Differentiation in putative male sex pheromone components across and within populations of the African butterfly <i>Bicyclus anynana</i> as a potential driver of reproductive isolation

Abstract:
Sexual traits are often the most divergent characters among closely
related species, suggesting an important role of sexual traits in
speciation. However, to prove this, we need to show that sexual trait
differences accumulate before or during the speciation process, rather
than being a consequence of it. Here, we contrast patterns of divergence
among putative male sex pheromone (pMSP) composition and the genetic
structure inferred from variation in the mitochondrial cytochrome
oxidase 1 and nuclear CAD loci in the African butterfly Bicyclus anynana
(Butler, 1879) to determine whether the evolution of “pheromonal
dialects” occurs before or after the differentiation process. We
observed differences in abundance of some shared pMSP components as well
as differences in the composition of the pMSP among B. anynana populations. In addition, B. anynana
individuals from Kenya displayed differences in the pMSP composition
within a single population that appeared not associated with genetic
differences. These differences in pMSP composition both between and
within B. anynana populations were as large as those found between different Bicyclus species. Our results suggest that “pheromonal dialects” evolved within and among populations of B. anynana and may therefore act as precursors of an ongoing speciation process.