Research

 The lab is pursuing a diversity of research projects spanning bee evolutionary genetics, bee social evolution, bee epidemiology and conservation, and parasitic wasp evolution:

Evolution and genetics of mimetic coloration in bumble bees

       The ~250 species of the cold-adapted bumble bees are exceptionally color diverse, comprising >400 different patterns in their setal pile coloration across their body segments. One of the main factors driving such variation is localized selection through Müllerian mimicry – taxonomically diverse species in the same geographic region have convergently evolved a similar color pattern because selection favors shared advertisement of their toxicity (their sting) to predators. Bumble bee color diversity thus provides extensive replicates for understanding how traits evolve rapidly and repeatedly at the genetic level and to understand how ecological factors influence the formation of mimicry complexes over time. Furthermore the segmental nature of their color change makes this a great system to understand the role of segmentation genes in phenotypic variation.

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Through an NSF CAREER project, we are developing the bumble bee system for understanding the genetic regulation of adaptive phenotypic variation. This involves several directions:

 The geographic distribution of mimicry

We are mapping the distribution of coloration in North American bumble bees, including both monomorphic and color polymorphic species (e.g., B. melanopygus, B. bifarius, B. flavifrons), to better characterize the extent of mimicry and the factors that may be driving mimetic color distribution (e.g., climate, historical biogeography). This includes examining both spatial and temporal correspondence of color forms and examining historical shifts in the distributions of color pattern hybrid zones. melanodist EzrayScope

 The genetic basis of mimicry in Western US bumble Bees

A major research focus is in determining the genetic basis of mimetic color transitions in western U.S. bees. In the Western U.S. bees transition from a Pacific coastal color pattern to a Rocky Mountain mimetic pattern. Some species occur in only one of these zones but others cross both regions and converge onto local patterns by switching from black to red coloration. We are determining the genetic loci driving this red-black color switch in two of these species: Bombus melanopygus and Bombus bifarius. We are examining the role of these isolated loci in driving similar color switches across the bumble bee radiation. Postdoc Li Tian is performing gene expression and validation work on targeted loci. Graduate student Sarthok Rahman is performing bioinformatic analyses using GWAS to target and annotate color loci. Collaborators: James Strange, Jeff Lozier.
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Photo Credit: Sam Droege, USGS Survey

 The genetic basis of yellow pigmentation in bumble bees

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Photo: J. Cnaani
We are also examining the genes that drive frequent black to yellow color switches in the subgenus Bombus s.s. using inbred laboratory colonies. We are currently testing isolated loci for the role of this gene across this incipient species complex and its function in pigmentation. Collaborator: Jonathan Cnaani.

 Bee development and pigmentation

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This direction includes several ongoing projects in the lab:

1) We are using a diversity of approaches (e.g., extractability, TLC, UV-Vis, LC-MS-MS, NMR, Raman Spectroscopy, FTIR, and ToF-SIMS) to determine the chemical nature of the pigments that comprise the the colored stripes of these bees. In addition to exploring pigmentation in bumble bees we are examining pigmentation across diverse insect lineages where the nature of pigmentation is unknown. These have been developed into classroom discovery modules in collaboration with Dan Sykes (PSU).

2) As a foundation for understanding underlying genetic mechanisms, we are developing morphological criteria for staging bumble bee pupae and are determining how the setae bearing these colors develop.

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3) We are studying the role of bee nutrition in color intensity and other factors (body size, colony development). Lab reared bumble bees tend to be a paler yellow than wild bees. By adjusting rearing parameters, we are testing what factors may influence color intensity, and thus we can better understand whether color is a bioindicator of nutritional quality and potentially involved in evolutionary trade-offs.

Bee pathogens and pollinator conservation

  Bumble bee diversity has changed dramatically in the last 20 years and it is believed that one of the factors contributing to this is the spread of bee pathogens. In addition to studying the general biology and evolution of bumble bees, we seek to contribute to growing data to help determine the major factors threatening these bees. As part of this we are pursuing multiple initiatives:

1) Modeling bee pathogen epidemiology. We are performing a large scale survey in central PA to understand epidemiology of bee pathogens across time and space. This project involves cross-pathogen screens in bumble bees, carpenter bees, and honey bees across the season to understand how pathogens are shared across communities, at what scale they spread, and the role of different species in pathogen overwintering and maintenance. Funding: NE SARE grant with Briana Ezray.

2) Understanding bee virus transmission across insect communities. We are studying whether DWV and BQCV, the two most common bee viruses, can be directly transmitted between honey bees, bumble bees, and nest commensals, including hive beetles and cockroaches, using laboratory experiments. Funding: NAPPC grant with Briana Ezray.

3) Determining the factors and duration of virus persistence in the environment. We are determining how long bee viruses persist in various conditions to understand the role the timing between bee floral visitors and floral morphology may play in pathogen transmission. Funding: NAPPC grant with Briana Ezray.

4) Determining how bee virus communities change over time. We are determining changes in bee virus strains and composition in honey bee pollen over the last decade to understand how temporally dynamic these communities can be. Funding: Apes Valentes grant with Briana Ezray.

5) Landscape factors that effect bumble bee pathogen loads. As part of a large collaborative grant (funding: Foundation for Food and Agriculture Research), we are comparing the role of a variety of landscape conditions throughout Pennsylvania on the virus load and immune gene upregulation in bumble bee communities. Primary Collaborators: Christina Grozinger, Margarita Lopez-Uribe

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The evolution of social parasitism in bumble bees

   Most bumble bees have a life history that starts with nest initiation by a lone queen who then produces several generations of workers that ultimately will rear some of their sisters to become new reproductive queens.  Some bumble bees, those in the subgenus Psithyrus, use a different strategy. They invade the young nests of other species, take over – either through killing or coinhabiting with the resident queen – and coerce the workers of this young colony to rear their reproductive offspring instead. Recent research on European species has revealed some of the strategies by which they manage to evade their hosts. In collaboration with Patrick Lhomme the lab is studying strategies of chemical and behavioral control in the lesser-known North American Psithyrus, including mechanisms of host evasion, differences in reproductive success by hosts, and potential for host imprinting. We are also studying species delimitation in North American Psithyrus using an integrative approach combining  genitalia morphology, DNA barcoding, and male cephalic gland chemistry, and in collaboration with Pierre Rasmont. psithyrusinvasion

Evolution of parasitic wasps

 1) Ichneumonoidea phylogenomics. We are using phylogenomic approaches to obtain a robust backbone phylogeny of the Ichneumonoidea, a lineage of wasps involved in parasitizing developing forms of a diversity of insects. Ichneumonoids comprise 3% of the species on earth and this radiation has made determining their historical relationships difficult. Resolving their relationships these will aid in understanding the evolution of parasitic strategies and understanding the factors promoting their diversification. Our ~450 gene, ~80 taxon dataset will aid resolution of relationships, while also examining the evolution of polydnavirus (PDVs) replication genes in these wasps. Polydnaviruses are co-evolved viruses imbedded into the genomes of some lineages of Ichneumonoidea used as a delivery system for immune-suppression genes into parasitized insect hosts. Collaborators: Barb Sharanowski, Andrew Deans, Jim Whitfield, and Alan and Emily Lemmon.

2) Mechanisms underlying galling in gall wasps. In collaboration with Istvan Miko and Andy Deans, we are utilizing transcriptomic approaches to understand genes expressed in various glands in different lineages of gall wasps which could be used by gall wasps to communicate with host plants to induce predictable gall morphologies.


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