Kristt A C, Lively C M, Levri E P, Jokela J
Department of Biology, Indiana University, Bloomington 47405-3700, USA.
Parasitology. 2000 Oct;121 ( Pt 4):395-401. doi: 10.1017/s0031182099006538.
Parasites should be better at infecting hosts from sympatric populations than allopatric populations most of the time (parasite local adaptation). In a previous study of a population of snail parasites (Microphallus sp.) from Lake Alexandrina, New Zealand, we found that Microphallus was more infective to snails (Potamopyrgus antipodarum) in shallow water but not in deep water. Here, we repeated the original study and also monitored the development of the parasite. We found that parasites from shallow water were more infective to hosts from shallow water and developed more rapidly in these hosts. In contrast, parasites from deep water were not more infective to hosts from deep water and did not develop more rapidly in them. These results suggest clinal variation in the susceptibility of these snails, with shallow-water snails more susceptible than deep-water snails. We offer 2 possible explanations for these results. First, gene flow in the Microphallus population is primarily from shallow to deep water, leading to an asymmetric pattern of local adaptation. Alternatively, snails from shallow water may be more susceptible for reasons independent of gene flow, perhaps due to differences in host condition between habitats.
大多数情况下，寄生虫感染同域种群宿主的能力应强于异域种群宿主（寄生虫的局部适应性）。在之前一项对来自新西兰亚历山德里纳湖的蜗牛寄生虫（微小隐孢子虫属）种群的研究中，我们发现微小隐孢子虫对浅水区域的蜗牛（新西兰泥蜗）感染性更强，而对深水区域的蜗牛感染性较弱。在此，我们重复了原研究，并监测了寄生虫的发育情况。我们发现，来自浅水区域的寄生虫对浅水区域的宿主感染性更强，且在这些宿主体内发育得更快。相比之下，来自深水区域的寄生虫对深水区域的宿主感染性并不更强，在这些宿主体内也没有发育得更快。这些结果表明这些蜗牛的易感性存在渐变，浅水蜗牛比深水蜗牛更易感染。我们对这些结果给出了两种可能的解释。第一，微小隐孢子虫种群中的基因流动主要是从浅水到深水，导致了局部适应性的不对称模式。或者，浅水区域的蜗牛可能由于与基因流动无关的原因而更易感染，也许是由于不同栖息地宿主状况的差异。
