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May 2005

Volume 165, Number 5
Am Nat 2005. Vol. 165, pp. 551–566
0003-0147/2005/16505-40602$15.00
DOI: 10.1086/429526

A Dimensionless Invariant for Relative Size at Sex Change in Animals: Explanation and Implications

Andy Gardner,1,2,*

David J. Allsop,1,3,

Eric L. Charnov,4, and

Stuart A. West1,§

1. Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, United Kingdom;

2. Department of Mathematics and Statistics and Department of Biology, Queen’s University, Kingston, Ontario, K7L 3N6, Canada;

3. School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia;

4. Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131; and Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331

Abstract:

Recent comparative studies across sex‐changing animals have found that the relative size and age at sex change are strikingly invariant. In particular, 91%–97% of the variation in size at sex change across species can be explained by the simple rule that individuals change sex when they reach 72% of their maximum body size. However, this degree of invariance is surprising and has proved controversial. In particular, it is not clear why this result should hold, given that there is considerable biological variation across species in factors that can influence the evolutionarily stable timing of sex change. Our overall aim here is to explain this result and determine the implications for other life‐history variables. Specifically, we use a combination of approaches to formalize and make explicit previous analytical theory in this area, examine the robustness of the empirical invariance result, and carry out sensitivity analyses to determine what the empirical data imply about the mean value and variation in several key life‐history variables.

Submitted September 1, 2004; Accepted December 16, 2004; Electronically published March 14, 2005

Keywords:

life history, sex allocation, protandry, protogyny, sequential hermaphroditism, Buckingham’s π theorem.

Editor: Jonathan B. Losos

Associate Editor: Peter D. Taylor

Cited by

Àngel Calsina, Jordi Ripoll. (2009) Evolution of age-dependent sex-reversal under adaptive dynamics. Journal of Mathematical Biology
Online publication date: 15-Apr-2009.
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M. LINDE, M. PALMER. (2008) Testing Allsop and West’s size at sex change invariant within a fish species: a spurious ratio or a useful group descriptor?. Journal of Evolutionary Biology 21:3, 914-917
Online publication date: 1-Jun-2008.
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Philip P. Molloy, Nicholas B. Goodwin, Isabelle M. Côté, John D. Reynolds, Matthew J. G. Gage. (2007) SPERM COMPETITION AND SEX CHANGE: A COMPARATIVE ANALYSIS ACROSS FISHES. Evolution 61:3, 640-652
Online publication date: 1-Apr-2007.
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Rachel Collin. (2006) SEX RATIO, LIFE-HISTORY INVARIANTS, AND PATTERNS OF SEX CHANGE IN A FAMILY OF PROTANDROUS GASTROPODS. Evolution 60:4, 735
Online publication date: 1-Feb-2006.
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