Abstract
Organisms can end up in unfavourable conditions and to survive this they have evolved various strategies. Some organisms, including nematodes, survive unfavourable conditions by undergoing developmental arrest. The model nematode Caenorhabditis elegans has a developmental choice between two larval forms, and it chooses to develop into the arrested dauer larva form in unfavourable conditions (specifically, a lack of food and high population density, indicated by the concentration of a pheromone). Wild C. elegans isolates vary extensively in their dauer larva arrest phenotypes, and this prompts the question of what selective pressures maintain such phenotypic diversity? To investigate this we grew C. elegans in four different environments, consisting of different combinations of cues that can induce dauer larva development: two combinations of food concentration (high and low) in the presence or absence of a dauer larva-inducing pheromone. Five generations of artificial selection of dauer larvae resulted in an overall increase in dauer larva formation in most selection regimes. The presence of pheromone in the environment selected for twice the number of dauer larvae, compared with environments not containing pheromone. Further, only a high food concentration environment containing pheromone increased the plasticity of dauer larva formation. These evolutionary responses also affected the timing of the worms’ reproduction. Overall, these results give an insight into the environments that can select for different plasticities of C. elegans dauer larva arrest phenotypes, suggesting that different combinations of environmental cues can select for the diversity of phenotypically plastic responses seen in C. elegans.
Highlights
Organisms have different ways to cope with unfavourable conditions
To investigate the evolution of the plasticity of formation of C. elegans dauer larvae we grew a genetically diverse C. elegans population (Teotonio et al 2012) in four different regimes that differed in the availability of food and in the presence of a synthetic ascaroside and selected the dauer larvae that developed in these environments
We found no differences in dauer larva formation in response to a change in the food concentration, a very low a 2015 The Authors
Summary
Some species can developmentally arrest ( known as diapause) to avoid these otherwise unfavourable conditions. Many free-living nematodes have an alternative, arrested third larval stage form called the dauer larva. Young larvae have a developmental choice between growing into a “normal” non-dauer larva or arresting their development as a dauer larva. This is best studied in the model nematode Caenorhabditis elegans where dauer larvae develop when there is overcrowding and a lack of food (Fig. 1A). Caenorhabditis elegans dauer larvae are a morphologically distinct, stress resistant, and long lived form and the stage most commonly found in the wild (Felix and Braendle 2010), suggesting that this stage is of critical importance in the ecology of C. elegans
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