Immune challenge does not impair short-distance escape speed in a newt

Animals may face trade-offs when several simultaneous functions or processes compete for limiting resources. In that context, allocation of resources to the most fitness-enhancing competing function can be prioritized. Immune response and locomotor performance are relevant fitness components, mainly due to their important roles as defence against pathogens and predators, respectively. However, both promote oxidative stress and consume energy and metabolites. Consistently, trade-offs between immune response and locomotion have been reported in some taxa. In this work, we examine whether an immune challenge hinders short-distance swimming speed of adult Iberian ribbed newts, Pleurodeles waltl. To that end, we inoculated Escherichia coli cell wall lipopolysaccharide (LPS), an innocuous antigen that triggers an immune response, in the sole pads of experimental newts, and phosphate buffer saline, with no physiological effect, in those of control newts. We estimated immune response as sole pad swelling and calculated swimming speed from videos of newts swimming towards a refuge nearby, 24 h and 7 days after inoculation. Sole pad swelling was greater in LPS-inoculated newts, but short-distance swimming speed was not affected by the immune challenge. These results could indicate priority allocation of resources to locomotion, which might be a consequence of compensatory mechanisms capable of avoiding locomotion impairment due to immune challenge. In any case, these findings could highlight the importance of short-distance escape as an antipredator strategy.