Freeman-Gallant Corey R, O'Connor Kathleen D, Breuer Megan E
Department of Biology, Skidmore College, 12866, Saratoga Springs, NY, USA.
Oecologia. 2001 May;127(4):517-521. doi: 10.1007/s004420000618. Epub 2001 May 1.
According to Hamilton and Zuk's hypothesis of parasite-mediated sexual selection, host-parasite coevolution maintains variation in male genetic quality and allows for strong intersexual selection in species with high rates of infection. In birds, most interspecific tests of this hypothesis relate the prevalence of blood parasites to some measure of the intensity of sexual selection. Such tests often rely on limited sampling of single populations to estimate species-wide infection rates, and many tests are thus vulnerable to intraspecific (geographic) variation in the evolutionary ecology of disease. Here, we used molecular techniques to examine variation in the prevalence of Plasmodium spp. across 14 populations of Savannah sparrows, Passerculus sandwichensis, in eastern North America. Plasmodium could not be detected in any of 68 island birds, but 34 of 119 (29%) mainland males, and 7 of 43 (16%) mainland females were infected. Among mainland birds, infection was common in southern populations but rare in New Brunswick, Canada. Overall, the prevalence of Plasmodium ranged from 0 to 60% across populations, although only 17.8% of birds were infected in the pooled (species-wide) sample. The extent of this geographic variation suggests that limited sampling of single populations is unlikely to yield accurate estimates of species-wide infection rates. However, among mainland Savannah sparrows, the prevalence of malaria correlated strongly with average male size and the degree of sexual size dimorphism. We speculate that either sexual selection leads to male-biased infection or, conversely, that high rates of infection promote the evolution of strong intersexual selection.
根据汉密尔顿和祖克提出的寄生虫介导的性选择假说，宿主 - 寄生虫的共同进化维持了雄性基因质量的变异，并使得在感染率高的物种中存在强烈的两性间选择。在鸟类中，对这一假说的大多数种间测试将血液寄生虫的流行率与某种性选择强度的度量联系起来。此类测试通常依赖于对单一群体的有限抽样来估计全物种的感染率，因此许多测试容易受到疾病进化生态学中种内（地理）变异的影响。在这里，我们使用分子技术研究了北美东部14个萨凡纳雀种群（Passerculus sandwichensis）中疟原虫属物种流行率的变异情况。在68只岛屿鸟类中均未检测到疟原虫，但119只大陆雄性鸟类中有34只（29%）以及43只大陆雌性鸟类中有7只（16%）被感染。在大陆鸟类中，感染在南部种群中很常见，但在加拿大新不伦瑞克省则很罕见。总体而言，疟原虫的流行率在不同种群中从0%到60%不等，尽管在合并的（全物种）样本中只有17.8%的鸟类被感染。这种地理变异的程度表明，对单一群体的有限抽样不太可能得出全物种感染率的准确估计。然而，在大陆萨凡纳雀中，疟疾的流行率与雄性平均体型以及两性体型差异程度密切相关。我们推测，要么是性选择导致雄性偏向性感染，要么相反，高感染率促进了强烈两性间选择的进化。
