MALE MATE CHOICE AS PREDICTED BY SPERM COMPETITION IN 13-LINED GROUND-SQUIRRELS

MALE mate choice is predicted to occur when males transfer nutrients to females during copulation, provide paternal care, or are otherwise limited in mating capacity1-7. Most commonly, field studies have revealed male choice to be focused on females offering high fecundity8-10. Here we describe male mating selectivity that appears to be driven by sperm competition: male thirteen-lined ground squirrels (Spermophilus tridecemlineatus) avoid copulating with previously mated females once the fertilization gain rate drops below the average obtainable from alternative matings. Although this behaviour seems advantageous to males, it limits the duration of female sexual activity. © 1990 Nature Publishing Group.