Abstract

Sexual conflict over reproductive investment can
lead to sexually antagonistic coevolution and
reproductive isolation. It has been suggested that,
unlike most models of allopatric speciation, the
evolution of reproductive isolation through sexually
antagonistic coevolution will occur faster
in large populations as these harbour greater
levels of standing genetic variation, receive larger
numbers of mutations and experience more
intense sexual selection. We tested this in bruchid
beetle populations (Callosobruchus maculatus)
by manipulating population size and standing
genetic variability in replicated lines derived from
founders that had been released from sexual
conflict for 90 generations. We found that after 19
generations of reintroduced sexual conflict, none
of our treatments had evolved significant overall
reproductive isolation among replicate lines.
However, as predicted, measures of reproductive
isolation tended to be greater among larger populations.
We discuss our methodology, arguing
that reproductive isolation is best examined by
performing a matrix of allopatric and sympatric
crosses whereas measurement of divergence
requires crosses with a tester line.