Spatial patterns of extra‐pair paternity: beyond paternity gains and losses

Abstract

Summary1. Most studies on extra-pair paternity (EPP) focus either on a specific male's extra-pair gains or his extra-pair losses. For an individual bird however, mate choice or mate availability may underlie strong spatial restrictions. Disregarding this spatial aspect may underestimate or mask effects of parameters influencing observed EPP patterns. 2. Here, we propose a spatially explicit model for investigating the probability of having extra-pair offspring (EPO) within local networks of breeding pairs. The data set includes all realized and unrealized potential extra-pair matings. This method is biologically meaningful because it allows (a) considering both members of an extra-pair mating and their social mates, and (b) direct modelling of the spatial context in which extra-pair behaviour occurs. The method has the advantage that it can provide inference about the relative contribution of spatial and non-spatial parameters, and about the relative importance of male and female neighbourhoods. 3. We apply this method to parentage data from 1025 broods collected over 12 breeding seasons in two independent study populations of blue tits (Cyanistes caeruleus). We investigate a set of predictions based on the EPP literature, namely that EPP depends on male age and body size, breeding density and breeding synchrony. In all analyses, we control for breeding distance, a parameter that is expected to influence EPP even under random mating. 4. The results show that older and larger males were more likely to sire EPO, but both effects decreased with increasing breeding distance. Local breeding density but not synchrony predicted whether a particular male-female combination had EPO, at least in one of the study areas. Apart from breeding distance, male age had the strongest effect on EPP, followed by a measure of breeding density. The method thus allows a comprehensive assessment of the relative importance of different types of spatial and non-spatial parameters to explain variation in the occurrence of EPP, while controlling for the fact that individuals that breed further apart are less likely to have EPO. 5. The proposed approach is not limited to investigate EPP, but can be applied to other behavioural interactions between two individuals, such as dominance, competition and (social) mating.

Sources of (co)variation in alternative siring routes available to male great tits (Parus major)

“…For instance, the immediate social environment of an individual (i.e., mediated by traits of neighboring males and females; e.g., Schlicht et al. ) might impact paternity loss and probability to gain extra‐pair paternity, provided that this social environment varies within males across‐years, thereby causing the observed variation in fertilization routes. Another factor that could cause residual variation in the fertilization routes is male age.…”

Timing of arrival in the breeding area is repeatable and affects reproductive success in a non‐migratory population of blue tits

“…In blue tits (and other species), yearling males are less likely to sire extra‐pair young than adult males (e.g. Schlicht et al, ). However, this cannot explain the current result, because all individuals in this study are adults.…”

“…It is a secondary cavity‐nester which readily accepts nest boxes for roosting and breeding. The majority of blue tits are socially monogamous, but extra‐pair paternity is common (Schlicht, Valcu, & Kempenaers, ). In our population, pairs produce one clutch per season, except when renesting after clutch or brood failure.…”

“…We extracted DNA from all blood samples and from all egg or nestling tissue samples, genotyped all samples using 14 highly polymorphic microsatellite markers and one sex chromosome‐linked marker, and determined parentage following the procedures outlined in Schlicht et al (). Because the identity of the biological mother is usually known with certainty, the probability of erroneous assignment of males as sires of the nestlings is close to zero.…”

Female collared flycatchers choose neighbouring and older extra‐pair partners from the pool of males around their nests

“…In addition to male traits, some environmental factors may influence the distribution of extra‐pair paternity. For example, spatial and temporal availability of potential extra‐pair partners should be considered (Schlicht et al ). Extra‐pair males are often neighbors (Smith , Neudorf et al , Mays and Ritchison , Pedersen et al ), but it is not always the case; extra‐pair males can also come from distant territories (Woolfenden et al , Canal et al ).…”