Department of Psychology, Norwegian University of Science and Technology, Norway.
Department of Psychology, University of Tromsø, Norway.
Physiol Behav. 2019 Mar 15;201:184-190. doi: 10.1016/j.physbeh.2019.01.010. Epub 2019 Jan 14.
Sexually receptive female rats normally copulate with several males during estrus, and multiple paternity is common. Sperm competition is therefore likely to occur. One response to competitive mating is to enhance sperm output per ejaculation and another is to augment the number of ejaculations. The latter alternative requires more intense copulatory behavior. In studies in a seminatural environment we observed that male rats did not modify their behavior according to the intensity of competition, whereas observations from standard observation cages suggested that they do so. In order to further evaluate the potential response to competitive mating, we observed male rats copulating in a pair situation, i.e. one male and one female, and in a situation where three males simultaneously copulated with one female. In addition to sexual behavior, social interactions were quantified. It was found that the males in the multiple male condition prolonged mount and intromission latencies, and displayed a reduced number of mounts. There was no change in the number of preejaculatory intromissions or the ejaculation latency. The multiple mating did not affect non-sexual interactions with the female, whereas the female displayed more nose-offs and rejections when copulating with three males. It is concluded that mating competition does alter the initiation of copulation in the male rat, whereas copulatory behavior, i.e. intromission and ejaculation, remains unchanged.
性活跃的雌性大鼠在发情期通常会与多个雄性大鼠交配，而且多父本现象很常见。因此，精子竞争很可能发生。一种应对竞争交配的策略是增加每次射精的精子输出量，另一种策略是增加射精次数。后一种选择需要更强烈的交配行为。在半自然环境下的研究中，我们观察到雄性大鼠不会根据竞争的激烈程度改变其行为，而在标准观察笼中的观察结果表明它们会这样做。为了进一步评估对竞争交配的潜在反应，我们观察了雄性大鼠在一对（即一雄一雌）交配和三只雄性同时与一只雌性交配的情况下的交配行为。除了性行为，还量化了社会互动。结果发现，在多只雄性的情况下，雄性的交配潜伏期和插入潜伏期延长，交配次数减少。前射精插入次数或射精潜伏期没有变化。多次交配不会影响雄性与雌性的非性行为互动，而当雌性与三只雄性交配时，会表现出更多的拒绝行为。因此，可以得出结论，交配竞争确实会改变雄性大鼠开始交配的行为，而交配行为（即插入和射精）则保持不变。
