Data from: Is sex advantageous in adverse environments? A test of the abandon-ship hypothesis

Understanding the evolution and maintenance of sexual reproduction remains a long-standing challenge in evolutionary biology. Stress often induces sexual reproduction in facultatively sexual species (those species capable of both sexual and asexual reproduction). The abandon-ship hypothesis predicts higher allocation to sex under stress to allow low-fitness individuals to recombine their genotype, potentially increasing offspring fitness. However, effective tests of the abandon-ship hypothesis, particularly in multicellular organisms, are lacking. Here we test the abandon-ship hypothesis, using cyanogenic and acyanogenic defense phenotypes of the short-lived perennial herb Trifolium repens. Cyanogenesis provides an effective defense against herbivores and is under relatively simple genetic control (plants dominant for cyanogenesis at two alleles express the defended phenotype). Thus, maladapted individuals can acquire adaptive defense alleles for their offspring in a single episode of sexual reproduction. Plants were grown under high- and low-herbivory treatments (plants were exposed to herbivorous snails) and a control treatment (no herbivory). Herbivores reduced growth and fitness in all treated plants, but herbivory induced higher sexual allocation only in maladapted (acyanogenic) individuals. Overall, our results support the abandon-ship hypothesis.

解析有性繁殖的演化历程与维持机制，始终是进化生物学领域长期存在的核心难题之一。胁迫环境往往会诱导兼性有性繁殖物种——即可同时开展有性与无性繁殖的物种——启动有性繁殖过程。弃船假说（abandon-ship hypothesis）预测，在胁迫环境下，生物会将更多资源分配给有性繁殖，使得适应度较低的个体能够重组自身基因型，从而潜在提升后代的进化适合度。然而，目前针对该假说的有效检验仍较为匮乏，在多细胞生物中开展的相关检验更是寥寥无几。本研究以短命多年生草本植物白三叶（Trifolium repens）的产氰与非产氰防御表型为实验材料，对弃船假说进行检验。产氰作用可为植物提供针对植食动物的有效防御，且其遗传调控机制相对简单：在两个等位基因位点上均携带产氰显性基因的植物，将表现出防御表型。因此，适应不良的个体仅需通过一次有性繁殖事件，即可为后代获取适应性防御等位基因。实验设置了高植食压力、低植食压力两组处理（植物均暴露于植食性蜗牛环境中），以及一组无植食压力的对照组。植食性蜗牛会降低所有处理组植物的生长状况与进化适合度，但仅在适应不良的非产氰个体中，植食胁迫才会诱导其提升有性繁殖的资源分配。综上，本研究结果支持弃船假说。