Landscape genomic insights into the historic migration of mountain hemlock in response to Holocene climate change.
OBJECTIVE
Untangling alternative historic dispersal pathways in long-lived tree species is critical to better understand how temperate tree species may respond to climatic change. However, disentangling these alternative pathways is often difficult. Emerging genomic technologies and landscape genetics techniques improve our ability to assess these pathways in natural systems. We address the question to what degree have microrefugial patches and long-distance dispersal been responsible for the colonization of mountain hemlock (Tsuga mertensiana) on the Alaskan Kenai Peninsula.


METHODS
We used double-digest restriction-associated DNA sequencing (ddRADseq) to identify genetic variants across eight mountain hemlock sample sites on the Kenai Peninsula, Alaska. We assessed genetic diversity and linkage disequilibrium using landscape and population genetics approaches. Alternative historic dispersal pathways were assessed using discriminant analysis of principle components and electrical circuit theory.


RESULTS
A combination of decreasing diversity, high gene flow, and landscape connectivity indicates that mountain hemlock colonization on the Kenai Peninsula is the result of long-distance dispersal. We found that contemporary climate best explained gene flow patterns and that isolation by resistance was a better model explaining genetic variation than isolation by distance.


CONCLUSIONS
Our findings support the conclusion that mountain hemlock colonization is the result of several long-distance dispersal events following Pleistocene glaciation. The high dispersal capability suggests that mountain hemlock may be able to respond to future climate change and expand its range as new habitat opens along its northern distribution.
Department of Geography, Texas A&M University, 810 Eller O&M Building, MS 3147 TAMU, College Station, Texas 77843-3147 USA jsjohnson@tamu.edu.
Jeremy S
JS
Johnson
Department of Geography, Texas A&M University, 810 Eller O&M Building, MS 3147 TAMU, College Station, Texas 77843-3147 USA.
Keith D
KD
Gaddis
Department of Geography, Texas A&M University, 810 Eller O&M Building, MS 3147 TAMU, College Station, Texas 77843-3147 USA.
David M
DM
Cairns
Texas A&M Institute for Genome Sciences and Society, Texas A&M University Veterinary Medical Research Building, MS 2470 TAMU, College Station, Texas 77433-2470 USA.
Kranti
K
Konganti
Department of Forest Genetics and Tree Breeding, Georg-August University of Göttingen, Büsgenweg 2, D-37077 Göttingen, Germany.|Department of Ecosystem Science & Management, Texas A&M University, 305 Horticulture and Forest Science Building, MS 2138 TAMU, College Station, Texas 77843-2138 USA.|N. I. Vavilov Institute of General Genetics, Russian Academy of Sciences, 3 Gubkina Str., Moscow 119333, Russia.|Genome Research and Education Center, Siberian Federal University, 50a/2 Akademgorodok, Krasnoyarsk 660036, Russia.
Konstantin V
KV
Krutovsky
D000413:Alaska; D002980:Climate; D057231:Climate Change; D017753:Ecosystem; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D023281:Genomics; D005838:Genotype; D018652:Hemlock / Q000235:genetics* / Q000502:physiology; D015810:Linkage Disequilibrium; D017422:Sequence Analysis, DNA; D014197:Trees
Pinaceae; Pleistocene; Tsuga mertensiana; ddRAD; genotyping-by-sequencing; isolation by resistance; landscape genetics; long distance dispersal; microrefugia