Courtship song does not increase the rate of adaptation to a thermally stressful environment in a Drosophila melanogaster laboratory population

Abstract

Courtship song in D. melanogaster contributes substantially to male mating success through female selection. We used experimental evolution to test whether this display trait is maintained through adaptive female selection because it indicates heritable male quality for thermal stress tolerance. We used non-displaying, outbred populations of D. melanogaster (nub1) mutants and measured their rate of adaptation to a new, thermally stressful environment, relative to wild-type control populations that retained courtship song. This design retains sexually selected conflict in both treatments. Thermal stress should select across genomes for newly beneficial alleles, increasing the available genetic and phenotypic variation and, therefore, the magnitude of female benefit derived from courtship song. Following introduction to the thermally stressful environment, net reproductive rate decreased 50% over four generations, and then increased 19% over the following 16 generations. There were no differences between the treatments. Possible explanations for these results are discussed.

Figure 1. Total surviving adult progeny per female.

Populations entered the thermal stress regime in generation 6. There was no difference between treatments (p = 0.64). Error bars are ± one standard error. See Table 1b.

Figure 2. Net reproductive rate per female.

This measure includes all adults that were available for collection each generation during the normal collection period. Populations entered the thermal stress regime in generation 6. There was no difference between treatments (p = 0.63). Error bars are ± one standard error. See Table 1a.