The cost of infidelity to female reed buntings

Abstract

Females of many socially monogamous bird species accept or even actively seek copulations outside the social pair bond. It has been shown that females profit from extrapair fertilization by increased offspring quality, but extrapair mating may also induce costs to females. We measured parental food provisioning and paternity in the reed bunting, Emberiza schoeniclus, a species with biparental brood care and high levels of extrapair paternity (EPP). We found a negative relationship between the proportion of EPP in broods and paternal care across the local population. Individual males adjusted food provisioning to the amount of EPP between sequential broods. Females did compensate for low male food provisioning. The cost of extrapair fertilizations to females is increased nestling mortality due to the social partner's reduction of brood care. If the mixed mating system of the reed bunting is at an evolutionary equilibrium, we expect that genetic fitness for males as well as for females is maximized. Any costs incurred by extrapair mating should therefore not exceed the benefits for both sexes.

Estimating genetic benefits of polyandry from experimental studies: a meta‐analysis

“…In many species, females gain no apparent direct benefits from mating but incur substantial costs when seeking additional mates (e.g. den Hollander & Gwynne, 2009; Suter et al , 2009). In such cases it is common to invoke genetic benefits to explain polyandry.…”

High level of extrapair fertilization in individual Tibetan azure‐winged magpies and their adaptive responses

“…Relative to the widespread of EPP in socially monogamous species, fewer EPM have been reported and in those reports the level of EPM is significantly lower than that of EPP (Griffith et al , Li et al ). The territoriality of breeders is the main reason for the reduction of the possibility of a female to parasitize a nest (Berger et al ).…”

“…The major cost of female cuckoldry in bi‐parental care systems is the reduction of parental care by cuckolded males, which has been considered as the major factor constraining an individual to engage in EPFs (Briskie et al , Suter et al , Perlut et al ). Therefore, if females do not rely on their social males for raising the brood, they can endure the cost and pursue more EPFs (Hoi‐Leitner et al , Møller , Arnold and Owens ).…”

“…This tradeoff between benefits and costs of EPFs has been widely used to explain EPFs in birds (Møller and Birkhead , Lifjeld et al , Hasselquist and Sherman , Perlut et al ). Yet, many empirical studies have indicated that cuckolded breeders do not change or even increase parental care for the mixed brood (Schwagmeyer et al , Bouwman et al , García‐Vigón et al , Du et al ). Such a counter‐intuitive response of cuckolded individuals is challenging toward explaining the evolution of EPFs in birds.…”

“…When parents cannot raise the entire brood under poor conditions, they may starve some chicks so that the others can survive as lower reproductive success outweighs the cost of starving some chicks under poor conditions (Clark and Wilson 1981, Forbes et al , Slagsvold and Wiebe ). Similarly, when cuckolding females produce a larger than average brood in their own nests and they allocate more paternity to their social mates than to extrapair males, such as in the spotless starling Sturnus unicolor (García‐Vigón et al ) and the Tibetan ground tit Pseudopodoces humilis (Du et al ), cuckolded males even increase paternal care for the mixed brood. The reason is that reduction of paternal care is costly for cuckolded males as their own offspring may starve in a larger, crowded nest (Du et al ).…”