Bet Hedging in a Guild of Desert Annuals

Abstract

Evolutionary bet hedging encapsulates the counterintuitive idea that organisms evolve traits that reduce short-term reproductive success in favor of longer-term risk reduction. It has been widely investigated theoretically, and many putative examples have been cited including practical ones such as the dormancy involved in microbe and weed persistence. However, long-term data on demographic variation from the actual evolutionarily relevant environments have been unavailable to test for its mechanistic relationship to alleged bet hedging traits. I report an association between delayed germination (a bet hedging trait) and risk using a 22-year data set on demographic variation for 10 species of desert annual plants. Species with greater variation in reproductive success (per capita survival from germination to reproduction x per capita fecundity of survivors) were found to have lower average germination fractions. This provides a definitive test using realistic data on demographic variance that confirms the life history prediction for bet hedging. I also showed that the species with greater long-term demographic variation tended to be the ones with greater sensitivity of reproductive success to variation among years in growing-season precipitation.

Diapause as escape strategy to exposure to toxicants: response of Brachionus calyciforus to arsenic

“…Banks of diapausing states contribute to prevent population extinction, supporting long-term species diversity, which could be a key aspect in allowing competitor coexistence (Chesson and Warner 1981;Cáceres 1997), while serving as a reservoir of genetic diversity. Also, incomplete termination of diapause has been considered a bet-hedging strategy of the individual producing dormant offspring, thus spreading risks (Venable 2007;García-Roger et al 2014).…”

Experimental evolution of bet hedging under manipulated environmental uncertainty in Neurospora crassa

“…However, empirical evidence for bet hedging remains scant [12]. Evidence is restricted to demonstrations of interspecific divergence [13] or population differentiation [14,15] in putative bet-hedging traits across environments that differ in predictability, or the documentation of the evolution of candidate bet-hedging traits under conditions in which they may be advantageous [16,17], with very few strong studies confirming fitness benefits of putative bethedging traits under fluctuating conditions [18][19][20][21]. Tests of bet hedging under field conditions are difficult because they require evaluating both environmental variance and its fitness effects over multiple generations.…”

Not only size matters: achene morphology affects time of seedling emergence in three heterocarpic species of <i>Anacyclus</i> (Anthemideae, Asteraceae)

“…This offers the chance to colonize new sites, free from sibling competition or other local sources of stress, whereas the remainder of the offspring stays in the same habitat (Gadgil, 1971;Levin & al., 1984;Schoen & Lloyd, 1984;Venable & Brown, 1993;Imbert & Ronce, 2001). Various authors have proposed that a bet-hedging strategy is likely to be favored in temporally variable environments because it increases geometric fitness, even if individual phenotypes may have a relatively lower mean fitness (Gillespie, 1977;Venable, 1985;Venable & al., 1987;Venable, 2007;Simons, 2011;Tielbörger & al., 2012).…”

“…This offers the chance to colonize new sites, free from sibling competition or other local sources of stress, whereas the remainder of the offspring stays in the same habitat (Gadgil, 1971;Levin & al., 1984;Schoen & Lloyd, 1984;Venable & Brown, 1993;Imbert & Ronce, 2001). Various authors have proposed that a bet-hedging strategy is likely to be favored in temporally variable environments because it increases geometric fitness, even if individual phenotypes may have a relatively lower mean fitness (Gillespie, 1977;Venable, 1985;Venable & al., 1987;Venable, 2007;Simons, 2011;Tielbörger & al., 2012).Among members of Asteraceae, the occurrence of heterocarpy is relatively high (Mandák, 1997;Imbert, 2002). Heterocarpic species in this family usually produce different achene morphs within the same capitulum (reviewed in Imbert, 2002), although exceptions in which achene variation occurs between aerial and subterranean capitula are known in Gymnarrhena micrantha (Koller & Roth, 1964) and Catananche lutea (Ruiz de Clavijo, 1995;Ruiz de Clavijo & Jiménez, 1998), and in Centaurea melitensis (Porras & Muñoz, 2000) between cleistogamous and chasmogamous capitula.…”