New Zealand Journal of Marine and Freshwater Research abstracts

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Movement of male Heterozius rotundifrons (Crustacea: Decapoda: Brachyura) depends upon local sex ratio

B. A. Hazlett

Department of Ecology and Evolutionary Biology
University of Michigan
Ann Arbor
MI 48109, United States

C. E. Bach

Department of Biology
Eastern Michigan University
Ypsilanti
MI 48197, United States

G. A. Thompson
C. L. McLay

School of Biological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
email: colin.mclay@canterbury.ac.nz

Abstract  Heterozius rotundifrons is a New Zealand endemic crab that lives in the intertidal zone and is found under rocks during low tides. We investigated the role of the local sex ratio (= under rock) in affecting movement patterns of this crab. In the laboratory, male crabs moved more when the sex ratio was male biased. Field surveys suggested that there is an upper limit to the number of males found under rocks, even as the number of females increases. Field manipulations demonstrated that when the sex ratio under a rock is female biased there is no effect on female movement but when the ratio is male biased, males move away more frequently and move further. This increased movement by males is probably related to avoidance of male-male competition for females.

Keywords  Heterozius; intertidal; male-male competition; movement patterns; sex ratio

M04094; Online publication date 18 February 2005
Received 28 April 2004; accepted 27 September 2004
New Zealand Journal of Marine and Freshwater Research, 2005, Vol. 39: 157–163
0028-8330/01/3901-0157 © The Royal Society of New Zealand 2005

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