THE COEVOLUTIONARY POTENTIAL OF A GENERALIST PARASITE, THE HEN FLEA CERATOPHYLLUS-GALLINAE

Hosts exert selection pressures on their parasites and it is often ass umed that host-parasite coevolution with each host is less intense in a generalist parasite than for a parasite with a narrow host range. Se lection pressure on the parasite, however, is rather determined by hos t specificity, i.e. the relative importance of each host, than simply by the range of hosts. The determination of host specificity requires an assessment of the prevalence and intensity of parasite infestation within each host's nests, as well as the local abundance of each host species. Since the hen flea, Ceratophyllus gallinae, is a rather gener alist parasite of birds it could be concluded that there has been weak coevolution with each of its hosts. By reviewing the literature on th e prevalence and intensity of hen flea infestations in bird nests we e stimated the number of individuals produced in the nest of each host s pecies. The comparative analysis shows (1) that the prevalence of infe station is highest in hole-nesting avian families, (2) that prevalence and intensity of infestation among bird families are highly correlate d, and (3) that hole-nesting Paridae have the highest intensities of i nfestation and harbour the majority of the flea population. These resu lts underline the fleas' potential for coevolution with Paridae despit e their extensive host range.