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 patterns of genetic and phenotypic variation associated with the invasion history. Here, we examined 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 complex signaling trait known to be subject to multiple selective pressures. We measured dewlap reflectance, pattern, and size in 30 non-native populations across the southeastern United States. As well, we quantified environmental variables known to influence dewlap signal effectiveness, such as canopy openness. Further, we used genome-wide data to estimate genetic ancestry, perform association mapping, and test for signatures of selection. We found that among-population variation in dewlap characteristics was best explained by genetic ancestry. This result was supported by genome-wide association mapping, which identified several ancestry-specific loci associated with dewlap traits. Despite the strong imprint of this aspect of the invasion history on dewlap variation, we also detected significant relationships between dewlap traits and local environmental conditions. However, we found limited evidence that dewlap-associated genetic variants have been subject to selection. Our study emphasizes the importance of genetic ancestry and admixture in shaping phenotypes during biological invasion, while leaving the role of selection unresolved, likely due to the polygenic genetic architecture of dewlaps and selection acting on many genes of small effect.

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.

The nuclear genomes of most animal species include segments of the mitogenome, but the count of these NUMTs varies greatly. This study examines the incidence of NUMTs derived from a 658 bp region of the cytochrome c oxidase I (COI) gene as a proxy for other coding regions of the mitochondrial genome. Analysis focuses on the most diverse group of terrestrial organisms, insects, because COI-based identification systems play a key role in clarifying their diversity, an essential antecedent to genome sequencing. Nearly 10,000 COI NUMTs ≥ 100 bp were detected in the genomes of 1,002 insect species with a range from 0–443. NUMT counts were similar among congeners, but differences among genera in a family were often large with genome size explaining 56% of the mitogenome-wide variation in counts. While many of these NUMTs possessed an indel or premature stop codon allowing their exclusion, the others could complicate species diagnosis as they averaged 10.1% divergence from their mitochondrial homologue. The count of NUMTs varies widely among insect lineages, peaking in groups that employ direct development or incomplete metamorphosis. They can raise the apparent species count by up to 22% when the 658 bp barcode region is examined while shorter targets (300 bp, 150 bp) elevate exposure (58–111%) to “ghost” species. As a result, NUMTs represent a particular complication for protocols (e.g., eDNA, metabarcoding) which employ short amplicons for biodiversity assessments.

Invasive species can impact native populations through competition, predation, and habitat alteration, but also genetically through hybridization. Potential outcomes of hybridization span the continuum from extinction to hybrid speciation and can be further complicated by anthropogenic habitat disturbance. Hybridization between the native green anole lizard (Anolis carolinensis) and a morphologically similar invader (A. porcatus) in south Florida provides an ideal opportunity to study interspecific admixture across a heterogeneous landscape of urban and forested habitats. We used reduced-representation sequencing to describe introgression in this hybrid system and to test for a relationship between urbanization and invasive ancestry. Our findings indicate that hybridization between green anole species was likely a limited, historic event, and that patterns of backcrossing have produced two distinct genetic clusters within the hybrid population. Genomic cline analyses revealed rapid introgression and disproportionate representation of invasive alleles at many loci, and no evidence for reproductive isolation between the two species. We also found a positive relationship between urbanization and invasive ancestry, although the mechanism driving this association remains unclear. Ultimately, our findings demonstrate the persistence of non-native genetic material even in the absence of ongoing immigration, indicating that selection favoring invasive alleles can override the demographic limitation of low propagule pressure. However, we also note that not all outcomes of admixture between native and invasive species should be considered intrinsically negative. Hybridization with ecologically robust invaders can lead to adaptive introgression, which may facilitate the long-term survival of native populations otherwise unable to adapt to anthropogenically mediated global change.

While adaptation is commonly thought to result from selection on DNA sequence-based variation, recent studies have highlighted an analogous epigenetic component as well. However, the extent to which these adaptive mechanisms to adaptation to environmental heterogeneity are redundant or complementary remains unclear. To address the underlying genetic and epigenetic mechanisms and their relationship underlying environmental adaptation, we screened the genomes and epigenomes of nine global populations of a predominately sessile marine invasive tunicate, Botryllus schlosseri. We detected clear population genetic and epigenetic differentiation, which were both significantly influenced by local environments, and the minimum annual sea surface temperature (T_min) was simultaneously identified as the top explanatory variable for both types of variation. However, there remain some degree of difference in population structure patterns between two levels, suggesting a certain level of autonomy in epigenetic variation. From the functional perspective, a set of functional genes and biological pathways were shared between two levels, indicating a conjoint contribution of genetic and epigenetic variation to environmental adaptation. Moreover, we also detected genetic- or epigenetic-specific genes/pathways in relation to a wide variety of core processes potentially underlying adaptation to local environmental factors, suggesting the partly independent relationship between two mechanisms. We infer that complementary genetic and epigenetic routes to adaptation are available in this system. Collectively, these mechanisms may facilitate population persistence under environmental changes and sustain successful invasions in novel but contrasting environments.