Female extrapair mate choice in a cooperative breeder: trading sex for help and increasing offspring heterozygosity

Abstract

Sexual conflict between males and females over mating is common. Females that copulate with extrapair mates outside the pair-bond may gain (i) direct benefits such as resources or increased paternal care, (ii) indirect genetic benefits for their offspring, or (iii) insurance against infertility in their own social mate. Few studies have been able to demonstrate the different contexts in which females receive varying types of benefits from extrapair mates. Here, I examined sexual conflict, female extrapair mate choice, and patterns of extrapair paternity in the cooperatively breeding superb starling Lamprotornis superbus using microsatellite markers. Although extrapair paternity was lower than many other avian cooperative breeders (14% of offspring and 25% of nests), females exhibited two distinct mating patterns: half of the extrapair fertilizations were with males from inside the group, whereas half were with males from outside the group. Females with few potential helpers copulated with extrapair mates from within their group and thereby gained direct benefits in the form of additional helpers at the nest, whereas females paired to mates that were relatively less heterozygous than themselves copulated with extrapair mates from outside the group and thereby gained indirect genetic benefits in the form of increased offspring heterozygosity. Females did not appear to gain fertility insurance from copulating with extrapair mates. This is the first study to show that individuals from the same population mate with extrapair males and gain both direct and indirect benefits, but that they do so in different contexts.

Bateman's principle is reversed in a cooperatively breeding bird

“…Although the functions of superb starlings' secondary sexual characteristics are not fully understood, both sexes have equally elaborate plumage [6], use similarly complex songs in a social context [10] and benefit from extra-pair matings [9]. Moreover, the opportunity for selection (measured as the standardized variance in relative fitness [11]) is greater in female than in male starlings [12], as it is in other cooperative breeders [8].…”

“…Moreover, females in cooperatively breeding species may be particularly likely to benefit from multiple mating because they can gain both indirect genetic benefits and direct benefits (e.g. additional parental care from helpers) through extra-pair matings [9].…”

The fitness consequences of kin-biased dispersal in a cooperatively breeding bird

“…Female-female competition for access to mates and/or breeding opportunities is thought to be common in superb starlings [10,11]. Using pairwise relatedness data generated from microsatellite markers [12], we searched for evidence of kin substructure among immigrant females of unknown origin in social groups.…”

Family feuds: social competition and sexual conflict in complex societies

“…Additionally, direct benefits-including those derived from extra-pair matings-are thought to be more important in birds than in insects [25,26]. Moreover, the presence of helpers in the group could actually release female breeders from the constraints of parental care and allow them to pursue extra-pair fertilizations because a potential retaliatory reduction in paternal care as a result of females being unfaithful to their mates could be compensated for by the additional helper care [88,101]. The relationship between extra-pair paternity (promiscuity) and sociality was studied in a sample of 267 species of birds [42].…”