How have genes and neural circuits evolved to generate behavioral diversity?
Where did novel genes come from and what do they do?
This is an extraordinary time to study the origins of biological diversity. Many deep and old evolutionary questions are being solved by the application of new technologies.
We develop new approaches and new tools to ask how molecular changes cause phenotypic evolution, especially the evolution of behavior. Also, we have begun to explore the enormous, under-studied problem of proteins of unknown function through functional studies of lineage-specific proteins that appear to confer insects with special abilities.
Evolution of Behavior
We aim to identify the genetic and neural basis for the evolution of behavior, because we believe that there may be general principles to behavior evolution, similar to the principles that have been revealed for morphological evolution (Stern & Orgogozo, 2009; Stern 2010). Our goal always is to identify the individual molecular changes that have contributed to evolutionary change, since we believe that these “quanta” of evolution provide the deepest insight into the evolutionary process.
Our behavior studies focus on the evolution of Drosophila male courtship song, a rapidly-evolving behavior. We have developed multiple tools to aid these studies, including high-throughput genotyping (Andolfatto et al. 2011) and phenotyping platforms (Arthur et al. 2013), and new transgenic reagents for multiple species (Stern et al. 2017).
Using these tools, we have been able to identify a mutation generating natural variation in courtship song (Ding et al. 2016) and to examine how individual homologous song neurons contribute to divergent songs in different fly species (Ding et al. 2019).
We continue to develop new tools and reagents to facilitate efficient discovery of the genetic and neural causes of behavior evolution.
Proteins of Unknown Function
30-50% of the genes in most genomes encode proteins of unknown function and represent an enormous gap in our understanding of biology. This vast ignorance is particularly acute for non-model organisms, which represent the overwhelming diversity of life on earth and include species that pose significant threats to human health and well-being.
We believe that recent technological advances make this an attractive time to study proteins of unknown function, especially in non-model organisms. We have begun to explore this problem by studying proteins of unknown function encoded by the aphid genome, where it is estimated that nearly 40% of genes are aphid-specific and encode unknown functions. Some aphids are major pests of agricultural crops and important vectors of plant viruses. We expect that many proteins of unknown function facilitate the aphid's ability to exploit plants, yet functional studies of novel aphid proteins are in their infancy.
Some time ago, Shuji Shigenobu discovered that two unusual families of novel proteins are transcribed specifically in bacteriocytes (Shigenobu & Stern 2013), the aphid cells that house endosymbiotic bacteria. Recently, we initiated a new collaboration with Shigenobu to determine the functions of these proteins. Other new studies in the lab are focused on additional novel families of aphid proteins. Stay tuned!
"I came to Janelia to do science with my own hands. I am an inveterate lab rat and I really appreciate the fact that I can spend all day, every day, doing experiments that enhance the lab's research. I feel incredibly lucky to be a post-doc in my own lab!"
David L. Stern, December 2014
"Throughout their careers [Thomas Hunt] Morgan and [his] students worked at the bench. The investigator must be on top of the research if he or she is to recognize unexpected findings when they occur."
Male Drosophila produce courtship songs by vibrating their wings. (Image credit: David L. Stern)
Males of some species perform a slow wing "rowing" to court females. (Image credit: Jessica Cande)
Specific thoracic neurons (labeled in green) are required for courtship song. (Image credit: Troy Shirangi)
Specific neurons in the larval brain of Drosophila are involved in perceiving aggregation pheromones. (Image credit: Joshua Mast)
Different enhancer of the shavenbaby gene drive expression in largely complementary domains of expression in the Drosophila embryo. Some of these enhancers have evolved to generate novel anatomy in closely related species. (Image credit: Ella Preger-Noon)
A male Drosophila melanogaster courts a female by "singing" to her. He extends and vibrates one wing to produce the machine-gun-like "pulse" song and the humming "sine" song.