Lichens host a diverse microbiome, whose variation and function ecologists are only beginning to elucidate. One ubiquitous component of this microbiome are endolichenic fungi: non-lichen-forming fungi that live intercellularly within the host lichen’s thallus. Like endophytic fungi in plant tissues, these fungi range from benign to parasitic, with some producing visible external structures and others remaining cryptic and detectable only through molecular techniques. For most of these fungi, we know little about their ecology or geographic distributions. We studied ecological determinants of the geographic distribution of one such endolichenic fungus, Unguiculariopsis lettaui, which produces distinct galls on the common and broadly distributed lichen, Evernia prunastri. Published literature provided only two prior records of U. lettaui in the United States, yet initial observations by students in an undergraduate research course indicated a high prevalence in coastal Northern California. We examined herbarium specimens to map the distribution of U. lettaui in North America. We then combined these maps with climate data and field surveys to evaluate which environmental factors limit the distribution of U. lettaui relative to its host, E. prunastri at different spatial scales.
Results/Conclusions
We examined 272 Evernia prunastri collections in the University of California Jepson herbarium as well as E. prunastri collections from 1025 systematic plot surveys across the United States conducted by the U.S. Forest Inventory and Analysis program. From these, we confirmed 79 additional observations of U. lettaui in North America. Except for two cases, U. lettaui was restricted to regions west of the Cascade and Sierra Nevada mountain ranges, ranging from southern Washington to central California. Field surveys in northern California indicated that the prevalence of U. lettaui infection is related to host abundance and atmospheric moisture availability. Our initial results suggest that the geographic range of this endolichenic fungus is restricted relative to that of its host. Studying the environmental determinants of host and symbiont distributions in lichens will allow ecologists to evaluate whether theory developed primarily in animal and plant models is more widely generalizable. Furthermore, our research demonstrates how we can harness the ecological data revolution by integrating existing biological collections, large-scale public data and undergraduate learning.