Genetic variation in Loudetia simplex supports the presence of ancient grasslands in Madagascar

Abstract

Societal Impact Statement Recognizing Loudetia‐dominated grasslands were widespread prior to human colonization highlights that open ecosystems were and continue to be an important component of Madagascar's biodiversity. A better understanding of the plant species that form grassland ecosystems is necessary for effective land management strategies that support livelihoods, but substantial financial and logistical barriers exist to implementing conservation genetic studies using contemporary genomic tools. Some challenges for population genetic analyses of non‐model polyploids lacking reference genomes can be ameliorated by developing computational resources that leverage a cost‐effective data generation strategy that requires no prior genetic knowledge of the target species. This may benefit conservation programs with small operating budgets while reducing uncertainty compared to status quo microsatellite assays. Summary The extent of Madagascar's grasslands prior to human colonization is unresolved. We used population genetic analyses of a broadly dominant C4 fire‐adapted grass, Loudetia simplex, as a proxy for estimating grassland change through time. We carefully examined the utility of target‐enrichment data for population genetics to make recommendations for conservation genetics. We explored the potential of estimating individual ploidy levels from target‐enrichment data and how assumptions about ploidy could affect analyses. We developed a novel bioinformatic pipeline to estimate ploidy and genotypes from target‐enrichment data. We estimated standard population genetic summary statistics in addition to species trees and population structure. Extended Bayesian skyline plots provided estimates of population size through time for empirical and simulated data. All Malagasy L. simplex individuals sampled in this study formed a clade and possibly indicated an ancestral Central Highland distribution of 800 m in altitude and above. Demographic models suggested grassland expansions occurred prior to the Last Interglacial Period and supported extensive grasslands prior to human colonization. Though there are limitations to target‐enrichment data for population genetic studies, we find that analyses of population structure are reliable. Genetic variation in L. simplex supports widespread grasslands in Madagascar prior to the more recent periods of notable paleoclimatic change. However, the methods explored here could not differentiate between paleoclimatic change near the Last Glacial Maximum and anthropogenic effects. Target‐enrichment data can be a valuable tool for analyses of population structure in the absence a reference genome.

Keywords

• anthropogenic climate change
• conservation genetics
• effective population size
• HybSeq
• polyploidy
• target‐enrichment