Meeting Abstract

74.3  Friday, Jan. 7  Habitat transition and ecological speciation with gene flow in Daphnia pulex species complex CONSTANTIN, A.*; CREASE, T.J.; CRISTESCU, M.E.; University of Windsor; University of Guelph; University of Windsor anna.const@gmail.com

The relative contribution of geography and ecology to the diversification of freshwater zooplankton is little understood. While allopatric isolation is considered the main mechanism of speciation, habitat transitions followed by ecological isolation remain largely unexplored. This work looks at the evolutionary consequences of habitat transition events in a relatively young ecological species pair, pond Daphnia pulex and lake Daphnia pulicaria, by surveying 363 individuals from 9 lake and 8 pond habitats in Ontario, Michigan, and Illinois, with a focus on 2 pond and 3 lake populations distributed in close geographic proximity. We conducted a phylogenetic and a population genetic study using the mitochondrial NADH dehydrogenase 5 gene, the nuclear Lactate dehydrogenase A locus, and 21 microsatellite markers. The phylogenetic survey revealed the occurrence of two different mitochondrial lineages; a “lake” type and a “pond” type within all 3 lakes. This finding is in contrast with the phylogenetic signal revealed by the nuclear markers, which consistently group Daphnia based on habitat. The strong phylogenetic discordant signal between nuclear and mitochondrial markers suggests that hybridization and introgression of pond D. pulex genes into the D. pulicaria genome has been occurring in lakes and that these events are relatively recent. Despite evidence for historical gene flow between pond and lake populations, high level of genetic differentiation was found between lakes and ponds and interestingly, migration rates were found to be higher from pond to lake than lake to pond, indicating a likely scenario of pond to lake habitat transition and suggesting the existence of strong habitat isolating barriers between pond and lake Daphnia.