ecology and evolution Flashcards
what is evolution
mutation + selection over time
what is evolution not?
progress toward ultimate or proximate goal
what is the idea of blending inheritance and who thought genetic inheritance was like this?
idea that the offspring have a blending of the parents traits; Darwin thought this but it is not really true
what is the idea of particulate inheritance?
that inheretence is particulate and that heredity factors remain unchanged in the offspring; variation is preserved with each generation
what are sources of heritable genetic variation?
point mutations (substitutions or insertion/deletions); chromosomal mutations (deletions, duplications, inversions, translocations)
what options do prokaryotes have for genetic variation?
slow processes: point mutations (nucleotide sub, insertion/deletion); gene duplication deletion, chromosomal rearrangement
and fast processes: phase variation, antigenic variation, hoizontal gene transfer (transformation (exogenous DNA), conjugation, transduction (phage)
what are the different types of horizontal gene transfer?
transformation (DNA from environment)
conjugation (DNA from another bacterium)
transduction (addition of DNA via bacteriophage)
what are the ways viruses can change their genes?
if viruses with segmented genomes coinfect a host, then can get a mixture of the genome and a new strain can result; this can happen with influenza
how does selection result?
variation + differential reproduction + heredity
How is diversity maintained in the face of selection?
The environment and the relationships between the animals change
What is circulation?
Evolving organisms can influence each other’s evolution by exerting selective pressure
What is special about coevolution of a host and pathogen?
The relationship is asymmetrical
What is the fitness of a pathogen without the host?
Zero
What is the fitness of a host without the pathogen?
Maximal
What is an asymmetry between the relationship of the host and the pathogen?
The pathogen is interested in the host but the host is not interested in the pathogen
What are some host factors in the coevolution of virulence?
Heterogeneity of resistance, recognition and avoidance of the pathogen, population size/density, life expectancy
What are some pathogen factors in the coevolution of virulence?
Transmission type, competition between strains, reproduction strategy (sexual or asexual), density dependence (ie how important is shape of host community to transmission)
Do long term relationships tend to have low or high virulence?
Low
What happened to myxomatosis virus virulence in rabbits over time?
Virulence decreased
Why does a low virulence relationship occur?
The host and pathogen have an arms race but externally it appears as though it is a low virulence relationship
What is the name for the concept that host and pathogen are in an arms race but the relationship looked like a low virulence relationship?
The red queen hypothesis
What is the prudent parasite hypothesis?
That the pathogen modulates its virulence so it attains maximum possible fitness
Are all relationships evolving toward lower virulence?
No
What is an example of a pathogen that has maintained high virulence over time? What is a possible reason?
Rabies. Because high virulence is important in its mode of transmisSion
How does geographic distance correlate with virulence
Increased geographical distance between animals is correlates with decreased virulence. Don’t want to kill you host before you can infect another!
What types of transmission favor evolution toward increased virulence?
Waterborne (eg in human diarrhea)
Coevolution of host and agent results in_____over time
Modulation
What is extirpation?
Local extinction
Can a host pathogen relationship lead to extirpation? Can it lead to global extinction?
Yes. No/unlikely
What is an animal that may have been globally wiped out by a host pathogen relationship? Why might this have been possible?
Gastric brooding frogs. Their range was very small
Honeycreepers and malaria–there was high virulence vs low virulence for the non native birds that introduced it
Why may the thylacine have gone extinct?
Parvovirus
What are three mechanisms that can result in disease induced extinction?
Small population, density dependent transmission, reservoirs
Why can small populations be driven to extinction by host pathogen relationships?
Because they may be driven to a non sustainable level where they are vulnerable to environment a shift or where they have less opportunity to generate genetic diversity
Why may density independent transmission lead to disease induced extinction? What is am example of density independent transmission?
STDs and vector born agents can maintain high transmission rated even in low density populations
Why can reservoirs lead to disease induced extinction ?
Multihost pathogens are survivors. (Higher effective population for pathogen? Can keep infecting yet wipe out one of the species?)
What is an example of pathogen extinction?
Rinderpest (cattle plague)
What has lead to most disease outbreaks?
Agriculture and domestication of animals: results in concentration of human and animal populations
What are three examples of human influence on coevolution of animal and disease
Habitat destruction and fragmentation
Domestication of animals (“unnatural selection”
Development of vaccines (“impenetrable” resistance of host)
Who is winning when humans interfere?
Domestication of livestock has tipped balance in favor of macro parasites (animals stay in one location, high density, high repro rate means new susceptibles introduced)
What are life history traits?
Survival, reproduction
What does parasitism do to the host?
Puts pressure on life history traits (survival and reproduction)
What does host evolution profess towards?
Reducing harm and maximizing fitness
How does the host reduce harm and maximize fitness?
Physiological and behavioural modifications
What is sexual selection?
The advantage that certain individuals have over other individuals of the same sex and species in exclusive relation to reproduction
What is the effect of male extravagance on fitness
It reduces survival while improving mating success, thus resulting in a net gain in fitness
What is the signal evolution theory of ornaments?
They provide information to the female regarding the fitness of the male (eg health, dominance, parasite load)
Describe how the airsacs of grouse demonstrate to the male the parasite load of the male?
The males with lice have petechial hemorrhages on their air sacs. These males are rejected by the female even though lice does not significantly affect their health
What is asymmetry in reindeer antlers positively correlated with?
Parasite burden
What is snood size of turkeys negatively correlated with?
Burden of coccidia
Are ornaments always honest? Why?
Yes. The production of ornaments is costly for the male.
Energy is required for development and maintenance. Increases likelihood of predation. Inhibition of movement. This high cost guarantees their honesty
What are the direct benefits of avoiding infected males?
- Avoiding becoming contaminated through sexual contact
- Avoiding transmitting pathogen to offspring (vertical, nest contam, direct exposure(
- Better parental care by healthy male
What are the indirect benefits of avoiding infected males?
Ornaments allow females to choose mates that are resistant to the parasites exploiting the host population. (At that time***)
What is the lek paradox?
If good genes selection is the driver for mate choice, why don’t the bad genes get eliminated from the pop?
What is the answer to the lek paradox?
The Hamilton Zulu hypothesis: it is not just any genes that are important, it is the genes for resistance. And the ones involved in resistance are always coevolving with the pathogen
What are the assumptions of the Hamilton Zuk hypothesis?
- Parasites affect the fitness of their hosts
- Parasites and hosts are continuously coevolving and there is some heritable variation on parasite resistance
- Expression of sexual ornament varies with parasite burden
Why is an experiment that tested the Hamilton Zuk hypothesis?
Tail length in swallows is related to tail length. Offspring of longer tailed males have fewer parasites than those with shorter tails no matter where they were raised. Thus resistance is inherited and demonstrated by the ornament
What happens when the female is infected (at least in the turkey?)
Infected females visited more males before soliciting copulation than control females did. Infected females had different snood preferences than control females. Possibly the infected females were looking harder for males with complementary genes
How had domestication affected sexual selection.
We have eliminated a lot of sexual selection. So we often take out the factor that sexual selection would select for. Eg if chickens allowed free mate selection they look at comb size which is linked to bone density and overall skeletal and egg health
