Agnew P, Koella J C
Experimental Ecology, ETH Zürich, ETH-Zentrum NW, Switzerland.
Proc Biol Sci. 1997 Jan 22;264(1378):9-15. doi: 10.1098/rspb.1997.0002.
Horizontally transmitted parasites are broadly predicted to be more virulent, or costly to host fitness, than those with vertical transmission. This is mainly because vertical transmission, from host parent to offspring, explicitly links the reproductive interests of both parties. Underlying this prediction is a general assumption that parasite transmission success is positively correlated with its virulence. We report results where infection of larval yellow fever mosquitoes Aedes aegypti with the microsporidian Edhazardia aedis was experimentally manipulated. The parasite's complex life cycle allowed comparisons between estimates of horizontal and vertical transmission on host fitness. Our measure of virulence was the fluctuating asymmetry (FA) of adult female wings. Hosts harbouring spores showed higher FAs than controls. Horizontally transmitting spores were associated with higher FAs than vertically transmitting spores. Furthermore, within hosts FA correlated positively with the number of horizontally transmitting spores, while no relation was seen with the number of vertically transmitting spores. A developmental mechanism uncoupling the relationship between vertical transmission and virulence is proposed.
一般预测，水平传播的寄生虫比垂直传播的寄生虫更具毒性，或者对宿主适应性的代价更高。这主要是因为从宿主亲代到子代的垂直传播明确地将双方的繁殖利益联系在一起。这一预测的基础是一个普遍假设，即寄生虫传播成功与其毒性呈正相关。我们报告了对幼虫黄热病蚊子埃及伊蚊感染微孢子虫伊氏埃汉德孢菌的实验操作结果。寄生虫复杂的生命周期使得能够比较水平传播和垂直传播对宿主适应性的估计。我们衡量毒性的指标是成年雌蚊翅膀的波动不对称性（FA）。携带孢子的宿主比对照组表现出更高的FA值。水平传播的孢子比垂直传播的孢子与更高的FA值相关。此外，在宿主体内，FA与水平传播孢子的数量呈正相关，而与垂直传播孢子的数量没有关系。我们提出了一种发育机制，将垂直传播与毒性之间的关系解耦。
