16Phenotypic plasticity can maintain population fitness in novel or changing environments if it allows the 17 phenotype to track the new trait optimum. Understanding how adaptation to contrasting environments 18 determines plastic responses can identify how plasticity evolves, and its potential to be adaptive in response 19 to environmental change. We sampled 79 genotypes from populations of two closely related but ecologically 20 divergent ragwort species (Senecio, Asteraceae), and transplanted multiple clones of each genotype into four 21 field sites along an elevational gradient representing each species' native range, the edge of their range, and 22 conditions outside their native range. At each transplant site, we quantified differences in survival, growth, 23 leaf morphology, chlorophyll fluorescence and gene expression for both species. Overall, the two species 24 differed in their sensitivity to the elevational gradient. As evidence of plasticity, leaf morphology changed 25 across the elevational gradient, with changes occurring in opposite directions for the two species. Differential 26 gene expression across the four field sites also revealed that the genetic pathways underlying plastic 27 responses were highly distinct in the two species. Despite the two species having diverged recently, 28 adaptation to contrasting habitats has resulted in the evolution of distinct sensitivities to environmental 29 variation, underlain by distinct forms of plasticity. 30 genotype-by-environment interactions, phenotypic plasticity, physiological plasticity, specialisation 32 33 62when the environment is predictable, leading to adaptive plasticity within the environmental limits 63 experienced during adaptation (Bradshaw 1965; Schlichting 1986; Baythavong and Stanton 2010). Whether 64 such plasticity will continue to be adaptive when exposed to novel conditions, such as those imposed by 65 4 climate change, remains an empirical issue (Ghalambor et al. 2007). Strong stabilising selection created by 66 predictable environments is expected to lead to specific plastic responses and reduce genetic variation for 67 plasticity (Oostra et al. 2018). By contrast, populations adapted to a wider range of habitats that are more 68 spatially and temporally variable are predicted to maintain genetic variation in plastic responses, increasing 69 the potential for selection on plasticity (Chevin et al. 2010). Detecting and characterising patterns of G×E for 70 a range of naturally occurring genotypes can help us understand whether evolutionary responses can occur 71 even if plasticity is constrained in certain directions (Via 1993; Chevin and Hoffmann 2017). 72 The genetic architecture underlying variation in plasticity is largely unknown (Fusco and Minelli 2010). 73 Plastic responses at the gene expression level are most likely controlled either by epiallelic control of the 74 genes themselves or allelic variation in the regulators of the genes (Rockman and Kruglyak 2006). If allelic 75 (sequence changes) or epiallelic (e.g. DNA me...

The evolution of plastic responses to external cues allows species to maintain fitness in response to the environmental variations they regularly experience. However, it remains unclear how plasticity evolves during adaptation. To test whether distinct patterns of plasticity are associated with adaptive divergence, we quantified plasticity for two closely related but ecologically divergent Sicilian daisy species (Senecio, Asteraceae). We sampled 40 representative genotypes of each species from their native range on Mt. Etna and then reciprocally transplanted multiple clones of each genotype into four field sites along an elevational gradient that included the native elevational range of each species, and two intermediate elevations. At each elevation, we quantified survival and measured leaf traits that included investment (specific leaf area), morphology, chlorophyll fluorescence, pigment content, and gene expression. Traits and differentially expressed genes that changed with elevation in one species often showed little changes in the other species, or changed in the opposite direction. As evidence of adaptive divergence, both species performed better at their native site and better than the species from the other habitat. Adaptive divergence is, therefore, associated with the evolution of distinct plastic responses to environmental variation, despite these two species sharing a recent common ancestor.

This study aims to explore the effect of environmental factors (temperature, light, storage time) on germination response and dormancy patterns in eight Mediterranean native wildplants, belonging to the Euphorbia L. genus. In detail, we considered E. amygdaloides subsp. arbuscula, E. bivonae subsp. bivonae, E. ceratocarpa, E. characias, E. dendroides, E. melapetala, E. myrsinites, and E. rigida. We collected seeds from natural plant populations and performed germination assays in climatic chambers at seven constant temperatures (from 5 to 35°C, with 5°C increments), and four fluctuating temperature regimes (8/15, 8/20, 8/25, and 8/30°C, with a 12/12 hr thermoperiod). Germination assays were set up both in dark (D) and in light/dark conditions (L/D, 12/12 hr photoperiod), after short and long seed storage (SS around 30 days and LS around 150 days). For all these species, except E. amygdaloides subsp. arbuscula, results show that the final germinated proportions were improved by a long storage period (>150 days), which supports the existence of nondeep physiological dormancy. Optimal temperature levels ranged from 14.3 to 21.3°C and base temperatures ranged from 5.6 to 12.1°C, while ceiling temperatures from 25.6 to 34.7°C. For none of these species, germinations were favored by an alternating daily temperature regime, while in several instances, germinations were quicker and more complete in darkness, than in an alternating light/dark regime. In some instances, extreme temperature levels (5 and 30°C) induced dormancy and germinations did not resume when seeds were exposed at optimal temperature levels. Results are discussed in terms of the dynamics of emergences and how this might be affected by climate changes.

Experiments on redroot pigweed (Amaranthus retroflexus L.) were conducted to investigate whether the germinative response to environmental conditions is affected by the time of seed set. Seeds were collected in the same field (Sicily, Southern Italy) in May, July and October; each lot was dry-stored from 15 to 400 days after harvest (DAH) and submitted to germination assays from 15 to 408C, both in continuous darkness (D) and in alternate light/darkness regime (L/D). For the three lots, over 15 DAH, the response to temperature and light regime was strongly affected by harvesting time. Seeds set in May, negatively affected by L/D, showed a high germination capability (.80%) at 95 DAH from 25 to 408C. Seeds set in July were favoured by L/D and required at least 170 DAH to reach 80% germination capability. Seeds set in October were also favoured by L/ D and gave a good germination capability only at 300 and 400 DAH. These results prove that seed germination behaviour in redroot pigweed is not independent of the time of the year in which seeds are produced and is due to both the environmental conditions experienced by the mother plant during seed maturation and those experienced by seeds after seed set.

As climate change transforms seasonal patterns of temperature and precipitation, germination success at marginal temperatures will become critical for the long-term persistence of many plant species and communities. If populations vary in their environmental sensitivity to marginal temperatures across a species' geographical range, populations that respond better to future environmental extremes are likely to be critical for maintaining ecological resilience of the species.Using seeds from two to six populations for each of nine species of Mediterranean plants, we characterized patterns of among-population variation in environmental sensitivity by quantifying genotype-by-environment interactions (G 9 E) for germination success at temperature extremes, and under two light regimes representing conditions below and above the soil surface.For eight of nine species tested at hot and cold marginal temperatures, we observed substantial among-population variation in environmental sensitivity for germination success, and this often depended on the light treatment. Importantly, different populations often performed best at different environmental extremes.Our results demonstrate that ongoing changes in temperature regime will affect the phenology, fitness, and demography of different populations within the same species differently. We show that quantifying patterns of G 9 E for multiple populations, and understanding how such patterns arise, can test mechanisms that promote ecological resilience.