Biology Seminar Series

When: Fridays, 12-1pm (unless otherwise indicated)

Where: Zoom

Every Friday during the academic year, the Department of Biology hosts an exciting seminar given by a guest speaker. Topics cover every aspect of biology, from whole organisms to molecular biology. Everyone is welcome to attend.

Full List 2021-2022

2021-2022 Schedule

Jan 28, 2022

Dr. Carolyn Wessinger, University of South Carolina

Evolutionary genetics of parallel floral evolution in penstemon wildflowers

https://utoronto.zoom.us/j/83362699493

Abstract

The wildflower genus Penstemon displays a remarkable pattern of parallel floral evolution, where flowers adapted to hummingbird pollinators have repeatedly evolved from ancestral bee pollination. I will discuss recent macroevolutionary modeling that suggests transitions from bee to hummingbird pollination in this genus occur more frequently than transitions in the reverse direction, and that hummingbird-pollinated lineages show reduced speciation rates. An untested hypothesis is that pollination by hummingbirds results in greater connectivity among populations, reducing the opportunity for allopatric speciation. The transitions from bee to hummingbird pollination in Penstemon have likely occurred recently, since hummingbird-pollinated species in Penstemon are nearly always sister to bee-pollinated species. I will discuss population genomic and quantitative genetic work in a focal sister species pair that suggests adaptive floral divergence involves relatively few genetic changes of major effects that maintain complex floral divergence, despite substantial shared genetic variation between sister species.

Host: Prof. Helene Wagner

Jan 21, 2022

Dr. Alonso Ramirez, North Carolina State

Urbanization and stream ecosystems in Puerto Rico: Biotic responses to major disturbances

POSTER; RECORDING

Abstract:

Urbanization is a major source of stress to stream ecosystems resulting in communities dominated by non-native species. In Puerto Rico, urban streams have high levels of pollutants, altered geomorphology, and most of the expected urban symptoms. However, they continue to maintain native biotic assemblages. In this seminar, I explore biotic responses to urban and non-urban disturbances and potential mechanisms by which native species are able to cope with urban impacts. Our focal watershed drains the San Juan metropolitan area, the most urbanized region in Puerto Rico.

Host: Dr. Shannon McCauley

Jan 14, 2022

POSTER 

Maliha Islam, PhD Student, Ted Erclik Lab
Concurrent temporal patterning of stem cells in the developing fruit fly brain

Abstract:

The Drosophila medulla, which is the largest neuropil in the optic lobe, is as an excellent model system in which to study the mechanisms that regulate neurogenesis. Its 40,000 neurons, which comprise over 90 cell types, are generated from a neuroepithelial crescent termed the outer proliferation center (OPC). Beginning at the onset of the third larval instar, and continuing for two days, a proneural wave converts each neuroepithelial cell into a neuroblast (NB), which subsequently divides asymmetrically to generate two neurons via an intermediate ganglion mother cell. It has previously been shown that two axes of positional information act on OPC NBs to generate neural diversity. In the temporal axis, a cascade of five genes--Homothorax, Eyeless, Sloppy paired, Dichaete and Tailless--are sequentially expressed in each of the medulla NBs as they age. In the spatial axis, the OPC crescent from which the NBs are generated is sub-divided into eight compartments (patterned by four genes: Vsx1, Optix, Rx, and Hh). Distinct neuronal types are generated by NBs based on their spatio-temporal address. Here, we describe a third patterning axis that further diversifies neuronal fates in the medulla. We show that the neuroepithelium from which the NBs are generated is itself temporally patterned by the sequential expression of five genes over the two-day period of neurogenesis. The temporal patterning of the neuroepithelium confers NBs from the same spatio-temporal address with unique identities based on the time that they are generated. Using clonal, EdU-birthdating and functional analyses, we show that NBs in the Vsx1-Hth spatio-temporal window generate not one, but five, distinct neuronal types over the course of neurogenesis. We further demonstrate that long-range temporal patterning extends beyond the Vsx1-Hth NB window and functions as a mechanism to couple neurogenesis with medulla circuit assembly.

Wassim Elkhatib, PhD Student, Adriano Senatore Lab

The evolutionary emergence of acid-sensing ion channels in Trichoplax adhaerens, an animal without a nervous system

Abstract

The degenerin/epithelial sodium channel (DEG/ENaC) superfamily emerged in the oldest animals on earth and have undergone extensive lineage specific evolution leading to very diverse functional properties. All DEG/ENaCs share a common structure made up of three subunits, with each subunit consisting of two transmembrane helices and a large extracellular domain. In invertebrate lineages, DEG/ENaCs have evolved a response to various ligands and sensory inputs, such as the touch sensing MEC4/10 channels in nematodes, the pheromone sensing pickpocket 25 channel in fruit flies and the peptide gated FMRFamide-gated sodium channel (FaNaC) channels in molluscs (snails). Deuterostome (Chordates, Hemichordates, & Echinoderms) DEG/ENaCs diverged into two functionally distinct groups; 1) ENaCs, which are constitutively open Na+ channels that regulate sodium reabsorption and blood pressure in the kidneys, 2) acid-sensing ion channels (ASICs) which fully activate in acidic environments, found in the central and peripheral nervous system, and play major roles in memory, stroke detection and pain sensation. Clearly, DEG/ENaC expansions across animal lineages is complex and until all major phyla are studied, their core properties and physiological functions will remain unknown. My lab studies Trichoplax adhaerens an early-diverging marine animal that has no synapses or muscles, yet conducts motile behaviours mediated by peptides. Using our Trichoplax transcriptome, we identified and cloned nine DEG/ENaC homologs dubbed Trichoplax adhaerens sodium channels 2-10 (TadNaC2-10). We functionally expressed TadNaC6 in Chinese hamster ovary cells (CHO-K1) and used in-vitro patch-camp electrophysiology to show that TadNaC6 is inhibited by extracellular acid and calcium, but activated by amiloride, a robust blocker of DEG/ENaCs. Our current work is revealing that TadNaC2 also forms functional channels that unexpectedly show great resemblance to deuterostome ASICs, although they lack many of the fundamental amino acids involved in deuterostome ASIC gating. Our work suggests the independent evolution of ASIC channels in Trichoplax adhaerens and the uncovering of DEG/ENaCs across all animal lineages and certain prokaryotic organisms.

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