Consumption of grass endophytes alters the ultraviolet spectrum of vole urine
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- Huitu, O., Helander, M., Lehtonen, P. et al. Oecologia (2008) 156: 333. doi:10.1007/s00442-008-0984-3
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Fungal endophytes of grasses are known to benefit their hosts directly by increasing resistance to herbivores through mycotoxins. We propose and test assumptions of a novel hypothesis according to which fungal endophytes of grasses may benefit their hosts also indirectly by increasing the conspicuousness of a mammalian herbivore, the field vole (Microtus agrestis), to its avian predators by enhancing the ultraviolet visibility of vole urine. We found that field voles feeding on endophyte-infected meadow ryegrass (Lolium pratense) lost body mass, while voles feeding on non-infected meadow ryegrass gained mass. More interestingly, the maximum peak intensity of ultraviolet fluorescence in the urine of voles feeding on endophyte-infected grass shifted from over 380 nm to circa 370 nm, which is the suggested maximum sensitivity of the ultraviolet pigments in the eyes of vole-eating raptors. Therefore, grazing on endophyte-infected grass alters the ultraviolet spectrum of vole urine, thus potentially enhancing its visibility to avian predators.