Genomic evidence of a widespread southern distribution during the Last Glacial Maximum for two eastern North American hickory species

Abstract

Aim Phylogeographical studies of temperate forest taxa often infer complex histories involving population subdivision into distinct refugia during the Last Glacial Maximum (LGM). However, some temperate deciduous trees may have been broadly distributed in southeastern North America during the LGM. We investigate genome‐wide genetic structure in two widespread eastern North American tree species to determine if range expansion from genetically isolated refugia or from a broader, less genetically subdivided region better explains their post‐glacial history. Location Eastern North America (ENA). Taxa Bitternut hickory (Carya cordiformis [Wangenh.] K.Koch) and shagbark hickory (Carya ovata [Mill.] K.Koch). Methods Genetic diversity and differentiation indices were calculated from >1,000 nuclear SNP loci genotyped in ca. 180 individuals per species sampled across ENA. Genetic structure was investigated using principle component analysis and genetic clustering algorithms. As an additional tool for inference, areas of suitable habitat during the LGM were predicted using species distribution models (SDMs). Results Populations across all latitudes showed similar levels of genetic diversity. Most genetic variation was weakly differentiated across ENA, with the exception of an outlier population of Carya ovata in Texas. Genetic structure in each species exhibited an isolation‐by‐distance pattern. SDMs predicted high LGM habitat suitability over much of the southeastern United States. Main conclusions Both hickory species likely survived the LGM in low‐density populations that were broadly distributed across southeastern North America and not highly genetically differentiated, except that the range‐edge Texas population of Carya ovata may represent a separate glacial refugium. Over most of ENA, genetic structure in both species is best explained by simple latitudinal range shifts and high gene flow among populations, rather than expansions from multiple, genetically isolated refugia as is characteristic of taxa from other Northern Hemisphere temperate regions of the world.

Westward range expansion from middle latitudes explains the Mississippi River discontinuity in a forest herb of eastern North America

“…This issue was evident in recent phylogeographical work conducted on two species of hickory (Carya spp. ), which are common deciduous trees of eastern North America (Bemmels & Dick, 2018;Bemmels et al, 2019). These works allow a direct comparison of SDMs based on historical climate data with analyses of whole genomes to identify range expansion origins (Bemmels & Dick, 2018;Bemmels et al, 2019 (Delcourt et al, 1980;Jackson et al, 2000;Peterson & Graves, 2016).…”

“…), which are common deciduous trees of eastern North America (Bemmels & Dick, 2018;Bemmels et al, 2019). These works allow a direct comparison of SDMs based on historical climate data with analyses of whole genomes to identify range expansion origins (Bemmels & Dick, 2018;Bemmels et al, 2019 (Delcourt et al, 1980;Jackson et al, 2000;Peterson & Graves, 2016). In this case and others, SDMs may lack the resolution to identify such microrefugia as they consider climatic averages over relatively large spatial and temporal scales (Ashcroft, 2010;Dobrowski, 2011;Franklin et al, 2013).…”

Phylogeography and the Evolutionary History of Sunflower (Helianthus annuus L.): Wild Diversity and the Dynamics of Domestication

“…Indeed, many such species have been found to have undergone dramatic range contractions into southern refugia during glacial periods and rapidly expanded northward as climates warmed following the LGM [23][24][25]57]. This general pattern of northward expansion from lower latitude refugial areas has also been observed in a number of widespread species, whose contemporary distributions span both glaciated and unglaciated North America: e.g., herbs (Asclepias exaltata [58], Campanulastrum americanum [59], Trillium erectum and T. grandiflorum [60,61], and Symplocarpus foetidus [62]); shrubs (Dirca paulustris [63], Viburnum lantanoides [64], Viburnum nudum complex [65], and the Lentago clade of Viburnum [66]); and trees (e.g., Acer rubrum and sacharum [67,68], Carya cordiformis and ovata [69,70], Fagus grandifolia [67,71], and Pinus strobus [72,73]).…”

Biogeographic Patterns of Ectomycorrhizal Fungal Communities Associated With Castanopsis sieboldii Across the Japanese Archipelago

“…Distribution ranges of most tree species have expanded and moved from the refugia in the Last Glacial Maximum. Thus, genotypes of individual host tree species have their own geographic structure (e.g., genotypic composition and diversity), called phylogeography (e.g., Magri et al, 2006; Petit et al, 2012; Bemmels and Dick, 2018). Such phylogeographic patterns of host species (e.g., differences in genotypes across site) can also influence the ECM fungal communities, as some evidence show that ECM fungi co-migrate with their hosts (Kennedy et al, 2011; Séne et al, 2018) or they show preference to certain intra-specific genotypes (Gehring et al, 2017; Patterson et al, 2019).…”