Transient local adaptation and source–sink dynamics in experimental populations experiencing spatially heterogeneous environments

Abstract

Local adaptation is determined by the strength of selection and the level of gene flow within heterogeneous landscapes. The presence of benign habitat can act as an evolutionary stepping stone for local adaptation to challenging environments by providing the necessary genetic variation. At the same time, migration load from benign habitats will hinder adaptation. In a community context, interspecific competition is expected to select against maladapted migrants, hence reducing migration load and facilitating adaptation. As the interplay between competition and spatial heterogeneity on the joint ecological and evolutionary dynamics of populations is poorly understood, we performed an evolutionary experiment using the herbivore spider mite Tetranychus urticae as a model. We studied the species's demography and local adaptation in a challenging environment that consisted of an initial sink (pepper plants) and/or a more benign environment (cucumber plants). Half of the experimental populations were exposed to a competitor, the congeneric T. ludeni . We show that while spider mites only adapted to the challenging pepper environment when it was spatially interspersed with benign cucumber habitat, this adaptation was only temporary and disappeared when the populations in the benign cucumber environment were expanding and spilling-over to the challenging pepper environment. Although the focal species outcompeted the competitor after about two months, a negative effect of competition on the focal species’s performance persisted in the benign environment. Adaptation to challenging habitat in heterogeneous landscapes thus highly depends on demography and source–sink dynamics, but also on competitive interactions with other species, even if they are only present for a short time span.

Spatial connectedness imposes local‐ and metapopulation‐level selection on life history through feedbacks on demography

“…Local and metapopulation‐level dynamics interact with each other and influence the adaptation of the individuals at both levels, with ecological population dynamics influencing evolutionary dynamics and the other way around (Hanski, ). Stress resistance, for instance, which we found to evolve in response to habitat fragmentation, can potentially turn into pre‐adaptation to other kind of stressors, that is, suboptimal host plants or novel habitats and enhance persistence under environmental change (Jenkins et al , ; De Roissart et al , ; Bisschop et al , ).…”

Performance in a novel environment subject to ghost competition

“…The novel host islands were placed in boxes with yellow sticky paper (Pherobank) at the bottom and Vaseline at the walls to avoid contamination between islands; this method is known to work from previous research (Alzate et al, 2017; Alzate, Etienne & Bonte, 2019; Bisschop et al, 2019). Eight islands (or replicates) received both T. urticae and T. ludeni.…”

Performance in a novel environment subject to ghost competition

“…Novel host islands were created by placing two 3-weeks-old cucumber plants, Cucumis sativus Tanja, in boxes with yellow sticky paper (Pherobank) at the bottom and Vaseline at the walls to avoid contamination between islands; this method is known to work from previous research (Alzate et al, 2017;Alzate, Etienne & Bonte, 2019;Bisschop et al, 2019). These units consisting of multiple plants are referred to as 'islands' because they represent isolated habitat.…”