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Brief research overview

 

We are interested in the genetic and neural bases of sensory evolution.


• How do closely related species (or populations) come to differ in their ability to sense and/or respond to common environmental stimuli?

• What are the genes and neurons involved in these changes?

• What are the evolutionary forces governing the modifications?

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We are also interested in evolutionary genomic topics, including local adaptation and the evolution of gene families.  These themes often overlap with our sensory biology questions and result in cross-disciplinary approaches that draw on tools from molecular neurogenetics, comparative genomics, and physiology.  Currently, the sensory modalities we are investigating are olfaction and temperature sensing, both of which evolve quickly and are often involved in local adaptation.  To do this work we utilize diverse Drosophila species and populations from around the globe.

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evolutionary expansion and contraction of sensory circuits

Sensory systems between species vary extensively. Some animals possess seemingly minimal and streamlined systems, while other animals have large and complex sensory systems.  Why do these changes arise, and what are the molecular pieces and evolutionary forces required to expand or contact these systems?

We are using evolutionarily recent gains and losses of olfactory receptors as a starting point for studying neural circuit evolution.  Given that most olfactory receptors express only a single receptor type, these copy number changes provide an initial 'label' for which species and cell types are good targets for functional studies.  We would like to know how these gains/losses relate to the underlying evolution of neural circuits, the evolution of odor tuning, and the evolution of behavior.

To address these questions this project draws on a combination of evolutionary genomic, molecular biology, and physiological approaches. Currently, we are using the OR67 subfamily as our model system because it is the most duplicated/deleted olfactory receptor among species closely related to D. melanogaster.

 

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mapping the genetic basis of sensory trait evolution

 

1. genetic and neural basis of temperature preference evolution

Given the small size of most insects, and the often large temperature differences that exist at their scale, the behaviors that enable efficient body temperature regulation are critical for their survival.  The tolerable range for insects varies between species, and this has been a topic that biologists have studied for a long time.  While the molecular and neuronal basis for temperature-related behavior is quickly becoming better understood in model systems, which of these molecules and neurons are involved in between-species changes in temperature-related behaviors is largely unknown.

We are using genone-wide between-species QTL approaches for mapping the genetic basis of temperature preference between young pairs of Drosophila species, and different populations of the same species.  The aim is to use recently diverged species and populations so that we can identify those factors that are involved the earliest steps of behavioral evolution. We are developing behavioral assays to pair with genomic sequencing approaches, and would like to known if the same loci (or type of loci) are repeatedly used among taxa, as well as potentially identifying new molecular players in temperature sensing pathways.

 

2. genetic basis of sensory cell population size evolution

One way that brains help to ensure that they recognize important objects or signals in the environment is by expanding the neuron populations that are 'tuned' to that object/signal.  The evolution of neuron population size (small number of sensory neurons evolving to bigger populations of neurons, and vise versa) is readily observed, even between closely related species.  However, the genetic bases for these changes is unknown.  To tackle this topic, we are using a between-species QTL approach to map the loci that underlie the expansion of olfactory receptor neurons.  We are looking at two independent neuronal expansion events, one that has occurred within OR22a-expressing neurons and one within IR75b-expressing neurons.  We are currently carrying out the fine mapping for the QTL that we identified.  This is an ongoing project that began in collaboration with Lucia Prieto-Godino,Tom Auer, Richard Benton, and David Stern.

 

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evolution of host specialization

The ecological specialization of insects ranges from generalist species (like the common fruit fly, D. melanogaster) to highly specialized species (like many butterflies or beetle that require a specific host plant).  Investigating species that have recently evolved to became a specialist provides opportunities to understand the genetic basis of how such a drastic change in lifesyle occurs, the evolutionary forces that drove the changes, as well as more specific questions about how sensory systems evolve in coordination with the ecological shift.  I am collaborating with Lucia Prieto-Godino to study the evolution of host specialization using a D. erecta as a model system.  D. erecta is found only in West Africa, and is believed to be a host specialist on Pandanus.  We are developing field sites in Africa, along with genomic and genetic approaches to develop this species for functional evolutionary and population genomic studies.