Development of Caenorhabditis elegans dauer larvae in growing populations

Abstract

For species that rely on ephemeral resources, genotype fitness will depend on traits that affect both population growth rates and dispersal. Understanding how such traits are related is central to understanding how they may evolve. Natural populations of Caenorhabditis elegans exhibit rapid population growth within resource-rich patches of decaying organic material and subsequent dispersal, primarily as developmentally-arrested dauer larvae, between patches. The properties of growing populations of C. elegans are, however, poorly understood. Here we show that food availability, dauer pheromone (a measure of conspecific population density) and temperature affect dauer larvae development in growing populations as would be predicted from analyses of single cohorts of worms. We also show that as food patch size increases, dauer larvae are formed prior to patch exhaustion and that the number of dauer larvae present increases after the patch is exhausted, i.e., worms that had not completed development as dauer larvae when the food was exhausted continue development in the absence of bacterial food. Crucially, the subsequent reproductive fitness of dauer larvae that complete development after the exhaustion of the bacterial food patch is reduced in comparison with dauer larvae that develop prior to patch exhaustion. These results demonstrate that population level analyses of C. elegans are feasible, support previous studies of the environmental factors affecting dauer larvae development and suggest an adaptive benefit for variation between isolates in the sensitivity of dauer larvae development.

Highly Polygenic Variation in Environmental Perception Determines Dauer Larvae Formation in Growing Populations of Caenorhabditis elegans

“…To further investigate this, we determined the number of dauer larvae present a week after food exhaustion, a situation known to increase the number of dauer larvae in N2 [29] . In this assay, analysis of N2 and CB4856 at food exhaustion indicated that only very few dauer larvae had formed at this point (mean ± SE of 12.5±3.66 in N2, with no dauer larvae observed in CB4856, n = 8 for both).…”

Effects of organic and conventional pesticides on plant biomass, nematode diversity and the structure of the soil food web

“…By contrast, in the pine forest soil bacterial-feeding nematodes with CP 2-5 increased almost three times more than in the farm soil. The occurrence of dauers is a product of food ex haustion (Green & Harvey, 2012) and they may appear as soon as 2 days after organic matter addition into the soil (Zelenev et al, 2004). Incorporation of N-rich plant biomass into the soil induce dauer formation (van Eekeren et al, 2009).…”

Genetic mapping of variation in dauer larvae development in growing populations of Caenorhabditis elegans

“…Population assays were performed as described by Green and Harvey (2012), except that agar concentration was varied, with normal, dauer agar, plates containing 20 g l À1 and sloppy agar plates containing 4 g l À1 . This corrected an initial issue with the population assays where the wild isolates tended to burrow into the agar, making recovery and counting impossible.…”

“…For the analyses of the wild isolates and of the ILs, populations were initiated with 100 ml of a 20% (wv À1 ) suspension of E. coli in water and monitored daily until food exhaustion, when the population size and the number of dauer larvae were determined as described by Green and Harvey (2012). Wild isolates were analysed in two experimental blocks with an N2 control in each block and 10 plates per isolate.…”

“…Given this, the ecological relevance of the extensive variation between C. elegans isolates in their sensitivity to dauer-inducing conditions as assessed by analysing age-matched individuals at high pheromone concentrations and limiting amounts of food (Viney et al, 2003;Harvey et al, 2008) is unclear. As methods to allow the analysis of dauer larvae development in growing populations have now been validated (Green and Harvey, 2012), we have investigated variation in dauer larvae formation in growing populations, conditions that, because of the dynamic nature of the food and pheromone levels in such assays, will more closely approximate the natural conditions experienced by the species.…”