Evidence for a recent genetic bottleneck in the endangered Florida Keys silver rice rat (Oryzomys argentatus) revealed by microsatellite DNA analyses
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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.
Keywordsbottleneck 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.
- Fairbridge RW (1974) The Holocene sea-level record in South Florida. In: Environments of South Florida: Past and Present. Miami Geol. Soc., Memoir 2 (ed. Gleason PJ), pp. 223–232Google Scholar
- Gaines MS, Diffendorfer JE, Tamarin RH, Whittam TS (1997) The effects of habitat fragmentation on the genetic structure of small mammal populations. Heredity 88:294–304Google Scholar
- Goodyear NC, Lazell., Jr. JD (1986) Relationships of the silver rice rat Oryzomys argentatus (Rodentia: Muridae). Postilla 198:1–7Google Scholar
- Goudet J (2001) FSTAT: A Program to Estimate and Test Gene Diversities and Fixation Indices (version 2.9.3). Available at http://www.unil.ch/izea/softwares/fstat.htmlGoogle Scholar
- Hanski I (1999) Metapopulation Ecology. Oxford University Press, Oxford UKGoogle Scholar
- Humphrey SR (1992) Lower Keys population of rice rat, Oryzomys palustris natator (in part). In: Humphrey SR, (ed), Rare and endangered biota of Florida, Volume I Mammals. University Press of Florida, Gainesville Florida, pp. 300–309Google Scholar
- Van Oosterhout C, Hutchinson WF, Wills DPM, Shipley P (2004) Micro-checker: Software for identifying and correcting genotyping errors in microsatellite data. Mol. Ecol. Notes, doi: 10.1111/j.1471–8286.2004.00684.x (online early)Google Scholar
- Piry S, Luikart G, Cornuet JM (1999) BOTTLENECK: A computer program for detecting recent reductions in the effective population size using allele frequency data. J. Hered., 90, 502–503. Available at: http://www.ensam.inra.fr/URLB/bottleneck/bottleneck.htmlGoogle Scholar
- Pritchard JK, Wen W (2003) Documentation for Structure Software: Version 2. Available at: http://pritch.bsd.uchicago. eduGoogle Scholar
- Soulé ME (1986) Conservation Biology: The Science of Scarcity and Diversity. Sinauer Associates, Sunderland MassachusettsGoogle Scholar
- U.S. Fish and Wildlife Service [FWS] (1999) Rice Rat Oryzomys palustris natator. In: Multi-Species Recovery Plan for South Florida. pp. 173–186Google Scholar
- Wilson AC, Cann RL, Carr SM, George M, Gyllensten UB, Helm-Bychowski KM, Higuchi RG, Palumbi SR, Prager EM, Sage RD, Stoneking M (1985) Mitochondrial DNA and two perspectives on evolutionary genetics. Biol. J. Linn. Soc. 26:375–400Google Scholar
- Wolfe JL (1982) Oryzomys palustris. Mammalian Species 176:1–5Google Scholar