"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

August 26, 2016

Trypanosoma tungara

This is the fourth and final posts in a series of posts written by students from my third year Evolutionary Parasitology unit (ZOOL329/529) class of 2016. This particular post was written by Sierra Weston and it is about how male Tungara frog end up receiving a parasitic present while trying to call out to female frogs.(see also the previous post about picky bat flies, monkey-infesting botflies, and the caring maternal side of a parasitoid wasp).

Like many species of frogs, during breeding season the males of the túngara frog produce a mating call to attract female frogs. But instead of just serenading his own species, the male frog may inadvertently be announcing his location to nearby frog-biting midges.

TFW you're trying to serenade the ladies and end up with a face full of 
blood-sucking midges. Photo from Fig. 1 of this paper
All adult frogs are at the mercy of a range of opportunistic and specialised insects, some of which are potential vectors for all kinds of blood parasite. There is a species of frog-biting midge (Corethrella spp.) which preys predominantly on the túngara frog (Engystomops pustulosus) - a species of small frog found in the region between the south of Mexico to northern South America. The female midge takes advantage of the male frog’s mating call during their breeding season as a host detection system. The midge follows the sound, finds the frog and voila, it gets a blood meal. A male can attract up to 511 midges in half an hour. Unfortunately, again for the poor frog, midges are the perfect vector for a wide variety of diseases and parasites including trypanosomes.

Trypanosomes are single-celled protozoan parasites that infects hosts from all vertebrate classes; birds, mammals, reptiles, fish and amphibians. Some of these protozoans can cause diseases, including sleeping sickness (Trypanosoma brucei gambiense), in humans, as well as making their hosts more susceptible to sickness. Although frog trypanosomes are a less studied group, there are some parasite-vector-host relationships that have been documented.

The study featured in this post investigated trypanosome infection in túngara frogs. The aim of the study was both to determine that trypanosomes affected the túngara frog and identify the species of parasite if present, and whether there is a difference in trypanosome prevalence between male and female frogs. Since it is the males that produce the mating call, it was predicted that any midge transmitted trypanosomes would only occur in male frogs.

The researchers confirmed the presence of trypanosomes in the blood of the frogs, but also observed that the parasites possessed a some unique characteristics that set them apart from previously described species. However, frog trypanosomes are also known to be able to significantly change their shape when infecting different hosts. This presents the possibility that the trypanosomes infecting the túngara frogs could be a previously identified species with a slightly altered form which make them more suited to life as a parasite in the túngara frog.

Through further analysis and DNA sequencing, researchers were able to confirmed the discovery of a new species of trypanosome: Trypanosoma tungara. In terms of prevalence in male and female hosts, results showed a much greater percentage of males infected with trypanosomes showing that the mating call results in the male frog being the ‘easiest’ and most predominant target for the frog-biting, trypanosome vectoring midges. There were also female frogs infected with trypanosomes, which was surprising because female frogs do not vocalise. A potential transmission path is presumed to be the close proximity of the frogs when they are in amplexus, (the mating ‘embrace’) which allows the midge to move directly from the male to the female frog.

X.E. Bernal, C. M. Pinto (2015) Sexual differences in prevalence of a new species of trypanosome infecting túngara frogs. Internations Journal for Parasitology: Parasites and Wildlife 5: 40-47

This post was written by Sierra Weston.

That wraps it up for ZOOL329 class of 2016 - I would like to thank all the students for their posts! Next month, it's back to writing my usual posts about newly published parasite-related papers which you might not have noticed, and/or papers that were not as widely covered by the press - so stay tuned for more!


  1. What I found the most interesting about frog trypanosomes was the fact that they are known to change shape when they infect different hosts, enough so that they might even be considered different species. The way the midge insects take advantage of the frog’s mating call in order to find the male frog was very interesting to learn about, as it displays a way in which the insect utilises a natural phenomenon to find its next blood meal. This leads to transmission of the parasite to the frog, making the midge insect the perfect vector for T.tungara, and a very cool transmission mechanism.

  2. It is so interesting to know that only the female Corethrella midges or the vectors has the ability to detect its male frog host, taking advantage of the frog’s mating call. Moreover, when the female midges locate their hosts, they do so in large quantities, it is also mentioned that 511 midges are drawn to the male frog every 30 minutes which is a lot. Another interesting fact about the parasite is that they can also infect the female species of the frog but only during the event where the males and the female frogs are in a “mating embrace”. The fact that these parasites are identified to be able to alter or change their form depending on what kind of hosts they infect is just scary and fascinating at the same time because they literally can change their shape or form and basically adjust to their ‘environment’, also they are in the same family as the infamous Trypanosoma brucei gambiense and the Trypanosoma cruzi, just with different vectors, but just as terrifying.

  3. I personally haven’t heard about parasites that take advantage of their host’s host’s mating behavior (in this case Trypanosoma tungara is able to use the blood sucking midge to get to its frog host). I also believe this example of parasitic host relation to be quite complex; because on one hand you have reproduction, that is supposed to increase survival but on the other hand mating behavior (component of reproduction) is negatively affecting the frog’s survival through attraction of midges. One can also see how this parasite has an edge, after being transferred to the male; the midge is also transferred to the female frogs during the mating embrace. Reading the blog made me come up with a few questions too. I would like to see studies investigating the difference in mating success following the attack of the blood sucking midges. Also, since amphibians are already under strain due to human activities (more so than other groups, as they are more sensitive to pollution (Bralower and Brice, PennState)), is the trypanosome able to take advantage of their poorer health compared to frog populations that aren’t under such a strain (living in a healthier environment)?

  4. The protozoan parasite Typanosoma tungara, a parasite that targets tungara frogs (Engystomops pustulosus). I thought that this was a super interesting parasite because the vector, the frog biting midge (Corethrella spp.), targets the male frogs due to their vocalization during mating season. Due to this, the prevalence in male frogs is much higher than in females because female frogs do not vocalize. The parasite is thought to be transmitted to the female frogs during mating, thus it could be considered a sexually transmitted disease in frogs!