The Atractidae is a family of nematodes (roundworms) which are found in the intestines or lungs of various vertebrate animals. Instead of producing eggs, the adults of this family of worms produce larvae that are ready to infect as soon as they leave their mother's womb. While it is well-known that a host already parasitised by an atractid nematode can infect themselves again thanks to the infective larvae, it is not entirely clear how this parasite get passed between different hosts.
For the paper we are looking at today, a team of scientists studied a species of atractid nematode which infects lizard - Cyrtosomum penneri - and conducted a series of experiments to figure out how this parasite transmit in Brown Anoles. They did this by administering larval worms in a number of different ways to lizards that they have previously de-wormed with anti-parasite drugs. To ensure that they can tell afterwards if the worms they found in the anoles were the ones they administered, the scientists labelled them with a fluorescent dye (the same type as the ones I have previously used in experimental infections to track larval flukes in bivalves: see here and here)
The larvae of many parasitic nematodes infect their hosts through being accidentally swallowed, usually while their hosts are feeding (this is commonly how mammalian herbivores like sheep, cattle, and horses become infected). However, when these scientists tried to do the same with C. penneri larvae by pippetting larval worms down the lizards' throat, none of the larvae were successful in establishing in the host.
Instead, they found the feces of anoles which had been fed parasite larvae were full of dead worms - presumably they were killed by gastric acid. Indeed, the environment in which C. penneri is usually found, down in the lower intestine, is pretty benign comparing with the acidic milieu of the stomach. But when they pipette larval C. penneri into the cloaca of the lizard, it worked every time. Instead of having a separate opening, lizards have a cloaca - a common opening for their intestinal, urinary, and reproductive tract. When lizards mate, they bring their cloaca together - and this is when C. penneri gets transmitted.
Yes, that's right - C. penneri is a sexually transmitted infection.
In the mating trials ran by those scientists, male lizards infected with the nematode passed it on to the female they mated with every single time, whereas the female lizard only passed the STI onto the male in seven out of the ten trials they ran. In addition to anoles, C. penneri is also found in a few other lizards species such as the Mediterranean house gecko and Eastern fence lizard. But while it infects those other lizards in addition to the Brown anole, for some reason it does not appear to parasitise the Carolina anole... which means that it would be interesting to consider what happens to the parasite when something like what you see at this link happens...
Reference:
Langford, G. J., Willobee, B. A., & Isidoro, L. F. (2013). Transmission, host specificity, and seasonal occurrence of Cyrtosomum penneri (Nematoda: Atractidae) in lizards from Florida. Journal of Parasitology99: 241-246
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| Photo taken by Charles R. Bursery Used with permission from Gerrut Norval |
The larvae of many parasitic nematodes infect their hosts through being accidentally swallowed, usually while their hosts are feeding (this is commonly how mammalian herbivores like sheep, cattle, and horses become infected). However, when these scientists tried to do the same with C. penneri larvae by pippetting larval worms down the lizards' throat, none of the larvae were successful in establishing in the host.
Instead, they found the feces of anoles which had been fed parasite larvae were full of dead worms - presumably they were killed by gastric acid. Indeed, the environment in which C. penneri is usually found, down in the lower intestine, is pretty benign comparing with the acidic milieu of the stomach. But when they pipette larval C. penneri into the cloaca of the lizard, it worked every time. Instead of having a separate opening, lizards have a cloaca - a common opening for their intestinal, urinary, and reproductive tract. When lizards mate, they bring their cloaca together - and this is when C. penneri gets transmitted.
Yes, that's right - C. penneri is a sexually transmitted infection.
In the mating trials ran by those scientists, male lizards infected with the nematode passed it on to the female they mated with every single time, whereas the female lizard only passed the STI onto the male in seven out of the ten trials they ran. In addition to anoles, C. penneri is also found in a few other lizards species such as the Mediterranean house gecko and Eastern fence lizard. But while it infects those other lizards in addition to the Brown anole, for some reason it does not appear to parasitise the Carolina anole... which means that it would be interesting to consider what happens to the parasite when something like what you see at this link happens...
Reference:
Langford, G. J., Willobee, B. A., & Isidoro, L. F. (2013). Transmission, host specificity, and seasonal occurrence of Cyrtosomum penneri (Nematoda: Atractidae) in lizards from Florida. Journal of Parasitology99: 241-246