Twenty-seven modes of reproduction in the obligate lichen symbiosis

Fungi exhibit some of the greatest reproductive diversity across Eukaryotes. In addition to sexual and asexual reproduction, fungi engage in parasexual (mitotic recombinatorial) processes to acquire new genetic variation. Reproduction has been studied extensively in numerous free-living fungi but comparatively less knowledge exists for lichenized fungi, which are assumed to reproduce only through sexual spores, asexual conidia, and specialized asexual lichen propagules. We present a new conceptual framework describing reproductive modes in lichens that includes sexual and asexual processes as well as accommodating the possibility of parasexual reproduction. To support the plausibility of some of these modes of reproduction, we reviewed data spanning more than 200 years of anatomical investigation. We recovered evidence supporting the possibility of 22 of 27 possible modes of reproduction and found no counter-evidence to suggest the remaining five do not occur in nature. This conceptual framework allows for a greater plurality of reproductive processes than previously acknowledged in lichens, exceeding that of their non-lichenized relatives.