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Abstract
Parasite infections in host populations frequently display seasonal patterns that can shape host behavior, fitness, and population dynamics. Despite recognition that seasonality plays a key role in infection dynamics across numerous host-parasite systems, the drivers of seasonal infection dynamics for different parasite life histories are often unknown. This lack of system-specific understanding restricts our ability to predict when and why parasite infections and their cascading effects on host populations will have the greatest impact. We investigated how seasonality and its associated environmental variables are related to the infection intensity of two parasitic nematodes with contrasting life cycle strategies: strongyle nematodes (direct life cycle) and lungworms (indirect life cycle). We conducted the study in two free-ranging ungulate species in Serengeti National Park, Tanzania: Coke’s hartebeest (Alcelaphus buselaphus) and topi (Damaliscus lunatus). We found a high prevalence of both parasites, with strongyle nematodes occurring in 95.5% of hartebeest and 93.1% of topi, and lungworms occurring in 100% of hartebeest and 99.7% of topi. Strongyle infection intensity peaked in the wet season but showed no strong association with precipitation, temperature, or animal density at the likely time of infection. In contrast, lungworm intensity peaked in the dry season and was associated negatively with precipitation and positively with animal occupancy. Our results highlight the importance of interactions between parasite life cycle and environmental variables in shaping seasonal infection patterns. Identifying when parasite intensities are highest is critical for predicting when hosts are under the greatest ecological pressure due to parasitism.