Genetic diversity and selection in North American red squirrels (Tamiasciurus hudsonicus): A Hamiltonian perspective into the processes and mechanisms of evolution.

摘要

The theory of natural selection has advanced our understanding in every aspect of biological sciences, yet despite this seeming ubiquity, there remain some components that are not fully resolved. Natural selection predicts the "selfish" advancement of genes that are optimally suited for their present environment. While the evolution of sexual recombination is still not fully understood, the red queen hypothesis proposes that sexual reproduction is a means to evolve resistance to parasites. In addition, the evolution of social behaviour can also contradict the basic premise of natural selection whereby helping to advance the genes of others would cost a reduction in the success of one's own genes. I investigated these issues using the North American red squirrel (Tamiasciurus hudsonicus) while developing and optimizing additional genetic resources for the squirrel family (Sciuridae). First, I developed a new molecular sex-typing system intended specifically for squirrels by designing new PCR primers on the Y chromosome. Secondly, I investigated the interaction between the phylogeographic history and broad scale genetic selection of the red squirrel throughout western North America. While evidence suggests the red squirrel did not have a northern refugium during the last glaciation, the strong decline in genetic diversity with latitude is likely the result of recolonization. Thirdly, I tested the genetic basis to parasite resistance and quantified the cost of parasite infection on reproductive success in male and female red squirrels. While a genetic architecture to parasite intensity was found through a negative correlation with heterozygosity in females, the influence of parasites on reproductive success was only apparent in males, with highly successful males having higher parasite intensity. Lastly, I presented the first observation of altruism directly supported by Hamilton's rule of inclusive fitness. Surrogate females always gained a fitness advantage by adopting related juveniles when circumstances allowed for the cost of adoption to be less than the benefit multiplied by their shared relatedness ( c < rb). These investigations into the mechanisms of genetic diversity and selection have provided much needed support for the basic assumptions of natural selection and evolutionary biology while also advancing our primary knowledge and available genetic resources.