Product Code Database
Buellia frigida is a species of saxicolous (rock-dwelling), crustose lichen in the family Caliciaceae. It was first described from samples collected from the British National Antarctic Expedition of 1901–1904. It is endemism to maritime and continental Antarctica, where it is common and widespread, at altitudes up to about . The characteristic appearance of this lichen features shades of grey and black divided into small patterns. The crusts can generally grow up to in diameter (smaller sizes are more common), although neighbouring individuals may coalesce to form larger crusts. One of the defining characteristics of the lichen is a textured surface with deep cracks, creating the appearance of radiating . These lobes, bordered by shallower fissures, give the lichen a distinctive appearance and textured surface.
In addition to its striking appearance, Buellia frigida shows adaptability to the harsh Antarctic climate conditions. The lichen has an extremely slow growth rate, estimated to be less than per century. Because of its ability to not only endure but to thrive in one of the Earth's coldest, harshest environments, Buellia frigida has been used as a model organism in astrobiology research. This lichen has been exposed to conditions simulating those encountered in outer space and on celestial bodies like Mars, including vacuum, ultraviolet radiation, and extreme dryness. B. frigida has demonstrated resilience to these space-related stressors, making it a candidate for studying how life can adapt to and potentially survive in the extreme environments found beyond Earth.
Darbishire also simultaneously described Buellia quercina, collected at the same type locality as B. frigidia, but with a more margin and lighter colour. MacKenzie rejected taxonomic value for variations in the black, grey, and whitish colours of the thallus due to anatomical variations of the lichen, and reduced B. quercina to synonymy.
A 2016 molecular phylogenetics study of the Caliciaceae included B. frigida in its analysis. In the constructed phylogenetic tree, this species appeared as sister group (closest evolutionary relative) to Amandinea coniops; the clade containing these two species was itself sister to Amandinea punctata; a similar result was obtained in a molecular analysis published in 2023. It is known that the genus Buellia itself is not monophyletic (derived from a single common ancestor).
Buellia frigida forms black, slightly shiny apothecia, which are often more or less sessile on the older areoles. The apothecia start as flat but become convex as they mature. When young, they have a appearance; when mature they are in form, and up to about 1 mm in diameter. The amphithecial cortex is about 15–17 μm thick, formed by a of isodiametric cells. Algae that initially exist between the medullary hyphae disappear as the apothecia age. The medulla of the apothecia consists of vertical brown hyphae that are loosely woven and connected to the thalline medulla. The is not differentiated in older apothecia; instead, the amphithecial cortex darkens, and the medullary hyphae shrink together after the algae disappear, creating the impression of a dimidiate proper margin (i.e. divided into two equal or nearly equal halves). The hypothecium is brownish, with a thickness ranging from 30 to 80 μm in the centre and thinning towards the margin, where it merges with the amphithecial cortex. The ascus, which contains the ascospores, stands approximately 90–110 μm tall. Paraphyses, measuring 2 μm in diameter, darken above the asci and have an internal partition, or septum. The asci are , with dimensions of 36–46 by 14.5–17 μm, and contain dark brown, bilocular ascospores (divided into two segments by a septum). These ascospores are occasionally only slightly constricted at the septum, and some may remain unilocular. They are typically ellipsoid, with dimensions of 9–13 by 5–8 μm.
Asexual , such as isidia or soredia, are not made by Buellia frigida. The lichen, however, does create pycnidium that originate from under the algal layer, appearing (with a rounded or bulbous form with a narrower portion or neck) to irregular and reaching sizes of up to 300 μm in diameter. A thin , consisting of very small-celled , surrounds the pycnidia. have a few septa and are branched at the base, measuring approximately 10 by 1 μm. The terminal are ellipsoid, measuring about 4 by 1 μm in size.
Buellia frigida is among the most common lichens in Antarctica, particularly in eastern regions. The distribution of B. frigida extends throughout Antarctica, from the Peninsula to rocky coastal areas and exposed rock formations in the interior. It is one of about 25 lichen species that occur circumpolar in coastal areas and extend inland to nunataks and mountains near the South Pole. It is the most widespread lichen in east Antarctica, including the Larsemann Hills, but it is somewhat rare in Marie Byrd Land and the King Edward VII Land, increasing in Victoria Land and most common on Antarctica's eastern coast. It is most abundant in Victoria Land's dry valley region and higher elevations above , known for cloud cover and summer snow. The lichen has been found at altitudes of up to . About marks the altitudinal limit at which lichens can survive in the Antarctic. Above this height, the long periods of exposure to winter temperatures and the lack of insulating snow cover on windblown rock faces is too harsh to support lichen life.
The species typically forms communities in wind-protected areas, particularly in rock cracks and on the leeward side of rocks. These communities can consist of B. frigida alone or occur with other saxicolous lichens such as Lecidea cancriformis, Acarospora gwynnii, Carbonea vorticosa, Pseudephebe minuscula, Physcia caesia, and Lecidella siplei. On the less lichen-populated Antarctic Peninsula, it is confined to the western part, south of 67°S latitude. Collections of Buellia frigida are typically made in coastal areas, and its inland range in the continent's interior remains unknown. It is one of 20 species of Buellia that occur in Antarctica.
Moisture availability determines Buellia frigidas distribution. At Cape Geology, southern Victoria Land, it primarily relies on meltwater from snowpack and occasional snowfalls for moisture in early summer. Despite the strong sunlight, the lichen survives in the combination of hydration, low temperatures, and intense light exposure. The distribution of lichen thalli on rock surfaces is influenced by the frequency and duration of meltwater moistening, reflecting its need for moisture.
Studies in continental Antarctica show the extremely slow radial growth rates of Buellia frigida. A monitoring study conducted in Yukidori Valley, no measurable increase in size was noted for any of the measured thalli after a five-year period. In the McMurdo Dry Valleys, the lichen growth rates varied across different sites, indicating responses to regional climate changes, including alterations in snowfall patterns. This adaptation over time demonstrates the lichen's resilience to changing environmental conditions in Antarctica, suggesting its use as an bioindicator of climate change in the region. Geographic information system technology has been used to detect subtle changes in the growth of Buellia frigida over a 42-year period. At radial growth rates of 0.0036 mm per year—about the thickness of an individual fungal hypha—some thalli are estimated to be at least 6,500 years old, dating back to the end of the Stone Age.
Studies on the population genetics of Buellia frigida indicate limited dispersal among regions in Antarctica, likely influenced by prevailing wind patterns and physical barriers such as . While the spores of B. frigida have the potential for wind-assisted dispersal, the lichen predominantly colonises specific areas conducive to its growth, particularly those with sufficient moisture during the short Antarctic summer, showing how environmental factors affect its dispersal. Samples of B. frigida collected from eastern Antarctica's Vestfold Hills and Mawson Station revealed minimal genetic variation: only three in the Vestfold Hills, differing by a single nucleotide. The most common genotype of B. frigida there matched specimens from Mawson Station, showing low genetic diversity across this large Antarctic region.
Tests expose B. frigida to stressors like vacuum, UV radiation, and desiccation to measure its viability and photosynthetic activity. These tests reveal that B. frigida maintains high post-exposure viability and sustains minimal damage to its photosynthetic capacity under these conditions. This resilience stems from protective mechanisms including morphological traits, secondary compounds, and anhydrobiosis during desiccation, features that also enable other extremotolerant lichens to survive.
Space experiments on the International Space Station (ISS) and in simulated Mars conditions tested the lichen's survival. One study showed that exposure to low Earth orbit conditions resulted in reduced viability of its fungal and algal components, but the fungal partner was less affected than the algal partner. Despite this, the lichen maintained its structure, showing resilience to an extraterrestrial environment. This indicated potential adaptation of this terrestrial organism to space conditions.
Different results came from the European Space Agency's Biology and Mars Experiment (BIOMEX) project, also conducted on the ISS. These experiments showed high mortality rates for both algal and fungal symbionts of B. frigida under similar low Earth orbit conditions, suggesting reduced survival potential in extreme extraterrestrial environments, questioning whether Mars could support this lichen. In additional BIOMEX studies, researchers examined the DNA integrity of B. frigida over 1.5 years. They used the Randomly Amplified Polymorphic DNA technique and observed DNA alterations in space-exposed lichen compared to Earth-based controls, indicating limited resistance of Buellia frigida to the conditions of space and Mars-like environments.
|
|
