Philopatry drives genetic differentiation in an island archipelago: comparative population genetics of Galapagos Nazca boobies (Sula granti) and great frigatebirds (Fregata minor)

Authors

  • Iris I. Levin,

    Corresponding author
    1. Whitney R. Harris World Ecology Center, University of Missouri – St. Louis, St. Louis, Missouri
    • Department of Biology, University of Missouri – St. Louis, St. Louis, Missouri
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  • Patricia G. Parker

    1. Department of Biology, University of Missouri – St. Louis, St. Louis, Missouri
    2. Whitney R. Harris World Ecology Center, University of Missouri – St. Louis, St. Louis, Missouri
    3. WildCare Center, Saint Louis Zoo, St. Louis, Missouri
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  • The work was supported by the Des Lee Collaborative Vision and by two grants from the Field Research for Conservation program of the Saint Louis Zoo, as well as grants to I. Levin and P. Parker from the Whitney R. Harris World Ecology Center and the Frank M. Chapman Memorial Fund of the American Museum of Natural History. I. Levin completed this work while supported by a Dissertation Fellowship from the University of Missouri – St. Louis.

Correspondence

Iris Levin, Department of Biology, University of Missouri – St. Louis, R223 Research Building, One University Blvd., St. Louis, Missouri 63121. Tel:+314 516 6165; Fax: +314 516 6233; E-mail: Iris.Levin@umsl.edu

Abstract

Seabirds are considered highly mobile, able to fly great distances with few apparent barriers to dispersal. However, it is often the case that seabird populations exhibit strong population genetic structure despite their potential vagility. Here we show that Galapagos Nazca booby (Sula granti) populations are substantially differentiated, even within the small geographic scale of this archipelago. On the other hand, Galapagos great frigatebird (Fregata minor) populations do not show any genetic structure. We characterized the genetic differentiation by sampling five colonies of both species in the Galapagos archipelago and analyzing eight microsatellite loci and three mitochondrial genes. Using an F-statistic approach on the multilocus data, we found significant differentiation between nearly all island pairs of Nazca booby populations and a Bayesian clustering analysis provided support for three distinct genetic clusters. Mitochondrial DNA showed less differentiation of Nazca booby colonies; only Nazca boobies from the island of Darwin were significantly differentiated from individuals throughout the rest of the archipelago. Great frigatebird populations showed little to no evidence for genetic differentiation at the same scale. Only two island pairs (Darwin – Wolf, N. Seymour – Wolf) were significantly differentiated using the multilocus data, and only two island pairs had statistically significant φST values (N. Seymour – Darwin, N. Seymour – Wolf) according to the mitochondrial data. There was no significant pattern of isolation by distance for either species calculated using both markers. Seven of the ten Nazca booby migration rates calculated between island pairs were in the south or southeast to north or northwest direction. The population differentiation found among Galapagos Nazca booby colonies, but not great frigatebird colonies, is most likely due to differences in natal and breeding philopatry.

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