Areej Al-Dailami
PhD Candidate, University of Toronto Mississauga
PI: Prof. Angela Lange & Ian Orchard
Title: The role of glycoprotein hormone GPA2/GPB5 in the ‘Kiss of Death’ bug, Rhodnius prolixus
Abstract: Glycoprotein hormones are formed by the heterodimerization of alpha and beta subunits. In vertebrates, there are five glycoprotein hormones, four of which have a common alpha subunit (GPA1) bound to a specific beta subunit (GPB1, GPB2, GPB3, or GPB4), and the fifth, thyrostimulin, is formed by the dimerization of GPA2 and GPB5 subunits. These hormones mediate physiological events such as development, metabolism, and reproduction. Interestingly, the only glycoprotein hormone present in invertebrates is GPA2/GPB5, which appears to play roles in development, diuresis, and reproduction. In my thesis, I have characterized the transcripts for the glycoprotein hormone GPA2/GPB5 and its receptor (LGR1) in fifth instar Rhodnius prolixus, the kissing bug, and a vector of Chagas disease. Sequence analyses reveal considerable identity and similarity of GPA2/GPB5 and LGR1 with those reported in other arthropod species. qPCR shows that both subunit transcripts, GPA2 and GPB5, and LGR1 transcripts are present in a variety of tissues, with greatest expression of the subunits in the central nervous system (CNS). Using immunohistochemistry, GPB5 is found to be expressed throughout the CNS and is present in neurosecretory cells in the brain and abdominal neuromeres and their neurohemal organs, indicating a neurohormonal role. In fifth instars, a reduction in LGR1 transcript expression (via RNA interference) leads to greater weight loss in unfed insects, a decrease in the size of blood meal consumed, and increased mortality rate in both unfed and fed insects. In adult females, downregulation of LGR1 transcript expression increases vitellogenin production, resulting in accelerated egg production, increased size and number of eggs laid, and reduced hatching percentage. Overall, our results suggest that GPA2/GPB5 signaling plays roles during a prolonged unfed state, in feeding-related events, and acts as a gonad-inhibiting hormone in the adult female R. prolixus.
Vicki Zhang
PhD Candidate, University of Toronto Mississauga
PI: Prof. Peter Kotanen
Title: Limits to Plant Invasions at the Edge of the Arctic
Abstract: Invasions by non-native plants are a widespread and serious problem in many regions, but tundra and taiga ecosystems remain relatively uninvaded. An exception is Churchill, Manitoba (58ºN), where over a hundred non-native plants have been recorded within the town footprint. While some invasive species have persisted for decades in human-disturbed areas, none has spread into natural subarctic ecosystems. It is unclear why these invasions have failed.
Using field experiments, I test the effects of potential barriers to northern invasions. Movement of invaded soils can overcome dispersal limitation by transporting non-native seeds to new areas. Non-native species have lower survival and performance in the tundra but performed better in the boreal forest. Additionally, some non-native species performed better in warmer microsites with higher soil nutrient content.
This suggests that several abiotic factors play an important role in invasion, but requirements to invasion success are not currently met. However, if invasion barriers are removed (i.e., soil is moved for construction, temperatures or nutrients are increased), there is a risk of invasions from human-disturbed areas into surrounding environments.
