Geographic patterns of genomic diversity and structure in the C4 grass Panicum hallii across its natural distribution

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 infra-specific 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 United States to generate 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.

Introduction to the Special Issue: The ecology and genetics of population differentiation in plants

“…This study provided significant evidence on the important role that epigenetic diversity may have to account for adaptation, but also highlighted the complex role of epigenetic variation as a source of phenotypic diversity with evolutionary relevance ( Medrano et al 2020 ). Finally, Palacio-Mejías et al (2021) evaluated large-scale geographic patterns of within-species genomic diversity in the C 4 grass Panicum hallii (Poaceae) across its distribution in North America (Mexico and USA) also merging RAD sequencing and species distribution models. The authors identified genetic clusters that followed the main ecoregions of the species across its range, and pinpointed South Texas as a major hotspot of genetic diversity with the co-occurrence of all genetic clusters and admixture between the two Panicum varieties of study.…”

“…In their study, Solé-Medina et al (2020) quantified how important increasingly dry conditions may be to limit the regeneration capacity of the species, which has important implications for our understanding of global climate change on plants at wide geographical scales. Finally, Palacio-Mejías et al (2021) quantified phenotypic divergence between two P. hallii varieties (var. hallii and var.…”

“…filipes ) in a common garden experiment in South Texas (USA). In this case, the authors used an experimental approach as a complement to characterize the divergence between the two Panicum varieties of study, finding important differences between them in morphological features, cold stress tolerance and lifespan ( Palacio-Mejías et al 2021 ).…”

“…1 ), contributed to this special issue. Studies covered various world regions: coastal areas of Peru and Ecuador ( Lin et al 2020 ), mountains in Europe and Japan ( Honjo and Kudoh 2019 ), the Iberian Peninsula ( Matesanz et al 2020 ; Medrano et al 2020 ; Muñoz-Pajares et al 2020 ), the Amazonian savannas ( Silva et al 2020 ), North America ( Yoko et al 2020 ; Palacio-Mejía et al 2021 ) and European temperate forests ( Solé-Medina et al 2020 ). Furthermore, plant functional types were also diverse ( Fig.…”

“…Furthermore, plant functional types were also diverse ( Fig. 2 ), encompassing annual herbs ( Lin et al 2020 ; Matesanz et al 2020 ; Silva et al 2020 ), a biennial herb ( Muñoz-Pajares et al 2020 ), perennial herbs ( Honjo and Kudoh 2019 ; Medrano et al 2020 ; Yoko et al 2020 ), a C 4 grass ( Palacio-Mejías et al 2021 ) and a deciduous tree ( Solé-Medina et al 2020 ).…”