Historical human activities reshape evolutionary trajectories across both native and introduced ranges

Abstract

The same vectors that introduce species to new ranges could move them among native populations, but how human‐mediated dispersal impacts native ranges has been difficult to address because human‐mediated dispersal and natural dispersal can simultaneously shape patterns of gene flow. Here, we disentangle human‐mediated dispersal from natural dispersal by exploiting a system where the primary vector was once extensive but has since ceased. From 10th to 19th Centuries, ships in the North Atlantic exchanged sediments dredged from the intertidal for ballast, which ended when seawater ballast tanks were adopted. We investigate genetic patterns from RADseq‐derived SNPs in the amphipod Corophium volutator (n = 121; 4,870 SNPs) and the annelid Hediste diversicolor (n = 78; 3,820 SNPs), which were introduced from Europe to North America, have limited natural dispersal capabilities, are abundant in intertidal sediments, but not commonly found in modern water ballast tanks. We detect similar levels of genetic subdivision among introduced North American populations and among native European populations. Phylogenetic networks and clustering analyses reveal population structure between sites, a high degree of phylogenetic reticulation within ranges, and phylogenetic splits between European and North American populations. These patterns are inconsistent with phylogeographic structure expected to arise from natural dispersal alone, suggesting human activity eroded ancestral phylogeographic structure between native populations, but was insufficient to overcome divergent processes between naturalized populations and their sources. Our results suggest human activity may alter species' evolutionary trajectories on a broad geographic scale via regional homogenization and global diversification, in some cases precluding historical inference from genetic data.

Otolith Microchemistry and Demographic History Provide New Insight into the Migratory Behavior and Heterogeneous Genetic Divergence of Coilia grayii in the Pearl River

“…This genetic drift has not taken place in all subpopulations. The downstream populations along the Pearl River Estuary exhibited stable size, where diverse haplotypes and high gene flow precludes the possibility of deep population structuring and impedes speciation [19]. For instance, the high genetic diversity of the specimens from HM, as well as the many haplotypes (singletons or doubletons with a widely distributed haplotype giving rise to a star-shaped network) and high polymorphism are consistent with population stability in this region [20].…”

“…Coilia grayii (Clupeiformes: Engraulidae) is a common anchovy that travels long distances in the estuarine area of the Pearl River and is distributed along the coasts from the East China Sea to the South China Sea as a forage fish [17,18]. During the spawning season (March-June), schools of anchovy stocks migrate between their spawning, feeding, and nursery grounds, while traveling in fresh or brackish water [19,20]. Surprisingly, some freshwater anchovies are found in the upper reaches of the Pearl River, which are hundreds of kilometers away from shore.…”

Shared and distinct patterns of genetic structure in two sympatric large decapods

“…Demographic connectivity in both species could also be human mediated. Adult lobsters and crawfish are prized as seafood and typically traded live, such that escape or release following anthropogenic transit could generate genetic homogenisation, which could be misinterpreted as natural gene flow between otherwise differentiated populations (Einfeldt et al, 2020). During the 1800s, crawfish were routinely transported from northern Spain to markets in France and Britain, although given that lobsters were similarly widely traded (Spanier et al, 2015), inherent ecological factors remain the most likely cause of interspecific differences in genetic structure.…”

Spatial population genetics in heavily managed species: Separating patterns of historical translocation from contemporary gene flow in white‐tailed deer

“…In particular, human‐mediated dispersal introduces both diversifying and homogenizing effects that prove difficult to disentangle (Epps & Keyghobadi, 2015; Seebens et al, 2017). This erodes adaptive and/ or spatial associations in that it disturbs the expected relationships between genetic differentiation and geographical or environmental proximity (Capinha et al, 2015; Einfeldt et al, 2020). Well‐intended actions, such as translocations and stockings, may also inadvertently obscure pre‐existing landscape genetic patterns (Brown et al, 2009; Laikre et al, 2010; Shephard et al, 2013).…”