Shorter life and reduced fecundity can increase colony fitness in virtual Caenorhabditis elegans

Abstract

In the nematode Caenorhabditis elegans, loss of function of many genes leads to increases in lifespan, sometimes of a very large magnitude. Could this reflect the occurrence of programmed death that, like apoptosis of cells, promotes fitness? The notion that programmed death evolves as a mechanism to remove worn out, old individuals in order to increase food availability for kin is not supported by classic evolutionary theory for most species. However, it may apply in organisms with colonies of closely related individuals such as C. elegans in which largely clonal populations subsist on spatially limited food patches. Here, we ask whether food competition between nonreproductive adults and their clonal progeny could favor programmed death by using an in silico model of C. elegans. Colony fitness was estimated as yield of dauer larva propagules from a limited food patch. Simulations showed that not only shorter lifespan but also shorter reproductive span and reduced adult feeding rate can increase colony fitness, potentially by reducing futile food consumption. Early adult death was particularly beneficial when adult food consumption rate was high. These results imply that programmed, adaptive death could promote colony fitness in C. elegans through a consumer sacrifice mechanism. Thus, C. elegans lifespan may be limited not by aging in the usual sense but rather by apoptosis‐like programmed death.

Abstract

Caenorhabditis elegans fitness can be viewed at the level of individual animals or of viscous, clonal populations of worms (or colonies). Behavior of an in silico model of C. elegans predicts that early death of postreproductive adults can increase colony fitness (measured as yield of dauer propagules) by reducing futile food consumption. This supports the occurrence of apoptosis‐like programmed organismal death in C. elegans, of the consumer sacrifice type, which limits lifespan.