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

Stefan Lüpold, David F. Westneat, Tim R. Birkhead

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


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.

Original languageEnglish
Pages (from-to)373-390
Number of pages18
JournalEvolutionary Ecology
Issue number2
StatePublished - Mar 2011

Bibliographical note

Funding Information:
Acknowledgments 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.


  • Body size
  • Icteridae
  • Inter-population variation
  • Mating system
  • Sperm length

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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