The Charismatic Chuckwalla: Conversation Through Genomics

BY SUSANA RINDERLE

Our desert ecosystems are currently facing unprecedented levels of habitat destruction due to development and climate change." - Alexandra Sumarli

Alexandra Sumarli is on a mission to influence conservation strategies through hard science. "Our desert ecosystems are currently facing unprecedented levels of habitat destruction due to development and climate change," she says. "In order to protect [desert species], we need to understand their basic biology. This includes understanding the evolutionary history of species and their population genetic structure. By doing this, we can prioritize protecting genetically distinct and vulnerable populations or species."

A PhD. student in ecology, evolution, and organismal biology at the University of California at Riverside, Alex is doing her part by revealing the evolutionary history of a widespread and charismatic lizard using genomic methods. That lizard, the common chuckwalla (Sauromalus ater), occupies the arid lands of southwestern North America and contains significant morphological variation in body size and color pattern. It is one of five species of Sauromalus. The other species are S. varius, S. hispidus, S. klauberi, and S. slevini, which are endemic to islands in the Gulf of California.

To conduct their research, Alex and her colleagues acquired tissue samples for DNA extractions from across the range of S. ater. These tissues were obtained from existing museum collections and through their own fieldwork in the southwestern USA and northern Mexico, including Borrego Springs and near Anza-Borrego Desert State Park. Next, they generated genomic sequence data using a library preparation technique called double-digest Restriction-Associated DNA sequencing (ddRADseq). Once they obtained and processed the genomic sequences, they looked for differences and similarities across populations of chuckwallas using population genomic methods. Finally, they inferred evolutionary relationships within the chuckwallas by building “phylogenetic trees,” which show evolutionary history and relationships over deep time.

Their findings strongly suggest that the common chuckwalla (S. ater) is comprised of two major evolutionary lineages: a continental group found mostly in North America (California, Nevada, Arizona, Utah, and Sonora) and a peninsular group found exclusively in the Baja California Peninsula. These species diversified in northeastern Baja California in the early Pliocene to late Miocene (approximately 5-6 mya) during the formation of the Gulf of California. There also appears to be additional biodiversity within both continental and peninsular lineages of S. ater. This suggests there may be other genetically distinct populations within these lineages that require further study.

“These findings highlight that our southwestern deserts harbor significant biodiversity, and that we need descriptive studies of this nature to understand how species diversify and persist over time,” says Sumarli. To that end, she’d like to collect more samples from the contact zone in northern Baja California where peninsular and continental S. ater meet to determine if there is ongoing gene flow.

Alex presented her research at the and at the “Anza-Borrego: In Focus” lecture series last April, highlighting the ways the biogeographic history of the Gulf of California influences the diversity of reptiles and amphibians in southwestern deserts. Her work was recently accepted for publication at The Biological Journal of the Linnean Society.

If you would like to reach Alex, please contact her at asuma001@ucr.edu.

- Alexandra Sumarli

- Alexandra Sumarli