During sexual intercourse, HIV-infected men transmit HIV through their semen, which carries free-floating virus as well as HIV-infected leukocytes. Traces of HIV have been detected on sperm as well, but the role they play in viral transmission has been a matter of debate. After all, men with vasectomies can transmit HIV. Now, Ceballos et al. show that HIV attaches to the surface of sperm and that these HIV carriers pass on the virus to DCs and other HIV targets.

Sperm express molecules known to interact with HIV’s envelope, such as heparan sulfate and mannose receptors. The authors show that HIV relies on heparan sulfate to attach to sperm, but not mannose receptors as previously predicted.

Once attached, the virus was transmitted from sperm to DCs in culture. The DC receptors CD4 and DC-SIGN were required for transmission, suggesting that DCs pick up the virus by binding to sperm rather than by ingesting them. DCs matured after interacting with the sperm, producing tolerance-promoting cytokines like interleukin-10. The authors speculate that this immune-suppressing profile, versus an inflammatory profile, might also help the virus spread.

Sperm might reach DCs by passing through microabrasions in the vaginal or anal lining that often form during intercourse, suggest the authors. Or they might contact the finger-like projections of DCs that extend to the surface of mucosal linings. Furthermore, the team found that a slightly acidic pH, similar to the pH in the vagina after sex, promoted HIV-sperm binding and the subsequent rate of sperm-related DC infection.

Source:
Rita Sullivan
Rockefeller University Press

The study shows that in most species males show more consistent, predictable behaviours, particularly in relation to parental care, aggression and risk-taking. Females, on the other hand, are more likely to vary their behaviour. They are also more likely to respond to these traits and therefore seem to be ‘choosier’ about the personality of a potential mate.

The research, which is published in the journal Biological Reviews (18 November 2009) draws on several studies, dating back to 1972. It is the latest study in a growing body of research from a University of Exeter team that links gender personality differences to sexual selection.

The authors believe sexual selection may hold the key to this variation. A concept originally developed by Charles Darwin, sexual selection is the theory that evolutionary traits can be explained by competition between one sex – usually males – for mates and by (female) mate choice. While the physical attributes resulting from sexual selection – from dazzling peacocks tails to over-sized antler horns – are well known, there has been much less of a focus on the impact on personality.

Lead author Dr Wiebke Schuett of the University of Exeter says: “Our study is the first to bring together research about the impact of sexual selection on personality in humans and other animals. Our study suggests that, while males tend to exhibit more pronounced personalities, including more predictable behaviour, in a range of different contexts, females are more receptive to these traits in males. We found a surprising level of similarity across a range of species.”

This paper supports research carried out by the same team, published in the journal Animal Behaviour (February 2009). The team studied the social and feeding behaviours of a population of zebra finches. They found that although the male zebra finches did not explore their environment more than the females, they were more consistent in their exploratory behaviour. The team concluded that males are more likely to be selected as mates if they are consistent in any behaviour that would be beneficial to a partnership and its offspring. This would include finding food or seeing off predators.

Dr Sasha Dall of the University of Exeter, the team leader, says: “This body of research suggests that male personality could have evolved in much the same way as signs of physical attractiveness – to help attract a mate. Scientists have not given the role of sexual selection in shaping animal personality much consideration in the past. We hope that our work will pave the way for further research in this rather overlooked subject.”

Dr Wiebke Schuett was funded by the European Social Fund.

The paper, entitled Sexual Selection and Animal Personality, can be accessed at http://www3.interscience.wiley.com/journal/119878059/issue (DOI: 10.1111/j.1469-185X.2009.00101.x).

Source: Sarah Hoyle
University of Exeter