Niche partitioning within an insect host: trypanosomatids Wallacemonas raviniae and Trypanosoma (Megatrypanum) sp. in the horsefly Hybomitra solstitialis

Abstract

Tabanids (horseflies and deerflies) represent the main vectors of Trypanosoma theileri species complex and are frequently infected by them. In these insects, the trypanosomes are transiently present in the midgut and develop predominantly in the ileum. During a survey of infections in tabanids, we encountered a horsefly, in which trypanosomatids were present not only in the ileum but also in the rectum. The analysis of 18S rRNA sequences of the parasites in both locations demonstrated that they represented a T. theileri -like trypanosome and the monoxenous species Wallacemonas raviniae previously described from a flesh fly, respectively. The investigation using light and transmission electron microscopy showed that the two parasites differed not only in their affinity to distinct hindgut sections, but also in the patterns of attachment to the cuticular lining, interaction between individual cells, and development of extracellular structures. Unlike most monoxenous trypanosomatids inhabiting the rectum, W. raviniae was not observed on rectal glands or in the close proximity to them indicating either a peculiarity of the parasite species or specific conditions in the insect host. Our results demonstrated that the two trypanosomatid species partitioned their niches within the horsefly host due to strikingly dissimilar life strategies.