Collaborative Research: Testing Hypotheses about Rates of Diversification & Controls on Diversification related to the Opportunities for Speciation vs Fate of Incipient Diverge

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All of combined planetary biodiversity owes its existence to the formation of new species. It is the newly formed boundaries separating one group of individuals from others that maintain the distinct and unique characteristics of individuals in each species. New species can form quickly or slowly. Depending upon this pace of species formation (i.e., the rate of diversification), the numbers of species within a group will differ. However, the diversification rate itself is not sufficient to understand why species diversity varies because there are multiple potential explanations for any estimated diversification rate. This research project will focus on statistically distinguishing among these different explanations in order to understand why species diversity differs across space, time, and among different groups of organisms. Specifically, by applying newly developed statistical models of species formation to genomic sequences from individuals collected across multiple populations within each of several hundred species, the research will distinguish between various potential controls on diversification. These alternative controls have never previously been tested within a single study. As such, the research will provide unprecedented insights into how the frequency of formation and persistence of isolated populations (and hence, the opportunities for new species to form) affects diversification rates. The targeted study group (North American Melanoplinae grasshoppers) includes representatives that span the climatic, geographic, and ecological conditions theorized to affect species formation, which will provide robust tests of how biodiversity is shaped. By illustrating the utility of population-level sampling within species in tests of species formation, the project will set a new benchmark for other researchers to consider for their own biodiversity studies. Such research is important to avoid misinterpretations about why biodiversity differs across geographic regions, or among habitats, or among groups of organisms that co-occur. The research will also highlight the importance of museum collections for genomic-era biodiversity studies, while enhancing this publicly accessible community resource through the addition of newly collected and curated specimens, including their DNA, ecological and geographic information. A complementary program of public and educational outreach activities built around the core research objective of why diversification might be promoted (or inhibited) across different landscapes or organismal groups will reach a diverse audience.Diversity differences observed across taxonomic groups reflect different rates of diversification. However, there are two fundamentally different controls on diversification dynamics (meaning there are different explanations for any given diversification rate): the evolution of reproductive isolation that affects the fate of incipient divergences versus the frequency with which isolated populations form and persist affecting the opportunities for speciation. Because diversification studies are typically carried out on phylogenetic estimates of species lineages, it has not been possible to test hypotheses about the opportunities for speciation. This research addresses this knowledge gap. Through combined theoretical and empirical studies and the generation of large-scale genomic data, the research will apply newly developed analytical methods to test hypotheses about diversification rates (based on phylogenetic estimates of species lineages) vs. the controls on diversification dynamics (based on phylogenetic estimates of species and population lineages). By testing for linkages between different controls on diversification dynamics with factors potentially affecting the formation of new species (e.g., fragmented habitats, topographically complex landscapes, or periods of climatic change, and species-specific traits), the work will address why these conditions might promote or inhibit the formation of new species. This will be the first study to establish potential linkages between the various controls on diversity dynamics (e.g., topographic complexity, geologic and climatic events, and selectively driven divergence). Leveraging the researchers’ extensive specimen collections with advances in collecting large-scale genomic data across hundreds of thousands of individuals and state-of-the-art analytics, the empirical dataset will contain almost complete taxonomic coverage of over 600 closely related grasshopper species (355 of which are from a single genus) that radiated recently (i.e., within the Pleistocene and Pliocene) in North America and Mexico. By combining the skillsets of researchers with taxonomic expertise and genomic and quantitative analytics, the research team will promote broad training and mentoring of graduate students, while also offering public and educational outreach activities developed by researchers with different backgrounds to reach diverse audiences and underserved communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.