UC Santa Barbara

Convergent evolution, the phylogenetically independent evolution of similar traits, offers a valuable avenue for investigating how complex traits originate and the predictability of evolution. Bioluminescence, the biological production of light by a living organism, is an excellent system for addressing these questions. Bioluminescence convergently evolved over 94 times, is morphologically and functionally diverse, and is encoded by many genes that can be functionally tested in the laboratory. In this dissertation, I begin by proposing an integrative approach to studying the convergent evolution of complex traits, focusing particularly on bioluminescence. Then, I provide evidence for the genetic basis of various biochemical mechanisms underlying three different bioluminescence systems. First, I identify a gene that may be used to modulate the availability of the bioluminescent substrate in an ostracod crustacean. I synthesize this result with previous studies on fireflies and sea pansies to show that these three distantly related taxa independently recruited members of an ancient gene family to modulate their bioluminescent substrates. Second, I identify a gene encoding a structural protein in the lens of light-producing organs in toadfishes. This gene may have originated in fish genomes via an ancient horizontal gene transfer from bacteria. After being maintained in fish genomes for over 300 million years, this gene was recruited to produce the lens of light-producing organs in toadfishes. Finally, I identify the gene encoding a bioluminescent protein in brittle stars. I provide functional evidence supporting the repeated evolution of bioluminescent proteins from the haloalkane dehalogenase gene family, which may have originated in metazoans from a horizontal gene transfer from bacteria. Altogether, my work illustrates how evolutionary convergence may recruit homologous and non-homologous genes, depending on the convergent function or structure, and highlights how ancient horizontal gene transfers may have long-term evolutionary implications for evolving novel structures and functions.