Evolution of obligate parasites

[aychamo]

Hey guys;

I just started a class in parasitology this fall, we haven't covered anything yet, just looked as some cases of people infected with parasites.

I was wondering how obligate parasites could have evolved. My thinking is that they were originally facultative parasites that found a niche in a host, and did so well in the host that features that would separate an obligate and facultative parasite were no longer selected for or against, thus eventually leaving a vestigial trait (such as eyes in blind cave bats).

I guess that makes sense? Since they were already in the host, things that would let them survive outside the host were no longer necessary and weren't a target of natural selection? Since natural selection wouldn't act on them, their quality would not matter and they could then become vestigial.

Assuming this is correct, would it be possible to look at an obligate parasite and see any vestigial traits?

Thank you
Aychamo

 

[iansmith]

From parasitology course, the prof did a small history of the possible evolution of parasite of parasitic flatworms. What he suggest that free-living nematodes probably started to find a niche in fish intestinal tract. As time pass, the adaption to the niche lead to facutlative parasite and then to abligated parasite.

Some parasite still have eye spot but it still might be in used as some have a certain time outside the host. Other have lost some organ system. For example, the Cestoda (tapeworms) have lost their gut through evolution.

I will look more into it.

 

[iansmith]

muscular system - YES

* Longitudinal, circular and transverse muscle cells allow contraction in every direction.
* Muscular system well developed in turbellarians and flukes, vestigial in cestodes.

http://www.bio.miami.edu/dana/160/160S04_14.html

Vestigial organ are probably hard to seen in most parasite because they are more simple organism lacking most of the complex system. In most parasite, there an organ reduction or disapearance rather than .

What you said is also right. I would not said that natural selection did not act on the parasite. It might be that parasite lacking some organs had an advantage over parasite having all the organs. These mutants would reproduce more quick. Also many parasite have asexual reproduction means. So a new advantage could spread quicker. Also there might selection against certain mutation that arose before other mutation. Some lost have a miminal effect if certain components are missing.

 

[aychamo]

Ahh, I see what you are saying about "not saying that natural selection didn't act on them." Perhaps lacking certain features would mean the parasite doesn't have to spend as much time "feeding" and can spend more time reproducing or what-not.

I *love* thinking of things in evolutionary terms.

 

[Nereid]

Ahh, I see what you are saying about "not saying that natural selection didn't act on them." Perhaps lacking certain features would mean the parasite doesn't have to spend as much time "feeding" and can spend more time reproducing or what-not.

I *love* thinking of things in evolutionary terms.

Have you been introduced to 'the world from the pov of a infectious bacterium (for humans)'? or 'why crowded human cities are GOOD!'

 

[aychamo]

No I haven't, are these books??

 

[Nereid]

No, it's just an interesting exercise; instead of thinking of the 'flu (say), or smallpox from our human point of view (pov), think of how the virus or bacterium 'views' humans ... how does it get its host to work for it? what conditions suit the nasty bug best? how does evolution drive the virus or bacterium to change (and how does its host respond)? Of course, these nasties don't have a 'purpose', or a mind ... but when looked at in evolutionary terms, it's really quite fascinating.

 

[Phobos]

It seems that specialization is a common theme in evolutionary history. Not too surprising that a parasite that once "played the field" found a particular niche & adapted specifically to that alone (especially since there are examples of parasites becoming simpler in their form as they evolved over time). Should be an interesting class.