Department of Biology Graduate Theses

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Genetic variation, but no evidence of evolved tolerance, for Daphnia in road salt polluted lakes in Ontario
Biology; Arnott, Shelley
Snowmelt and rain carry road salt from paved surfaces through the watershed via runoff and groundwater. When road salt reaches lakes, it increases the salinity, often measured as chloride concentration (Cl- mg/L). Salinization negatively impacts freshwater organisms, including Daphnia pulicaria, a common crustacean zooplankton grazer that is integral to healthy ecosystems and maintenance of ecosystem services. Daphnia are sensitive to environmental changes, but studies have shown they are capable of rapid evolution. We investigated intraspecific variation in salt sensitivity among D. pulicaria collected from 10 lakes in southeastern Ontario. Lakes were distributed along a Cl- gradient from <1 mg Cl-/L (unimpacted by road salt) to 271 mg Cl-/L, which is above the Canadian Water Quality Guidelines for chronic exposure (120 mg Cl-/L) but below the guideline for acute exposure (640 mg Cl-/L). Acclimation can influence tolerance so we tested the effect of acclimation on acute 48-hour salt tolerance for Daphnia grown at low (18 mg Cl-/L) and high (218 mg Cl-/L) Cl-. Our results indicate that acclimation to higher salt concentrations does not improve salt tolerance. Our acute toxicity tests conducted under common garden conditions show a range of salt tolerances for Daphnia originating from different lakes. Daphnia from Presqu’ile Bay (26.2 mg Cl-/L Lake Ontario, Brighton, ON, CA) and Lake Wilcox (194 mg Cl-/L, Richmond Hill, ON, CA) had the highest salt tolerances in this study, with lethal concentrations for 50% (LC50) of the test individuals of 2251 mg Cl-/L and 2328 mg Cl-/L, respectively. Verona Lake had the lowest LC50, at 1809 mg Cl-/L. However, there was no impact of lake chloride on the salt tolerance of Daphnia, providing no evidence of evolved salt tolerance in southeastern Ontario. This suggests that either the current salinities are not predominant selection forces in these lakes, or evolved tolerance is coupled with an evolutionary trade-off. Further research is needed to understand the standing variation of salt tolerance within local populations, and variation across different regions, to inform decisions regarding freshwater ecosystem conservation and roadway management.
Multi-Level Responses of Benthic Macroinvertebrates to Experimental Microplastic Pollution in a Boreal Lake
Correa Braga Camara A Neves, Natasha; Biology; Orihel, Diane
The effects of plastic pollution on freshwater benthic macroinvertebrates are not well understood. In the present study, we investigated the effects of microplastics on benthic macroinvertebrates under an environmentally relevant gradient of pollution. Twelve open-bottom limnocorrals were deployed in the littoral zone of a boreal lake at the International Institute for Sustainable Development – Experimental Lakes Area in Ontario, Canada. In June 2022, a mixture of polymers (polystyrene, polyethylene terephthalate, and polyethylene) was added to the limnocorrals to achieve target sediment concentrations of 251 to 2,511,886 microplastic particles per kg of dry weight sediment. Naturally pre-colonized leaf litterbags (5x3 mm mesh size) were added to the limnocorrals and sampled after eight weeks of microplastic exposure to characterize the benthic macroinvertebrate community. We quantified the relationship between sediment microplastic concentrations and benthic macroinvertebrate responses at the organismal (head size of Hyalella azteca), population (sex ratio of Hyalella azteca and relative abundance of nine taxa), and community (total abundance, diversity, structure) levels. We found evidence of moderate effects of microplastic on the sex ratio of Hyalella azteca (F1,10 =5.88, p = 0.036), and weak effects on total richness (lm, F1,10 = 3.827, p = 0.079) and community structure (PERMANOVA pseudo-F1,34 = 1.99, p = 0.083) of benthic macroinvertebrates. Moreover, we found no evidence of effects of microplastics on size of Hyalella azteca nor on total abundance or diversity of benthic macroinvertebrates. The results of this study suggest that under ecologically relevant conditions, exposure to microplastics may only have minor effects on benthic macroinvertebrates, at least on the short term.
Environmental Correlates of Early-Life Growth, Natural Selection, and Components of Phenotypic Variation in a Long-Term Experimental Study System of Black-Legged Kittiwakes
Sauve, Drew; Biology; Friesen, Vicki; Charmantier, Anne
In the face of global environmental change, the ability to predict adaptation has become a priority. To make predictions of adaptation, we must understand how environmental factors shape phenotypic expression, natural selection, and genetic variation. In my dissertation, I explore the effects of natural and experimental environments on phenotypes, selection, and genetic variation using pedigrees, nestling growth traits, and nestling survival data from three long-term seabird monitoring programs. In most chapters, I focus on a Northeastern Pacific population of black-legged kittiwakes Rissa tridactyla. First, I review weather conditions' various impacts on nestling avian growth. Next, I use a sliding window approach to analyze three long-term seabird datasets. I use these analyses to identify specific periods of environmental variation that correlate with nestling growth, assess changes in environmental predictors across years, and predict future nestling growth under climate change. My findings reveal specific breeding season periods that are strongly associated with variation in nestling growth. These associations suggest warmer conditions may result in poorer growth for two of the three species studied. Further, windows of environmental influence changed between historical and contemporary periods, emphasizing the need to investigate how such changes might affect adaptation to changing environments. In my final chapters, I use data from a kittiwake food supplementation experiment to examine the relationship between food conditions, the variability of selection strength, and variance components of nestling kittiwake size traits. I find that natural selection is strongest in early ontogeny, in non-food supplemented nestlings, and for the youngest nestlings in a brood. Selection magnitude varied among years, but annual variation in magnitude was similar for all treatment and hatching order groups. Warming conditions have mixed effects on selection that depend on food supplementation and hatching order. Finally, I use pedigree data to find higher annual variance and evolvability of mass and wing-length in non-food supplemented nestlings, suggesting potential cohort effects and increased evolutionary potential in non-food supplemented nestlings. Together, my results help identify and fill gaps in our understanding of the ability of natural populations to adapt to ongoing climate change.
Beetlejuice, Beetlejuice, Beetlejuice: The role of antimicrobial secretions in competition in the burying beetle, Nicrophorus orbicollis
Kendrick, Julia; Biology; Bonier, Frances
An organism’s ability to survive and reproduce is often related to its ability to compete for resources. Competition can be intense for organisms that rely on temporally or spatially limited or unpredictable resources. Carrion is often both limited and unpredictable, and is particularly valuable because it is nutrient rich. Animals that use carrion face intense competition from microbes, which can make the carcass unpalatable or inhospitable. I investigated adaptations to competition with microbes in the burying beetle, Nicrophorus orbicollis. Burying beetles require vertebrate carcasses to reproduce, and use anal secretions containing antimicrobial components and beneficial gut microbes to protect a carcass during breeding. Anal secretions might delay carcass decay and prevent pathogenic competitor microbes from colonizing the carcass during larval rearing. However, the proximate mechanisms by which these antimicrobial effects occur, whether through endogenous immune defenses of the beetle and/or direct competition between gut and carcass microbes, remain unknown. Fungal gut symbionts might play a critical role in competition with harmful carrion consuming microbes, and until now the direct effects of fungal gut symbionts on competition between burying beetles and carcass microbes have not been tested. I determined the competitive consequences of experimentally disrupting fungal symbionts from the gut microbiome of N. orbicollis by measuring treatment effects on carcass preparation behaviours, anal secretion antimicrobial potency, and carcass decomposition rate. Results demonstrate the importance of the gut microbiome in behavioural plasticity, but suggest that fungal microbial symbionts might not produce antimicrobial compounds to directly compete with other carrion consuming microbes or impact the rate of carcass decomposition. Our findings contribute to our understanding of symbiotic relationships organisms have with their gut microbes, and the complex strategies some organisms use to compete for scarce resources.
Intra- and interspecific variation in salt tolerance of the sunflowers Helianthus annuus and H. paradoxus
Dain, Aaron; Biology; Yakimowski, Sarah
Environmental salinity is an abiotic stressor to most plants, and human activity is predicted to increase land salinization worldwide. Some ‘halophytic’ plants have evolved specialized mechanisms to tolerate high salinity. However, most plants (glycophytes) are limited in ability to tolerate salt. Little is known about intraspecific variation of salt tolerance in glycophytes. Here, I use a growth chamber experiment to investigate intraspecific variation in phenotypic traits of Helianthus annuus in response to salinity, and interspecific variation between H. annuus and related halophyte, H. paradoxus. H. annuus seeds were collected from saline areas around Great Salt Lake (Utah), from low-salinity areas in Utah, Colorado, and Nevada; and H. paradoxus seeds from New Mexico. Soil salinity data from 26 Great Salt Lake H. annuus population sites (10 of which were included in this experiment) were used to quantify environmental salinity associated with populations in this region. Juvenile plants received three salt treatments: control (non-saline), moderate (90 milliequivalent NaCl), and high salinity (180 mEQ NaCl). Plants were phenotyped for above- and below-ground biomass, root/shoot ratio, height and leaf growth rate, and leaf succulence. A subset of plants were analysed for leaf ion content. Moderate salinity treatment reduced the size and growth rate of H. annuus but not H. paradoxus, whereas high salinity reduced the size and growth rate of both species. Saline-origin H. annuus plants exhibited lower vigour but lower proportional decrease in above-ground biomass and leaf growth rate than non-saline-origin plants. Quantitative analysis revealed that environmental sodium-sulfur interaction predicts lower biomass, height growth rate, and leaf growth rate of H. annuus. H. annuus exhibits a salt-exclusion strategy, maintaining low leaf sodium, high potassium/sodium ratio, and high potassium-sodium selectivity. Meanwhile, H. paradoxus phenotype is divergent, with low biomass, low growth rate, high leaf succulence, and extreme accumulation of leaf sodium and sulfur. While plasticity of growth-defense trade-offs appears to account for most of H. annuus’ salt tolerance, low biomass plasticity of saline-origin populations may represent an evolutionary shift toward a stress-tolerant life history strategy. Salt tolerance appears to lack rapid evolvability in glycophytes, therefore salinization threatens plant ecosystems.

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