Socio-ecological conditions and female infidelity in the Seychelles warbler

Abstract

Within socially monogamous breeding systems, levels of extra-pair paternity can vary not only between species, populations, and individuals, but also across time. Uncovering how different extrinsic conditions (ecological, demographic, and social) influence this behavior will help shed light on the factors driving its evolution. Here, we simultaneously address multiple socio-ecological conditions potentially influencing female infidelity in a natural population of the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis. Our contained study population has been monitored for more than 25 years, enabling us to capture variation in socio-ecological conditions between individuals and across time and to accurately assign parentage. We test hypotheses predicting the influence of territory quality, breeding density and synchrony, group size and composition (number and sex of subordinates), and inbreeding avoidance on female infidelity. We find that a larger group size promotes the likelihood of extra-pair paternity in offspring from both dominant and subordinate females, but this paternity is almost always gained by dominant males from outside the group (not by subordinate males within the group). Higher relatedness between a mother and the dominant male in her group also results in more extra-pair paternity—but only for subordinate females—and this does not prevent inbreeding occurring in this population. Our findings highlight the role of social conditions favoring infidelity and contribute toward understanding the evolution of this enigmatic behavior.

Age‐dependent changes in infidelity in Seychelles warblers

“…In territories with cooperative breeding, helpers provide load‐lightening to the dominant pair (van Boheemen et al., 2019; Hammers et al., 2019) and this might liberate dominant females from the costs imposed by male retaliation (Mulder, Dunn, Cockburn, Lazenby‐Cohen, & Howell, 1994). Contrary to the expectation based on this logic, the presence of helpers is not associated with higher dominant female extra‐group reproduction in the Seychelles warbler (Raj Pant et al., 2019).…”

“…By including age of first reproduction and age of last reproduction (or longevity) in addition to age in the same mixed model, this approach allows us to quantify the within‐individual effect of age (expressed by the age term) while controlling for selective appearance and disappearance (expressed by age of first and last reproduction/longevity, respectively). Here, we modelled selective appearance using the age of first dominance for males, to account for when they could potentially start breeding (virtually all paternity is obtained by dominant males in the Seychelles warbler; Raj Pant et al., 2019). Because females can reproduce before gaining dominance, we used the age at which females were first assigned an offspring as subordinates or the age of first dominance—whichever came first (subsequently termed “age of first dominance” for simplicity).…”

Contemporary evolution of the viral-sensing TLR3 gene in an isolated vertebrate population

“…Although 44% of female subordinates gain reproductive success by co-breeding, male subordinates rarely gain paternity (Richardson et al, 2002;Raj Pant, Komdeur, Burke, Dugdale, & Richardson, 2019). Extra-pair paternity is frequent in this species (Richardson et al, 2001), with 41% of offspring fathered outside the natal territory (Raj Pant et al, 2019).…”

“…Some adult birds delay independent breeding and become subordinates (Kingma, Bebbington, Hammers, Richardson, & Komdeur, 2016), and may help raise offspring (Komdeur, 1992, Hammers et al 2019. Although 44% of female subordinates gain reproductive success by co-breeding, male subordinates rarely gain paternity (Richardson et al, 2002;Raj Pant, Komdeur, Burke, Dugdale, & Richardson, 2019). Extra-pair paternity is frequent in this species (Richardson et al, 2001), with 41% of offspring fathered outside the natal territory (Raj Pant et al, 2019).…”

Haematocrit, age and survival in a vertebrate population

“…We found that haematocrit was lower in female, compared to male, Seychelles warblers, but only for dominant breeders. This suggests an effect of reproduction on haematocrit, given that dominant breeders produce the vast majority of offspring in the population (Richardson et al, 2001;Raj Pant et al, 2019) and sampling coincided with peaks in breeding activity (Komdeur and Daan, 2005). A welldocumented phenomenon (see Fair et al, 2007) in female birds is reproductive anemia -a reduction in haematocrit during egg-laying due to the pleiotropic effects of elevated estrogen (Williams et al, 2004;Wagner et al, 2008).…”