EEB405, BIO220 and Coevolution

• EEB405 Temperate Field Biology applications are open
• Consider applying for a field course to learn field research in ecology and evolution
• Dates: May 18 to 31, 2025
• Location: Koffler Scientific Reserve
• The application deadline is January 31, 2025
• More info: www.ksr.utoronto.ca

Beyond BIO Activities

• Beyond BIO events are optional and meant to be fun and informative for BIO220 students
• More info can be found on Quercus under Modules -> Beyond BIO

Upcoming Beyond BIO Events

• BIO220 Social! will be held Tuesday January 14th at 2:10 pm in Room RW 010 in Ramsay Wright, with trivia and snacks
• Birds & Wildlife of Toronto on Thursday January 23rd from 11:10 am – 12:00 pm in room RW 432 with refreshments and snacks

Lecture 2: Human – Agricultural Coevolution

• Addresses coevolution, how humans coevolve with agricultural species, and the imprint of coevolution on genomes

Coevolution Explained

• Coevolution involves reciprocal evolutionary responses between a pair of species, driven by selection imposed by each other
• Sexual coevolution involves reciprocal evolutionary responses between the two sexes, again caused by selection imposed by each other
• Human agricultural coevolution occurs between humans and their agricultural species due to selection imposed by each other
• Evolution by natural selection is a process that relies on ecology to provide selection
• Genetics provides the material transmitted across generations

Human Ecology

• Includes culture and the organisms humans interact with

Human Milk Digestion

• Humans digest milk using the lactase enzyme to get useful milk-based products

Lactase Production

• Usually declines in adulthood
• In people of North European origin, lactase production persists through adulthood, enabling milk digestion
• A decline in lactase results in lactose intolerance
• Wild-type means to be lactose intolerant as an adult

Lactase Persistence

• Is present in many humans of European origin, allowing for the digestion of milk
• Changes in the lactase gene in European populations strongly correlated with the ability to digest lactose as an adult
• The substitutions are the causal variants
• The substitutions were favored by natural selection

Prediction

• Other human populations with lactase persistence should have the same substitutions or similar enzyme changes
• Populations practicing dairy agriculture should have lactase persistent phenotypes, and demonstrate genetic evidence of past selection at the lactase gene

Populations in Africa

• Practice dairy farming, some show this lactose tolerance
• African cultures with dairy farming also have distinctive forms of the lactase gene
• DNA sequence differences correlate significantly with the ability to digest lactose

Conclusions

• Strengthens the inference that these molecular variants affect the phenotype
• Independent phenotype evolution in different populations supports the driving force of natural selection

Chance vs Determinism

• Single events are due to chance alone or to deterministic processes
• Independent lines of evidence confirm deterministic explanations by rejecting chance

Convergent Evolution

• Is the independent evolution of the same trait in different groups and could be populations or species
• Allows for stronger evidence that selection is at work
• In the case of lactase persistence, convergent evolution appears to use the same genes

Timeline

• Studies of Neolithic human remains (10,000 years B.C.E.) suggest that they were unable to digest lactose as adults
• Cattle domestication did not occur until approximately 7,500 to 9,000 B.C.E.
• Lactase persistence in Europeans subsequently evolved around 5,000 to 7,000 B.C.E.

Lactase Gene Studies

• Studies show mutations in lactase associated with lactase persistence into adulthood
• Has strong evidence of replicated association between genotype and phenotype
• Independent derivation supports adult milk digestion as an example of convergent evolution

Salivary Amylase

• AMY1 encodes salivary amylase, which begins starch digestion in the mouth
• AMY1 shows copy number variation
• More copies, more enzyme, more digestion
• AMY1 copy number expansion in humans linked to agriculture

Lactase Persistence Mutations

• Have been detected in older Central Asian samples (5,000 years ago)
• Despite the presence of the mutation, it has not increased in frequency

Fermented Milk

• Central Asia produces fermented milk products and LP alleles are is present without increasing in frequency
• Hypothesis: Fermented milk products contain bacteria that ferment milk are ingested with it, aiding digestion
• Allows for calories, calcium, vitamin D, lipids, and proteins to be consumed

Genetic Evidence

• It is evident of past selection at the lactase gene
• Population genetics are applied

Genomic Differences

• The fate of mutations that change amino acids (replacement = non-synonymous) versus those that do not (synonymous)
• Regions of the genome that experience selection will have lower genetic variability
• More differentiation between populations at selected sites than the 'rest of the genome'

Types of Mutation

• Neutral will result in similar properties of both replacement and synonymous mutations
• Deleterious will result in lower population frequencies for replacement mutations
• Beneficial mutations will result in more replacement mutations than synonymous mutations

Alleles

• Longer lines show longer sections of the genome that are totally homozygous
• This indicates low variation in this region of the genome
• This natural cause selection is for evolution of lactase persistence

Molecular Level

• There is evidence of adaptation in lactase.

Key Concepts

• There is coevolution, convergent evolution, chance and determinism, and pop gen predictions of selection
• Includes what selection does to variation and how rate of recombination affects this
• Allele frequency differences indicate adaptation

Information on EEB405 field course applications, upcoming optional BIO220 Beyond BIO events, and lecture 2 about the human-agricultural coevolution. The field course is held at Koffler Scientific Reserve. Beyond BIO events are optional and meant to be fun and informative for BIO220 students.