Good genes sexual selection in nature

Abstract

Whether the mate sampling and choice performed by females in nature influences offspring performance is a controversial issue in theory and an open empirical question. Pronghorn (Antilocapra americana) females engage in an obvious and energetically expensive mate sampling process to identify vigorous males. Although individual females sample independently, their choices converge on a small proportion of males that sire most young. Offspring of attractive males were more likely to survive to weaning and to age classes as late as 5 years, resulting in a selection differential, calculated by expected differences in lifetime number of offspring weaned, of 0.32 against random mating. Enhanced survival to weaning appeared to be accomplished by faster growth rates. Females compensated for matings with a less attractive mate by elevating rates of milk delivery to their young. Because pronghorn males do not have costly ornaments, we conclude that female choice for good genes can exist in the absence of ornaments. Furthermore, female choice may be important and unrecognized as a force that can lower population genetic load.

Fig. 1.

The yearly distribution of number of offspring sired by the total population of breeding-age pronghorn males.

Fig. 2.

The cumulative number of offspring sired across the 4 study years by all males that sired at least one offspring. Each bar represents a single male.

Fig. 3.

Expected offspring survival to weaning (line indicates prediction; shaded area indicates 95% confidence interval) as a function of sire attractiveness as predicted by a generalized linear latent and mixed model program that removed the effects of maternal identity and birth year.

Fig. 4.

Kaplan–Meier survival functions for offspring of attractive (upper line) versus nonattractive (lower line) males. See text for the definition of attractiveness.

Fig. 5.

Estimates of total suckling time of pronghorn fawns during peak lactation as a function of the total number of offspring sired in the 4-year study period by the sire.