Female control of offspring paternity in a western population of red-winged blackbirds ( Agelaius phoeniceus )

In male birds, testosterone (T) plays an important role in aggressive and mate-attraction behaviour. In the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis, extra-group copulations (EGCs) occur frequently, but are not accompanied by sexual courtship displays as in within-pair copulations. Paternity is nearly always gained by primary males. We investigated whether T levels and sperm storage capability (cloacal protuberance (CP)) in adult primary and subordinate males were related to timing of egg laying, levels of cuckoldry and extra-group paternity (EGP) opportunities. During the sexually active period before egg laying, T levels and CP were only elevated or enlarged (respectively) in primary males, and some suggestion was found that subordinate males do not invest in elevated T levels. The peak in T occurred during the fertile period of the female partner and corresponded to the peak period of male sexual displays and mate guarding, but was independent of cuckoldry risk (density of neighbouring primary males). CP was also enhanced during this period; however, CP but not T remained elevated after egg laying by their mates, and CP but not T was positively related to EGP opportunities (density of neighbouring fertile females). We conclude that T is involved in sexual courtship displays and mate guarding, but not in gaining EGCs. These findings contrast with those in other species where EGP involves elaborate sexual displays.

Section: Introductionmentioning

confidence: 99%

Testosterone, cuckoldry risk and extra–pair opportunities in the Seychelles warbler

Crommenacker

Richardson

Groothuis

et al. 2004

“…intrusion pressure from extra-pair males, and female extra-pair behaviour (e.g. Alatalo et al 1987;MÖller 1987;Hanski 1994;Gray 1996). Some genetic studies have shown that the risk of paternity is a¡ected by a variety of factors, including breeding density and operational sex ratio (Gibbs et al 1990;Westneat et al 1990;Gowaty & Bridges 1991;Birkhead & MÖller 1992;MÖller & Birkhead 1993;Hasselquist et al 1995).…”

Section: Introductionmentioning

confidence: 99%

Mate guarding in the Seychelles warbler is energetically costly and adjusted to paternity risk

Komdeur

2001

134

100

Males may increase their ¢tness through extra-pair copulations (copulations outside the pair bond) that result in extra-pair fertilizations, but also risk lost paternity when they leave their own mate unguarded. The ¢tness costs of cuckoldry for Seychelles warblers (Acrocephalus sechellensis) are considerable because warblers have a single-egg clutch and, given the short breeding season, no time for a successful replacement clutch. Neighbouring males are the primary threat to a male's genetic paternity. Males minimize their loss of paternity by guarding their mates to prevent them from having extra-pair copulations during their fertile period. Here, I provide experimental evidence that mate-guarding behaviour is energetically costly and that the expression of this trade-o¡ is adjusted to paternity risk (local male density). Freeliving males that were induced to reduce mate guarding spent signi¢cantly more time foraging and gained signi¢cantly better body condition than control males. The larger the reduction in mate guarding, the more pronounced was the increase in foraging and body condition (accounting for food availability). An experimental increase in paternity risk resulted in an increase in mate-guarding intensity and a decrease in foraging and body condition, and vice versa. This is examined using both cross-sectional and longitudinal data. This study on the Seychelles warbler o¡ers experimental evidence that mate guarding is energetically costly and adjusted to paternity risk.

“…With regard to social mates, the assumption is reasonable, because red-winged blackbirds are socially polygynous and most evidence indicates that resident females do not constrain new females from settling on territories (Searcy & Yasukawa 1995). With regard to extra-pair mates, there is evidence from other populations of both male (Westneat 1992) and female control (Gray 1996). Should females not control EPM in this population, most of the predictions above no longer hold, although male control of EPM could still produce some consistency in female mating patterns between years.…”

Section: Introductionmentioning

confidence: 99%

Sequential mating patterns suggest extra–pair mating is not part of a mixed reproductive strategy by female red–winged blackbirds

Weatherhead

1999

Studies aimed at determining why female birds often produce o¡spring sired by males other than their social mates generally compare traits of social and genetic mates. Here I examine paternity patterns in nests of the same female red-winged blackbirds (Agelaius phoeniceus) in successive breeding seasons. Returning females preferentially selected their former social mates as their new social mates when those males were present. However, paternity patterns were much less consistent. A female's behaviour (faithful versus unfaithful) in one year did not predict her behaviour the following year. Females unfaithful in successive years did not prefer the same extra-pair males. Females unfaithful in one year that switched social mates the next year did not preferentially choose their former extra-pair mates as their new social mates. By switching genetic mates, females did not generally improve the quality of their mates. These results, together with previous analyses, suggest that female blackbirds in this population have little control over extra-pair mating. Although females may bene¢t from extra-pair mating because extra-pair males are generally longer lived, paternity patterns in this population are not consistent with extra-pair mating being part of a ¢nely tuned female reproductive strategy.