Reinforcement in the banded darter Etheostoma zonale: the effect of sex and sympatry on preferences

Reinforcement occurs when selection against hybrid offspring strengthens
behavioral isolation between parental species and may be an important
factor in speciation. Theoretical models and experimental evidence
indicate that both female and male preferences can be strengthened upon
secondary contact via reinforcement. However, the question remains whether
this process is more likely to affect the preferences of one sex or the
other. Males of polygynous species are often predicted to exhibit weaker
preferences than females, potentially limiting the ability for
reinforcement to shape male preferences. Yet, in darters (Percidae:
Etheostoma), male preference for conspecific mates appears to arise before
female preferences during the early stages of allopatric speciation, and
research suggests that male, but not female, preferences become reinforced
upon secondary contact. In the current study, we aimed to determine
whether the geographically widespread darter species Etheostoma zonale
exhibits a signature of reinforcement, by comparing the strength of
preference for conspecific mates between populations that are sympatric
and allopatric with respect to a close congener, E. barrenense. We
examined the strength of preference for conspecifics for males and females
separately to determine if the preferences of one or both sexes have been
strengthened by reinforcement. Our results show that both sexes of E.
zonale from sympatric populations exhibit stronger conspecific preferences
than E. zonale from allopatric populations, but that female preferences
appear to be more strongly reinforced than male preferences. Results
therefore suggest that reinforcement of female preferences may promote
behavioral isolation upon secondary contact, even in a genus that is
characterized by pervasive male mate choice.