The Selective Interactions of Dispersal, Dormancy, and Seed Size as Adaptations for Reducing Risk in Variable Environments

Venable, D. Lawrence; Brown, Joel S.

doi:10.1086/284795

Cited by 888 publications

(832 citation statements)

References 36 publications

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“…Variation in the waiting time until seed gemination may respond adaptively to temporal variation in habitat quality (Venable and Brown, 1988); persistence in the seed bank increases the likelihood that at least some seeds will germinate when conditions for growth are good. FLP persistence may sometimes allow a pathogen to moderate the dynamic risk imposed by host-density fluctuations, so that at least some new infections occur when the density of susceptibles is high.…”

Section: Discussionmentioning

confidence: 99%

Free-living pathogens: Life-history constraints and strain competition

Caraco

Wang

2008

Journal of Theoretical Biology

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Many pathogen life histories include a free-living stage, often with anatomical and physiological adaptations promoting persistence outside of host tissues. More durable particles presumably require that the pathogen metabolize more resources per particle. Therefore, we hypothesize functional dependencies, pleiotropic constraints, between the rate at which free-living particles decay outside of host tissues and other pathogen traits, including virulence, the probability of infecting a host upon contact, and pathogen reproduction within host tissues. Assuming that pathogen strains compete for hosts preemptively, we find patterns in trait dependencies predicting whether or not strain competition favors a highly persistent free-living stage.

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Section: Discussionmentioning

confidence: 99%

Free-living pathogens: Life-history constraints and strain competition

Caraco

Wang

2008

Journal of Theoretical Biology

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“…Such constraints may become less of a driving force with decreasing relatedness, which might explain why we found an increase in seed weight between but not within species. Indeed, seed weight has been characterised as one element of a co-evolving complex of characters including dispersal, seed dormancy, plant biomass, niche specialisation, and competition ability (Venable and Brown 1988;Rees 1997). Consequently, an increase in seed size at higher altitude may involve changes of several traits causing a change of the taxonomic status of the plants concerned.…”

Section: Intra-specific Differences In Seed Weightsmentioning

confidence: 99%

Seed weight increases with altitude in the Swiss Alps between related species but not among populations of individual species

2005

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Seed weight is a crucial plant life history trait, determining establishment success and dispersal ability. Especially in stressful environments, larger seeds may be selected at the expense of seed number, because larger seeds have a better chance of giving rise to an established offspring. We tested the hypotheses that between related species-pairs and among populations of single species a similar trend for increasing seed weight with increasing altitude should be present. Firstly, we measured seed weights from 29 species-pairs, with one species occurring in lowland areas and a congeneric species from high altitudes. Seeds of the alpine species were 28±8% larger than seeds from lowland species (P<0.01). Compared to the related lowland species, 55% of the alpine species had heavier seeds, 3% (one species) had lighter, and 41% had seeds of approximately equal weight. Secondly, we compared seed weights among populations of four species from different habitats and with different life histories. Seeds from between 11 and 34 populations per species were sampled along altitudinal gradients of 800-1,500 m (ca. 800 m in Scabiosa lucida, ca. 1,000 m in Saxifraga oppositifolia, ca. 1,000 m in Epilobium fleischeri, and ca. 1,500 m in Carex flacca). In all the four species, we found no indication for heavier seeds at higher altitudes. Our results indicate a selection pressure for species with heavier seeds at higher altitude, but the trend does not seem to operate across all cases. Phylogenetic constraints may limit the correlation among altitude and seed weight, operating particularly against selection for larger seed size, the closer populations and species are related to each other.

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“…Seed trait variation observed among taxa may represent coadapted syndromes involving several seed traits (Venable and Brown 1988;Kalisz 1989;Rees 1997). Among species, seed size varies by over 10 orders of magnitude (Westoby et al 1992).…”

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confidence: 99%

“…Diversification bet-hedging strategies are selected for under conditions of environmental unpredictability, and this has been widely cited in the theoretical literature as an explanation for seed trait variance (e.g., Cohen 1966;Westoby 1981;Venable 1985;Venable and Brown 1988;Evans and Cabin 1995;Simons and Johnston 1997). In monocarpic plants, persistence depends critically on seed and seedling survival among seasons, whereas polycarpic plants can avoid risk by spreading reproduction over multiple seasons.…”

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confidence: 99%

Environmental and Genetic Sources of Diversification in the Timing of Seed Germination: Implications for the Evolution of Bet Hedging

2006

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Abstract. Environmental variation that is not predictably related to cues is expected to drive the evolution of bethedging strategies. The high variance observed in the timing of seed germination has led to it being the most cited diversification strategy in the theoretical bet-hedging literature. Despite this theoretical focus, virtually nothing is known about the mechanisms responsible for the generation of individual-level diversification. Here we report analyses of sources of variation in timing of germination within seasons, germination fraction over two generations and three sequential seasons, and the genetic correlation structure of these traits using almost 10,000 seeds from more than 100 genotypes of the monocarpic perennial Lobelia inflata. Microenvironmental analysis of time to germination suggests that extreme sensitivity to environmental gradients, or microplasticity, even within a homogeneous growth chamber, may act as an effective individual-level diversification mechanism and explains more than 30% of variance in time to germination. The heritability of within-season timing of germination was low (h 2 ϭ 0.07) but significant under homogeneous conditions. Consistent with individual-level diversification, this low h 2 was attributable not to low additive genetic variance, but to an unusually high coefficient of residual variation in time to germination. Despite high power to detect additive genetic variance in within-season diversification, it was low and indistinguishable from zero. Restricted maximum likelihood detected significant genetic variation for germination fraction (h 2 ϭ 0.18) under homogeneous conditions. Unexpectedly, this heritability was positive when measured within a generation by sibling analysis and negative when measured across generations by offspring-on-parent regression. The consistency of dormancy fraction over multiple delays, a major premise of Cohen's classic model, was supported by a strong genetic correlation (r ϭ 0.468) observed for a cohort's germination fraction over two seasons. We discuss implications of the results for the evolution of bet hedging and highlight the need for further empirical study of the causal components of diversification.Key words. Diversification bet hedging, dormancy, environmental unpredictability, heritability, microplasticity, phenotypic plasticity, seed germination. Cole's (1954) renowned result-showing that the fitness of an annual and a perennial plant are equal given that the annual produces just one seed more than the perennialprompted the development of life-history theory by underscoring the evolutionary importance of age(stage)-dependent survival. Mortality at the seed and seedling stage is expected to be much higher than at later stages, especially for annual plants that produce a large number of small seeds (Harper 1977). From the perspective of life-history evolution, the importance of the timing of germination is clear: upon germination, a plant steps from the least to the most vulnerable stage of its life cycle. Thus, the ti...

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The Selective Interactions of Dispersal, Dormancy, and Seed Size as Adaptations for Reducing Risk in Variable Environments

Cited by 888 publications

References 36 publications

Free-living pathogens: Life-history constraints and strain competition

Free-living pathogens: Life-history constraints and strain competition

Seed weight increases with altitude in the Swiss Alps between related species but not among populations of individual species

Environmental and Genetic Sources of Diversification in the Timing of Seed Germination: Implications for the Evolution of Bet Hedging

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