Evolutionary Biology seminars

Natural selection affects not only selected alleles, but also indirectly affects all genes near selected sites on the genome. An increasing body of evidence suggests that this linked selection is an important driver of evolutionary dynamics throughout the genomes of many species, implying that we need to substantially revise our basic understanding of molecular evolution. This session brings together early-career researchers working towards a quantitative understanding of the prevalence and effects of linked selection.

Animals exhibit extraordinary variation in their behaviour, yet little is known about the neural mechanisms that generate this diversity. My lab has been taking advantage of the rapid diversification of male courtship behaviours in Drosophila to gain insight into how evolution shapes the nervous system to generate species-specific behaviours. By translating neurogenetic tools from D. melanogaster to closely related Drosophila species, we have begun to directly compare the homologous neural circuits and pinpoint sites of adaptive change. Across species, P1 interneurons serve as a conserved and key node in regulating male courtship: these neurons are selectively activated by the sensory cues carried by an appropriate mate and their activation triggers enduring courtship displays. We have been examining how different sensory pathways converge onto P1 neurons to regulate a male’s state of arousal, honing his pursuit of a prospective partner. Moreover, by performing cross-species comparison of these circuits, we have begun to gain insight into how reweighting of sensory inputs to P1 neurons underlies species-specific mate recognition. Our results suggest how variation at flexible nodes within the nervous system can serve as a substrate for behavioural evolution, shedding light on the types of changes that are possible and preferable within brain circuits.

The human brain, in particular the cerebral cortex, has undergone rapid expansion and increased complexity during recent evolution. One striking feature of human corticogenesis is that it is highly protracted in time, from prenatal stages of neurogenesis (taking months instead of days in the mouse), to postnatal stages of neuronal maturation and circuit formation (taking years instead of weeks in the mouse). This prolonged development is thought to contribute in an important fashion to increased cortical size, but also enhanced circuit complexity and plasticity. Here we will discuss how the species-specific temporal patterning of corticogenesis is largely intrinsic to cortical progenitors and neurons, and involves human-specific genes and cell properties that underlie human brain evolution, as well as our selective sensitivity to certain brain diseases.

Gerald Joyce explores attempts to reconstruct features of RNA-based life in the laboratory. Under the RNA world hypothesis, early organisms used RNA to store information and catalyze replication before the emergence of DNA genomes. Directed evolution has produced RNA enzymes that copy diverse templates, synthesize structured and catalytic RNAs, and amplify short templates in an RNA-catalyzed analogue of the polymerase chain reaction. A variant can make DNA from an RNA template, suggesting a possible route between RNA and DNA genomes. Joyce also describes cross-chiral enzymes that synthesize RNA of opposite handedness and can assemble their own enantiomers from fragments. The lecture examines these complementary approaches to replicating functional RNA, their relevance to the origins of life, and potential diagnostic and clinical applications.