Seminar from Tetsuto Miyashita (Canadian Museum of Nature)

This week we will have an exit seminar from Tetsuto Miyashita (Canadian Museum of Nature).
There will be coffee and snacks before the seminar. Please bring your own mug.
Thursday 4:00PM, HSC 1A5 and on zoom (Passcode: cElegans).
Jawless Fishes, Ancient and Engineered: Unconventional Model Systems to Understand Major Evolutionary Transitions
Abstract: In organismal evolution, history can and often does repeat itself, but some transitions appear to be rare and constrained, and select few may even seem non-reversible. Vertebrate jaws evolved only once around 450 million years ago and never became lost in any descendant lineage. To understand this one-off event, I present two case studies. 1) Internal skeletal structures of a 400-my-old jawless fish that branched immediately before the first jawed vertebrate. This animal, named Norselaspis, has been considered having primitive, lamprey-like anatomy. I will show that Norselaspis is much closer to sharks in its brain, heart, and fin morphology under the seemingly archaic look of its external skeleton. Thus, many sensory and locomotory adaptations attributed to jawed vertebrates have much deeper origins among jawless vertebrates. 2) Zebrafish mutants engineered with loss of function in jaw joint formation. These mutant zebrafish lose a jaw joint through skeletal fusion and thus become functionally jawless, realizing a reversal that has never occurred in jawed vertebrate evolution. The mutant fish surprisingly survive and remain viable. They accommodate the functional jaw loss by drastically remodelling their skulls into a phenotype resembling Munch’s “Scream”. I argue that this line can serve as a model to explain how macroevolution can occasionally involve a leap of phenotype, even though such large-effect mutations are almost always deleterious.
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