PROJECT SUMMARY
Invasive species, which can carry diseases, decimate food crops and threaten biodiversity, are immensely
successful in new environments, but the biological mechanisms that enable their spread remain elusive. Some
invasive species show signs of rapid adaptation to new habitats, but few studies have captured post-invasion
adaptation in real time. Additionally, invasive species colonizing multiple habitats simultaneously offer the
opportunity to study the longstanding question of whether evolution is predictable. To understand how quickly
and predictably organisms adapt to newly colonized environments, detailed genomic studies of repeated
incipient invasions are necessary. In this study, we will genetically and phenotypically characterize North
American populations of the African Fig Fly, Zaprionus indianus, to test for local adaptation and parallel
evolution in its ongoing invasion. This tractable model organism arrived in North America less than two
decades ago and rapidly spread. Our data suggest it is locally extirpated from temperate habitats each winter
and re-colonizes these locales each spring. Our central hypothesis is that Z. indianus undergoes predictable
post-colonization adaptation across multiple locations and years, resulting in repeated changes in allele
frequencies and ecologically relevant phenotypes. To test this hypothesis, we will collect, sequence, and
phenotype isolates from along the East Coast of North America and from two focal Virginia orchards over
multiple years. In Aim 1, we will quantify genetic and phenotypic variation in North American populations by
generating pooled sequencing of populations collected along a latitudinal gradient to test for clinally varying
polymorphisms over two sampling years. We will also phenotype lines collected at different latitudes to test for
clinal differences in morphological, life-history, and stress tolerance phenotypes. Repeated clinal and
phenotypic differentiation would present evidence for rapid adaptation to local environments. In Aim 2, we will
sample and sequence flies from two geographically separate Virginia orchards over three growing seasons to
test for alleles and phenotypes that predictably change following invasion. These experiments will allow us to
identify the genomic targets of post-invasion adaptation and quantify the predictability of evolution. In Aim 3,
we will characterize the putative target of a recent selective sweep in North American flies: a 600 kb haplotype
that is common in Virginia, intermediate frequency in Florida, and not found in Africa. We will generate outbred
populations fixed for alternate alleles and perform RNAseq to test for differential gene expression associated
with alternate haplotypes. Phenotyping experiments will explore the potential functional targets of this sweep,
allowing us to dissect the biological function of a genomic signal of selection. Collectively, these experiments
will take a multipronged approach to test for post-invasion adaptation and parallel evolution in real time. This
study will provide a framework to understanding rapid adaptation to novel environments and predicting
evolutionary trajectories of future invasive species, which may lead to solutions to control their spread.