Snake and lizard brain evolution unveils multiple links between brain complexity and locomotion

What is it about?

Traditionally, studies assessing the impact of specific animal behaviors on brain organization have mainly focused on volumetric and linear measurements of brain regions. We hypothesized that a crucial trait, deeply influencing an organism life, like locomotion (fundamental for foraging, escaping predators, etc.) could potentially trigger variations at multiple and deeper levels of brain biological organization, ranging from morphology to cell distribution and gene activation patterns. We adopted a multidisciplinary approach and exploited the extraordinary diversity and the wide array of locomotor strategies squamate reptiles (lizards and snakes) exhibit. Our results highlighted a strong locomotor signature in the cerebellum, a brain subdivision deeply involved in motor control, motor learning and online motor correction. The shape, cellular distribution of cortical neurons and gene activation profile of this brain subdivision all correlated with locomotor behavior independently of the evolutionary relationship occurring between the species analyzed. Our study demonstrates, for the first time, the existence of specific brain patterns, involving multiple neuroanatomical features, in vertebrates adopting similar lifestyles.

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Photo by Felix Serre on Unsplash

Photo by Felix Serre on Unsplash

Why is it important?

We highlighted that animals with similar behavior share specific types of brain. Our study suggests that locomotion is evolutionarily correlated with key changes in cerebellar structure, in addition to morphological changes expected in structures such as limb and skeleton. Importantly, these findings show that brain subdivisions in snakes and lizards are not uniform structures but rather evolved independently, thus supporting a mosaic model of brain evolution. Altogether, our work provides a framework for the evolution of cerebellum and locomotor strategies in vertebrates (fish, amphibians, reptiles, birds and mammals) and highlights how future comparative vertebrate studies of organ system-ecology relationships could benefit from adopting a multi-level integrative approach.