Article

Within-clutch egg size asymmetry covaries with embryo sex in the yellow-legged gull Larus michahellis

Behavioral Ecology and Sociobiology (Impact Factor: 3.05). 10/2009; 63(12):1809-1819. DOI: 10.1007/s00265-009-0808-4

ABSTRACT Non-random sex allocation may occur whenever the expected reproductive value of sons and daughters differs, as is the case
when the sexes differ in susceptibility to environmental conditions or maternal effects (e.g. egg size and hatch order). Under
such circumstances, covariation between egg and clutch characteristics and egg sex may be expected, and this covariation should
vary with maternal state or ecological conditions. In this 2-year study (2007–2008), we examined sex allocation in relation
to egg and clutch traits in the yellow-legged gull Larus michahellis, a species where male chicks are larger and more susceptible to harsh rearing conditions than female ones. In 2008, eggs
were more likely male early in the season in two- but not three-egg clutches, and large eggs were more likely males late in
the season. No egg/clutch traits predicted egg sex in 2007. Within-clutch egg mass asymmetry (the difference in egg mass between
the first- and last-laid eggs) predicted sex in both years. In 2007, clutches with smaller egg mass variation were more likely
to contain males, while in 2008 this relationship held for the last-laid egg and was reversed for the preceding egg(s). Laying
order and sex of the previous egg did not predict egg sex, providing no evidence of sex-specific oocyte clustering. Thus,
the relationships between egg sex and egg/clutch traits differed among years, suggesting a phenotypically plastic response
of females to extrinsic conditions, and involved within-clutch egg mass asymmetry, a trait likely reflecting variation in
maternal quality and/or reproductive tactics, which has been largely neglected in previous studies of sex allocation.

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    • " egg size increased . These patterns could be driven by sex effects on egg shape and / or egg composition . Our simple index of egg shape , based on length and width , was identical for male and female eggs ( Table 3 ) , but shape could nonetheless differ in more complex ways . Egg shape can vary with laying order ( e . g . , Blanco et al . 2003 ; Rubolini et al . 2009 ) ; therefore , any sex bias with laying order could produce differences in egg shape between the sexes . Although we found no sex ratio difference with respect to egg order , our power was limited . Väisänen et al . ( 1972 ) reported that fourth eggs of 28 red - necked phalarope clutches were longer than earlier eggs ; we fail to dupli"
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    ABSTRACT: Fisher's sex ratio theory predicts that on average parents should allocate resources equally to the production of males and females. However, when the cost/benefit ratio for producing males versus females differs, the theory predicts that parents may bias production, typically through underproduction of the sex with greater variation in fitness. We tested theoretical predictions in the red-necked phalarope, a polyandrous shorebird with sex-role reversal. Since females are larger and therefore potentially more expensive to produce and may have greater variation in reproductive success, we predicted from Fisher's hypothesis a male bias in population embryonic sex ratio, and from sex allocation theory, female biases in the clutches of females allocating more resources to reproduction. We measured eggs and chicks and sexed 535 offspring from 163 clutches laid over 6 years at two sites in Alaska. The embryonic sex ratio of 51.1 M:48.9 F did not vary from parity. Clutch sex ratio (% male) was positively correlated with clutch mean egg size, opposite to our prediction. Within clutches, however, egg size did not differ by sex. Male phalarope fitness may be more variable than previously thought, and/or differential investment in eggs may affect the within-sex fitness of males more than females. Eggs producing males were less dense than those producing females, possibly indicating they contained more yolk relative to albumen. Albumen contributes to chick structural size, while yolk supports survivorship after hatch. Sex-specific chick growth strategies may affect egg size and allocation patterns by female phalaropes and other birds.
    Behavioral Ecology and Sociobiology 12/2014; 68(12):1939-1949. DOI:10.1007/s00265-014-1800-1 · 3.05 Impact Factor
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    • "It should be noted that the latter analysis was based on a larger number of males than females from first-laid eggs, while the converse was true in last-laid eggs (see samples sizes in Fig. 2). At present, given that our analyses are based on all chicks that survived to 4 days of age (when sex of the chicks was determined), we are unable to conclude if this uneven distribution of the sexes between first-and lastlaid eggs was due to a difference between the sexes in hatching rate or in post-hatching survival or even to an association between sex and position in the laying sequence (but see Rubolini et al. 2009). Therefore, we cannot rule out the possibility that avidin had interacted with the sex of the embryo in determining hatching and survival prospect of the chicks. "
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    • "It should be noted that the latter analysis was based on a larger number of males than females from first-laid eggs, while the converse was true in last-laid eggs (see samples sizes in Fig. 2). At present, given that our analyses are based on all chicks that survived to 4 days of age (when sex of the chicks was determined), we are unable to conclude if this uneven distribution of the sexes between first-and lastlaid eggs was due to a difference between the sexes in hatching rate or in post-hatching survival or even to an association between sex and position in the laying sequence (but see Rubolini et al. 2009). Therefore, we cannot rule out the possibility that avidin had interacted with the sex of the embryo in determining hatching and survival prospect of the chicks. "
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    ABSTRACT: Maternal effects through albumen quality are largely unexplored, despite the fundamental role that albumen exerts as source of proteins and water, as well as for antimicrobial defence of the embryo. We analysed the variation of two major albumen antimicrobials, avidin and lysozyme, by extracting samples from freshly laid eggs of the yellow-legged gull (Larus michahellis) and by correlating their levels to egg features. Lysozyme concentration increased along the laying sequence, while avidin concentration decreased. Both antimicrobials declined during the season. In addition, avidin concentration declined from first- to last-laid male eggs, whereas the opposite was true among the female eggs. We also analysed chick body mass and size and immune response, in relation to albumen antimicrobial levels in their original egg while controlling for potential covariation between egg quality and rearing conditions by cross-fostering eggs between nests. Tarsus length decreased with avidin concentration, particularly early in the season. Avidin concentration negatively predicted tarsus length of chicks and the phytohaemagglutinin response of females, but not males. However, chick phenotype did not covary with lysozyme albumen concentration. This is the first study where maternal effects mediated by albumen antimicrobials are investigated in relation to both sex and egg features in any wild bird species. Whether the observed patterns of variation in antimicrobial concentration are the by-product of maternal physiological constraints, or reflect adaptive allocation strategies, cannot be ascertained. The covariation between chick cell-mediated immunity and albumen avidin concentration might be causal, according to the documented effects of albumen proteins on immunity in other species. KeywordsAlbumen-Antimicrobial proteins-Avidin-Lysozyme-Maternal effects-Yellow-legged gull-Cross-fostering
    Behavioral Ecology and Sociobiology 04/2010; 64(5):845-855. DOI:10.1007/s00265-010-0901-8 · 3.05 Impact Factor
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