Only females in poor condition display a clear preference and prefer males with an average badge

<p>Abstract</p> <p>Background</p> <p>Female condition-dependent variation in mate preference may have important evolutionary implications, not only within the same population but also among populations. There are few experiments, however, on how condition and/or genotype influences female mate preferences. The black throat patch of the male house sparrow, <it>Passer domesticus</it>, is an intensively studied plumage trait. It is often referred to as a 'badge of status' and seems to be involved in female mate choice, but differences exist among populations. Between-population variation in mate preference may occur for condition-dependent mate preferences. We tested the hypothesis that female preference may vary with female quality (body condition). Therefore, we measured female preference for badge size using an aviary two-choice test in which females were presented with two males that had different sizes of badges (enlarged or averaged).</p> <p>Results</p> <p>Overall we did not find a female preference for enlarged or average badges, but low-quality females spent more time near average badge males. Conversely, high-quality females did not show a clear preference.</p> <p>Conclusions</p> <p>Collectively, these results indicate that female preference varies with female quality. Differences in female condition are causes of within-population variation in mating preferences. To our knowledge, our results provide one of the first experimental evidences that variation in preference for a male ornament is associated with female condition. In our study, however, only females of low condition displayed a clear mate preference. Differences observed among populations could be partly explained by differences in female condition.</p

Sex and the selfish herd: sexual segregation within nonmating whirligig groups

The fitness costs and benefits at different positions in fish shoals, bird flocks, and insect swarms can be asymmetric; a group's edge may provide more feeding opportunities, but also greater predator risk. Animals make trade-offs between these selection pressures based on individual differences in traits including satiation level, ability to avoid predators, and sex. Previous studies did not evaluate the impact of sex on group positioning in these types of nonhierarchical, nonmating groups called congregations. A controlled laboratory experiment was conducted, using marked whirligig beetles (Coleoptera: Gyrinidae), to test for sexual segregation and why different sexes might choose different positions. Soon after a disturbance, males often were found at the periphery and females at the center of groups. There was also an overlying influence of feeding on position; satiated individuals moved toward the center and hungry individuals toward the periphery. Several minutes after a disturbance, sexual segregation disappeared, but segregation due to hunger persisted. Sexual segregation in this study was best explained by the predator avoidance hypothesis, not the energy needs hypothesis. Females weighed less than males; this may make them more at risk to predation because of reduced swimming speed or less mechanical protection from their exoskeleton. No difference between the sexes was found in the volume of their defensive chemicals. This is one of the first studies to show that sex influences position of individuals within simple nonmating groups (congregations) and suggests that more attention should be given to positional sex differences within shoals, flocks, herds, and swarms. Copyright 2007, Oxford University Press.