Parasitic Bat Flies (Diptera: Streblidae and Nycteribiidae): Host Specificity and Potential as Vectors

Abstract

Host specificity gauges the degree to which a parasite occurs in association with host species and is among the most fundamental properties of parasite–host associations. The degree of specificity is indicative of myriad properties of the host and parasite and of their ecological and evolutionary relationships. Bat flies are highly specialized bloodfeeding ectoparasites of bats worldwide and were historically viewed as unspecific. In the bat fly—bat system, numerous properties actually or potentially interrupt the linkage of parasite to host and should thus decrease specificity. Such properties of bat flies include a life history strategy requiring females to leave the host, an off-host pupal stage, and high dispersal capability of many species. For hosts, properties include high diversity, mobility, sociality, and multispecies roosting environments. These and other biological and ecological characteristics of bats and flies should together facilitate interspecific host transfers and over time lead to nonspecific host–parasite associations. Despite these properties, large and carefully executed biodiversity surveys of mammals and parasites unequivocally demonstrate the high host specificity of many bat flies, and molecular sequence data promise to demonstrate that many cases of lowered specificity are misunderstood due to unresolved parasite species boundaries. On the other hand, experimental approaches have suggested that host specificity is context dependent and may be lessened in cases of ecological disturbance and in particular when novel host–parasite associations are created. Evolution and maintenance of specificity in bat flies depends in part on the encounter and compatibility properties of bats and on the reproductive potential of the flies on available host species. Moreover, the degree to which parasites have coevolved immunological compatibility with their hosts, thereby diminishing immunological surveillance and response, may also serve to maintain high host specificity. Although worldwide bat species on average harbor higher diversity of parasites and pathogens than any other mammalian group, the likelihood of bat flies vectoring disease agents across host species of bats, and particularly to distantly related mammals such as humans, may be relatively small.