MATING TYPES IN DIVERSE RACES OF PARAMECIUM CAUDATUM

¹ From the Zoöogical Laboratory, Johns Hopkins University

1. An investigation of the numbers and interrelations of the mating types in Paramecium caudatum in cultures derived from single animals isolated from wild cultures was carried out. Of 93 clones from 26 natural sources the mating types are still to be identified in 3 clones from 2 natural sources.

2. The clone cultures could be divided into mating types in several non-interbreeding groups. Animals from cultures of different groups did not conjugate when mixed with one another. Within each group two mating types were found. Animals from cultures of different mating types belonging to the same group conjugated when mixed together. Four non-interbreeding groups of mating types have been definitely established and the occurrence of five groups is highly probable.

3. In regard to the geographical distribution of the mating types, no evidence was found for the formation of local groups of mating types which would not conjugate with animals from other localities.

4. Ordinarily, conjugation occurred only when animals from two different mating types were mixed but under certain conditions some clones conjugated without mixture.

5. It was found that ordinarily such conjugation was not the result of the production of two mating types at autogamy as in P. aurelia.

6. In one case (clone M, type III) both mating types of a group were produced in a clone but it was not possible to correlate this fact with a preceding autogamy.

7. It was found that the mating reaction itself (clumping of the animals) would occur under nutritive conditions which would not permit the completion of conjugation.

8. The temperature both before and after mixing the mating types has a definite effect on the proportions of the animals conjugating. Very little or no conjugation occurred when the animals were kept at the extremes of temperature (9° and 28° and 31°) after mixture. A low temperature prior to mixture caused more conjugation in Group 2, less in Group 3.

9. None of the five groups of mating types gave any indications of a diurnal periodicity.

10. Group 3 animals are obviously smaller than Group 1 or Group 2 animals.

11. In Group 1, there is a difference in size between the mating types; type I is larger than type II.

12. Type II animals "self" (conjugate without mixture) much more frequently than type I animals.

13. In mixtures between animals of different types the largest percentage conjugate in Group 3 and the smallest in Group 1.

14. No differences were found between Group 1, 2, and 3 in their response to the toxic effects produced by races G, H, and 47 of P. aurelia. The clones which form Groups 4 and 5 are resistant to the lethal effect of H.

15. A possible explanation of the conflicting results on the effect of environmental factors on conjugation obtained by earlier workers on P. caudatum was presented.