Environmental factors and metagenesis in the hydroid Eleutheria dichotoma

The effects of five environmental factors, (i) photoperiod, (ii) temperatur e, (iii) feeding rate, (iv) population density, and (v) cadmium pollution, on the metagenic life cycle of the hydromedusa Eleutheria dichotoma were re searched by observing changes in life history. Water temperature, feeding r ates and cadmium pollution had significant effects on the medusa generation and changed the relative frequencies of sexually versus vegetatively repro ducing medusae. Furthermore, the number of brooded planula larvae was affec ted by cadmium and medusa body size by temperature. Suspected mutational ef fects of cadmium were not detected. The findings suggest that although deve lopment appears to be strongly genetically predetermined, environmental fac tors can have a significant effect on both the initiation and the reproduct ive: output of sexual reproduction. As a general response to unfavorable en vironmental conditions the percentage of sexually reproducing medusae as we ll as the number of brooded planula larvae is increased. The potential indi cators of seasonal change, photoperiod and temperature, had no significant effect on the complex life history of E. dichotoma. The findings suggest th at although the life history is sensitive, to environmental factors E. dich otoma does not take advantage of seasonally changing environmental factors to adapt its life cycle to the particularities of a seasonal environment.