Impact of temperature shifts on the joint evolution of seed dormancy and size

Abstract

Seed dormancy and size are two important life-history traits that interplay as adaptation to varying environmental settings. As evolution of both traits involves correlated selective pressures, it is of interest to comparatively investigate the evolution of the two traits jointly as well as independently. We explore evolutionary trajectories of seed dormancy and size using adaptive dynamics in scenarios of deterministic or stochastic temperature variations. Ecological dynamics usually result in unbalanced population structures, and temperature shifts or fluctuations of high magnitude give rise to more balanced ecological structures. When only seed dormancy evolves, it is counter-selected and temperature shifts hasten this evolution. Evolution of seed size results in the fixation of a given strategy and evolved seed size decreases when seed dormancy is lowered. When coevolution is allowed, evolutionary variations are reduced while the speed of evolution becomes faster given temperature shifts. Such coevolution scenarios systematically result in reduced seed dormancy and size and similar unbalanced population structures. We discuss how this may be linked to the system stability. Dormancy is counter-selected because population dynamics lead to stable equilibrium, while small seeds are selected as the outcome of size-number trade-offs. Our results suggest that unlike random temperature variation between generations, temperature shifts with high magnitude can considerably alter population structures and accelerate life-history evolution. This study increases our understanding of plant evolution and persistence in the context of climate changes.

Keywords: climate change; eco‐evolutionary dynamics; life‐history traits; seed dormancy; seed size; structured population model; temperature shifts and fluctuations.

Figure 1

Life cycle of seed‐adult stages. Note: α denotes the probability of dormant seeds

Figure 2

Ecological equilibria for a spectrum of seed dormancy (α, a–c) and of seed size (γ, d–f) when the alternative trait is fixed. Note: The red arrows indicate the evolutionary direction; filled red circles () represent different evolutionary equilibria in respective conditions, while open blue circles () represent the values of evolved trait after simulations of 5.0 × 10⁷ steps (the fixed trait values are shown in each panel and the initial values of evolved trait (α or γ) are 0.5; seeds (black curves) and adults (green curves) are shown in pairs distinguished by alphabet numbers; that is, the same number means the number of seeds and adults in the same simulation condition

Figure 3

Pairwise invasibility plots (a) and evolutionary dynamics (b). Note: For A, the evolved morphs of seed dormancy and size are discriminated in black and gray, respectively; shades in black and gray depict leading eigenvalues (λ_L) larger than one (marked by + sign; otherwise, marked by − sign), thus possibly invaded by mutants and its edges in cross shape represent λ_L equal to 1; ES and CS represent evolutionary stability and convergent stability, respectively; For B, one convergent and noninvasible singularity exists for seed size, marked in red dashed line and termed continuously stable strategy (CSS, which corresponds to an evolutionarily stable equilibrium where no evolutionary dynamics exist); no ESS (i.e., noninvasible singular strategies) exists for seed dormancy and it evolves toward zero, marked in red dashed line

Figure 4

Evolutionary end points and corresponding number of populations for the independent evolution of seed dormancy (a,b) and size (c,d) after numerical simulations of 5.0 × 10⁷ and 1.0 × 10⁸ steps. Note: The error bar for each end points or the number of populations (i.e., seeds or adults) is calculated by 20 replicates for each set of simulations; sd represents standard deviation (i.e., temperature variation); the values of fixed trait and the initial evolved trait (α or γ) are 0.5; graphic representation of the simulation dynamics was provided in Figs. S1 and S2

Figure 5

Evolutionary end points and corresponding number of populations for the joint evolution of seed dormancy and size after a numerical simulation of 5.0 × 10⁷ and 1.0 × 10⁸ steps. Note: The error bar for each end points or the number of populations (i.e., seeds or adults) is calculated by 20 replicates for each set of simulations; sd (in axis labels) represents standard deviation (i.e., temperature variation); the initial matrices (α, γ) and (seeds, adults) are (0.5, 0.5) and (5, 5), respectively; graphic representation of the simulation dynamics was provided in Fig. S4