Do single point condition measurements predict fitness in female pronghorn (Antilocapra americana)?

Condition is frequently used in evolutionary studies as an estimator of fitness. Broad theoretical interpretations of condition include many different attributes that can influence fitness, but in practice, researchers commonly employ condition measures (e.g., body-fat scores or size-adjusted body mass) that have uncertain relationships with reproductive success. In addition, researchers typically rely on condition estimates that are made once. Empirical studies investigating the relationship between condition and fitness are nearly absent. We examined the effect of maternal condition on current and future reproductive success in a wild population of pronghorn (Antilocapra americana (Ord, 1852)). We used body condition scoring and date of annual molt to measure female condition, and mass-size residuals to measure offspring condition at birth. We found that current reproductive success lowered female condition, and that poor condition reduced subsequent prenatal growth rates. However, poor condition did not reduce postnatal offspring condition or future reproductive success. We suggest that the elapsed time should be taken into consideration when making predictions based on single point condition measures. The assumption that condition predicts fitness requires further empirical test.