Ice‐age persistence and genetic isolation of the disjunct distribution of larch in Alaska

Abstract

Larix laricina (eastern larch, tamarack) is a transcontinental North American conifer with a prominent disjunction in the Yukon isolating the Alaskan distribution from the rest of its range. We investigate whether in situ persistence during the last glacial maximum (LGM) or long‐distance postglacial migration from south of the ice sheets resulted in the modern‐day Alaskan distribution. We analyzed variation in three chloroplast DNA regions of 840 trees from a total of 69 populations (24 new sampling sites situated on both sides of the Yukon range disjunction pooled with 45 populations from a published source) and conducted ensemble species distribution modeling (SDM) throughout Canada and United States to hindcast the potential range of L. laricina during the LGM. We uncovered the genetic signature of a long‐term isolation of larch populations in Alaska, identifying three endemic chlorotypes and low levels of genetic diversity. Range‐wide analysis across North America revealed the presence of a distinct Alaskan lineage. Postglacial gene flow across the Yukon divide was unidirectional, from Alaska toward previously glaciated Canadian regions, and with no evidence of immigration into Alaska. Hindcast SDM indicates one of the broadest areas of past climate suitability for L. laricina existed in central Alaska, suggesting possible in situ persistence of larch in Alaska during the LGM. Our results provide the first unambiguous evidence for the long‐term isolation of L. laricina in Alaska that extends beyond the last glacial period and into the present interglacial period. The lack of gene flow into Alaska along with the overall probability of larch occurrence in Alaska being currently lower than during the LGM suggests that modern‐day Alaskan larch populations are isolated climate relicts of broader glacial distributions, and so are particularly vulnerable to current warming trends.

Distribution Pattern of Endangered Plant Semiliquidambar cathayensis (Hamamelidaceae) in Response to Climate Change after the Last Interglacial Period

“…It is generally thought that the large-scale climate shock in the last glacial maximum had a huge impact on the distribution of species, rapidly shrinking the distribution of species [64,65]. However, we found that LGM climate had little impact on the distribution of S. cathayensis, which is similar to Larrix laricina [66,67]. The results showed that the simulation error of LGM precipitation is larger than that of temperature, and the distribution of evergreen broad-leaved trees may be more sensitive to low precipitation than to low temperature due to the limitation of precipitation [68,69].…”

Andean and California condors possess dissimilar genetic composition but exhibit similar demographic histories

“…A common strategy to restore genetic diversity is the translocation of individuals to augment small and declining populations (Moritz, 1999; Whiteley et al., 2015). However, the motivation for restoring genetic diversity is often based on genetic surveys of modern populations, which assumes that past genetic diversity was always higher (Matocq & Villablanca, 2001; Napier et al., 2020). Nevertheless, long‐term effects of translocations have been rarely assessed, and findings are inconsistent across systems: Some translocations have succeeded in increasing population fitness by incorporating new alleles (Johnson et al., 2010; Whiteley et al., 2015), while others have failed by underestimating the negative effects of genetic homogenization, outbreeding depression, disease transmissions or behavioral divergence (e.g., Deredec & Courchamp, 2007; Grauer et al., 2017; Kock et al., 2010; Manlick et al., 2017).…”

Forest‐permafrost feedbacks and glacial refugia help explain the unequal distribution of larch across continents

“…Alaska is geographically isolated from the rest of northern America by the Canadian Rocky Mountains. Genetic studies show that gene flow between the populations from Alaska and the rest occurred only unidirectionally out of Alaska, probably by long‐distance pollen transportation via the prevailing westerly winds (Napier et al, 2020). And although Alaska was connected with the Russian Far East during the Pleistocene glacial periods by the Bering Land Bridge (Elias & Crocker, 2008), Alaskan lineages apparently could not be genetically rescued by populations from the Russian Far East.…”

“…In contrast, in eastern Canada, in the region of Labrador and Quebec, larches were already established by 13 ka BP, before the arrival of the competitors Picea and Abies , resulting in a more genetically connected population (Warren et al, 2016). Napier et al (2020) focused on the history of the disjunct Alaskan population of L. laricina . Their genetic study reinforced the evidence of the glacial survival and genetic isolation of the Alaskan population (Napier et al, 2020).…”

“…Napier et al (2020) focused on the history of the disjunct Alaskan population of L. laricina . Their genetic study reinforced the evidence of the glacial survival and genetic isolation of the Alaskan population (Napier et al, 2020).…”