Influence of drift and admixture on population structure of American black bears in the Central Interior Highlands 50 years after translocation

Puckett, E. E. et al. 2014. Molecular Ecology 23: 2414-2427

Objectives
During the 19th and early 20th centuries, back bears experienced both overall range contraction and local extirpation (Smith and Clark 1994?).  In the 60s and 70s, black bears were translocated from Minnesota and Manitoba to  Arkansas, and since then the population size has increased. It has since 8 been  generations since translocation, given a generation time of 6.3 years  (Onorato et al 2004).  There are some physical barriers, including rivers, highways, and discontinuous forest habitat.

"Bottlenecks, founder events (Nei et al 1975), and genetic drift (Nei and Tajima 1981) often result in decreased genetic diversity and increased population differentiation". On the other hand, migration can decrease the effects of drift due to gene flow.

The objective of the study was to identify population structure of bears in the 50 years following translocation and test for signatures of remnant genetic lineages.

Methods:
15 microsatellites for 7 studies, totally n=643 bears

• identified parent offspring pairs with ml-relate and removed on individual from meac
• deviations from HWE with ARLEQUIN
• null alleles with Micro-checker.
• differences in allelic richness with Kruskal-Wallis test
• population structure with STRUCTURE, and analysed hierarchical substructure we separate analyses for each of K=4 under admixture
• migration using BAYESASS.
• demographic history with DIYABC, and tested different hypotheses: admixture, founder, split

mtdna with cytochrome b.

• aligned data wtih GENEIOUS
• assigned new haplotypes to Wooding and Ward's clades with MRBAYES.
• identified substitution rate with FINDMODEL
• haplotype and nucleotide frequencies in ARLEQUIN.

Results

STRUCTURE results at successive numbers of K reflect the varying processes effecting differentiation between population.

Haplotypic diversity mirrored nuclear genetic diversity. Admixture was the best supported model. Lower frequency hapolotypes at the tips of the network suggest new mutations derived from haplotypes occupying internal nodes, but distinct haplotypes could be remnant original ones, recent mutations, or the result of introduction from translocation.

Drift supported by decreased Fst values from the sources in MN and Manitoba to the study area

Mamagement implications: conserve gene flow, afford protection to subpopulations