Morissette, O. | Search bioRxiv

bioRxiv2022

Environmental determinants of invasion hotspots and refugia at a river scale: implications for conservation of native biodiversity

Introductions of exotic invasive species are a global disturbance for natural habitats. The severity of invasions can greatly vary from local to global scales, as observed in invasion refuges, exhibiting lower-than-expected invasion intensity. In this study, we analyzed the effects of water conductivity and wetland presence on the density of the round goby (Neogobius melanostomus) in a large-scale study (> 1300 sites), spanning a 400 km stretch of the St. Lawrence River (Canada). Our results showed that round goby density was null in sites with water conductivity under 100 {micro}S/cm and increased toward a probable biological optimum at 300 {micro}S/cm. The presence of wetlands appeared to also decrease round goby density along the conductivity continuum. Similarly, fish community diversity was maximal outside of the round goby water conductivity optimum. Hence, low water conductivity (<100 {micro}S/cm), in interaction with the presence of wetlands, can provide a refuge for native aquatic species, establishing a simple risk assessment tool for managers. Our results also highlighted the high value of wetland conservation for conservation of native species biodiversity.

ecology↗

bioRxiv2022

Spatiotemporal changes in genetic diversity and structure of a recent fish invasion in eastern North America

Introduced and geographically expanding populations experience similar eco-evolutionary challenges, including founder events, genetic bottlenecks, and novel environments. Theory predicts that reduced genetic diversity resulting from such genetic phenomena limits the colonization success of introduced populations. We examined an invasive population of a Eurasian freshwater fish, Tench (Tinca tinca), that has been expanding geographically in eastern North America for three decades. Using genomic data, we evaluated evidence for single versus multiple introductions and the connectivity of the population across the entire range in which it has been spreading. Tench exhibited low levels of genetic diversity, a lack of marked population subdivision across time and space, and evidence of a recent genetic bottleneck. These results suggest that the invasion stemmed from a single introduction, consistent with the reported invasion history. Furthermore, the large genetic neighbourhood size and weak within-population genetic substructure suggest high connectivity across the invaded range, despite the large area occupied, and no evidence of substantial diminution of genetic diversity from the invasion core to the margins. As eradicating the species within a ~112 km radius would be necessary to prevent recolonization, eradicating Tench is likely not feasible at watershed--and possibly local--scales. Management should instead focus on reducing abundance in priority conservation areas to mitigate adverse impacts. Our study supports the argument that introduced populations can thrive despite recent bottlenecks and low levels of genetic diversity, and it suggests that landscape heterogeneity and population demographics can generate variability in spatial patterns of genetic diversity within a single range expansion.

genomics↗