The Evolutionary Ecology of Seed Germination of Arabidopsis Thaliana: Variable Natural Selection on Germination Timing

Abstract

Germination timing of Arabidopsis thaliana displays strong plasticity to geographic location and seasonal conditions experienced by seeds. We identified which plastic responses were adaptive using recombinant inbred lines in a field manipulation of geographic location (Kentucky, KY; Rhode Island, RI), maternal photoperiod (14-h and 10-h days), and season of dispersal (June and November). Transgressive segregation created novel genotypes that had either higher fitness or lower fitness in certain environments than either parent. Natural selection on germination timing and its variation explained 72% of the variance in fitness among genotypes in KY, 30% in June-dispersed seeds in RI, but only 4% in November-dispersed seeds in RI. Therefore, natural selection on germination timing is an extremely efficient sieve that can determine which genotypes can persist in some locations, and its efficiency is geographically variable and depends on other aspects of life history. We found no evidence for adaptive responses to maternal photoperiod during seed maturation. We did find adaptive plasticity to season of seed dispersal in RI. Seeds dispersed in June postponed germination, which was adaptive, while seeds dispersed in November accelerated germination, which was also adaptive. We also found maladaptive plasticity to geographic location for seeds dispersed in June, such that seeds dispersed in KY germinated much sooner than the optimum time. Consequently, bet hedging in germination timing was favorable in KY; genotypes with more variation in germination timing had higher fitness because greater variation was associated with postponed germination. Selection on germination timing varied across geographic location, indicating that germination timing can be a critical stage in the establishment of genotypes in new locations. The rate of evolution of germination timing may therefore strongly influence the rate at which species can expand their range.

Aberrant clones: Birth order generates life history diversity in Greater Duckweed, Spirodela polyrhiza

“…In desert annual plants, for example, moisture provides a partially reliable cue for future success, and diversification bet hedging may concurrently evolve around norms of reaction, increasing the variance in germination events among progeny of individuals within (Donohue et al., 2005; Simons, 2014) and among seasons (Clauss & Venable, 2000; Cohen, 1966; Evans, Ferriere, Kane, & Venable, 2007; Gremer et al., 2016; Philippi, 1993), thus reducing risk of low or zero parental fitness.…”

Response to selection and evolvability of invasive populations

“…enemies, food resource, temperature, salinity) and the intrinsic responses of populations to the extrinsic forces, such as phenotypic plasticity or evolutionary adaptation. Populations vary in their intrinsic responses, with some populations having greater plasticity or evolutionary potential than others (Huey et al 2000;Weinig 2000a;Carroll et al 2001;Reznick and Ghalambor 2001;Lee 2002;Parker et al 2003;Blair and Wolfe 2004;Bossdorf et al 2005;Donohue et al 2005b). In addition, populations could respond in a complex manner, with both phenotypic plasticity and selection contributing to invasive success (Lee 2002), but aside from a few notable case studies (Weinig 2000a, b;Weinig and Delph 2001), their relative importance and fitness tradeoffs remain unclear.…”

“…Direct measurements of selection response in invasive or colonizing populations are still rare (Gibbs 2002;Lee 2002;Donohue et al 2005a;Santos et al 2005). Eurytemora affinis is a major component of food webs in estuarine and salt marsh ecosystems in the Northern Hemisphere.…”

The maladaptive significance of maternal effects for plants in anthropogenically modified environments

“…Environmental cues such as precipitation, temperature, light and nutrient availability were historically indicative of ecologically reliable outcomes, such as suitable early-season germination (Khurana and Singh 2001;Donohue et al 2005;Wolfe and Mazer 2005). These reliable cues perhaps increased offspring fitness when plant phenotypes were modified from environmentally induced maternal effects.…”