Sex-differential herbivory in androdioecious Mercurialis annua.

Males of plants with separate sexes are often more prone to attack by herbivores than females. A common explanation for this pattern is that individuals with a greater male function suffer more from herbivory because they grow more quickly, drawing more heavily on resources for growth that might otherwise be allocated to defence. Here, we test this 'faster-sex' hypothesis in a species in which males in fact grow more slowly than hermaphrodites, the wind-pollinated annual herb Mercurialis annua. We expected greater herbivory in the faster-growing hermaphrodites. In contrast, we found that males, the slower sex, were significantly more heavily eaten by snails than hermaphrodites. Our results thus reject the faster-sex hypothesis and point to the importance of a trade-off between defence and reproduction rather than growth.

2010 Iowa Youth Survey State of Iowa Results, June 2011

The Iowa Department of Public Health (IDPH) collaborated with schools in Iowa to conduct the 2014 Iowa Youth Survey (IYS). In a series of surveys that have been completed every two or three years since 1975. The survey is conducted with students in grades 6, 8, and 11 attending Iowa public and private schools. The IYS includes questions about students’ behaviors, attitudes, and beliefs, as well as their perceptions of peer, family, school, neighborhood, and community environments.

Rapport sur les honneurs et récompenses militaires : le 28 janvier 1792 ([Reprod.]) / fait à l'Assemblée nationale, au nom du Comité d'instruction publique ; par M. Viennot,... ; impr. par ordre de l'Assemblée nationale

Collection : Les archives de la Révolution française ; 11.1a.449

Sex-chromosome turnovers induced by deleterious mutation load.

In sharp contrast with mammals and birds, many cold-blooded vertebrates present homomorphic sex chromosomes. Empirical evidence supports a role for frequent turnovers, which replace nonrecombining sex chromosomes before they have time to decay. Three main mechanisms have been proposed for such turnovers, relying either on neutral processes, sex-ratio selection, or intrinsic benefits of the new sex-determining genes (due, e.g., to linkage with sexually antagonistic mutations). Here, we suggest an additional mechanism, arising from the load of deleterious mutations that accumulate on nonrecombining sex chromosomes. In the absence of dosage compensation, this load should progressively lower survival rate in the heterogametic sex. Turnovers should occur when this cost outweighs the benefits gained from any sexually antagonistic genes carried by the nonrecombining sex chromosome. We use individual-based simulations of a Muller's ratchet process to test this prediction, and investigate how the relevant parameters (effective population size, strength and dominance of deleterious mutations, size of nonrecombining segment, and strength of sexually antagonistic selection) are expected to affect the rate of turnovers.