During range expansion, dispersing individuals encounter novel environments with different evolutionary pressures that theoretically increase propensity to disperse and fecundity but decrease competitive ability. Dispersal, competition, and fecundity (DCF) have been classically studied singularly or as two naturally, negatively correlated traits. However, evolutionary selection of multiple traits may increase survivorship, competitive behavior, and colonization rate, affecting metapopulation dynamics, increasing range expansion speed, and promoting interspecific coexistence. Thus we asked, (1) what phenotypes evolve at the range margin compared to the range core when DCF traits are selected individually or in conjunction with another trait? and (2) how do these populations interact with a competing species?
To simulate environments similar to a range core and edge, we created 22 genetic lines in which each DCF trait was individually or consecutively selected for dispersal-competition lines. The flour beetle species Tribolium castaneum and T. confusum were used as they naturally coexist and have different life history traits. Each DCF trait was measured every other generation. Dispersal propensity was defined as proportion emigrated. Competition comprised the number of surviving offspring in the presence versus the absence of the competing species. Lastly, fecundity was the offspring count from a mated pair.
Results/Conclusions
Three generations have been selected for each of the 22 treatments. During this time, the low dispersal, low competition groups had lower emigration for both T. castaneum (t4=2.77, p=0.025) and T. confusum (t2=7.928, p<0.01). However, when comparing all low and high dispersal selected lines together, high dispersal lines had a significantly greater proportion emigrating (t38=1.738, p=0.045). Competitive abilities did not change in the first two generations despite treatment. However, fecundity increased in each line (t86=19.75, p<0.001).
With the greater dispersal propensity in the high selected lines, range expansion speed will also increase. Although multiple trait interactions have not been observed, the project will continue for an additional 5 generations. We predict that high dispersers will continue to increase their range expansion speed, but this increase will be less for those that are consecutively selected for competitive ability. However, intraspecific competitive ability selection will increase survivorship when in a community. We predict that it is the combination of selected traits that allow for persistent range expansion, not just opposing trait tradeoffs.