Why do colder mothers produce larger eggs? An optimality approach

Area of Science:

• Evolutionary biology
• Ecology
• Reproductive biology

Background:

• Maternal effects on offspring size are common, with larger offspring often produced at lower temperatures.
• The adaptive significance of temperature-driven variation in egg size remains largely undetermined.
• Optimal offspring size may vary across different thermal environments.

Purpose of the Study:

• To investigate the relationship between offspring size and performance across three temperatures in zebrafish (Danio rerio).
• To assess the adaptive significance of temperature-mediated offspring size variation.
• To determine if offspring size is adaptively adjusted to thermal conditions.

Main Methods:

• Examined the effects of egg size on pre- and post-hatching performance at different temperatures.
• Developed an optimality model to predict optimal offspring size at each temperature.
• Experimentally tested the model's predictions by observing offspring sizes produced by zebrafish.

Main Results:

• Offspring size had variable effects on performance, depending on life-history stage and temperature.
• The optimality model predicted specific offspring sizes for each temperature: largest at low, intermediate at high, and smallest at intermediate temperatures.
• Experimental results confirmed the model's predictions, showing zebrafish mothers produced offspring sizes matching the predicted rank order.

Conclusions:

• Zebrafish mothers adaptively manipulate offspring size in response to temperature-driven changes in performance.
• Optimality approaches are valuable tools for understanding the adaptive significance of offspring size variation.
• Temperature is a key environmental factor influencing maternal investment in offspring size.