Sperm precedence

Drnevich J. M., Hayes E. F. and Rutowski R. L. (2000) Sperm precedence, mating interval, and a novel mechanism of paternity bias in a beetle (Tenebrio molitor L.). Behav. Ecol. Sociobiol. 48, 447 -51. 

Siva-Jothy M. T., Blake D. E., Thompson J. and Ryder J. J. (1996) Short- and long-term sperm precedence in the beetle Tenebrio molitor. a test of the adaptive sperm removal hypothesis. Physiol. Ent. 21, 313-316. 

Wade, M. J., and Arnold, S. J., 1980, The intensity of sexual selection in relation to male sexual behaviour, female choice, and sperm precedence, Anim. Behav., 28 446. 

When a variable with the values EPC = 1, IPC = 0 is entered into a multiple regression analysis of the number of sperm in the first copulatory sample produced by each couple, it has a regression coefficient significantly different from zero. As soon as hours since last ejaculation is entered into the equation, however, the EPC variable loses significance, suggesting that the reduced number of sperm in EPC ejaculates may be linked to the fact that EPCs may often be preceded by a more recent ejaculation than other ejaculations. 

Figure 7. Influence of the time interval between a male masturbating and then inseminating a female on the number of sperm inseminated and the number of spenn retained. Although longer abstinence times (masturbation to copulation) increases the number of sperm ejaculated into the woman, the number of sperm she retains does not increase (Baker and Beilis 1993a,b). If the competitiveness of an ejaculate is a trade-off between the age and number of sperm, ejaculates preceded by masturbation a day beforehand may well be the most competitive for an EPC male (Baker 1996).

Men inseminate fewer sperm if they have masturbated beforehand, the amount depending on how recently the masturbation occurred (Baker and Beilis 1993a). The flow-back study shows, however, that the number retained by the female does not decrease (Fig. 7). Inseminates preceded by masturbation are retained in higher proportions and similar numbers as inseminates not so preceded. Yet the sperm inseminated are younger. They should therefore live longer inside the female and, whether the sperm competition proceeds as a lottery, a race or as warfare, could be at a competitive advantage. 

Studies using animals and humans suggest that cannabis docs disrupt the reproductive system in both males and females. For example, chronic marijuana use has been associated with decreases in the number of sperm and sperm motility among men. The potential effects of these disruptions on fertility arc difficult to specify. Frequent use of cannabis by women may produce nonovulatory menstrual cycles, in which menstruation is not preceded by the release of an ovum. As in the males, the delayed effects of these disruptions on fertility are not known. In their reviews, Ehrenkranz and Hembree (1986) Budney, Moore, and Vandrey (2004) and Zimmer and Morgan (1997) concluded that disruptions in reproductive function arc not obvious, although subtle alterations may be operative. 

Bearer, E.L. and Friend, D.S. (1982), Modification of anionic-lipid domains preceding membrane fusion in guinea pig sperm. J. Cell Biol. 92 604-615. 

Mammalian fertilization is the result of a precisely regulated series of cellular interactions. This process can be divided into a number of component stages, including the following (i) the early events that precede egg fusion, consisting of the preliminary event of sperm capacitation, sperm penetration of the cumulus oophorus, zona pellucida adhesion, initiation and completion of acrosome reactions, penetration of the zona pellucida, egg plasma membrane contact and fusion and (ii) the late events that occur within the egg that consist of sperm nuclear decondensation followed by pronuclear consolidation and syngamy. 

Gonzalez-Martinez, M., Guerrero, A., Morales, E de De La Torre, L., and Darszon, A. (1992). A depolarization can trigger Ca uptake and the acrosome reaction when preceded by a hyperpolarization in L pictus sea urchin sperm. Dev.Biol. 750 193-202. 

In this section the development of the procedures to separate and purify protamine from sperm heads or nucleoprotamine, prepared as described in the preceding sections, will be reviewed historically according to the principle of the procedures. 

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