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

Abstract

As species do not live in isolation from each other, they are faced with an elementary choice when searching for a mating partner: a choice between conand heterospecific individuals. Despite the remarkable research effort on hybridization and its avoidance, there are still some less well covered areas, e.g. what is the role of males in hybridization, what patterns are found in sympatric wild populations, what role do alternative reproductive tactics (ARTs) have on the likelihood of heterospecific matings, and what are the true costs of heterospecific interactions. In this thesis I first quantify the frequency of hybridization, backcrossing and heterospecific matings in sympatric wild populations of Calopteryx splendens and C. virgo damselflies in Finland. The possible influence of population densities, relative abundances of the species, and operational sex ratios on the frequency of heterospecific matings is also investigated. The second aim is to investigate how the intensity of territorial competition influences males' reproductive response to a heterospecific female. Finally, I dissect the importance of male ARTs on hybridization propensity and I attempt to quantify the reproductive costs that males' hybridization propensity inflicts among the tactics. The results imply a major role for C. splendens males in heterospecific reproductive interactions between the study species. Especially territorial males seem to be prone to hybridization, and the prevalence of hybridization is increased with a high availability of C. virgo females. Hybridization seems to be costly because there was high discordance between heterospecific mating frequency and observed numbers of hybrids. However, heterospecific courtship did not reduce conspecific mating success. The results also show that C. splendens males are able to adjust their level of heterospecific courtship according to the competitive environment as well as to the ART it follows. My thesis is a step towards understanding the causes of species reproductive interactions in wild populations.