New insights into possible causes of male infertility

Timing of sperm capacitation varies reproducibly among men

Sperm must mature functionally in the process of capacitation to become able to fertilize. Capacitation depends on membrane lipid changes, and can be quantitatively assessed by redistribution of the ganglioside G_M1, the basis of the Cap‐Score™ sperm function test. Here, differences in Cap‐Score were compared among and within men at two time points. Ejaculates were liquefied, washed, and incubated for 3 hr under capacitating (Cap) conditions, then fixed and analyzed immediately (Day0); after being incubated 3 hr under Cap conditions then maintained 22–24 hr in fix (Day1‐fix); or after 22–24 hr incubation under Cap conditions prior to fixation (Day1). In all cases, a light fixative previously shown to allow membrane lipid movements was used. Day1‐fix and Day1 Cap‐Scores were greater than Day0 (p < 0.001; n = 25), whereas Day1‐fix and Day1 Cap‐Scores were equivalent (p = 0.43; n = 25). In 123 samples from 52 fertile men, Cap‐Score increased more than 1SD (7.7; calculated previously from a fertile cohort) from Day0 to Day1‐fix in 44% (54/123) of the samples. To test whether timing of capacitation was consistent within an individual, 52 samples from 11 fertile men were classified into either “early” or “late” capacitation groups. The average capacitation group concordance within a donor was 81%. Median absolute deviation (MAD; in Cap‐Score units) was used to assess the tightness of clustering of the difference from Day0 to Day1‐fix within individuals. The average (2.21) and median (1.98) MAD confirmed consistency within individuals. Together, these data show that the timing of capacitation differed among men and was consistent within men.

Ovulatory shifts in female sexual desire

Women's reproductive biology imposes heavy obligatory costs of parental investment, creating strong selective forces hypothesized to shape female mating psychology around critical decisions such as the choice of partner, the timing of sexual intercourse, and the timing of reproduction. We propose that female sexual desire has evolved as one adaptation among several designed to regulate these decisions. We hypothesize (a) an increase in desire as conception probability increases, but only among women who are in committed long-term relationships; and (b) a shift in the desire for a primary partner as compared with extra-pair partners as ovulation approaches, dependent upon a woman's evaluation of her primary partner's relative quality. We tested several predictions derived from these hypotheses in a study of 173 women who were not taking oral contraceptives. Results confirmed Hypothesis 1: An ovulatory peak in sexual desire was found only for mated women; for unmated women, conception probability and sexual desire were uncorrelated. Hypothesis 2 was partially supported. Among mated women, those with higher conception probability exhibited higher levels of in-pair sexual desire relative to those at lower conception probability. Conception probability and relationship length interacted significantly to predict extra-pair desires, such that women in longer relationships were more likely to experience desire for extra-pair partners during periods of high conception probability. The pursuit of an in-pair conceptive strategy (as opposed to an extra-pair conceptive strategy) was also associated with the occurrence of sexual activity in the relationship.