Sex Allocation in a Monogamous Bird: Advantaged Matrilines and Sons with Silver Spoons

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Animal Reproduction

Background:

• Parental investment theory suggests mothers favor offspring sex based on resource availability and fitness returns.
• Offspring sex ratio adjustment is a key maternal strategy influenced by environmental and genetic factors.
• Understanding these dynamics is crucial for explaining reproductive strategies in socially monogamous species.

Purpose of the Study:

• To investigate the influence of early rearing conditions on offspring development and recruitment.
• To examine the covariance between parental quality and genetic predisposition in offspring sex ratio.
• To determine how primary offspring sex ratios are shaped by parental investment in Carolina wrens.

Main Methods:

• A mixed cross-fostering approach was employed to disentangle genetic and environmental effects.
• Data on offspring growth, condition, and recruitment were collected.
• Parental provisioning rates and clutch sex ratios were monitored.

Main Results:

• Male offspring grew larger than females and benefited more from paternal provisioning.
• Females adjusted offspring sex ratios, overproducing sons when paired with high-provisioning males.
• Maternal condition and inherited traits influenced clutch size and sex ratio, favoring daughters.

Conclusions:

• Sex ratio variation in Carolina wrens is shaped by a balance of matrilineal inheritance and environmental influences on parental investment.
• Offspring sex allocation is a complex adaptive strategy responding to both immediate and long-term fitness prospects.
• Paternal investment significantly impacts male offspring success, influencing maternal sex allocation decisions.