CEB Committe on Evolutionary Biology

Spotlight : Tim Sosa

Tim Sosa

Tim carrying a bucket of fish out of a creek bed in Sacatepequez, Guatemala. 

I study how freshwater animals invade new territories over time. I use DNA to reconstruct their ancestry (molecular phylogenetics), and with knowledge of their ancestry, I try to identify routes of colonization (phylogeography), timing of colonization events (historical biogeography), and trends in morphological evolution (geometric morphometrics). Right now I'm working with a group of freshwater fishes called Characiformes, which includes some familiar fish like neon tetras, freshwater hatchetfishes, and piranhas. Altogether, there are around 1,700 known species, mostly in South America and Africa. However, several lineages invaded North America 3-7 million years ago, after Panama joined North and South America together after a long separation dating back to the Jurassic period. The colonization of North America by tetras was part of a major event called the Great American Interchange, which also gave North America opossums, porcupines, and armadillos, and gave South America camels, deer, and foxes.

Since the Characiformes arrived in North America, they have expanded their range as far north as Texas, and have diversified into perhaps 50 species adapted to a variety of environments. I am using their ancestry, coupled with distribution, to find out 1) how geology and climate affects their ability to spread; 2) how environmental and biotic factors affect their morphological evolution; and 3) where we might expect them to spread, or die out, in the future as we continue to alter global climate. To this end, I sequence DNA (to reconstruct their ancestry), take many morphological measurements (to quantify body shape), and aggregate ecological data from throughout the Americas (to connect both of the preceding to environment). I have conducted fieldwork for this project in Guatemala, and for other projects in various parts of the US, and this fall I will be in the field again (stay tuned for details!). I conduct genetic research and most morphological research at Chicago's Field Museum, although I have benefited from collaborators and resources at a variety of other institutions. Most of all, I benefit from a rich variety of thinkers and researchers, both faculty and students, at the University of Chicago. Thanks for reading, and please don't hesitate to email me with questions, ideas, or proposed collaborations.