Extra-pair paternity in birds

Abstract

Since the first molecular study providing evidence for mating outside the pair bond in birds over 30 years ago, >500 studies have reported rates of extra-pair paternity (EPP) in >300 bird species. Here, we give a detailed overview of the current literature reporting EPP in birds and highlight the sampling biases and patterns in the data set with respect to taxonomy, avian phylogeny and global regions, knowledge of which will be crucial for correct interpretation of results in future comparative studies. Subsequently, we use this comprehensive dataset to simultaneously test the role of several ecological and life history variables. We do not find clear evidence that variation in EPP across socially monogamous species can be explained by latitude, density (coloniality), migration, generation length, genetic structuring (dispersal distance), or climatic variability, after accounting for phylogeny. These results contrast previous studies, most likely due to the large heterogeneity within species in both EPP and the predictor of interest, indicating that using species averages might be unreliable. Despite the absence of broadscale ecological drivers in explaining interspecific variation in EPP, we suggest that certain behaviours and ecological variables might facilitate or constrain EPP, as indicated by our finding that EPP was negatively associated with latitude within noncolonial species, suggesting a role of breeding synchrony. Thus, rather than focussing on general explanations for variation in EPP across all species, a future focus should be on how various aspects of ecology or life history might have driven variation in EPP among groups of species or populations of the same species. Hence, we argue that variation in EPP can be partly explained when taking the right perspective. This comprehensive overview, and particularly the dataset provided herein will create a foundation for further studies.

Keywords: mating system; microsatellites; parentage; polyandry.

Figure 1

The number of publications per year reporting extra‐pair paternity rates in birds that were included in our dataset after using our rules of exclusion (N = 484 publications). Note that the number of publications for 2017 reflects studies published before 1 August 2017 only

Figure 2

Histogram showing distributions of (a) percentage extra‐pair offspring, and (b) percentage of broods with at least one extra‐pair offspring for biparental socially monogamous and cooperatively breeding species

Figure 3

A phylogenetic tree showing the average proportion of EPP (blue bars) for all sampled socially monogamous bird species, with zero EPP indicated by an empty circle. Orders (in bold) and passerine family names are given to indicate their location in the tree. Taxonomy was based on information provided in Jetz et al. (2012), drawn using a tree based on the Hackett backbone (Hackett et al., 2008) and the Interactive Tree of Life website (Letunic & Bork, 2016)

Figure 4

Average (±SD) EPP rates for biparental socially monogamous passerine families. Only studies based on ≥50 offspring and families where multiple species were sampled were included. Numbers on top indicate the sample sizes (number of species)

Figure 5

A phylogenetic tree showing the distribution of availability of EPP rates for all 194 bird families reported in Jetz et al. (2012). Blue circles indicate families in which EPP has been determined in at least one species, with filled circles indicating EPP > 0 and open circles indicating EPP = 0. Drawn using a tree based on the Hackett backbone (Hackett et al., 2008) and the Interactive Tree of Life website (Letunic & Bork, 2016)

Figure 6

Map showing locations of studies reporting extra‐pair paternity in birds. Levels of EPP at the offspring level are indicated with coloured circles, studies only reporting EPP at the level of the brood are indicated with a square. Map drawn using qgis 3.4 (QGIS Development Team, 2018). For studies that did not report their exact location, approximate coordinates were derived from Google Maps on the basis of the description provided (see Appendix S1)

Figure 7

Repeatability of extra‐pair paternity rates for two randomly selected populations of each of the 49 bird species that have been sampled in more than one population

Figure 8

Boxplot showing the percentage of extra‐pair offspring for species nesting in ‘forest’ (N = 99 species) and ‘reed’ type (N = 10 species) vegetation (Table S5). The box plots show the median, 25th and 75th percentiles; the whiskers indicate the values within 1.5 times the interquartile range and the circle is an outlier

Figure 9

The relationship between extra‐pair paternity and absolute latitude, with each data point reflecting one of the 403 studies on biparental socially monogamous species. The size of the symbols indicates the sample size

Figure 10

The relationship between extra‐pair paternity and latitude for four socially monogamous species that have been sampled in at least 10 different populations. Trendlines show the predictions from a GLM testing the association between latitude and the proportion of extra‐pair offspring for each species (see Model 6 in Appendix S1)