Abstract
Lichens illustrate how individuality in eukaryotes is composite, complex and multidimensional.
Lichen thalli are complex holobionts, which have originated from
cyclical symbiosis involving a fungus, one or several photoautotrophs-green
microalgae, cyanobacteria or both, and abundant non-photosynthetic bacteria.
Lichenization allows the partners to thrive in extreme environmental conditions.
Buellia zoharyi Galun is a lichen prevailing in Biological Soil Crusts (BSC) in xeric
areas. It seems to be specific to gypsum and carbonated soils. Six populations
were selected, three on Miocene gypsum soils from the Iberian Peninsula and
three more growing in other substrata: two from the Canary Islands and another
one from the Balearic Islands. Also, herbarium samples from Morocco and
Greece were included. The B. zoharyi mycobiont was identified using ITS rDNA
as barcode. Green microalgae phylogenetic analyses were made using both
chloroplast (LSU rDNA) and nuclear (nrDNA ITS) molecular markers. In addition,
ultrastructural microscopic techniques were used to characterize each
phycobiont found.
Our results suggest the presence of at least three different Trebouxia lineages.
Furthermore, phycobiont coexistence inside a single thallus occurs in all the
populations analyzed, defined by the presence of at least two taxa of intrathalline
symbiotic microalgae. The intrathalline coexistence of different algal species
and/or genera inside a single lichen thallus has recently been reported by our
team. This process could be advantageous under extreme environmental
conditions, and might be a common phenomenon in ecologically adaptive
lichens, as in the case of B. zoharyi