Uncoupling the links between male mating tactics and female attractiveness

Because not all females are equally attractive, and because mating reduces the chances of getting further copulations, males should prefer better-quality mates. In this paper, we use the Trinidadian guppy (Poecilia reticulata) to explore the effects of two non-correlated measures of female quality--size and reproductive status--on male mating decisions. All male guppies employ two alternative mating tactics. We found that large females, particularly those from a high predation site, were the target of most sneaky mating attempts. The response persisted in fish raised under standard conditions over several generations in the laboratory. In addition, non-pregnant females received more courtship displays. We conclude that males can discriminate among females and that they uncouple their mating tactics to track different axes of quality.

Possible role of female discrimination against 'redundant' males in the evolution of colour pattern polymorphism in guppies

Multiple paternity of offspring can result from active preferences on the part of females or sexual harassment by males. We examined sexual responses of female guppies to a previous mate versus a novel male (experiment 1) or to a male with a colour pattern similar to that of the previous mate versus a novel male (experiment 2). Females showed significantly more sexual responses to courtship by novel males than to previous mates in experiment 1 or to males that resembled previous mates in experiment 2. These results suggest that females discriminate actively against previous mates, and extend this discrimination to males with similar colour patterns to previous mates. This could lead to negative frequency-dependent sexual selection against common colour patterns (a 'redundant male effect'), which could contribute to the maintenance of the extraordinarily high levels of genetic polymorphism in guppy colour patterns.

Observed versus indirect estimates of incidence of open-angle Glaucoma

Incidence data on open-angle glaucoma (OAG) are limited and difficult to obtain. To date, few studies have reported incidence directly measured from population-based cohorts. Other reported estimates have been derived indirectly from age-specific prevalence by using several assumptions, and their validity is unknown. To the authors' knowledge, this report presents the first comparison of observed versus indirect estimates of OAG incidence based on data from the population-based Barbados Incidence Study of Eye Diseases (1992-1997) (n= 3,427; 85 percent participation). The observed 4-year incidence of OAG was 1.2 percent (95 percent confidence interval (CI):ages 60-69 years, and 4.2 percent (95 percent CI: 2.6, 6.3 percent) in persons at ages 70 or more years. When incidence was calculated from the prevalence data, power function fitting achieved a closer approximation to observed incidence than did logistic curve fitting. Calculated incidence rate for each group were similar when assuming mortality that was equal (incidence rate= 0.7, 1.3, 2.3, and 4.8 percent) or differential (incidence rate= 0.7, 1.2, 2.4, and 4.8 percent). Other nonlogistic approaches also increased the resemblance of observed and calculated estimates. The absence of longitudinal data, reasonably valid incidence estimates of OAG were obtained from available prevalence data. These estimation techniques can be useful when OAG incidence estimates are required for research or public health purposes. (AU)