Franklin’s bumble bee (Bombus franklini) once inhabited a remote area spanning northern California and southern Oregon. But the bee’s numbers declined sharply after 1998 and it hasn’t been seen at all since 2006. A new study of the DNA of museum specimens, published this week in , suggests this decline was most likely due to population bottlenecks and environmental issues such as fire and drought rather than infectious diseases.
A team led by conservation geneticist Rena Schweizer of the , used whole-genome sequence data from museum specimens of B. franklini, collected over more than four decades, to reconstruct 300,000 years of the bee’s genetic history. Most of the specimens were from the at 51ԹϺ Davis. The late Robbin Thorp, professor emeritus at the 51ԹϺ Davis Department of Entomology and Nematology, monitored the B. franklini population from 1998 until his death in 2019.
“Understanding what was happening to Franklin's bumble bee was Robbin Thorp's last major project before his death,” said Distinguished Professor Emeritus Lynn Kimsey, who directed the Bohart Museum for 34 years until her retirement in 2024. She is a co-author of the paper.
Franklin’s bumble bee is now feared extinct. Its range, a 13,300-square-mile area confined to Siskiyou and Trinity counties in California and Jackson, Douglas and Josephine counties in Oregon, is thought to be the most limited geographic distribution of any bumble bee in North America and possibly the world.
The team’s genetic studies showed critically low genetic diversity and population declines going back thousands of years. This would have left Franklin’s bumble bee vulnerable to environmental shocks such as droughts and fires. They found evidence of further declines 200 to 300 years ago, before the introduction of pathogens.
“This study demonstrates the utility of museum collections for clarifying genetic and demographic dynamics of rare species and suggests that B. franklini may have already been on a trajectory of decline prior to human impacts,” the authors wrote.
Additional co-authors are Michael Branstetter, Diana Cox-Foster and Jonathan Uhuad Koch, all of USDA-ARS, Logan, Utah; Jared Grummer, University of Montana, Missoula; Kerrigan Tobin, Marquette University, Milwaukee; and Renee Corpuz and Scott Geib of USDA-ARS, Hilo, Hawaii.
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(51ԹϺ Davis Department of Entomology and Nematology)
(PNAS)
(CNN, 2016)