Herbivory mediates grass-endophyte relationships.

GUNDEL, P.E.; OMACINI, M.; MARTINEZ-GHERSA, M.A.; GHERSA, C.M.

ECOLOGY

Año: 2008 vol. 89 p. 3542 - 3545

0012-9658

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} @font-face {font-family:AdvTimes; panose-1:0 0 0 0 0 0 0 0 0 0; mso-font-charset:0; mso-generic-font-family:auto; mso-font-format:other; mso-font-pitch:auto; mso-font-signature:3 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:ES;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> In the recent paper by Koh and Hik (Ecology, 88(11): 2752-2757) the pattern of Neotyphodium spp. endophyte infection frequency is shown to be related with the gradient of grazing pressure by two native herbivores, pikas (Ochotona collaris) and hoary marmots (Marmota caligata) in Yukon Territory (Canada). The grazing gradient is determined by the behavior of herbivores, being high “on” boulder fields and low “far” from there. The mechanism invoked to explain the pattern of infection frequency is the relative fitness of endophyte-infected and uninfected plants along this gradient. According to the defensive mutualism and optimal defense theories (Clay 1993, Zangerl and Rutledge 1996), infected hosts with alkaloid-based deterrents would be favored where grazing was consistently high, while uninfected plants or infected plants without deterrents would be favored where herbivory was low or absent. To reinforce the hypothesis, a trial was carried out to evaluate pikas selectivity for endophyte-infected and uninfected plants sampled from “on + near” and “far” from boulder fields. Herbivores were able to discriminate endophyte-infected and uninfected Festuca altaica plants from boulder fields, but they did not discriminate when plants came from meadows. In summary, the authors conclude that grazing pressure and herbivory selectivity is the major factor generating the pattern in endophyte infection frequency. Hence, endophyte infection is viewed as an adaptive trait in the environment with high grazing pressure. In our opinion, Koh and Hik (2007) present little information supporting that differences in endophyte infection frequency and herbivore avoidance of infected grasses were mainly a consequence of the distinct longer term grazing history of the grasses mediated by the deterrence fungus effect. We propose that the effect of herbivores on infection frequency might as well be mediated through selection of phenotypic traits not related to antiherbivory (e.g. compensatory growth ability; Karban and Baldwin 1997, Sullivan et al. 2007), or through an interaction with other environmental factors that can affect both partners to a different extent (Hill et al. 2005, Rasmussen et al. 2007)