Sexual reproduction and hybridization in Chlamydomonas smithii and C. reinhardtii (Chlorophyceae, Volvocales)

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Abstract
The interfertility of C. smithii Hoshaw et Ettl and C. reinhardtii Dangeard was studied by examining mating efficiencies, zygospore germination rates and burst sizes and F1 progeny survival rates from intra- and interspecific matings. Mating efficiency varied among the 4 possible crosses and was highest in the C. reinhardtii intraspecific cross and lowest with the C. smithii (-) C. reinhardtii (+) cross. Germination rates of zygospores from all crosses exceeded 58%, although some differences were noted between crosses. Most zygospores produced from matings involving C. smithii (+) gametes yielded 4 progeny, while most zygospores from matings involving C. reinhardtii (+) gametes yielded 8 progeny. Survival of F1 progeny exceeded 83% with all crosses, although some differences were present between crosses. Certain aspects of the sexual cycle were apparently influenced chiefly by the (+) mating type strain involved in the crosses. The presence of morphological differences which distinguish C. smithii and C. reinhardtii evidently does not correlate with the existence of genetic barriers to interbreeding.

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