Behavioral Ecology and Sociobiology

, Volume 13, Issue 4, pp 239–241 | Cite as

Why are males bigger than females in pre-copula pairs of Gammarus pulex?

  • Jonathan Adams
  • Paul J. Greenwood


In natural streams, males are bigger than females in precopula pairs of the freshwater amphipod Gammarus pulex. A set of experiments is described, the results of which are consistent with the hypothesis that males are larger as a result of a mechanical constraint and not intrasexual competition for mates. Where the male in a pair is relatively larger than the female the swimming performance is superior to those pairs in which the male and female are of similar sizes. This minimises the risk of being washed downstream by the current.


Swimming Performance Natural Stream Mechanical Constraint Intrasexual Competition Freshwater Amphipod 
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  2. Darwin C (1874) The descent of man and selection relation to sex, 2nd edn. Murray, LondonGoogle Scholar
  3. Wheeler P, Greenwood PJ (1983) The evolution of reversed sexual dimorphism in birds of prey. Oikos 40:145–149Google Scholar

Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • Jonathan Adams
    • 1
  • Paul J. Greenwood
    • 2
    • 3
  1. 1.Department of ZoologyUniversity of Newcastle upon TyneNewcastleEngland
  2. 2.Department of Adult and Continuing EducationUniversity of DurhamDurhamEngland
  3. 3.Department of ZoologyUniversity of DurhamDurhamEngland

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