Cycle 11 - Evolutionary Ecology

Question 1

Outline the various types of species/population interactions

Answer 1

Question 2

Define co-evolution

Answer 2

Co-evolution: occurs when genetically based, reciprocal adaptation occurs in two or more interacting species

Question 3

Explain commensalism

Answer 3

Commensalism

• One species benefits from and the other is unaffected by the interactions
• Rare in nature because few species are unaffected by the interactions of others
• Ex., oxpeckers eat organisms off hosts and do not cause harm to the host

Question 4

Explain mutualism

Answer 4

Mutualism

• Both partners benefit
• Common
• Ex., co-evolved relationships between flowering plants and animal pollinators

Question 5

Explain parasitism

What are the types of parasites?

Answer 5

Parasitism

• One species benefits and harms the host
• Differ from predators because they do not directly kill their prey
• Ex., vampire bats are parasites because their sole means of survival depends on obtaining blood from their host

Endoparasites (tapeworms, flukes, roundworms) live within the host

Ectoparasites (leeches, mosquitoes) feed on the exterior of the host

Question 6

Explain why close mutualisms can be risky

Answer 6

Mutualism can place species on the edge of survival –> extinction of one must lead to change or the extinction of both if said species was only source of survival)

Question 7

Explain factors that provide an advantage in the evolutionary arms race

Answer 7

1. Generation time: affects how rapidly one party can evolve
   
   • Ex., rapid antibiotic resistance
2. Larger population size: likelihood that they will stumble across some sort of beneficial mutation

• I.e., anything that gives a high mutation rate/fast rate of evolution

Question 8

Define the ‘life-dinner principle’

Answer 8

Prey-predator relationship: prey is running for its life while predator is running for dinner

Selection is stronger on prey because it only has one chance to survive the encounter; predator won’t die if it misses one meal

Question 9

What is the prudent parasite hypothesis?

Answer 9

Prudent-parasite hypothesis: parasite should always minimize virulence

• Virulence decreases over evolutionary time
• Parasites hat are highly virulent have probably only recently jumped to a new host

Question 10

What is the trade-off hypothesis?

Answer 10

Trade-off hypothesis: parasites balance costs/benefits of virulence

• High virulence reduces survivorship of current host, but may enhance transmission to new hosts
• Optimal virulence can depend on transmission mode and ecology of parasite/host

Question 11

Compare ultimate and proximate explanations

Answer 11

Ultimate explanation: appeals to evolutionary origins and to the previous selection pressures that may have caused the trait to increase in frequency over time (ex., bird is singing because over evolutionary time, male birds that sang a lot were better able to attract mates)

Proximate explanations: proximate explanations have to do with the biochemical and physiological underpinnings of a trait (ex., bird sings because of hormones, because it is happy/angry)

Question 12

Explain ways in which disease symptoms may represent adaptations by the host or by the parasite

Answer 12

Adaptations by host:

• Some symptoms help us expel the parasite, eg, coughing, vomiting
• Fever helps kill bacteria by raising body temperature
• Anemic people → low blood iron levels prevents some bacteria from replicating

Adaptations by parasite:

• Runny nose and sneezing increase parasite’s ability to jump to new host
• Stomach and intestinal upset causes diarrhea, which makes it easier for parasite to spread via water supply

Question 13

Expain why selection does not necessarily improve health and wellness over time

Answer 13

• Selection only acts to improve fitness - the ability to pass on one’s genes
• Doesn’t act to maximize health and well-being
• There is always a trade-off

Question 14

Explain the ways in which humans’ current environment differs from our ancestral environment, and how this may affect human health

Answer 14

1. Higher access to food resources → increased lifetime number of menstrual cycles
2. Increased population density and social group size → easier for diseases to spread → parasites become more virulent
3. Better personal hygiene, clean water → decreased risk of infectious diseases, eg. mumps, tuberculosis, hepatitis A, but increased risk of autoimmune disorders, eg. multiple sclerosis, type 1 diabetes, asthma

Question 15

What is antagonisitc pleoitropy?

Answer 15

Antagonistic pleiotropy: a trait or allele increases one aspect of fitness, but decreases another aspect of fitness

These harmful traits are likely maintained through heterozygote advantage

Ex., sickle-cell anemia vs. malaria

Question 16

Explain why traits that reduce survival very late in life are not likely to be strongly selected against

Answer 16

1. Not everyone survives to old age
2. So, selection is much stronger on fitness that increases survivability earlier in life than alter in life, even if they reduce longevity
3. Traits that reduce late-life fitness but have no effect on early-life are selected against, but only weakly (not many ancestors made it to a late age)

Question 17

Explain the arguments that humans are no longer evolving

Answer 17

Selection

• Minimal selection pressures
• Getting better at protecting ourselves from illness
• Low famine in western world

Genetic drift vs. gene flow

• More interbreeding from different geographical areas

Genetic drift not very powerful

• Becomes less and less important as technological travel increases

Mutation

• Genetic screening to correct potentially harmful mutations

Question 18

What is a selective sweep?

Answer 18

Selective sweep: when a favourable new mutation increases in frequency, adjacent stretches of DNA come along for the ride (hitch-hiking)

Through this analysis, it has been found that there has been a recent acceleration of human adaptive evolution since the last 30 or 40,000 years

Question 19

Give some examples of recent human adaptation

Answer 19

Examples of recent human adaptation:

1. Adaptations to new food sources (ex. amylase, lactase persistence)
2. Adaptations to new environments (ex. oxygen transport in high-altitude populations; pale skin in high-latitude populations)
3. Adaptations to parasites (immune receptors)
4. Brain size and language (ASPM and FOXP2 genes)

Question 20

Explain the utility hypothesis of brain size

Answer 20

Utility hypothesis: language, tool use, and planning lead to survival and thus increased fitness

• Ex., an individual is smart enough to create a throwing axe to kill more animals –> more food –> increased fitness

Question 21

Explain the mind-mating hypothesis of brain size

Answer 21

Mating-mind hypothesis: art, wordplay, humour and music lead to mating success and thus increased fitness

• Note: sexually selected traits like these are usually sexually dimorphic (i.e. restricted to one sex), but they are found in both sexes because modern humans are monogamous –> both sexes are choosy)