The role of phenotypic plasticity in the establishment of range margins

Abstract

It has been argued that adaptive phenotypic plasticity may facilitate range expansions over spatially and temporally variable environments. However, plasticity may induce fitness costs. This may hinder the evolution of plasticity. Earlier modelling studies examined the role of plasticity during range expansions of populations with fixed genetic variance. However, genetic variance evolves in natural populations. This may critically alter model outcomes. We ask: How does the capacity for plasticity in populations with evolving genetic variance alter range margins that populations without the capacity for plasticity are expected to attain? We answered this question using computer simulations and analytical approximations. We found a critical plasticity cost above which the capacity for plasticity has no impact on the expected range of the population. Below the critical cost, by contrast, plasticity facilitates range expansion, extending the range in comparison to that expected for populations without plasticity. We further found that populations may evolve plasticity to buffer temporal environmental fluctuations, but only when the plasticity cost is below the critical cost. Thus, the cost of plasticity is a key factor involved in range expansions of populations with the potential to express plastic response in the adaptive trait.

Shallow environmental gradients can cause range margins to form

“…Similarly to Eriksson and Rafajlović [2021, 2022], we modelled a monoecious population with nonoverlapping generations expanding from the central region of a unidimensional habitat composed of 180 demes, each with the carrying capacity of K = 100 individuals. At the beginning of the simulations, the central region of 36 demes was filled with locally well adapted populations (Methods).…”

“…Pairs of haploid gametes from the same deme were then chosen uniformly at random to form new zygotes (as such, selfing was possible by chance). After reproduction, parents were removed from the population, and the newly formed zygotes dispersed according to a discretised Gaussian function with mean 0 and standard deviation σ = 1 (as in [Eriksson and Rafajlović, 2022]). After dispersal, the zygotes were treated as adults, and the cycle entered the next generation.…”

“…We performed individual-based simulations to investigate how the presence of two adaptive traits impacts on the process of range expansion and on the establishment of range margins. To this end, we extended the simulation framework used in Eriksson and Rafajlović [2021, 2022]. Simulations were custom-made and implemented in Matlab.…”

“…Notably, we find that, at the margins, the steepening gradient is shallower when the second, constant, gradient (b (2) ) is larger. Recall that a constant gradient by itself cannot cause the formation of non-trivial range margins (sensu Eriksson and Rafajlović [2022]).…”

Climate-driven variation in biotic interactions provides a narrow and variable window of opportunity for an insect herbivore at its ecological margin

“…Climate change is causing widespread shifts in species' geographic range limits [1][2][3]. The extent of such shifts depends on species' life histories, potential for plastic responses and the quality of available habitat at the expanding margin [4][5][6]. Habitat availability may itself be determined by the process of range expansion: range shifts have recently been identified as a cause, rather than consequence, of increased dietary generalism at poleward range margins in herbivorous insects [7,8].…”