Sitting on the fence: Individuals, distributions, and reproductive strategies in the bird’s nest fungus <i>Nidula candida</i>

Bird's nest fungi (<i>Nidula candida</i>) growing along ~18-year-old cedar fences in Pacific Spirit Regional Park, Vancouver, British Columbia, Canada, produce abundant, persistent peridia containing basidiospore-bearing, egg-like peridioles. To reconstruct the initial mode of reproduction of the populations, 37 peridia were collected following a geometric sampling design, with 8-10 peridia collected 6-222 cm apart from each of four fence segments. We cultured dikaryotic mycelium from one whole peridiole from each peridium and 105 monokaryons from basidiospores from 8 peridioles. We then tested mycelial compatibility by confronting pairs of dikaryons and sexual compatibility by mating the monokaryons from basidiospores. The resulting genetic patterns allowed us to map genetic individuals back to their fence segments. The dikaryotic mycelia that grew from whole peridioles fell into six mycelial compatibility groups, with one or two groups per 3-7 m fence segment. Consistent with an outcrossing origin, four different mycelial compatibility groups had different mating types. The largest compatibility group covered over 6 m of fence, producing 114 peridia and ~4.2 billion spores. One compatibility group was present at two fence sites ~40 m apart, suggesting asexual dispersal. This can potentially be explained by somatic growth from the walls of dispersed peridioles. Dikaryons generated by mating sibling monokaryons isolated from basidiospores from the same peridiole showed mycelial incompatibility in 86% of pairings. Thus, the compatible dikaryotic mycelia emerging from whole peridioles likely represent clones of parental mycelium rather than recombinant meiotic hyphae from basidiospores. Asexual reproduction from dispersed fruit body tissue is unusual in Agaricales, but in <i>N. candida</i> fence-hopping of peridioles splashed from peridia and germinating as clonal, parental-type dikaryotic mycelia may have contributed to expansion of a genet along the fence.