Sons accelerate maternal aging in a wild mammal.

Area of Science:

• Evolutionary biology
• Gerontology
• Reproductive biology

Background:

• Aging (senescence) involves physiological decline, affecting reproduction and survival.
• Senescence patterns vary, and evolutionary theories on early reproduction's impact are debated.
• Existing theories don't account for sex differences in parental resource needs.

Purpose of the Study:

• To investigate how offspring number and sex ratio affect female reproductive senescence.
• To test evolutionary predictions linking early reproductive effort to aging.
• To explore the role of sex allocation in individual variation in senescence.

Main Methods:

• Utilized long-term data from a bighorn sheep population.
• Analyzed the relationship between early-life offspring weaned (number and sex ratio) and later reproductive senescence.
• Examined actuarial senescence (survival) in relation to early reproduction.

Main Results:

• Female reproductive senescence accelerated with a higher proportion of sons weaned between ages 2-7 years.
• No significant cost of early-life reproduction was found for actuarial senescence (survival).
• Offspring sex ratio, not just number, is a key factor in female reproductive aging.

Conclusions:

• Offspring sex ratio influences the rate of reproductive senescence in female bighorn sheep.
• Findings integrate life history theory and sex allocation, explaining variation in aging.
• Offspring sex ratio may be a crucial factor in individual senescence rates across species, potentially including humans.