A Dimensionless Invariant for Relative Size at Sex Change in Animals: Explanation and Implications
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.
Cited by
Online publication date: 15-Apr-2009.
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*Corresponding author; e‐mail: andy.gardner@ed.ac.uk.
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†E‐mail: david.allsop@bio.usyd.edu.au.
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‡E‐mail: rlc@unm.edu.
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§E‐mail: stu.west@ed.ac.uk.



