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

Abstract

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.