First-Cohort Advantage Hypothesis: A New Twist on Facultative Sex Ratio Adjustment

Wright, Debra D.; Ryser, Jan T.; Kiltie, Richard A.

doi:10.1086/285732

Cited by 33 publications

(29 citation statements)

References 11 publications

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“…For example, in birds and mammals, seasonal sex ratio patterns can reflect conditional sex allocation when birth date differentially affects the reproductive success of the sexes (for example, if earlier born sons are superior 18 or mature sooner 19 ). For these models to apply to our system, however, all individuals born in spring and autumn would have to compete for the same set of mates at some point in the future.…”

Section: Discussionmentioning

confidence: 99%

Adaptive sex allocation in anticipation of changes in offspring mating opportunities

2013

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Sex allocation theory explains why most species produce equal numbers of sons and daughters, and highlights situations that select for deviation from this norm. Past research has, however, heavily focused on situations with discrete generations. When temporally varying generational overlap affects future mate availability, models predict cyclical shifts in sex allocation, but these predictions have not yet been appropriately tested. Here we provide evidence that mosquitofish (Gambusia holbrooki) populations possess a suitable life history: some autumn-born females bred alongside their own offspring, while such overlap was rare or absent for spring-born females and for all males. Our analytic model of sex allocation for these populations produced a perfect rank-order correlation between observed birth sex ratio biases and theoretical predictions, with stronger biases observed as the extent of female generational overlap increased. This is the first robust evidence that sex allocation theory accounts for cases when mating opportunities vary predictably over time.

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Section: Discussionmentioning

confidence: 99%

Adaptive sex allocation in anticipation of changes in offspring mating opportunities

2013

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“…This is true in Virginia Opossums (Didelphis virginiana: Wright et al 1995), Meadow Voles (Microtus pennsylvanicus: Dobson and Myers 1989), and Gray-tailed Voles (Microtus canicaudus: Bond et al 2003), and this pattern has been termed the first-cohort advantage hypothesis (Wright et al 1995). In Virginia Opossums, females had more male-biased first litters than second litters, possibly due to the increased reproductive fitness of males born earlier (Wright et al 1995). Additionally, in Meadow Voles, more male-biased litters were born earlier in the season than later, corresponding to a similar pattern in litter size, which also declined as the season progressed (Dobson and Myers 1989).…”

Section: Discussionmentioning

confidence: 94%

“…We expect that in species that have a much longer birthing period or multiple litters within a year, seasonal sex ratio biases would be more prominent. This is true in Virginia Opossums (Didelphis virginiana: Wright et al 1995), Meadow Voles (Microtus pennsylvanicus: Dobson and Myers 1989), and Gray-tailed Voles (Microtus canicaudus: Bond et al 2003), and this pattern has been termed the first-cohort advantage hypothesis (Wright et al 1995). In Virginia Opossums, females had more male-biased first litters than second litters, possibly due to the increased reproductive fitness of males born earlier (Wright et al 1995).…”

Section: Discussionmentioning

confidence: 98%

Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, <em>Odocoileus virginianus</em>

Saalfeld

Ditchkoff

Ozoga³

et al. 2007

Can Field Nat

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Since Trivers and Willard first proposed their hypothesis concerning the adaptive advantages of producing a particular offspring sex in relation to maternal condition in 1973, it has been at the forefront of scientific research concerning sex ratios with most subsequent studies focusing on maternal condition as a key contributor to variations in sex ratios. Another factor that could greatly influence sex ratios, although has been only infrequently examined in mammalian species, is birth date. We investigated how birth date influenced offspring sex ratios in White-tailed Deer (Odocoileus virginianus). Since date of birth can greatly influence an individual’s fitness and reproductive success, we suggest that birth date may be an alternative strategy in determining offspring sex ratios. Since it has been shown that the lifetime reproductive fitness of a mother can be increased by producing a particular sex during a particular time, we hypothesized that more male offspring should be born earlier in the season due to their increased reproductive potential from being born at this time. Offspring born earlier will have a head start in development and therefore have greater potential for increased body size and dominance later in life, traits that greatly influence male reproductive success. In this study, we found that maternal condition did not affect offspring sex ratio in a captive population of White-tailed Deer in Michigan; however, birth date did. We found that more males tended to be born during the second and fourth birthing periods, while more females were born during the first, third and fifth periods. In addition, we found that males born earlier in the season had greater mass the following spring than those born later, a trend that was not as dramatic in females. These results lend moderate support to our hypothesis that in White-tailed Deer offspring sex will tend to vary according to timing of birth and relative reproductive advantages gained by a particular sex being born at that time.

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“…Studies on vertebrates have demonstrated sex differences in the effect of birth date on fertility (Conover, 1984), age at maturity (Daan et al, 1996), and in mating success because of intrasexual selection (Wright et al, 1995;Smallwood and Smallwood, 1998). Similarly, a sex difference in the timing of arrival to breeding sites such as PAT should arise when the relationship between timing and reproductive success varies with sex.…”

Section: Discussionmentioning

confidence: 99%

“…For example, sex differences in hatch date distribution have been shown in two ectothermic vertebrates in which there is temperaturedependent sex determination (TSD; Harlow and Taylor, 2000;Conover, 2004). Similarly, the sex ratio of offspring varies with season in some birds and mammals (Dijkstra et al, 1990;Wright et al, 1995;Daan et al, 1996;Smallwood and Smallwood, 1998). Another well-documented pattern of sexual difference in seasonal timing is protandrous arrival timing (PAT, not to be confused with protandry as a form of sequential hermaphroditism), which is early male arrival at breeding sites because of sex differences in the timing of migration or transition to adulthood.…”

mentioning

confidence: 99%

A Sex Difference in Seasonal Timing of Birth in a Livebearing Fish

Schultz¹

2008

Copeia

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First-Cohort Advantage Hypothesis: A New Twist on Facultative Sex Ratio Adjustment

Cited by 33 publications

References 11 publications

Adaptive sex allocation in anticipation of changes in offspring mating opportunities

Adaptive sex allocation in anticipation of changes in offspring mating opportunities

Seasonal Variation in Sex Ratios Provides Developmental Advantages in White-tailed Deer, <em>Odocoileus virginianus</em>

A Sex Difference in Seasonal Timing of Birth in a Livebearing Fish

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