Data from: Rethinking asexuality: the enigmatic case of functional sexual genes in Lepraria (Stereocaulaceae)

The ubiquity of sex across eukaryotes, given its high costs, strongly
suggests it is evolutionarily advantageous. Asexual lineages can avoid,
for example, the risks and energetic costs of recombination, but suffer
short-term reductions in adaptive potential and long-term damage to genome
integrity. Despite these costs, lichenized fungi have frequently evolved
asexual reproduction, likely because it allows the retention of symbiotic
algae across generations. The lichenized fungal genus Lepraria is
thought to be exclusively asexual, while its sister genus Stereocaulon
completes a sexual reproductive cycle. A comparison of sister sexual and
asexual clades should shed light on the evolution of asexuality in lichens
in general, as well as the apparent long-term maintenance of asexuality in
Lepraria, specifically. In this study, we assembled and annotated
representative long-read genomes from the putatively asexual Lepraria
genus and its sexual sister genus Stereocaulon, and added short-read
assemblies from an additional 22 individuals across both genera.
Comparative genomic analyses revealed that both genera were heterothallic,
with intact mating-type loci of both idiomorphs present across each genus.
Additionally, we identified and assessed 29 genes involved in meiosis and
mitosis and 45 genes that contribute to the formation of fungal sexual
reproductive structures (ascomata). All genes were present and appeared
functional in nearly all Lepraria, and we failed to identify a
general pattern of relaxation of selection on these genes across the
Lepraria lineage. Together, these results suggest that Lepraria may be
capable of sexual reproduction, including mate recognition, meiosis, and
production of ascomata. Despite the apparent maintenance of
machinery essential for fungal sex, over 200 years of careful observations
by lichenologists have produced no evidence of canonical sexual
reproduction in Lepraria. We suggest that Lepraria may have
instead evolved a form of parasexual reproduction, perhaps by repurposing
MAT and meiosis-specific genes. This may, in turn, allow these lichenized
fungi to avoid the long-term consequences of asexuality while maintaining
the benefit of an unbroken bond with their algal symbionts.