The effect of male-male competition and ornament size on mean and variance of courtship intensity towards heterospecific and conspecific females

Abstract

Discrimination between hetero- and conspecifics is the elementary choice an individual performs when searching for potential mates. The level of selectivity and strength of species discrimination is modified by variance in the quality of females, level of the male’s reproductive investment, mate search costs, and the competitive environment. The effect of the competitive environment on both species discrimination and conspecific mate choice has seldom been studied simultaneously. We experimentally manipulated territorial competition ofCalopteryx splendensdamselfly males in the wild, and asked two questions. First, does increased competition influence the territorial males’ responses towards introduced heterospecificC. virgofemales. The effect of the size of the territorial males’ sexual ornaments (wing spot) on their responses towards females was also investigated. Second, does increased competition influence the territorial males’ response towards conspecific females? The effect of the size of the territorial males ornament was again investigated. The mean level of response towards heterospecific females did not change between the control (i.e., no competitors presented) and the competition (i.e., two competitors presented) treatments, but the variance of responses towards heterospecifics was greater in the competition treatment. The territorial males’ responses towards conspecific females did not change between control and competition treatments. These results indicate individual differences in the behavior of males towards heterospecifics when territorial competition was experienced. The observed pattern of discrimination might be adaptive when overall reproductive success is considered.