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Crossing to safety: Dispersal, colonization and mate choice in evolutionarily distinct
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populations of Steller sea lions, Eumetopias jubatus.
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Greg O’Corry-Crowe, Tom Gelatt, Lorrie Rea, Carolina Bonin, Michael Rehberg
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Supporting information
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Structure Analysis
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Model-based cluster analysis of nDNA data from Steller sea lions using STRUCTURE 2.3.4. Analysis of 399
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pups from established rookeries in the Eastern and Western DPS (with admixture model of ancestry)
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that did not use prior sample group location and found K=2 population clusters as the most consistent
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with the data. Each individual is represented by a vertical line with estimated membership, Q, in each
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cluster denoted by different colors.
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A. Established rookeries, K=2
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Akutan
Amak Clubbing Pinnacle Atkins Chowiet
Chirikov
Marmot Sugarloaf Seal
Rocks
Hazy
Forrester
Rocks
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admixture
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BayesAss Analysis of recent migration in Steller sea lions.
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We also investigated the utility of the program BayesAss (v. 1.3; Wilson & Rannala 2003) to
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accommodate source-colony dynamics when estimating the magnitude and direction of recent
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migration. We conducted extensive runs with a range of starting parameters (i.e., 3 - 30 x106
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runs, alpha = 0.15 - 0.30, different seeds) for four strata: (1) eastern population, (2) White
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Sisters rookery, (3) Graves Rocks rookery, and (4) western population. This method requires
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substantial genetic differentiation among populations/strata and ‘assumes relatively low levels
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of migration, and the proportion of migrant individuals into a population cannot exceed 1/3 of
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the population total each generation’ (BayesAss documentation; Wilson &Rannala 2003). This
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method is not really designed for the kind of contemporary source-colonist dynamics we are
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investigating as some ‘populations’ are completely comprised of immigrants or recent
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decedents of immigrants from others.
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We found that BayesAss gave consistent and biologically meaningful results when we only
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compared the established rookeries in the western and eastern populations, that is, we
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consistently recorded low rates of recent dispersal (m = 0.013-0.056) in either direction (Table
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SP1).
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Table S1. Genetic estimates of recent immigration into Steller sea lion populations. Means
(±95% confidence intervals) of the posterior distribution of the proportion of individuals that are
migrants (m) based on the analysis of multi-locus genotypic data in BayesAss. To insure
convergence, 10 separate runs, each with 3 X 106 iterations, preceded by a burn-in period of 1 X
106 iterations were conducted.
East
West
East
0.944 (0.899-0.982)
0.056 (0.018-0.101)
West
0.013 (0.001-0.035)
0.987 (0.965-0.999)
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However, when the newest rookeries were added into the analysis the results were more
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complicated and difficult to interpret. Many runs gave biologically meaningful results that were
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consistent with results from other analysis: low dispersal into the eastern and western
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population (m=0.003 – 0.014) and substantial dispersal from the established populations into
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the new rookeries (m=0.128-0.312). See Table S2 as an example.
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Table S2. Genetic estimates of recent immigration into two Steller sea lion populations and two new
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rookeries. Means (±95% confidence intervals) of the posterior distribution of the proportion of
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individuals that are migrants (m) based on the analysis of multi-locus genotypic data in BayesAss.
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Results from one of 10 runs each with 20 X 106 iterations and preceded by a burn-in period of 1 X 106
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iterations are presented.
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East
White Sisters
Graves
West
East
0.976 (0.932-0.999)
0.007 (1.97e-05-0.035)
0.003 (2.31e-05 -0.013)
0.014 (3.95e-04 -0.050)
White Sisters
0.311 (0.277-0.330)
0.670 (0.667-0.681)
0.003 (2.81e-05 -0.014)
0.015 (1.52e-04 -0.050)
Graves
0.138 (0.082-0.189)
0.005 (1.22e-04 -0.018)
0.671 (0.667-0.681)
0.188 (0.134-0.242)
West
0.009 (4.18e-05 -0.029)
0.003 (8.96e-06 -0.013)
0.005 (1.05e-05 -0.017)
0.982 (0.959-0.999)
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Other runs, however, yielded a net migration of individuals from the newest rookeries to the
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established rookeries in either population. For example, a lot of eastern population pups were
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often assigned to White sisters instead of the east (Table S3). We believe this may be because
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although White Sisters is the new rookery it has slightly higher frequencies of some common
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alleles in the east. It is not clear then how this might influence the other pairwise estimates for
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migration rate, for example, between White Sisters and the other strata including Graves Rocks.
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Table S3. Genetic estimates of recent immigration into two Steller sea lion populations and two new
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rookeries. Details of Table layout and run conditions as in Table S2.
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East
White Sisters
Graves
West
East
0.674 (0.667-0.689)
0.308 (0.275-0.330)
0.003 (2.74e-05 -0.011)
0.016 (1.8e-04-0.046)
White Sisters
0.069 (1.53e-04 -0.097)
0.801 (0.747-0.950)
0.006 (4.78e-05 -0.022)
0.124 (0.030-0.214)
Graves
0.020 (1.8e-04 -0.042)
0.109 (0.053-0.190)
0.670 (0.667-0.680)
0.200 (0.129-0.265)
West
0.003 (1.47e-05 -0.011)
0.010 (1.58e-04 -0.035)
0.005 (2.07e-05 -0.030)
0.982 (0.947-0.998)
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In conclusion, BayesAss did identify a close relationship between White Sisters and the eastern
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population and between Graves Rocks and the western population but estimates of the
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magnitude and direction of dispersal were unstable. It appears likely therefore that treating the
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new colonies as ‘populations’ in BayesAss is inappropriate.
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