Bite force, body size, and octopamine mediate mating interactions in the house cricket (Acheta domesticus)

Mating interactions are rife with conflict because the evolutionary
interests of males and females seldom coincide. Intersexual conflict
affects sexual selection, yet the proximate factors underlying male
coercive ability and female resistance are poorly understood. Male combat
outcomes are often influenced by bite force, with superior biters being
more likely to achieve victory over poorer biters in a range of species,
including crickets. If good performers also achieve mating success through
sexual coercion, then bite force might play a role in intersexual conflict
as well. We tested the capacity of bite force to influence mating
interactions in house crickets both directly by measuring bite forces of
males and females and by altering male bite capacity through
neuropharmacological manipulation. In addition, the invertebrate
neurotransmitter octopamine both mediates aggression and underlies
motivation to bite in male house crickets. By blocking octopamine
receptors through the application of an antagonist, epinastine, we tested
the effects of reduced bite force on male mating success. Our results show
that male bite capacity, in combination with body size, influences both
the likelihood and the outcomes of mating interactions, whereas treatment
of males with epinastine eliminates motivation to mate. Our results
suggest a functional role for bite force in affecting both sexual conflict
and sexual selection and expand our knowledge of the influence of biogenic
amines on reproductive behavior.