Plasticity of the thermal requirements of exotherms and adaptation to environmental conditions

Abstract

In exothermal organisms, temperature is an important determinant of the rate of ecophysiological processes, which monotonically increase between the minimum (td min) and maximum (td max) temperatures typical for each species. In insects, td min and td max are correlated and there is a approximately 20°C interval (thermal window WT = td max − td min) between them over which insects can develop. We assumed that other exotherms have similar thermal windows because the thermal kinetics of their physiological processes are similar. In this study, we determined the thermal requirements for germination in plants. Seeds of 125 species of Central European wild herbaceous and crop plants were germinated at nine constant temperatures between 5 and 37°C, and the time to germination of 50% of the seeds D and rate of germination R (=1/D) were determined for each temperature and the Lactin model used to determine td min, td max, and WT. The average width of the thermal windows for seeds was significantly wider (mean 24°C, 95% CI 22.7–24.2°C), varied more (between 14.5 and 37.5°C) and development occurred at lower temperatures than recorded for insects. The limiting temperatures for germination, td min and td max, were not coupled, so the width of the thermal window increased with both a decrease in td min and/or increase in td max. Variation in WT was not associated with taxonomic affiliation, adult longevity, or domestication of the different species, but tends to vary with seed size. Plants are poor at regulating their temperature and cannot move to a more suitable location and as a consequence have to cope with wider ranges in temperatures than insects and possibly do this by having wider thermal windows. Synthesis: The study indicated specificity of WT in different exotherm taxa and/or their development stages.

Thermal thresholds for seed germination in Mediterranean species are higher in mountain compared with lowland areas

“…The existence of adaptively significant variation in seed germination responses (thresholds and thermal time) amongst groups of species or populations has recently been highlighted in relation to the timing of germination in the field and thus niche competitiveness (Meyer et al ., 1997; Daws et al ., 2002; Honek et al ., 2014; Dürr et al ., 2015; Picciau et al ., 2018; Tudela-Isanta et al ., 2018). Here we have extended such an approach to model the characteristics of Mediterranean species and, in so doing, revealed a shift in germination syndromes between lowland and upland species.…”

Evolutionary responses to environmental change: trophic interactions affect adaptation and persistence

“…Parameters for the temperature dependence of vital rates a j and b j were measured on phytoplankton [38] to improve the Eppley curve. Parameters for thermal niche widths were measured on diverse taxa including arthropods, amphibians, reptiles, molluscs, fishes [39], plants [40] and phytoplankton [41], and we focus on a reduced range of values to account for variability in temperature that reduces the limits of the thermal niche [42].…”

The role of invertebrates in seedling establishment in a heterocarpic plant, Atriplex sagittata

“…The bracteoles of morph B are usually smaller than bracteoles of morph C but variation in shape and size is enormous (length 5–15 mm, width 3–11 mm) and the reliable distinction of enclosed seeds according to bracteole size is not possible. Morphs A and B are dormant, poorly germinate and enter a persistent soil seed bank, whereas seeds of morph C are non‐dormant, germinate at a wide range of temperatures (Honek et al, ) and do not persist in the soil bank (Mandak & Pysek, ).…”