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

Area of Science:

• Evolutionary Biology
• Population Genetics
• Marine Ecology

Background:

• Understanding human impacts on species dispersal is crucial for conservation and evolutionary studies.
• Distinguishing human-mediated dispersal from natural dispersal is challenging due to their simultaneous effects on gene flow.
• Historical shipping practices, specifically the use of sediment ballast, represent a unique system to study past human-mediated dispersal.

Purpose of the Study:

• To disentangle the effects of human-mediated dispersal from natural dispersal on population genetic structure.
• To investigate the historical gene flow and population dynamics of two marine invertebrates, *Corophium volutator* and *Hediste diversicolor*, introduced to North America from Europe.
• To assess how historical human activities have shaped the evolutionary trajectories of these species.

Main Methods:

• Genomic analysis using Restriction site Associated DNA sequencing (RADseq) to derive Single Nucleotide Polymorphisms (SNPs).
• Investigated genetic patterns in *Corophium volutator* (n=121; 4,870 SNPs) and *Hediste diversicolor* (n=78; 3,820 SNPs).
• Phylogenetic network and clustering analyses were employed to infer population structure and relationships.

Main Results:

• Detected significant genetic subdivision within both introduced North American and native European populations.
• Phylogenetic analyses revealed distinct population structures and high levels of reticulation within ranges, alongside clear splits between European and North American populations.
• Observed genetic patterns were inconsistent with those expected from natural dispersal alone, indicating human activity's influence.

Conclusions:

• Historical human-mediated dispersal eroded ancestral phylogeographic structure among native populations.
• Human activity was insufficient to overcome divergence between naturalized populations and their sources, leading to global diversification.
• Human activities can significantly alter species' evolutionary trajectories, causing regional homogenization and global diversification, and potentially obscuring historical genetic data.