4. Discussion
Our study provides the first genome-scale perspective into
diversification of the lichen forming fungal genus Niebla –
endemic to the Pacific coast of Baja California Sur, Baja California and California, highlighting dynamic
speciation in this clade of symbiotic fungi. Our data support the
perspective of a species-rich genus, and that many species are indeed
sympatric, occurring in close association, while single species
populations have also been recognized, mostly near the range limits of
the genus (Spjut 1996; Spjut et al., 2020). Although candidate species
inferred from genome-scale do not support current phenotype-based
species circumscriptions, morphologically similar specimens having the
same chemotype collected from distinct localities along the coast of
Baja California were consistently delimited as separate species-level
lineages using RADseq data, further supporting a model of micro-endemism
in Niebla (Spjut et al., 2020). On the other hand, morphological
parameters applied to distinguish species could be revised to agree with
molecular data, while chemical variation in lichen metabolites need
further study such as triterpenes in N. lobulata (Spjut,
1996) that may correlate with species differences (Spjut et al., 2020),
and isodivaricatic acid found in type specimens of N. eburnea(Spjut-Rakatondraibe comm., Oct 2016) instead of divaricatic acid as
reported for N. homalea from the putative type locality (Zhang et
al. 2020). Nevertheless, similar to an earlier study using multi-locus
sequence data (Spjut et al., 2020), we found that robust, consistent
species delimitations were difficult to infer, even with thousands of
RADseq loci. Below we discuss the implications of our findings in
relationship to the challenge of species delimitation and characterizing
diversity in Niebla.