Abstract
Seaports are introduction hotspots for invasive alien species (IAS). This is especially true for rodents, which have accompanied humans around the globe since the earliest days of ocean-going voyages. The rapid spread of IAS soon after arrival in a new environment is facilitated by further human-mediated transport or landscape features, like roads. By measuring genetic diversity and structure to investigate dispersal pathways, we gained insight into the transport, spread and establishment stages of a biological invasion, leveraging the most common rodent species (R. norvegicus) in this setting. We characterized the genetic structure of three Norway rat populations along a busy industrial road used by trucks to access the Port area in Paranaguá city (Brazil). A total of 71 rats were genotyped using 11 microsatellite markers. The results revealed a pattern of gene flow contrary to the expected stepping-stone model along the linear transect, with the two furthest apart populations being clustered together. We hypothesize that the observed outcome is explained by natural dispersal along the corridor being lower than human-mediated transport. The sampled area furthest from the port is a gas station frequented by trucks which are considered the most likely mode of transportation. In terms of management strategies, we suggest more emphasis should be put on cargo surveillance to lower the risk of Norway rat dispersal, not only for biosecurity, but also for sanitary reasons, as this port is a major grain trading point.
Highlights
Biological invasions are a serious threat to biodiversity around the world, causing disturbances to ecosystems, and threats to human health and negative impacts on agriculture (Myers et al 2000; Miller et al 2016)
Our study included a total of 71 individuals: 25 from the Port area (20 carcasses collected by the zoonosis control team and 5 captured in live traps), 24 from Area 2 (11 carcasses found in the area and 13 captured in live traps) and 22 from the Area 3 (11 carcasses found in the area and 11 captured in live traps)
In France, Desvars-Larrive et al (2019) found Isolation by Distance (IBD) pattern for two out of three sampled municipalities, but in contrast with those findings, our analysis suggests that the genetic patterns of rats from the two furthest apart sampling areas (Port-Area 3) are more similar, than between either Port-Area 2 or Area 2-Area 3, indicating that rats, in Paranaguá, disperse by self-dispersion, and by human assistance
Summary
Biological invasions are a serious threat to biodiversity around the world, causing disturbances to ecosystems, and threats to human health and negative impacts on agriculture (Myers et al 2000; Miller et al 2016). Especially from the genus Rattus, are commensal species considered to be the most widely introduced vertebrates, accompanying humans around the globe (Drake and Hunt 2009). Their occurrence often has a dramatic impact on native biodiversity, affecting individual demographic rates, genetic (through hybridization), trophic structure and/or resources availability (Parker et al 1999), and they are causing massive economic loss because of destruction of grains and stocked materials (Pimentel et al 2000). Seaports are considered introduction epicentres for invasive alien species (IAS) (Drake and Lodge 2004; Miller et al 2016). It is crucial that ports implement surveillance measures, such as containment facilities and the use of biocontrol agents, chemicals (toxins) or mechanical devices (traps), to control, and prevent the establishment and spread of alien species in a new environment (Lodge et al 2006; Gren 2008)
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