Investigating population structure and resource use diversity in Lake Huron Lake (Coregonus clupeaformis) and Round (Prosopium cylindraceum) Whitefish using compound specific stable isotopes analysis

Abstract

Aquatic thermal pollution from electricity generation, via once-through cooling systems, poses a potential threat to freshwater ecosystems. Research has shown that elevated temperatures can have adverse effects on whitefish reproduction and development, potentially leading to population decline. Despite these risks, there is limited understanding of whitefish population structure in areas affected by once-through cooling in Lake Huron. Population structure assessments are typically conducted with genetic methodologies but population mixing in Lake Huron complicates detection. In addition, genetic methodologies are not able to capture recent ecological aspects of population structure, necessitating the use of additional marker types. The stable isotopes of carbon (δ13C) and nitrogen (δ15N) are biochemical markers that reflect differences in prey, habitat, and trophic position within food webs making these isotopes valuable in differentiating ecological populations. Bulk stable isotope analysis (BSIA) has been used in previous research but interpretation is often confounded by various factors that contribute to isotopic variation. Compound specific stable isotope analysis (CSIA) of amino acids offers higherresolution information, allowing for the examination of baseline resource use and trophic position estimation for a sampled consumer. My research aimed to investigate the ecological population structure and baseline resource use diversity of spawning phase lake and round whitefish in Lake Huron by using CSIA. I evaluated the influence of sex, size, year, and sample site on baseline isotopic values and trophic position, examined baseline resource use by comparing isotopic niche size and overlap, and assessed the usefulness of additional amino acids for detecting population structure. I found extensive variation in δ13C phenylalanine values and moderate variation in δ15N phenylalanine for both species suggesting diversity in food web membership. While δ13C values were comparable by site to previous BSIA research, δ15N values showed differences, highlighting the advantage of CSIA in accurately assessing baseline resource use. Differences in baseline resource use among sites indicates differences in food web membership suggesting the presence of different ecological populations. Temporal factors, such as year, influenced baseline isotopic values, potentially indicating shifts in baseline resources or foraging strategies. Additionally, the biological factors such as sex and total length showed associations with baseline isotopic values, suggesting potential differences in foraging ecology and habitat use. Trophic position varied within sites for both species indicating diversity in generalist feeding strategies not connected to sample location. Lake and round whitefish separated into two areas of isotopic niche space, with δ13C values driving the differentiation. However, there was species overlap within these niche spaces suggesting the use of similar baseline resources or foraging within the same food webs. The depleted and enriched δ13C phenylalanine isotopic niche spaces may be connected to larger geographic regions of origin, and not connected to specific sample locations. Previous research using BSIA supports this, indicating broad differences in δ13C based on geographic region. The use of amino acids beyond phenylalanine and glutamine in ecological research using CSIA is uncommon despite their potential value. For δ13C, both essential and non-essential amino acids differentiated isotopically similar groups within species. Future investigations of baseline resource use may be enhanced by the inclusion of multiple amino acids to delineate ecological populations. For δ15N, the additional amino acids distinguished between the whitefish species. Overall, CSIA provided valuable insights into lake and round whitefish ecology, particularly in understanding spatial and temporal variations in baseline resource use and foraging behavior.