Local Adaptation in Festuca arizonica Infected by Hybrid and Nonhybrid Neotyphodium Endophytes

Abstract

Cool-season grasses often harbor obligate fungal symbionts from the genus Neotyphodium, and these symbiota can function as a single ecological unit. Previous studies have shown that gene flow in Neotyphodium in Festuca arizonica is low enough such that populations could diverge and form local adaptations. A reciprocal transplant experiment was performed between two F. arizonica/Neotyphodium populations in Arizona, Clint's Well and Flagstaff, using symbiota with the most common Neotyphodium genotypes in each population, to test for local adaptations. The genetic difference between populations is potentially large as Neotyphodium from Clint's Well are of hybrid origin. Local environmental variation was the most important source of variation for F. arizonica/Neotyphodium symbiota growth, with individuals at Flagstaff growing larger and individuals at Clint's Well not reproducing. Local environment and the source population of the symbiota interacted to affect vegetative growth. Symbiota from Clint's Well, which harbor hybrid Neotyphodium, had higher volume/wet mass and volume/dry mass ratios but only in the marginal Clint's Well habitat. The local environment also affected F. arizonica/Neotyphodium reproduction because only symbiota transplanted to Flagstaff reproduced. Symbiota from Clint's Well produced more panicles, whereas symbiota from Flagstaff with nonhybrid Neotyphodium produced greater seed mass per panicle. Overall seed mass production was not different, suggesting that the two strategies are functionally equivalent. We find that F. arizonica/Neotyphodium symbiota vary geographically, but potential local adaptations are only apparent in marginal habitats and may be related to the evolutionary history of the Neotyphodium part of the symbiota.