Conservation Genetics

, Volume 6, Issue 4, pp 575–585 | Cite as

Evidence for a recent genetic bottleneck in the endangered Florida Keys silver rice rat (Oryzomys argentatus) revealed by microsatellite DNA analyses

  • Yunqiu WangEmail author
  • Dean A. Williams
  • Michael S. Gaines


Low levels of genetic variation are thought to contribute significantly to the higher extinction rates of endemic island populations compared to their mainland counterparts. We used six microsatellite loci to compare the genetic structure of the endangered silver rice rat (Oryzomys argentatus) population in Saddlebunch Key, Florida to the mainland population of the closely related marsh rice rat (Oryzomys palustris natator) in Everglades National Park. Allelic richness and gene diversity are significantly lower in Saddlebunch Key than in the larger mainland population, and the two populations are significantly differentiated as measured by both F-statistics and Bayesian clustering methods. These findings support the classification of the Keys population as a “distinct vertebrate population” by the U.S. Fish and Wildlife Service. Current gene diversity (H E) is higher than expected under mutation-drift equilibrium in Saddlebunch Key, indicating a genetic bottleneck. The Keys population also exhibits a mode shift in its allele frequency distribution which suggests a very recent bottleneck has occurred and is consistent with reports of recent population declines. Although habitat loss and exotic species pose a more immediate and serious threat to silver rice rats, the continued loss of genetic variation may contribute to their long-term extinction risk due to inbreeding or by lowering the population’s ability to adapt to future environmental changes. The protection of habitat and the removal of introduced predators and competitors may help increase the population size of silver rice rats and lower their risk of extinction, both from a demographic and a genetic perspective.


bottleneck endangered island population microsatellite rice rats 


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We thank Phil Frank of the Key West National Wildlife Refuge (U.S. Fish and Wildlife Service) for providing the silver rice rat samples. This research received significant support from the Department of Interior’s Critical Ecosystems Studies special funding initiative for Everglades restoration, administered by the National Park Service. Our work has also been supported by the U.S. Geological Service’s Florida Integrated Science Centers and the University of Miami. Rejane Lamazares provided laboratory assistance. Numi Mitchell provided helpful discussions on the manuscript and access to unpublished data on the population size of silver rice rats. Comments by Amanda Hale, Colin Hughes, John Purcell, Carles Vilà, and two anonymous reviewers improved this manuscript.


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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  • Yunqiu Wang
    • 1
    Email author
  • Dean A. Williams
    • 1
  • Michael S. Gaines
    • 1
  1. 1.Department of BiologyUniversity of MiamiCoral GablesUSA

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