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1 July 2000 Genetic and Environmental Factors Affecting Mating Type Frequency in Natural Isolates of Tetrahymena thermophila
Muhittin Arslanyolu, F. Paul Doerder
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In Tetrahymena thermophila mating type alleles specify temperature sensitive frequency distributions of multiple mating types. A-like alleles specify mating types I, II, III, V and VI, whereas B-like alleles specify mating types II through VII. We have characterized the mating type distributions specified by several A- and B-like genotypes segregated by genomic exclusion from cells isolated from a pond in northwestern Pennsylvania. The B-like genotypes are alike in specifying very low frequencies of mating type III, but differ with respect to the frequencies of other mating types, particularly II and VII. An A-like genotype specifies a high frequency of mating type III and is unstable in successive generations for the expression of mating type II, suggesting a possible modifier. Inter se crosses performed at 18 °C, 28 °C and 34 °C showed that each genotype specifies a frequency distribution that is uniquely affected by temperature. No mating type was affected the same way by temperature in all genotypes. In A/B heterozygotes, the B-like genotype exhibited partial dominance. The genotypes described here differ significantly from previously described genotypes from the same pond, indicating that there are numerous mating type alleles. For frequency-dependent selection to equalize mating type frequencies, it must act not only on complex multiple alleles but also on the response of mating type alleles to temperature.

Muhittin Arslanyolu and F. Paul Doerder "Genetic and Environmental Factors Affecting Mating Type Frequency in Natural Isolates of Tetrahymena thermophila," The Journal of Eukaryotic Microbiology 47(4), 412-418, (1 July 2000).
Received: 8 November 1999; Accepted: 3 April 2000; Published: 1 July 2000

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ecological genetics
frequency-dependent selection
mating type alleles
population genetics
temperature sensitivity
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