Genetic and morphological evolution following a founder event in the dark-eyed junco, Junco hyemalis thurberi

Authors

  • C. A. Rasner,

    1. Section of Ecology, Behaviour and Evolution 0116, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA,
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  • P. Yeh,

    1. Section of Ecology, Behaviour and Evolution 0116, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA,
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  • L. S. Eggert,

    1. Section of Ecology, Behaviour and Evolution 0116, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA,
    2. Smithsonian Institution, Molecular Genetics Laboratory, 3001 Connecticut Avenue NW, Washington, DC 20008, USA,
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  • K. E. Hunt,

    1. Section of Ecology, Behaviour and Evolution 0116, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA,
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  • D. S. Woodruff,

    1. Section of Ecology, Behaviour and Evolution 0116, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA,
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  • T. D. Price

    Corresponding author
    1. Section of Ecology, Behaviour and Evolution 0116, Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA,
    2. Department of Ecology and Evolution, University of Chicago, 1101 E. 57th Street, Chicago, IL 60637, USA
      Trevor Price, Department of Ecology and Evolution. E-mail: pricet@uchicago.edu
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Trevor Price, Department of Ecology and Evolution. E-mail: pricet@uchicago.edu

Abstract

An isolated population of dark-eyed juncos, Junco hyemalis, became established on the campus of the University of California at San Diego (UCSD), probably in the early 1980s. It now numbers about 70 breeding pairs. Populations across the entire natural range of the subspecies J. h. thurberi are weakly differentiated from each other at five microsatellite loci (FST = 0.01). The UCSD population is significantly different from these populations, the closest of which is 70 km away. It has 88% of the genetic heterozygosity and 63% of the allelic richness of populations in the montane range of the subspecies, consistent with a harmonic mean effective population size of 32 (but with 95% confidence limits from four to > 70) over the eight generations since founding. Results suggest a moderate bottleneck in the early establishment phase but with more than seven effective founders. Individuals in the UCSD population have shorter wings and tails than those in the nearby mountains and a common garden experiment indicates that the morphological differences are genetically based. The moderate effective population size is not sufficient for the observed morphological differences to have evolved as a consequence of genetic drift, indicating a major role for selection subsequent to the founding of the UCSD population.

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