Genetic differentiation of caribou herds and reindeer in Northern Alaska Karen H. Mager, Kevin E. Colson, and Kris J. Hundertmark Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA Figure 2. STRUCTURE analysis of Alaskan caribou and reindeer under a two-population scenario. Each vertical line represents an individual whose genotype is partitioned into one or two colors indicating the individual’s assigned membership in the reindeer (gray) or caribou (red) genetic population. Herds of sampling origin are separated by vertical black lines. Figure 1. Number of samples per herd (n) from herds sampled (Map from: Alaska Department of Fish and Game Caribou management report of survey- inventory activities 1 July June C. Healy, editor. Project 3.0. Juneau, Alaska.) Porcupine (PCH) n = 53 Central Arctic (CAH) n = 19 Teshekpuk (TCH) n = 52 Western Arctic (WAH) n = 48 Wales Reindeer (RD) n = 34 Introduction Four herds of caribou on Alaska’s North Slope constitute management units, yet the extent to which the herd concept approximates the genetic population structure is unknown. Caribou need to be managed at the population level and an understanding of herd connectivity is important given the changing North Slope landscape. Historical interactions between caribou and domestic reindeer have led many to question the potential for introgression of reindeer genes into the North Slope herds. In particular, some have speculated that Teshekpuk herd animals descended from escaped domestic reindeer in the 1940s, and that the herd may be unique. Research Questions 1.Can the North Slope herds be genetically delineated? 2.What is the population structure of North Slope caribou and to what extent does it resemble the four-herd concept? 3.Is there evidence for introgression of reindeer genes into caribou herds or vice versa? Methods Blood samples were collected from caribou of the four North Slope Alaskan herds and from reindeer in Wales, Alaska (Figure 1). DNA was amplified at 18 microsatellite loci. Allelic diversity, allelic richness and Fst were calculated for each population and overall. North Slope population structure—determining the most likely number of population clusters and assignment of individuals to clusters—was inferred using program STRUCTURE. Results Microsatellite variability All 18 loci were polymorphic (5–25 alleles/locus; mean 16.2). Allelic richness adjusted for sample size was similar across all caribou herds (10.11–10.48) but lower in reindeer (7.78). Conclusions Caribou and reindeer could be clearly differentiated using traditional and individual-based statistics. If reindeer and caribou did interbreed in the recent past, those reindeer genes have largely disappeared from herds. Gene flow among herds is sufficiently high enough to homogenize them, though weak differentiation of WAH and PCH suggest that distance may reduce gene flow. ACKNOWLEDGEMENTS This research was funded by National Fish and Wildlife Foundation grant #1499, and benefited from pilot research supported by an early-career award to Dr. Hundertmark from Alaska EPSCoR (NSF award #EPS ). K. Mager was supported by fellowships from the UAF Resilience and Adaptation IGERT (NSF award ) and Alaska EPSCoR. Biologists from Alaska Dept. of Fish and Game, U.S. Fish and Wildlife Service, and the Yukon government provided samples—many are members of the CARMA network. The Ongtowasruk reindeer herd owners allowed me to collect samples from their animals, with help from the UAF reindeer research program. Thanks to CARMA for funding my travel to this year’s meeting. Genetic structure The most likely number of population clusters inferred from STRUCTURE was two. These clusters appear to correspond closely to subspecies (Alaskan caribou and domestic reindeer) based on the proportion of each herd’s membership in the two clusters (Table 2). Each individual was assigned primarily to its own subspecies with three exceptions—one RD individual’s genotype was assigned almost entirely to the caribou cluster, and two individuals (1 RD and 1 CAH) appeared to have 30% and 40%, respectively, of their genotype assigned to the opposite cluster (Figure 2). Herd differentiation Fst estimates between caribou herds were not significant except for PCH-WAH. Fst estimates between reindeer and each caribou herd were highly significant (Table 1).