A study by researchers from CSIC and the Complutense University of Madrid led by RJB-CSIC scientist Sergio Pérez-Ortega and published in the journal 'Global Ecology and Biogeography', addresses for the first time the diversity of fungi and algae in symbiosis on a large scale, allowing the use of the framework of ecological interaction networks.
Lichens are stable symbioses formed by photosynthetic fungi and algae and are often considered paradigms of mutualistic relationships. In Antarctica, lichens, with about 600 known species, are the most diverse group of organisms that inhabit this continent. Although in recent years progress has been made in the knowledge of the algae that form lichen symbioses, very little is known about how these fungi and algae interact in the context of the communities they form.
Using the theoretical framework of ecological interaction networks, which has been developed mainly to study the properties of pollinator-plant interaction networks, a team of researchers from the Consejo Superior de Investigaciones Científicas (CSIC) and the Universidad Complutense de Madrid (UCM) has studied the relationships between fungi and photosynthetic partners in lichen communities growing on rocks in one of the most hostile regions for life on the planet, the Transantarctic Mountains in continental Antarctica.
This team, led by the researcher of the Real Jardín Botánico-CSIC Sergio Pérez-Ortega and integrated by researchers from the Museo Nacional de Ciencias Naturales-CSIC, the Centro de Investigaciones sobre Desertificación, a joint center of CSIC, Universidad de Valencia and Generalitat Valenciana, and UCM has investigated the algae associated with 77 species of lichen-forming fungi in more than 750 samples along a latitudinal transect ranging from 76ºS to 85ºS, which is the limit of macroscopic life in Antarctica.
“The large number of samples, collected mainly by researchers Leopoldo G. Sancho (UCM) and Asunción de los Ríos (MNCN-CSIC) in often extremely adverse conditions, represent a major milestone, as they have enabled us to address for the first time the diversity of interactions of these organisms on a large scale, allowing the use of the framework of ecological interaction networks,” said Sergio Pérez-Ortega.
The results of the study, which have just been published in the journal Global Ecology and Biogeography, have shown that, “despite the dramatic adverse conditions that exist in all locations during practically the whole year, with extreme temperatures, low rainfall and hurricane-force winds, the fungus-algae relationships at the community level show properties that do not vary and are maintained throughout the entire transect,” added the RJB-CSIC researcher.
A surprising specialization of fungi
These properties include low connectivity in the studied networks and high specialization of fungi by their algae. “This high specialization is surprising and goes against previous hypotheses that had suggested that fungal-algal relationships became more generalist as conditions became more extreme,” said MNCN-CSIC researcher Asunción de los Ríos. “Even at the limits of macroscopic life, at 85ºS, the vast majority of species continue to behave as specialists, which could be related to strong evolutionary constraints,” she added.
The researchers have also observed that there is a great change in the interactions that occur between the regions studied along the gradient whose main origin “is not in the change of fungi and algae that form the interactions, but in the change interactions themselves, ie, although the organisms are present in several locations, they may not interact with each other, indicating that a fungus-algae combination may be optimal in certain microclimatic conditions but not so successful in others”, pointed out Miguel Verdú, researcher at the Desertification Research Center (CIDE, CSIC-UV-GVA).
The results obtained with this study represent, in the opinion of the research team, a great advance in the knowledge of lichen symbiosis, in general, and contribute to a better understanding of the biology of lichens in one of the most sensitive ecosystems to environmental changes such as Antarctica.
Reference:
Sergio Pérez-Ortega, Miguel Verdú, Isaac Garrido-Benavent, Sonia Rabasa, T.G. Allan Green, Leopoldo G. Sancho & Asunción de los Ríos (2023). Invariant properties of mycobiont-photobiont networks in Antarctic lichens. Global Ecology and Biogeography. DOI: https://onlinelibrary.wiley.com/doi/10.1111/geb.13744
CIDE Communication
