"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.

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