Table_7_The nematode Caenorhabditis elegans and diverse potential invertebrate vectors predominantly interact opportunistically.XLSX

Some small animals migrate with the help of other, more mobile animals (phoresy) to leave short-lived and resource-poor habitats. The nematode Caenorhabditis elegans lives in ephemeral habitats such as compost, but has also been found associated with various potential invertebrate vectors. Little research has been done to determine if C. elegans is directly attracted to these invertebrates. To determine whether C. elegans is attracted to compounds and volatile odorants of invertebrates, we conducted chemotaxis experiments with the isopods Porcellio scaber, Oniscus asellus, and Armadillidium sp. and with Lithobius sp. myriapods, Drosophila melanogaster fruit flies, and Arion sp. slugs as representatives of natural vectors. Because phoresy is an important escape strategy in nature, especially for dauer larvae of C. elegans, we examined the attraction of the natural C. elegans isolate MY2079 in addition to the laboratory-adapted strain N2 at the dauer and L4 stage. We found that DMSO washing solution of Lithobius sp. and the odor of live D. melanogaster attracted C. elegans N2 L4 larvae. Surprisingly, the natural isolate MY2079 was not attracted to any invertebrate during either the dauer or L4 life stages and both C. elegans strains were repelled by various compounds from O. asellus, P. scaber, Armadillidium sp., Lithobius sp., and Arion sp. feces. We hypothesize that this is due to defense chemicals released by the invertebrates. Although compounds from Lithobius sp. and D. melanogaster odorants were mildly attractive, the lack of attraction to most invertebrates suggests a predominantly opportunistic association between C. elegans and invertebrate vectors.

部分小型动物可借助移动能力更强的其他动物实现携播（phoresy），以此逃离短命且资源匮乏的生境。
秀丽隐杆线虫（Caenorhabditis elegans）栖息于堆肥等短暂生境中，且已被发现与多种潜在无脊椎动物媒介存在关联。目前针对秀丽隐杆线虫是否会主动趋向此类无脊椎动物的相关研究仍较为有限。
为探明秀丽隐杆线虫是否会趋向无脊椎动物的相关化合物与挥发性气味物质，我们以等足目动物潮虫（Porcellio scaber）、普通卷甲虫（Oniscus asellus）、球潮虫属（Armadillidium sp.）物种，石蜈蚣属（Lithobius sp.）多足类、黑腹果蝇（Drosophila melanogaster）以及蛞蝓属（Arion sp.）物种作为天然媒介代表，开展了趋化性实验。
鉴于携播是自然界中重要的逃逸策略，尤其针对秀丽隐杆线虫的dauer幼虫（dauer larvae），我们针对实验室驯化菌株N2与天然分离株MY2079，分别在dauer幼虫与L4期两个阶段检测了其趋向行为。
实验结果显示，石蜈蚣属物种的二甲基亚砜（DMSO）洗脱液以及活体黑腹果蝇的气味，可吸引秀丽隐杆线虫N2菌株的L4期幼虫。
令人意外的是，天然分离株MY2079在dauer幼虫或L4期均未表现出对任何受试无脊椎动物的趋向性；且两种秀丽隐杆线虫菌株均会被普通卷甲虫、潮虫、球潮虫属、石蜈蚣属以及蛞蝓属物种粪便中的多种化合物驱避。
我们推测该现象源于无脊椎动物释放的防御性化学物质。尽管石蜈蚣属物种的提取物与黑腹果蝇的气味仅具有轻度吸引作用，但多数无脊椎动物无法引发秀丽隐杆线虫的趋向性，这表明秀丽隐杆线虫与无脊椎动物媒介之间主要为机会共生关系。