"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

April 20, 2014

Controrchis sp.

Extreme weather events can cause significant changes to ecosystems and their inhabitants. When Hurricane Iris made landfall at Belize, it caused widespread devastation in its wake. The study we are featuring today was a part of a larger project to look at how Hurricane Iris affected a population of black howler monkeys (Alouatta pigra) which has been monitored since 1998. In the aftermath of the hurricane, the number of monkeys in the forest decreased by 78 percent until their population began to stablise and increase three and a half years later. But aside from such outwardly visible impacts, there were also other changes afoot within the monkeys themselves.
Photo of black howler monkey by Ian Morton

A team of scientists interested in monitoring the recovery carried out a study to see how this has affected the monkeys' parasites. It is possible that these primates are harbouring higher parasite loads than they did before the hurricane due to the stress of living in a disturbed habitat. The scientists collected samples of monkey fece over the course of 3 years and look for parasite eggs. They also measured the level of cortisol, a hormone associated with stress, present in the fecal sample, and collected data on other aspects of the monkey's behaviour to see if they were associated with their parasite burden.

Photo of Controrchis eggs
from here
The black howler monkeys were found to have five species of roundworms and a species of digenean fluke (based on the presence of their eggs in the monkey poop), but the prevalence and abundance of those parasites were not associated with the level of stress hormones. Instead, nematode (roundworms) prevalence was heavily dependent on population density and the size of the groups in which the monkeys gathered. This is to be expected as these worms are transmitted via accidental ingestion of eggs or larvae from the host's feces. The more monkeys there are around in a given area, the more opportunities for these particular parasites to be passed on. This is similar to what has previously found in other studies on primate parasites. But the only factor that successfully predicted the occurrence of the digenean trematode fluke Controrchis was the amount of leaves the monkeys consumed.

While black howler monkeys usually prefer a diet filled with fruit, in the aftermath of Hurricane Iris there were no fruit-bearing plants in the forest for 18 months. So the monkeys were forced to go on a leaf-based diet instead of the fruit-based one they enjoyed before the hurricane, and the plant most readily available and palatable to the monkeys was Cecropia. These fast-growing leafy plants usually happens to be the first on the scene in the wake of such habitat disturbances. They do not contain as much fibre as other plants and have little in the way of noxious defensive chemicals - which makes Cecropia excellent fodder for the black howler monkeys. Cecropia also contains a lot of what these monkeys need in a balanced diet, so in the absence of fruits, the howler monkeys munched readily on these nutritious greens

But why is the consumption of Cecropia associated with the prevalence of Controrchis? The fluke does not use leaves and vegetation as a mean of transmission (unlike Fasciola the liver fluke), instead, Controrchis uses ants as a go-between to get in their vertebrate host. But these monkeys don't really have a taste for ants, so why is Controrchis prevalence linked to the amount of leaves they have consumed? That is because Cecropia also happens to be myrmecophtyes, or ant-plants. Monkeys that are chowing down those leafy greens are also inadvertently swallowing a lot of ants, which means taking onboard a lot of Controrchis waiting to make a connection with a suitable monkey host.

For another more detailed take on this paper, from the lead author herself, see this post here

Behie, A. M., Kutz, S., & Pavelka, M. S. (2014). Cascading Effects of Climate Change: Do Hurricane‐damaged Forests Increase Risk of Exposure to Parasites?. Biotropica 46: 25-31.

April 9, 2014

Bivitellobilharzia nairi

A little over a year ago, I wrote a post about Bivitellobilharzia loxodontae - a species of blood fluke that lives in the African forest elephant. Today I am writing about a study on another species from that genus - Bivitellobilharzia nairi - which parasitises the Indian elephant. However in a newly published study, it turns out the Indian elephant is not the only thick-skinned mammal that harbours this fluke.

Photo of Indian rhino by Krish Dulal
The study we are featuring today took place in southern Nepal at the Chitwan National Park (CNP). Researchers collected fecal samples from both domesticated and wild Indian elephants for examination and as expected, they found B. nairi eggs amongst the samples. But it was when they started looking in the poop of Indian rhinoceros that they found the unexpected. These rhinoceros do not take a dump just anywhere; they are creatures of habit and defecate at specific spots call faecal middens - which is how they mark their territory. When the researchers dug through the contents of those middens, they found blood fluke eggs amidst the rhino dung in half of the fourteen middens they sampled from.

The eggs had the characteristic look of schistosome eggs - an ovoid with a hook at one end (see below). But they were not just any blood fluke eggs, they looked very similar to the eggs of B. nairi - the elephant blood fluke. When the researchers sequenced specific marker section of the fluke eggs' DNA, they found that it matched the known sequences for B. nairi, showing that what is usually thought of as just an elephant parasite can also find a home in the Indian rhinoceros. Furthermore, the B. nairi eggs they recovered from the rhino dung were completely viable, showing that the rhino is a natural and commonly used host for this parasite and that they did not end up there by accident

Image of Bivitellobilharzia nairi egg from here
Evolutionarily speaking, elephants and rhinoceros are fairly far apart on the mammalian tree - the last common ancestor they shared lived about 100 million years ago in the era of non-avian dinosaurs. So what is an elephant schistosome doing in a rhino? Despite their specialised adaptations for living in the circulatory system and evading the immune reactions of their particular hosts, throughout their evolutionary history, schistosome have made a number of leaps across divergent animal taxa. One such jumps had allowed the ancestors of schistosomes to evolve from a sea turtle-infecting parasite into one which live in the blood of warm-blooded animals like birds and mammals. While elephants and rhinoceros have had disparate evolutionary paths for at least a hundred million years, clearly their physiology are similar enough for B. nairi to successfully survive in both. In addition, their shared habitat provided the fluke with plenty of opportunity to encounter and adapt to the rhinoceros.

So there is more than one way for two (or more) different species to end up with the same parasite. You can either share a recent common ancestry, or you can share the same habitat which gives the parasite ample opportunities to cross the evolutionary gulf between different hosts.

Devkota, R., Brant, S.V., Thapa, A. & Loker, E.S. (2014) Sharing schistosomes: the elephant schistosome Bivitellobilharzia nairi also infects the greater one-horned rhinoceros (Rhinoceros unicornis) in Chitwan National Park, Nepal. Journal of Helminthology 88: 32–40