Chapter 14: Evolutionary Biology

What is Cholera?

A disease that causes fatal diarrhea and dehydration

What is epidemiology?

The study of incidence, frequency, distribution, and control of infectious disease in defined populations

What did John Snow study?

An epidemic of cholera struck London in 1854, John Snow prepared a map of infected people and water pumps this was the first epidemiological study

What is the germ theory of disease?

microorganisms cause disease, contagious diseases are caused by germs

Who proposed the germ theory of disease?

Louis Pasteur in 1858 the year before Darwin published origin of species

Why is germ theory the post important breakthrough in modern medicine?

- Identified numerous pathogens

- Development of antiseptic surgery

- Discovery of antibiotics

- Improvements to sanitation

What is tuberculosis?

Bacterial infection of the lungs

How are pathogens and hosts in a evolutionary arms race?

They are in conflict, when vertebrates respond to pathogens the pathogens will evolve around it

How do vertebrates (humans) respond to pathogens?

The body recognizes billions of foreign proteins and responds aggressively then remembers the structure of that pathogens proteins

The nature of pathogens

Pathogens have large population sizes, short generation times, and high mutation rates

Why does the flu virus need to continue to evolve?

External proteins initiate infection, they are also the primary proteins recognized in host immune system, so virus needs to change or find a naive host

What are antigenic sites?

specific parts of a foreign protein that the immune system recognizes and remembers

What was the flu strain hypothesis?

Flu strains with novel (new) antigenic sites will have a selective advantage, the study used sequences of hemagglutinin in previous strains from 1068-87 with high mutation rates

What study followed the flu strain hypothesis? (1965-1996)

Of the 331 substitutions 58% were silent, 42% were replacement, 18 codons in hemagglutinin had more replacement substitutions than silent, all 18 were in antigenic sites and under positive selection

Why was the study on the flu virus important?

Was used to find that the human immune system does exert strong selection on flu virus genes and they used this data to predict the next flu virus

How does the flu virus evolve?

One survivor will be the ancestor of all the future flu strains and the survivor will have the most substitutions in codons

Are pigs the vector of flu transmission?

Humans can infect pigs with the flu and pigs can infect humans with the flu, pigs are infected by birds

What was the worst influenza epidemic?

The 1918 flu epidemic that caused 50-100 million deaths

What study was conducted based on the 1918 flu epidemic?

flu virus was isolated from a 1918 flu victim and preserved in permafrost, nucleoprotein gene was sequences to indicate host specificity, it looks similar to human and swine

What is the H1N1 virus?

swine flu gene, interspecies transmission of influenza genes

What are antibiotics?

Chemicals that kill bacteria by disrupting particular biochemical processes, for populations of bacteria an antibiotic quickly becomes a powerful selective agent

What happens when an antibiotic is applied to a population of bacteria?

The antibiotic quickly sorts the resistant individuals ( those that can tolerate the drug) from the susceptible ones ( those that cannot tolerate the drug and will die)

What evidence is there that antibiotics select for resistant bacteria?

- On the small scale studies have been conducted of bacterial evolution within an individual

- On the larger scale researchers can compare the incidence of susceptible versus resistant bacteria strains among patients who are newly diagnosed and those who have relapsed after antibiotic treatment

How have researchers studied selection by antibiotics for resistant bacteria?

examine relationship over time between the fraction of patients with resistant bacteria and society wide level of antibiotic use

Why might antibiotic resistance be costly for bacteria?

Evidence shows some pathogens revert to sensitivity in absence of antibiotics, other pathogens or strains of pathogens do not appear to suffer a fitness cost

What is the prediction of antibiotic resistant bacteria?

The level of resistance should track antibiotic consumption

What is the best defence against antibiotic resistant bacteria?

Avoid letting bacteria populations evolve resistance by using antibacterial products, taking care when prescribing antibiotics, isolation of patients with resistant strains, and avoiding foodborne bacteria

What is the hypothesis about the evolution to benignness (recent entrance)?

It has traditionally been contended that pathogens are only virulent when they have newly begun using humans as hosts, over time they evolve to benign coexistence

What is the perfect pathogen?

One that does not harm its host very much so that the pathogen can continue to live, reproduce, and be transmitted

Why was the evolution to benignness hypothesis wrong?

Pathogens evolve to the optimal level of virulence, natural selection may select for higher virulence or lower virulence depending on the rate of transmission, new pathogens are less likely to be highly virulent because they have not adapted to a hosts immune system

What is the coincidental evolution hypothesis?

Some pathogens are not natural human pathogens and have not evolved with humans but they may occasionally infect humans and make them sick

What are examples of the coincidental evolution hypothesis?

Tetanus, and Legionnaires disease, accidental pathogens do occur but they are the exception and not the rule

What is the shortsighted evolution hypothesis?

Because pathogens reproduce within hosts, traits that increase their short term fitness may actually be detrimental, high virulence could cause immediate fitness but would lead to long term low fitness is pathogen is to virulent to pass on

What is an example of the short sighted evolution hypothesis?

Polio which normally infects cells that line the digestive tract and causes few symptoms. Occasionally, the virus infects cells of the nervous system with tragic consequences

What is the trade off hypothesis (transmission rate)?

Pathogens evolve to the optimal amount of virulence based on rate of transmission,

What is the nature of pathogen transmission according to the trade off hypothesis?

Pathogens that are easily transmitted can have very high virulence and host death will not prevent transmission, pathogens that are difficult to transmit must have lower virulence or they will kill the host without being transmitted

What might cause higher virulence?

Higher transmission rates (ex HIV)

How was the trade off hypothesis tested?

Found that bacteria phages that infect E.coli and were artificially transmitted faster evolved higher virulence than more slowly transmitted phages

Why did the flu transmit so fast in 1918?

In trenches in world war 1 soldiers wee cramped in close quarters so it spread faster, when soldier died another took his place this cause very high transmission which lead to high virulence

Why might cells of an individual express different alleles?

Because of heterozygosity, mutations in particular cells may also lead to different evolutionary paths

What is interesting about cancer cell mutations?

Cancerous cells have new mutations and tumors have more mutated DNA compared to normal cells

How might natural selection differ between cancerous and normal cells?

Cancerous cells have faster generation times, they can genetically diverge more quickly than healthy cells

What is COVID-19?

A virus caused by a novel coronavirus (SARS-CoV-2), it emerged in Wuhan China, covid-19 stands for coronavirus disease of 2019 (outbreak year)

What are coronaviruses?

Large family of viruses that usually cause mild or moderate upper respiratory illnesses like the common cold, most circulate among animals such as pigs, camels, bats, and cats, but occasionally jump to humans

What is the lethality of coronaviruses?

Four out of the seven known viruses cause only mild to moderate disease, three new viruses have emerged in the past two decades that cause serious and widespread illness and can be lethal in humans

SARS -CoV-1

Emerged in november 2002 in 26 countries, over 8k cases and 774 known deaths, disappeared in 2004

Middle East Respiratory syndrome ( MERS-CoV)

Emerged in april 2012 in 27 countries, 2500 cases and 858 known deaths, continues to spread with localized outbreaks

SARS-CoV-2 (COVID-19)

Emerged in december 2019 and was global, 768 million cases and 6.9 million deaths, 103.4 million cases in the US and 1,12 million deaths

How do Covid-19 and the flu differ?

They both have similar symptoms and modes of transmission but they are different viruses

How dangerous is the flu?

Infects 9-45 million americans per year, 140k-810k hospitalizations and 20k-61k deaths per year

Where did covid come from?

Pneumonia cases were documented in december 2019 in people who had been exposed to fish, livestock, or wild animal markets in china, these markets sell animals that are sold and killed and skipped, these are ample conditions for virus transmission, likely a zoonotic disease

What is the history of covid 19?

Originated in bats that have caused disease before, disease shows evidence of host shifts, potential of bat groups to continue spreading disease

What was the most likely path of transmission? (covid)

Bats to humans

Bats to pangolin ( or other mammal) then to humans

Why is covid genetically able to bind to human cells?

Gene for spike protein in virus has a 12 nucleotide insertion this mutation may help protein bind tightly to cells which is a crucial step in its evolution from animal disease

What is the ACR2 protein in humans?

ACE2 is a human protein in airways that spike binds to

What is an example of selection imposed by modern life?

Lactose tolerance, lactase enzyme breaks down milk sugar and there is no advantage to producing lactase after weaning, however humans have a long history of drinking cows milk and many have inherited the ability to keep making lactase

Breast cancer and natural selection

1 in 8 women contract it in the US some die while still in childbearing age, if heritable natural selection should remove or reduce frequency, it could be caused by a pathogen (viral) or be genetic and environmental

How does the mouse breast cancer study explain susceptibility of breast cancer?

High incidence of cancer in regions were more mice are infected with mammary tumor virus (MMTV), breast cancer may be caused by a virus but particular alleles and environmental factors may make people more susceptible

What are the two hypothesis of why fevers may have evolved?

1) May represent manipulation of the host pathogen, if this is correct then reducing the fever would probably help the host combat the infection

2) Fever may be an adaptive defense against pathogens, if this is correct then taking drugs that alleviate fever might be counterproductive to recovery

Which fever hypothesis is correct?

Hypothesis 2, evidence from iguanas suggests this

Fever study in iguanas ( evidence for 2nd fever hypothesis)

study found that iguanas develop a behavioral fever in response to bacteria, to distinguish between the two hypothesis the researchers infected iguanas and manipulated their temperatures in an incubator

What does evolutionary theory predict for parenthood?

Individuals should direct more of their parental caregiving to their own genetic offspring than to the genetic offspring of others

How do male reed bunting birds adjust their parental care effort?

Males adjust parental care effort based on who they feed.

Who conducted a study on male reed bunting birds' parental care?

Mark Flinn observed family units for six months.

What did Mark Flinn find about fathers with step and biological children?

Fathers with both step and biological children spend more time and get along better with biological children.

What is a higher risk associated with step-parents in reed bunting families?

There is a higher risk of children being killed by a step-parent.

Why are humans so difficult to study?

Often exempt from natural selection and can perform spite or altruism with little to no fitness cost, some human behaviors and emotions likely evolve because of natural selection on ancestors