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.