Seasonality can induce coexistence of multiple bet-hedging strategies in Dictyostelium discoideum via storage effect

TL;DR

This study demonstrates that seasonal environmental fluctuations can promote the coexistence of multiple bet-hedging strategies in Dictyostelium discoideum through a storage effect, explaining observed genetic diversity.

Contribution

It introduces a model showing how seasonality enables coexistence of diverse strategies via a storage effect in a non-spatial setting.

Findings

Seasonality induces a storage effect promoting coexistence.

Distinct starvation time distributions are necessary for coexistence.

Multiple growth-starvation cycles enhance strategy survival.

Abstract

D. discoideum has been recently suggested as an example of bet-hedging. Upon starvation a population of unicellular amoebae splits between aggregators, which form a fruiting body made of a stalk and resistant spores, and non-aggregators. Spores are favored by long starvation periods, but vegetative cells can exploit resources in fast-recovering environments. This partition can be understood as a bet-hedging strategy that evolves in response to stochastic starvation times. A genotype is defined by a different balance between each type of cells. In this framework, if the ecological conditions are defined in terms of the mean starvation time (i.e. time between onset of starvation and the arrival of a new food pulse), a single genotype dominates each environment, which is inconsistent with the huge genetic diversity observed in nature. We investigate whether seasonality, represented by a periodic alternation in the mean starvation times, allows the coexistence of several strategies. We use a non-spatial (well-mixed) setting where different strains compete for a pulse of resources. We find that seasonality, which we model via two seasons, induces a temporal storage effect that can promote the stable coexistence of multiple genotypes. Two conditions need to be met. First, the distributions of starvation times in each season cannot overlap in order to create two well differentiated habitats within the year. Second, numerous growth-starvation cycles have to occur during each season to allow well-adapted strains to grow and survive the subsequent unfavorable period. Additional tradeoffs among life-history traits can expand the range of coexistence and increase the number of coexisting strategies, contributing towards explaining the genetic diversity observed in D. discoideum