Diagnosing confounded Bateman gradients

Area of Science:

• Evolutionary Biology
• Sexual Selection
• Behavioral Ecology

Background:

• The Bateman gradient quantifies the fitness benefits of increased mating success.
• Confounding factors can misrepresent the strength of precopulatory sexual selection.
• Understanding these confounders across diverse biological systems is limited.

Purpose of the Study:

• To investigate how different covariances confound the male Bateman gradient.
• To identify which covariates are most problematic.
• To offer methods for diagnosing and interpreting confounded Bateman gradients.

Main Methods:

• Simulation of 9 biological scenarios with confounded male mating success and reproductive success.
• Analysis of covariances between mating success and female fecundity, egg allocation, or ejaculate traits.
• Exploration of the impact of anisogamy and sperm competition levels.

Main Results:

• Covariances with female fecundity/egg allocation confound male Bateman gradients more than ejaculate traits.
• This effect is pronounced in systems with high anisogamy and no sperm competition.
• Partial Bateman gradients improve interpretation when covariates are confounders.

Conclusions:

• Female fecundity and egg allocation are significant confounders of the male Bateman gradient.
• Empirical researchers should consider mating order and state causal assumptions.
• Partial Bateman gradients offer a more accurate measure of precopulatory sexual selection when confounding occurs.