Growing up in the shadows // Life through rose coloured glasses


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.