Fresh start after rough rides: understanding patterns of genetic differentiation upon human-mediated translocations

Biological invasions via translocations are a textbook case of globalization’s impact on species distributions. Human-mediated transport helps species to overcome natural spatial boundaries and establish populations, often from a small number of individuals, in ecosystems previously unreachable through natural range expansion. The result is a discontinuous species distribution, with connectivity between the native and non-native range dependent on the recurrence of human-mediated species movement. The genetic diversity of introduced individuals represents a random fraction of the original diversity in the native range, but because connectivity is lost, non-native populations are bound to evolve independently. As a result, translocations can reshuffle genetic diversity in non-native populations, and thus, differentiation patterns arising after introduction may constitute the first step of novel evolutionary trajectories. By performing a meta-analysis on 5516 mitochondrial sequences of 20 different species, we explored whether life- and evolutionary history could explain differentiation among non-native populations of recently translocated organisms. We observed a general pattern consisting of reduced differentiation among non-native populations whose introduction derived from a single and intentional translocation, suggesting that these human actions play a role in reshaping genetic variance in non-native ranges. Additionally, we found geographic distance to be a poor predictor of population differentiation on the non-native range when compared to averaged evolutionary distances—the opposite being true for the native range—reinforcing connectivity break imposed by translocation events. Understanding the factors driving the distribution of genetic diversity upon translocations might not only facilitate the development of plans to mitigate the dispersal of invasive species but also to explore the emergence of novel evolutionary trajectories.