Bat-ectoparasitic fly relationships in a seasonally dry tropical forest in Brazil.

Bat ectoparasitic flies are hematophagous insects highly specialized to parasitize only bats. Knowledge about how biotic and abiotic factors can influence ecological relationships between parasites and hosts is in general incipient. Large information gaps are even worst in biodiversity-rich, but poorly sampled areas like Brazil's Caatinga, the largest tropical dry forest in South America. We used bats and their highly specialized ectoparasitic flies as a study model to clarify some aspects of this host-parasite system in this semiarid environment. We conducted fieldwork at 55 sites in the Caatinga, between April 2017 and March 2020 and collected 1300 flies (19 species) on 333 bats (15 species). Bat ectoparasitic flies were highly host-specific, had an aggregated distribution, frequently formed infracommunities with only one species, and had a male-biased sex ratio. Except for the prevalence of the streblid fly Strebla guajiro on Carollia perspicillata, which was significantly higher in the rainy season, bat flies showed no preference - expressed by frequency and intensity of infestation - for host sex, and their interspecific relationships were not mediated by rainfall. Other variables that could potentially be interfering in this host-parasite relationship deserve further attention, especially in environments such as the Caatinga where there is great seasonal variation. Furthermore, the existence of species-specific responses must be taken into account.