Invasive Raccoons in Europe Show Genetic Signs of Climate Matching to Native Habitats

In one of the most detailed genomic investigations of a mammal invasion to date, researchers have traced how raccoons (Procyon lotor), one of Europe’s most successful invasive species, carry signatures of adaptation that link them not to North America as a whole, but to a specific slice of their native range. The study, published in the journal NeoBiota, compared the genomes of raccoons from two climatically distinct native populations in the United States with six invasive populations spread across Germany, Poland and Czechia, and found evidence that habitat similarity, not just geographic origin, shapes invasion success.

Raccoons are famously adaptable omnivores, thriving in forests, wetlands and cities alike. Native to North America, they were first introduced to Germany in the 1930s and have since colonised most of the European continent, spreading from at least four separate introduction events in central Germany, along with independent establishments in France, Italy, Spain, the former USSR and Czechia. Their rapid expansion has made them a model system for understanding why some species flourish after being translocated while others fail.

The research team collected 162 tissue samples between 2021 and 2023, drawing from native populations near Melbourne, Florida and between Lincoln and Syracuse, Nebraska, and from invasive populations in Brandenburg, Hessen and Saxony-Anhalt in Germany, two national parks in Poland, and an isolated population in Czechia descended from zoo escapes. Using reduced representation sequencing, a technique that samples thousands of genome-wide markers at relatively low cost, they generated an initial dataset of more than five million single nucleotide polymorphisms, which was filtered down to 55,760 high-quality SNPs for selection scans.

The genetic structure analyses told a clear demographic story. Florida raccoons formed their own distinct cluster, while Nebraska animals shared ancestry components with the European invaders. Among the invasive populations, Hessen formed a homogeneous cluster consistent with its role as the primary introduction site, Polish populations at the eastern invasion front clustered together, and the Czech population stood out as the most genetically differentiated and isolated. Notably, the analyses revealed substantial admixture between German and Polish populations, reflecting ongoing eastward expansion.

As expected for an invasive species, the European raccoons showed a genome-wide reduction in genetic diversity compared with their native counterparts. Nucleotide diversity, allelic richness and both observed and expected heterozygosity were all significantly lower in the invasive range, and native populations carried an order of magnitude more private alleles. Yet despite this loss, the invaders retained enough variation for selection to act upon, a pattern consistent with the restoration of adaptive diversity through admixture of genetically divergent founders from multiple introductions.

The most striking finding emerged from outlier detection. Using two complementary methods, BAYESCAN and pcadapt, the team identified 92 SNPs showing patterns of differentiation inconsistent with neutral evolution. A second approach, the C2-contrast statistic implemented in BAYPASS, identified 113 SNPs whose allele frequencies diverged between the native and invasive ranges. When the researchers examined allele frequencies in detail, a remarkable pattern appeared: most candidate variants were shared at high frequency between the Nebraska population and the invasive populations of Germany and Poland, while being absent or nearly absent in Florida.

This pattern suggests parallel selection pressures between the invasive European range and the part of the native range that shares its climate. Nebraska’s continental climate, with monthly temperatures and rainfall resembling those of central Europe, and its wetlands and pine forests, mirror the habitats occupied by the invasive populations. Florida’s subtropical conditions, by contrast, present a very different selective environment. The authors caution that demographic history, including the possibility that Nebraska-like populations were the actual source of the European introductions, cannot be fully excluded, but the convergence of climate, habitat and genetic signals points to the importance of habitat matching in invasion biology.

Gene ontology enrichment analysis revealed what kinds of traits selection may be favouring. Candidate genomic regions were associated with reproduction and hormonal pathways, cognitive function and neurological processes, stress response, immunity, muscle contraction and energy production. These functions map neatly onto the raccoon’s invasive toolkit: high reproductive rates, behavioural flexibility and problem-solving abilities that help exploit new food sources, and the aerobic capacity that underpins dispersal. Enrichment in genes related to mitochondrial respiration and oxidative stress response is typically linked to adaptation to contrasting thermal environments, consistent with the climatic differences between populations.

The findings carry practical implications for managing the raccoon’s ongoing European expansion. Because eradication is considered unlikely, management focuses on protecting vulnerable native species and habitats, and the study’s results could help prioritise regions at greatest risk. Perhaps most intriguingly, the weakest selection signals were detected in the isolated, least diverse Czech population, hinting that restricting gene flow between invasive populations might limit their adaptive potential. For a generalist species with a broad climatic niche, that is a valuable lever.

More broadly, the study delivers a message that resonates across invasion science: predicting where an invasive species will thrive requires looking beyond the geographic extent of its native range to the specific characteristics of the habitats it evolved in. Native conditions may pre-adapt populations for similar environments elsewhere, and even a famously versatile species like the raccoon appears to owe part of its European conquest to the quiet alignment of climate between continents. As invasions accelerate worldwide, genomic tools like these are becoming essential for anticipating which species will establish where, and for intervening before adaptation locks an invader into its new home.

Subject of Research: Local adaptation and climate matching in invasive raccoon populations in Europe

Article Title: Signatures of differential local adaptation indicate climate matching with specific native-range habitats in invasive raccoons ( Procyon lotor )

Article References: Kołodziejczyk, J., Konopiński, M. K., Hoffman, E. A., & Biedrzycka, A. (2026). Signatures of differential local adaptation indicate climate matching with specific native-range habitats in invasive raccoons (Procyon lotor). NeoBiota, 106, 235-264. https://doi.org/10.3897/neobiota.106.182495

Image Credits: AI Generated

DOI: 10.3897/neobiota.106.182495

Keywords: invasive species, raccoons, Procyon lotor, local adaptation, population genomics, RAD sequencing, climate matching, genetic diversity, Europe, selection signatures, NeoBiota, invasion biology