Caenorhabditis elegans dauer recovery in response to range of bacteria

Many species use dormant stages for habitat selection by tying recovery from the stage to informative external cues. Other species have an undiscerning strategy in which they recover randomly despite having advanced sensory systems. We investigated whether elements of a species' habitat structure and life history can bar it from developing a discerning recovery strategy. The nematode Caenorhabditis elegans has a dormant stage called the dauer larva that disperses between habitat patches. On one hand, C. elegans colonization success is profoundly influenced by the bacteria found in its habitat patches, so we might expect this to select for a discerning strategy. On the other hand, C. elegans' habitat structure and life history suggest that there is no fitness benefit to varying recovery, which might select for an undiscerning strategy. We exposed dauers of three genotypes to a range of bacteria acquired from the worms' natural habitat. We found that C. elegans dauers recover in all conditions but increase recovery on certain bacteria depending on the worm’s genotype, suggesting a combination of undiscerning and discerning strategies. Additionally, the worms' responses did not match the bacteria's objective quality, suggesting that their decision is based on other characteristics.

Methods
2000 dauer worms of each worm strain were plated on 5x107 CFU bacteria and allowed to roam around the plate for three hours. At the end of this period, worms were washed off the plates, treated with 1% SDS for 30 minutes, then washed multiple times to remove the SDS. For each worm/bacteria combination, ten small aliquots (~20 uL) were spotted onto a fresh plate and examined for dead and live worms.