Local Adaptation of Male Sexual Fitness in Drosophila melanogaster

Mate competition gives rise to sexual selection, and healthier, more
vigorous males are likely to be superior competitors. Because most genes
are likely to impact an individual’s vigor, sexual selection should act
across much of the genome to favor the same alleles as natural selection,
thereby promoting adaptation. On the other side of the coin, adaptation to
an environment should enhance male sexual fitness in that environment
because it is likely to increase the overall vigor of individuals within a
population. Surprisingly, there are few tests of this latter prediction,
and results are mixed. Taking advantage of a long-term evolution
experiment involving replicate populations of Drosophila melanogaster, we
performed a reciprocal transplant in which populations evolved in one of
two alternative larval environments were reared in each of these two
environments. Larval survival was quantified as an index of non-sexual
fitness reflective of adaptation to their local larval environment, and
the sexual fitness of the males that ecolosed was then compared via a
comprehensive measure that included pre- and post-copulatory reproductive
success in a competitive assay performed under conditions that closely
mirrored those to which the populations had been evolving. Body size
(adult dry weight) and development time (egg-to-adult eclosion) were also
recorded for males and females that eclosed from the reciprocal
transplant. The results add support to the idea that local adaptation to
the abiotic environment enhances male sexual fitness.