Marc Tollis

Postdoctoral Research Scholar
Biodesign Institute
Arizona State University

I am an evolutionary biologist using statistical genetics, bioinformatics and field work to investigate:

Evolution of Cancer Suppression across Mammals
Large mammals such as elephants and whales have thousands of times more cells and live as long or longer than humans, yet do not get cancer at the same rate as humans. This observation is called Peto's Paradox, and suggests that elephants and whales have adapted to suppress cancer during their evolution (Tollis et al. 2017). We will be investigating the molecular evolution of tumor suppressor genes, proto-oncogenes, and regulatory regions in the genomes of African and Asian elephants (Loxodonta africana and Elephas maximus) as well as available whale genomes to understand how these species are able to avoid cancer. We are also sequencing and assembling the complete genome of the humpback whale (Megaptera novaeangliae) for this effort. We hope to uncover nature's toolbox and utilize the shared genetic code of all mammals to illuminate potential avenues for human cancer prevention.

Comparative Genomics of Reptiles
Only recently has the NGS era for vertebrates began to focus on the scaly side of the Tree of Life, and many questions about the evolution of reptiles can now be answered. I am involved in several reptile genome projects, including three anole lizards and the Mojave desert tortoise (Gopherus agassizii) (Edwards, Tollis et al. 2016). I am also generating the transcriptomic resource that will be used to understand the developmental responses of ectotherms to global climate change, using the eastern fence lizard (Sceloporus undulatus) as a model.

Phylogenetics and Historical Biogeography
I have always had a profound interest in the history of life on Earth, and have been involved in many projects that have used genetic data to model ancient patterns of dispersal, gene flow, and population divergence. I published the first molecular phylogeographic study of the genomic model organism Anolis carolinensis (Tollis et al. 2012; Tollis and Boissinot 2014; Manthey, Tollis et al. 2016). I also have contributed to the discovery of several cryptic frog species endemic to the Ethiopian highlands (Freilich et al. 2014), and have used the diversification of baboons in Africa as a comparative model to the history of our own species on that continent
(Boissinot et al. 2014).

Genomic Mechanisms of an Adaptive Radiation
Lizards in the genus Anolis are a prime example of terrestrial adaptive radiation. By comparing complete genomes, I am investigating the acceleration of natural selection that has occurred as a response to ecological opportunity and resulted in morphological diversification. We have also been testing for positive selection on genes that drive the development of ecologically important traits, such as limbs. This research will lay the groundwork for studies that will eventually test whether the deterministic nature of convergent morphological evolution has been governed by similar genomic mechanisms.

The Evolution of Transposable Elements
I am very interested in understanding the interaction between a host genome and its incipient genomic elements, and how this interplay affects the structure of the genome. In my doctoral work I used a population genetic framework to demonstrate that the fate of transposons in a vertebrate genome is affected by the demographic history of the host and depends on a balance between natural selection and genetic drift (Tollis and Boissinot 2011; Tollis and Boissinot 2013). I have also been comparing whole genomes of reptiles to understand lineage-specific patterns of transposable element diversity and abundance, and my goal is to relate these patterns to either the phenotypic diversity or rate of molecular evolution within each lineage.