# Asymmetric biotic interchange across the Bering land bridge between Eurasia and North America

## TL;DR

The study shows that species moved more frequently from Asia to North America during certain periods, influenced by climate changes.

## Contribution

The paper presents new evidence of asymmetric dispersal patterns across the Bering land bridge using time-calibrated phylogenies.

## Key findings

- Dispersal from Asia to North America peaked during the late Oligocene warming.
- North America to Asia dispersal was consistently lower but had peaks in the Eocene and Miocene.
- Environmental changes strongly influenced dispersal patterns between continents.

## Abstract

The exchange of biotas between Eurasia and North America across the Bering land bridge had a major impact on ecosystems of both continents throughout the Cenozoic. This exchange has received particular attention regarding placental mammals dispersing into the Americas, including humans after the last glacial period, and also as an explanation for the disjunct distribution of related seed plants in eastern Asia and eastern North America. Here, we investigate bi-directional dispersal across the Bering land bridge from estimates of dispersal events based on time-calibrated phylogenies of a broad range of plant, fungus and animal taxa. We reveal a long-lasting phase of asymmetrical biotic interchange, with a peak of dispersal from Asia into North America during the late Oligocene warming (26–24 Ma), when dispersal in the opposite direction was greatly decreased. Influx from North America into Asia was lower than in the opposite direction throughout the Cenozoic, but with peak rates of dispersal at the end of the Eocene (40–34 Ma) and again in the early to middle Miocene (16–14 Ma). The strong association between dispersal patterns and environmental changes suggests that plants, fungi and animals have likely dispersed from stable to perturbed environments of North America and Eurasia throughout the Cenozoic.