DOI: 10.5061/dryad.zpc866t8x
title: Sea ice reduction drives genetic differentiation among Barents Sea polar bears

description: Loss of Arctic sea ice due to climate change is predicted to reduce both
 genetic diversity and gene flow in ice-dependent species, with potential
 negative consequences for their long-term viability. Here, we tested for
 the population-genetic impacts of reduced sea ice cover on the polar bear
 (Ursus maritimus) sampled across two decades (1995–2016) from the Svalbard
 Archipelago, Norway, an area that is affected by rapid sea ice loss in the
 Arctic Barents Sea. We analysed genetic variation at 22 microsatellite
 loci for 626 polar bears from four sampling areas within the archipelago.
 Our results revealed a 3-10% loss of genetic diversity across the study
 period, accompanied by a near 200% in genetic differentiation across
 regions. These effects may best be explained by a decrease in gene flow
 caused by habitat fragmentation due to loss of sea ice coverage, resulting
 in increased inbreeding of local polar bears within the focal sampling
 areas in the Svalbard Archipelago. This study illustrates the importance
 of genetic monitoring for developing adaptive management strategies for
 polar bears and other ice-dependent species.
description: The Norwegian Polar Institute, Tromsø, Norway, collected the
 samples used in this study during a long-term project on the ecology of
 polar bears in the Barents Sea. To the best of our knowledge, the sampling
 protocol remained consistent across time. Polar bears were anesthetised
 from helicopters by remote injection of the drug Zoletil, and thereafter
 recovered. Tissue samples (biopsy samples and disks of skin from ear
 tagging) from these georeferenced bears (based on last sampling for bears
 captured several times) were frozen. We obtained samples from a total of
 626 live captured individuals from the Svalbard Archipelago from 1995 to
 2016. We allocated the 626 genotyped polar bears to the above mentioned
 four areas based on sampling locations: NWS (<i>n</i> = 123),
 NES (<i>n</i> = 110), SWS (<i>n</i> = 241), and
 SES (<i>n</i> = 152). We did not distinguish between coastal
 <i>vs</i> offshore bears based on movement data due to
 inevitable issues with sample sizes across spatiotemporal groups.
 Moreover, we included all available bears in our study and therefore
 (some) family groups are present in the data, including some cubs captured
 together with their mother. We divided the 22-year sampling period into
 five temporal groups (female age at primiparity typically 5 years): T1:
 1995–1999; T2: 2000–2004; T3: 2005–2009; T4: 2010–2014; T5: 2015–2016 per
 sampling location but excluded periods with fewer than 10 individuals
 (Dataset 1: 5, 5, 5, 5 and 2 year groups). Thus, our final dataset
 comprised 16 spatiotemporal groups and 622 individuals. Polar bears were
 genotyped using 27 previously-published nuclear microsatellite or short
 tandem repeat (STR) loci: G1D, G10L, G10B, G10C, G10M, G10P, G10X, MU05,
 MU10, MU15, MU23, MU50, MU51, MU59, MU61, G10H, G10J, G10O, G10U, MSUT2,
 MSUT3, MSUT6, MSUT8, CXX20, LIST11016 and LIST11020. We resolved the
 fluorescently labelled multiplex PCR products together with the GeneScan
 LIZ500 (Applied Biosystems) internal size standard on an ABI 3730 DNA
 Analyzer without diluting the amplicons and by using a four-second
 injection time. Then, we scored individual genotypes based on fragment
 size via GENEMAPPER v. 4.1 (Applied Biosystems) and then verified the
 called genotypes manually. We assessed the presence of genotyping errors
 resulting from allelic dropout, stuttering, and null alleles using
 MICRO-CHECKER 2.2.3. Please see the article and Appendix S1 for more
 detail. 
description: This repository contains the genotypic data and metadata
 file used to run the analyses for this paper and a readme file that
 contains an explanation of the columns in the dataset. Detailed
 information on how the datasets were generated can be found in the
 associated manuscript referenced above and its supplements.