- Author: Kathy Keatley Garvey
if you hike a short distance up a meandering trail, you'll see a landscape of turrets, the work of solitary, ground-nesting digger bees, Anthophora bomboides standfordina.
The nests remind us tiny sandcastles. The female bees did that!
In the early spring you'll see the bees nectaring on wild radish and other flowers.
These digger bees are found along the sandy cliffs of beaches along the Pacific Coast, not just Bodega Head. They're sometimes called the “Stanford bumble bee digger” because its subspecies name, “stanfordiana,” refers to a 1904 Stanford University collection.
They are bumble bee mimics; they mimic the yellow-faced bumble bee, Bombus vosnesenskii.
It was Robbin Thorp (1933-2019), distinguished emeritus professor, UC Davis Department of Entomology and Nematology (ENT), who alerted us to them. He studied them at the Bodega Marine Reserve and loved to share his research.
So, on every trip to the Bodega Head, we scramble up the trail to see what the bees are doing. Of course, when they're overwintering, we don't see them at all, just the turrets.
Fast forward to today. On the ENT website, we posted a research story today that began 'Microbes found in the immature stages of a solitary bee that nests in sand cliffs along Pacific Coast beaches may be helping the bee defend itself from pathogens and protect it from cold stress, according to newly published research led by microbiologist Shawn Christensen of the Rachel Vannette Lab, UC Davis Department of Entomology and Nematology."
The research publication, “Symbiotic Bacteria and Fungi Proliferate in Diapause and May Enhance Overwintering Survival in a Solitary Bee,” appears in the current issue of the journal, International Society for Microbial Ecology (ISME), and is posted on the National Library of Science website.
“Contrary to what has previously been assumed and found in other systems, we found that dormant--also called diapausing--bees have more abundant symbiotic bacteria and fungi,” said Christensen, a doctoral candidate and the 2024 recipient of the Merton Love Ecology and Dissertation Award, an annual award that celebrates the university's most outstanding doctoral dissertation in the fields of ecology and evolutionary biology. He's scheduled to receive his doctorate this month.
The six-member research team, including colleagues from Cornell University, UC Riverside and the University of Arizona, also found “that the microbiome of this solitary bee is very consistent--the same taxa appear in most brood cells, in similar proportions,” said Christensen. “This is uncommon in solitary species, which normally have variable microbiomes due to lack of social transmission. We are still exploring this unique aspect!”
Vannette, associate professor and vice chair of the department and an international leader in microbial ecology, researches interactions between plants, insects and microbes. She is a principal investigator of a National Science Foundation grant that funded the project.
“Previous work on bee-microbe interactions has shown how gut bacteria benefit honey bees and other corbiculate social bees but these microbes are limited to social bees,” Vannette told us. “We wondered if solitary bees also associate with beneficial microbes and uncovered this previously undescribed partnership between bees, fungi and bacteria. This study opens up new questions in bee ecology and host-microbe interactions: how do solitary bees maintain specific associations with bacteria and fungi? What chemistry are Streptomyces using to suppress fungi? Does this association benefit bees? We think it is likely but ongoing work will examine these questions.”
“We are also thrilled to find this unique symbiosis in a bee species that has been well-studied by previous faculty at UC Davis, including RobbinThorp,” Vannette said. “UC Davis nematologist Harry Kaya, with graduate student Robin Giblin, also described Bursaphelenchus seani, a nematode that inhabits Anthophora bomboides. Our lab is also investigating links between the brood cell microbiome and the nematodes in this bee species.”
Other co-authors of the paper are
- Quinn McFrederick, assistant professor at UC Riverside who studies symbionts (pathogens, commensals, and mutualists) of wild and solitary bees
- Bryan Danforth, professor at Cornell University, who specializes in bee systematics and evolution
- Stephen Buchmann, pollination ecologist affiliated with the Departments of Entomology and of Ecology and Evolutionary Biology at the University of Arizona
- Sriram Srinivas, then a UC Davis undergraduate researcher in the Vannette lab
Check out Thorp's presentation on digger bees that he delivered at the “Proceedings of the Symposium on Biodiversity of Northwestern California” in October, 1991, in Santa Rosa.
Also check out the wonderfully done PBS Deep Look Video, This Bee Builds Sandcastles at the Beach.
Let's dig the digger bees.
![A digger bee, Anthophora bomboides standfordina, heading to her nest at Bodega Head. Note the ant. (Photo by Kathy Keatley Garvey) A digger bee, Anthophora bomboides standfordina, heading to her nest at Bodega Head. Note the ant. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/107454.jpg)
![At Bodega Head you can see turrets made by solitary, ground-nesting digger bees, Anthophora bomboides standfordina. (Photo by Kathy Keatley Garvey) At Bodega Head you can see turrets made by solitary, ground-nesting digger bees, Anthophora bomboides standfordina. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/107455.jpg)
![A digger bee, Anthophora bomboides standfordina, nectaring on wild radish. (Photo by Kathy Keatley Garvey) A digger bee, Anthophora bomboides standfordina, nectaring on wild radish. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/107456.jpg)
![Here I am! Anthophora bomboides standfordina, at Bodega Head, Sonoma County. (Photo by Kathy Keatley Garvey) Here I am! Anthophora bomboides standfordina, at Bodega Head, Sonoma County. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/107459.jpg)
- Author: Kathy Keatley Garvey
A member of the Microbiology Graduate Group and the laboratory of community ecologist Rachel Vannette, associate professor and vice chair of the UC Davis Department of Entomology andNematology, he will deliver the Merton Love seminar from 3 to 4:30 p.m., Friday, May 24 in Room 1230 of Walker Hall. The Zoom link:
https://ucdavis.zoom.us/j/99429777483.
The award memorializes Robert Merton Love (1909-1994), emeritus professor of agronomy and range science, who served on the UC Davis faculty from 1940-1976.
“Shawn's thesis work spans microbiology, ecology and evolutionary biology, combined with careful natural history, to document novel species interactions between hosts and microbial communities,” said Vannette, who nominated him for the award. “Each chapter has broad implications for the ecology and evolution of host-microbe interactions. Shawn's work has already reframed the conditions under insect-microbe interactions are thought to hold relevance and evolve. His research has highlighted the utility of natural history observations of microbes and sampling understudied life history stages (overwintering developing insects).”
“Overall, Shawn's dissertation is an example of how detailed observations combined with fearless experimental dissection of interesting phenotypes can yield novel descriptions of species interactions that change the field's perception of when and where microbial communities are important,” she said.
“Shawn's first chapter describes adaptations of a flower specialist bacteria to acquiring resources from pollen—a nutrient source specific to flowers,” Vannette said. “Our lab was interested in the ecology of the flower-dwelling bacteria Acinetobacter, but Shawn took a new look at this bacterium, examining its growth morphology in nectar and in association with pollen. He noticed that this bacterium co-localized with pollen and grew exponentially more in the presence of pollen. To explore this phenotype, he designed new media and assays (microwaving pollen) to determine that Acinetobacter benefits the most from live pollen via stimulating pollen to germinate (within minutes!), then digesting it. Shawn then designed a series of experiments to examine if this ability was unique to this bacterial clade or shared among many floral microbes (it seems to be specific to Acinetobacter).”
“He collected brood cells (nectar and pollen balls along with developing larvae) from these locations at multiple points through bee development and examined not only the bacteria and fungal community composition through insect development, but also examined changes in microbial abundance at each life stage,” Vannette said. “In contrast to my (and the literature's) predictions, Shawn showed that microbial abundance peaks during larval overwintering, when solitary bees and other holometabolous insects are predicted to have voided their microbial gut communities. Instead, healthy A. bomboides hosts the highest abundance of fungi and bacteria during the fall—a wet season where pathogen abundance is also highest.”
Christensen received accolades and widespread media coverage for the first chapter of his dissertation, “Nectar Bacteria Stimulate Pollen Germination and Bursting to Enhance Microbial Fitness,” published in July 2021 in Current Biology. His second thesis chapter on the microbes associated with Anthophora bomboides, has just been accepted for publication by the International Society of Microbial Ecology (ISME).
And more good news: Christensen is a" co-principal investigator on a newly awarded grant by JGI to sequence the genome of the yeast," Vannette said, "and explore its functional potential in renewable energy and is applying to continue to leverage this system's potential in antifungal chemistry and evolution of pathogen defense.”
Every time we see the nests of Anthophora bomboides stanfordiana on the sand cliffs at Bodega Head, we think of the scientists, including Shawn Christensen and Rachel Vannette, who study them. The late Robbin Thorp, UC Davis distinguished emeritus professor, UC Davis Department of Entomology and Nematology, researched them decades ago.
Check out PBS' Deep Look video, "This Bee Builds Sandcastles at the Beach," and you'll never go to Bodega Bay without thinking of these digger bees.
/span>![Close-up of Anthophora bomboides stanfordiana building a nest on the sand cliffs of Bodega Head. This is the solitary bee that UC Davis doctoral candidate Shawn Christensen studies. (Photo by Kathy Keatley Garvey) Close-up of Anthophora bomboides stanfordiana building a nest on the sand cliffs of Bodega Head. This is the solitary bee that UC Davis doctoral candidate Shawn Christensen studies. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/106730.jpg)
![The sand cliffs of Bodega Head are home to digger bees--bumble bee mimics--Anthophora bomboides stanfordiana. (Photo by Kathy Keatley Garvey) The sand cliffs of Bodega Head are home to digger bees--bumble bee mimics--Anthophora bomboides stanfordiana. (Photo by Kathy Keatley Garvey)](/blogs/blogcore/blogfiles/106731.jpg)
- Author: Kathy Keatley Garvey
Congratulations to UC Davis doctoral students Shawn Christensen, Lexie Martin and Iris Quayle!
They each won the President's Prize (first-place) for their graduate student research presentations this week at the Entomological Society of America (ESA) meeting in National Harbor, Md.
That's quite a feat and well-deserved! From bees to beetles...
Shawn and Lexie are members of the lab of associate professor and community ecologist Rachel Vannette, who serves as vice chair of the UC Davis Department of Entomology andNematology. Iris studies with professor and arachnologist Jason Bond, the Evert and Marion Schlinger Endowed Chair in Insect Systematics for the department, and associate dean, College of Agricultural and Environmental Sciences.
Shawn competed in the Plant-Insect Ecosystems (P-IE) Section, Apiculture; Lexie in the P-IE Section, Pollinator Biology; and Iris in Systematics, Evolution, and Biodiversity (SysEB) Section, Biogeography.
Shawn, who has advanced from doctoral student to doctoral candidate, presented his research, titled "Bee Specific! Solitary Bee (Anthophora bomboides) Hosts a Specialized Core Microbiome through Development." Lexie delivered her presentation on "Establishment and Health Impacts of Floral and Intraspecific Microbes in Bees." And Iris? “Colorless but Never Dull: Unraveling Population Genetics and Color Evolution in ‘White' Darkling Beetles (Onymacris).” (See news story)
Iris earlier won first-place for her graduate student presentation at the annual meeting of the Pacific Branch of ESA (PBESA), held in April in Seattle. This was her first-ever presentation at a scientific meeting. “Iris has hit the ground running in all respects," Professor Bond commented at the time. "Winning the student paper award, the first time ever presenting her research, reflects her exceptional capabilities as a scientist and as a future professor and teacher. Iris comes from a non-traditional STEM background and it is exactly those experiences that will continue to contribute to her success as she evolves as a scientist. I predict that this is only a prelude of things to come.”
Iris is focusing her dissertation on the evolutionary relationships and color/trait evolution in Onymacris. Tenebrionidae (darkling beetles) comprise “more than 80 percent of all known beetle species in the Namib desert (Southern Africa) where the genus Onymacris contains a rarity unexpected from aptly named darkling beetles--the presence of several species with striking ‘white' elytra (wing sheaths).” (See news story)
The complete list of student winners--first, second and third places--is posted on the ESA site.
Founded in 1889, ESA is the largest entomological organization in the world. Its more than 7,000 members are affiliated with educational institutions, health agencies, private industry, and government.
![These three UC Davis doctoral students won the President's Prize in their specific categories at the Entomological Society of America meeting in National Harbor, Md. From left are Shawn Christensen, doctoral candidate and Lexie Martin, doctoral student, both of the Rachel Vannette lab; and doctoral student Iris Quayle of the Jason Bond lab. These three UC Davis doctoral students won the President's Prize in their specific categories at the Entomological Society of America meeting in National Harbor, Md. From left are Shawn Christensen, doctoral candidate and Lexie Martin, doctoral student, both of the Rachel Vannette lab; and doctoral student Iris Quayle of the Jason Bond lab.](/blogs/blogcore/blogfiles/103121.jpg)
![UC Davis doctoral student Iris Quayle delivering her presentation at the Entomological Society of America meeting. She won the President's Prize, or first place, in her category. (Photo by Emma Jochim) UC Davis doctoral student Iris Quayle delivering her presentation at the Entomological Society of America meeting. She won the President's Prize, or first place, in her category. (Photo by Emma Jochim)](/blogs/blogcore/blogfiles/103122.jpg)
- Author: Kathy Keatley Garvey
The top honors went to:
- Doctoral candidate Shawn Christensen and doctoral student Alexia "Lexie" Martin, both of the lab of associate professor and community ecologist Rachel Vannette, vice chair of the department; and
- Doctoral student Iris Quayle of the lab of professor and arachnologist Jason Bond, the Evert and Marion Schlinger Endowed Chair and associate dean, College of Agricultural and Environmental Sciences.
Christensen competed in the Plant-Insect Ecosystems (P-IE) Section, Apiculture; Martin in the P-IE Section, Pollinator Biology; and Quayle in the Systematics, Evolution, and Biodiversity (SysEB) Section, Biogeography.
Shawn Christensen. Christensen presented "Bee Specific! Solitary Bee (Anthophora bomboides) Hosts a Specialized Core Microbiome through Development."
His abstract: "Host-microbe interactions are important for the development and fitness of many macroorganisms. While social bees are dependent on a vertically transmitted gut microbiome, solitary bees, which comprise the vast majority of species diversity within bees, lack a specialized gut community. We explored the microbiome associated with the complete life cycle of the ground-nesting polylectic solitary bee Anthophora bomboides standfordiana, including bacterial and fungal composition and abundance. In contrast to expectations, we found that immature stages of this solitary bee maintain a distinct core microbiome consisting of Actinobacteria and one yeast species. Stage-specific shifts in microbial abundance and community composition occur most notably during bee diapause, during which the abundance of bacteria and fungi increased dramatically. We tested two adaptive hypotheses regarding the role of the microbiome in bee ecology. First, isolated brood cell Streptomyces strains were found to inhibit growth of multiple often pathogenic filamentous fungi, suggesting a role in pathogen protection during the long period of diapause. Second, sugar alcohol composition changed in tandem with major changes in microbial abundance suggesting links with bee metabolism or overwintering biology. Our results suggest that this Anthophora species hosts a conserved core microbiome that may provide key fitness advantages through larval development and overwintering. Much work remains to examine the nature of bee-microbiome ecology, but our study reframes the conditions thought to promote the evolution and maintenance of symbiosis."
Co-authors: Rachel Vannette and Sriram Srinivas, UC Davis; Quinn McFrederick, UC Riverside; Bryan Danworth, Cornell University; and Stephen Buchmann, University of Arizona
Her abstract: "Bees interact with and in some cases benefit from a diverse community of microbes, which can be obtained through intraspecific interactions or the environment. Due to differences in sociality, bee species vary in their main route of microbial acquisition and their dependence on microbes. Despite the observation that intraspecific transmission of microbes is imperfect and environmental microbes are nearly ubiquitous in flowers, the potential impacts of intraspecific versus floral microbes on overall pollinator health have not been evaluated. This study uses two model bee species - one social (Bombus impatiens) and one solitary (Osmia lignaria)--to assess the establishment and health impacts of floral and intraspecific microbes. 2x2 factorial experiments were performed on B. impatiens microcolonies and O. lignaria females to selectively introduce intraspecific microbes and/or floral microbes. Survivorship and reproduction were measured to assess bee health and fitness, and DNA extractions and amplicon sequencing were performed on bee guts to evaluate microbial establishment. The results of this study will inform how microbes from different acquisition routes establish in the host, shape the gut microbiome, and affect host health. Since many macroorganisms encounter both intraspecific and environmental microbes, this study provides a framework for similar work in other organisms."
Co-author: Rachel Vannette, UC Davis
Her abstract: "In the Namib Desert, one of the largest and oldest deserts, the genus Onymacris contains a rarity for darkling beetles (Tenebrionidae) – the presence of eight species with striking ‘white' elytra (ranging from stark white to tan/striped). This study seeks to examine the phylogenetic relationships among white Onymacris species to test whether multiple derivations of white elytra is due to convergence or introgression. Population genomic data (3RAD) was generated from all white species of Onymacris with intraspecific sampling for four widespread species (O. marginipennis, O. bicolor, O. candidipennis, O. langi cornelii). Phylogenetic trees were inferred from 995 loci using concatenated and coalescent-based methods. The analyses supported two clades: langi and bicolor each of which contain species with pure white elytra. Variational autoencoder (VAE) clustering analysis shows a pattern of genetically isolated populations (bicolor) and gene flow indicating introgression (langi). These analyses also infer a potential new Angolan species sister to O. marginipennis in need of evaluation. Ancestral character state and biogeographic reconstruction resolve the timing of white species' color expression against the backdrop of sand sea emergence and increased aridity in the Namib, a landscape renown for ‘pocket speciation' and an impressive amount of darkling beetle diversity accounting for nearly 80% of the known endemic beetle fauna. Dynamic coloration provides a fascinating system through which to examine the role of ecological pressures and evolutionary mechanisms but requires a phylogenetic framework to understand organisms' potential adaptations to extreme environments, which is increasingly vital in the face of global trends aridity trends."
Co-authors: Lisa Chamberland, James Starrett and Jason Bond, UC Davis
The full list of student winners--first, second and third places--is here.
Founded in 1889, ESA is the largest entomological organization in the world. Its more than 7,000 members are affiliated with educational institutions, health agencies, private industry, and government.
![President's Prize honors in the ESA graduate student competitions went to (from left) Shawn Christensen and Lexie Martin, both of the Rachel Vannette lab; and Iris Quayle of the Jason Bond lab. President's Prize honors in the ESA graduate student competitions went to (from left) Shawn Christensen and Lexie Martin, both of the Rachel Vannette lab; and Iris Quayle of the Jason Bond lab.](/blogs/blogcore/blogfiles/103100.jpg)
- Author: Kathy Keatley Garvey
So when we viewed KQED's Deep Look video, “This Fly Torpedoes a Bindweed Bee's Nest,” on YouTube at https://youtu.be/gJHCoP4WqMc, we were totally amazed. It's nothing short of spectacular.
The crew filmed the bees in a nesting area outside the UC Davis Stebbins Cold Canyon Reserve, near Winters.
UC Davis scientists Shawn Christensen, a fifth-year doctoral candidate in the laboratory of community ecologist Rachel Vannette, UC Davis Department of Entomology and Nematology, were among those collaborating with the Deep Look production.
“Shawn has done a lot of work on this bee and with Deep Look, and he also leads our lab's work on Anthophora bomboides, a bumble bee mimic, and studies microbial associates of pollen and solitary bees,” said community ecologist and associate professor Rachel Vannette, a Chancellor's Fellow and vice chair of the Department of Entomology and Nematology.
The bees, also known as digger bees or chimney bees, are specialists on bindweed, commonly known as morning glory. “The females use pollen only from one plant species and are active through the late spring and early summer,” said Vannette, an international leader in microbial ecology who studies interactions between plants, insects and microbes.
Native to California, the bindweed turret bees dig underground nests, many with structures called turrets at the nest entrance. They provision the nests with pollen for their future offspring, and then lay their eggs inside.
Quirós also consulted with seven other scientists: Stephen Buchmann, University of Arizona; Andy Calderwood, Ventura County Deputy Agricultural Commissioner; Neal Evenhuis, Bishop Museum of Honolulu, Hawaii; Paul Havemann, UC Davis Natural Reserve System; Keng-Lou James Hung, University of Oklahoma; Doug Yanega, UC Riverside, and James Carey, a naturalist who researches and videos bindweed turret bees in the Santa Monica Mountains National Recreational Area.
Josh Cassidy, the lead producer and cinematographer, filmed all the footage except for the male bees fighting with each other (00;17;14- 00;25;22 in the video). James Carey, who filmed that incredible footage, “has been regularly monitoring and filming bindweed turret bees since 2016 in Rancho Sierra Vista/Satwiwa, an open space in the Santa Monica Mountains,” Quirós said. “James also filmed the shot at 04;17-04;21 showing nests in the Santa Monica Mountains covered up at the end of the nesting season."
Christensen, a member of the UC Davis Microbiology Graduate Group and anticipating his doctorate in the spring of 2024, is an evolutionary biologist turned microbiologist. Christensen also researches other native bees, including Melissodes and Colletes.
Vannette focuses her research on the chemical and microbial ecology of plant-pollinator interactions and how microbes influence plant defense and resistance against insect pests. On its website, the Vannette lab is described as "a team of entomologists, microbiologists, chemical ecologists, and community ecologists trying to understand how microbial communities affect plants and insects--sometimes other organisms, too. We often study microbial communities in flowers, on insects or in soil. We rely on natural history observations, and use techniques from chemical ecology, microbial ecology and community ecology. In some cases, we study applied problems with an immediate application including pathogen control or how to support pollinators.”
We're looking forward to more research from the Vannette lab, including their work on Anthophora bomboides, a bumble bee mimic that forms turrets in sand dunes (including the sand cliffs at Bodega Head).
Most people are unaware that there are more than 20,000 known bee species in the world, and 4,000 of them are native to the United States. Of the 20,000 known bee species, 70 percent are ground-nesting bees. California alone is home to more than 1600 species.
And just one of those species is the bindweed turret bee, Diadasia bituberculata, that forages on morning glories. Glory bee...
![A bindweed turret bee, Diadasia bituberculata, foraging for pollen on bindweed, aka morning glory. (Photo by Rachel Vannette) A bindweed turret bee, Diadasia bituberculata, foraging for pollen on bindweed, aka morning glory. (Photo by Rachel Vannette)](/blogs/blogcore/blogfiles/101296.jpg)
![A close-up of a bindweed turret bee, Diadasia bituberculata (Photo by Rachel Vannette) A close-up of a bindweed turret bee, Diadasia bituberculata (Photo by Rachel Vannette)](/blogs/blogcore/blogfiles/101297.jpg)
![UC Davis community ecologist Rachel Vannette at work. She is an associate professor, Chancellor's Fellow and vice chair of the UC Davis Department of Entomology and Nematology. UC Davis community ecologist Rachel Vannette at work. She is an associate professor, Chancellor's Fellow and vice chair of the UC Davis Department of Entomology and Nematology.](/blogs/blogcore/blogfiles/101298.jpg)
![A close-up of a turret formed by a bindweed turret bee. (Photo by Rachel Vannette) A close-up of a turret formed by a bindweed turret bee. (Photo by Rachel Vannette)](/blogs/blogcore/blogfiles/101299.jpg)