Table of Contents
International Journal of Evolutionary Biology
Volume 2012 (2012), Article ID 201921, 8 pages
Research Article

Is Evolution of Mating Preferences Inevitable? Random Mating in the Multisex System of Tetrahymena thermophila

1Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA
2Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA

Received 7 May 2012; Accepted 23 August 2012

Academic Editor: Jeremy L. Marshall

Copyright © 2012 Sujal S. Phadke et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Ciliate mating systems are highly diversified, providing unique opportunities to study sexual differentiation and its implications for mating dynamics. Many species of ciliates have multiple (>2) sexes. More sexes may mean more choice and an opportunity for evolution of preferential mating. We asked if the multiple sexes of the ciliate Tetrahymena thermophila mate preferentially among each other. We quantified pairing frequencies among four sexes of T. thermophila using experiments that allowed the sexes to compete as mating partners. We found that all sexes mated equally frequently among each other, that is, we found no evidence of preferential mating with respect to sex. This suggests that the “mate choice” in this ciliate is binary, between whether to form a pair or not and, in this regard, sex facilitates only self-/non-self-distinction. Thus, presence of multiple sexes does not necessarily result in the evolution of mating bias, which could decrease the maximum amount of mating that would otherwise be possible in a population. Our result of random mating verifies a key assumption in the theoretical model of sex ratio evolution in T. thermophila. Investigation into molecular differences between the sexes will be necessary to reveal the mechanistic basis of random mating among them.