Mate choice could be random in female rats (Rattus norvegicus)

Mate choice could be random in female rats (Rattus norvegicus). Olivia Le Moëne, Eelke M. Snoeren. Physiology & Behavior, https://doi.org/10.1016/j.physbeh.2017.10.031

Highlights
•    Female rats prefer the male visited first in a multiple partners paradigm.
•    This mate selection is not based on the male rats, but on the location of the male.
•    It suggests that mate choice in female rats is random.

Abstract: Female mate choice is often investigated in terms of reproductive success in order to understand how male characteristics contribute to sexual attractiveness. Previous studies have found that females rats prefer mating with their first encounter rather than males visited subsequently, suggesting that the rewarding value of this first encounter is enough to reinforce mating with the first partner. Using a multiple chambers paradigm, we allowed female rats to copulate freely with three males placed each in a different chamber. Then, we switched the males' position, and let the female interact with them freely again within the same session. We tested whether female mate choice was relying rather on a preferred male rat or on a preferred mating location. The results showed that females spent most time with the male in the chamber of 1st entry in the beginning, but as soon as male rats switched chambers, the female rat continued to copulate with the new male in the same chamber of 1st entry, instead of mating with her previously preferred male rat. This suggests that the male preference is an artefact of location preference. Therefore, female mate choice seems to be rather random than the consequence of an individual choice based on male characteristics. This finding, although contradictory with the intuitive feeling that mate choice is a crucial feature in sexual and reproductive behavior, is supported by several recent observations. In the coming years, behavioral neuroscience should bring light to the brain processes at work in random mate choice.

Keywords: Female rats; Multiple partner; Sexual behavior; Mate choice; Location

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The procedures were similar to those previously described [1]. At the start of the experiment, a (sexually experienced, hormonally primed) female rat was placed in the
middle chamber of the multiple chambers set-up. The subject was allowed to move freely and habituate to the chambers for 5 minutes. Then, for another 5 minutes, the female was placed in the middle chamber, while three (sexually experienced) male rats were positioned in the three surrounding small chambers. During this time, the openings were blocked with a wire mesh allowing the female subject to see, smell and hear the male rats without any possibility of physical contact (habituation phase). The number of times the female rat sniffed the opening of each of the male chambers was determined, as an indicator of olfactory preference [10, 11].

After the habituation phase, the openings were unblocked and the female rat was allowed to move freely between the chambers for another 15 minutes (copulation phase A). During this period, the following behaviors were scored for each male: order in which the males were visited, latency to first visit, number of visits, time spent in the chambers, number of sniff episodes to the openings of the chambers, and the number of mounts, intromissions and ejaculations per male. In addition, the number of paracopulatory behaviors the female performed in the chamber of each male were counted.

After the copulation phase A, the male rats were quickly randomly placed in a different chamber and the test continued for another 15 minutes (copulation phase B). During this period, the same parameters were scored as during copulation phase A. All sessions were conducted with chambers containing “dirty bedding” that consisted of the smell of several male and female rats. This was done to limit the (potential) effects of bedding odors after the switch.