Outcrossing in Caenorhabditis elegans increases in response to food limitation

Abstract

Theory predicts that organisms should diversify their offspring when faced with a stressful environment. This prediction has received empirical support across diverse groups of organisms and stressors. For example, when encountered by Caenorhabditis elegans during early development, food limitation (a common environmental stressor) induces the nematodes to arrest in a developmental stage called dauer and to increase their propensity to outcross when they are subsequently provided with food and enabled to develop to maturity. Here we tested whether food limitation first encountered during late development/early adulthood can also induce increased outcrossing propensity in C. elegans. Previously well-fed C. elegans increased their propensity to outcross when challenged with food limitation during the final larval stage of development and into early adulthood, relative to continuously well-fed (control) nematodes. Our results thus support previous research demonstrating that the stress of food limitation can induce increased outcrossing propensity in C. elegans. Furthermore, our results expand on previous work by showing that food limitation can still increase outcrossing propensity even when it is not encountered until late development, and this can occur independently of the developmental and gene expression changes associated with dauer.

Keywords: C. elegans; dauer; food restriction; mating system; offspring diversity; outcrossing; selfing; self‐fertilization; starvation; stress.

FIGURE 1

Outcrossing rates of hermaphrodites paired with males on mating plates with an undiluted E. coli food source (red squares) or with E. coli diluted by a factor of 10⁻⁷ (green triangles). Data pooled across replicate experimental runs. Each point represents the outcrossing rate on one mating plate. Left panel: hermaphrodites from the inbred mixed mating lab strain CB4856 paired with males from an obligately outcrossing strain of CB4856. Right panel: hermaphrodites from the mutagenized and genetically diverse mixed mating population CW1‐30 paired with males from the mutagenized and genetically diverse obligately outcrossing population F5 (both mutagenized populations derived from CB4856). Error bars represent ±1 standard error of the mean. *p< 0.05; **p < .01.

FIGURE 2

Frequency of nondisjunction (selfed) males produced by isogenic‐CB4856 Caenorhabditis elegans hermaphrodites assayed on control plates with an undiluted E. coli food source (red squares), or on plates with E. coli diluted by a factor of 10⁻⁷ (green triangles). Each point represents the frequency of male offspring on one assay plate. Error bars represent ±1 standard error of the mean.