In the midst of global climate change, it is crucial to understand the spatial patterns of biodiversity and its underlying ecological and evolutionary mechanisms, including neglected groups in the tree of life such as bryophytes (liverworts, mosses, and hornworts). These lineages share some important characters with tracheophytes (e.g., embryonic development and elaboration of the sporophyte generation), but also, they have retained characters from their freshwater algal ancestors (e.g., desiccation tolerance, poikilohydry, and dominant gametophyte). Because of their unique biology, they are ideally suited for addressing questions in evolutionary biology, functional morphology, and biodiversity.
This Dissertation consists of three independent but interconnected topics using mosses as a study system. In Chapter 1, I aim to understand the patterns of diversity and community structure of mosses along elevation and moisture gradients in Central Chile. Chapter 2 addresses the evolutionary history of the dryland moss Syntrichia Brid. Chapter 3 focuses on functional morphology in relation to external water-conduction in Syntrichia.
The goal of Chapter 1 was to investigate the diversity of mosses along an elevational gradient in Central Chile. I used phylogenetic approaches (phylogenetic diversity, relative phylogenetic diversity, and phylogenetic turnover) to measure the diversity and community structure of 25 sites along an elevation gradient in Central Chile. To understand the composition of moss communities according to soil moisture, each site was subdivided into three subsites arranged perpendicularly to a water source (e.g., creek) ranging from completely dry to fully moist. The phylogenetic pattern suggested that environmental filtering was responsible for the co-occurrence of closely related taxa at low and high elevations, and that competition had a minimal effect on community assembly. Phylogenetic turnover revealed changes in community composition along elevation and soil moisture.
In Chapter 2, I aimed to investigate the evolutionary, biogeographic history, and trait evolution of Syntrichia, through the most comprehensive phylogenetic analysis performed up-to-date. A combined phylogeny based on a hundred nuclear loci plus a robust morphological matrix suggested that Syntrichia is monophyletic with 10 major subclades. It is very likely Syntrichia originated in South America in the early Eocene and dispersed to other landmasses via dispersal. The genus experienced major diversification events in South America and Northern Hemisphere, the areas with the current greatest species diversity. Habitat preferences (e.g., soil, rocks, and trees) might be associated with evolutionary changes in water-related traits.
Chapter 3 explored how the moss Syntrichia absorbs, conducts, and retains water externally, a process known as ectohydry. I used a diverse range of microscopic techniques for observing anatomy as well as experimental approaches to understand the rate of conduction and dehydration. I propose a new framework for studying ectohydric capabilities that include three spatial scales (cell anatomy, stem architecture, and whole clump) and timing to become fully hydrated. There was a trade-off between speed of conduction and holding capacity that could be associated with the life history of each species.
This dissertation is a contribution to the understanding of several fundamental questions in the biology of mosses. This work will provide the basis for future research in the field of evolution, ecology, and functional morphology.
