# Does the Colonizing Population Exhibit a Reduced Genetic Diversity and Allele Surfing? A Case Study of the Midday Gerbil (Meriones meridianus Pallas) Expanding Its Range

## TL;DR

This study examines how genetic diversity and allele surfing occur in a gerbil population expanding into new areas due to desertification in Russia.

## Contribution

The study provides empirical evidence of allele surfing in a natural population during range expansion.

## Key findings

- Colonizing populations show reduced genetic diversity compared to core populations.
- Rare alleles increase in frequency in colonizing populations, indicating allele surfing.
- Marginal populations exhibit strong genetic differentiation and structuration.

## Abstract

We live in a changing world, and human-induced landscape changes cause shifts and expansions of ranges of living organisms worldwide. During range expansions, animals and plants invade and colonize new areas, which may have dramatic ecological and evolutionary consequences. We studied the genetic consequences of range expansion in the desert rodent, currently colonizing new areas in Kalmykia (Southern Russia) following the desertification of rangelands. We found that genetic diversity in the colonizing population was lower than in the range core. Moreover, the colonizing population exhibited strong spatial structuration and increased frequencies of genetic variants (alleles) rare in the source population—signatures of allele surfing, a phenomenon theoretically predicted but, so far, rarely observed in natural populations. Our findings provide new insights into understanding the genetic consequences of range expansions and are important for managing expanding populations and invasions.

Colonizing populations at the leading edge of range expansion are expected to have a reduced genetic diversity and strong genetic structure caused by genetic drift and allele surfing. Until now, few studies have found the genetic signatures of allele surfing in expanding wild populations. Using mtDNA markers, we studied the genetic structure of the population of midday gerbils (Meriones meridianus) expanding their range to the west in Kalmykia (southern Russia) following the new cycle of desertification, re-colonizing areas abandoned in the mid-2010s. In the colonizing population, we found a reduced genetic diversity, the redistribution of haplotype frequencies—in particular, in favor of variants rare in the core population—and strong genetic structure combined with strong differentiation from the core population—patterns suggestive of allele surfing on the wave of expansion. In terms of genetic diversity and spatial structuration, the western edge population sampled in 2008 before its collapse in 2017 occupies the intermediate position between the current colonizing and core population. This suggests that reduced genetic diversity and increased genetic differentiation are general features of marginal populations, enhanced by the founder and allele-surfing effects at the leading edges of expanding ranges.