Sexual and asexual reproduction in a natural population of Hydra pseudoligactis

BELL, G., and L. M. WOLFE. 1985. Sexual and asexual reproduction in a natural population of Hydra pseudoligactis. Can. J. Zool. 63: 851 -856. Populations of Hydra pseudoligactis were censussed during 1980198 1 in a lake and a small pond in southern Quebec. Both natural and artificial substrates (glass slides) were used. Population density rose during the early part of the sedson to a maximum in June-July, after which a decline in the rate of asexual budding drove density down. The decline in budding rate lagged about 2 weeks behind the increase in density. High local population density on the glass slides reduced rates of budding and caused dispersal from crowded slides. Sexual individuals appeared in the middle of the growing season, near the time of maximal density, when rates of asexual budding had begun to fall. Moreover, sexual individuals were more frequent in the site where and in the year when budding rates were lower; 66% of the variance in the frequency of sexual individuals between dates in the pond was explained by variance in the number of buds borne by asexual individuals. These results are held to be consistent with the interpretation of sexuality as a device to reduce competition between offspring in a spatially heterogeneous environment.