Ladies who've settled down with Mr. Stable over Mr. Sexy are more likely to be distant and critical to their stable but not-so-sexy partners during high fertility compared to women with more sexually desirable men.

While numerous studies on reproductive survival have proven that women are more attracted to and more likely to mate with stable rather than purely attractive men in order to secure a more lasting environment to raise her offspring, the latest study of heterosexual couples show that sexual attraction trumps social stability in a time that is, arguably, most important.

"A woman evaluates her relationship differently at different times in her cycle, and her evaluation seems to be colored by how sexually attractive she perceives her partner to be," researcher Martie Haselton, a professor of psychology and communication studies at the University of California-Los Angeles, said in a statement.

However, researchers noted that the negative feelings appear to be fleeting and don't seem to affect a woman's long-term commitment to her romantic relationship.

"Even when these women are feeling less positive about their relationship, they don't want to end it," lead study author Christina Larson, a doctoral candidate in social psychology at UCLA, said in a statement.

To study the changing behavior of women during ovulation, the researchers pinpointed the ovulation cycles of 41 undergraduate women who were in long-term relationships with men. The women were asked to rate the sexual attractiveness of their partners based on questions like, "How desirable do you think women find your partner as a short-term mate or casual sex partner, compared to most men?"

Participants were also asked to answer questions designed to measure their partner's stability or suitability as a long-term mate, including questions about how her partner's present and future financial status compares with that of most men.

Researchers then asked the women to report the quality and state of her romantic relationship at two different periods during her ovulation cycle: right before ovulation when she is most fertile and at low fertility.

Results from the study showed that when women were asked about the quality of their relationship, their feelings remained the same. However, when researcher asked the women how close they felt to their partner, the participants with less sexy partners on average reported less feelings of intimacy and greater aloofness toward their partner as they became more fertile. Researchers noted that the opposite was true for women paired with sexually-desirable men.

Researcher repeated the experiment with 67 new participants, but researchers asked women to list irritating characteristics like moodiness, childishness and thoughtlessness that occurred in their partner. Researchers found that women with less sexy partners were significantly more likely to identify bad characteristics in their partners during the high-fertility period than the low-fertility period.

Researchers said that the findings suggest that women's changing preferences may stem from mating strategies that might have provided an evolutionary benefit long ago.

"Since our female ancestors couldn't directly examine a potential partner's genetic makeup, they had to base their decisions on physical manifestations of the presence of good genes and the absence of genetic mutations, which might include masculine features such as a deep voice, masculine face, dominant behavior and sexy looks," Haselton said.

"It is possible that we evolved to feel drawn to these visible markers because, at least in the past, they proved to be indicators of good genes. Ancestral women who were attracted to these features could have produced offspring who were more successful in attracting mates and producing progeny," she said.

Researchers plan on studying whether such shift in a woman's perceptions of her partner damages her relationship over time. Researchers also plan on studying whether the change in behavior is perceived by the male partners of these women.

"We don't know if men are picking up on this behavior, but if they are, it must be confusing for them," Larson said.

The study is expected to be published in the November issue of the peer-reviewed journal Hormones and Behavior.