Hemoparasites Do Not Affect Life-History Traits and Cellular Immune Response in Treefrog Hosts Boana cordobae

SIMPLE SUMMARY: Unicellular blood parasites are common in amphibians all over the world. It is poorly understood whether the hemoparasite load can cause disease or affect life-history traits. Our study on the neotropical treefrog Boana cordobae from Argentina quantified the hemoparasite load in 37 individuals and focused on their cellular immune response (leukocyte profile) and the potential effects on the life-history traits size, body condition, and age. Thirty frogs were infected by either hemogregarines or trypanosomes or both in high intensities, a prevalence unprecedented in other anuran hosts. Yet, none of them showed externally visible signs of disease or aberrant behavior. The leukocyte profile did not differ significantly between parasite-free controls and infected frogs. Age-adjusted size, body condition, and age were not affected significantly by hemoparasite load, but most parasite-free frogs were young first-breeders, suggesting that infections take place after sexual maturation of the hosts. Vectors transmitting trypanosomes and/or hemogregarines to B. cordobae remain to be identified and studied in detail. ABSTRACT: We provide the first evidence for hemoparasites in the endemic Cordoba treefrog Boana cordobae. We collected 37 adult frogs at 1200 m a.s.l. in the Comechingones Mountains in the Córdoba province (Argentina). Each individual was sexed, then snout–vent length and body mass were recorded, a toe was collected for skeletochronological age determination, and a slide with a blood smear was prepared for hemoparasite screening, before releasing the frogs in situ. A total of 81% (n = 30) of the frogs were infected by hemogregarines and trypanosomes with a high intensity of infections. Dactylosoma was found for the first time in Argentina. Hemoparasites had no significant effect on the leukocyte profile, which we assessed from the May–Grünwald–Giemsa-stained blood smears. The neutrophils/lymphocytes ratio, indicative of stress, was insignificantly higher (0.06) in parasitized frogs than in parasite-free individuals (0.04). Infected frogs were larger than the controls, but this effect vanished when correcting size data for age. Young frogs (first-breeders) dominated the age distribution of parasite-free individuals, suggesting that infection of frogs takes usually place after sexual maturation. Vectors transmitting hemoparasites to B. cordobae remain to be identified. We demonstrate that moderate to high intensities of hemoparasites do not significantly affect the cellular immune response of B. cordobae, or any of the life-history traits studied, nor did they show any external sign of disease.