Abstract
Aim We examined contemporary genetic structure of brown bears ( Ursus arctos ) in a recently deglaciated landscape to identify the number and geographical range of populations, the level of admixture, landscape features that limit or promote genetic connectivity, and probable population sources of bears in Glacier Bay following the end of the Little Ice Age ( LIA ). We sought to determine whether brown bears exhibit genetic structure corresponding with landscape features and whether source populations of recent colonizers could be determined using nuclear genetic markers. Location Southeast Alaska is composed of many islands, fjords and ice‐covered lands with a complex history of changing glaciation and sea level throughout the Pleistocene and into the Holocene. Glacier Bay was again covered by ice during the LIA until c . 260 years ago when rapid retreat began exposing land for colonization. Methods We used DNA microsatellites to examine the genetic diversity of 105 brown bears. We identified the number of genetically distinct populations and the degree of admixture using Bayesian allele frequency assignment tests, determined colonizing population sources based on fixation and differentiation indices, and tested correlations between the genetic relatedness and a suite of landscape models. Results The shoreline of Glacier Bay hosts brown bears from at least two distinct genetic populations which may represent contemporary colonizing sources. There is also indication of a third group specific to Glacier Bay that may represent a historical colonizing population. The three genetic populations overlap in northern Glacier Bay, with relatively low admixture between the populations, indicating current immigration. Main conclusions Glacier Bay fjord inhibits dispersal and funnels recolonizing bears from east and west refugia in a northward direction. At the northern end of Glacier Bay these populations are currently coming into secondary contact after hundreds and possibly thousands of years of separation, creating a population‐level biological contact zone.