Sex Ratio Variation in Relation to Maternal Condition and Parental Investment in Wild Reindeer Rangifer t. tarandus

Theory suggests that a male in good condition at the end of the period of parental investment will outproduce a sister in similar condition, while she will outproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. As maternal condition declines from good to poor, the fetal sex ratio should decline from a high proportion of males to a high proportion of females. Data from 1525 domestic reindeer (Rangifer tarandus) in six different herds slaughtered during December and January in 1976 through 1979 do not support a relationship between the sex of the fetus and either the condition of the mother or her age.

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Male-biased litter sex ratio in the southernmost Iberian population of edible dormouse: a strategy against isolation?

Animal Biology ◽

10.1163/15707563-00002512 ◽

2016 ◽

Vol 66 (3-4) ◽

pp. 415-425

Author(s):

Mariona Ferrandiz-Rovira ◽

Lídia Freixas ◽

Ignasi Torre ◽

Sílvia Míguez ◽

Antoni Arrizabalaga

Keyword(s):

Sex Ratio ◽

Iberian Peninsula ◽

Sex Allocation ◽

Resource Competition ◽

Lifetime Reproductive Success ◽

Maternal Condition ◽

Ratio Variation ◽

Iberian Population ◽

Isolation Effects ◽

Edible Dormice

Litter sex ratio is a key component of parental fitness due to its impact on lifetime reproductive success. Multiple causes may lay at the origin of sex ratio variation among species and populations, such as maternal condition, local resource competition, presence of helpers, habitat quality or inbreeding levels. Whereas variation in sex allocation between species is relatively well understood, it is still unclear how and why litter sex allocation differs within species. Here, we present an analysis of litter sex ratio variation in two populations of edible dormice (Glis glis) over nine years of study. Populations are situated in the Montnegre and Montseny massifs in Catalonia (NE Iberian Peninsula). The Montnegre population is nowadays an isolated population located at the southernmost range edge of the species in the Iberian Peninsula. Litter sex ratio was male-biased in Montnegre but balanced in Montseny, whereas both populations showed a balanced adult sex ratio. We suggest that this differential sex allocation investment in Montnegre, may be a strategy to overcome isolation effects in this massif, as males are the dispersing sex in this and other rodent species.

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Extreme sex ratio variation in relation to change in condition around conception

Biology Letters ◽

10.1098/rsbl.2007.0089 ◽

2007 ◽

Vol 3 (4) ◽

pp. 395-397 ◽

Cited By ~ 58

Author(s):

Elissa Z Cameron ◽

Wayne L Linklater

Keyword(s):

Reproductive Success ◽

Sex Ratio ◽

Actual Condition ◽

Maternal Condition ◽

Feral Horses ◽

Ratio Variation ◽

Extreme Variation ◽

Before And After ◽

Per Se ◽

The Relationship

Adaptive theory predicts that mothers would be advantaged by adjusting the sex ratio of their offspring in relation to their offspring's future reproductive success. Studies investigating sex ratio variation in mammals have produced notoriously inconsistent results, although recent studies suggest more consistency if sex ratio variation is related to maternal condition at conception, potentially mediated by changes in circulating glucose level. Consequently, we hypothesized that change in condition might better predict sex ratio variation than condition per se . Here, we investigate sex ratio variation in feral horses ( Equus caballus ), where sex ratio variation was previously shown to be related to maternal condition at conception. We used condition measures before and after conception to measure the change in condition around conception in individual mothers. The relationship with sex ratio was substantially more extreme than previously reported: 3% of females losing condition gave birth to a son, whereas 80% of those females that were gaining condition gave birth to a son. Change in condition is more predictive of sex ratio than actual condition, supporting previous studies, and shows the most extreme variation in mammals ever reported.

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