Introductions of invasive species to new environments often result in
rapid rates of trait evolution. While in some cases these evolutionary
transitions are adaptive and driven by natural selection, they can also
result from non-adaptive processes associated with the invasion history.
Here, we examined the role of adaptive and non-adaptive evolutionary
processes in the brown anole (Anolis sagrei), a widespread invasive
lizard for which genetic data have helped trace the sources of
non-native populations. We focused on the dewlap, a signaling trait
known to be subject to multiple selective pressures. We measured dewlap
reflectance, pattern, and size in non-native populations across the
southeastern United States. We combine these trait measurements with
quantification of environmental variables known to influence dewlap
signal effectiveness, such as canopy openness. Further, we use
genome-wide data to estimate ancestry and to perform association mapping
for dewlap traits. We found that among-population variation in dewlap
characteristics is best explained by ancestry, as contributed by
invasion history. This result was supported by genome-wide association
mapping, which identified several ancestry-specific loci associated with
dewlap traits. Despite the strong imprint of invasion history on dewlap
variation, we also detect significant relationships between dewlap
traits and local environmental conditions. Thus, our results are also
consistent with natural selection influencing trait evolution during the
brown anole invasion. Our study clarifies the importance of ancestry and
admixture in shaping phenotypes during biological invasion, while also
showing that some traits can respond adaptively to conditions
encountered in the invasive range despite potential constraints imposed
by invasion history.