Question

A population of timber rattlesnakes in eastern Kentucky is surveyed to estimate genetic diversity and structuring of the species across the landscape. Six populations are tissue sampled and are genetically analyzed; these appear to be metapopulations that are fragmented and separated by surface mining. The following data describe the distribution of genetic diversity within this population. HP = 9%; DPT = 91%. Explain these findings and why they may or may not be important knowing that 3 of these 6 populations are at risk due to surface mining permits being issued for land they occupy. HP = mean diversity within populations DPT = Mean divergence among populations HT = total genetic variation (mean total heterozygosity) HT = HP + DPT

Answer 1

Genetic variation describes naturally occurring genetic differences among individuals of the same species. This variation permits flexibility and survival of a population in the face of changing environmental circumstances. Consequently, genetic variation is often considered an advantage, as it is a form of preparation for the unexpected.

Mean diversity within populations indicate the level of diversity observed in the genotype of species within a population which could be smaller or larger while mean divergence among populations is the diversity observed among the species of different populations. In this case, the diversity observed is higher in 'among the populations' than within the populations which is indicative of the fact that genetic drift has occurred between species. Typically, genetic drift occurs in small populations, where infrequently-occurring alleles face a greater chance of being lost. Once it begins, genetic drift will continue until the involved allele is either lost by a population or is the only allele present at a particular gene locus within a population. Both possibilities decrease the genetic diversity of a population.

Genetic drift is common after a population experiences a population bottleneck. A population bottleneck arises when a significant number of individuals in a population die or are otherwise prevented from breeding, resulting in a drastic decrease in the size of the population. Genetic drift can result in the loss of rare alleles and can decrease the size of the gene pool. Genetic drift can also cause a new population to be genetically distinct from its original population, which has led to the hypothesis that genetic drift plays a role in the evolution of new species.

If the individuals at either end of the range reconnect and continue mating, the resulting genetic intermixing can contribute to more genetic variation overall. However, if the range becomes wide enough that interbreeding between opposite ends becomes less and less likely, and the different forces acting at either end become more and more pronounced, and the individuals at each end of the population range may eventually become genetically distinct from one another.

As relative allele frequencies change, relative genotype frequencies may also change. Each genotype in the population usually has different fitness for that particular environment. In other words, some genotypes will be favored, and individuals with those genotypes will continue to reproduce. Other genotypes will not be favored: individuals with those genotypes will be less likely to reproduce. Unfavorable genotypes take many forms, such as increased risk of predation, decreased access to mates, or decreased access to resources that maintain health. Overall, the forces that cause relative allele frequencies to change at the population level can also influence the selection forces that shape them over successive generations.

These findings are important in understanding the role of environmental factors in the genetic divergence. 3 out of the 6 populations are at a high risk due to surface mining because the gentic divergance is low in these population leading to lesser adaptation to the environmental conditions compared with the other populations.