermediate or occasionally extreme environments, potentially facilitating range expansion of parental species. We assessed the distribution of Daphnia dentifera, D. galeata and their interspecific hybrids across 44 lakes in China (using mitochondrial and microsatellite markers), and related it to geographical and environmental lake descriptors. Parental species were geographically separated: D. dentifera occurred in western and central China, and D. galeata in eastern and central China, whereas hybrids were found in the western and central parts of country. However, after controlling for geographical differences, the effect of environment on species distribution was strong and significant. Specifically, D. dentifera w...