Life through rose coloured glasses

science

Interested in the manuscript? Read our paper in the Journal of Experimental Biology ! (and you can find all of the data and scripts here.)

Adapt or die. That’s the motto– and across our amazing tree of life we see mind-bending examples of animals adapting to their environment for the sake of success and survival.

Here again we are carried to the world of poison frogs. In these experiments we focus on phytotelm-breeders– in other words, frogs that deposit their tadpoles into small pools of water formed by vegetation. Think about a leaf axil, palm bract, or treehole.

Tadpoles are stuck in these minuscule pools until metamorphosis. Albeit minuscule, these pools represent an entire world for a tadpole– they may only be the volume of a coffee cup, but until this point, our little tadpole friend has never been anywhere else in its entire aquatic life. For a tadpole, a pool is the beginning and end of their universe. The water they live in, the creatures they interact with, the rise and setting of the sun– all of this has only ever been experienced from within the confines of a leaf axil.

And that really got me thinking.

It’s not hard to see the differences in these little ephemeral worlds once you start looking at them. Some are big, some are small. Some have lots of jungle stuff in them (debris, animals, unspecified gunk and goop) while others are as clear as drinking water. Looking at the water of these nurseries, I thought to myself that there has to be an effect of growing up in a tea-coloured pool.

Do tadpoles raised in tinted water see the world through rose-coloured glasses? Or is it more like growing up in the shadows, where one must navigate an entire universe with the lights turned off?

Embedded in this question we can disentangle the threads of biology: does the visual system of tadpoles adapt to turbid conditions (or do other senses compensate for the challenge to vision) or are tadpoles doomed to simply have to survive in ephemeral darkness?

As we do what science does, the “I” quickly became “We” as this idea gained traction with my mentors and friends. We began to think more about this question and we thought it would be interesting to consider how tadpoles with different life histories may respond differently to growing up in turbid conditions– how does growing up in coloured water affect the behaviour of a voracious predator versus a that of a tadpole dependent on maternally-provided food?

Vision plays an important role for both of these species’ interactions: one to subjugate, kill, and consume (our beloved cannibal tadpole: Dendrobates tinctorius) and the other must recognise incoming mothers (or incoming predators!) and respond appropriately (a beautiful Costa Rican poison frog called Oophaga pumilio). So, we thought why not test how wild tadpoles (that have developed in a wide range of nurseries) respond to the visual stimuli of various predators!

I ran these experiments in French Guiana and Costa Rica; in French Guiana I used D. tinctorius tadpoles from various pools and paired tadpoles with the visual stimulus of either a conspecific (remember, these guys are cannibals) or a dragonfly larva, which is an avid tadpole predator. In Costa Rica, I collected O. pumilio tadpoles from various bromeliad axils and paired tadpoles with either a conspecific (while not predatory, previous work has established that tadpoles will kill each other if they are placed together in a pool) or a spider.

Here’s what emerged as true. First of all, the developmental conditions of larval nurseries (the little coffee-mug universes) play an important role in how both species perceive risk (Panels B, D). We see that D. tinctorius tadpoles from turbid conditions are much less active when faced with any visual stimuli (Panel B) and that tadpoles from clear pools make the distinction between visual stimuli, where tadpoles move a lot more and interact more with the visual stimulus (i.e. centre of the arena) when they see conspecific tadpoles! O. pumilio shake up the box too– tadpoles are more active in novel contexts that more closely match the luminosity of their developmental environments. This is a fancy way of saying tadpoles from clear pools are more active on white backgrounds while tadpoles from turbid pools are more active on black backgrounds.

Overall, these data show us that the natural history of both species shapes species’ behaviours. The colour of a tadpole’s universe has measurable effects on their responses in novel contexts, just in different ways.

These results have important implications for visual plasticity of animals in response to environmental change. Our results serve as a useful model to understand animal responses to habitat disturbance and how communities may shift when visually-guided animals are challenged.

**Personal tangent**: First, for me personally– I got to take a little thought in my head and watch it play out in real life. That’s enormously satisfying (and you can read about how I got to this point from a previous blog post). Professionally, I learned how to quantify pool darkness (turbidity is actually not the **technically correct** word in our case here, but we won’t get into that because the verbiage surrounding light and photic environments will keep us here for years) using various methods, I had the opportunity to work with a new frog species in Costa Rica, and I just generally grew as a person interacting with all these new people and scientists in varied contexts. So thank you everyone for teaching me, supporting me, and nurturing these ideas into something coherent and beautiful! A big thank you to Bibiana Rojas (KLIVV), Jenny Stynoski (U of Costa Rica) and Carola Yovanovich (U of Sussex) for being the most wonderful people ever in the history of ever.

In the eye of the tadpole

science

Tadpole responses to environments with limited visibility: what we (don’t) know and perspectives for a sharper future

Access our peer-reviewed Perspective article here.

Throughout my encounters with different languages I have always been fascinated by words that cannot easily be translated. Some words hold a certain weight, cultural insinuation, or biological inference that isn’t fully described when translated on a word-to-word basis. For me, as a young French girl, my family would describe me as “gourmande” which is essentially a lover of delicacies in large quantities. Not so easy to translate into English without the misinterpretation of being a glutton. . .

Anyway. One of my favourite untranslatable words is umwelt, which from German is directly translated into “environment” in English, but is more profound at its core. In high school I learned this was the word used to describe the world perceived (or experienced) by a particular organism. For example, I might mistakenly design a task where I ask an animal to differentiate between two colors that they are biologically unable to distinguish (like red and purple for dogs) or I may not consider colors that are vital for the animal’s perception (like UV in birds and bees), and from there draw false conclusions. Being misled in this way stems from not considering an organism’s umwelt which has limited our understanding of aggression, cooperation, and intelligence throughout the animal kingdom.

The various nurseries where tadpoles are deposited to develop. Water samples in the top panel corresponds to the pool where they were sampled in the bottom panel.

But, we’re doing a bit better now. And that’s what this Perspective article is all about– briefly, (to get you up to speed on the system set up) various tadpoles from different species are deposited in a large range of aquatic nurseries. From size to water color and pool turbidity, it seems pretty intuitive that these vastly different rearing environments would have different implications for the larvae developing within them. What happens to tadpole eyeballs when they grow up in the dark? How does growing up in the dark affect behaviour (i.e., scavenging, predation, sociality)? Does that carry over across metamorphosis?

From a proximate perspective could the eye actually change? Is there even a precedence for this? (yes, there is. . . think along the lines of Vitamin A ratio shifts recorded in fishes 😉 ) From a behavioural perspective, what happens to predatory tadpoles (e.g. Dendrobates tinctorius) when their visual landscape breaks down; what about the tadpoles that depend on visual cues from their parents for feeding (e.g. oophagy by Oophaga pumilio)?

What happens, indeed! I have no clue. But look at this big ol’ gaping hole ready for questions!

Curious for more hypotheses and my first drawings published in a real, live journal? Check out our recently published paper in Frontiers in Ecology and Evolution.

A tadpole’s guide to the galaxy

science

Read our open access paper published in Ecology and Evolution

Up in the treetops hides an entire unexplored verdant palace.

It’s easy to forget that there are spheres of existence that occur beyond what is directly observable–we could get poetic here and talk about the feeling of looking out into the stars or into the ocean’s abyss, but from a more ordinary standpoint, it’s easy to forget about life directly under our feet or above our line of sight.

In the Amazon with trees reaching several stories tall, your mind might wander to the birds and monkeys that so noisily call from above– but there are other animals that make use of the vertical gradient from the forest floor to the treetops that aren’t winged or . . . thumbed(?) and make for much less annoying roommates. We, of course, are led back to our fabulous amphibian friends. In this study I am here to take you on three different narratives between the lives and interactions of three different species of Neotropical frogs and provide you a brief introduction to a tadpole’s guide to the galaxy.

^{Illustrations by Andrius Pašukonis}

In this study, we went through the jungle looking for babies.

Which is a great sentence on its own, but I’ll elaborate. Following babies is good for several reasons: first, it saves us the trouble from having to follow the parents which would (1) be exhausting and (2) a waste of time. By identifying tadpoles, we can say with certainty that at least one adult of that species has been at the location in a not-so-distant past. Secondly, these microhabitats (also called phytotelmata, also called pools) are . . . small. . . and thus, it’s quite easy to measure a ton of chemical aspects of the pool, identify the kind/density of predators, and cons/heterospecifics.

This gives us a really beautiful picture of the ecology of these habitats and also shines a light into the decisions parents make when deciding where to deposit their tadpoles. What is shaping deposition decisions in frogs, and does it change dramatically based on the natural history of the species?

You might be tempted to think that water accumulating in plants and trees and dead palms is created equal. But not to the frogs, friends. Not to the frogs.

A brief backgound: Allobates femoralis is a small poison frog that can’t climb for shit. They are great parents, where fathers will dutifully carry their babies to small pools of water throughout the jungle. Osteocephalus oophagus is an arboreal froggo, which means that they chill in the trees pretty much their whole lives. These guys are a bit different from the poison frogs: they deposit their eggs in small pools (into which the tadpoles then hatch)– then mamas will come and feed their babies unfertilized eggs as a nutritious snack throughout tadpole development!

Dendrobates tinctorius is a little amphibious spider money with amazing parenting skills and is just overall just the best creature out there. Their tadpoles are aggressive cannibals and survive an amazing range of chemical properties.

So, what did we find, climbing ’round the forest for two years?

Unsurprisingly, we see that A. femoralis dads deposit their babies on the ground, which is not all that surprising as adults can’t climb. O. oophagus, the arboreal frog, actually climbs down these humungous trees to deposit their egg clutches around 1.5-2m in height (6ish feet). We explore why parents might do this below. Finally, D. tinctorius can’t be bothered to care: from the forest floor to the tops of trees, dads will sometimes make huge energetic decisions regarding where to put their babies.

So, into what kinds of pools are these babies being deposited within their respective vertical columns?

The diversity of occupied phytotelmata pools throughout the jungle.

Interestingly, for A. femoralis (grey points below) and O. oophagus (yellow points below), deposition decisions are pretty clearly be delineated by pool size and height– these decisions fit nicely within the context of the parental care strategies of both species.

We find that O. oophagus tadpoles almost exclusively occur in small phytotelmata with close to zero leaf litter (a variable that can help inform water turbidity); in other words: small, clear tiny pools. And this makes sense, right? Remember that mamas feed their babies trophic eggs, so clear water is probably important for the maintenance of potential feeding cues; also, feeding their babies means consistent, nutritious meals, which may be what allows them to choose these extremely small pools (higher risk of drying out counteracted by short development times from yummy eggs). Small pools also exclude other aquatic predators (such as dragonfly larvae), which is another advantage of choosing these dangerously small pools. A. femoralis tadpoles on the other hand occur in larger pools terrestrially– these pools can be big and murky– this means more predator risk, but also more food opportunity (i.e. detritus) resulting from the decomposing leaves, which is what tadpoles of these species primarily eat. Leaves and sticks in these pools also provide some much needed hiding places for these tadpoles to hang out and hide.

Again, here we are stumped by the amazing flexibility of D. tinctorius. Because these tadpoles appear to tolerate such vast conditions, we spend the rest of our time looking at the pool choices of this species to see if there was any particular condition they preferred.

Well, the story is not so simple– but in broad strokes here’s what we found: D. tinctorius tadpoles occur in higher densities in pools that occur higher in the treetops, these pools are also chemically distinct– they have higher alkalinity (KH), hardness, and salinity– which may all be important variables for tadpole growth and development (which is the next step to experimentally explore).

Overall, the beauty of this study are its contributions to natural history and behaviour of poorly studied species. I think one of the coolest parts of being a biologist is having the opportunity to work with the natural world, ask questions, and slowly untwine the nature of why things are and how they came to be. If you enjoyed this brief overview, feel free to take a look at our paper in Ecology and Evolution which you can access here .

Shine bright like a tadpole

science

Visible implant elastomer success in early larval stages of a tropical amphibian species

Access the peer-reviewed article here: https://peerj.com/articles/9630/

When we observe animals, be it in the jungle, under water, or even in your own back yard, we learn to recognize individuals over time. Maybe you know your neighbourhood squirrel because it has a ripped ear, or you notice a butterfly because it has a unique pattern. This process, the act of distinguishing individuals, is fundamental in behavioral research.

But what do you do when all of your individuals within a population look similar?

In this study, I attempted (along with one of my best friends, Guillermo Garcia-Costoya and my advisor Bibiana Rojas) to tag young poison frog tadpoles with fluorescent elastomer tags. This is especially interesting because, to date, tropical larval amphibians had never been tagged; further, we marked the smallest and youngest amphibious animal ever recorded.

Now you see me, now you don’t:

When tracking tags across development we find that the probability of retention and observation differ across time. This means that just because someone didn’t observe the tag doesn’t mean that the tag is actually lost. This is important to take into account when working with mark-recapture studies.

What’s so cool about elastomers is that they’re small and durable. We now have work showing that we can tag tiny little tadpoles (before they have cool back patterns or are transported by their fathers!) and find out where they are carried or even how tadpole communities change over time in small water holdings. This methodology will hopefully be of use to future biologists who working in conservation or on behavior in the tropics.

Hungry to learn more about cool science?

Read the paper

A Quick Guide to Cannibalism

science

Review written by Chloe Fouilloux, Eva Ringler, and Bibiana Rojas

Animals can sometimes be downright bizarre. We, as biologists, still don’t quite understand why animals behave the way they do, but every day we get a little bit closer to a more complete reality of the natural world that we observe. One of the most fascinating behaviors I have ever watched is that of cannibalism, where an individual kills and then consumes part or whole of another individual of the same species. And although it’s weird, it’s not rare at all; in fact, it’s present in every animal clade alive on Earth today! Mothers eat their babies, fathers feed their babies to other babies, babies eat each other. . . the carnage is truly ubiquitous.

Feel free to download our quick guide to cannibalism– but watch out! It’s a slippery slope to becoming fascinated with this deliciously intriguing behavior 😉

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