Secondary Sex Ratios and Egg Sequence in Herring Gulls

Ryder, John P.; Termaat, Beatrice M.

doi:10.2307/4087556

Cited by 20 publications

(19 citation statements)

References 8 publications

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“…In lesser snow geese (Chen caeruleslens caerulescens), Ankney (1982) reported that the first two eggs laid produced more males (64%) than the last two (28%), although a larger sample of the same species failed to find any relationship (Cooke and Harmsen, 1983). Ryder (1983) found for ringbilled gulls (Larus delawarensis) that during three reproductive seasons the first egg in the brood consistently produced more males (63.7% of males, 3 years of combined data), the second one produced more females (38.8% of males), and the sex ratio of the third laid egg did not differ from unity (43.1% of males), in agreement of predictions 2 and 4 of the present model.…”

Section: Evidence So Farsupporting

confidence: 89%

“…In contrast, an increasing number of studies in birds (Ankney, 1982;Badyaev et al, 2002;Bednarz and Hayden, 1991;Bortolotti, 1986;Clutton-Brock, 1986;Ryder, 1983;Velando et al, 2002) and mammals (Gosling et al, 1984;Fernández-Llario et al, 1999;Vanderbergh and Hugget, 1994) have noted that offspring sex is not independent of positions within the brood, and it appears to be associated with the hatching/birth/weight rank in ways that might correlate with some environmental feature at the level of individual offspring.…”

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confidence: 99%

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Sex allocation within broods: the intrabrood sharing-out hypothesis

Carranza

2004

Behavioral Ecology

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Selection is expected to cause parents to adjust the sex of their offspring when the environment is predictable during development, and it is expected to affect each sex differently. When several offspring compete for limited resources, the environmental conditions acting on the brood are not a good predictor of the conditions affecting individual offspring. There is evidence for some species that, regardless of any bias in brood sex ratio, the sex of individual offspring within a brood may be related to its position in the hatching/birth/weight rank, in ways that might correlate with the expected share of available resources. Here I propose that parents may be selected to adjust offspring sex within the brood, provided that some depreciable environmental quality is unequally distributed among siblings in a predictable manner. I call this the ''intrabrood sharing-out'' hypothesis and present a graphical model to derive predictions about the relationship between offspring sex and positions within the brood. The model considers that sibling competition not only produces differences in the mean share of resources among siblings, but it also increases the predictability of the share obtained by high-ranking sibs and decreases the predictability of the share for low-ranking ones. Consequently, parents should be selected to deal with such a distribution by promoting the conditions to make it more predictable and then adaptively adjust the sex of particular siblings, especially in high-ranking positions within the brood, rather than to modify the sex ratio of the brood as a whole.

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Section: Evidence So Farsupporting

confidence: 89%

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confidence: 99%

Sex allocation within broods: the intrabrood sharing-out hypothesis

Carranza

2004

Behavioral Ecology

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“…Maternal condition during egg laying is clearly a very important parameter, which may underlie the sex ratio variations reported in several correlative studies. Variation in this parameter is likely to explain the patchy observations of sex ratio skews in nonexperimental studies, e.g., being sometimes found in a particular group such as gulls and sometimes not (11,15,(30)(31)(32).…”

Section: Discussionmentioning

confidence: 99%

Experimental demonstration that offspring sex ratio varies with maternal condition

Nager

Monaghan²,

Griffiths³

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

333

289

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Sex ratio theory predicts that, if prevailing ecological or social circumstances differentially inf luence the fitness benefits of offspring of each sex, parents should adjust their production accordingly to maximize fitness. For species in which sex is chromosomally determined, such as birds and mammals, a differential effect of maternal condition on the fitness of male and female young is one important route whereby selection is expected to favor a bias in the offspring sex ratio at birth or egg laying. However, despite its central place in sex allocation theory, this hypothesis has rarely been tested in wild populations. We manipulated maternal condition upward and downward in a sexually dimorphic wild bird and examined the effect on offspring survival and on offspring sex ratio. The survival to f ledging of male, but not female, young was substantially reduced if they came from less well provisioned eggs produced by females in relatively poor condition. As female condition, and thereby her capacity to produce high quality eggs, declined, she progressively skewed the sex ratio of her eggs toward females; i.e., she produced more of the sex with the higher survival prospects. The decline in the survival of male offspring, and the sex ratio bias, was removed when maternal condition was enhanced. These results provide experimental evidence of an adaptive, facultative adjustment of sex ratio in response to changes in maternal condition in wild birds.

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“…In birds, the sex of offspring often correlates with laying order (Howe 1976;Ankney 1982;Ryder 1983;Weatherhead 1985;Bortolotti 1986;Edmunds & Ankney 1987;Dijkstra et al 1990;Olsen & Cockburn 1991;Bednarz & Hayden 1991;Clotfelter 1996;Dzus et al 1996;Leroux & Bretagnolle 1996;Heinsohn et al 1997;Kilner 1998;Albrecht 2000;Velando et al 2000). This may be a side effect of other (e.g.…”

Section: Cases Where Evidence For Adaptive Sex Ratio Manipulation Is mentioning

confidence: 99%

Parental care and adaptive brood sex ratio manipulation in birds

Hasselquist

Kempenaers

2002

Phil. Trans. R. Soc. Lond. B

168

128

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Under many circumstances, it might be adaptive for parents to bias the investment in offspring in relation to sex. Recently developed molecular techniques that allow sex determination of newly hatched offspring have caused a surge in studies of avian sex allocation. Whether females bias the primary brood sex ratio in relation to factors such as environmental and parental quality is debated. Progress is hampered because the mechanisms for primary sex ratio manipulation are unknown. Moreover, publication bias against nonsignificant results may distort our view of adaptive sex ratio manipulation. Despite this, there is recent experimental evidence for adaptive brood sex ratio manipulation in birds. Parental care is a particularly likely candidate to affect the brood sex ratio because it can have strong direct effects on the fitness of both parents and their offspring. We investigate and make predictions of factors that can be important for adaptive brood sex ratio manipulation under different patterns of parental care. We encourage correlational studies based on sufficiently large datasets to ensure high statistical power, studies identifying and experimentally altering factors with sex-differential fitness effects that may cause brood sex ratio skew, and studies that experimentally manipulate brood sex ratio and investigate fitness effects.

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Secondary Sex Ratios and Egg Sequence in Herring Gulls

Cited by 20 publications

References 8 publications

Sex allocation within broods: the intrabrood sharing-out hypothesis

Sex allocation within broods: the intrabrood sharing-out hypothesis

Experimental demonstration that offspring sex ratio varies with maternal condition

Parental care and adaptive brood sex ratio manipulation in birds

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