Data from: Predation drives stable coexistence ratios between red and green pea aphid morphs

We conducted field surveys and experiments to evaluate the hypothesis that predation is an important driving factor determining the degree of coexistence between red and green morphs of the pea aphid Acyrthosiphon pisum. Theory suggests that the different colour morphs are differentially susceptible to natural enemies and selection by predation which in turn leads to variable relative abundances of red and green morphs among host plants across landscapes. Our field surveys on pea and alfalfa revealed, however, that the colour morphs tended to coexist closely in a ratio of one red to three green aphids across fields with different host plant monocultures. Experimentation involving manipulation of the relative abundances of the two colour morphs on host plants pea and alfalfa with and without predator presence revealed that red morphs had higher or same fitness (per capita reproduction) than green morphs on both pea and alfalfa only when in the proportion of one red/three green proportion. Moreover, experimentation evaluating predator efficiency revealed that red morphs are safest from predation when in a 1 : 3 ratio with green morphs. These results suggest that in addition to predation selection effects, red morphs may behaviourally choose to associate with green morphs in a narrow 1 : 3 ratio to maximize their fitness. This evidence, along with existing published data on red and green morph anti-predator behaviour indicates that a 1 : 3 red and green morph coexistence ratio is driven by a balance between predation pressure and behavioural assorting by red morphs across landscapes. In this way predators may have ecological-evolutionary consequences for traits that affect the colour morphs' proportion and tolerances to selective pressure.

本研究通过野外调查与室内实验，验证了捕食作用是决定豌豆蚜（Acyrthosiphon pisum）红色与绿色体色型个体共存程度的关键驱动因素。相关理论指出，不同体色型的豌豆蚜对天敌的敏感性存在差异，捕食选择作用随之产生，进而导致不同景观尺度下寄主植物上红色与绿色型蚜虫的相对丰度存在波动。然而，针对豌豆与苜蓿的野外调查结果显示，在不同单一种植寄主植物的农田中，两种体色型蚜虫始终以近似1红:3绿的比例紧密共存。通过调控豌豆、苜蓿寄主上两种体色型蚜虫的相对丰度，并设置有无天敌存在的实验组，结果发现：仅当两种体色型以1红:3绿的比例共存时，红色型蚜虫在豌豆与苜蓿寄主上的适合度（单头繁殖力）均高于或等于绿色型。此外，针对天敌捕食效率的实验结果表明，当红色型与绿色型蚜虫以1:3的比例共存时，红色型个体的被捕食风险最低。上述结果表明，除捕食选择作用外，红色型蚜虫可能通过行为选择，以严格的1:3比例与绿色型个体聚集，从而最大化自身适合度。结合已发表的红色与绿色型蚜虫反捕食行为相关数据，本研究结果证实：1:3的红绿色型共存比例，是由不同景观尺度下的捕食压力与红色型蚜虫的行为偏好性聚集共同维持的动态平衡。由此可见，天敌可通过相关途径，对影响体色型比例及其对选择压力耐受性的性状产生生态-进化层面的效应。