Investigating Biologic Repeatability at Different Biological Levels

Repeated evolution in biology is widespread among morphologic forms but also recognized at essentially all biological levels. Organisms achieving the same functional goal is reported at the level of simple biochemical pathways, complex tissue types, and even social behaviors. Before the advent of the sequencing revolution, studies of repeated evolution centered on morphologic data. With the power of current DNA technologies researchers are increasingly focusing on understanding how repeated forms at the phenotypic level arise at the genetic level. Most of the trait's biologists' study are likely continuous and polygenic in nature. Additionally, within diploid sexual organisms, these traits often could exist within populations which consist predominantly of standing genetic variation, opening the door for drift to create genetic variance dictated by history and not fitness. To investigate genetic repeatability from standing genetic variation and retain a possible insight into macroevolutionary outcomes I designed an experiment using two recently diverged species of Drosophila. To create a parallel phenotypic response, we designed a parallel divergent artificial selection experiment in D. melanogaster and D. simulans predominantly selecting on a multi-trait index of proportional length of the three major leg segments. We complimented the phenotypic experiment with population-based whole genome DNA sequencing of individuals from the initial populations and the evolved populations artificially selected for fifteen generations. An experimental design resulting in low estimates of Ne and concurrently strong selection yielded a complicated and idiosyncratic genetic response even within replicates of a species. Evolve and Resequence and convergent evolution experimental designs and null hypotheses often use an expectation that repeated genetics underlies repeated phenotypes. We suggest more skepticism that repeated phenotypes might not be the product of parallel genetic responses for complex quantitative traits..