A Donor Registry: Genomic Analyses of Posidonia australis Seagrass Meadows Identifies Adaptive Genotypes for Future-Proofing

Abstract

Globally, anthropogenic climate change has caused declines of seagrass ecosystems necessitating proactive restoration approaches that would ideally anticipate future climate scenarios, such as marine warming. In eastern Australia, estuaries with meadows of the endangered seagrass Posidonia australis have warmed and acidified over the past decade, and seagrass communities have declined in some estuaries. Securing these valuable habitats will require proactive conservation and restoration efforts that could be augmented with restoration focussed on boosting resilience to future climate. Understanding patterns of selection and where seagrass meadows are adapted to particular environmental conditions is key for identifying optimal donor material for restoration. We used single nucleotide polymorphisms and genotype by environment analyses to identify candidate loci under putative selection to environmental stressors and assess genomic variation and allelic turnover along stressor gradients. The most important physicochemical variables driving selection were associated with temperature, water turbidity, and pH. We developed a preliminary 'donor registry' of pre-adapted P. australis genotypes by mapping the distribution of alleles to visualise allelic composition of each sampled seagrass meadow. The registry could be used as a first step to select source material for future-proofing restoration projects. A next step is to establish manipulative experiments that will be required to test whether pre-adapted genotypes confer increased resistance to multiple environmental stressors.

Keywords: climate change; estuaries; genotype environment associations; gradient forest; single‐nucleotide polymorphisms.

FIGURE 1

Posidonia australis meadow, Fly Point, Port Stephens, New South Wales. Photo: MJN.

FIGURE 2

Map of locations of sampled Posidonia australis meadows in NSW. Data represent the four most important environmental variables for each meadow used in genotype × environment analyses. AvTemp = average temperature (°C); MaxTemp = maximum temperature (°C); pHRange = difference between highest and lowest observed pH values; TurbRange = difference between highest and lowest observed turbidity measure (NTU).

FIGURE 3

Gradient forest analysis for 141 candidate SNPs in Posidonia australis meadows. Left—relative importance for each environmental variable that describes frequencies in allelic turnover. Right—cumulative importance curves showing overall pattern of genomic compositional change (y‐axis) for nine environmental variables (x‐axis). Turnover functions for each curve are aggregated across all candidate loci. The maximum height of each curve indicates the relative amount of allelic turnover, and the relative importance of each environmental variable.

FIGURE 4

Site based SNP allele distributions mapped to allelic turnover plots and environmental gradients for the four most important variables: average temperature, turbidity range, maximum temperature, and pH range. Reference homozygote alleles are light blue, heterozygotic loci are orange, and alternate homozygotes are red. Dotted lines connect approximate point of allelic turnover between turnover plot and allelic distribution histograms.