Wilson Kenneth, Thomas Matthew B, Blanford Simon, Doggett Matthew, Simpson Stephen J, Moore Sarah L
Institute of Biological Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom.
Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5471-5. doi: 10.1073/pnas.082461999.
Parasite transmission generally exhibits some form of positive density dependence. Thus, as population density increases, so too does the per capita risk of becoming infected. Under such circumstances, natural selection should favor individuals that use cues associated with population density to determine the optimal allocation of resources to disease resistance mechanisms. As a consequence, individuals experiencing crowded conditions are predicted to be more resistant to parasites and pathogens than those experiencing low-density conditions. This phenomenon (termed "density-dependent prophylaxis") [Wilson, K. & Reeson, A. F. (1998) Ecol. Entomol. 23, 100-101] is predicted to be particularly prevalent in outbreak pest species and in species exhibiting density-dependent phase polyphenism, such as the desert locust, Schistocerca gregaria. Here we show that, as predicted, desert locusts reared under crowded conditions are significantly more resistant than solitary locusts to the entomopathogenic fungus, Metarhizium anisopliae var. acridum, a key natural disease of acridids and an important agent in locust and grasshopper biocontrol. Moreover, enhanced pathogen resistance in crowded locusts is associated with elevated antimicrobial activity, but not with any difference in thermal preferences or behavioral fever response. These results have implications for understanding the development and biocontrol of locust plagues.
寄生虫传播通常表现出某种形式的正密度依赖性。因此，随着种群密度增加，人均受感染风险也会增加。在这种情况下，自然选择应有利于那些利用与种群密度相关的线索来确定对抗病机制资源的最优分配的个体。结果，预计处于拥挤环境中的个体比处于低密度环境中的个体对寄生虫和病原体更具抗性。这种现象（称为“密度依赖性预防”）[威尔逊，K. & 里森，A. F.（1998年）《生态昆虫学》23卷，第100 - 101页]预计在爆发性害虫物种以及表现出密度依赖性阶段多型现象的物种中尤为普遍，比如沙漠蝗，即群居沙漠蝗。在此我们表明，正如所预测的，在拥挤条件下饲养的沙漠蝗比独居沙漠蝗对昆虫病原真菌绿僵菌蝗变种（蝗虫的一种关键自然疾病以及蝗虫和蚱蜢生物防治中的一种重要媒介）具有显著更强的抗性。此外，拥挤蝗虫中增强的病原体抗性与抗菌活性升高有关，但与热偏好或行为性发热反应的任何差异无关。这些结果对于理解蝗灾的发展和生物防治具有启示意义。
