Human-mediated contact zone between endemic and invasive <i>Barbus</i> species (Osteichthyes: Cyprinidae) in a regulated lowland river: genetic inferences and conservation implications

<div><p></p><p>Genetic surveys of the endemic Padanian barbel <i>Barbus plebejus</i> (Osteichthyes: Cyprinidae) were completed on the lowland Adda River, a heavily regulated Italian Alpine river in which the European <i>Barbus barbus</i> is invasive. Both <i>Barbus</i> species are of the large fluvio-lacustrine ecophenotype and thus they share habitats in the river. Mitochondrial (<i>N</i> = 35) and nuclear (<i>N</i> = 256) DNA sequences were completed with the aim of estimating the extent and genetic consequences of the <i>B. barbus</i> invasion. The phylogenetic analyses, based on <i>cyt b</i> mtDNA, <i>S7</i> ribosomal protein and growth hormone (<i>GH</i>) nuclear genes, revealed 59 haplotypes as <i>B. plebejus</i> and 37 as <i>B. barbus</i>. Genetic diversity values (H and π) and the mismatch distribution analyses indicated <i>B. plebejus</i> was still experiencing demographic radiation from a modest number of founders. The <i>B. barbus cyt b</i> haplotypes suggested their original source was the River Danube. Through analysing the nuclear paralog sequences, evidence was provided of consistent genetic admixture between <i>B. plebejus</i> and <i>B. barbus</i>, being recorded in over 40% of the sampled fishes, indicating that their ecological and biological interactions are disrupting the genetic integrity of <i>B. plebejus</i>. Bayesian analysis and factorial correspondence analysis then revealed that the habitat fragmentation of the Adda River is not limiting population connectivity. It was apparent there has been recent and rapid upstream dispersion of <i>B. barbus</i>, with individuals overcoming barriers to their migration through using fish passes and/or through translocation between impounded sections by anglers. The potential conservation implications of this for the endemic <i>Barbus</i> species are discussed.</p>