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No seasonal sex ratio shift despite sex-specific fitness returns of hatching date in a lizard with genotypic sex determination

Uller, Tobias LU and Olsson, Mats (2006) In Evolution 60(10). p.2131-2136
Abstract
Sex allocation theory predicts that mothers should adjust their sex-specific reproductive investment in relation to the predicted fitness returns from sons versus daughters. Sex allocation theory has proved to be successful in some invertebrate taxa but data on vertebrates often fail to show the predicted shift in sex ratio or sex-specific resource investment. This is likely to be partly explained by simplistic assumptions of vertebrate life-history and mechanistic constraints, but also because the fundamental assumption of sex-specific fitness return on investment is rarely supported by empirical data. In short-lived species, the time of hatching or parturition can have a strong impact on the age and size at maturity. Thus, if selection... (More)
Sex allocation theory predicts that mothers should adjust their sex-specific reproductive investment in relation to the predicted fitness returns from sons versus daughters. Sex allocation theory has proved to be successful in some invertebrate taxa but data on vertebrates often fail to show the predicted shift in sex ratio or sex-specific resource investment. This is likely to be partly explained by simplistic assumptions of vertebrate life-history and mechanistic constraints, but also because the fundamental assumption of sex-specific fitness return on investment is rarely supported by empirical data. In short-lived species, the time of hatching or parturition can have a strong impact on the age and size at maturity. Thus, if selection favors adult sexual-size dimorphism, females can maximize their fitness by adjusting offspring sex over the reproductive season. We show that in mallee dragons, Ctenophorus fordi, date of hatching is positively related to female reproductive output but has little, if any, effect on male reproductive success, suggesting selection for a seasonal shift in offspring sex ratio. We used a combination of field and laboratory data collected over two years to test if female dragons adjust their sex allocation over the season to ensure an adaptive match between time of hatching and offspring sex. Contrary to our predictions, we found no effect of laying date on sex ratio, nor did we find any evidence for within-female between-clutch sex-ratio adjustment. Furthermore, there was no differential resource investment into male and female offspring within or between clutches and sex ratios did not correlate with female condition or any partner traits. Consequently, despite evidence for selection for a seasonal sex-ratio shift, female mallee dragons do not seem to exercise any control over sex determination. The results are discussed in relation to potential constraints on sex-ratio adjustment, alternative selection pressures, and the evolution of temperature-dependent sex determination. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Evolution
volume
60
issue
10
pages
2131 - 2136
publisher
Wiley-Blackwell
external identifiers
  • scopus:33751330206
ISSN
1558-5646
DOI
10.1111/j.0014-3820.2006.tb01850.x
language
English
LU publication?
no
id
569a6f89-1eee-44bb-9120-ed7500556204 (old id 4731489)
date added to LUP
2014-11-11 13:22:39
date last changed
2017-09-03 04:53:30
@article{569a6f89-1eee-44bb-9120-ed7500556204,
  abstract     = {Sex allocation theory predicts that mothers should adjust their sex-specific reproductive investment in relation to the predicted fitness returns from sons versus daughters. Sex allocation theory has proved to be successful in some invertebrate taxa but data on vertebrates often fail to show the predicted shift in sex ratio or sex-specific resource investment. This is likely to be partly explained by simplistic assumptions of vertebrate life-history and mechanistic constraints, but also because the fundamental assumption of sex-specific fitness return on investment is rarely supported by empirical data. In short-lived species, the time of hatching or parturition can have a strong impact on the age and size at maturity. Thus, if selection favors adult sexual-size dimorphism, females can maximize their fitness by adjusting offspring sex over the reproductive season. We show that in mallee dragons, Ctenophorus fordi, date of hatching is positively related to female reproductive output but has little, if any, effect on male reproductive success, suggesting selection for a seasonal shift in offspring sex ratio. We used a combination of field and laboratory data collected over two years to test if female dragons adjust their sex allocation over the season to ensure an adaptive match between time of hatching and offspring sex. Contrary to our predictions, we found no effect of laying date on sex ratio, nor did we find any evidence for within-female between-clutch sex-ratio adjustment. Furthermore, there was no differential resource investment into male and female offspring within or between clutches and sex ratios did not correlate with female condition or any partner traits. Consequently, despite evidence for selection for a seasonal sex-ratio shift, female mallee dragons do not seem to exercise any control over sex determination. The results are discussed in relation to potential constraints on sex-ratio adjustment, alternative selection pressures, and the evolution of temperature-dependent sex determination.},
  author       = {Uller, Tobias and Olsson, Mats},
  issn         = {1558-5646},
  language     = {eng},
  number       = {10},
  pages        = {2131--2136},
  publisher    = {Wiley-Blackwell},
  series       = {Evolution},
  title        = {No seasonal sex ratio shift despite sex-specific fitness returns of hatching date in a lizard with genotypic sex determination},
  url          = {http://dx.doi.org/10.1111/j.0014-3820.2006.tb01850.x},
  volume       = {60},
  year         = {2006},
}