Temperature and precipitation, but not geographic distance, explain genetic relatedness among populations in the perennial grass Festuca rubra

Abstract

Abstract Aims Knowledge of genetic structure of natural populations and its determinants may provide key insights into the ability of species to adapt to novel environments. In many genetic studies, the effects of climate could not be disentangled from the effects of geographic proximity. We aimed to understand the effects of temperature and moisture on genetic diversity of populations and separate these effects from the effects of geographic distance. We also wanted to explore the patterns of distribution of genetic diversity in the system and assess the degree of clonality within the populations. We also checked for possible genome size variation in the system. Methods We studied genetic variation within and among 12 populations of the dominant grass Festuca rubra distributed across a unique regional-scale climatic grid in western Norway, Europe and explored the importance of temperature, precipitation and geographic distance for the observed patterns. We also explored the distribution of genetic diversity within and among populations, identified population differentiation and estimated degree of clonality. The analyses used microsatellites as the genetic marker. The analyses were supplemented by flow cytometry of all the material. Important Findings All the material corresponds to hexaploid cytotype, indicating that ploidy variation does not play any role in the system. The results indicate that temperature and precipitation were better predictors of genetic relatedness of the populations than geographic distance, suggesting that temperature and precipitation may be important determinants of population differentiation. In addition, precipitation, alone and in interaction with temperature, strongly affected population genotypic diversity suggesting increased clonality towards the coldest and especially the coldest wettest climates. At the same time, individuals from the coldest and wettest climates also had the highest individual genetic diversity, suggesting that only the most heterozygous individuals survive under these harsh climates. Most of the genetic variation was distributed within populations, suggesting that most populations have sufficient genetic diversity to adapt to novel climatic conditions. The alpine populations, i.e. populations which are likely the most endangered by climate change, however, lack this potential due to the high levels of clonality as detected in our study.