Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring

Trivers, Robert; Willard, Dan E.

doi:10.1126/science.179.4068.90

Cited by 3,455 publications

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“…It is well known that certain organisms, such as the haplodiploid Hymenoptera, can adjust their sex ratio according to local conditions (see Charnov, 1982). Situations in which individuals are allowed to vary their sex ratios in response to certain local conditions have been discussed in the literature (Trivers and Willard, 1973;Werren and Charnov, 1978;Charnov et al, 1981;Clutton-Brock et al, 1981;Werren, 1980Werren, , 1983, and a few such models are presented in Frank (1985). For example, the proportion of males produced by fig wasps is positively correlated with deme size (Frank, 1983a(Frank, , 1983b.…”

Section: Discussion Of Assumptions and Methodsmentioning

confidence: 99%

Hierarchical selection theory and sex ratios I. General solutions for structured populations

Frank

1986

Theoretical Population Biology

214

158

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Models of sex-ratio evolution in structured populations are derived with G. R. Price's covariance form for the hierarchical analysis of natural selection (1970, Nature 227, 520-521). Previous work on competition among related males for mates (local mate competition), competition among related females for a limiting resource (local resource competition), inbreeding, group selection, and asymmetry of genetic inheritance between males and females, are subsumed under a general formulation for sex-ratio biases in structured populations. I found that the evolutionarily stable strategy sex ratio (males : females) for diploids is 1 -p",: 1 -pf, where p m is the regression coefficient of relatedness of the controlling genotypes on males competing for mates, pf is the regression of controlling genotypes on females that compete for a fixed, limiting resource, and there is no inbreeding. For inbreeding and no competition among females, the evolutionarily stable strategy is 1-p m : 1 + p,,,,, where NT, is the regression of controlling genotypes on females' mates.CC 1986 Academic Press, Inc.Many interesting behaviors reflect a tension between the selfish pursuits of some individual or entity within a local group, and the extent to which the ultimate success of that individual also depends on the vigor of its local group. To name just a few of the most popular puzzles, there are the (almost) sterile castes of social insects, in which workers rarely produce offspring, but perhaps gain by the greater success of their colony, which contains a high proportion of identical genes (Hamilton, 1964(Hamilton, , 1972. There is the kin group, where the principle of self-sacrifice for a relative depending on the level of relatedness (Hamilton, 1964) has been accepted as one of the guiding principles of behavioral ecology. Meiotic and gametic drive are further examples the increased success of part of the genome that possibly reduces the overall success of the genome (e.g., Haldane, 1932;Hamilton, 1967;Alexander and Borgia, 1978;Eberhard, 1980;Cosmides and Tooby, 1981). The most recent slogan capturing this idea is "selfish DNA with self-restraint": genetic elements that can replicate and spread within the genome; but the ultimate success of the elements (relative 312

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Section: Discussion Of Assumptions and Methodsmentioning

confidence: 99%

Hierarchical selection theory and sex ratios I. General solutions for structured populations

Frank

1986

Theoretical Population Biology

214

158

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“…For example, in a polygynous species a mother in poor condition is predicted to have more daughters, and a mother in good condition more sons. There are data from some species consistent with this hypothesis (Trivers and Willard, 1973), although the existence and ubiquity of a labile birth sex ratio in vertebrates has been questioned (Myers, 1978;Williams, 1979). Nearly all of the species that have been examined to test the Trivers-Willard hypothesis are of the sort that have sequential broods and a negative correlation in resources expended in one period and those available in the next, these species being mostly ungulates and primates.…”

Section: Robustness Of Equal Allocationmentioning

confidence: 99%

“…These two assumptions are clearly unrealistic. Trivers and Willard (1973) were the first to note that in polygynous mammalian species, returns on male investment differ from returns on female investment, and that this may affect sex ratio patterns.…”

Section: Allocation When Resources Vary Among Individualsmentioning

confidence: 99%

“…Many organisms fall into this category, for which there is no quantitative theory. The Trivers and Willard (1973) hypothesis is a qualitative prediction suggesting that the sex ratio at birth produced by an individual should be skewed in favor of the sex with greater reproductive returns. For example, in a polygynous species a mother in poor condition is predicted to have more daughters, and a mother in good condition more sons.…”

Section: Robustness Of Equal Allocationmentioning

confidence: 99%

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Individual and population sex allocation patterns

Frank

1987

Theoretical Population Biology

161

127

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A variety of sex allocation models is considered in which (i) the reproductive returns on investment in males differ from the returns on investment in females, (ii) the amounts of resources available for reproduction vary in the population, (iii) the costs of making male and female reproductive structures differ, and (iv) the conception sex ratio may be fixed and there may be an initial minimum investment per offspring. Results of these models include quantatitive predictions for both individual-and population-level sex allocation, an opportunity to study the magnitude of changes in predicted patterns as key variables change, and therefore an analysis of the robustness of Fisher's equal investment theory. One example is that Fisher's argument is extremely robust for high fecundity organisms, but, in low fecundity organisms, is sensitive to differences between the sexes in reproductive returns on investment per offspring, a situation that occurs in many vertebrates to which Fisher's theory is often applied. A second example is that individual-and population-level patterns often depend strongly on the distribution of resources available for reproduction among individuals in the population. AcademicPress, Inc.

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“…Kuze et al (2008) speculate that this can also be explained by the Trivers and Willard (1973) hypothesis: mothers at Sepilok suffer from low health because of the stress caused by a high degree of gregariousness around feeding platforms and a high level of parasite exposure, and thus they produce a disproportionately high number of daughters to sons. Furthermore, captive Pongo also exhibited a significantly different sex ratio at birth from the Camp Leakey orangutans.…”

Section: Sex Ratio At Birthmentioning

confidence: 99%

Reproductive parameters of female orangutans (Pongo pygmaeus wurmbii) 1971–2011, a 40-year study at Tanjung Puting National Park, Central Kalimantan, Indonesia

Galdikas

Ashbury

2012

Primates

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This study presents reproductive parameter data gathered by direct observation over a 40-year period (1971-2011) of the provisioned free-ranging population of orangutans at Camp Leakey in Tanjung Puting National Park, Central Kalimantan, Indonesia. Age at first reproduction, interbirth interval (IBI), sex ratio at birth, and infant mortality for 19 female orangutans (11 first-generation wild-born ex-captive mothers and 8 second-generation mothers) are included in this analysis. Age at first reproduction among the first-generation mothers was similar to that among wild orangutans, while second-generation mothers had a significantly earlier age at first reproduction. IBIs were similar among first-and second-generation mothers and were significantly shorter than those recorded in studies of wild orangutan populations. There was an expected male-biased sex ratio at birth and a slightly higher than expected rate of infant mortality when compared to wild populations. Infant mortality was primarily seen among second-generation mothers who gave birth before the age of 12, and among first births of some first-generation mothers. These results lend support to the ecological energetics hypothesis, which predicts that increased diet quality leads to a faster rate of reproduction. Abstract This study presents reproductive parameter data gathered by direct observation over a 40-year period of the provisioned free-ranging population of orangutans at Camp Leakey in Tanjung Puting National Park, Central Kalimantan, Indonesia. Age at first reproduction, interbirth interval (IBI), sex ratio at birth, and infant mortality for 19 female orangutans (11 first-generation wild-born ex-captive mothers and 8 second-generation mothers) are included in this analysis. Age at first reproduction among the first-generation mothers was similar to that among wild orangutans, while second-generation mothers had a significantly earlier age at first reproduction. IBIs were similar among first-and second-generation mothers and were significantly shorter than those recorded in studies of wild orangutan populations. There was an expected male-biased sex ratio at birth and a slightly higher than expected rate of infant mortality when compared to wild populations. Infant mortality was primarily seen among second-generation mothers who gave birth before the age of 12, and among first births of some first-generation mothers. These results lend support to the ecological energetics hypothesis, which predicts that increased diet quality leads to a faster rate of reproduction.

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Natural Selection of Parental Ability to Vary the Sex Ratio of Offspring

Cited by 3,455 publications

References 12 publications

Hierarchical selection theory and sex ratios I. General solutions for structured populations

Hierarchical selection theory and sex ratios I. General solutions for structured populations

Individual and population sex allocation patterns

Reproductive parameters of female orangutans (Pongo pygmaeus wurmbii) 1971–2011, a 40-year study at Tanjung Puting National Park, Central Kalimantan, Indonesia

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