Pontier D, Fromont E, Courchamp F, Artois M, Yoccoz N G
UMR-CNRS 5558 'Biométrie, Génétique et Biologie des Populations, Université Claude Bernard Lyon 1, Villeurbanne, France.
Proc Biol Sci. 1998 Feb 7;265(1392):167-73. doi: 10.1098/rspb.1998.0278.
Hochberg and co-workers have predicted that an increase in host adult mortality due to parasites is balanced by an earlier age at first reproduction. In polygynous species we hypothesize that such a pattern would lead to diverging selection pressure on body size between sexes and increased sexual size dimorphism. In polygynous mammals, male body size is considered to be an important factor for reproductive success. Thus, under the pressure of a virulent infection, males should be selected for rapid growth and/or higher body size to be able to compete successfully as soon as possible with opponents. In contrast, under the same selection pressure, females should be selected for lighter adult body size or rapid growth to reach sexual maturity earlier. We investigated this hypothesis in the domestic cat Felis catus. Orange cats have greater body size dimorphism than non-orange cats. Orange females are lighter than non-orange females, and orange males are heavier than non-orange males. Here, we report the extent to which orange and non-orange individuals differ in infection prevelance for two retroviruses, feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV). FIV is thought to be transmitted almost exclusively through aggressive contacts between individuals, whereas FeLV transmission occurs mainly through social contacts. The pattern of infection of both diseases is consistent with the higher aggressiveness of orange cats. In both sexes, orange cats are significantly more infected by FIV, and tend to be less infected by FeLV than other cats. The pattern of infection is also consistent with an earlier age at first reproduction in orange than in non-orange cats, at least for females. These results suggest that microparasitism may have played an important role in the evolution of sexual size dimorphism of domestic cats.
霍赫贝格及其同事预测，寄生虫导致的宿主成年死亡率增加会被首次繁殖年龄提前所平衡。在一夫多妻制物种中，我们假设这种模式会导致两性在体型上的选择压力分化，并增加两性体型差异。在一夫多妻制哺乳动物中，雄性体型被认为是繁殖成功的一个重要因素。因此，在恶性感染的压力下，雄性应该被选择快速生长和/或体型更大，以便能够尽快成功地与对手竞争。相比之下，在相同的选择压力下，雌性应该被选择成年体型更轻或生长更快，以便更早达到性成熟。我们在家猫（Felis catus）中研究了这一假设。橙色猫比非橙色猫具有更大的体型差异。橙色雌性比非橙色雌性更轻，橙色雄性比非橙色雄性更重。在这里，我们报告了橙色和非橙色个体在两种逆转录病毒——猫免疫缺陷病毒（FIV）和猫白血病病毒（FeLV）的感染率上的差异程度。FIV被认为几乎完全通过个体之间的攻击接触传播，而FeLV的传播主要通过社交接触。两种疾病的感染模式与橙色猫更高的攻击性一致。在两性中，橙色猫感染FIV的比例显著更高，并且与其他猫相比，感染FeLV的比例往往更低。这种感染模式也与橙色猫比非橙色猫首次繁殖年龄更早一致，至少对于雌性来说是这样。这些结果表明，微寄生虫可能在家猫两性体型差异的进化中发挥了重要作用。
