Host-parasite interactions in perpetual darkness: macroparasite diversity in the cavefish Astyanax mexicanus

Astyanax mexicanus has repeatedly colonized cave environments, displaying evolutionary parallelisms in many troglobitic traits. Despite being a model system for the study of adaptation to life in perpetual darkness, parasites infecting cavefish are practically unknown. In this study, we investigated the macroparasite communities of 18 cavefish populations from independent lineages and compared them with the parasite diversity of their sister surface fish populations, with the aim of better understanding the role that parasites play in the colonization of new environments. Thirteen parasite taxa were found in cavefish populations, including a subset of 10 of the 27 parasite taxa known for the surface populations. Parasites infecting the cavefish belong to five taxonomic groups: trematodes, monogeneans, nematodes, copepods, and acari. Monogeneans are the most dominant group, found in 14 caves. Macroparasites include species with direct life cycles and some trophically-transmitted parasites, including invasive species. Surprisingly, cave vs surface paired comparisons indicate higher parasite richness in the caves. The spatial variation in parasite composition across the caves suggests historical and geographical contingencies of the host-parasite colonization and the potential evolution of local adaptations. Base-line data on parasite diversity of cavefish populations of A. mexicanus sets the ground to explore the role of divergent parasite infections under contrasting ecological pressures (cave vs. surface environments) in the evolution of cave adaptive traits.