A decade of sexual selection studies reveals patterns and processes of fitness variation in male collared lizards

Abstract

Territory defence is widely assumed to be adaptive because it enhances reproductive success. However, empirical evidence for such a benefit is scarce or nonexistent for many types of territorial organisms. The roles of intraspecific aggression versus interactions with females in successful breeding by territorial males are also still poorly understood in lower tetrapods, including lizards. We address both of these important issues using 10 years of data on genetic parentage combined with field behavioural studies in collared lizards, Crotaphytus collaris . As predicted, territorial males (T-males) had more mates, sired markedly more total offspring and sired more surviving offspring with more females than did nonterritorial (NT) males. Territorial males in structurally simpler habitats sired a higher proportion of each female's offspring than their counterparts in complex habitats, indicating that the ability of T-males to accrue mating benefits is highest where topography maximizes contact with multiple females. All measures of T-male reproductive success increased with travel rate but decreased with the time spent courting individual females, suggesting a fitness trade-off between these behaviours. We found no evidence that aggressive behaviour was linked to any component of male fitness. Hence, activities of territory owners appear to be shaped by sexual selection to enhance mating opportunities rather than to aggressively dominate same-sex rivals. Our study illustrates the value of long-term research documenting behaviour and fitness of free-ranging individuals over multiple reproductive cycles in evaluating fundamental questions about the adaptive significance of social tactics. • Territorial male collared lizards had higher fitness than nonterritorial males. • Territorial tactics increased mating more effectively in simpler habitats. • Fitness of territory owners increased with travel but not with aggressive behaviour. • Limiting courtship per female promoted travel to interact with additional mates. • Male behaviour is selected to enhance interactions with multiple female mates.