Data from: A test of genetic models for the evolutionary maintenance of same-sex sexual behaviour

The evolutionary maintenance of same-sex sexual behaviour (SSB) has
received increasing attention because it is perceived to be an
evolutionary paradox. The genetic basis of SSB is almost wholly unknown in
non-human animals, though this is key to understanding its persistence.
Recent theoretical work has yielded broadly applicable predictions centred
on two genetic models for SSB: overdominance and sexual antagonism. Using
Drosophila melanogaster, we assayed natural genetic variation for male SSB
and empirically tested predictions about the mode of inheritance and
fitness consequences of alleles influencing its expression. We screened 50
inbred lines derived from a wild population for male–male courtship and
copulation behaviour, and examined crosses between the lines for evidence
of overdominance and antagonistic fecundity selection. Consistent
variation among lines revealed heritable genetic variation for SSB, but
the nature of the genetic variation was complex. Phenotypic and fitness
variation was consistent with expectations under overdominance, although
predictions of the sexual antagonism model were also supported. We found
an unexpected and strong paternal effect on the expression of SSB,
suggesting possible Y-linkage of the trait. Our results inform
evolutionary genetic mechanisms that might maintain low but persistently
observed levels of male SSB in D. melanogaster, but highlight a need for
broader taxonomic representation in studies of its evolutionary causes.