Sex allocation based on relative and absolute condition.

Area of Science:

• Evolutionary biology
• Ecology
• Genetics

Background:

• Traditional models predict sex allocation based on relative individual condition.
• Environmental fluctuations can lead to biased sex ratios and loss of condition-dependent sex allocation in short-lived organisms.
• The role of relative condition assessment in temperature-dependent sex determination (TSD) is not fully understood.

Purpose of the Study:

• To investigate the importance of relativity in defining individual condition for TSD in fluctuating environments.
• To model how environmental fluctuations and relative condition assessment influence sex ratios in short-lived and long-lived organisms.
• To explore the evolutionary implications of condition relativity on TSD reaction norms.

Main Methods:

• Development of a simulation model for TSD in fluctuating environments.
• Examination of how relativity in condition influences TSD reaction norms.
• Comparison of model predictions with empirical data from painted turtles.

Main Results:

• Short-lived organisms evolve switchlike TSD reaction norms when allowed to define condition relatively, preventing biased sex ratios.
• Long-lived organisms also evolve switchlike reaction norms but with less relative condition definition, leading to biased sex ratios.
• Painted turtle TSD reaction norms partially track mean annual temperature, supporting the model's predictions.

Conclusions:

• Relativity in condition assessment is crucial for preventing biased cohort sex ratios in short-lived organisms with TSD.
• TSD reaction norms evolve to be switchlike, with the degree of relativity influencing their adaptation to environmental fluctuations.
• This framework advances understanding of multifactorial sex determination and frequency-dependent selection on sex in vertebrates.