Evolutionary Ecology

, Volume 25, Issue 2, pp 373–390 | Cite as

Geographical variation in sperm morphology in the red-winged blackbird (Agelaius phoeniceus)

  • Stefan LüpoldEmail author
  • David F. Westneat
  • Tim R. Birkhead
Original Paper


Many species differ genetically, physiologically, and morphologically between geographically distinct populations, typically in response to variation in ecological and climatic variables. Little is known, however, about geographical variation in sperm morphology. Sperm morphology is under strong sexual selection, has been shown to evolve rapidly, and often co-varies with other reproductive traits (e.g., testis size or mating system) that differ between populations in some species. The aim of this study was to establish whether sperm morphology varies between populations of the red-winged blackbird (Agelaius phoeniceus), a species with an enormous breeding range and marked inter-population variation in both body size and mating system. We found (1) highly significant variation in sperm morphology among study sites, (2) a gradual increase in sperm length from the southwest to the northeast of the breeding range, and (3) a strong negative association between sperm length and body size. However, the relationship with the mating system remains unclear. Several hypotheses to explain these patterns are proposed.


Inter-population variation Mating system Sperm length Body size Icteridae 



We thank J. Homan, G. Linz, L. Reinhardt, A. Trutsch, and K. Yasukawa for their help in the field, R. Byrd, J. Cummins, D. Elwonger, L. Merrill, T. Muir, J. Rivers, V. Rohwer, S. Tupper, S. Werner, and M. Whitfield for providing additional sperm samples, the SPU meeting at Syracuse University for insightful discussion, and R. Montgomerie, R. Snook and three anonymous reviewers for valuable comments on the manuscript. S.L. was supported by the Janggen-Poehn Foundation, Swiss National Science Foundation, a Sheffield University ORS Award, a Lauff Research Award, a KBS Visiting Graduate Student Fellowship, and an NSF LTER Graduate Research Award; D.F.W. by the University of Kentucky; and T.R.B. by the Leverhulme Trust.

Supplementary material

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Supplementary material 5 (DOC 34 kb)


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Stefan Lüpold
    • 1
    • 2
    Email author
  • David F. Westneat
    • 3
  • Tim R. Birkhead
    • 1
  1. 1.Department of Animal and Plant SciencesUniversity of SheffieldSheffieldUK
  2. 2.Department of BiologySyracuse UniversitySyracuseUSA
  3. 3.Department of BiologyUniversity of KentuckyLexingtonUSA

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