Spatial patterns of genomic variation and temporal genomic offset in a
common grassland plant and their relation to seed transfer zones
Abstract
Introduction of large amounts of seeds is essential for restoration of
temperate grasslands and is often regulated by seed transfer zones.
These zones are commonly derived from abiotic parameters only. In order
to evaluate seed zones as a means for the protection of genetic
diversity and to avoid potential detrimental effects such as
maladaptation and homogenisation of seed transfer within zones,
empirical data on spatial genetic structure is paramount. Here, we
focussed on Galium album, a widespread perennial grassland species,
which we thoroughly sampled on average once per 25 km x 25 km in all of
Germany. Based on 9,403 SNP loci, we described the genetic structure
using Bayesian clustering. We identified four spatially coherent genetic
clusters that were rarely congruent with the current seed zones.
Therefore, current zone-based seed transfer potentially distorts and
homogenises some spatial differentiation. Yet, we found significant
isolation-by-distance among seed zones, showing that they still reflect
a substantial part of spatial genetic differentiation. Seed transfer
practice is challenged by climate change that shifts adaptive
requirements for populations. We conducted redundancy analysis
(RDA)-based genotype-environment association (GEA) analysis, and
assessed necessary genomic turnover to maintain current levels of
adaptation (temporal genomic offset). The resulting patterns suggest
that climate change might impose a risk for regional adaptation in parts
of Southern and Central Germany. We found that targeted assisted
migration across seed zone borders might in some cases mitigate the most
adverse GEA disruptions in seed zones that do not harbour suitable donor
material themselves.