Environmental and evolutionary drivers of mutualistic network dynamics in communities of neotropical orchids and their mycorrhizal fungi.

The Orchidaceae, with more than 28,000 species, is the most diverse plant family known. Colombia, with more than 4,200 species registered, has the greatest diversity of orchid species. These species play an important role in the forest ecosystem functioning, as well as offering a valuable biological resource for commercialization of native biological diversity. However, orchids are facing drastic population declines due to habitat loss and climate change, and for effective conservation of this diversity it is essential that we understand the ecological and evolutionary processes that promote and maintain this diversity. Orchid diversity is thought to have arisen largely because of specialized interactions with pollinator species; however, in mountainous regions, such as the tropical andes, the role played by environmental abiotic factors is still unclear. Furthermore, orchids also have a specialized interaction with mycorrhizal fungi (OMF), mainly those in the genera Tulasnella, Ceratobasidium and Sebacina, which is essential for seed germination and seedling establishment, and provides nutrition to adult plants. The role of OMF in determining orchid distributions, diversification, and community assemblage is still unclear, with more studies necessary, particularly in the tropical epiphytic orchids that represent the majority of the species in the family. In order to mitigate the effects of climate change on orchid species in regions of high diversity such as the tropical andes, we need to understand the structure and dynamics of orchid communities together with the species with which they interact over the range of climatic niches. This study aims to understand the community assemblage and interaction networks between orchids and their mycorrhizal fungi in three orchid communities across an altitudinal gradient in the Western Cordillera of the andes in the Valle del Cauca. We will generate DNa barcoding data to both identify the orchid plants present, and also to determine the phylogenetic diversity of the orchid community. additionally, through direct PCR amplification using fungal specific primers, we will determine the diversity of orchid mycorrhizal fungi associated with each orchid species within and between the communities. Using interaction network analyses, we will determine the structure and dynamics of the orchid mycorrhizal interaction networks across the altitudinal gradient. Finally, through the implementation of a co-phylogenetic test we will explore the congruence between the phylogenetic trees of orchids and OMF to determine the evolutionary factors governing the structure and function of this mutualistic relationship across an andean altitudinal gradient. This knowledge is essential in order to develop conservation management plans for these priority plant species that promote community resilience in the face of climate change.