“Most people are afraid of them. Why would you want to look at something that’s scaly and has something crawling on it?” Levi Storks, an assistant professor at the University of Detroit, laughs when asked. But that’s what got him interested in lizards as a child. He would catch them, pet them and watch them for hours.
Now, as an evolutionary biologist, Dr. Storks studies reptiles like lizards To fill the research gap: We don’t have a complete picture of how animal brains and behavior are connected.
Traditionally, complex behaviour has been linked to brain size and brain-to-body size ratios. But researchers have discovered new information that further complicates this picture. For example, by analysing the brains of closely related lizard species from the lush biodiversity of Puerto Rico, Dr. Storks and his team found hints of a relationship between diverse habitats and brain complexity.
one of Recently Published Papers In the journal Biology Letters“Cognitive demands are likely to be greater in more complex habitats, as an animal must coordinate movement along a larger number of possible paths,” the researchers write.
Similar lizards, different habitats
Lizards are a broad group of reptiles that includes many species with diverse characteristics. Anoles are a distinctive genus of lizards known for their distinctive features, including the ability to change skin color, a hanging fan around the neck, and adhesive toe pads for climbing vertical surfaces. Anoles are common in the Americas, especially in tropical and subtropical regions.
Puerto Rico is an island in the Caribbean Sea. Its forests are a mix of diverse ecosystems, including tropical rainforests and dry forests like El Yunque (mountainous cloud forest). The island is home to unique flora and fauna, including endangered species, and is very biodiverse.
Both in 2019 and 2021, it was the summer season when Dr. Storks and members of his team traveled to Puerto Rico to collect samples.“There were lizards literally everywhere,” he recalls. “That’s one of the reasons people come here to study anoles,” in their rich natural environment.
The team collected 64 anoles belonging to six species, but they belonged to the same ecomorph class. That is, although these anoles belonged to different species, they played the same ecological role and thus shared many physical traits. The genetic data also showed that these species had a common ancestor 20-30 million years ago – this is not a very long time in evolutionary history.
The relationship between anoles is significant. When studying brains and behavior, between members of otherwise unrelated species, it’s hard to know which cause caused which effect. But “anoles are very close in terms of many things. That means that when their brains are compared, a lot of things are similar except for the habitat part. And so we can be pretty certain that habitat is doing something,” Dr. Storks said.
The team collected anoles of the following species: Anolis evermanni, Anolis stratulus, Anolis cristatellus, anolis gundlachii, Anolis krugiAnd Anolis pulchellus,
from one 2014 study In a study conducted by other researchers, the team had data about how complex the anoles’ habitat was. Those scientists followed more than 80 anoles of six species for at least 20 minutes and recorded (in pictures) how their movements responded to features around them. They paid attention to how many options the anoles had and which options they preferred. For example, they looked at how many branches the anoles could reach, what obstacles were in the way, and how much distance they had to travel.
Based on the anoles’ habitat and behaviour, the team divided the six species into three groups: ‘grass bush’, ‘trunk ground’, and ‘trunk crown’.
Dr. Storks said a lizard living on tree trunks moves in a way that’s similar to a country road. It can just go up and down, side to side. But lizards living on tree trunks have to move even on small branches, a challenge that’s akin to the stress of living in a city. They have to figure out how best to negotiate a network of options to get to their destination.
Thus, different habitats generate different levels of complexity.
Neurons in complex habitats
When the team airlifted the lizards from Puerto Rico to their labs at the University of Detroit, team members dissected their brains to analyze differences in their neural structure.
The way the brain processes information depends on many factors, including neuron number, neural plasticity, signal processing speed, synapse density, and the diversity of cell types. But recently researchers have preferred to analyze neuron density because it appears to be a good indicator of the brain’s processing capacity.
The team examined neuron numbers in three regions of the anoles’ brain: the telencephalon, the cerebellum, and the rest of the brain.
Each of these parts contributes to the complex functions of the brain, from basic survival to complex thought processes. Specifically, the telencephalon is involved in sensory integration and higher cognition; the cerebellum is responsible for motor coordination and learning; and the rest handles sensory input and motor output.
The study found that the number of neurons increased with habitat complexity in the telencephalon and the rest of the brain, except for the cerebellum, across the six species. Anoles living in more complex habitats, including the canopy of trees, had a higher density of neurons than anoles living between tree trunks and grasses and shrubs.
The findings suggest that differences in the neuroanatomy of Puerto Rican anoles, which have similar social structures, diets and sensory systems, may be a result of differences in their habitat.
Similar studies have also been carried out on other vertebrates such as Aegean wall lizards, three-spined sticklebacks and others. Zebrafish It has also been found that individuals living in more complex habitats perform better in spatial learning tasks. Other studies have reported similar findings at the level of neuroanatomy and cognition.
The role of the brain in development
Some? 320 million years agoReptiles, mammals, and birds had a common ancestor. During evolution, organisms evolved from that common ancestor that were very different from one another in appearance, behavior, and functioning.
“We have all these animals that evolved from the same kind of brain. It’s crazy to think that we now have all these animals whose brains are very similar, but also slightly different,” says Dr. Storks. “It’s a really powerful organ that’s constantly changing.”
Many studies have discussed the brain, especially the human brain, but not much research has been done to learn how the brain has evolved over time or how differently the brain functions in different species.
“These differences are really interesting, especially when you’re thinking about evolution,” Dr. Storks said.
Monika Mondal is a freelance science and environment journalist.
Published – September 05, 2024 05:30 AM IST