Density-dependent dispersal and its impacts on reproductive traits

Background/Question/Methods: As landscapes become increasingly fragmented, the metapopulation concept becomes a valuable tool for managing endangered species or slowing the spread of invasive species. Dispersal is a key component of metapopulations. We know that individuals vary in their sensitivity to local environmental conditions (e.g. density), causing some to disperse and others to stay. While individual variation in dispersal tendency is well known, what is less clear is how individuality in dispersal affects the array of other traits relevant to population growth. Variation in dispersal can produce clusters of similar phenotypes in local habitat patches, known as spatial sorting. Spatial sorting by dispersal and the traits genetically correlated with the disperser phenotype can affect key ecological processes such as reproduction. Here, we connect the multi-level processes of individual variation in dispersal with spatial sorting to understand the ecological and evolutionary feedbacks that affect landscape population dynamics. We hypothesize that selectively breeding long and short distance disperser lines based on sensitivity to patch quality will select for genetically correlated reproductive traits, e.g. fecundity, and behavioral traits, e.g. novel host acceptance, that will lead to spatial sorting. We performed an artificial selection experiment using seed beetles, Callosobruchus maculatus, for 8 generations. Afterwards, we performed multiple behavioral tests to assess if traits of female reproductive investment and novel host acceptance coevolved with dispersal.

Results/Conclusions: After 8 generations, the long-distance disperser lines moved significantly farther than the control lines, suggesting that they evolved a higher sensitivity to patch quality. We reared all lines in a common garden environment for one generation and measured fecundity and novel host acceptance. We expect to find that females from long-distance disperser lines will have a reduced fecundity and increased acceptance of novel hosts, whereas females from short-distance disperser lines will have a high fecundity and low acceptance of novel hosts compared to controls. These expected differences should lead to spatial sorting of a population which affects the spread and connectivity of patches within a landscape. This project aims to experimentally determine the traits correlated with dispersal to understand how individual sensitivity to diminishing habitat quality leads to spatial sorting of populations and the associated impacts on regional population dynamics.