98 Phylodiversity of green algae (chlorophyta) from desert microbiotic crusts

Abstract

Deserts are not thought of as biodiversity hotspots, but desert microbiotic crust communities represent a largely unknown community type rich in diversity of eukaryotic and prokaryotic taxa. These ecologically important communities have received much attention because of their role in nutrient cycling and soil stabilization in deserts, but they defy characterization by the traditional approach to assessing biodiversity by counting species. While genetically diverse, taxa characteristic of desert crusts are difficult to identify to the species level due to convergent evolution toward simple morphologies, phenotypic plasticity, or poor knowledge about particular lineages. Focusing on the green algae, we show that while biodiversity is difficult to measure in these communities, phylodiversity provides a surrogate measure that more accurately portrays the diversity of organisms, and one that is standardized across the variety of life histories, reproductive strategies and morphological variability that creates problems with species‐counting measures. Bayesian phylogenetic inference uses MCMC simulation to generate phylogenies sampled in proportion to their Bayesian posterior probability. The length of a segment in any of these trees corresponds to the amount of change in the lineage, measured as the expected number of substitutions/nucleotide site. Comparisons of segment lengths corresponding to desert vs. other green algal lineages provides a means of addressing questions of relative genetic diversity, or phylodiversity, without complications arising from the difficulty of counting species. Our data illustrate the impact of desert green algae to overall knowledge of the green algal phylogenetic tree.