Effects of habitat disturbance on parasite infection and stress of the endangered Mexican stream salamander Ambystoma ordinarium

Amphibians are one of the most vulnerable groups of tetrapods with 41% of species considered threatened with extinction. In amphibians, an increase in stress level is an early physiological response to factors associated with habitat degradation. In vertebrates, stress increases the susceptibility to parasite infections and is associated with changes in the number of blood cells, and therefore the proportion of the leukocytes, neutrophils to lymphocytes (N/L ratio) is used as a proxy measure of stress hormones. In this study, we used such leukocyte profiles to analyze stress levels and evaluate parasite load to elucidate the health condition of the endangered Mexican stream salamander, Ambystoma ordinarium. The habitat quality of streams inhabited by A. ordinarium was evaluated by Rapid Bioassessment Protocols (RBPs). We selected three streams with the highest RBPs scores as the undisturbed streams and three with the lowest scores as the disturbed streams. In each stream, we determined leukocyte profile and searched for ecto/endoparasites on sampled individuals. We report for the first time the leukocyte profile of A. ordinarium. A significantly higher N/L ratio was found in salamanders from disturbed vs. undisturbed streams. We also found a higher parasitic infection in salamanders from disturbed streams. Our results suggest that low habitat quality can increase stress levels and susceptibility to parasitic infections, thereby compromising the long-term persistence of populations of this species in disturbed habitats.