Letharia lupina

Genomic work on wolf lichens suggests that Letharia species are typically haploid and heterothallic (self-incompatible), with each thallus carrying only one of two mating type idiomorphs. In a wide survey of samples, researchers used PCR (polymerase chain reaction) to test for mating-type genes and found that North American populations of L. lupina include both mating types in roughly equal proportions, consistent with regular sexual reproduction even though apothecia are seldom produced.^[7] Long-read metagenomic sequencing has also produced a high-quality reference genome for L. lupina (about 49 Mb assembled into 31 contigs). In that same sample, analysis of sequencing depth and genetic variation indicated that the thallus contained at least two distinct fungal haplotypes, suggesting that individual thalli may sometimes include more than one genotype.^[8] Metagenomic sequencing of one L. lupina thallus, however, showed a triploid-like genetic signal; the authors interpreted this as evidence of hybridization between L. lupina and another Letharia lineage, and discussed several mechanisms that could generate such individuals.^[7] A targeted DNA screen for lichen-associated basidiomycete yeasts detected cystobasidiomycete yeasts in all three tested thalli of L. lupina; in the same assay, the two Tremella targets screened for were not detected in those samples.^[9] Culturing of surface-sterilised thallus sections has also yielded other lichen-associated fungi; in one study, a filamentous fungus identified as Anthostomella pinea was isolated from L. lupina material and later characterised with whole-genome sequencing.^[10] Genome mining of L. lupina has suggested extensive potential for secondary metabolism: one analysis of its published genome predicted 42 biosynthetic gene clusters, including 21 predicted polyketide clusters. The same study discussed prenyltransferase genes in lichen-forming fungi that are often annotated as dimethylallyltryptophan synthases, but argued (from comparative analyses) that most are more likely involved in modifying tyrosine- and polyketide-derived compounds than indole alkaloids, which have not been reported from lichens.^[11]

In western North America, Letharia lupina is widely distributed and, in the authors' assessment, is encountered more often than L. vulpina s. str.; sequenced material in their study identified L. lupina as the predominant lineage among North American samples. It is also the more widespread of the two lineages in North America, extending east of the Continental Divide into Alberta and Saskatchewan and southwards through parts of the interior western United States (including Montana, Wyoming, south-western South Dakota, Utah, and Nevada). In mountainous regions it spans a broad elevational range, from valley bottoms to treeline, roughly 190–3,370 m (620–11,060 ft).^[3] It has also been reported from Veracruz in eastern Mexico. In North America, the lineage later described as L. lupina was reported as most common in the interior western mountains, whereas L. vulpina more often occurs in warmer coastal mountains near the Pacific, although the two can occur together locally.^[4]

The species commonly grows on old fence posts and on the bare (decorticated) trunks and branches of conifers (especially Pinus), but also occurs on conifer bark, including that of Abies, Calocedrus, Picea, and Pseudotsuga. On hardwoods it most often colonizes exposed wood (reported from Arbutus, Arctostaphylos, Populus and Salix), but it has also been observed on bark-covered (corticated) branches of Betula and Quercus. Saxicolous (rock-dwelling) thalli have occasionally been found on granitic outcrops. Outside North America, it has been reported from the Atlas Mountains of Morocco (on Cedrus atlantica)^[5] and from Switzerland, with the Swiss photobiont belonging to the same algal clade as North American material.^[3]