Dagan Yael, Kosman Evsey, Ben-Ami Frida
School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, 6997801, Tel Aviv, Israel.
Institute for Cereal Crops Improvement, Tel Aviv University, 6997801, Tel Aviv, Israel.
BMC Ecol. 2017 Dec 13;17(1):40. doi: 10.1186/s12898-017-0152-x.
The persistence of high genetic variability in natural populations garners considerable interest among ecologists and evolutionary biologists. One proposed hypothesis for the maintenance of high levels of genetic diversity relies on frequency-dependent selection imposed by parasites on host populations (Red Queen hypothesis). A complementary hypothesis suggests that a trade-off between fitness costs associated with tolerance to stress factors and fitness costs associated with resistance to parasites is responsible for the maintenance of host genetic diversity.
The present study investigated whether host resistance to parasites is traded off with tolerance to environmental stress factors (high/low temperatures, high salinity), by comparing populations of the freshwater snail Melanoides tuberculata with low vs. high clonal diversity. Since polyclonal populations were found to be more parasitized than populations with low clonal diversity, we expected them to be tolerant to environmental stress factors. We found that clonal diversity explained most of the variation in snail survival under high temperature, thereby suggesting that tolerance to high temperatures of clonally diverse populations is higher than that of populations with low clonal diversity.
Our results suggest that resistance to parasites may come at a cost of reduced tolerance to certain environmental stress factors.
自然种群中高遗传变异性的持续存在引起了生态学家和进化生物学家的极大兴趣。一个关于维持高水平遗传多样性的假说依赖于寄生虫对宿主种群施加的频率依赖选择（红皇后假说）。一个补充假说认为，与对压力因素的耐受性相关的适合度成本和与对寄生虫的抗性相关的适合度成本之间的权衡是宿主遗传多样性得以维持的原因。
本研究通过比较低克隆多样性与高克隆多样性的淡水螺类瘤拟黑螺种群，调查了宿主对寄生虫的抗性是否与对环境压力因素（高温/低温、高盐度）的耐受性相互权衡。由于发现多克隆种群比低克隆多样性的种群受到更多寄生虫感染，我们预计它们对环境压力因素具有耐受性。我们发现克隆多样性解释了高温下蜗牛存活率的大部分变异，从而表明克隆多样的种群对高温的耐受性高于低克隆多样性的种群。
我们的结果表明，对寄生虫的抗性可能是以降低对某些环境压力因素的耐受性为代价的。
