Molecular evolution of olfaction

How do chemosensory gene repertoires evolve?

Odorant receptor subfamily dynamics in corbiculate bees. See Brand and Ramirez 2017 for more information.

Animals have evolved sophisticated sensory systems that can detect and discriminate environmental chemicals and provide precise information about food, enemies, and mating partners. The chemosensory system of insects – including the senses of smell and taste – relies on a suite of chemosensory genes expressed in sensory sensillae. It is the interaction of chemical molecules with these chemosensory proteins that initiates the signal transduction and transmission toward the olfactory centers in the insect brain. The entire repertoire of the chemosensory genes expressed in the chemosensory organs determines the spectrum of chemicals that an insect species can detect and eventually ‘sense’. I am interested in the molecular mechanisms that shape the chemosensory gene set in insects – especially in bees. This includes the evolution of genomic organization, gene duplications, and the importance of positive selection in gene diversification.

Publications: Brand et al. 2015, Brand and Ramirez 2017, Brand et al. 2018

How do evolutionary changes in odorant receptors impact receptor function?

Distribution of non-synonymous amino acid substitutions across domains in Odorant Receptors under divergent selection. How do they contribute to functional changes? See Brand et al. 2015 for more information.

Odorant receptors represent one of the largest gene families in insect genomes. Most bee genomes (including orchid bees!) encode between 140 and 170 functional odorant receptor genes that together define the majority of the volatile chemical detection capability of the sense of smell. Insects detect olfactory signals and cues via olfactory sensory neurons located in sensillae on the antenna. Each olfactory sensory neuron expresses odorant receptor proteins on the cell membrane. Chemical molecules are ligands to these receptors and trigger neurophysiological responses that are subsequently integrated by the brain. We have identified several odorant receptor genes with mutations that evolve under strong positive selection in single lineages of orchid bees. I am currently working on the functional characterization of these candidate genes in different lineages to understand the functional repercussions of the observed mutations and positive selection pressures.

What role does the evolution of pheromone communication play in speciation?

 I investigate the genetic mechanisms of changes in perfume production, chemosensory detection, and their importance in the generation and maintenance of species boundaries in sibling species of orchid bees. Specifically I am using population genetics to understand interspecific and intraspecific divergence between closely related species. Further, I analyze the chemical perfume composition of males throughout populations and species (Popchem if you will..) and test whether changes in chemistry are correlated with changes in the genome. This way I combine perfume chemistry and chemosensory gene evolution in a population genetic framework to understand the importance of chemosensory diversification in orchid bee speciation. In addition, I am testing divergent odorant receptors between populations and species for functional differences. Together, this has the potential to understand the role of olfactory gene evolution in speciation.

Neurobiology and perfume collection in orchid bees

What is the genetic basis of perfume collection behavior?

Orchid bee males collect scents to produce perfumes throughout their entire life and store them in pouches in their hindlegs. Although compounds have to be collected from multiple sources in extremely heterogeneous habitats, perfume phenotypes of experienced males are not only species-specific in compound composition but also in the relative abundance of compounds. How do male orchid bees regulate the collection of a large number of scents in distinct quantities from their environment in order to produce highly specific pheromone (perfume) blends? It has been shown that males do not reassess the chemicals they already collected. I am testing what mechanism (for example odor memory) orchid bee males use to produce a species-specific perfume that includes a variety of different chemicals from different sources and what the molecular mechanisms are.

What is the neurological basis of olfactory processing in orchid bees?

In collaboration with Jean-Christophe Sandoz at the CNRS in France, I recently analyzed the morphology of olfactory brain regions to test whether changes in perfume communication occur alongside changes of brain regions important for the formation of the sense of smell. I am also interested in how the orchid bee brain is organized in comparison to other bee species to understand the evolution of perfume collection.

Publication: Brand et al. 2018

3D reconstruction of an orchid bee brain






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