From a Holiday Haul to a Citywide Infestation
In the early 1950s a young traveler returning from northern Italy inadvertently introduced a handful of European wall lizards (Podarcis muralis) into Ohio. The cargo consisted of roughly ten individuals, yet today hundreds of thousands—perhaps even millions—scurry across Cincinnati and its suburbs. Such explosive growth from a minuscule founder group contradicts the classic expectation that small invasive populations succumb to inbreeding depression and fail to establish.
DNA Clues Reveal a Brief Genetic Bottleneck
Researchers from Ohio State University and Ohio Wesleyan University compared the genetic makeup of three groups: native Italian lizards, two Cincinnati sub‑populations, and a modest colony from nearby Columbus. The analysis, published in *Molecular Ecology*, confirmed that Cincinnati’s lizards experienced a genetic bottleneck when the original few founders reproduced. However, the bottleneck was remarkably short‑lived. Rapid, prolific breeding quickly replenished genetic diversity, allowing the population to sidestep the detrimental effects of inbreeding.
Why Cincinnati Was a Perfect Match
Beyond sheer reproductive speed, the urban environment itself played a pivotal role. Eric Gangloff noted that, despite geographic distance, Milan’s climate and habitat echo those of Cincinnati. The city offered a climate range suitable for thermoregulation, abundant sun‑warmed walls, and, crucially, minimal competition from native reptiles. These conditions created an ecological vacuum that the newcomers could instantly occupy.
Urban Affinity and Behavioral Shifts
DNA scans also uncovered subtle alterations in genes linked to behavior. Such changes hint at an adaptation to city life—perhaps a reduced fear of human structures or a modified foraging strategy. Notably, the lizards remain largely confined to urban zones; they have not colonized surrounding rural landscapes in large numbers, suggesting a strong attachment to the built environment.
Implications for Invasion Biology
The Cincinnati case illustrates that successful invasions often hinge on a synergy of traits: high fecundity, environmental compatibility, and lack of native rivals. It also underscores the influence of metropolitan settings in shaping evolutionary pathways. Understanding these dynamics can improve predictions about which species might become future urban pests and inform management strategies aimed at curbing their spread.
Source: https://scientias.nl/waarom-cincinnati-nu-vol-zit-met-italiaanse-muurhagedissen/#respond
