Males among many species, including humans, evaluate cues of sperm competition risk and adjust accordingly their sperm competition tactics. The number of potential sexual rivals can serve as an index of sperm competition risk. Therefore, men may adjust their in-pair copulatory interest in accordance with the presence of sexual rivals. Using self-reports from 45 married men, we test the hypothes...

sperms are highly specialized cells for delivering dna from male to the ovum. incredibly, wide degree of diversity in sperm morphology in their basic structures i.e. head, middle piece and tail is found across species. differences in terms of overall size of the sperm, shape and number of sperm produced are also incredible. one of the key for this variations or diversity in sperm may be associa...

We present a model of sperm competition that incorporates both sperm and nonsperm parts of the ejaculate. Our primary focus is on determining how ejaculate composition and size evolves as a function of the effects of seminal fluid on male reproductive success and as a function of asymmetry in sperm usage by females. The model predicts that different patterns of investment in sperm and seminal p...

Males in many taxa are known to exhibit behavioural plasticity in response to the perceived intensity of sperm competition, reflected in Drosophila melanogaster by increased copulation duration following prior exposure to a rival. We tested the prediction that males do not adjust their copulation effort in response to the presence of a competitor in Drosophila species where there is little or n...

Ornithologists have known for a long time that males of monogamous bird species sometimes copulate with females from other pairs, but it is only in the last few years that researchers have shown that these extra-pair copulations can result in offspring and increase male reproductive success. Males time their extra-pair copulations to coincide with the period when females are fertilizable, and t...

Sperm from Drosophila simulans that carry a sex-ratio distorter is preferentially lost from females' sperm-storage organs. This suggests that sperm dumping is a major factor affecting sperm competition in this species, and may have evolved in response to sex-ratio distorters.

heavy metal pollutions of aquatic ecosystems have already raised many concerns on aquaticorganisms’health and survival especially on their sperm. the effects of a single metal on sperm may be totallydifferent from cocktail of several metals because of their interactions, so the effects of zinc, cadmium andcalcium on the trout and carp sperms and their competition have been examined by incubatio...

Most females mate with many males. This can be costly, but the benefits to females are often unclear. A new study raises the possibility that females could benefit through an unconventional genetic pathway, while also showing that males can inadvertently increase rival males' fitness in surprising ways.