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TWiP 66 letters


Andre writes:

Dear Vincent,

To my great delight, I just discovered your podcasts twiv, twim and twip.

The first twip I heard, about Strongyloides stercoralis, although informative and interesting, seemed to have several inaccuracies. I was not able to find the email from Dick Despommier, and therefore I am writing to you.

Dick said that Strongyloides, when it enters into the host, becomes a protrandrous hermaphrodite adult. Actually this is not true. The parasitic stage of Strongyloides is a female that reproduces by parthenogenesis.

He also said that a protrandrous nematode is first male and then becomes female, so that it can self-fertilize. Actually, as I said, Strongyloides is not a hermaphrodite and therefore it cannot be protrandrous. The only nematode parasites that I know to be a protrandrous hermaphrodites are worms of the genus Rhabdias, which usually infect amphibians and reptiles.

C. elegans is a good example for a protrandrous hermaphrodite nematode. The term protrandrous means that the organism first produces male gametes and later shifts to the production of female gametes. The only difference between C. elegans hermaphrodites and females of closely related species is the ability of the hermaphrodites to produce a limited amount of sperm just before becoming adult. These "female-bodied C. elegans with sperm" are not considered males because they cannot transfer their sperm to other individuals. The sperm of these worms are stored in the spermatheca and used for self-fertilizing the oocytes produced during adulthood. C. elegans males are morphologically very different from hermaphrodites, produce only sperm, and have specialized mating structures used to find and fertilize the hermaphrodites.

My field of specialization is actually evolution of modes of reproduction of nematodes. I study a free-living nematode that can produce males, females and hermaphrodites. In many ways, it resembles parasitic nematodes, because larvae that sense the lack of food become "dauers", which is the dispersive stage of free-living nematodes. Dauers are the equivalent larval stage as the infective stage in parasites. Dauers can resist to harsh environmental conditions, crawl in arthropods and be transported to new places. For the species of nematode that I study, the dauers develop into self-reproducing adults once they encounter a habitat with food. This makes sense, because they can then colonize new environments without the need of a mating partner. The larvae that grow in an environment with enough food develop into females and males.

In case you are interested in reading more about it, check the paper Chaudhuri et al in the website



Noah writes:

Dear Prof. Racaniello,
I have been a huge Twiv, Twip, and twim listener for about a year, I love the show.. Twip the most.. I love listening to you and that Deponia guy.. you guys make me laugh but more importantly I have attained a great deal of knowledge from the podcasts can't help but tell my collieges about the amazing things you two talk about from Toxoplasmosis or several parasite epidemics.

I am writing you b/c tommorow night I am going to post you as The American of the Day in my facebook group because of your great
accomplishments and devotion to educate the public about science. If you get time on the 10/23/13 search the Facebook group American of the Day and you will see your photo and bio added to our list of great Americans... it's a small and I have a feeling you won't have time but thankyou so much for the podcasts there is nothing like it out there, if it wasn't for you guys I would have to read these journals all by myself and that gets both confusing and lonely. Thanks again-

Noah RN --- Lebanon PA

Devin writes:

Hey guys:

I am from the San Francisco Bay Area and I wanted to extend my appreciation for the show! I listen to both TWIP and TWIV and would be disappointed if you didn't produce the show into the future. The conversations require the listener to pay attention a bit more than the average podcast, I believe. This may, in part, be due to the use of terminology that I often find myself looking up during the podcast or later when I've heard it more than once on the show. As a result I feel like I'm in on a conversation that I normally wouldn't be and this inspires me to try even harder to understand the concepts.

One more thing: While out at a bar the other day I had randomly met someone who had his Phd in the biosciences (I don't remember specifics -- I studied Earth & Planetary Science) and I had mentioned that I listen to TWIV and TWIP and he knew who Vincent was, which led to him to add your podcast to his iTunes at the bar.

Keep up the good work. I looked for your podcast page on Facebook and didn't find it -- did I miss something? If not, you should create one. Its a good way to promote your show.

Remember for every person that writes an email there's probably a bunch more that want to but just don't get to it.

Thanks guys!

John writes:

Dear Professors,

It is 1 degree outside my window as I write three comments about TWiP 63.

1. You wondered how Plasmodium DNA ended up in ape feces. I learned biology when life was made of cells rather than molecules, so I think of the body not as a big amino acid sequence but rather as a series of tubes. With this old-fashioned background, I thought the path dismissed by Dickson was obvious.

The liver recycles old red blood cells to recover iron. It dumps the rest of the cell contents into the intestines. If it recycles an
infected red blood cell, the waste may include Plasmodium DNA.

2. How do merozoites know when to stop producing copies of themselves and make gametocytes instead? I can imagine three mechanisms:

(a) random chance

(b) a molecular clock like telomeres, which allow cells to count generations

(c) environmental cues related to overpopulation, such as oxygen concentration

If you give me a grant and a lab I would be happy to watch a team of grad students investigate.

3. Do I understand correctly that a deadly infection can result from just one Plasmodium sporozoite cell lodging in the liver? (15 minutes in)

Scott writes:


As a resident of Latin America, it was with some interest that I noted this story in Science Daily. I would appreciate your comments:

As I have, on several occasions, discovered the insect vector in my living space, this parasite is of some concern to me.

I would like to know if the parasite is a threat to the two cats who live in the house with me, or my dog who lives in my yard. I have not been able to find any information on the veterinary implications of this parasite.

Regards and thanks for a great podcast,
Cartago, Costa Rica

Neva writes:

Hi Dickson and Vincent,

I guess the tri-caster medical device is almost here. If this is viable, very cool! What's next?

Rice University researchers have developed a noninvasive technology that accurately detects low levels of malaria infection through the skin in seconds with a laser scanner. The "vapor nanobubble" technology requires no dyes or diagnostic chemicals, and there is no need to draw blood.

Never miss your great podcasts!

Neva from Buda

J writes:

I got recommended your podcast from a colleague. I just wanted to know what song by RJ do you play in your intro? I emailed him and he thought it was "Guitar Sounds" but it's not quite right. Do you mind posting the title somewhere ?




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