Myco- and photobiont associations in crustose lichens in the McMurdo Dry Valleys (Antarctica) reveal high differentiation along an elevational gradient

Abstract

Climatically extreme regions such as the polar deserts of the McMurdo Dry Valleys (78° S) in Continental Antarctica are key areas for a better understanding of changes in ecosystems. Therefore, it is particularly important to analyze and communicate current patterns of biodiversity in these sensitive areas, where precipitation mostly occurs in form of snow and liquid water is rare. Humidity provided by dew, clouds, and fog are the main water sources, especially for rock-dwelling crustose lichens as one of the most common vegetation-forming organisms. We investigated the diversity and interaction specificity of myco-/photobiont associations of 232 crustose lichen specimens, collected along an elevational gradient (171–959 m a.s.l.) within the McMurdo Dry Valleys. The mycobiont species and photobiont OTUs were identified by using three markers each (nrITS, mtSSU, RPB1, and nrITS, psbJ-L, COX2). Elevation, positively associated with water availability, turned out to be the key factor explaining most of the distribution patterns of the mycobionts. Pairwise comparisons showed Lecidea cancriformis and Rhizoplaca macleanii to be significantly more common at higher elevations and Carbonea vorticosa and Lecidea polypycnidophora at lower elevations. Lichen photobionts were dominated by the globally distributed Trebouxia OTU, Tr_A02 which occurred at all habitats. Network specialization resulting from myco-/photobiont bipartite network structure varied with elevation and associated abiotic factors. Along an elevational gradient, the spatial distribution, diversity, and genetic variability of the lichen symbionts appear to be mainly influenced by improved water relations at higher altitudes.

Macroclimatic conditions as main drivers for symbiotic association patterns in lecideoid lichens along the Transantarctic Mountains, Ross Sea region, Antarctica

“…To get a better coverage of the latitudinal gradient (Fig. 1 a), additionally, 159 lichen samples (collected at 102 different localities) from the Area 5, McMurdo Dry Valleys (MDV), were obtained from the studies of Wagner et al 10 and Perez-Ortega et al 50 , including the solely lecideoid lichen species of the genera Carbonea, Lecanora, Lecidella, Lecidea and Rhizoplaca . All newly processed specimen were determined by Ulrike Ruprecht.…”

“…The rock surface is often highly weathered, which results in a higher water retention capacity, providing the most needed life source for the organisms to survive 7 , 8 . The only moisture available to rock-dwelling organisms is provided by clouds, fog, dew, sparse precipitation and melting snow 9 , 10 . Additionally, the aspect of the slopes, ridges and depressions as well as the wind regime have an important impact by creating different surface temperatures in small areas 11 , 12 .…”

“…However, nonlinear climatic conditions along gradients caused by additional factors, e.g. special wind systems, can be detected effectively with biological systems that act as bioindicators 10 , 20 – 22 . Additionally, they not only enable the survey of the current state but can also reliably indicate changes in environmental conditions 23 .…”

“…Many analyses focused on myco-/photobiont associations have demonstrated that they react sensitively to even small environmental gradients 10 , 33 . These results allow the conclusion that mycobionts which are less specialized to specific locations and are able to use a broader range of photobionts, such as the widespread species Lecidea cancriformis in continental Antarctica 10 , 16 , are less vulnerable to climate changes. Low photobiont specificity may improve the performance of the lichen symbiosis, e.g.…”

“…Additionally, genetic identity can play a significant role in shaping myco-/photobiont associations along gradients 39 or may also lead to turnover zones, suggesting that photobionts are replaced by others as environmental conditions change 40 . An influence on the selection of Trebouxia OTUs due to temperature combined with water availability was suggested in several studies as a key factor of photobiont selection of lichens in Antarctica 10 , 41 . Due to the sensitive response of lichen communities to climatic change with modified species compositions and reduced diversity 20 , 42 – 44 , lichen growth, abundance and diversity are expected to be negatively affected by climatic changes 44 .…”