Source-sink migration of natural enemies drives local maladaptation of
victim populations in edge habitats
Abstract
Natural enemies are critical drivers of species biogeography. Local
adaptation of victim populations in edge habitats is particularly likely
to be limited by enemies. We experimentally tested this hypothesis using
a model microbial system, bacterium Pseudomonas fluorescens
(victim) and a lytic bacteriophage (enemy). When evolving alone,
bacterial populations in a low temperature environment (10°C) showed
obvious abiotic adaptation in terms of increased growth performance; and
immigration of bacteria from an optimal environment (28°C) reduced such
evolutionary adaptation. However, when phages were present, no
significant abiotic adaptation was observed. Crucially, phage immigrants
from source populations even caused maladaptation (decreased growth
performance relative to the ancestral genotype), and bacterial
adaptation was less affected when both bacteria and phages had joint
migration. Our results demonstrate intraspecific apparent competition
mediated by enemies with which prosperity in core habitats can
exacerbate hardship in edge habitats.