Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Dr. Deborah MacLatchy

Advisor Role

Thesis Supervisor

Second Advisor

Dr. Andrea Lister

Advisor Role

Committee Member

Third Advisor

Dr. Jim McGeer

Advisor Role

Committee Member

Abstract

Using a flow-through laboratory bioassay, experiments investigated the effects of limited feeding, increased temperature, ammonium chloride (NH4Cl), and 17α-ethinylestradiol (EE2) on juvenile mummichog (Fundulus heteroclitus) growth. Weight measurements were taken every three days as the apical growth endpoint. Gene expression was examined by qPCR for genes in the GH (growth hormone)-IGF1 (insulin-like growth factor 1) pathway, including gh, igf1, and their receptors (ghra, ghrb, igf1ra, igf1rb). In Experiment 1, juvenile mummichog were exposed to excess or limited feed for 21 days. The limited-fed mummichog weighed less, were shorter, and exhibited lower liver igf1 and muscle ghra mRNA expression than the control. In Experiment 2, juvenile mummichog were exposed to 0, 125, or 200 mg/L NH4Cl for 21 and 33 days. Growth was not altered by Day 21; however, 200 mg/L NH4Cl-exposed mummichog exhibited a decrease in liver ghra and ghrb mRNA expression compared to the control. After 33 days, NH4Cl-exposed mummichog weighed less but those exposed to 200 mg/L NH4Cl expressed higher liver igf1 and ghrb mRNA expression than the control. In Experiment 3, juvenile mummichog were exposed to control (salt water), 250 mg/L NH4Cl, or 250 ng/L EE2 at 20 and 25°C for 21 days. NH4Cl-exposed mummichog weighed less than controls, starting on Day 3 and Day 9 for fish at 20 and 25°C, respectively, and those at 25°C exhibited higher liver igf1ra and igf1rb mRNA expression. EE2 did not affect growth; EE2-exposed mummichog at 20°C exhibited higher liver igf1ra and igf1rb mRNA expression. When adult post-spawning female mummichog were exposed to Experiment 3 conditions, EE2-exposed mummichog at 25°C had higher weights and increased liver igf1 and igf1rb mRNA expression. Exposure to 25°C also increased ovary weights. NH4Cl reduced liver weights but increased liver igf1Rb in NH4Cl-exposed mummichog at 25°C. Together, these experiments demonstrate that food quantity, temperature, NH4Cl, and EE2 influence mummichog growth. Variability in molecular endpoints indicates the need for further studies and consideration of alternate mechanisms, including other hormonal pathways; the GH-IGF1 pathway might not be the main factor driving the mummichog growth effects caused by these environmental stressors.

Convocation Year

2024

Convocation Season

Spring

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