Reptiles are nature’s mappers

“Can you see it?” I asked my fellow researcher one evening in the summer of 2022. “Not yet,” the researcher replied, “but I am sure it is hiding somewhere inside. There is no way for it to escape.” The two of us, along with three other researchers, were looking for Dritto, a male garden lizard (Calotes versicolor) that had escaped from our experimental plot at the campus of the Gandhi Krishi Vigyana Kendra in Bengaluru. I was certain that the lizard had escaped from the fenced plot. For the last five days, the lizard had been frequenting one area of the plot. We suspected that it had found a way out through here. Dritto eventually returned to the plot, but five days later, it escaped again.

This time, we confirmed its escape route. This indicated that in the three months since it was under observation, the lizard had gained a spatial understanding of the plot. Dritto was one of the nine garden lizards my team and I had been studying as part of a project with The Rufford Foundation, UK, to understand how the spatial learning abilities of reptiles help them forage for food. The fenced plot, a 2 m by 2 m vegetable cropland, was divided into patches with different pest infestations. We explored whether the lizards would be able to identify patches based on the location of pests. The results showed that reptiles indeed had the ability to choose a “better” foraging patch and remember it.

The cognitive and spatial learning abilities of reptiles are often underestimated. Charles Darwin noted that reptiles and many such “lower creatures” (those with primitive characteristics as compared with humans or other advanced animals) do possess intelligence and cognition, though these are less sophisticated. However, in recent years, scientists have found that even though reptiles and humans have evolved separately, they share certain neuron types. This means that reptiles have their fair share of intelligence.

Higher cognitive abilities, including spatial memory, are important to an animal for a variety of ecologically relevant behaviours like mating, foraging and establishing territory. How animals identify and remember the spatial location, however, is still to be understood. So far, research shows that reptiles use landscape components to form a map. For example, while moving around in a field, a tree could be a landmark with respect to which they remember a location. In cognitive science, these cues are called “beacons”. The importance of using a beacon in reptiles was confirmed by researchers from Spain in 2001. In a study published in Animal Cognition, they showed how removing a “beacon” (a red panel) disoriented pond slider turtles (Pseudemys scripta) and deviated them from reaching an end point in a maze. Another group of researchers from Macquarie University, Sydney, conducted a series of trials with eastern water skinks (Eulamprus quoyii). They found that the reptiles were able to recognise and remember a “safe refuge” when threatened and made fewer mistakes in reaching it over time. The results are published in 2014 in Proceedings of the Royal Society B: Biological Sciences.

Reptiles could also be using egocentric cues, such as the left or right side of a path, or allocentric cues like spatial relationships between the goal and the cue. If explained in human terms, these cues would be similar to the direction, “10 metres to the right of the light post.” Research also proves that reptiles follow chemical cues through the vomeronasal organ to select habitats, prey as well as mates. But even in the absence of these cues, they can effectively use landscape components to attach memory to and recollect spaces.

Potential implications

During our research in Bengaluru, we observed that not only did Dritto and other lizards choose the “richer” foraging grounds, but they also allocated more time here. This indicates several opportunities for humans, particularly in terms of managing crop pests. According to the UN Food and Agricultural Organization, the world loses 20-40 per cent of crop yields to pests, incurring a global economic loss of US $290 billion. The conventional strategy to protect crops is pesticide application, however, it poses known risks to ecosystem health, crop quality, farmland biodiversity and human health. Some pests are also known to develop resistance to pesticides after repeated exposure. Biological pest regulation, in which farmers use the natural biodiversity to control pests, is a less costly but more effective strategy for crop protection.

A 2023 review I co-authored with researchers from Ashoka Trust for Research in Ecology and the Environment, Bengaluru and the University of Lincoln, UK, highlights the potential of harnessing natural cognitive abilities in improving biological pest regulation. Several reptile species are already known to be influenced colour, odour and taste. The review suggests that these preferences and learnings be manipulated to encourage the pest predators to target infested croplands, thereby controlling the crop pests. The spatial learning ability of reptiles can also be considered for similar experiments.

Utilising the cognitive abilities of reptiles to improve their pest regulatory role would mean a decrease in dependence on chemicals and eventually improve biodiversity in farmlands. It’s time to recognise the real potential of reptiles.

Deyatima Ghosh is post-doctoral researcher at Nanjing Forestry University, China and visiting researcher at University of Lincoln, UK

This was first published in the 1-15 July 2024 print edition of Down To Earth