L4- Evolution of parasitism Flashcards
What is the “arms race”?
A series of escalating mutual counter adaptations by the 2 lineages to exploit or inhibit exploitation by the other
What is coevolution?
Continuous fine tuning of the host parasite relationship
Describe 3 types of symbiosis?
Commensalism – no metabolic dependence
Mutualism – obligatory relationship – both benefit
Parasitism – one partner benefits, metabolic dependence, may cause harm to host
Features of nematode phyla?
Species richness
Numerical abundance
Ecological omnipresence
Estimated to be 1 to 10 million nematode species on earth.
Nematodes can exceed 1 million individuals per meter squared.
Fresh water, marine, terrestrial, extreme environments.
Range of ecological niches: Free living, predators, parasites.
What are the 3 main principles in the evolution of parasitism?
Loss of otherwise essential genes through mutualisitic relationship with bacterial endosymbiont
Horizontal gene transfer
Parasitic features evolving under free living conditions - the concept of pre-adaptation (while the nematode was free living and that gave it an advantage in a parasitic relationship)
What’s strange about the different types of nematodes?
They look the same but some are parasitic and some aren’t.
Most are just parasitic for some part of their life.
What suggests some characteristic of nematodes that favours evolution of parasitism?
Molecular phylogenetic approaches – show parasitism evolved at least 7 times in nematodes!
4 groups animal nematode parasites
3 groups of plant nematode parasites.
Brugia malayi – animal parasite
Life cycle?
Have female parasite which have eggs which develop into microfilariae. It’s these microfilariae that circulate in the host. The mosquito take up the microfilariae and there’s a devlopment stage within the mosquito. And then mosquito will infect the host again.
Meloidogyne incognita – plant parasite. Life cycle?
Eggs in root system of host. J2 (juvenile stage 2) develops in egg. J2 penetrates plant root; migrates between cells; induces multinuclear cells. Moults x3 to adult.
Pristionchus pacificus -beetle associated. Necromenic. Life cycle?
Pristionchus makes an association with a beetle. Very similar life cycle to C. elegans.
Pristionchus lays eggs. The eggs hatch and become L1s then L2s. Then very interesting- the L2 can either arrest into a Dauer larva under times of stress, or it can carry on to L3 then l4 in normal pathway.
Loss of otherwise essential genes- example? (detailed)
1st principal of evolution of parasitism
Brugia malayi – major human filarial parasite (animal parasite transmitted by mosquito)
Genome analysis – 20% of gene predictions are B. malayi specific - indicates huge pool genes involved in nematode defending itself in its habitat.
However, Genome shows loss of genes encoding enzymes required for biosynthesis of purine, heme and riboflavin. These are essential for its survival. 9/10 of the genes needed to make puring are absent. 6/7 of genes encoding in enzymes encoding haem are absent. And all of the genes to make riboflavin are absent.
Brugia malayi has evolved so it can source these things from a host or endosymbiotic bacetia Wolbachia. So this has become reliant on the host to survive.
Do remember- it appears simple but parasites often genomic complexity
Brugia malayi survival?
It has lost otherwise essential genes. So can’t make purine, haem and riboflavin. So it sources these from a host or endosymbiotic bacteria- Wolbachia.
Meloidogyne incognita and M. hapla?
Plant parasites are of agricultural importance
Life style very different to animal parasites
All have a stylet to puncture plant cell wall to provide multinucleated plant cells which worms feeds on.
Called “Root-knot nematodes”
Horizontal gene transfer in Meloidogyne incognita and M. hapla?
Genomes of the two species are rich in cell wall degrading carbohydrate-active enzymes (CAZymes) (eg cellulases, xylanases).
This is odd. No counterpart in most other animals, absent from free-living nematodes , most similar to genes of bacteria, so the hypothesis is that horizontal gene transfer occured from bacteria also in the roots of plants were transferred to these nematodes and then selected for retention of parasitism enhancing genes.
(from rhizobia)
Explain the concept of pre-adaptation?
Change in the ecology of organisms. Changed from free living to parasitic. this requires some changes in the organism.
These transitions are helped by adaptations to the current environment before they are parasitic. So adaptations that may be useful in future to be parasite.
