Facultative sex ratio adjustment by western bluebird mothers with stay-at-home helpers-at-the-nest

Dickinson, Janis L.

doi:10.1016/j.anbehav.2003.07.022

Cited by 58 publications

(42 citation statements)

References 26 publications

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“…Our finding that delayed dispersal is favoured on highquality territories with abundant winter resources in western bluebirds, which only rarely have helpers, supports the hypothesis that direct fitness benefits accruing via personal survival and reproduction can generate patterns of delayed dispersal that lead to opportunistic, kin-directed cooperative breeding (Dickinson 2004). In this, our experimental study is in concordance with the results of observational studies in a diversity of animals, including humans, where correlative evidence has linked resources to male philopatry and male-biased inheritance (Towner 2001).…”

Section: Discussionsupporting

confidence: 78%

“…Western bluebirds possess three attributes that allow isolation of factors critical to testing the importance of territory quality in facilitating delayed dispersal. First, although factors favouring delayed dispersal and helping behaviour are tightly coupled in most cooperative breeders, they are separable in western bluebirds, because sons delaying dispersal until after winter only rarely remain home to become helpers during the breeding season (Dickinson et al 1996;Dickinson 2004). Second, western bluebird families hold winter territories based on a discrete, measurable, winter resource: oak mistletoe (Phoradendron villosum), which can be quantified and manipulated to determine the importance of resource abundance (Kraaijeveld & Dickinson 2001).…”

Section: Introductionmentioning

confidence: 99%

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Winter resource wealth drives delayed dispersal and family-group living in western bluebirds

Dickinson

McGowan

2005

Proc. R. Soc. B.

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Delayed dispersal, where offspring remain with parents beyond the usual period of dependence, is the typical route leading to formation of kin-based cooperative societies. The prevailing explanations for why offspring stay home are variation in resource wealth, in which offspring of wealthy parents benefit disproportionately by staying home, and nepotism, where the tendency for parents to be less aggressive and share food with offspring makes home a superior place to wait to breed. These hypotheses are not strict alternatives, as only wealthy parents have sufficient resources to share. In western bluebirds, Sialia mexicana, sons usually delay dispersal until after winter, gaining feeding advantages through maternal nepotism in a familial winter group. Experimentally reducing resource wealth (mistletoe) by half on winter territories caused sons to disperse in summer, even though their parents remained on the territory during the winter. Only 8% of sons remained with their parents on mistletoe-removal territories compared to 50% of sons on control territories (t 9,10 Z3.33, p!0.005). This study is the first to demonstrate that experimentally reducing wealth of a natural food resource reduces delayed dispersal, facilitating nepotism and family-group living. The results clarify the roles of year-round residency, resource limitation and relative wealth outside the breeding season in facilitating the formation of kin-based cooperative societies.

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Section: Discussionsupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Winter resource wealth drives delayed dispersal and family-group living in western bluebirds

Dickinson

McGowan

2005

Proc. R. Soc. B.

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“…Thus, in this case an unbiased population sex ratio is consistent with the repayment hypothesis because females across different contexts adaptively allocate their offspring's sex. Western bluebirds (Sialia mexicana) also show evidence of facultative control (Dickinson 2004), but in general our meta-analysis shows that these species are the exception rather than the rule (with an average effect size close to zero). There is no general tendency across species to produce the helping sex when breeders are deficient of help.…”

Section: Rarity Of Facultative Production Of the More Helpful Sexmentioning

confidence: 64%

Sex Allocation Patterns across Cooperatively Breeding Birds Do Not Support Predictions of the Repayment Hypothesis

Khwaja

Hatchwell

Freckleton

et al. 2017

The American Naturalist

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Online enhancements: appendix. Dryad data: http://dx.doi.org/10.5061/dryad.9bk88. abstract:The repayment hypothesis predicts that reproductive females in cooperative breeding systems overproduce the helping sex. Thanks to well-documented examples of this predicted sex ratio bias, repayment has been considered an important driver of variation in sex allocation patterns. Here we test this hypothesis using data on population brood sex ratios and facultative sex allocation from 28 cooperatively breeding bird species. We find that biased sex ratios of helpers do not correlate with production biases in brood sex ratios, contrary to predictions. We also test whether females facultatively produce the helping sex in response to a deficiency of help (i.e., when they have fewer or no helpers). Although this is observed in a few species, it is not a significant trend overall, with a mean effect size close to zero. We conclude that, surprisingly, repayment does not appear to be a widespread influence on sex ratios in cooperatively breeding birds. We discuss possible explanations for our results and encourage further examination of the repayment model.

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“…Given the details of the models presented here and elsewhere (Wild and Taylor 2005), species with extended periods of biparental care, such as bird species (Komdeur and Pen 2002), are good candidates for study. In addition, juvenile helping, the effects of local resource competition, and conflict between mates are thought to influence avian sex ratios in many cases (Gowaty 1993;Clotfelter 1996;Komdeur et al 1997;Ewen et al 2003;Berg 2004;Dickinson 2004).…”

Section: Discussionmentioning

confidence: 99%

Sex Ratios When Helpers Stay at the Nest

Wild

2006

Evolution

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Abstract. This study investigates the evolution of the sex ratio (parental investment in sons) when breeding adults are supported by help provided by nonbreeding individuals of one sex. The study also assumes that the helping sex remains on its natal site to compete for the opportunity to breed, whereas the nonhelping sex disperses. Two kinselection models are presented, both of which incorporate the age structure found in many natural populations where such helping occurs. The first model assumes that helpers increase the survival of their parents. The second model assumes that helpers are indiscriminant: a helper chooses to increase the survival of a random pair of adults breeding on its natal patch. In both models, sex ratios are not always biased toward the sex that provides the most help. When helpers do not discriminate (second model), the direction of sex-ratio bias is determined solely by the size of the benefit of helping behavior. When this benefit is small, sex-ratio evolution is primarily influenced by local resource competition and sex ratios are biased toward the nonhelping (dispersive) sex. If the benefit of help is large enough, the effect of local resource competition is reduced and sex-ratio bias favors the helpful sex. When helpers help only their parents, the same qualitative relationship exists between the direction of sex-ratio bias and the benefit of helping. In this case, however, the direction of sex-ratio bias is also influenced by the size of the social group, mortality, and which individual (mother or father) controls the sex ratio. This study also investigates a sex-ratio conflict that exists between mates. Helping behavior of nonbreeders can act to alleviate the disparities between the optimal sex ratio from the perspective of a mother and that from the perspective of a father. This consequence of helping has not been previously recognized.

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Facultative sex ratio adjustment by western bluebird mothers with stay-at-home helpers-at-the-nest

Cited by 58 publications

References 26 publications

Winter resource wealth drives delayed dispersal and family-group living in western bluebirds

Winter resource wealth drives delayed dispersal and family-group living in western bluebirds

Sex Allocation Patterns across Cooperatively Breeding Birds Do Not Support Predictions of the Repayment Hypothesis

Sex Ratios When Helpers Stay at the Nest

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