Betts, A., C. Gray, M. Zelek, R. C. MacLean, and K. C. King. 2018. High parasite diversity accelerates host adaptation and diversification. Science 360: 907-911.
Blog: Auggie.Ts
Dr. Alex Betts, Junior Research Fellow, St. Hilda’s College, Department of Zoology, University of Oxford, United Kingdom. He studies evolution.
Background: An evolutionary hypothesis which first proposed by Leight Van Valen the "Red Queen Hypothesis": organisms must constantly adapt, survive, and proliferate not only to gain a reproductive advantage but also simply to survive while pitted against ever-evolving opposing organisms in a constantly changing environment. The main finding of the experiment is that an increasing parasite diversity accelerates coevolutionary arms races and leads to greater generalist host resistance.
The traditional host-parasite coevolution was studied in a pairwise framework but it contradicts the natural world because of this model so rare. Instead, their relationships are much more complex and commonly involves with multiple species of the parasite within the host. The diverse parasite and their antagonistic interactions with hosts can have greater evolutionary pattern can create coevolutionary consequences. The host-parasite system is highly useful because the following model can be observed in real time.
Prediction: Heavily infected hosts can be under strong natural selection as they are unlikely to reproduce, and they produce strong selection on parasites as resistant hosts, so they can fight them off. The outcome from these interactions should drive rapid host evolution and produce more divergence among host populations. Also, increasing parasite diversity alters the mode of coevolution between hosts and parasites.
Methods: To test this hypothesis, an experimental coevolution approach to an in vitro bacterium-phage system using Pseudomonas aeruginosaas the host model, infected with five viral lytic parasites including bacteriophages PEV2, LUZ19, LUZ7, and LMA2 which are some obligated deadly parasites to the host. More specifically, these parasites attack one of the three specific cell surface receptors (Lipopolysaccharides LPSs, Ton-B-dependent receptors, or type IV pili), and hosts typically evolve resistance by modifying or deleting these attachment sites by injecting their lethal DNA. The parasites now have to adapt to this condition of resistance. Now the relationships were tested whether this parasite diversity shapes the mutual antagonism with hosts over evolutionary time.
Results: the outcome of the experiment shows that relative to infection by single parasite species, parasite diversity can drive rapid evolution of host resistance. Host populations also become more evolutionary divergence from each other. Eventually, this genomic split between populations could lead to the formation of a new species of host and phage.
Based on the changes through mutations in host and parasite genome, these changes often fall into one of the two competing descriptions: Arms Race and Red Queen. Arms race: host resistance and parasite infectivity continue and the future host populations will have better resistance than the ancestral population. On the other hand, Red Queen, coevolution is dominated by patterns of rotating strategies to match the current opponent and it should be more effective with the current opponent which means that it is less suitable for the past opponents.
In summary, parasite communities can produce a rapid antagonistic coevolution. With increasing parasite diversity, coevolution shifts in favor of stronger arms races between hosts and parasites. As parasite diversity increases, coevolution speeds up. Parasites and hosts can both evolve into a greater level of resistance and infectivity. Having the ability of hosts to use generalized resistance mechanisms is more important to the higher rate of evolution.
This paper is a great example of parasite roll in species diversification in a natural ecosystem. I do like this paper and it was easy to read. My questions: is this the hidden mechanism for all diverse ecosystems with high diversity areas such as amazon and other rain forested biotic regions?
Very cool paper. My question following this paper would be about the types of physical consequences a parasite causes, can they find patterns in increasing host allele frequencies for different consequences caused by parasites in various types of organisms?
ReplyDeleteI'm having some trouble understanding Figure 2. But other than that, this is a super interesting paper. I thought Red Queen and arms race mean the same thing! So I'm glad I came across this paper to clear things up.
ReplyDeleteThis was neat! The first paper did not necessarily distinguish between Red Queen and Arms Race, so it was interesting that these authors considered them endmembers. Near the beginning of the paper they tested if one of the parasites drove rapid evolution. How would that work?
ReplyDeleteGoing off some of the other comments, I think it is interesting that they distinguished co-evolution and arms race as one side of the evolutionary process, and the red queen as another, the red queen hypothesis speaks to the required constant evolution of a clade. While the text was straight forward, I wasn't sure what some of the figures were supposed to be showing. I could see clear differences between the test populations, but what those differences meant were not always clear to me.
ReplyDeleteVery interesting paper!Whenever I think about parasites I think about worms and mammals. It was cool to see a solid example with bacteria and virus. Overall, it is very intriguing how long would it take the evolution of this kind of interaction between organisms that have longer cycles, and what direction it would take.
ReplyDeleteI agree, this was a very cool paper. I think, the most interesting part is the suggestion in the last paragraph that parasites might be the "fuel" for higher evolutionary and diversification rates at biodiversity hostspots. This has been suggested before, but this paper provides empirical support (e.g. figure 2 B)
ReplyDeleteIn response to your question, I doubt that all diversity in highly diverse areas is due to parasite-host arms races. However, this paper was certainly interesting, and it gave me some food for thought (I never think about parasites...except for when I have them).
ReplyDeleteI loved this paper. Parasites have to be some of the coolest organisms ever, so reading about there interactions and their co-evolution is awesome. Also I'm glad it talked about the difference between The Red Queen dynamics and the Arms Race. I've heard about the Red Queen in other classes but I didn't know too much about it so it was nice reading it more in depth.
ReplyDeleteHad never heard the distinction between Red Queen and arms race, so that was interesting to read. I'm confused how to read figure 2.a, any help clarifying would be great.
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