138 Randel Lecture: Reproductive Behavior – the basis of reproductive success

Abstract

Abstract In domesticated, promiscuous species like sheep, mate choice is constrained by breeding strategies with limited mate choice. The proportion of rams with limited sexual interest in ewes is nearly 30% of the total number of breeding rams. Rams with low sexual interest detect putative sexual signals from ewes but fail to act in a suitable manner. While a tempered reward mechanism with decreased dopamine synthesis in the mid-brain of low sexually performing rams may partially account for this behavior, how the ewe responds to low-sexually performing rams remained unknown. Ewes are relatively undemonstrative in the expression of sexual behavior. The most widely expressed behavior from the ewe is the increased ambulatory behavior to seek out and affiliation with a ram. The expression of this behavior is estrogen dependent and likely increases the sexual interest of the ram and the reproductive success of the ewe. Rams with low sexual interest do mate and sire lambs. It might be expected that ewe affiliation behavior would increase when the ratio of ewes to rams is high (ie. breeding intensity) or sexual interest is low. This does not appear to be the case since ewes express more proceptive behavior toward rams with greater sexual interest. Ewes spent more time in affiliation with high sexually performing rams (P < 0.001) 57.7% (±3.3) than those expressing low sexual interest (23.8% [± 3.4]). Rams expressing high sexually interest garner more solicitous looks from ewes than do low performing rams. Time in affiliation highly correlated with expression of ram behaviors including number of mounts, total anticipatory, and consummatory behavior. While ewes exhibited increased number of purposeful moves toward high performing rams, movement away from the ram to did not differ by expression of male behavior. In conclusion, ewe behavior does not compensate for low sexual interest from the ram and would not be expected to contribute to the reproductive success of rams expressing low sexual interest.