Ecology-L8-Why are we vulnerable to disease?

why is activating the immune system costly? give an example of a plant that does this, what does NS prefer?

• immune responses require energy ad resources that could be used for growth or reproduction

• rice: down regulates growth when activating immunity: use gibberellin to shift resources from rgwoth→ defense

• when overexpresisng immune systems→plants are smaller

• NS favours larger plants if disease is low

what behavioural examples show that immunity is very costly? 2 PT

• pea aphids: drop leaves to escape wasps- energy time and cost

• tadpoles avoid parasites→spends less time foraging

• avoiding infection reduces feeding→lowers fitness

what are the risks immune systems have towards self? what agents and 2 examples

• can harm the host: ROS kill pathogens but damage host tissues

• AMPs- can harm invaders and host cells

• drosophila: reducing immunity can improve survival by limiting self damage even if pathogen levels increase

• covid19- immune responses can cross react with human proteins- autoimmune like damage

what does NS prioritise over health? JF

• priorisies offspring- doesn’t care about health as long as offspring has been produced

• Japanese frogs with chytrid fungus call louder→to increase mating success even if it shortens lifespan→increases reproductive success

what is the terminal investment hypothesis? JF example

• when survival chances are low due to infections→ organisms invest more in reproduction rather than immunity

• infected frogs: large ovaries and more eggs

how does infection influence reproductive strategies and ageing? BFB

• if species expects to survive- invests in immunity

• if it expects to die, like Japanese frogs→will invest in reproduction

• blue footed boobies- mature individuals may reduce reproduction ad invest in immunity(likely to survive) while much older invest in reproduction

what is selection shadow? in opossums

• island possums- lower predation and live longer, age slower and more clutches- late cancer

• mainland→high predation, die earlier, less babies and less time for ageing traits to matter

• late acting stations like cancer resistance are selected on islands because animals live long enough to reproduce more

• on mainland- animals die by predation of bobcats before late life→no selection for cancer resistance

• NS is weak late in life→

what is the mutation accumulation hypothesis?

• deleterious mutations that act in old age are selected against

• selection is ineffective late in life as reproduction has occured→late acting mutations accumulate over evolutionary time

• hamrful old age mutations ar not selected against after reproduction as selection cant “see them”

• may explain ageing- NS won’t select against these

what is antagonistic pleiotropy? an example!!! of a gene

• gene is beneficial early in life ie higher reproduction but harmful later ie disease

• NS favours early reproductive success even if it causes late life decline

• BRCA- increases fertility early hut raises breast/ovarian cancer risk later

• may explain ageing

what is an evolutionary mismatch? why does this happen? an example?

• selection is so slow- organisms may be mismatched to modern environments

• modern humans→reduced pathogen exposure nowadays but still have storng immune systems→probably a cause of autoimmune disease

• selection hasn’t caught up yet

why do pathogens evolve faster than hosts? HIVwh

• HIV has huge population sizes and high mutation rates

• faster generation times, means more mutations and rapid evolution

• pathogens often evolve faster than hosts- gaining an advantage in an evolutionary arms race

what is antagonistic co-evolution?

an arms race

• hosts evolve resistance mutations- spread through populations

• pathogens evolve counter mutations to overcome reistsance

• each adaption- followed by counter adaptions

• repeated cycles of fixation