Skewed Brood Sex Ratio and Sex-Biased Hatching Sequence in Harris's Hawks

Bednarz, James C.; Hayden, Timothy J.

doi:10.1086/285149

Cited by 113 publications

(70 citation statements)

References 43 publications

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“…For example, male-biased offspring sex ratios earlier in the season have been reported in Haris' hawk (Parabuteo unicinctus) (Bednartz and Hayden 1991) and American kestrels (Falco sparverius paulus) (Smallwood and Smallwood 1998), while in marsh harriers (Circus aerinosus) the offspring sex ratio is male-biased later in the season (Zijlstra et al 1992). The change in sex ratio in Haris' hawks involves sequential clutches, where the sex ratio of the first clutch is biased toward males and the offspring in this first clutch are larger than those in subsequent clutches.…”

Section: Discussionmentioning

confidence: 99%

Breeding ecology and bias in offspring sex ratio in little grassbirds (Megalurus gramineus)

et al. 2003

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Little grassbirds (Megalurus gramineus) are small, sexually monomorphic passerines that live in reed beds, lignum swamps and salt marshes in southern Australia. The breeding biology and patterns of sex allocation of the little grassbird were investigated over a single breeding season. Our observations of this species in the Edithvale Wetland Reserve revealed a highly male-biased population sex ratio, with some breeding territories containing several additional males. Nevertheless, there was little compelling evidence that little grassbirds breed cooperatively. The growth rates of male and female nestlings were similar and, as predicted by theory, there was no overall primary sex ratio bias. However, the primary sex ratio was female-biased early in the breeding season and became increasingly male-biased later in the breeding season.

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Section: Discussionmentioning

confidence: 99%

Breeding ecology and bias in offspring sex ratio in little grassbirds (Megalurus gramineus)

et al. 2003

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“…Charnov and Bull (1977) (see also Bull 1981) expanded condition-dependent sex allocation to environmental sex determination, providing an adaptive hypothesis for the occurrence of temperature-dependent sex determination (TSD) that proposes developmental temperature is the fitness-altering condition that determines investment in ovaries or testes (Gutzke and Crews 1988; Janzen 1995;Shine 1999;Warner and Shine 2008). Condition dependence in sex allocation has been expanded to sex biases based on individual size, paternal quality, parental rank, hatching order, and season (Werren and Charnov 1978;Charnov 1979a;Burley 1981;Silk 1983;Bednarz and Hayden 1991;Daan et al 1996).According to sex allocation theory, sex allocation should be based on individual condition relative to the condition of competitors, not on absolute condition (Charnov et al , 1981 Charnov 1982;West 2009). The TW hypothesis predicts that mothers of relatively good condition should invest more in sons than mothers of relatively poor condition (Trivers and Willard 1973).…”

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confidence: 99%

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confidence: 99%

Sex Allocation Based on Relative and Absolute Condition

2010

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Sex allocation theory has provided a remarkably successful framework for predicting investment in offspring sex or in egg versus sperm for invertebrates and plants (Charnov 1982;Wrensch and Ebbert 1993;Hardy 2002), yet sex ratio biases in amniote vertebrates seem unsystematic and often are explained a posteriori. The frequent mismatch between theory and empirical data in amniotes raises doubts as to whether adaptive sex allocation occurs in these taxa and highlights the need for expanded study focusing on long-lived organisms.Many hypotheses of sex allocation for amniote vertebrates are based on condition dependence of sex allocation (Charnov 1982; Cockburn et al. 2002;West 2009). An individual invests in sons versus daughters or eggs versus sperm depending on individual condition, such as resource availability, body size, or incubation temperature. That a sex-specific fitness advantage of body size might select for size-dependent sex allocation was first proposed for sex-changing invertebrates (Ghiselin 1969). Subsequently, the Trivers-Willard hypothesis (TW; Trivers and Willard 1973) proposed that offspring sex in mammals may be linked to maternal condition if condition influences the lifetime fitness of one offspring sex more than the other. Charnov and Bull (1977) (see also Bull 1981) expanded condition-dependent sex allocation to environmental sex determination, providing an adaptive hypothesis for the occurrence of temperature-dependent sex determination (TSD) that proposes developmental temperature is the fitness-altering condition that determines investment in ovaries or testes (Gutzke and Crews 1988; Janzen 1995;Shine 1999;Warner and Shine 2008). Condition dependence in sex allocation has been expanded to sex biases based on individual size, paternal quality, parental rank, hatching order, and season (Werren and Charnov 1978;Charnov 1979a;Burley 1981;Silk 1983;Bednarz and Hayden 1991;Daan et al. 1996).According to sex allocation theory, sex allocation should be based on individual condition relative to the condition of competitors, not on absolute condition (Charnov et al. , 1981 Charnov 1982;West 2009). The TW hypothesis predicts that mothers of relatively good condition should invest more in sons than mothers of relatively poor condition (Trivers and Willard 1973). This is because each sex competes for lifetime reproductive success only with members of the same sex, so that the quality of a son or daughter is defined only with respect to their sexual competitors (other sons and daughters in the population). If sex allocation were based on absolute condition, a year with extreme condition values would vastly overproduce one sex, and frequency-dependent selection on sex would favor a mutant that produced the rare sex. The resulting prediction is that the optimal sex allocation versus condition reaction norm should be relative, shifting in response to changes in the population distribution of condition, and that an equilibrium cohort sex ratio would be maintained. When individuals are not allowed to def...

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“…of raptors have demonstrated biased sex allocation with respect to laying date (Dijkstra et al 1990;Olsen & Cockburn 1991;Zijlstra et al 1992;Daan et al 1996), laying sequences within broods (Bortolotti 1986;Edwards et al 1988;Bednarz & Hayden 1991;Leroux & Bretagnolle 1996) and maternal condition (Wiebe & Bortolotti 1992). Although these studies explained adaptive sex ratio manipulation at the individual level, they also reported overall male-biased sex ratios of nestlings or fledglings at the population level, with the except of one study (Dijkstra et al 1990).…”

Section: Other Important Investigationsmentioning

confidence: 99%

Sex Ratio among Fledglings of Blakiston's Fish Owls.

Hayashi

Nishida‐Umehara

2000

Japanese Journal of Ornithology

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The sex ratio of 137 fledglings, from 91 broods, of Blakiston's Fish Owls Ketupa blakistoni raised in Hokkaido, Japan, over the period 1985-99, was analyzed. The sex ratio of fledglings was significantly male-biased (81 males. and 56 females; P=0.04) although no significant difference was detected when it was compared to the expected value (50% males) for each brood size (one or two). Logistic regression analysis did not reveal any significant effects of the locations of breeding sites on the sex ratio of fledglings. Young male owls suffered higher mortality than females. It is suggested that the male-biased sex ratio at fledging is moderated toward parity during the post-fledging stage. Factors considered to attribute to the skewed sex ratio at fledging of Blakiston's Fish Owl were: sexual dimorphism, local resource competition (LRC) and demographic stochasticity resulting from the small population size. Sexual dimorphism suggested that the male-biased sex ratio of fledglings was qualitatively consistent with Fisher's theory. However, sexual dimorphism alone does not quantitatively explain the male-biased sex ratio in Blakiston's Fish Owls. Differential natal philopatry between the sexes suggests that LRC is occurring. The small population size of the Hokkaido population is considered to be the most alarming factor from a conservation point of view.

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Skewed Brood Sex Ratio and Sex-Biased Hatching Sequence in Harris's Hawks

Cited by 113 publications

References 43 publications

Breeding ecology and bias in offspring sex ratio in little grassbirds (Megalurus gramineus)

Breeding ecology and bias in offspring sex ratio in little grassbirds (Megalurus gramineus)

Sex Allocation Based on Relative and Absolute Condition

Sex Ratio among Fledglings of Blakiston's Fish Owls.

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