Individual condition and inflammatory response to PHA in the subterranean rodent Ctenomys talarum (Talas tuco-tuco): A multivariate approach

Abstract

Several components of individual condition can modulate immune function in vertebrates. One of the most common techniques used by ecologists to estimate immune responsiveness in wild populations is the phytohemagglutinin (PHA)-skin test, which is usually considered a proxy of cell- mediated activity. To determine the influence of individual condition on the magnitude of this immune index we assessed the variability in the inflammatory response to PHA in the subterranean solitary rodent, Ctenomys talarum (Talas tuco-tucos), including 18 variables associated with different aspects of individual condition that are indicative of physical, physiological, parasitological and immunological state. A partial least square (PLS) regression analysis was performed on the condition and the response variables to identify those having greater contribution to overall variation in the response. The first two components explained together 77.5% of the maximum achievable explained variance in the inflammatory response to PHA (60% of total variance). Abundance of eggs of Trichuris pampeana, eosinophil, monocyte and neutrophil counts, together with reproductive condition were identified as the most important variables affecting the inflammatory response. The first component negatively associated the inflammatory response to PHA with the abundance of the nematode T. pampeana, and with counts of eosinophils and monocytes. The second component negatively associated the inflammatory response to PHA with reproductive condition, neutrophils and eosinophils. We discuss the general negative effect of infection on the immune responsiveness of wild animals and highlight the usefulness of the multivariate approaches in providing information on physiology, parasitology and health relationships to assess patterns of variation in immune responses.