Browsing by Subject "Sexual selection"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Restricted
    Animal personality and biological markets: rise of the individual
    (2009) Jacobs, David S
    The last decade has seen the emergence of two new developments in behavioural ecology: the discovery of animal personalities and a new approach to the analyses of animal behaviour, biological markets. Although both regard individual differences in behaviour as adaptive in their own right, these two developments appear, at first glance, to be opposing approaches to analysing animal behaviour. Personalities consist of suites of behaviours that are correlated across situations (e.g. some animals are consistently more or less aggressive across situations than other animals) and assumes that animals are limited in their response to their environment. By contrast, the biological market approach considers organisms as traders of commodities (e.g. food or grooming) where the exchange rates of commodities changes with time and is influenced by shifts in the abundance and demand for the commodity, as happens in human markets. Biological markets thus view animal behaviour as extremely plastic whereas the putative existence of animal personalities suggests that animal behaviour may be relatively inflexible. However, the two approaches may be more similar than heretofore realized and may be complementary rather than opposing. Here I briefly review each approach and show how animal personalities can arise from a biological market situation.
  • Thumbnail Image
    Item
    Open Access
    Can foraging ecology drive the evolution of body size in a diving endotherm?
    (Public Library of Science, 2013) Cook, Timothée R; Lescroël, Amélie; Cherel, Yves; Kato, Akiko; Bost, Charles-André
    Within a single animal species, different morphs can allow for differential exploitation of foraging niches between populations, while sexual size dimorphism can provide each sex with access to different resources. Despite being potentially important agents of evolution, resource polymorphisms, and the way they operate in wild populations, remain poorly understood. In this study, we examine how trophic factors can select for different body sizes between populations and sexes in a diving endotherm. Dive depth and duration are positively related to body size in diving birds and mammals, a relationship explained by a lower mass-specific metabolic rate and greater oxygen stores in larger individuals. Based on this allometry, we predict that selection for exploiting resources situated at different depths can drive the evolution of body size in species of diving endotherms at the population and sexual level. To test this prediction, we studied the foraging ecology of Blue-eyed Shags, a group of cormorants with male-biased sexual size dimorphism from across the Southern Ocean. We found that mean body mass and relative difference in body mass between sexes varied by up to 77% and 107% between neighbouring colonies, respectively. Birds from colonies with larger individuals dived deeper than birds from colonies with smaller individuals, when accounting for sex. In parallel, males dived further offshore and deeper than females and the sexual difference in dive depth reflected the level of sexual size dimorphism at each colony. We argue that body size in this group of birds is under intense selection for diving to depths of profitable benthic prey patches and that, locally, sexual niche divergence selection can exaggerate the sexual size dimorphism of Blue-eyed Shags initially set up by sexual selection. Our findings suggest that trophic resources can select for important geographic micro-variability in body size between populations and sexes.
  • Thumbnail Image
    Item
    Restricted
    Causes of secondary sexual differences in plants — Evidence from extreme leaf dimorphism in Leucadendron (Proteaceae)
    (2010) Midgley, Jeremy J
    In extreme cases leaves in male plants of the dioecious genus Leucadendron (Proteaceae) are up to an order of magnitude smaller than female leaves. This secondary sexual dimorphism (SSD) in leaf size has previously been suggested to be due to intra-male sexual selection, leading to an increase in male allocation to reproduction in dimorphic species. After critically evaluating previous data provided to support this hypothesis, I suggest on both theoretical grounds and on re-analysis that this argument is unlikely and unsupported. Leaf size dimorphism could theoretically evolve directly due to disruptive ecological selection between genders, leading to niche dimorphism either within or between habitats. I test this ecological causation hypothesis by providing data on specific leaf area (sla) and water use efficiency (δ 13C) of leaves from males and females of several Leucadendron species. Results confirm the expectation of minimal gender differences. I argue that leaf dimorphism is a consequence of selection on flower size and architecture.