Infection with Babesia bovis increases Rhipicephalus microplus metabolic rates

Babesia bovis is a protozoan pathogen that is transovarially transmitted to offspring in Rhipicephalus microplus. Infection increases metabolic rate in some insects; however, it is unknown if infection creates an energetic trade-off in ticks. To test the hypothesis that carrying B. bovis increases metabolic rate, CO2 production was measured in replete R. microplus females that fed on infected calves and resulting R. microplus offspring at egg and larval stages. Replete females were measured for 20 minutes/day with a flow rate of 60 ml/min for 3 consecutive days in a MAVEn-FT (Sable Systems). Clusters of eggs were collected in makeshift containment tubes with fine mesh to allow for air flow. Eggs and larvae were measured for 30 minutes at 5 ml/min. Hemolymph, free of host blood, was extracted from replete females to determine infection status and blood smears were used to observe the presence of kinetes. Successfully hatched larvae were also tested for the presence of B. bovis using PCR. Metabolic rate was significantly higher in infected females compared with uninfected females (F1,88 = 11, p = 0.0013). Eggs from infected females also exhibited higher metabolic rates than eggs from uninfected females (F1,263 = 55.73, p < 0.00001). Our results show that infection with B. bovis increases metabolic rate of R. microplus as gravid females, eggs, and larvae. This is the first study examining metabolic consequences of infection on R. microplus across several life stages. Infection-induced increases in metabolic rate may lead to energetic tradeoffs including longevity and immunity.