Environmentally resistant life-stages that allow escape during poor conditions have been widely examined theoretically as a mechanism underlying species coexistence in fluctuating environments. Dormancy is an important life-history strategy that allows individuals to avoid hostile conditions, yet experimentally determining if and when dormancy rescues populations from competitive exclusion has remained a challenge. Here, we use the nematodes Caenorhabditis elegans and its natural competitor C. briggsae to test the role of dormancy for coexistence in fluctuating environments. Under unfavourable conditions, these worms enter an alternative, long-lived, non-feeding larval stage that helps them disperse and survive until circumstances improve. This dauer stage is the functional equivalent of dormancy. We selected strains of C. elegans that had their propensity to become dormant manipulated genetically, then conducted competition assays between C. elegans and C. briggsae under fluctuating temperature conditions. Our study is the first to our knowledge to manipulate the dormancy pathway to test the role of this storage mechanism and serves as an empirical example that clarifies when dormancy can help or hinder species coexistence.
Results/Conclusions
Consistent with previous work, we found that C. elegans outcompetes C. briggsae at cold temperatures, C. briggsae outcompetes C. elegans at warm temperatures and both species produce dormant worms in temperature fluctuation experiments. C. elegans has an increased propensity to enter dormancy under high temperatures when it is being outcompeted by C. briggsae. However, C. briggsae also has an increased propensity to enter dormancy at high temperatures, despite outcompeting C. elegans under those conditions. We also competed C. briggsae with strains of C. elegans that had been genetically manipulated to have either higher or lower propensities to enter dormancy. We found that strains with both elevated and dampened dormancy levels, relative to the wild type, reduce the ability of C. elegans to coexist with C. briggsae. Together, these results suggest that the wild-type propensity of C. elegans to enter dormancy may be optimal for coexistence with C. briggsae. The results of this work provide empirical evidence for adaptive bet-hedging and clarify the role of dormancy for coexistence in fluctuating environments.