CARBON DIOXIDE TENSION AND SEXUAL DIFFERENTIATION IN HYDRA

¹ Laboratory of Physical Biology, National Institute of Arthritis and Metabolic Diseases National Institutes of Health, Public Health Service, Department of Health, Education, and Welfare, Bethesda, Maryland

1. One hundred-and 10-hydra cultures of Hydra littoralis and 10-hydra cultures of H. pseudoligactis and H. (sp.) were maintained 14-50 days in culture solutions equilibrated with gas mixtures varying in CO₂ content from 0.0% to 5.6%.

2. Two culture solutions and three methods of gassing cultures were used.

3. The results were:

a. Asexual H. littoralis began to differentiate sexually within 1-4days under all experimental conditions; initial sexual differentiation was temporary and was often followed by a second period of gonad development. In several experiments, percentages of sexual hydras tended to rise and fall together, regardless of treatment.

b. H. littoralis cultures containing 46-72% sexual animals bubbled 22 hours daily with room air or 5% CO₂ in air were 95-100% asexual by day 12. Continued bubbling for the next 4 weeks with 5% CO₂ in air was as effective as bubbling with room air in maintaining asexuality.

c. No sexual differentiation occurred in H. pseudoligactis or H. (sp.) cultures exposed 18 days to elevated pCO_2. There was no sexual differentiation in H. pseudoligactis cultures exposed 18 days to room air. However 5% of H. (sp.) in room air were sexual from day 9 to day 13.