Taxonomy: A precursor to understanding ecological interactions among schistosomes, snail hosts, and snail-eating fishes

We have observed a dramatic decrease in the abundance of snail-eating fishes and an increase in the prevalence of schistosomiasis among village residents and expatriate tourists at Lake Malawi, Africa, over the past two decades. We hypothesized that these observations were linked by a cause-and-effect relationship and that the observed decrease in fish molluscivores permitted an increase in the abundance of snails that are intermediate hosts to schistosomes; we proposed a sampling protocol to determine these relationships. Initially, we thought that intensive study of the interactions among fish, intermediate-host snails, and human schistosomes in southern Lake Malawi could be applied to other areas throughout the lake. More than two-thirds of the cichlid species in Lake Malawi are undescribed, the taxonomy of the Bulinus snails is poorly known, and not all strains of Schistosoma hematobium have been identified. Before we can identify the interactions among these components of the system and effectively manage snail-eating fishes, we must be able to accurately delimit the taxonomic units (e.g., species, populations, and demes) within each of the above groups.