Conservation Genetics

, Volume 18, Issue 2, pp 453–466 | Cite as

Temporal shifts in the saltmarsh–Nelson’s sparrow hybrid zone revealed by replicated demographic and genetic surveys

  • Jennifer Walsh
  • W. Gregory Shriver
  • Maureen D. Correll
  • Brian J.  Olsen
  • Chris S. Elphick
  • Thomas P.  Hodgman
  • Rebecca J.  Rowe
  • Kathleen M. O’Brien
  • Adrienme I. Kovach
Research Article

Abstract

Conservation of threatened or endangered species in a hybrid zone requires a comprehensive understanding of interspecific dynamics over time and space. We evaluated changes in location and composition of a hybrid zone over a 15-year period (with replicated sampling in 1997–2000 and 2011–2013) for saltmarsh (Ammodramus caudacutus) and Nelson’s (A. nelsoni) sparrows, two tidal marsh specialists of high conservation priority in the northeastern United States. We combined genetic analyses using microsatellite and mitochondrial markers with species distribution patterns. In both time periods, replicate genetic sampling (n = 85; five sites) and field population surveys (93 sites) were conducted. We compared the distribution of parental species and hybrids and estimates for hybrid zone width and center between the two time periods. An increase in the relative proportion of Nelson’s sparrows in sympatric marshes and an approximate doubling of hybrid zone width provides evidence for expansion. Introgression rates increased over time for neutral loci but declined for a mitochondrial gene and two gene-associated loci under the influence of selection, as expected under a speciation model with barriers to gene flow. On average, the center of the hybrid zone shifted 60 km southward over the 15 years. We placed our findings within a policy framework to evaluate management options for hybrids. We conclude that despite increasing rates of introgression, hybridization poses a substantially lesser threat to parental populations than the imminent consequences of sea-level rise and habitat degradation. Based on our current knowledge of hybrid zone dynamics in this system, we conclude that the conservation of hybrids is warranted along with parental species at this time.

Keywords

Saltmarsh sparrow Nelson’s sparrow Hybrid zone Temporal stability Range expansion Hybrid conservation 

Notes

Acknowledgements

Funding for this project was provided by the United States Fish and Wildlife Service through its Region 5, Division of Natural Resources, National Wildlife Refuge System, State Wildlife Grant # U2-5-R-1, and the Northeast Regional Conservation Needs Grant Program, by the New Hampshire Agricultural Experiment Station, through a USDA National Institute of Food and Agriculture McIntire-Stennis Project # 225575, and by the National Science Foundation Grant # DEB-1340008. This is Scientific Contribution Number 2702 of the New Hampshire Agricultural Experiment Station. Sampling was conducted in accordance with the Institutional Animal Care and Use Committee of the University of New Hampshire (100605, 130604). The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

Supplementary material

10592_2016_920_MOESM1_ESM.pdf (464 kb)
Supplementary material 1 (PDF 464 KB)

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Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  • Jennifer Walsh
    • 1
  • W. Gregory Shriver
    • 2
  • Maureen D. Correll
    • 3
  • Brian J.  Olsen
    • 3
  • Chris S. Elphick
    • 4
  • Thomas P.  Hodgman
    • 5
  • Rebecca J.  Rowe
    • 1
  • Kathleen M. O’Brien
    • 6
  • Adrienme I. Kovach
    • 1
  1. 1.Department of Natural Resources & the EnvironmentUniversity of New HampshireDurhamUSA
  2. 2.Department of Entomology & Wildlife EcologyUniversity of DelawareNewarkUSA
  3. 3.School of Biology and EcologyUniversity of MaineOronoUSA
  4. 4.Ecology & Evolutionary Biology and Center for Conservation & BiodiversityUniversity of ConnecticutStorrsUSA
  5. 5.Maine Department of Inland Fish & WildlifeBangorUSA
  6. 6.U.S Fish and Wildlife ServiceRachel Carson National Wildlife RefugeWellsUSA

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