Isospora atticorae n. sp. (Apicomplexa: Eimeriidae) from the white-thighed swallow Atticora tibialis (Cassin, 1853) (Passeriformes: Passeri: Hirundinidae) in Brazil

Abstract

Background The diversity of coccidians in Neotropical wild avifauna remains significantly underestimated, particularly within the family Hirundinidae. While cosmopolitan and widely distributed hosts like Hirundo rustica Linnaeus, 1758 dominate the literature with three described Isospora spp., ecological traits of other swallows may drive different parasitic dynamics. This study provides the first integrative characterization of a coccidian parasite from Atticora tibialis (Cassin, 1853), a resident swallow strictly associated with complex and preserved Neotropical forest biomes. Methods Fecal samples were collected from three White-Thighed Swallows, A. tibialis , captured using mist nets in the Itatiaia National Park, Southeastern Brazil, during field expeditions in 2023 and 2024. Oocysts were processed through standard flotation and morphological analyses. Molecular characterization was performed by extracting genomic DNA from isolated oocysts and sequencing of a locus of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. Phylogenetic trees were reconstructed using Bayesian Inference and Maximum Likelihood. Results One bird was positive for coccidia (33.3% prevalence), and a new species is formally proposed herein: Isospora atticorae Dorna-Santos et Berto n. sp. The sporulated oocysts are pyriform, measuring on average 24 × 21 μm. A unique, distinguishing feature among congeners parasitizing the same host family is the presence of a distinct micropyle. A single, robust polar granule is present, and an oocyst residuum is absent. Sporocysts are ellipsoidal to lemon-shaped, with a mean size of 16 × 10 μm. Stieda and sub-Stieda bodies are present. A sporocyst residuum occurs among the vermiform sporozoites, which exhibit refractile bodies and a barely discernible nucleus. The obtained cox1 gene sequences were identical and shared 97–99% similarity with Isospora spp. from oscine birds (Passeri). In the phylogenetic tree, I. atticorae n. sp. clustered within a well-supported monophyletic clade of oscine-associated Isospora spp., closely grouped with Isospora spp. from Serinus canaria (Linnaeus, 1758) and Turdus migratorius Linnaeus, 1766. Conclusions The characterization of I. atticorae n. sp. highlights how the restricted distribution and forest dependence of A. tibialis favor localized parasite diversification and narrow host specificity within Neotropical biomes, contrasting with the dynamics of widely distributed migratory swallows. Globally, I. atticorae n. sp. is established as the first representative from the family Hirundinidae to be characterized from an integrative perspective through the sequencing of a mitochondrial locus, as well as the fifth nominally described species in this avian family, and the first in the Neotropical region.

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