AUTHOR=Shao Yi-Zhen , Yuan Zhi-Liang , Liu Yan-Yan , Liu Feng-Qin , Xiang Rui-Chen , Zhang Yuan-Yuan , Ye Yong-Zhong , Chen Yun , Wen Qian 

TITLE=Glacial Expansion or Interglacial Expansion? Contrasting Demographic Models of Four Cold-Adapted Fir Species in North America and East Asia

JOURNAL=Frontiers in Ecology and Evolution

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2022.844354

DOI=10.3389/fevo.2022.844354

ISSN=2296-701X

ABSTRACT=<p>Understanding and forecasting species’ response to climate change is a critical need for future conservation and management. Two expansion hypotheses, the glacial expansion versus the interglacial expansion, have been proposed to interpret how cold-adapted organisms in the northern hemisphere respond to Quaternary climatic fluctuations. To test these two hypotheses, we originally used two pairs of high-low elevation firs from North America (<italic>Abies lasiocarpa</italic> and <italic>Abies balsamea</italic>) and East Asia (<italic>Abies chensiensis</italic> and <italic>Abies nephrolepis</italic>). <italic>Abies lasiocarpa</italic> and <italic>Abies chensiensis</italic> are widely distributed in high-elevation regions of western North America and central China. <italic>Abies balsamea</italic> and <italic>Abies nephrolepis</italic> occur in central North America and northeast China, with much lower elevations. These fir species are typical cold-adapted species and sensitive to climate fluctuations. Here, we integrated the mtDNA and cpDNA polymorphisms involving 44 populations and 585 individuals. Based on phylogeographic analyses, recent historical range expansions were indicated in two high-elevation firs (<italic>Abies lasiocarpa</italic> and <italic>Abies chensiensis</italic>) during the last glaciation (43.8–28.4 or 21.9–14.2 kya, 53.1–34.5 or 26.6–17.2 kya). Such glacial expansions in high-elevation firs were further confirmed by the evidence of species distribution modelling, geographic-driven genetic patterns, palynological records, and current distribution patterns. Unlike the north American firs, the SDM models indicated unremarkable expansion or contraction in East Asia firs for its much more stable conditions during different historical periods. Taken together, our findings highly supported that high-elevation firs experienced glacial expansion during the Quaternary climate change in East Asia and North America, as interglacial expansion within low-elevation firs. Under this situation, the critically endangered fir species distributed in high elevation would have no enough higher elevational space to migrate. Facing the increasing global warming, thus we proposed <italic>ex-situ</italic> conservation of defining conservation units as the most meaningful strategy.</p>