Understanding Variation in Extra-Pair Paternity in Birds: A Focus on Neotropical Birds

Abstract

Variation in life-history traits has long captivated ecologists and evolutionary biologists. Classical studies of life-history theory identify latitudinal clines in life-history traits and, as a result, there are now several ecological and evolutionary hypotheses that attempt to explain this variation. Extra-pair paternity is considered a life-history trait, and much research has been done to try to disentangle the causes of variation in this trait. One ecological hypothesis proposed to explain geographic variation in extra-pair paternity is the breeding synchrony hypothesis. The prediction of this hypothesis is that synchrony increases towards the poles because of shorter breeding seasons; rates of extra-pair paternity are therefore expected to increase towards higher latitudes. However, the scarcity of studies of extra-pair paternity rates among Neotropical birds to date makes it difficult to predict any direction of change. In this chapter I argue that it is still premature to look at why species differ in extra-pair paternity rates, as the sampling of species that inhabit the Neotropics, the most biodiverse realm on Earth, is still very poor and insufficient. In addition, I agree with other researchers that our scientific views are biased by studies in the less diverse Palearctic and Holarctic realms, which may have slowed our understanding of the patterns and processes in the Neotropics. I explore here these two perspectives by examining interspecific variation in genetic mating system in the swallow genus Tachycineta, and look at geographic variation in synchrony and extra-pair paternity. I found that differences in rates of extra-pair paternity among species of this genus are not explained by differences in their breeding synchrony, and that the large variation in breeding synchrony experienced by the different species/populations is not related to latitude. In fact, neither synchrony nor extra-pair paternity followed the predicted pattern of latitudinal variation. Work on Tachycineta helps redress the paucity of information on tropical and south temperate species and the underrepresentation of closely related taxa that characterized previous studies. It also reminds us of the complexity of relationships among life-history traits and their environmental influences, forcing us to consider more than one hypothesis and causal path in explaining hemisphere-wide patterns in life-histories.