Brief research overview
We are interested in the genetic and neural bases of sensory diversification, as well as general evolutionary genomic topics (including the genetics of local adaptation and speciation). We draw on approaches from neurogenetics, population/comparative genomics, and behaviorial biology. Currently, the sensory modalities we are using as models to investigate these questions are chemosensation and thermotaxis, both of which evolve quickly and are involved in local adaptation. To do this work we utilize diverse Drosophila species and populations from around the globe.
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 changes 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 fly olfactory neurons 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 molecular biology, physiology, and genomic approaches. Currently, we are using the Or67a subfamily as our model system because it is the most duplicated/deleted olfactory receptor among species closely related to D. melanogaster.
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 genome-wide between-species 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.