Evol Ecol Res 2: 1067-1071 (2000)     Full PDF if your library subscribes.

Dimensionless invariants for the optimal size (age) of sex change

Eric L. Charnov1 and Unnur Skúladóttir2

1Department of Biology, The University of New Mexico, Albuquerque, NM 87131-1091, USA and 2Marine Research Institute, Skúlagata 4, PO Box 1390, IS-121 Reykjavík, Iceland

Author to whom all correspondence should be addressed.


Optimization models have been widely and successfully used in evolutionary ecology to predict the attributes of organisms; perhaps the greatest quantitative success is in the area of sex allocation (sex ratio, sperm versus eggs for hermaphrodites, time as a male [female] for a sex changer), where the fact of having only one mother and one father makes Darwinian fitness a simple product of gain-via-male times gain-via-female. Previous work on sex change used the maximization of this male–female product to successfully predict the direction and age (size) for sex change, and that age has been shown to imply a breeding sex ratio biased towards the first sex. This paper unites recent advances in the comparative demography of organisms with indeterminant growth with the theory of optimal sex change to predict some new invariance rules for the relative age (size) of sex change. One of these rules is strikingly confirmed in a long-term study of the size-at-sex-change in the northern shrimp, Pandalus borealis, off Iceland.

Keywords: dimensionless analysis, evolutionarily stable strategy, life history, sex allocation.

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