DISSERTATION RESEARCH: Morphological Diversification of Anostomimorph and Curimatimorph Fishes

University Of Chicago, Chicago IL

Investigators

Abstract

Non-technical abstract: Dissertation Research: Morphological diversification of anostomimorph and curimatimorph fishes. Why is biodiversity distributed unequally across the tree-of-life? Some groups of species have evolved extraordinary anatomical variation while other groups contain many species that look and act similar. To begin to understand how and why the general phenomenon of unequal diversification occurs, this research will investigate how and why a specific lineage of South American fishes related to piranhas and tetras evolved an anatomical diversity very much greater than that of the lineage of its closest relatives. This case study is rare and valuable because it approximates a naturally controlled experiment. Because the two groups of fishes contain equal numbers of species, share a recent common ancestor (and therefore began to evolve independently at the same time) and live together throughout tropical South America, the differences in their diversities cannot be explained by differences in net speciation rate, age, or environmental effects. The removal of these factors leaves at least two potential explanations of the observed differences in diversity. The differences may be due to random evolution, or an intrinsic feature of anatomy or ecology shared only by the more diverse group may promote the evolution of new morphologies. This research program will investigate these two alternatives by 1) using a detailed anatomical study to reconstruct the genealogical relationships, or "trees-of-life" for these fishes, 2) measuring the anatomical differences between these species from an extensive series of x-ray images and 3) performing a novel analysis that combines the measurements of anatomical differences and trees-of-life with computer simulations of evolution. This analysis will test whether diversities as different as those observed could have evolved randomly. If the analysis were to reject the hypothesis of random evolution, then it would be likely that an intrinsic difference drove one group to diversify greatly while the other did not. If the second alternative is supported, this project will identify the anatomical and ecological features most likely to have catalyzed the evolution of novelties in the more diverse group. Future studies can then test whether the evolution of similar properties in other groups of organisms generally promotes the genesis and maintenance of biodiversity. In a broad sense, this study will help reveal why biodiversity is not distributed equally across the tree-of-life for all organisms. The methods developed for use in this project are transferable to studies of a wide variety of other organisms and will be made freely available via the Internet. This project will also promote international collaboration on the study of an important group of tropical fishes valued as food throughout South America, prized for their ornamental beauty worldwide and that serve important ecological roles as part of the most species-rich freshwater fish fauna in the world. Current and potential collaborations include work on the discovery and description of new species, the building of natural history collections in the United States and in South America, and conservation biology. Results from this work also fuel a continuing dialogue about biodiversity with students and museum visitors through a series of exhibits and public presentations.