Data from: Patterns of genetic differentiation in Colorado potato beetle correlate with contemporary, not historic, potato land cover

Changing landscape heterogeneity can influence connectivity and alter
genetic variation in local populations, but there can be a lag between
ecological change and evolutionary responses. Temporal lag effects might
be acute in agroecosystems, where land cover has changed substantially in
the last two centuries. Here, we evaluate how patterns of an insect
pest's genetic differentiation are related to past and present
agricultural land cover change over a 150-year period. We quantified
change in the amount of potato, Solanum tuberosum L., land cover since
1850 using county-level agricultural census reports, obtained allele
frequency data from 7,408 single-nucleotide polymorphism loci, and
compared effects of historic and contemporary landscape connectivity on
genetic differentiation of Colorado potato beetle, Leptinotarsa
decemlineata Say, in two agricultural landscapes in the USA. We found that
potato land cover peaked in Wisconsin in the early 1900’s, followed by
rapid decline and spatial concentration, whereas it increased in amount
and extent in the Columbia Basin of Oregon and Washington beginning in the
1960’s. In both landscapes, we found small effect sizes of landscape
resistance on genetic differentiation, but a 20x to 1,000x larger effect
of contemporary relative to historic landscape resistances. Demographic
analyses suggest population size trajectories were largely consistent
among regions, and therefore are not likely to have differentially
impacted the observed patterns of population structure in each region..
Weak landscape genetics associations might instead be related to the
coarse resolution of our historical land cover data. Despite rapid changes
in agricultural landscapes over the last two centuries, genetic
differentiation among L. decemlineata populations appears to reflect
ongoing landscape change. The historical landscape genetics framework
employed in this study is broadly applicable to other agricultural pests,
and might reveal general responses of pests to agricultural land use
change.