The evolution of extra-pair paternity and paternal care in birds

Abstract

Extra-pair paternity (EPP) influences the relatedness between social parents and offspring. Therefore, one might expect the level of EPP to influence levels of paternal investment. Here, we investigated the effect of variation in EPP rates on male contributions to parental care within a phylogenetic framework of up to 271 primarily socially monogamous bird species representing 85 families. We used proportion of male provisioning and occurrence of male incubation and nestbuilding as measures of paternal care. We tested the relationship between EPP rates and different components of paternal care while controlling for various life-history traits, namely lifespan, clutch size, and body mass in a phylogenetic path analysis framework. EPP was significantly negatively associated with the occurrence (i.e., whether males participate or not) of male nestbuilding and incubation, but not with the relative amount (proportion) of nestbuilding or incubation performed by the male. Importantly, the proportion of provisioning and biomass delivery by males was clearly negatively associated with EPP. These analyses thus confirm that the effect of EPP on proportion of provisioning visits by males is similar to proportion of biomass delivery, an often assumed but rarely tested assumption. Analysing only Passerine species provided similar results, although only proportion of provisioning was significantly negatively associated with EPP. This study, therefore, provides the most comprehensive support to date of a negative relationship between EPP and paternal care across species. However, a causal relationship between EPP and paternal care cannot necessarily be concluded. We also identify key methodological improvements for future research within the topic.

Keywords: extra-pair paternity; incubation; life history; nestbuilding; parental care; phylogenetic path analysis; provisioning.

Figure 1

Phylogenetic path diagrams conceptualizing the relationships between key life-history traits, EPP for the four different measurements of paternal care: (a) occurrence of male nestbuilding; (b) occurrence of male incubation; (c) proportion of male provisioning; and (d) proportion of male biomass delivery. Values on each path arrow show phylogenetic regression coefficients, with bold values indicating statistically significant associations (P < 0.05). Sample size (n) for each analysis is also shown under the paternal care measure box.

Figure 2

Relationships between the four different measurements of parental care and EPP. Each datapoint represent a species and the phylogenetic regression lines are shown.

Figure 3

The evolution of EPP and proportion of male provisioning for 108 species, with both male provisioning proportion and EPP estimates color-coded. Both scales ranges from 0% (red) to 100% (dark blue), and EPP ranges from 0% to 65%, while proportion of male provisioning ranges from 0% to 100%. The timescale is in million years ago (Ma).