By Edwin B. Smith
University of Mississippi
A University of Mississippi professor’s comparisons between two lineages of Galapagos tortoises provide new insights into the evolution of the former species and open new doors for biologists to study evolution.
Ryan C. Garrick, associate professor of biology, co-authored a paper on “A New Lineage of Galapagos Giant Tortoises Identified from Museum Samples,” which appears in the February issue of the peer-reviewed journal Heredity.
“This work used ancient DNA techniques, in which the bones of turtles that died over 100 years ago were used to characterize the genetic makeup of the population that previously existed on one of the islands, San Cristobal “, said Garrick. “This was coupled with sampling and DNA sequencing of the turtle population that lives on this same island today.”
When historical and contemporary gene pools were compared, researchers found that they were vastly different from each other. Almost all of the historical samples belonged to a lineage of turtles distinct from all the others that exist on the many islands of the archipelago.
Moreover, there is evidence that the two lineages co-existed. Indeed, one of the historical samples – collected alive in 1906, during an expedition led by the California Academy of Sciences – was genetically similar to the turtle population that inhabits San Cristobal Island today.
“This work shows that the evolutionary history of an iconic group like the Galapagos giant tortoises is complex, such that some surprises have yet to be discovered despite all years of intensive study,” Garrick said. “Simple explanations often don’t hold water.”
For example, when the historical line died out, the island should have later been colonized by what we call the contemporary line, he said. Instead, the two lineages co-existed and likely competed for limited resources.
“Obviously there was only one winner,” Garrick said.
Equally important, Garrick’s work highlights the value of museum collections.
“DNA from the bones of long-dead turtles served as a critical window into the past, allowing comparison with the present,” he said. “Natural history collections, such as those that preserve animal and/or plant tissue for future use by researchers, are often undervalued.
“We have shown here that without these scientific expeditions which today seek to collect and document biodiversity, tomorrow’s research would suffer.”
Understanding the evolutionary history of giant tortoises on San Cristobal Island may hold further clues to reconstructing the history of tortoises across the Galapagos Archipelago. Additionally, the recognition of an additional lineage of giant tortoises on San Cristobal Island may have implications for taxonomy, the field of biological research concerned with species description and naming.
“We are continuing these two lines of research by collecting and analyzing additional data,” Garrick said.
Garrick’s research promises to reveal even more information, said Brice Noonan, UM’s interim president and associate professor of biology.
“Dr. Garrick’s work on one of the most fascinating species of the Galapagos, a region inextricably linked to biological evolution in the minds of not only scientists but the general public, continues to reveal surprising facets of a complex evolutionary history,” says Noonan. “This research group has greatly improved our understanding of Galapagos biota, and I look forward to seeing what this group will reveal next.”
The biologist collaborated as part of an international research team on the discovery of a new species of giant Galapagos tortoise, findings which were included in the October 2, 2015 issue of PLoS ONE, a peer-reviewed journal published by the Public Library of Science. Working within a group led by Yale University, Garrick used genetic data to help uncover the existence of the new species on Santa Cruz Island in the Galapagos.
Garrick was also the author of related articles previously published in the journals Scientific Reports, Ecology and Evolution, and Molecular Ecology.
A member of the Ole Miss faculty since 2012, Garrick received his bachelor’s and doctorate degrees from La Trobe University in Australia. He was previously a postdoctoral fellow at Virginia Commonwealth University and Yale University.
His research interests are insect evolution, molecular ecology, biogeography, population genetics and conservation biology.