Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Guglielmo, Christopher G.

Abstract

Methylmercury (MeHg) is an environmental contaminant that has a high biomagnification potential with potent neurotoxic effects. Insectivorous bats may be readily exposed to MeHg through their diet. To test the effect of exposure on torpor and body composition in silver-haired bats (Lasionycteris noctivagans), I measured total mercury (THg, combination of inorganic and methylmercury) through fur samples and quantitative magnetic resonance analysis, temperature sensitive radio tags, and respirometry data from these bats to quantify body composition and torpor use. THg levels varied 20-fold with heavier and fatter bats having higher levels, suggesting that individuals that routinely eat more accumulate more THg. THg was not related to torpor use at 25 and 17°C, however, at 10°C, bats with higher THg levels used more torpor. This was characterized by fewer but longer torpor bouts. This study provides insight into the tolerance of MeHg in bats, and potential adverse effects that it may elicit.

Summary for Lay Audience

Heavy metals have many potent toxic effects on organisms that encounter them. One such metal is methylmercury (MeHg), which primarily affects the brain and nervous system when it is ingested. Bats that feed on insects may be readily exposed to MeHg through their diet. This is because many insects that bats feed on begin their lives in aquatic environments, which is the main habitat of methylating microorganisms. The tolerance levels and effects that bats exhibit when exposed to MeHg are not well understood, and thus, this study aimed to determine the effect of MeHg on body composition and torpor in silver haired bats, a migratory bat species in North America. Torpor is a state of reduced metabolic rate that leads to a drop in body temperature. Bats heavily rely on torpor to save energy as they have high metabolic rates. Torpor is especially important during migration, as this is an energy intensive process. I received fur samples, as well as data on body mass, body composition and torpor use in silver-haired bats that were collected during previous studies at Long Point, ON, Canada. By testing these fur samples for mercury content, I was able to construct a variety of models that investigated the correlation between the fur mercury content and the body mass, body composition and torpor use in these bats. From this, I concluded that bats who were heavier and fatter had higher total mercury concentrations than bats that were not as well nourished. This may suggest that bats who are consistently eating more, are accumulating more mercury. In the previous studies, torpor use was measured at multiple temperatures, and at higher temperatures the mercury content of the bat did not significantly affect its torpor usage. However, at colder temperatures, bats with higher mercury concentrations engaged in more torpor, where they used fewer but longer torpor bouts. This study provides insight into a bat’s tolerance of heavy metals, and potential adverse effects that this may elicit.

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