This study was undertaken to compare the observed heterozygosity values in Devil Lake and Knowlton Lake. In each lake, the observed heterozygosity at various loci was determined through the analysis of autoradiographs and microsatellite data, the values obtained were input into the Doh program and the average observed heterozygosity in each value were calculated. The average observed heterozygosity for lake trout from Devil Lake was approximately 0.114 larger than the average observed heterozygosity in Knowlton lake. It was determined that the observed heterozygosity of lake trout from Devil Lake was not significantly higher (p=3.43e-12) than lake trout from those in Knowlton Lake. There are several factors that may have contributed to the results, such as niche divergence, restricted gene flow, the presence of dams, and exposure to dangerous pollutants.
Introduction
Through the analysis of DNA microsatellite diversity, one can accurately compare the observed heterozygosity values in lake trout (Salvelinus namaycush) found in Devil Lake and Knowlton Lake, allowing one to generate relevant conclusions related to conditions and lake factors favored lake trout and their life cycles.
Lakes Devil and Knowlton are natural, deep, highly sensitive cold-water lakes that serve as a habitat for species such as the lake trout. The lake tout is of particular interest due to the species’ vulnerability to overexploitation and invasive species as a result of its life cycle (Shuter et al. 1998). In order to survive cold, unproductive ecosystems, lake trout are dependent upon their slow growth, late maturation, and low reproductive potential (Aherne et al. 2004). Lake trout require cold water with high dissolved oxygen concentrations, hence, they are highly vulnerable to warming trends and temperature fluctuations (Guzzo and Blanchield, 2011). In particular, lake trout populations concentrated in small lakes that undergo annual thermal stratification, are expected to experience changes in physical and biological properties as a result climate change and subsequent thermal stress (Aherne et al. 2004). There is also evidence that lake trout populations from central and eastern Ontario are becoming extinct, decreasing genetic variation, as optimum summer habitats were absent or limited as the temperature of water becomes too hot (Heggenes and Røed, 2006). High heterozygosity, a measure indicative of high genetic variation, in lake trout has been associated with differences in traits such as cranio-skeletal features and fin length related to factors such as resource partitioning and niche divergence (Ballie et al. 2016). Water depth itself acts as a driver of genetic and phenotypic differentiation with visible genetic discontinuities among different depths, suggesting gene flow is hampered by water depth, rather than geography or ecotype (Baillie et al.2016).
By calculating the observed heterozygosity of the lake trout in lakes Devil and Knowlton, using microsatellite diversity one can examine factors influencing genetic variation in lake trout and determine lake trout’s ideal habitat. This understanding of the processes underlying diversification can be used aid individuals in formulating conservation plans and countering anthropogenic factors in lake trout habitats.
Results
The average observed heterozygosity of lake trout from Lake Devil was 0.493 and the average observed heterozygosity of lake trout from Lake Knowlton was 0.379. It was determined that the observed heterozygosity of lake trout from Lake Devil (n=25, 6 loci) were not significantly higher (p=3.43e-12) than lake trout from Lake Knowlton (n=25, 6 loci).
Discussion
The observed heterozygosity of lake trout from Lake Devil was not significantly higher than the lake trout from Lake Knowlton. This marginal deviation is likely related to the similar properties shared by the lakes such as the occurrence of thermal stratification, which is caused by fluctuations in temperature. The varied ecological gradients, consisting of factors such as temperature, salinity, and oxygenation, are correlated with depth and vary in aquatic zones. Therefore, individual lake trout with certain inherited traits have a tendency to survive and reproduce at a higher rate, altering the pool of alleles and preventing lake trout in different zones from mating with one another via isolation-by-depth and morphological or behavioral traits. Ultimately, this may lead to differentiation through niche divergence and restricted gene flow. As a similar process brought on by the varying properties in aquatic zones, similar levels of genetic variation and heterozygosity exist in both lakes. Differentiation among lake trout in Lake Superior, manifests itself in the form of four distinct ecotypes ( which have been associated with differences in traits related to trophic resources partitioning and depth (Baillie et al. 2016).Taking this into consideration, it is possible that lake trout from Devil Lake likely have a higher average observed heterozygosity than lake trout from Knowlton Lake as Devil Lake has a higher maximum depth of approximately 44.5m, which could result additional trophic zones and, thus, more genetic variation.
According to the results it can be seen that average observed heterozygosity in lake trout from Devil Lake was approximately 0.114 larger than lake trout from Lake Knowlton could be due to the existence of a dam in Devil Lake. The fragmentation of Devil Lake may have led to increased genetic variation in the lake’s trout population due to the fact that as time passages, the restricted flow of genes can propel natural selection and create local adaptations. This differentiation has been well document in brown trout’s tendency to establish differentiated populations over short distances (i.e. same lake) as a result of semi-barriers that generate small populations and genetic drift, culminating in fluctuations in allele frequencies (Heggenes and Røed, 2006).
On the other hand, the average observed heterozygosity of lake trout from Knowlton Lake is smaller than that of lake trout from Devil lake due the prevalence of pollutants and contamination as a result of the surrounding land being used for agriculture. The land surrounding Devil Lake is primarily used as Woodland, Wetland, and Residential land, while the areas surrounding Knowlton are used for Woodland and architecture and, subsequently, there is a likely a higher concentration of pollutants (specifically, pesticides and fertilizers) that run-off into the lake. The probable increased levels of contamination in Knowlton Lake contribute to a smaller lake trout population size and, therefore, lake trout from Knowlton lake have a lower average heterozygosity. Borgmann (1998) observed the high levels of pollutants and heavy metals were found in the tissues of lake trout in Northern Ontario that were larger in size and older in age. Due to the death of an atypical number of lake trout at a young age because of presence of pollutants, the number of offspring carrying heterozygous genes would likely decrease with every generation and, subsequently, this lake trout population would have a lower heterozygosity (Volckaert and Zouros 1989).