Lecture 18 - Extended Phenotypes

what is a phenotype?

any observable characteristic or trait of an organism including morphology, physiology and behavior

extension of phenotypes

phenotypic expression can happen outside of the genotype, things that are produced by individuals are a phenotype, they can vary, influence fitness and be exposed to selection or things produced in other individuals

how does phenotype apply to host and parasite interactions?

the gene in the parasite influences the phenotype of the host

Ro

number of new infections generates by a single infected individual in a fully susceptible population

what is Ro dependent on?

the replication or growth within a host and the opportunities for transmission between hosts

what are the 3 broad categories of extended phenotypes of parasites?

host behavioral modification, morphological modification and molecular modification

what is the purpose of these host modifications?

to increase the fitness of the parasite by facilitating the growth, reproduction or transmission of the parasite

adaptive for the parasite

generates a fitness benefit to parasites that led to natural selection for trait

adaptive for the host

generates a fitness benefit to hosts that led to natural selection for trait

coincidental by product infection

trait dint evolve by benefit or natural selection but it may have some beneficial side effect, no apparent reason for its evolution

toxoplasma gondii

can cross the blood brain barrier and infect vertebrate of any vertebrate mammal

how do infected mice act?

more active, explore more, less likely to startle, more aggressive over territories and slower reaction times

is behavioural manipulation of the rodent by the parasite to increase transmission to its definitive host?

yes because when researchers soaked bedding in cat or rabbit urine they found that the infected rats gravitated towards the cat urine

posterodorsal medial amygdala

involved in innate reproductive behaviour and found that it was more active in infected cats when smelling cat urine compared to female rats

what is the timing of the behavioural manipulation by toxoplasma gondii?

cysts accumulate in the brain of the infected rodents over time cause parasite gets into brain and forms cysts

how does the strength of the behavioral manipulation chnage>

the more cysts are produced the more dopamine is produced which is responsible for regulating behaviour so the more activity there is the more behavioural changes there are

cougars + wolve host-parasite interaction

cougars and wolves overlap in range so they poop and wolves get exposed to it infecting them and these infected wolves are more likely to be pact leaders so they lead uninfected ones into situations where they are likely to get infected

fungal infections in ants

ants infected with multiple species of fungi turn into zombies that engage in death grips onto vegetation and the location of death is parasite-species specific

death grips

grips on and ant dies with fungus growing out of it then fungal spore is released infecting any ant in the area

does the behavior only happen in the presence of the parasite?

yes cause uninfected ants are found in trees while all infected ants are found low to the ground

what happened when infected ants were moved to the canopy?

fungus failed to grow normally and never produced a stroma

what happened when infected ants were moved to the ground

14/16 disappeared in less than 24 hrs and the other 2 grew abnormally before disappearing too

how do mosquitoes exposed to malaria parasites become infectious?

takes 10 to 14 days where the parasites get sucked up, oocysts develop in gut wall, turn into sporozoites and they migrate to salivary glands when they are infectious

what happens when a human gets bite by a malaria infected mosquito?

the sporozoites are injected with mosquito bite then the infection travels from the liver to red blood cells to gametocytes where they become transmissible

oocyst stage

exposed parasite that is not yet infectious so feeding behavior is reduced and they respond in a way that is beneficial to to their host

sporozoite stage

parasite is ready for transmission so biting activity is dramatically increased and more aggressive

is reduced feeding behavior after recent exposure specific to malaria parasites?

no because the same feeding reduction is seen in mosquitoes exposed to heat killed E coli

is increase in feeding behaviour when infectious specific to malaria parasites?

yes because in the e coli one the behavior rate did not dramatically shift between the oocyst and sporozoite stages

how do infected hosts differ from uninfected hosts?

hosts that are infected with the transmissible malaria forms attract more mosquitoes than the uninfected or asexual parasite hosts

how was host attractiveness measured

researchers identified compounds that make infectious hosts smell different and made healthy hosts smell like infectious ones and infectious hosts smell healthy

altered host attractiveness experiment results

found that mosquitos were drawn to healthy hosts that were made to smell like infectious hosts and they avoided infectious hosts that were made to smell like healthy hosts