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Journal of Ornithology

, Volume 157, Issue 4, pp 1017–1027 | Cite as

Stable isotopes and mtDNA reveal niche segregation but no evidence of intergradation along a habitat gradient in the Lesser Whitethroat complex (Sylvia curruca; Passeriformes; Aves)

  • Stephen C. Votier
  • Simon Aspinall
  • Stuart Bearhop
  • David Bilton
  • Jason Newton
  • Per Alström
  • Paul Leader
  • Geoff Carey
  • Robert W. Furnes
  • Urban Olsson
Original Article

Abstract

Niche segregation plays a critical role in the speciation process, but determining the extent to which taxa are geographically or ecologically isolated is challenging. In this study, we use stable isotopes of carbon (δ13C), nitrogen (δ15N), hydrogen (δ2H) and oxygen (δ18O) to test for ecological differences among taxa in the Lesser Whitethroat Sylvia curruca complex. Analysis of mitochondrial DNA (mtDNA) revealed 6 distinct haplotype groups, which conform to at least 5 distinct taxa. Stable isotopes provided insight into geographical and broad-scale ecological differences among haplotypes. The most striking isotope differences were between the populations inhabiting Siberian boreal forest (S. c. blythi) from the one inhabiting semi-desert in Kazakhstan (S. c. halimodendri). It is generally assumed that these two populations form a morphological cline along a gradient from mesic to xeric habitat. Our sample includes a large proportion of morphologically intermediate individuals that appear to represent a hybrid population. However, in all of these, there is strict correspondence between haplotype and isotope signature, suggesting an ecological division on the breeding grounds between all our samples of these two taxa. The lack of ecologically intermediate individuals among our sample of morphologically intermediate ones thus speaks against the existence of a cline. The two taxa blythi and halimodendri emerge as potential models for the study of the early stages of the speciation process. While differences in stable isotopes may be largely influenced by geography, we also demonstrate how, in specific instances (such as the alleged cline reported here), they may be used to evaluate niche segregation between taxa, providing information of importance for determination of species limits.

Keywords

δ13δ15δ18δ2Phylogeography Speciation Warbler Sylvia curruca Cline Stable isotopes 

Zusammenfassung

Stabile Isotope und mtDNA machen Aussagen über Nischenbildung bei Klappergrasmücken ( Sylvia curruca ; Passeriformes; Aves), bieten aber keine Beweise für stufenlose Übergänge entlang eines Habitatgradienten innerhalb dieses Artkomplexes

Die Abtrennung und Bildung von Nischen spielen bei der Artbildung eine wesentliche Rolle. Es ist aber schwierig zu bestimmen, in welchem Ausmaß einzelne Taxons geographisch oder ökologisch voneinander isoliert sind. In unserer Untersuchung analysierten wir stabile Isotope von Kohlenstoff (δ13C), Stickstoff (δ15N) und Sauerstoff (δ18O), um die Taxons innerhalb des Artkomplexes Klappergrasmücken auf ökologische Unterschiede hin zu testen. Die Analyse der mitochondrialen DNA (mtDNA) ergab 6 eindeutige Haplotypen, die wenigstens 5 eindeutigen Taxons zuzuordnen sind. Die stabilen Isotope ermöglichten auf breiter Ebene einen Einblick in die geographischen und ökologischen Unterschiede zwischen den Haplotypen. Die herausragendsten Unterschiede bei den stabilen Isotopen gab es zwischen den Populationen der nordsibirischen borealen Wälder (S. c. blythi) und denen der Halbwüsten Kasachstans (S. c. halimodendri). Bislang wurde angenommen, dass diese beiden Populationen aus morphologischer Sicht eine Ökokline von halbfeuchten zu trockenen Habitaten darstellen. Unsere Stichprobe enthielt jedoch einen großen Anteil Individuen eines morphologischen “Zwischen-Typs”, der eine Hybrid-Population darzustellen schien. Aber für all diese Individuen gab es einen klaren Zusammenhang zwischen den Haplotyp- und den Isotopen-Signaturen, was für eine ökologische Trennung der jeweiligen Brutgebiete unserer Stichproben der beiden Taxons spricht. Dass es unter den morphologischen Zwischenformen unserer Stichprobe nicht auch ökologische Zwischenformen gab, spricht deshalb gegen die Existenz einer Ökokline. Die beiden Taxons blythi und halimodendri bieten sich als mögliche Modelle für die Untersuchung der frühen Stadien des Artbildungs-Prozesses an. Während die Unterschiede bei den stabilen Isotopen vermutlich in erster Linie von geographische Gegebenheiten beeinflusst werden, können wir auch zeigen, wie sie in bestimmten Fällen (z.B. für die angebliche Ökokline) benutzt werden können, um die Nischen-Abtrennung zwischen Taxons zu bewerten und damit wichtige Informationen für die Bestimmung von Spezies-Grenzen zu geben.

Notes

Acknowledgments

We would like to thank Andrew Grieve, Andrew Lassey, Peter Kennerley, Annika Forsten, Lars Svensson, Brydon Thomason and Tony and Helen Mainwood for help in the field and for helpful discussions. We are very grateful to Edward Gavrilov and Martin Stervander for providing samples. This work was funded by Jornvall Foundation (to P.A.), the Sound Approach (to P.A. and U.O.), the Chinese Academy of Sciences Visiting Professorship for Senior International Scientists (No. 2011T2S04, to P.A.) and a grant from the Natural Environment Research Council (for stable isotope analysis) and the Eric Hosking Charitable Trust (to SCV).

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Copyright information

© Dt. Ornithologen-Gesellschaft e.V. 2016

Authors and Affiliations

  • Stephen C. Votier
    • 1
  • Simon Aspinall
  • Stuart Bearhop
    • 2
  • David Bilton
    • 3
  • Jason Newton
    • 4
  • Per Alström
    • 5
  • Paul Leader
    • 6
  • Geoff Carey
    • 6
  • Robert W. Furnes
    • 7
  • Urban Olsson
    • 8
  1. 1.Environment and Sustainability InstituteUniversity of ExeterCornwallUK
  2. 2.Centre for Ecology and ConservationUniversity of ExeterCornwallUK
  3. 3.Marine Biology and Ecology Research CentreUniversity of PlymouthPlymouthUK
  4. 4.NERC Life Sciences Mass Spec. Facility, SUERCGlasgowUK
  5. 5.Department of Animal Ecology, Evolutionary Biology CentreUppsala UniversityUppsalaSweden
  6. 6.Asia Ecological Consultants LtdHong KongChina
  7. 7.College of Medical, Veterinary and Life Sciences, Graham Kerr BuildingUniversity of GlasgowGlasgowUK
  8. 8.Department of Biology and Environmental ScienceUniversity of GothenburgGothenburgSweden

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