Evolutionary Ecology

This week’s lab focused on the theories of Charles Darwin, Hardy-Weinberg, and the natural selection of the peppered moth. Charles Darwin is a naturalist known for his ideas on evolution, regarding species. Darwin is the author of “The Origin of Species” where he discusses his argument on evolution which consists of four parts: competition, variation, inheritance, and survival & reproduction. Basically, Darwin believed that all species have variation based on genetics, specifically inherited traits. Organisms with the most favorable traits would be able to survive, reproduce, and pass their traits on to the next generation. Organisms with the most favorable traits showed a greater evolutionary fitness; this term is defined by the number of surviving offspring produced by an individual in comparison to less well-endowed individuals.
This experiment focused on the response of the peppered moth (Biston betularia) to industrial pollution. In 19th century England, industrialization and domestic coal fires caused soot filled air pollution. This air pollution caused the death of lichen located on tree trunks and the darkening of tree trunks. The darkening of the tree trunks benefitted the dark-colored melanistic moth, and hurt the populations of the light-colored mottled moth. The melanistic gene is dominant and genotypically represented as MM or Mm; the mottled gene is recessive and represented as mm. Moths with the melanistic gene were better camouflaged when on the darkened trees; this allotted them with safety from predators, like birds. Mottled moths did not have an advantage when on the blackened trees, causing a decline in their population in areas with high pollution. This lab is a simulation of this occurrence. We will be testing the evolution and fitness of melanistic and mottled moth populations in areas of low, moderate, and high pollution.

Which genotype performed well in your simulation? How did the environment influence survivability?

In the high pollution environment, the melanic genotype (MM) had a higher chance of survival than the other phenotypes respectively. This high chance of survival was due to the characteristic of melanic being favored in this type of environment. Additionally, the more polluted the area was according to Kettleweel’s experiment, the least likely the melanic moths were to be eaten by prey. In the moderate polluted environment, the melanic genotype (Mm) had a better chance of survival than the other genotypes observed. This chance of events was due to the characteristics of the environment favoring moths who displayed a more balanced camouflage to dark body type ratio than the melanic (MM) genotype did from surrounding predators.

How did the allele frequencies vary across generations? How did the environment influence the allele frequencies?

The allele frequencies appeared to fluctuate across generations taking, into consideration the random chance of events that could occur in each stimulation. In the high polluted environment for instance, the alleles for genotypes MM, and Mm appeared to almost triple in number from the beginning to the end of the stimulation, while the alleles for genotype mm were rather low in number. In the moderate polluted environment however, the roles were slightly reversed. The allele frequency in genotypes Mm and mm appeared to outnumber that of genotype MM respectively. As mentioned, this could be due to various factors or random chance of events throughout each new generation. The last environment, which was the least polluted, showed a remarkable difference in allele frequencies. All alleles for genotypes MM and Mm were completely wiped due to the phenotypic expressions of each. The genotype mm was the only one out of the three to produce alleles after selection had occurred due to the mottled moth’s ability to completely camouflage itself from surrounding predators.

	MM	Mm	mm
Before Selection	0	0	12
After Selection	0	0	12
Survival Rate (ω)	0	0	1.00
Estimated Fitness (λ)	0	0	1.00

	MM	Mm	mm
Before Selection	6	14	8
After Selection	3	10	7
Survival Rate (ω)	0.50	0.71	0.88
Estimated Fitness (λ)	0.57	0.81	1.00

	MM	Mm	mm
Before Selection	40	20	2
After Selection	40	19	0
Survival Rate (ω)	1.00	0.95	0
Estimated Fitness (λ)	1.00	0.95	0

How did the relative fitness of your genotypes change from the first generation to the last generation? What do your results suggest about the organism’s ability to survive?

Relative fitness is defined as the survival rate of a phenotype relative to the maximum survival of other phenotypes in the population. In this experiment, the relative fitness of the moth directly correlated to the moth’s phenotype and environment. In the first trial of each pollution level, the Melanic, Mm, moth had the highest relative fitness, due to it being a control value for each simulation. This shifted from the first generation to the last generation in all of the pollution levels. In low pollution, the mottled moth had the highest fitness; due to the loss of the MM and Mn, melanic, populations in generation 1. The relative fitness of the moderate pollution was also highest in the mottled moth population. The homozygous dominant melanic moth had the highest relative fitness in the high pollution simulation. These results support basic ideas of adaptations and survival. When organisms are put into a changing environment, one phenotype becomes the improved phenotype under these conditions, with greater reproductive success, and the population has a greater fitness (Mundy 2007). In the areas of low pollution, mottled moths were able to survive and reproduce because industrial processes were not as successful in polluting the area, in comparison to other areas. This allowed for mottled moths to be better camouflaged on lighter tree trunks—leading to survival and reproduction. As areas became more polluted, a slow shift began in the desirable phenotype of the moth. As seen in Tables 1 and 2, MM and Mm populations had a relative fitness of 0 in areas of low pollution, but in the area of moderate pollution, a drastic increase can be seen in both populations. The increase of polluted tree trunks led to the increase in melanistic moth populations.

Read the article, “Man’s new best friend? A forgotten Russian experiment in fox domestication”. Explain how Belyaev selected for tame foxes. Describe some of the expected and unexpected changes that occurred in the foxes over generations. What do the changes suggest about artificial selection?

Jason G. Goldman’s article “Man’s new best friend? A forgotten Russian experiment in fox domestication” explores the research of Russian geneticist Dmitri K. Belyaev. Belyaev’s research of tame foxes followed a time in Russia when genetics was considered a pseudoscience. He was interested in the domestication of dogs, but Belyaev chose to focus on foxes, a relative of dogs and wolves, in his research. Specifically, Belyaev believed that the domestication of animals from wild animals was highly based on the tameness of the animal. He tested this by attempting to domesticate wild silver foxes with a strong selection criteria for inherent tameness. Belyaev selected for tame foxes by testing their reactions to an experimenter. When the fox reached sexual maturity it was given a tameness score, this score was based on the fox’s tendency to approach the experimenter and its tendency to bite the experimenter. The least fearful and aggressive foxes were chosen to breed; over the years, Belyaev’s research led to 40 generations of tame, domesticated foxes. Some of the changes due to domestication of the foxes include eagerness for human interaction, need for attention, licking & sniffing of caretaker, wagging of tails, reduction in fear of new people and objects, and less trepidation in new locations. Physically, many of the domesticated foxes now had floppy ears, short or curly tails, changes in fur color, and changes in skull shape. Artificial selection is defined as a process in the breeding of animals by which the breeder chooses to perpetuate only those forms having certain desirable inheritable characteristics. The changes observed by Belyaev’s research represent the importance of artificial selection, pertaining to evolution and genetics.

Reference: Mundy NI (2007) Coloration and the genetics of adaptation. PLoS Biol 5(9): e250. doi:10.1371/journal.pbio.0050250

The introduction was completed by Nia Alston. Questions 1 and 2 were answered by Jayla Watkins. Alston completed questions 3 and 4. Alston and Watkins worked collaboratively to complete the graphs and tables.