Ploidy of symbiotic endophytes determine host response to environment

Background/Question/Methods

Neotyphodium fungi are asexual, obligate, vertically transmitted, endosymbionts infecting C₃ grasses. Neotyphodium may be haploid or possess multiple ploidy levels due to hybridization events. Increased ploidy is thought to infuse genetic variation and increase fitness of the host in varying environments. However the hypothesis that hybrid endophytes increase host fitness, has yet to be rigorously tested. We determined uninfected, hybrid and non-hybrid frequencies in 24 natural populations of Arizona fescue and monitored critical environmental variables (soil moisture, soil nutrients, heat load, aspect, and elevation).
Results/Conclusions

The frequency of nonhybrid and hybrid endophytes varied significantly among the 24 host populations, with some populations harboring no hybrids while others contained greater than 75% hybrids. Interestingly, the frequency of hybrids was associated with 1) low summer soil moisture and 2) low soil nitrogen levels, whereas nonhybrid infected hosts were associated with comparatively higher soil nutrient levels. These results support the hypothesis that hybridization of microbial plant symbionts may increase survival and persistence of the hosts in stressful environments.