Жаңа серікке деген қызығушылық құбылысы

Sexual phenomenon
The Coolidge effect is a biological phenomenon seen in animals, whereby males exhibit renewed sexual interest whenever a new female is introduced, even after sex with prior but still available sexual partners. To a lesser extent, the effect is also seen among females with regard to their mates. The evolutionary benefit to this phenomenon is that a male can fertilize multiple females. This type of mating system can be referred to as polygyny, where one male has multiple female mates, but each female mates with only one or a few males.

Behavioral endocrinologist Frank A. Beach claims in a 1974 letter to have introduced the term "Coolidge effect" in either 1958 or 1959. He attributed the neologism to

The joke appears in a 1972 book (Aggression in Man and Animals, by Roger N. Johnson, p. 94).

The original experiments with rats applied the following protocol: A male rat was placed into an enclosed large box with four or five female rats in heat. He immediately began to mate with all the female rats repeatedly until he eventually became exhausted. The Coolidge effect is attributed to an increase in dopamine levels and the subsequent effect upon an animal's limbic system. In a study conducted by Fiorino et al., male rats were used to study the role of the mesolimbic dopamine system on their sexual behaviour. In a study conducted by Wood et al., male rats were divided into three conditions, and were presented with a cotton ball laden in either saline (control group), estrous vaginal smear of a familiar female (experimental group), and estrous vaginal smear of a novel female (experimental group). An experiment performed on an external fertilizing fish called Rhodeus amarus, also known as the European bitterling, was used to show that sperm can be allocated differently if a novel partner is around, but that it also happens if there is male male competition. Wedell et al. suggest a theory that when a male allocates sperm so that he can save sperm for novel partners, he limits himself and the mate by possibly investing too little sperm to their partners which in return can inseminate only a few eggs therefore making reproduction less successful. This could even possibly force females to seek more copulation to ensure successful reproduction. These types of evidence of sperm allocation would suggest that Coolidge effect will determine how much sperm is invested into females, and if possible, sperm will be allocated so that sperm can be evenly distributed for multiple mates. Overall, it is typically seen that allocation changes due to male male competition and whether a novel partner is encountered or not.

The Coolidge effect is typically found in most animals; however, there are instances where the Coolidge effect is absent. Because the females in this species control copulation, to test the Coolidge effect in males, two dead females were used. Another study that focused on the Coolidge effect in simultaneously hermaphroditic species confirmed the validity of the Coolidge effect in freshwater snail Lymnaea stagnalis. Biomphalaria glabrata, another simultaneous hermaphrodite freshwater snail, does not exhibit sex specific effects of partner novelty, and thus there is either no Coolidge effect in the species or no difference between the degrees to which the effect is expressed in the respective sexes.

Though there is not just a single reason why males will choose a novel partner, there have been experiments that show that the major determining factor for detecting a novel partner is olfactory preference. An experiment using Long Evans rats, showed that odor played a major role in distinguishing the difference between a novel partner and familiar partner. Another study also examined not only olfactory preference but also what part of the brain targeted the olfactory preference. The conclusion from this experiment was also consistent in rats and monkeys, since damage to this region of the brain impaired standard recognition memory, which would suggest that the hippocampal region of the brain is not crucial in social behavior memory, but rather, the perirhinal entorhinal cortex. This effect of olfaction has also been observed in invertebrates such as flies. In a study conducted by Tan and colleagues, the role of olfaction in species recognition was examined using flies, Drosophila melanogaster, which processed a mutated Orco gene, which codes for a co receptor that is important for olfaction. Another study performed on rats showed the same results, but found data that concluded that reaching optimal chances of impregnating their mates happened after resting for 15 days. These experiments would suggest that one of the major limitations on the Coolidge effect is the physical boundaries of gamete production. Research examining female rats has lent its support, wherein female rats showed a higher incentive motivation for unknown males over ones they had just copulated with. In a study conducted in 2013, researchers conducted an experiment to test if the Coolidge effect could be observed in female rats. In their experiment, they assigned female rats to one of two conditions: paced or non paced. In the paced condition, females were able to control the timing of copulation, while in the non paced condition males regulated the timing of mating. Females in the paced condition were placed into an arena that was divided into two compartments which contained holes that only the female could pass through. The female was placed on one side of the divided arena, and the male was placed in the opposite side; this allowed the female to enter and exit the male's side depending on the circumstances, therefore regulating the timing of copulation. In the non paced condition, both the female and male rats were placed in an undivided arena and were allowed to mate. In both conditions, females were exposed to a constant, familiar male followed by a novel male. Their results found that females showed a significant increase in proceptive behaviours when a novel mate was present, but only if the female could regulate mating. Repeated mating with the same male also resulted in a decrease in proceptivity, which is thought to suggest sexual satiety. These results suggest that the Coolidge effect may also be present in female rats. Lester and Gorzalka developed a model to determine whether or not the Coolidge effect also occurs in females. Their experiment, which used hamsters instead of rats, concluded that it does occur to a lesser degree in females, where the evolutionary advantage of mating with multiple partners is less straightforward. It is possible that the presence of the Coolidge effect in females could serve to optimize the female's reproductive success, and prevent mating with a sterile male. Mating with multiple males may reduce the probability that the female's gametes will not be successfully fertilized.