Spiny-rayed fishes are one of the most successful radiations of vertebrate animals, with about 17,000 species and astonishing morphological and ecological diversity that includes many culturally and economically important species such as tunas, flounders, seahorses, largemouth bass, and guppies. This diverse group represents one of the last great frontiers to understand vertebrate evolution. In this project, the evolutionary relationships among more than 260 families of these fishes will be studied with several methods of phylogenetic inference using DNA sequence data from 16 protein-coding nuclear genes from specimens of 1,500 species. The phylogenetic trees depicting evolutionary relationships among these groups will be combined with more than 40 fossil calibration points to produce a time-calibrated branching diagram of the evolutionary history of these fishes. This time-calibrated phylogeny and a large anatomical data set of functionally important characteristics of the feeding and locomotor systems from over 1,000 species will then be used to compare the rates of speciation and rates of morphological evolution in lineages that live in the five major habitat types: coral reefs, temperate reefs, near-shore soft bottom, pelagic marine, and freshwater. There is a strong theoretical expectation from previous work that freshwater lineages will show high rates of speciation while coral reefs will show the highest rates of speciation and morphological evolution, but these expectations have never been addressed empirically.
This research will strengthen our understanding of the evolutionary relationships and major evolutionary dynamics of the most poorly understood and yet dauntingly successful radiation of vertebrate animals on the earth today. Over 20,000 new gene sequences and the morphological data set from over 1,000 species will be made available to the scientific community. The project will support the development of three postdoctoral scholars and has a major undergraduate training program.
The researchers involved in the Causes and Consequences of Diversification in Spiny-Rayed Fishes grant helped generate the first explicit evolutionary tree for what was the largest unresolved group of all vertebrates, placed that evolution in a temporal context, and explored the diversification and macroevolution of this important group of fishes and its constituents. To explore the timing and diversification of the spiny-rayed fish radiation and its major groups, these researchers placed 45 fossil fishes into a proper phylogenetic context to allow for time-calibrating the spiny-rayed fish tree of life. Using fossil-calibrated evolutionary hypotheses, the researchers identified 14 major radiations and identified four groups of marine fishes (coral-reef blennies and gobies, deep-sea snailfishes, and open-ocean tunas) and freshwater cichlids that have significantly higher rates of speciation compared to other spiny-rayed fish groups. Further investigations of these coral-reef fishes and cichlids showed that the major radiations evolved before the K/T boundary, but that the major shifts in their speciation and diversification occurred after this mass extinction event. In addition to these broad-scale evolutionary scenarios, specific new hypotheses regarding the repeated evolution of morphological or physiological specializations were explored using the new hypotheses of relationships. These studies have explored the impact of bioluminescence, biofluorescence, salt tolerance, venom, and pharyngognathy. In the case of pharyngognathy (primarily chewing and grinding with the pharyngeal or jaw teeth), this specialization evolved approximately seven times in spiny-rayed fishes, often in diverse groups such as the cichlids. Similarly, bioluminescence and bioflourescence, in combination, were shown to have evolved more than 50 times in ray-finned fishes. This research further indicated that the features of these species-specific luminescent systems often vary in color and/or shape between genders and, therefore, may be important in reproductive isolation and diversification in spiny-rayed fishes and their close allies. Exploring evolutionary scenarios across spiny-rayed fishes was simply not possible prior to this funded research project. The Field Museum component of this research project supported the training of three undergraduate students (two graduating and entering doctoral programs in ecology and evolutionary biology), three graduate students, and one postdoctoral fellow (recently hired into a tenure-track biology faculty position). Beyond this hands-on training of seven young scientists and a medical doctor, this research was broadly disseminated to the general public. The revised spiny-rayed fish tree of life and studies of fish bioluminescence and biofluorescence were utilized in the Creatures of Light exhibit and associated lectures at The Field Museum that were viewed by more than 500,000 visitors in Chicago, premiered at the American Museum of Natural History, and is now at the Canadian Museum of Nature. This scientific research played an important role in Field Museum donor and member events as well as the 26 episodes of the "What the Fish?" podcast series that was downloaded more than 82,500 times. The resulting work from The Field Museum was published in more than 16 publications that were picked up by the popular press including articles in venues ranging from CNN to Natural History magazine to The Los Angeles Times to Slate to e! Science News to The New York Times.
