Abstract

Geographic patterns of within-species genomic diversity are shaped by evolutionary processes, life history and historical and contemporary factors. New genomic approaches can be used to infer the influence of such factors on the current distribution of infraspecific lineages. In this study, we evaluated the genomic and morphological diversity as well as the genetic structure of the C4 grass Panicum hallii across its complex natural distribution in North America. We sampled extensively across the natural range of P. hallii in Mexico and the USA to generate double-digestion restriction-associated DNA (ddRAD) sequence data for 423 individuals from 118 localities. We used these individuals to study the divergence between the two varieties of P. hallii, P. hallii var. filipes and P. hallii var. hallii as well as the genetic diversity and structure within these groups. We also examined the possibility of admixture in the geographically sympatric zone shared by both varieties, and assessed distribution shifts related with past climatic fluctuations. There is strong genetic and morphological divergence between the varieties and consistent genetic structure defining seven genetic clusters that follow major ecoregions across the range. South Texas constitutes a hotspot of genetic diversity with the co-occurrence of all genetic clusters and admixture between the two varieties. It is likely a recolonization and convergence point of populations that previously diverged in isolation during fragmentation events following glaciation periods.

Highlights

  • Genetic variation is the raw material necessary to understand evolution and adaptation to diverse environmental conditions (Conner and Hartl 2004; Randall et al 2008; Jump et al 2009)

  • 28 localities were represented by a single individual, but most localities were represented by 2–22 individuals (4.5 individuals in average)

  • All samples collected in the central part of Mexico in the states of Mexico and Michoacan formed a clade with the P. lepidulum control sample, which had been collected in the same area

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Summary

Introduction

Genetic variation is the raw material necessary to understand evolution and adaptation to diverse environmental conditions (Conner and Hartl 2004; Randall et al 2008; Jump et al 2009). A plant species’ life history, including breeding system and dispersal mechanisms, has an influence on the genetic diversity and distribution of species (Hamrick and Godt 1996; Ellegren and Galtier 2016). Current plant species distributions are the result of geological events that have had influence on soil patterns and changes in climate. Climatic fluctuations during the Quaternary have caused the contraction and expansion of species distribution, with remarkable genetic consequences (Hewitt 2000). The current ecological conditions covering a species’ distribution can affect genetic structure as a result of local adaptation to these environments. Linking these processes across spatial and temporal scales can help identify the drivers of the current genetic structure of plant populations

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