Since my early teenage years, I have been fascinated by a simple yet profound question: why does life look the way it does? From the colors of animals to the patterns in nature, I have always been curious about the forces shaping the world around us. This curiosity has stayed with me, leading to questions that, years later, I would explore through research.

For example, picture yourself walking through a dense temperate forest in summer. The canopy above is thick, allowing only small patches of sunlight to filter through. It feels cool, shaded, and even at midday, the light is diffuse. Now, step out into a sunlit clearing... Suddenly, the brightness is overwhelming, it is warmer, and there is nowhere to hide from the sun’s glare. The contrast is striking. It is these kinds of environmental differences that shape life in remarkable ways, including one of the most visually striking traits of all: color.

For animals living in these environments, this difference in light exposure is more than just a momentary sensation - it is a powerful evolutionary force. Color plays a crucial role in thermoregulation, camouflage, and communication, but the mechanisms shaping global patterns of color variation remain debated, often yielding contrasting results even within closely related groups (Goldenberg et al. 2022). Latitudinal and altitudinal distributions, body size, activity patterns, conspicuousness, and their underlying selective forces have all been proposed as key factors influencing animal coloration, yet disentangling their relative contributions has proven challenging. In our recent study, we set out to explore this complexity in squamates (lizards and snakes), testing how these environmental and ecological variables shape brightness evolution across more than a thousand species. Among all the factors examined, one stood out above the rest: habitat openness.

But as with any ambitious research question, the road to answering it was far from simple. Our study spanned five years, supported by student projects for data collection, and built on our 2021 study focused on image color data (Goldenberg et al. 2021), refining methods to ensure accurate brightness measurements across diverse squamate species. We gathered data on 1,372 species but ultimately analyzed 1,249, excluding 33 aquatic species due to inconsistent lighting conditions, omitting 18 for which we couldn't retrieve suitable images, and making further refinements based on the latest taxonomic reclassifications. In total, we examined nearly 11,000 images. Yet, some of the biggest challenges had nothing to do with numbers or coding. They were about finding basic ecological information.

Despite squamates being one of the most studied groups of vertebrates, details about where many species live – such as whether they thrive in high or low altitudes, or found on rocky or sandy substrates  - were frustratingly scattered. We found ourselves diving into obscure field guides (thank you Google Translate!), deciphering contradicting accounts, and, yes, occasionally procrastinating when the sheer scale of the task became overwhelming. Because, let’s be honest, when faced with thousands of missing data points, it is all too tempting to virtually travel around the world examining plates, maps, and explorer histories.

In the end, though, persistence paid off. Our results showed that habitat openness is a strong predictor of brightness - squamates in open environments tend to be significantly brighter than their forest-dwelling counterparts. Even more fascinating, we found that shifts in brightness over evolutionary time associates with past climatic fluctuations, suggesting that as Earth's ecosystems changed, so did the selective responses shaping non-avian reptile coloration. While the other examined ecological and environmental factors also influenced brightness, none showed as strong or consistent effect as habitat openness. This suggests that exposure to direct sunlight and the need for thermoregulation have been primary forces in shaping color evolution in squamates over millions of years.

The Bigger Picture

Our results suggest that brightness variation in squamates is associated with habitat openness and its underlying selective forces. At the same time, they highlight the complexity of color evolution, revealing the trade-offs and interactions between multiple ecological and evolutionary pressures across different phylogenetic levels. This underscores the importance of examining trait evolution at different taxonomic scales to fully grasp the mechanisms shaping biodiversity.

By leveraging the dataset presented in our study, future research can gain deeper insights into how species may respond to changing environmental conditions. This knowledge has the potential to inform conservation strategies and improve predictions about species' responses to future climate scenarios, ultimately enhancing our understanding of biodiversity dynamics in an ever-changing world.

What started as a simple question - how does the environment shape color? - turned into a deep-time evolutionary story spanning millions of years. And like stepping out of the shade and into the open sun, this research sheds new light on how animals respond to the world around them.

References

Goldenberg, J., D’Alba, L., Bisschop, K., Vanthournout, B., & Shawkey, M. D. (2021). Substrate thermal properties influence ventral brightness evolution in ectotherms. Communications biology, 4(1), 26. https://doi.org/10.1111/oik.09152

Goldenberg, J., Bisschop, K., D'Alba, L., & Shawkey, M. D. (2022). The link between body size, colouration and thermoregulation and their integration into ecogeographical rules: a critical appraisal in light of climate change. Oikos, 2022(6), e09152. https://doi.org/10.1038/s42003-020-01524-w