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Consumption of grass endophytes alters the ultraviolet spectrum of vole urine


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.

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We thank Peter Banks and anonymous referees for helpful comments on the manuscript, Marjo Anttila for help in rearing the plants, Sini Isola for helping with the voles and Riitta Koivikko for analyzing fluorescence from the urine samples. This work was supported by grants from the Academy of Finland (no. 106036 to O. H., no. 202799 to K. S.). This research adhered to the Association for the Study of Animal Behaviour/Animal Behavior Society Guidelines for the Use of Animals in Research, the legal requirements of Finland and all institutional guidelines.

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Correspondence to Otso Huitu.

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Communicated by Anssi Laurila.

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Huitu, O., Helander, M., Lehtonen, P. et al. Consumption of grass endophytes alters the ultraviolet spectrum of vole urine. Oecologia 156, 333–340 (2008).

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  • Fluorescence
  • Lolium pratense
  • Microtus agrestis
  • Predation
  • Reflectance