Origins and drivers of parasitism Flashcards
What are the different symbiotic interactions?
Which onces cause harm, no effect or a benefit?
Give an example of a parasite that causes mutualism?
Define symbiosis
Two or more different organisms living together (not necessarily mutualistically)
Define parasitism?
What are the three rules they tend to follow?
A non-mutual symbiotic relationship between species, where the parasite benefits at the expence of the host
- Parasitism is a life strateft that evolved many times independently
- Parasites do not typically kill their host
- The term parasite is most often restricted to eukaryotes
For a parasite and a pathogen, whats the following?
Cause?
Kills host?
Need specific host to complete life cycle?
Typically used for?
Define a obligate/ facultative parasite
A obligative parasitic organism that cannot complete its life cycle without exploiting a suitable host. If it cannot obtain a host then it will fail to reproduce
A Facultive parasite is an organism that may resort to parasitic activity, but does not absolutelt rely on any host for completion of its life cycle
Define Monoxeneous/ Dixeneous parasites
Monxeneous characterises a parasite whose development is restricted to a single host species
Dixeneous characterises a parasite whose development is restricted to more than one host species
Define an Ecto-/ Endo- parasite
An endoparasite is one that lives inside of its host
An ectoparasite is one that lives outside of its host
How many origins of parasitism are there?
What organisms do parasites originate from?
All parasites had a free-living ancestor
Tell me about the organism Apicomplexa and what it originates from?
Apicomplexa
secretes factors through Apicomplexa when arrives at cell that it wants to infect
more information as important parasite
chloroplast has 2 membranes in plants and in mitochondria. they are endosymbiotic bacteria
Apicomplexa has 4 membranes as is also endosymbiotic, but it is a whole alga. it’s a eukaryote inside of a eukaryote which eventually become photosynthetic
Apicomplexa example for how a parasite originates from algae
large phylum of parasitic alveolates
most possess a unique form of organelles that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure
Why do parasites evolve so often?
- often a fuzzy boundary between free-living and parasitic lifestyle. Remember facultative parasites like Naegleria?
- many human gut parasites could be viewed as commensal because no obvious reduction to host fitness is observed
What is the apical complex used in?
What is the following, in the complex…
- Apicomplexan
- Colpodella
- Chromera
the apical complex, which is used in the invasion of apicomplexan parasites into animal cells (e.g., in Toxoplasma, Plasmodium), is used for predation in their free-living relatives, the colpodellids … and is also present in related alga like chromera
Apicomplexan= parasite
Colpodella= predator
Chromera= phototroph
Give an example of a predated parasitism
simultaneous division of one apicomplexan cell into many (endopolyogeny aka schizogony) is not an adaptation to disease but in fact predated parasitism
many other traits once thought to be adaptation to parasitism- e.g., trypanosome coat proteins, the microsporidian infection apparatus- were found in free-living parasite relative
these and other observations may explain why parasitism has evolved repeatedly in groups with suitable sets of characteristics= preconditions
The preconditions blue boundaries between parasites and free-living species. It could mean that repeated origin of parasitism in some groups in inevitable and not a heavily adaptive process
What changes as parasites evolve?
Parasites not always ‘simplified’- may have a complex life cycle
But they may have simplified organelles. for example, mitochondria in anaerobic parasites: Giardia (diplomonads), Cryptosporidium (apicomplexans), Trichomonas, microsporidia are no longer able to respire
Parasite synthesis of purines, pyrimidines, heme, fatty acids is often lost. the compounds are salvaged from the host
- nucleotide salvage in plasmodium and microsporidia
What are the four important ways in which parasite genomes are transformed?
Large-scale loss of genes: for function supplied by the host cell
Streamlining: reduction in redundant genes/ pathways- one way to do one thing
Expansion in specific genes: gene families related to infection and parasite-host interaction –> novelty
Change in DNA position and structure: higher AT content, reduction in gene UTRs, reduction in introns, repeats, transposable elements, non-coding DNA
What does the nuclear genome in plasmodium have compared to that in humans?
The nuclear genome in plasmodium has 23 MB (mega bases?) compared to 3 GB in humans
What do the mitochondria in plasmodium encode?
Tell me about the mitochondria in cryptosporidiumn
The mitochondria in plasmodium encode only 3 protein-coding genes compared to 13 in humans. Mitochondria in Cryptosporidium lack genome altogether
Tell me about the plastid= apicoplast in plasmodium
The Plastid= apicoplast in plasmodium is greatly reduced compared to plants and AT-rich (85% AT content). some apicoplasts have >90% AT
Parasite genomes
How do new parasitic species emerge?
State the ways
Co-speciation
Host switch
Within a host
Tell me about Co-speciation
A form of coevolution in which the speciation of one species dictates speciation of another species and is most common studies in host-parasite relationships
Tell me about host switch
This can be a sudden and accidental colonisation of a new host species by a few parasite individuals capable of establishing a new and viable population there
Tell me about how a new species will form within a host?
Within host evolution limits the utility of sampling a single genome per host for reconstructing transmission relationships, conferring a benefit to sequencing several genomes per host
What are some more possible variations of parasite speciation (black lines) within their hosts (yellow)
Tell me about cospeciation with pocket gophers
Pocket gophers (Geomyidae) and lice- a strong pattern of cospeciation (a) is reinforced by correlated evolutionary rates in parasite and host sequences (b)
What is cospeciation based on?
genes
Different lice species can infect different doves. But when do they not survive?
different lice species can infect different doves. however, they do not survive on non-native hosts of different size because they cannot escape preening. Thus, host defence behaviour reinforces (partial) cospeciation with the parasite
host defence behaviour reinforces cospeciation
What do Adelphoparasites cospeciate with?
A host bery closely related to the parasite itself
Parasite and host populations naturally vary in what?
Their genes and this contains multiple genotypes (combinations of alleles), which arose by mutation
Tell me about the distribution of parasites with host-parasite co-evolution
The distribution of parasites is not uniform- most hosts are uninfected, a few hosts bear much of the load
If Parasites exploit common host genotypes then what does this lead to?
What does this go on then to produce?
parasites exploit common host genotypes –> more resistant host genotypes become common –> parasites able to infect these are positively selected –> selective sweeps
(old allele= trait is replaced by new in a population)
The produces red queen dynamics: an arms race defence (host adaptation) and defence evasion (parasite counter-adaptation)
What are the consequences of host-parasite co-evolution?
being a rare host genotype can be advantageous because parasites will adapt to the most common host genotype
parasites and hosts can become locally adapted to the local population of the other (depends on their migration rates)
What are some important concepts with Host-parasite co-evolution?
transmission (ease of spread) and virulence (harm to host) are linked
Low transmission often means low virulence= keeping host active enough to spread the parasite
High transmission often means high virulence= parasite is selected for maximum reproduction as transmission will spread the parasite
… but the best strategy on the trade-off between transmission and virulence
overcrowding of hosts increases transmission rate- important in farming
Parasites do not typically kill their host, why?
if host population size decreases to threshold –> parasite cannot infect enough new hosts –> would drop out before the host
–> parasites are unlikely to be responsible for species extinction more than other causes (such as habitat destruction or fragmentation
What can parasites be a factor in and give an example
They can be a factor in extinction though! if a lethal parasite has fast transmission of host remain infective for a long time –> all hosts in a population may become infected
What are some major challenges ahead?
farming and aquaculture: hosts often in high-density monoculture, sometimes clonal= no genetic variation!)
Threatened species: small populations, reduced genetic variation
What can parasites then contribute to?
parasites can thus contribute to demise of host species that they can cross-infect. this is often facilitated by human-mediated transmission
due to frequent host specificity in parasites, a dead host means a dead parasite –> not in parasites interest
