Inferring dispersal patterns in aquatic insects from Bayesian gene flow analysis and model selection

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Although dispersal is a central life-history trait for the understanding of organismal distributions, little is known regarding dispersal rates and modes in freshwater organisms. This is especially true for long-distance dispersal (>10km) which is important for (re-)colonization of new or re-stored habitats. In contrast to hololimnic invertebrates, most aquatic insects are not solely restricted to instream dispersal, but are potentially capable of active over-land dispersal in the wing-carrying adult stage. We chose three species of aquatic insects from different orders (Ephemeroptera, Plecoptera, Trichoptera) as model species to test the hypothesis that populations of merolimnic insects are effectively connected across stream catchments by gene-flow through adult long-distance (>10km) dispersal. Rates and directions of currently ongoing gene flow will be investigated within and among streams in the well-characterized Fulda/Werra stream system and adjacent catchments. First we will investigate genetic differentiation of populations within and among catchments using high-resolution microsatellite analysis. In order to distinguish between present and past gene flow, we will use genotypic data to check for recent immigrants and to assign them to source populations. This approach will allow estimating currently ongoing gene flow for all three model species within our study region. In addition, we will implement historical abundance data and genetic information in various models differing in the rates and modes of dispersal. Best models for each species will be chosen using model-selection. Gathered information on dispersal modes (in-stream vs. across-stream) and rates of the three model species will help to understand connectivity of aquatic insect populations in lotic systems and will contribute to our understanding of recolonization processes in restored fresh-water ecosystems.