Communication among sagebrush benefits receiver plants and is slightly more effective among kin

Background/Question/Methods

Communication among individuals that reduces herbivory has been found for at least ten plant species including sagebrush.  It has been unclear whether less herbivory translates into increased fitness in this and other systems.  We examined survival of two cohorts of seedlings, and survival and flowering for 12 years of young established plants with experimentally clipped or unclipped neighbors.  We found that responding to cues was beneficial but why do damaged plants emit cues that may provide an advantage to their neighbors?  Emitting cues may not be a choice for damaged plants, cues may serve other valuable functions unrelated to herbivory, and/or they may be signals intended for other branches on the same plant or for nearby kin.  Previous work indicated that plants communicated more effectively with genetically identical clones compared to non-self individuals.  Here we asked: Do plants communicate more effectively among close relatives compared to more distantly related individuals?  Large individuals had one branch receiving cues from an experimentally clipped close relative and a second branch receiving cues from a clipped distant relative.  A second experiment with more replication examined communication between individuals with varying levels of relatedness using regression.  In both experiments we assayed herbivory throughout the season.

Results/Conclusions

Overall, there were small detectable benefits of responding to cues resulting from artificial clipping.  Seedlings were more likely to survive to the end of their first dry season with clipped neighbors.  We found no differences in survival of established plants although plants with clipped neighbors produced more branches and inflorescences over 12 years than plants with unclipped neighbors.  Communication was more effective among genetically identical clones and slightly more effective among more closely related individuals.  In paired tests, branches receiving cues from closely related clipped neighbors received less herbivory than branches receiving cues from distantly related clipped neighbors.  Effect sizes due to relatedness were small and not detectable in regression analysis of a field experiment that also included spatial patchiness in herbivore damage.