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Simultaneous failure of two sex-allocation invariants: implications for sex-ratio variation within and between populations.

Rodrigues AM, Gardner A - Proc. Biol. Sci. (2015)

Bottom Line: Both of these invariants have stimulated a great deal of theoretical and empirical research.Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers.Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK Wolfson College, Barton Road, Cambridge CB3 9BB, UK ammr3@cam.ac.uk.

ABSTRACT
Local mate competition (LMC) occurs when male relatives compete for mating opportunities, and this may favour the evolution of female-biased sex allocation. LMC theory is among the most well developed and empirically supported topics in behavioural ecology, clarifies links between kin selection, group selection and game theory, and provides among the best quantitative evidence for Darwinian adaptation in the natural world. Two striking invariants arise from this body of work: the number of sons produced by each female is independent of both female fecundity and also the rate of female dispersal. Both of these invariants have stimulated a great deal of theoretical and empirical research. Here, we show that both of these invariants break down when variation in female fecundity and limited female dispersal are considered in conjunction. Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers. Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.

No MeSH data available.


Related in: MedlinePlus

Facultative sex allocation under self-knowledge. (a,c) High-fecundity mothers (blue line, H) are favoured to produce relatively less female-biased sex ratios, whereas low-fecundity mothers (red line, L) are favoured to produce relatively more female-biased sex ratios, in viscous populations (d < 1), and the population average sex ratio strategy (dashed line) becomes more female-biased as the population becomes more viscous (lower d), under haploidy and diploidy (a), and under haplodiploidy (c). (b,d) High-fecundity mothers (blue line, H) are favoured to invest relatively more into sons than are low-fecundity mothers (red line, L) in viscous populations (d < 1), and the population average allocation to sons (dashed line) decreases as the population becomes more viscous (lower d), under haploidy and diploidy (b), and under haplodiploidy (d). We arbitrarily set the total number of offspring of a high-fecundity mother to 100. Parameter values: k = 0, ρ = 0.5, s = 0.75.
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RSPB20150570F2: Facultative sex allocation under self-knowledge. (a,c) High-fecundity mothers (blue line, H) are favoured to produce relatively less female-biased sex ratios, whereas low-fecundity mothers (red line, L) are favoured to produce relatively more female-biased sex ratios, in viscous populations (d < 1), and the population average sex ratio strategy (dashed line) becomes more female-biased as the population becomes more viscous (lower d), under haploidy and diploidy (a), and under haplodiploidy (c). (b,d) High-fecundity mothers (blue line, H) are favoured to invest relatively more into sons than are low-fecundity mothers (red line, L) in viscous populations (d < 1), and the population average allocation to sons (dashed line) decreases as the population becomes more viscous (lower d), under haploidy and diploidy (b), and under haplodiploidy (d). We arbitrarily set the total number of offspring of a high-fecundity mother to 100. Parameter values: k = 0, ρ = 0.5, s = 0.75.

Mentions: We have also assumed that there is one high-fecundity mother and one low-fecundity mother in every patch, such that a female's knowledge of her own fecundity immediately provides knowledge of her patchmate's fecundity. Accordingly, the facultative adjustment scenario falls within a category of models that have been termed ‘complete knowledge’ models [9]. An alternative model could consider that each female's fecundity is determined independently of her patchmates', such that some patches would contain two high-fecundity mothers, some would contain two low-fecundity mothers, and others would contain one high-fecundity mother and one low-fecundity mother. This scenario may then fall within a category of models that have been termed ‘self-knowledge’ models [9]. This could occur, for example, if mothers cannot assess the fecundity of other mothers directly, or if mothers decide their sex allocation before they encounter their patchmates [9]. If we assume that a fraction ρ of newborn females become high-fecundity mothers and a fraction 1 − ρ become low-fecundity mothers, independently of where and with whom they settle to breed, and that a focal female is aware of her own fecundity but not the fecundity of her patchmate, then we find that high-fecundity mothers are favoured to produce more sons than are low-fecundity mothers and that high-fecundity mothers are favoured to invest relatively more into sons as the population becomes more viscous (figure 2). That the CMH invariant breaks down in this scenario was already known for the special case of full dispersal (d = 1; [9]), and here we have also shown that the dispersal invariant breaks down in the context of variable fecundity as well.Figure 2.


Simultaneous failure of two sex-allocation invariants: implications for sex-ratio variation within and between populations.

Rodrigues AM, Gardner A - Proc. Biol. Sci. (2015)

Facultative sex allocation under self-knowledge. (a,c) High-fecundity mothers (blue line, H) are favoured to produce relatively less female-biased sex ratios, whereas low-fecundity mothers (red line, L) are favoured to produce relatively more female-biased sex ratios, in viscous populations (d < 1), and the population average sex ratio strategy (dashed line) becomes more female-biased as the population becomes more viscous (lower d), under haploidy and diploidy (a), and under haplodiploidy (c). (b,d) High-fecundity mothers (blue line, H) are favoured to invest relatively more into sons than are low-fecundity mothers (red line, L) in viscous populations (d < 1), and the population average allocation to sons (dashed line) decreases as the population becomes more viscous (lower d), under haploidy and diploidy (b), and under haplodiploidy (d). We arbitrarily set the total number of offspring of a high-fecundity mother to 100. Parameter values: k = 0, ρ = 0.5, s = 0.75.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4590475&req=5

RSPB20150570F2: Facultative sex allocation under self-knowledge. (a,c) High-fecundity mothers (blue line, H) are favoured to produce relatively less female-biased sex ratios, whereas low-fecundity mothers (red line, L) are favoured to produce relatively more female-biased sex ratios, in viscous populations (d < 1), and the population average sex ratio strategy (dashed line) becomes more female-biased as the population becomes more viscous (lower d), under haploidy and diploidy (a), and under haplodiploidy (c). (b,d) High-fecundity mothers (blue line, H) are favoured to invest relatively more into sons than are low-fecundity mothers (red line, L) in viscous populations (d < 1), and the population average allocation to sons (dashed line) decreases as the population becomes more viscous (lower d), under haploidy and diploidy (b), and under haplodiploidy (d). We arbitrarily set the total number of offspring of a high-fecundity mother to 100. Parameter values: k = 0, ρ = 0.5, s = 0.75.
Mentions: We have also assumed that there is one high-fecundity mother and one low-fecundity mother in every patch, such that a female's knowledge of her own fecundity immediately provides knowledge of her patchmate's fecundity. Accordingly, the facultative adjustment scenario falls within a category of models that have been termed ‘complete knowledge’ models [9]. An alternative model could consider that each female's fecundity is determined independently of her patchmates', such that some patches would contain two high-fecundity mothers, some would contain two low-fecundity mothers, and others would contain one high-fecundity mother and one low-fecundity mother. This scenario may then fall within a category of models that have been termed ‘self-knowledge’ models [9]. This could occur, for example, if mothers cannot assess the fecundity of other mothers directly, or if mothers decide their sex allocation before they encounter their patchmates [9]. If we assume that a fraction ρ of newborn females become high-fecundity mothers and a fraction 1 − ρ become low-fecundity mothers, independently of where and with whom they settle to breed, and that a focal female is aware of her own fecundity but not the fecundity of her patchmate, then we find that high-fecundity mothers are favoured to produce more sons than are low-fecundity mothers and that high-fecundity mothers are favoured to invest relatively more into sons as the population becomes more viscous (figure 2). That the CMH invariant breaks down in this scenario was already known for the special case of full dispersal (d = 1; [9]), and here we have also shown that the dispersal invariant breaks down in the context of variable fecundity as well.Figure 2.

Bottom Line: Both of these invariants have stimulated a great deal of theoretical and empirical research.Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers.Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK Wolfson College, Barton Road, Cambridge CB3 9BB, UK ammr3@cam.ac.uk.

ABSTRACT
Local mate competition (LMC) occurs when male relatives compete for mating opportunities, and this may favour the evolution of female-biased sex allocation. LMC theory is among the most well developed and empirically supported topics in behavioural ecology, clarifies links between kin selection, group selection and game theory, and provides among the best quantitative evidence for Darwinian adaptation in the natural world. Two striking invariants arise from this body of work: the number of sons produced by each female is independent of both female fecundity and also the rate of female dispersal. Both of these invariants have stimulated a great deal of theoretical and empirical research. Here, we show that both of these invariants break down when variation in female fecundity and limited female dispersal are considered in conjunction. Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers. Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.

No MeSH data available.


Related in: MedlinePlus