Reproductive success and mate choice in Long-Evans rats.

In the present study, mating behavior was observed in female rats that were given the opportunity to mate with two male rats simultaneously. Eleven sexually naïve, naturally cycling rats were assigned to one pair of sexually experienced cohabitating male rats. Each female rat was mated during proestrous with her assigned pair of males. Eight females successfully became pregnant and gave birth to healthy pups (approximately 9 pups/litter). After the offspring were weaned, paternity of each pup was determined using microsatellite DNA markers. Based on this analysis, it was determined that one male in each pair sired the majority of the pups in the litter. No male sexual behaviors or characteristics distinguished male rats that sired the majority of pups from those that sired few or none of the pups. Furthermore, neither female mate preference nor measures of paced mating behavior differed between male rats that had a reproductive advantage from those that did not. Finally, ejaculation order also failed to predict reproductive success of the male rats. Together, these results suggest that reproductive success of some male rats may not depend on specific mating behaviors, but rather their success may depend on physiological or genetic traits that make them unique.

"Coffee, tea and me": moderate doses of caffeine affect sexual behavior in female rats.

The present study evaluated the effects of acute caffeine administration on paced mating behavior and partner preference in ovariectomized rats primed with estrogen and progesterone. In Experiment 1, female rats were tested for paced mating behavior following acute administration of caffeine (15 mg/kg). Caffeine shortened the latency to return to a male following an ejaculation. Although this dose of caffeine did not alter the likelihood of leaving a male after receiving sexual stimulation, locomotor activity did increase significantly. Experiment 2 evaluated the dose response characteristics of caffeine (7.5, 15, 30 mg/kg) administration on paced mating behavior. Replicating Experiment 1, caffeine at the lower doses shortened the latency to return to a male following an ejaculation. Finally, to determine whether the effects of caffeine (15 mg/kg) on contact-return latency reflect a change in sexual motivation or merely an inability to inhibit locomotion, rats were tested for partner preference (intact male vs. estrous female) following caffeine administration (Experiment 3). Although caffeine did not disrupt preference for a sexual partner, caffeine selectively increased visits to the male when physical contact was possible. Collectively, these results suggest that the effects of caffeine on female mating behavior may reflect an increase in both sexual motivation and locomotor activity.