Does sexual bimaturation affect the cost of growth and the operational sex ratio in an extremely size-dimorphic reptile?

Ecoscience ◽  
2009 ◽  
Vol 16 (2) ◽  
pp. 175-182 ◽  
Author(s):  
Grégory Bulté ◽  
Gabriel Blouin-Demers
Keyword(s):  
Sex Ratio ◽  
Operational Sex Ratio ◽  
The Cost

Female-biased mortality induced by male sexual harassment in a feral sheep population

1996 ◽  
Vol 74 (10) ◽  
pp. 1812-1818 ◽  
Author(s):  
Denis Réale ◽  
Patrick Boussès ◽  
Jean-Louis Chapuis
Keyword(s):  
Sex Ratio ◽  
Bimodal Distribution ◽  
Ovis Aries ◽  
Operational Sex Ratio ◽  
High Survival ◽  
Sexually Dimorphic ◽  
Female Mortality ◽  
Male Mortality ◽  
Sheep Population ◽  
The Cost

In contrast to most populations of sexually dimorphic ungulates, a 3-year study revealed a tertiary sex ratio (the number of males per female at sexual maturity) strongly biased towards males in the Île Longue feral sheep (Ovis aries) population (Kerguelen subantarctic archipelago). This population presents a main winter lambing season and a secondary summer lambing period. The sex ratios of lambs and lamb carcasses were even. The skewed sex ratio of adults was therefore attributed to shorter longevity of females. We showed that (i) male monthly mortality followed a bimodal distribution with peaks corresponding to the two rutting periods. Male mortality was, however, highest during the winter even though less rutting occurred in this season than in the summer, suggesting that harsher winter conditions enhance the cost of mating competition; (ii) female mortality was related to the rutting activity of males but not to lambing. Female mortality peaked in the summer despite plentiful food resources. This period corresponds to the main rutting peak, suggesting a high survival cost of mating for females. Female mortality due to male harassment was confirmed by direct observations and examination of females injured during rutting periods. This situation may be due to a strongly male-biased operational sex ratio in the population, associated with an inability of males to establish a stable dominance hierarchy within a large flock.

scholarly journals Sex Chromosome Meiotic Drive in Stalk-Eyed Flies

Genetics ◽  
1997 ◽  
Vol 147 (3) ◽  
pp. 1169-1180 ◽  
Author(s):  
Daven C Presgraves ◽  
Emily Severance ◽  
Gerald S Willrinson
Keyword(s):  
Sex Ratio ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Meiotic Drive ◽  
Operational Sex Ratio ◽  
Genetic Modifiers ◽  
Ratio Distortion ◽  
The Impact ◽  
Sex Ratio Distortion

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13–17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

scholarly journals Deer Indirectly Alter the Reproductive Strategy and Operational Sex Ratio of an Unpalatable Forest Perennial

2020 ◽  
Vol 195 (1) ◽  
pp. 56-69
Author(s):  
Lalasia Bialic-Murphy ◽  
Christopher D. Heckel ◽  
Robert M. McElderry ◽  
Susan Kalisz
Keyword(s):  
Sex Ratio ◽  
Reproductive Strategy ◽  
Operational Sex Ratio
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