# Reintroduction Without Genetic Bottlenecks: Preserving Diversity in Restored Populations of the Critically Endangered Riverine Shrub Myricaria germanica

## TL;DR

Restoring populations of the endangered shrub Myricaria germanica using a single diverse source can maintain genetic diversity and avoid risks from mixing.

## Contribution

Shows that reintroduction from a single genetically variable source can preserve diversity and avoid outbreeding risks in restored populations.

## Key findings

- Restored populations had genetic diversity comparable to natural populations along the Isar River.
- Differentiation between seed source and restored sites was modest (PhiPT = 0.12).
- Targeted reintroduction can safeguard genetic variation and avoid long-term risks like outbreeding depression.

## Abstract

River regulation has profoundly altered hydrological regimes in alpine floodplains, leading to severe habitat loss and population declines of specialist species such as Myricaria germanica. Since the early 2000s, extensive reintroduction programs have been implemented to counteract the consequences of channelization and embankment, aiming to prevent the extinction of this characteristic gravel‐bank shrub. Yet, the genetic outcomes of these measures remain largely unexplored, while the potential influence of founder and bottleneck effects on restoration success remains uncertain. We analyzed genetic variation within and among natural and restored populations along the rivers Isar and Lech in southern Germany and northern Austria. Restored populations exhibited genetic diversity comparable to natural populations along the Isar, and differentiation between seed source and restored sites was modest (PhiPT = 0.12). Our findings show that restoration relying on a single, genetically variable source population can successfully maintain local genetic diversity. This highlights that targeted reintroduction can safeguard genetic variation while avoiding possible long‐term risks of excessive mixing, such as potential outbreeding depression or reduced fitness, thereby supporting the persistence of this iconic riverine species under ongoing environmental change.

Anthropogenic river regulation has severely reduced habitats of alpine floodplain specialists such as Myricaria germanica. Analyses of natural and restored populations along the Isar and Lech Rivers revealed that reintroduction from a single, genetically variable source can maintain local genetic diversity, with only modest differentiation from the seed source. These findings demonstrate that targeted restoration based on a well‐chosen source population can safeguard local genetic variation while avoiding uncertain long‐term risks of excessive mixing, thereby supporting the persistence of this iconic species in the face of changing environmental conditions.