Disease ecologists are interested in how parasites - organisms that make their home in or on another larger animal - are distributed, and how they exert an influence on the natural world. Parasites are implicated in regulating predator-prey population cycles, nutrient cycling, animal reproduction, speciation, social behavior and much more.
As you can see in the picture at left, we get extremely excited about collecting animal SH!#T. In this program we also screen for blood- and ecto-parasites.
Our research on parasites at the Los Amigos Research Station began in 2012 with a focus on two primate species, the saddleback and emperor tamarin. Since then, we have expanded our research to include the entire primate community - all 11 species. Over the next few years we anticipate further expansions of this program to incorporate terrestrial mammals, bats, and birds. We aspire to study parasites on as many trophic levels as possible.
1. Which parasites do different primate host species carry? Which are shared between species, and which are host specific? Do these primates possess any parasites in common with humans?
2. How are parasites distributed throughout host populations? Does each host individual have an equal share of parasites? If not, who tends to have more or less parasites, males/females, old/young, breeders/non-breeders.
3. How do parasites affect the health of their hosts? Are individuals with certain parasites actually sick or unhealthy? Do they exhibit different behaviors? Do parasitized individuals alter their diet (e.g. to self-medicate)? Do healthy individuals avoid parasitized individuals?
4. If we think of the host as the environment, then how do multiple parasites within the same host interact? These situations are referred to as concomitant infections, and they are the norm in nature. Parasites can interact directly by competing for space or other resources, or indirectly by activating or deactivating aspects of the host immune system. Do parasites that are in the same tissue interact more strongly than parasites that are in separate tissues?
To study parasites, which tend to be VERY small, we first have to collect samples. Most parasite studies of wild primate populations are limited to non-invasively collected fecal samples. Since we have an animal mark and recapture program, we are also able to collect blood samples for hemoparasites, and scan the external surface of an animal for ectoparasites. Here, you can see what a thin blood smear made in the field looks like. We stain the smears and then evaluate them under the microscope for hemoparasites.
All the samples we collect are brought back to a field laboratory where we use a variety of methods to preserve both parasite DNA and parasite morphology.
We also extract host sex hormones (androgens and estrogens) and stress hormones (cortisol) from fecal samples. Additionaly, we conduct total white blood cell counts and leukocyte differentials on the blood smears. We search for correlations between these data and variation in parasitism.
Next Generation Sequencing
We use a variety of tools to screen for parasites to ensure that we miss nothing.
We have discovered a variety of blood parasites in the tamarins. Here is a picture of one microfilarid. Microfilariae, not this species, are responsible for causing filariasis in humans.
Here is a selection of fecal parasite found in the feces of the tamarins. Eggs and larval stages are most common, which to the untrained eye are extremely difficult to spot and differentiate. These pictures are taken at a magnification that is 400 stronger than what the naked-eye. For example, 76 micrometers is .076 millimeters, which is .0076 centimeters - that's REALLY small! These parasites can be distinguished by morphology to broad taxonomic levels only.
Using morphology we can only identify parasites to broad taxonomic levels. Thus, we use molecular techniques to accurately determine the species of parasites in our study populations. The picture above shows a phylogenetic tree and it indicates that our parasite group (labeled in blue) clusters with a filarid species (a worm that occupies the blood of its host) called MANSONELLA MARIAE. To create this, we extracted parasite DNA from our samples, found a unique section of sequence, and compared it to reference sequences from other research labs around the world.
For each parasite that we find, we keep track of how infection status changes over time. We have a unique vantage point because we collect samples from known individuals for multiple years. Here is a glimpse of data for a Trypanasome parasite. Certain Trypanosomes (not this one) cause Chagas disease and African sleeping sickness. On the left you can see how the proportion of infected individuals in the whole population has changed from 2012 to 2014. On the right you can see how individual infection status has changed over time. The darker the line, the more individuals that have taken that path; for example, many individuals acquired an infection between 2013 and 2014, but hardly any lost an infection during that same period, in both sexes.
We hope you enjoyed this brief tour of our disease ecology research program. We invite you to contact us with any questions.
What better way to end than with a picture of a spider monkey poop sample that was collected by our research team in 2015. As you can see, most of the sample is in the collection bag, but some remains on the backpack. Sherlock Holmes might deduce that this excellent researcher was poised IMMEDIATELY below the primate. Perhaps, during a moment of ease, the researcher took his eyes off the monkey, and it grasped the opportunity to take aim and nail him. Not many people can brag of being pooped on by a threatened species of spider monkey now, can they?