MALE MATE CHOICE IN A NATURAL-POPULATION OF THE PARASITIC COPEPOD LERNAEOCERA-BRANCHIALIS (COPEPODA, PENNELLIDAE)

Variations in age and sex structure of a natural population of the cop epod Lernaecocera branchialis, parasitic on flounder, Platichthys fles us were examined in a 15-month study. Recent laboratory studies and li terature on reproductive strategies indicate that male mate choice in this species should depend on the sex ratios of the parasite on its ho sts, and on the age and mating status of females. Sex ratios suggested a strong intra-male competition for females. The ratio of chalimus 4 and virgin adult females (preferred stages) to adult males exceeded 1 female: 4 males on 50% of the hosts. In four out of the six sampling p eriods, more than 50% of hosts harboured more adult males than the tot al number of females. The males preference for the different female st ages was estimated from the number of precopula and copula association s. The data were fitted to a logistic regression model. At most sex ra tios, males preferred chalimus 4 and virgin adult females, and discrim inated against younger stages. Mated females were about as attractive as the youngest larval stages at female-biased sex ratios, but they we re chosen more frequently at strongly male-biased sex ratios. Most adu lt L. branchialis females had copulated more than once, and some had a ccommodated at least 5 ejaculates in the their sperm storage organs. T he patterns of mate guarding and potential for sperm competition stron gly suggest that L. branchialis males take the intrasexual competition into account when choosing mates. On this basis, they minimize guardi ng time and maximize the possibility of paternity.