System Pride

Most scientists will tell you that their study system is the best study system. If they use a model system, their system is the best because it’s easy to bring to the lab, it’s appropriate for a broad array of questions, and it already has decades of research built around it. If they use a non-model system, it’s perfect because it adds to our understanding of global diversity/processes, it represents an open niche for one to make their name, and it may be more likely to reveal novel discoveries. But the degree to which a study system is defended and justified varies greatly across systems, and it seems as though system pride often increases as a function of distance from humans.

System Pride

 The invertebrate biologists go bonkers for their barnacles.

inverts

 The plant ecologists take pride in their perennials.

plantman

 And the soil biologists smile at the stratification of the soil pit they’ll push you into if you dis their soil.

soilpit

And there is an awful lot of system pride among the parasitologists, who are constantly defending their work because of the disgust that’s so attached to the term “parasite”. We study the “abusers of life”- the reviled alien creatures that live in guts, tissue, and feces. A cheetah may kill an antelope instantly (forever ridding its prey of true love, happiness, and reproductive success) while the lowliest tapeworm may only take a few bites. But – let’s face it – to most people that cheetah is way sexier.

parasite cheetah

Due in part to their system pride, parasitologists have recently begun to ask an important question: what role do parasites play in ecosystem function, and how are parasites important components of biodiversity? And recently the BBC did a piece on just this question, asking:

“What would happen if all the parasites disappeared?”

You should definitely read the article for yourself if you get the chance. The author, Lucy Jones, interviewed a number of eminent parasite ecologists, including Andres Gomez, Kevin Lafferty (who we met in Bocas), Jaap de Roode, Levi Morran, and Luis Zaman. And the piece quickly became an interesting thought experiment, covering everything from human health, to population regulation, to niche partitioning. One scientist even posited that, in the absence of host-parasite red queen dynamics, sex would disappear!!!

The moral of the BBC story was that, without the tremendous diversity of parasitic interactions, our world would change drastically and probably for the worst. And I certainly believe that to be true. But is that really unique to the disappearance of parasites? It seems the complete disappearance of any group of organisms would cause fundamental changes in the way our ecosystems work. Try to imagine a world without vertebrates, a world without invertebrates, a world without plants, or… a world without soil.

desolation

System pride may sometimes seem silly or even annoying, but it is integral to the progress of biology. It is developed through a deep and intimate knowledge of a system- and without it, we would not have the understanding of each system’s importance to our world. We need the bird lovers, the fossil hunters, and the fungiphiles. We need people who are passionate about different units of biodiversity, as well as the connections that link them.

-Tara-

Advertisements

Comparing Agua Salud and BCI

Yesterday (17/1/15) we visited the Agua Salud Project. Agua Salud is an experimental forest alongside the canal where researchers are studying forest dynamics and hydrology. While Jefferson Hall was giving us a tour of the area I was struck by the differences between Agua Salud and Barro Colorado Island, both in terms of methodology and scientific impetus. Agua Salud is designed to study how the Canal Zone can be managed in a way that is beneficial to humans and the environment, as well as how forests change over time. BCI is used as a study area to intimately understand how organisms interact on one island. It demonstrates how different motivations can affect what questions scientists ask and how we try to answer those questions.

One of the major goals of the Agua Salud Project is to study how vegetation can be used to control water dynamics in the Panama Canal. The idea is that forested areas will absorb water during the rainy season, which will help to prevent the canal from flooding. Forested areas also have the potential to facilitate the release of water during the dry season, which can help fill the canal when water is more limited. Together, these processes are known as the “sponge effect” and are driven by soil properties and evapotranspiration. Just a few years ago a severe flood threatened to demolish the dams that control the canals water level, a disaster that would have implications for the global economy and cost Panama a lot of money to fix. Experiments at Agua Salud are looking at what species of trees can be grown along the Canal Zone that will facilitate the sponge effect while also providing other benefits to the community. Most of the trees that are being examined will be sustainably harvested and sold as timber. If reforestation can be shown to be an economically feasible venture, then people will have an incentive to invest in reforesting much of the area. This sort of experiment differs markedly from much of the work we have seen at Barro Colorado Island. At BCI, experimental manipulations are usually prohibited and work is being done to answer questions about maintenance of diversity, animal behavior, and any number of biological processes. To me, both of these experiments are fascinating and relevant. It is interesting to think about the motivation behind these different questions and how the balance between them might switch in the future.

Not all work at Agua Salud is centered on management practices and some experiments seek to answer questions similar to those being examined on BCI. In addition to studying the effects of timber farms on hydrology, experiments are also being conducted to measure dynamics of forest succession across the Agua Salud forest. This is done by setting up many plots across the island and monitoring the relative success of trees grouped into categories ranging from early to late successional. Researchers are looking at how nutrient availability, specifically nitrogen, affects forest succession. These questions are similar to some of the questions that are being looked at in one 50ha plot on BCI, where researchers have measured and mapped every single tree greater than 1cm in diameter over the past 30 years, allowing them to look at forest dynamics with incredible spatial resolution. At Agua Salud, Jefferson Hall explained that they chose to look at more plots with less resolution so that they could control for heterogeneity across the landscape. I think that it is important to think about the tradeoffs between these two approaches and how they contrast and compliment each other. This is definitely relevant to us young scientists as we design our own research projects to carry out over the next few months.

Thoughts?

-AK

Parental care in the three-toed sloth and the greater anis

In the natural world we can observe a wide variation in the type of care and amount of resources that parents invest in the offspring. Parental care is defined as any form of parental behavior that increases the fitness of the offspring. Parental care includes preparation of nests and burrows, production of large eggs (which are generally associated with increase hatchability and the survival of the young), care of eggs or the young inside or outside the parent’s body, provisioning of young before and after birth and care of the offspring after nutritional independence.  Parental investment, however, is generally defined as the action of parents that increases the fitness of their offspring at the cost of the parents’ future reproduction. In many species, investment is limited in producing eggs or live offspring, whereas in other species both parents invest in substantial periods of parental care, sometimes even after nutritional independence, as in several bird species and some mammals including humans (Gonzalez-Voyer, A and N. Kolm, 2010). The energy put into parental care is an investment by the parents to successfully pass their genes from one generation to the next.

Here we briefly describe parental care in the three-toed sloth which we saw in its natural environment and was particularly captivating, and the Greater Ani, which is a fascinating bird which Christie Riehl talked about in her presentation.

In humans, we often see mothers feeding their babies and holding them in their arms providing protection.  In nature, we find mammals that live in tall trees, and also show strong affection and provide protection to their offspring in similar ways to humans. An interesting example is the three-toed sloths which can be found living high up in the forest canopy. Female sloths give birth to a single offspring once a year. After mating, the male leaves and doesn’t provide any parental care to the young. Baby sloths are held ventrally to the mother, which is the way the mother protects the baby from predation and provides protection. At the San Lorenzo Canopy Crane, which is around 52 m high and 54 m long, we saw a three-toed female sloth with her baby sitting at the top of a tree. It was amazing to see a female sloth with her baby and to watching how the mother protected her baby from the intense gusts of winds at the top of the canopy. She even moved from her sitting position as the crane approached the tree she was on.

Three-toed female sloth and her baby. Photo credit: Flor Santiago

 

An interesting example of parental care and investment in birds is the Greater Anis (Crotophaga major). A number of females Anis lay their blue eggs in the nests and then share incubation and feeding. Each breeding female removes any eggs in the communal nest prior to laying her first egg. Each female stops removing eggs after she has laid her first egg, presumably to avoid accidentally ejecting her own egg. Females who lay first, therefore, nearly always lose their first eggs to ejection, while females who lay last typically lose none. The number of eggs that are ejected increases with group size, since multiple females rarely begin laying on the same day.

A communal nest of a breeding group of Greater Anis, containing 10 eggs laid by three unrelated adult females. Photo credit: Christina Riehl

A communal nest of a breeding group of Greater Anis, containing 10 eggs laid by three unrelated adult females. Photo credit: Christina Riehl

 

Interestingly, female anis can also act as nest parasites, “dumping” their eggs in the nests of neighboring groups and providing no subsequent parental care. Host groups do have a defense against being parasitized, however. Ani eggs actually change color over time, allowing adults to distinguish between freshly laid eggs and those that have already been incubated. If a parasitic female manages to sneak into a host nest and lay her eggs during the same time window as the host females, the host group can’t recognize the parasitic egg. But if the parasitic egg is laid asynchronously relative to the host clutch, the hosts can recognize and reject it. Unlike most birds that breed cooperatively, Greater Anis nest in groups with genetically unrelated individuals. Because individuals in breeding groups gain no benefits from kin selection, theory predicts that the direct benefits of cooperation – as well as the incentives to compete and cheat – must be quite high (http://gradworks.umi.com/34/63/3463317.html).

 

 

Thanks for reading,

Anakena and Christina

 

Descartes’ Intellectual Descendants?

I would like to preface this post by first saying; I am a scientist. Yes, I realise this seems like a nonsensical statement to make, but hear me out. Scientists of all shapes and sizes are trained in a particular manner, and a particular way of seeing the world. This is not a fault of the discipline; it is simply a means by which to efficiently instruct budding researchers and inquisitive minds. Consequently, however, this instruction method constructs a certain way of perceiving the world, and a set of values that shape this view. As a natural scientist, my worldview is shaped by many pioneering individuals (most of them men, but that is a topic for another time); one of these highly influential men, apart from Charles Darwin, is René Descartes.

Descartes saw the world through a very black and white lens. Animals were lower beings that simply behaved like clocks- non-feeling beings that acted out of a set of pre-programmed responses and bodily functions. Humans were the only sentient beings on the planet, thus justifying our superior cognitive abilities. Now, I am not saying that natural scientists have not evolved from this basic perception of the world, but where Descartes saw the organs of animals as simple pieces of a larger clockwork, we now look at the genome of species and the environmental factors of their species’ range, and dissect behavioural patterns. Natural selection acts on phenotypes (the physical features of a species), thus affecting the genotype (genetics) of that species. This is drilled into our heads, justifiably, from day one of your first undergraduate intro to biology course. While we now know more than our predecessors could have ever imagined about how the world works, the fundamental simplification of animal biology remains.

Now, how does this seemingly meandering rant relate to the course? Here’s my tie-in. We recently had a lecture on the potential of “insight” in spiders. The lecturer began the talk by saying outright, that he did not want to call this “cognition” or “consciousness”, for fear of ridicule from the scientific community. Thus he instead chose to use the word “insight” in an attempt to avoid the suggestion that he’s implying spiders have any independent cognitive abilities. He presented what he called “preliminary evidence” to support the idea that spiders possess problem-solving capacities beyond what is “pre-programmed” by natural selection. My point of contention with this lecture does not lie with his suggestion that lower animals have the ability to independently think, my issue is quite the opposite; why is this still such a sore spot within the scientific community? Why is it so difficult for us to accept that perhaps we are not the only species capable of problem solving, of feeling, of consciousness of the world around us?

Maybe I have a naïve view of the world, in which I think we have moved beyond thinking humans are a superior species, and have developed the maturity to see that we are not so unique. We break the world down into dichotomies so to better understand it, but this leaves us missing out on so much more. Why is our default setting to believe that no other animal could possibly match our cognitive abilities; why don’t we instead believe the opposite, unless proven otherwise? Now, I realise that a good deal of scientific research supports the fact that our neurological abilities are quite advanced, and that other animals have simpler neurological capacities. There is still, however, so much we don’t know, and using ignorance as an excuse for arrogance is not something I feel entirely comfortable with.

And now, for my last point in this extended diatribe; perhaps the reasoning for our narrow worldview lies in its simplicity and its beneficial functionality for human development and research. If we start to think that all species have some form of sentience, how might we continue to destruct the environment in the name of energy or residential development? How might we continue research on disease prevention or agrological innovation, when such research is dependent on the sacrifice of other organisms? I believe that everyone- not just scientists- face these types of moral dilemmas. There is no right answer, and honestly, we need many of these developments for the good of our own species’ survival and basic needs. We can’t simply stop eating and drinking to avoid harming the planet; we are just as fuelled by the will to survive as any other species on Earth. Embracing the idea that other organisms’ might not be so much lower than ourselves poses a moral predicament that threatens our own survival. Maybe we are simply being driven to ignore this idea by our own basic animal biology that we try so hard to distance ourselves from.

Thank you for reading!

Victoria

Barro Colorado, Mixing Colors

You may enjoy hours exploring and admiring this piece of paradise: this haven of tranquility where nature harmoniously concentrated a lush variety of animals and plants, some of which have co-evolved seeming friendships persisting beyond any individual’s time on this island.

The clarity of water from small streams, in their quiet meandering gently crossed by the grooves of beautiful trails, contrasts with the thousand-and-one surrounding shades of green shrubs and brown stubble. Seemingly deserted puddles exhibit joyful dances, their floating insects occasionally darting beneath the fallen leaves dappled in canopy-filtered sunlight.

You may not behold this landscape with indifference for its spectacle will remain indelibly in your heart.

IMG_1350photo 3

 Anakena Castillo-Indicasat-aip

Edition by Holly and Sofía (McGill University)

Long live our queen, the parasite

Ant Day, like so many cherished holidays of my youth, has come and passed. We spent the day bushwhacking through Pipeline Road with myrmecologists Andy Suarez and Corrie Moreau, and then excavated some leafcutter nests with Hubi Herz to extract queens, fungal gardens, and have a look at nest architecture (while destroying the yard of a certain STRI researcher). Hopefully, some photos will circulate our flickr in the near future (though I can’t take responsibility for any of them). Check ’em out, a deer got involved. The only comment I’ll make on the actual field work is that collecting ants and digging up nests is utterly exciting, like the best scavenger hunt you’ve ever been on. This is how all biology used to be, inclusive to the point that anyone could get involved by just walking outside and looking around. Let’s blame James Watson and call it a day.

This blog post pertains to the origin(s) of eusociality, so here’s a quick disclaimer: I don’t subscribe to one theory, and I generally oppose anything that polarizes folks with as much acrimony as we’ve seen in the past few years after the Nowak et al. paper that redacted kin selection. Sure, I’ve always looked at Hamilton’s famous inequality with healthy skepticism, but that may simply be because there’s math involved. If this paragraph hasn’t made sense so far, here’s a quick review of eusociality and some major explanations that are on the table, after which I’ll bring up a new idea, imparted unto me on this very special day.

I think I eschew defining an always-applicable set of rules preempting eusociality, taking more of an “I know it when I see it” approach, with the caveat that there are definitely some key features upon which we can all agree. The three basic pre-requisties are: overlapping generations (queens and daughters operate side-by-side), cooperative brood care, and division of labor. Humans pretty much meet these conditions, but what separates boring old human interaction from the extreme communism of the insect societies is reproductive altruism; that is, workers, who retain the original plumbing required to reproduce, have almost no reproductive potential. This feature puzzled Darwin, as it challenged the very idea that all organisms should operate in a way that maximizes their fitness, or the likelihood that they’ll pass on their genes to the next generation. In light of natural selection, how could sterility ever be selected for?

The ongoing war is between two major theories: kin selection and group selection. Kin selection invokes Hamilton’s rule that predicts self-sacrificing behavior if it increases one’s inclusive fitness; that is, the probability of one’s genes being passed on indirectly, like through a sister or a brother (you do share half your genome with your siblings, after all). Because of haplodiploid sex determination, which is seen in many eusocial societies (but not all!), sisters are more closely related to each other than they are to their mothers and/or potential daughters. Therefore, having more sisters, rather than having children, is the more efficient way to make sure your genes are better spread around. Group selection is pretty self-explanatory and encompasses all eusocial societies, predicting that living in groups is selected for for some obvious reasons, like strength in numbers. The queen is an ovary: protect her, protect the genome, protect the lineage.

Like I said, I don’t think one is the absolute truth. On Ant Day, I learned about a new possibility. Andy brought up an idea that really interested me, adding to an arsenal of potential explanations for the repeated emergence of eusociality. Apparently, Robert Trivers, in between developing parental investment theories and attending Black Panther meetings, introduced and quickly abandoned the notion that worker sterility as maintained by queen presence (via pheromonal “blocking” of ovariole development, for example) is an example of queen parasitism. That is to say: queens parasitize their daughters, which double as hosts, eliminating their reproductive potential so she can wallow in the joys of motherhood while her daughters do the heavy lifting. I can’t find too much written on this, but I think the general idea is that workers, unable to reproduce, either die alone or stick around and benefit from inclusive fitness effects. With this model, there’s no altruism, and every selfless action that appears to be “for the good of whole” ultimately stems from victimization of the non-queen castes. You are thinking: this is the least romantic of the explanations. In honey bees, if the queen dies (long live the queen) and a new queen can’t be raised, worker ovarioles develops and at least a few workers will gracelessly start laying eggs. Because their eggs can only produce males (recall: haplodiploidy!), their colony is doomed and their laying is a blitz to send out half their genome with the hopes that a new colony can be founded. Or is this just what they’re like in solitary state, without their queen, the parasite?

Watching leafcutter trails and army ant swarms, the coordination of action is overwhelming. Everyone just “knows” what to do, and carries out a caste-specific task in an unquestioning, stereotyped manner. To think all of this is orchestrated by antagonistic interaction is an incredible premise, one that I hope to explore and possibly test in the future. If it is the case, then eusocial societies are the most fantastic exercises in population control.

Thoughts welcome.

ian

Biologists: What are we really up to?

So, the ant day we had a couple of days ago was fantastic, I’ve been watching those little guys crawl around since arriving to Panama so it was great to finally learn about how they go through life here in the tropics. However, there was one thing that I just couldn’t get out of my mind, the whole “leave the forest as you found it” comment. Now I suspect that we would all be in agreement with this, if you turn up a log, turn it back over, if you pick something up, put it back where you found it. No biologist (hopefully) wants to make life for these guys living in the tropics harder than it already is. So after all nodding in mutual agreement about trying to make as little disturbance as possible, we then proceeded to cut down and chop a tree into smaller pieces in order to expose the ant colony sheltered within. Now don’t get me wrong, I thoroughly enjoyed seeing how they partition within the tree, it was definitely a cool experience, but I could certainly appreciate the irony of the situation.

The paths we took to get here were all unique, and I love listening to people describe the circumstances that resulted in their current position in life. Ultimately, we all have a deep love and appreciation for life, as well as a need to learn more about the world we live in. However, is it possible for us to study the habitats we’re so fascinated with, without some level of destruction? Even when studying parasites, which may arguably be one of the more important considering how little is known, the only way to isolate and study them, is through crushing their hosts, the snails. There are probably very few people who would argue that parasites don’t need to be studied, many of their ecological contributions are not well-known. However, will we ever be able to fully study and understand our system without a certain level of destruction? And if not where do we draw the line? When does the information we gain from looking at our system outweigh the cost of removing it in the first place and does it truly matter?

Thanks for reading yall and feel free to share any opinions,

-Lynette

Why do invading hosts leave their parasites behind?

Earlier this week we visited Mark Torchin at the Naos research station where he delivered an excellent talk on the importance of parasites to ecosystem processes. A portion of his talk focused on the “Enemy Release Hypothesis”, a fundamental theory in invasive species ecology that has generated over 1800 publications and greater than 40,000 citations.

The Enemy Release Hypothesis posits that as non-native species enter new habitats they leave their enemies behind (Keane & Crawley 2002). In their natural habitats these species’ enemies (predators, parasites, and pathogens) typically regulate their populations, allowing for coexistence with their natural competitors (via “apparent competition”). Without these enemies, however, introduced species lose that form of regulation and can then outcompete the native species.

At the end of Mark’s talk, Patrick Jansen raised a valuable question about this theory:

Why aren’t enemies introduced with the invaders? 
Why are enemies “left behind”?

When species are introduced they tend not to take their predators with them for obvious enough reasons. But parasites that live on or within their hosts can easily make the journey because of their tight physical connection. So why aren’t all of a host’s parasites introduced with the host? There are many factors that may prevent parasite introduction, and one of the simplest is the life cycle of the parasite itself.

As parasite trophic strategies vary, so do their life cycles and their modes of transmission. Some parasites have one-host life cycles and are transmitted horizontally, meaning they only require one host species to reproduce and are transmitted from one individual to another. This is the dominant strategy of the feather lice that infect birds, as well as the head lice that infect us.
Head Lice Life Cycle

One-host parasites can also be vertically transmitted from parent to offspring. Indeed, there are some parasites of humans that utilize the breast milk pathway in order to move from mother to child. In addition to horizontal and vertical transmission, there is transmission via autoinfection wherein the host can reinfect itself. A classic example of autoinfection is the human pinworm. If a person (often a child) consumes a pin worm egg, the adult pin worm becomes gravid with eggs as she moves toward the rectum. At night while the person is sleeping, the pin worm exits the anus and lays eggs around it that are encased in a substance that causes intense itching. When the person scratches the area, those eggs are easily moved to the fingers where they can then reinfect the person or any person they may come into contact with.

 

Pinworm

One-host parasites can probably follow invaders efficiently, given that the introduced population contains enough infected individuals to establish. Pinworms, for instance, are thought to have followed humans during their migration into the new world (Araujo et al. 2008)

If we go up a level in complexity, we find parasites that spend a portion of their lives on their hosts, and a portion of their lives in the environment. This is the case for the human hookworm which spends part of its life molting and maturing in the soil. Humans acquire infections by walking barefoot in high hookworm areas- the hookworms can penetrate the foot tissue and then migrate through the body. Because of their dependence on environmental factors, abiotic filtering may prevent establishment of parasites with this form of life cycle.

hookworm

And then we get to the parasites with multi-host life cycles, like the trematodes we examined earlier this week. Complex life cycle parasites have 2 or more hosts that are critical for completion of their life cycles. If, during an introduction, any of these hosts are missing, the parasite will not be able to establish. Parasites with multi-host life cycles may vary in how generalist or specialist they are, but typically have at least one life history stage where they are highly host-specific. The composition of the invaded community and the parasite’s degree of specificity will then determine in part whether or not the parasite can be introduced.

schisto

So is the capacity for a parasite to invade correlated with the simplicity of of its life cycle? This is one idea in the field, but there are certainly additional factors that may play important roles, including how the invasion occurs, the size of the invading population, the prevalence of the parasite, and its pathogenicity.

-Tara-

Around Fort Sherman, Panamá

A few days ago, we went to visit Fort Sherman, located in the province of Colon, on the Caribbean coast of Panama. The Fort was an important rainforest warfare training site for US soldiers from 1953 until 1999. This site forms part of the Parque Nacional San Lorenzo, created in June 1999, and consisting of 12,000 ha of humid rainforest.

During the walk, we noticed a huge diversity of plants and animals, mainly butterflies, along the trail. The location of the fort is considered as a hybrid zone for studies of speciation. For example, the butterflies that belong to the genus Heliconius are from the tropics, and they show a huge diversity of wings patterns. This genus have been under rapid speciation and divergence, and also show an amazing amount of convergence in wing pattern due to mimicry.

We had the opportunity to catch some species of Heliconious and we were able to observe different behavior  traits like the one presented by H. sara where the IMG_1675males from smaller sizes are very territorial. Furthermore, during the field trip we  were able to observe how the butterflies use niche partition and we saw a flying representant of the hyribrid zone Anartia fatima and comimetic individuals like H. melpomene and H. erato.

Xylaria sp

Xylaria fungi

 

As  well, on the trunks, we observed fungi that belong to the Xylaria genus, some of them are known as producers of bioactive compounds. Commonly, this genus is found growing over dead wood.

Finally, we arrived at the San Lorenzo Canopy Crane, which is around 52 m high and 54 m long. The crane is used in several studies, such as structure and dynamics of the upper canopy, biodiversity of different organisms, and biotic interactions, like pollination and herbivory. The experience of being on the top of the crane was amazing, the landscape formed by the different kinds of trees mixed with the view of the Chagres river was one of the best things during the trip.

Canopy Crane

One of the most charismatic megafauna that we had the encountered was a three-toed sloth. The individual that we had the opportunity to see was a female (Bradypus variegatus) with her baby, as you can see in the picture. This animals are characteristic for being lethargic, and for spending a great part of their time hanging in trees, where they even mate and give birth.Take a look at this very cool project,, done in Barro Colorado, which recorded sleep activity with an electroencephalogram (EGG) attached to the sloth’s head. They discovered that sloths do not sleep that much, only approximately 9.5 hours per day, probably due to the necessity of continuously foraging, and being alert to predators. 

DSC01962

 

It is really wonderful the huge diversity of organism interacting between them in a single place, from the microorganisms to the biggest tree. We hope that ecological protected areas, like Parque Nacional San Lorenzo, remain preserved to many generations will be able enjoy the great experience to be there.

Gracias por leer,

Librada y Flor

Continue reading

Algae, Moths, Fur, & Feces: The Curious Case of the Sloth-Moth Symbiosis

A few days ago, our group was given the incredible opportunity of riding a canopy crane operated by the Smithsonian Tropical Research Institute high up above the forest canopy at Fort Shermin, Panama.

While exploring the canopies, we were fortunate enough to find a brown-throated three-toed sloth (Bradypus variegatus) mother and her baby clinging to the limb of a tree and foraging on nearby leaves. This encounter reminded me of the curious symbiotic relationship these creatures have with the organisms that call sloth fur their home.DSC00890

Of all the mammals we have encountered in the tropical forests of Panama thus far, the two- and three-toed sloths are among the most fascinating in terms of their life history and behavior. Both two- and three-toed sloths are remarkably slow-moving animals with low metabolic rates as a consequence of their folivorous diets. Since they subsist almost entirely on hard-to-digest leaves filled with fiber, cellulose, and toxic secondary compounds, sloths have evolved a sedentary life-style to allow ample time for the microbiota in their numerous lengthy guts to release the scarce nutrients found in leaves and make them available to the sloths. In fact, studies have suggested that sloths may have the slowest mammalian digestive rate, with an average of 16 days required to pass a meal entirely! However, this intimate and drawn-out relationship with microbes is not the only symbiosis in which sloths partake.

In a fascinating triumvirate of mutualistic adaptations, a group of moths, known as sloth moths (Lepidoptera: Pyralidae), obligatively inhabit the fur of some sloth species and use sloth feces as an egg laying substrate. However, until recently scientists were unsure of why three-toed sloths descend from the canopy to the ground to defecate before returning to the treetops. A new paper in the Proceedings of the Royal Society posits an explanation that is driven by another denizen of sloth fur, algae (Trichphilus welckeri). By presenting evidence of the algae feeding both sloth moths and the sloth itself, while also gaining nutrients from decomposing sloth moths, Pauli et al. 2015 have shown a possible explanation for the strenuous and seemingly unnecessary weekly trip to the toilet some sloths make. In turn for providing moths with an oviposition substrate, nutrients for their larvae, and safety from predators, sloths are able to optimize algae production and supplement their nutrient-low diet with algae from their own fur. Some may ask, then, why would the sloths not simply eat the moths and forgo the algae altogether? I don’t think a sloth could even close its mouth fast enough to catch anything faster than algae!

IMG_0793

Though often viewed as odd, awkward animals, sloths clearly demonstrate the incredible elegance with which creatures have managed to survive through evolutionary time.

Thanks for your attention and I hope you enjoyed reading!

-Scott