title: Crossing to safety: dispersal, colonization and mate choice in evolutionarily distinct populations of Steller sea lions, Eumetopias jubatus.
abstract: Population growth typically involves range expansion and establishment of new breeding sites, while the opposite occurs during declines. Although density dependence is widely invoked in theoretical studies of emigration and colonization in expanding populations, few empirical studies have documented the mechanisms. Still fewer have documented the direction and mechanisms of individual transfer in declining populations. Here, we screen large numbers of pups sampled on their natal rookeries for variation in mtDNA (n = 1106) and 16 microsatellite loci (n = 588) and show that new Steller sea lion breeding sites did not follow the typical paradigm and were instead colonized by sea lions from both a declining (Endangered) population and an increasing population. Dispersing individuals colonized rookeries in the distributional hiatus between two evolutionarily distinct (Φ¯(st) = 0.222, R¯(st) = 0.053, K = 2) metapopulations recently described as separate subspecies. Hardy-Weinberg, mixed-stock and relatedness analysis revealed levels of interbreeding on the new rookeries that exclude (i) assortative mating among eastern and western forms, and (ii) inbreeding avoidance as primary motivations for dispersal. Positive and negative density dependence is implicated in both cases of individual transfer. Migration distance limits, and conspecific attraction and performance likely influenced the sequence of rookery colonizations. This study demonstrates that resource limitation may trigger an exodus of breeding animals from declining populations, with substantial impacts on distribution and patterns of genetic variation. It also revealed that this event is rare because colonists dispersed across an evolutionary boundary, suggesting that the causative factors behind recent declines are unusual or of larger magnitude than normally occur.
authors.affiliation: Harbor Branch Oceanographic Institute, Florida Atlantic University, 5600 U.S. 1 north, Fort Pierce, FL, 34946, USA; Southwest Fisheries Science Center, 8901 La Jolla Shores Drive, La Jolla, CA, 92037, USA.
authors.forename: Greg
authors.initials: G
authors.lastname: O'Corry-Crowe
authors.forename: Tom
authors.initials: T
authors.lastname: Gelatt
authors.forename: Lorrie
authors.initials: L
authors.lastname: Rea
authors.forename: Carolina
authors.initials: C
authors.lastname: Bonin
authors.forename: Michael
authors.initials: M
authors.lastname: Rehberg
mesh_terms: D000413:Alaska; D063147:Animal Distribution; D000818:Animals; D005075:Biological Evolution; D004272:DNA, Mitochondrial / Q000235:genetics; D005828:Genetics, Population; D052586:Mating Preference, Animal; D018895:Microsatellite Repeats; D008957:Models, Genetic; D008969:Molecular Sequence Data; D058974:Phylogeography; D011157:Population Dynamics; D046070:Sea Lions / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D004272:DNA, Mitochondrial
keywords: Steller sea lion; colonization; density dependence; microsatellite; mixed-stock