Development of the vertebrate scleral cartilage
Most vertebrates, with the notable exclusion of snakes and mammals, have a cartilaginous skeletal element in their sclera, which provides support to the eyeball. In teleost fishes, this cartilage can eventually give rise to bony ossicles that provide additional support in high-pressure environments.
Diagrams of whole-mount Snapping Turtle specimens showing their elaborate scleral cartilage cup. From Franz-Odendaal, 2006, Zoology.
Despite the wide distribution of scleral cartilage amongst vertebrates, very little is known about how it develops. From great paucity of literature on scleral cartilage arise many questions regarding the formation of the skeletal element, and variation amongst species.
My Ph. D. research will investigate the genetic and developmental underpinnings of the mysterious scleral cartilage in a variety of representative species.
Temperature-Dependent Sex Determination in a Northern Population of Snapping Turtle (Chelydra Serpentina)
Unlike mammals and birds, whose sex is conferred to them genetically via heteromorphic sex chromosomes, many reptiles and some actinopterygian fishes have their sex determined by incubation temperatures they experience during embryonic incubation. This process is known as temperature-dependent sex determination or TSD.
Given this direct link to environmental temperature, it is intuitive to believe that climate change may affect the sex ratios of these species with TSD. Indeed, this has been found to be the case with some crocodilians and many species of marine turtle. These alarming feminizing trends have the potential to skew sex ratio, affecting demography in negative ways.
Under the supervision of Dr. Njal Rollinson at University of Toronto, I studied temperature-dependent sex determination in a population of turtles from Algonquin Provincial Park. I created a mathematical model to predict sex ratios of snapping turtles in the wild under TSD, which was previously not possible. This research could save countless hatchling turtles if it is used as a non-lethal sex ratio monitoring tool.
I have the great pleasure of working on this incredibly interesting project, which was spearheaded and performed for over two decades by Dr. Ronald J. Brooks from University of Guelph.
Presented at the Canadian Herpetological Society Conference (Sept 17, 2016): Link to Program
Left: a candled C. serpentina embryo showing development of the embryo and blood vessels in the egg. Candling is a very simple technique used to determine whether eggs are viable and assess how they are growing. Right: C. serpentina eggs lined up after being collected from a wild nest. The eggs are numbered and stored in moist vermiculite.
Character Scoring in Chicken Embryos
During my undergraduate program at McGill University, I completed an independent thesis study on morphological character scoring in embryonic Gallus gallus, as a comprehensive test of Haeckel and von Baer’s laws. I scored 400 arm characters from stages 25-41 in the chick embryo, plotting them onto a time-calibrated phylogenetic tree of birds and theropods in order to test whether (1) early developed characters correspond to earlier nodes in the tree, and (2) whether later-developed characters undergo more evolutionary transitions.
This project was supervised by Dr. Hans Larsson and advised heavily by Donald Fowler.
Above: a late-stage cleared and stained Gallus gallus embryo with dissected arm.
Investigating the Effects of Water Level Drawdown from Hydroelectric Dams in Sediments
After working as a field assistant to a joint fish-invertebrate-limnology project between the labs of Dr. Chris Solomon and Dr. Irene Gregory-Eaves (McGill University), I completed an independent thesis project investigating organic matter deposition in sediment from 10 lakes in Maine, New Hampshire, and Quebec. While in the field I was also responsible for sampling and dissecting fish.
My fieldwork was funded by a competitive Biodiversity Science Discovery Award.
Above: myself in lake Memphremagog, holding a Brown Bullhead to be measured, weighed, and released.