BackgroundPre-zygotic barriers often involve some form of sexual selection, usually
interpreted as female choice, as females are typically the choosier sex.
However, males typically show some mate preferences, which are increasingly
reported. Here we document previously uncharacterized male courtship
behavior (effort and song) and cuticular hydrocarbon (CHC) profiles in the
hybridizing crickets Gryllus firmus and G. pennsylvanicus.
These two species exhibit multiple barriers to gene exchange that act
throughout their life history, including a behavioral barrier that results
in increased time to mate in heterospecific pairs.ResultsWe demonstrated that male mate choice (as courtship effort allocation) plays
a more important role in the prezygotic behavioral barrier than previously
recognized. In gryllids females ultimately decide whether or not to mate,
yet we found males were selective by regulating courtship effort intensity
toward the preferred (conspecific) females. Females were also selective by
mating with more intensely courting males, which happened to be
conspecifics. We report no differences in courtship song between the two
species and suggest that the mechanism that allows males to act
differentially towards conspecific and heterospecific females is the
cuticular hydrocarbon (CHC) composition. CHC profiles differed between males
and females of both species, and there were clear differences in CHC
composition between female G. firmus and G. pennsylvanicus
but not between the males of each species.ConclusionAlthough many barriers to gene exchange are known in this system, the
mechanism behind the mate recognition leading to reduced heterospecific
mating remains unknown. The CHC profiles might be the phenotypic cue that
allow males to identify conspecifics and thus to adjust their courtship
intensity accordingly, leading to differential mating between species.