Experimental evolution of bet hedging in rotifer diapause traits as a response to environmental unpredictability

Abstract

The adaptive response of organisms to unpredictable environments is increasingly recognized as a central topic in fundamental and applied evolutionary ecology. Selection due to environmental unpredictability can act on multiple traits of an organism's life cycle to reduce the impact of high environmental variance. The aim of this research was to study how unpredictability selects for diapause traits: 1) the timing of sex (a proxy of the timing of diapausing egg production), and 2) the diapausing egg hatching fraction (a proxy of diapause duration). We used an experimental evolution approach with the facultative sexual rotifer Brachionus plicatilis. Laboratory populations experiencing two contrasting regimes of environmental fluctuation (predictable versus unpredictable) evolved divergently over a short time span (< 77 days). The populations under the unpredictable regime showed an earlier initiation of sexual reproduction and a lower hatching fraction of diapausing eggs than populations under the predictable regime. These findings demonstrate empirically the existence of bet‐hedging strategies in B. plicatilis regarding both traits, consistent with theoretical predictions of bet‐hedging evolution under conditions of unpredictable environmental variance. Given that scenarios of increased environmental variability are expected to occur in the near future, a comprehensive understanding of the role of bet‐hedging strategies is necessary for predicting population responses to environmental change.

Variation in the life cycle of monogonont rotifers: Commitment to sex and emergence from diapause

“…Laboratory and field studies with Brachionus are consistent with a theory that the overall propensity for sexual reproduction in a population, determined by the mixis threshold and mixis ratio, should decrease as the predictability of the environment increases (see Tarazona, García‐Roger, & Carmona, ). In ephemeral habitats where hydroperiod duration is unpredictable, early and extensive sexual reproduction leading to resting‐egg production should guard against short hydroperiods, and be critical for long‐term survival of the population.…”

“…By the end of the experiment, there was rapid evolution; the permanent cultures had significantly higher mixis thresholds, significantly lower mixis ratios, and significantly lower resting‐egg production. Tarazona et al () reported a similar, rapid evolution for decreased propensity for sex in a predictable environment. Mixtures of individuals from 30 clones were cultured for seven growing cycles (population growth to production of resting eggs) where the length of the cycles was either constant (28 days) or variable (4‐53 days).…”

“…This variation may be beneficial in assuring that some stem females will hatch at times when environments are suitable for their growth and reproduction. In B. plicatilis , resting eggs produced by different clonal populations varied in their diapause duration and propensity to hatch, suggesting the evolution of diversified bet‐hedging (Martinéz‐Ruiz & García‐Roger, ; Tarazona et al, ; review by García‐Roger et al, ). Some eggs produced by a clone hatched upon first exposure to a hatching stimulus while others hatched only after a second exposure, and clones differed in the frequency of these categories.…”

Shifts in phenological mean and synchrony interact to shape competitive outcomes

“…Bet‐hedging life‐history strategies increase fitness in unpredictable environments (Tarazona et al. , Rocha et al. , Shima et al.…”

Empirical evidence for fast temperature-dependent body size evolution in rotifers

“…As reviewed by Declerck & Papakostas, (2017, this issue), experimental evolution was previously used in the case of rotifers to test hypotheses on the evolution of sex (Becks & Agrawal, 2010, 2012Fussmann et al, 2003), the combination of different life-history traits (Stelzer, 2011;Smith & Snell, 2014), and the adaptation to food composition (Declerck et al, 2015). The most recent studies using experimental evolution in rotifers focus on sexual reproduction (Haafke et al, 2016) and bethedging strategy (Tarazona et al, 2017). In the present study, we focus on body size, a single, crucial lifehistory trait, evolving in response to temperature.…”