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.
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.
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?
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 .
Aaaand, we’re back! This time around I was able to play around with manipulating physical (size) and genetic (relatedness) variables between aggressive cannibal tadpoles (the infamous Dendrobates tinctorius) in collaboration with Lutz Fromhage, Janne Valkonen, and Bibiana Rojas.
The D R A M A is for real. . . it turns out that both size and relatedness play a role in driving aggression between tadpoles, where individuals are more aggressive towards a counterpart with increased size asymmetries and decreased genetic relatedness. In other words, large non-siblings are significantly more aggressive than large siblings (exhibiting almost twice the amount of aggressive behaviors).
But it doesn’t stop there.
The most fascinating thing (IMO) is the shift in latency to aggression depending on relatedness. We find that there is inversion in biting behavior as size differences increases, where sibling pairs with large size differences attack significantly faster than non-siblings. Thus, although large siblings were less aggressive overall, they had a shorter latency to aggression in dyads with large size differences.
Is that not simply fascinating? Why are siblings who are quite disproportionate in size demonstrating aggressive behavior so quickly? Perhaps that biting is not simply an aggressive behavior, but a means for identification and the assessment of relatedness? Or perhaps it is a behavioral response to establish dominance within a pair?
No matter how you slice it, there is something going on in their little tadpole brains where individual behavior is different when faced with non-related or related individuals. From this clear kin discrimination and really cool cognition work headed by Fischer (2020), we believe that there is kin recognition in Dendrobates tinctorius. To read more about the details of our study and learn about aggression in cannibals, check out our OA paper in Behavioral Ecology!
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.
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 😉