Effect of an immune challenge on the anti-predator response of the green Iberian frog (Pelophylax perezi): the influence of urban habitats

Previous studies suggest that immune-challenged individuals need to allocate resources to the immune system to combat infection, reducing escape ability and increasing the vulnerability of infected individuals to predators. Such behavioural responses might change in anthropogenic habitats where the balance between predation risk and countering infections can differ from that in natural habitats. We experimentally explored whether fighting an infection has an effect on hiding behaviour in a frog (Pelophylax perezi), and whether frogs from urban ponds respond differently from those from natural forested ponds. Independently of habitat type, we found no evidence for changes in hiding behaviour of male frogs before and after they were immune challenged (injected with lipopolysaccharide) or not (injected with phosphate-buffered saline). We also explored whether immune response (phytohaemagglutinin assay) or morphological traits (head width, body condition, body size and length) were related to variation in hiding time, but we did not find a relationship between the measured traits and behavioural response for males from either habitat. In conclusion, we show that frog anti-predator behaviour is not always affected by an immune challenge and the effect of urban habitats can be weaker than expected, at least in species that could be pre-adapted to the novel environmental conditions.