Local adaptation to host plants in herbivorous insects: A meta‐analysis

Local adaptation, wherein populations are well‐adapted to local biotic and abiotic conditions, is a common outcome of natural selection and a driver of diversification. Previous theory identified two criteria to detect local adaptation: (a) the home‐away criterion compares the fitness of a population in its home environment to its fitness in a different environment and (b) the local‐foreign criterion examines differences in fitness between a local and a foreign population when experiencing the local environment. We conducted a meta‐analysis synthesizing empirical evidence of insect herbivores' local adaptation to their host plants using both criteria to assess how diet breadth, geographic distance among populations, herbivore taxonomic affiliation, herbivore clonality, the herbivore response variable measured, taxonomic distance among host plants and features of the study design impact the likelihood of detecting local adaptation. Overall, we found patterns consistent with herbivore local adaptation using both the home‐away and local‐foreign criteria. Herbivore diet breadth, taxonomic affiliation and geographic distance between herbivore populations did not affect the likelihood of finding local adaptation. In contrast, the detection of local adaptation varied with herbivore clonality, the specific response variables measured, taxonomic distance among host plants and elements of the experimental design. These findings clarify the conditions under which local adaptation emerges in the world's most diverse group of multicellular organisms. Read the free Plain Language Summary for this article on the Journal blog.