Evolutionary bet-hedging in the real world: empirical evidence and challenges revealed by plants

Abstract

Understanding the adaptations that allow species to live in temporally variable environments is essential for predicting how they may respond to future environmental change. Variation at the intergenerational scale can allow the evolution of bet-hedging strategies: a novel genotype may be favoured over an alternative with higher arithmetic mean fitness if the new genotype experiences a sufficiently large reduction in temporal fitness variation; the successful genotype is said to have traded off its mean and variance in fitness in order to 'hedge its evolutionary bets'. We review the evidence for bet-hedging in a range of simple plant systems that have proved particularly tractable for studying bet-hedging under natural conditions. We begin by outlining the essential theory, reiterating the important distinction between conservative and diversified bet-hedging strategies. We then examine the theory and empirical evidence for the canonical example of bet-hedging: diversification via dormant seeds in annual plants. We discuss the complications that arise when moving beyond this simple case to consider more complex life-history traits, such as flowering size in semelparous perennial plants. Finally, we outline a framework for accommodating these complications, emphasizing the central role that model-based approaches can play.

Modes, mechanisms and evidence of bet hedging in rotifer diapause traits

“…a Diversification occurring among females within the same clone; b diversification haphazardly occurring within the offspring of single females within a clone; and c diversification (E for 'Early' and L for 'Late' hatchers) occurring within the offspring of a single female within a clone following a trend (e.g. a monotonic variation with mother age so that E diapausing eggs are typically produced at advanced laying order) different types of bet hedging has been previously suggested in plants in the case of the timing of flowering, where the evolution of the trait results from a balance between conservative and diversified bethedging components (Rees et al, 2004Childs et al, 2010).…”

“…By doing so, the candidate bet-hedging trait would maximize the geometric mean of fitness (Gillespie, 1974;Childs et al, 2010;Starrfelt & Kokko, 2012). Therefore, bet-hedging traits are apparently sub-optimal under the averaged environmental conditions, but they are adaptive over long time scales.…”

“…Theoreticians distinguish between two basic modes of bet hedging (for review, see Childs et al, 2010), which are typically referred to as conservative and diversified bet hedging (Seger & Brockmann, 1987;Philippi & Seger, 1989). These modes result from risk avoidance at the individual level or risk spreading among related individuals of the same genotype, respectively.…”

“…Martínez-Ruiz & García-Roger (2015) proposed that diversification in the timing of diapausing egg hatching could occur through the following ways: (1) Each inseminated sexual female within a clone, as a result of an independent reproductive event, may probabilistically produce a single phenotype (all 'Early' or all 'Late', in Schröder's terminology; see Fig. 1a), which would be an instance of the 'adaptive coin-flipping' modality of bet hedging operating at the mother level (Oloffson et al, 2009;Childs et al, 2010). (2) Each inseminated sexual female within a clone may produce resting eggs with different phenotypes ('Early' and 'Late'; see Fig.…”

“…the fraction of diapausing eggs hatching at the beginning of a new growing season) (Schröder, 2005;García-Roger et al, 2014). However, because bethedging traits must fulfil a set of conditions (see below) and there are various possible modes of bet hedging (Oloffson et al, 2009;Childs et al, 2010), the proper identification of the above-mentioned traits as bet-hedging traits is still uncertain.…”