Why do some taxa have more species than others? One hypothesis to explain this phenomenon is “evolvability”: lineages with an intrinsic ability to evolve novel morphologies also have an increased ability to speciate. Several key predictions can be made based on differential evolvability across clades. More evolvable lineages should have higher richness and diversification rates, and have more phenotypic disparity and rates of phenotypic evolution. Lineages that enjoy fast phenotypic evolution should also diversify into a larger variety of ecological niches. Finally, key innovations leading to adaptive radiations may actually be traits that also promote evolvability through an increase in morphological and functional diversity.
My dissertation tests these macroevolutionary predictions within the ray-finned fishes (Actinopterygii), which comprise about half of vertebrate diversity, with over 30,000 described species across nearly 500 families. Fishes are an excellent study system due to their high species richness as well as exceptional phenotypic and ecological diversity, which are distributed unevenly across the fish tree of life. Fishes are also intensively harvested for human consumption, leading to potentially disastrous impacts on their diversity and their ability to serve as ecological role players and as a human food source.
My dissertation aims to answer questions in three general areas:
What processes drive the rate of lineage origination and the rate of phenotypic (body shape) evolution? Is there a correlation between speciation rates and rates of character evolution? Are certain environments (e.g., coral reefs) associated with increased rates of phenotypic evolution? How have mass extinction events (e.g., the Cretaceous-Paleogene) altered the trajectory of fish morphological evolution?
Rabosky DL, Santini F, Eastman J, Smith SA, Sidlauskas B, Chang J, Alfaro ME. (2013). Rates of speciation and morphological evolution are correlated across the largest vertebrate radiation. Nature Communications 4:1958. doi:10.1038/ncomms2958
Rabosky DL, Mitchell JS, Chang J. (2017). Is BAMM flawed? Theoretical and practical concerns in the analysis of multi-rate diversification models. Systematic Biology doi:10.1093/sysbio/syx037
How pervasive is commercial exploitation of fishes across phenotypes? Are there fish with certain body shapes that are disproportionately exploited? What is the association between exploitation, body shape, and environment?
How can researchers overcome general problems in high-throughput collection and analysis of phenotypic data?
Chang J, Alfaro ME. (2016). Crowdsourced geometric morphometrics enable rapid large-scale collection and analysis of phenotypic data. Methods in Ecology and Evolution 7(4):472–482. doi:10.1111/2041-210X.12508