Christina M. Grozinger – Research Interests
Genomic analysis of chemical communication in honey
bees.
Chemical communication plays an important role in many
insect species, and is particularly critical for regulating behavior and colony
organization in social insects.
Furthermore, it is becoming increasingly apparent that chemical
communication is exquisitely tuned to the environmental context and physiological
differences in both the signaling and receiving animal, and thus represents a
subtle and intricate system for coordinating the activities of thousands of
individuals in a colony. My research program seeks to understand the
molecular and physiological basis of modulation of chemical communication in
honey bees, both in terms of production of the chemical signal and
responsiveness of the receiving individual.
These studies will not only shed light on the molecular pathways
underlying olfaction, behavior, and chemical ecology, but will also serve as
the basis for applied research into novel methods for improving honey bee
breeding, colony health and management.
This research seamlessly integrates behavioral studies (both in the
field and in the lab), physiological assays, chemical ecology, functional
genomics, and comparative studies with other pollinator species.
The effect
of reproduction on honey bee queen physiology, behavior and pheromone
production. Honey
bees have a number of reproductive states, including virgin queens, laying
virgin queens, instrumentally inseminated queens, and naturally mated queens (Winston 1987). For these
different reproductive states, we can monitor behavior (ie, egg-laying behavior
or taking mating flights) pheromone production, ovary activation, and gene
expression in both the brain and ovaries using microarray analysis. Queen
pheromone production, in particular, is critical to colony organization and
health, since it regulates many aspects of worker behavior (including worker
reproduction and foraging) and inhibits rearing of new queens and swarming,
which can reduce colony strength (Slessor et al. 2005). Ultimately, our goal is to understand the
physiological processes that cause post-mating changes in queens. At the molecular level, we hope to match gene
expression patterns with specific physiological or behavioral changes. These studies will identify candidate genes
and pathways that can serve as the basis for further functional analyses or as
markers for breeding programs. This
research has been conducted by two graduate students (Sarah Ayroles and Elina
Lastro) and a post-doctoral associate (Freddie-Jeanne Richard), in
collaboration with Professor David Tarpy (NCSU). It is supported by funding from USDA-NRI,
NCSU, and the Eastern Apiculture Society.
We have found that brain gene expression and queen
pheromone profiles are significantly modified by insemination quantity, in
studies using instrumentally inseminated and natural mated queens (Ayroles et al. in prep; Richard et al. in revision). Furthermore,
workers are attuned to these differences and are preferentially attracted to
the pheromone produced by multiply mated queens. Our studies have demonstrated that both
stretch receptors in the oviducts and seminal proteins appear to trigger
post-mating changes (Richard et al. in prep). Given that
instrumental insemination is critical for honey bee breeding and selection
(particularly to prevent accidental mating with Africanized bees), these
results will allow us to develop modifications to the instrumental insemination
process to further improve queen quality and colony health. These studies
suggest that the production of queen pheromone is exquisitely sensitive to
factors associated with reproduction and mating.
The effect
of activation of the immune system on chemical communication. With the
sequencing of the bee genome, it has become apparent that bees have fewer
immune genes than solitary insects (Evans et al. 2006), suggesting that they use modified behavioral
responses to control diseases and pests.
Indeed, strains bred for resistance to Varroa mites have improved hygienic behavior, leading to reduced
parasite load (ie, Harbo and Harris 2006). We seek to characterize another behavioral
response: modulation of chemical communication between diseased workers and
queens and their nestmates. We have
demonstrated that activation of the worker immune system alters cuticular
hydrocarbon profiles and social interactions (Richard et al. submitted). We will
expand on these studies to explore the effect of different types of immune
responses, and include microarray analysis to correlate changes in social
interactions with gene expression differences.
Thus these studies should provide insights into the molecular events associated
with immune responses and the biosynthetic pathways associated with hydrocarbon
production. Chemical communication of disease states has not been broadly
investigated, and could have far-reaching impacts in chemical ecology and pest
management. This research has
recently received funding from the USDA-NRI and is being conducted by
post-doctoral associate Freddie-Jeanne Richard.
Modulation
of pheromone responsiveness in worker bees. While responses to pheromones
are typically considered to be instinctive and hard-wired, it is clear that
responses can be modulated by environmental context, or the physiology and
genotype of the receiving individual. We are studying the molecular mechanisms
underlying modulation of response to queen mandibular pheromone (QMP). QMP is rather unusual pheromone, in that it
can cause both short-term changes in behavior (attraction the pheromone source)
and long-term changes in behavior and physiology, including inhibiting rearing
of new queens and worker reproduction, and slowing the transition from nursing
to foraging (Slessor et al. 2005). QMP causes
profound changes in brain gene expression, significantly altering expression of
hundreds of genes (Grozinger et al. 2003). Furthermore,
these brain expression profiles correlate with the behavioral effects of QMP.
We have demonstrated that the short- and long-term
responses QMP can be uncoupled; thus, they appear to operate by different
mechanisms (Grozinger et al. 2007). Furthermore,
modulation of physiological state (ie, nurses vs foragers, or treatment with a
juvenile hormone analog) can affect responses to pheromone (Grozinger and Robinson 2007). We are now
expanding our studies to consider genotypic modulation of responses to QMP
(Ayroles and Grozinger, unpublished data).
We have initiated a series of studies using a
pheromone-responsive gene, Kr-h1,
identified in our microarray analysis (Grozinger et al. 2003). We have
studied physiological factors that modulate its expression, and have found that
it is regulated by juvenile hormone (Grozinger and Robinson 2007) and cGMP (Fussnecker and Grozinger in prep). Furthermore, in collaboration with Tzumin Lee (University
of Massachusetts, Worcester), we have found that it plays an important role in
regulating neuronal properties and structure in Drosophila (Shi et al. 2007). Since Kr-h1
is a transcription factor that regulates expression of other genes, we will now
use Drosophila transgenic strains in
microarray studies to identify these genes.
This work is being performed by graduate student Brendon Fussnecker, and
is supported by a subcontract of an NIH-NIDCD grant to Gene Robinson (UIUC).
Finally, we are beginning to address the roots of
pheromone-mediated behavior in social insects.
Preliminary investigations (in collaboration with Guy Bloch, Hebrew
University of Jerusalem) with Kr-h1
revealed that its expression is strongly downregulated by queen presence in
bumble bees. Interestingly, in both
bumble bees and honey bees, queen presence/pheromone regulates worker ovary
development and juvenile hormone levels (Bloch and Hefetz 1999). Thus, Kr-h1’s ancestral role may have related
to reproduction and/or hormone levels.
References
Ayroles SD, Richard FJ, Tarpy DR, Grozinger CM (in
prep); Bloch G, Hefetz A (1999) J Chem
Ecol 25(4): 881-896; CCD Steering
Committee. Colony Collapse Disorder Action Plan; 2007; Beltsville, MD; Committee on the Status of Pollinators in
North America NRC (2007); Evans JD,
Aronstein K, Chen YP, Hetru C, Imler JL et al. (2006) Insect Mol Biol 15(5):
645-656; Fischer P, Grozinger CM
(submitted); Grozinger CM, Robinson GE
(2007) J Comp Physiol A Neuroethol Sens Neural Behav Physiol 193(4):
461-470; Grozinger CM, Fischer P,
Hampton JE (2007) Naturwissenschaften 94(5): 375-379; Grozinger CM, Sharabash NM, Whitfield CW,
Robinson GE (2003) Proc Natl Acad Sci U
S A 100 Suppl 2: 14519-14525; Harbo J,
Harris J (2006) American Bee Journal 146(5): 447-448; Richard F-J, Grozinger CM, Aubert A
(submitted); Richard FJ, Tarpy DR,
Grozinger CM (in prep) ; Richard FJ,
Tarpy DR, Grozinger CM (in revision) ;
Shi L, Lin S, Grinberg Y, Beck Y, Grozinger CM et al. (2007) Dev
Neurobiol; Slessor KN, Winston ML, Le
Conte Y (2005) J Chem Ecol 31(11): 2731-2745;
Winston ML (1987) The Biology of the Honey Bee. Cambridge, MA: Harvard
University Press. 281 p.