Can Dormancy Affect the Evolution of Post‐Germination Traits? The Case of Lesquerella Fendleri

Abstract

Seed dormancy, which is thought to have evolved in response to unpredictable environmental variability, has led to the existence of seed banks–populations of dormant, viable seeds in the soil. Seed banks are theoretically important to both the demography and genetic structure of plant populations. The presence of seed dormancy can also affect the evolution of traits not directly associated with dormancy and germination. Theoretical models have suggested that the existence of dormancy can influence the rate of evolution of post—germination traits. The eventual outcome (e.g., allele frequencies) may be influenced as well, leading to adaptive syndromes of germination and post—germination traits. Seeds that germinate in different conditions may experience different selective regimes for post—germination traits. If there are trade—offs between the fitness of post—germination traits in different environments, then seeds that germinate in the environment to which their post—germination traits are adapted will be at a selective advantage. If differences in germination and post—germination traits are genetically based, then potentially adaptive genetic correlations between germination and post—germination traits may evolve. We feel that investigating the ecological and evolutionary importance of these correlations requires an empirical approach. As a first step, here we ask whether the conditions necessary for such syndromes to arise exist in a particular plant population. We show that conditions favoring the joint evolution of dormancy and post—germination traits leading to adaptive syndromes exist in the mustard, Lesquerella fendleri, in central New Mexico. First, Lesquerella experiences the sort of variation in environmental conditions that would be expected to lead to adaptive trade—offs in the expression of post—germination traits for individuals that differ in germination traits. Annual precipitation varies greatly from year to year so that germination in drier years would be expected to select for more xerophytic traits. Within a year, microenvironmental spatial variation exists. Lesquerella growth and reproduction are sensitive to both year—to—year and microenvironmental variation. Second, the seed bank can affect both the demographic and genetic structure of the population. Dormant seeds remain viable for at least 3 yr and can mitigate the negative demographic effects of reproductive failure. Allozyme differences exist between seeds that germinate in the field and seeds that remain dormant, suggesting that the evolutionary potential of the aboveground population is influenced by dormancy. Finally, the necessary genetic and environmental variation is present. Both germination percentage and post—germination traits (e.g., leaf morphology) vary among and within populations as well as among environmental treatments. Thus, the potential exists for Lesquerella to respond to selective differences between temporal or spatial environments. We suggest experimental approaches for assessing the extent to which seed dormancy h...

Produção de mudas de espécies das Restingas do município do Rio de Janeiro, RJ, Brasil

“…Porém, mesmo com condições ideais para estes parâmetros, sementes viáveis de muitas espécies não germinam, sendo consideradas sementes dormentes. A dormência das sementes provavelmente evoluiu em resposta à variabilidade e à imprevisibilidade ambiental (Evans & Cabin 1995). Muitas sementes de árvores tropicais perdem a viabilidade em poucos dias e, segundo Fenner (1985), isto estaria relacionado com a previsibilidade de seus hábitats, onde as oportunidades para a reprodução ocorrem freqüentemente.…”

Seed bank persistence of clonal weeds in contrasting habitats: implications for control

“…Seed dormancy is thought to have evolved in response to unpredictable environmental variability and might lead to the existence of soil seed banks-populations of viable seeds in the soil (e.g. Ellner 1985;Evans and Cabin 1995;Thompson et al 1997;Easterling and Ellner 2000;Rice and Dyer 2001).…”

“…Soil seed banks play an important role in many plant populations as they can buffer populations from temporal variation (Klinkhamer et al 1987), mitigate the demographic effects of reproductive failure (Evans and Cabin 1995) and conserve genetic variation (Menges 2000). An understanding of seed behaviour in the soil is thus essential for the management of plant populations.…”

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

“…Variance in time to germination and hatching asynchrony have mostly been discussed in the context of among-season delays, or dormancy (Cohen 1966;Silvertown 1984;Philippi 1993;Nilsson et al 1994;Evans and Cabin 1995;Andersson and Milberg 1998;Clauss and Venable 2000;Easterling and Ellner 2000), but considerable asynchrony within a season also exists (e.g., Kalisz 1986;Biere 1991a;Clauss and Venable 2000;Simons and Johnston 2000a;Galloway 2002). Because the timing of germination is closely associated with fitness, explaining variance in this trait is of broad evolutionary interest.…”

“…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.…”