What tree skinks know about change: A story in colour and shape

Note from Martin Whiting: This blog posts details a chapter of Birgit Szabo’s PhD recently published in Animal Behaviour and represents an enormous amount of work. Birgit did a 9-month cognition experiment, which could be the longest lizard cognition experiment thus far conducted. (Let us know if it isn’t!) The work is in collaboration with David Tait and Richard Byrne (St. Andrews) and Birgit’s PhD supervisors (Martin Whiting and Dan Noble).

Written by Birgit Szabo

Animals often live in complex environments. They also experience seasonal changes in weather and food availability and changes to their social environment, just to name a few. Reacting appropriately to these changes is crucial to survival. One important skill when facing unpredictable events is behavioural flexibility, the ability to adapt behavior to novel situations. We can look for behavioural flexibility in animals by testing their ability to abandon a previously learned rule.

We presented tree skinks (Egernia striolata), a family-living skink from south-eastern Australia, with a multi-stage visual discrimination task to find out how flexible they are when learning to find food based on colours and shapes.

Figure 1. Tree skink (Egernia striolata) found in arboreal as well as rocky habitats throughout eastern Australia. This species is active during the day and lives in small, stable family groups. Photo by Martin Whiting.

Why did we choose tree skinks? They live in social groups—small family units including an adult pair and their offspring. Social living has many benefits, but can also be challenging. The demands faced from living in a complex social environment can influence the general intelligence of individuals (“social intelligence hypothesis”), making them smarter. We wanted to know if a social life made these lizards better able to cope with change.

In the first stage of our experiment, we presented lizards with a choice between two stimuli: an X and a triangle. The food dish in front of the X provided a food reward, while the dish in front of the triangle did not. After lizards had learned which shape was the rewarded one, we switched the rule. Suddenly the reward was found in front of the triangle. With this simple change, we were able to find out how fast these lizards can stop looking for the food in front to the now wrong X and change their approach to looking for it in front of the triangle. We repeated this simple reversal test two more times with different shapes. Our lizards were able to adjust their choice and learned to respond to the previously unrewarded stimulus in all reversal stages. Contrary to findings from studies of other animals, our skinks did not take longer to learn the reversals compared to the initial acquisition stage.

Figure 2. Lizards were presented with a choice of two cards. Food was available in front of only one stimulus. This lizard is on its way to making a choice.

Figure 3. Schematic setup of the experiment. Two ramps were placed on one end of the tub, 15cm apart, with the water bowl in between and the hide at the starting position on the other side of the tub. Cue cards were fixed to the back of the enclosure on top of each ramp with a food dish directly in front. Lizards were not able to see into the food dishes from the starting position but were able to see the cards from any point in the enclosure.

Starting from the third stage, cue cards included both a shape and a colour (background) dimension. The addition of a second dimension is important because we wanted to know how well lizards pay attention and how they react to a change in dimensional relevance compared to the change in stimulus relevance tested during the reversals. This is called an extra-dimensional shift: Instead of changing to the formerly unrewarded stimulus within the shape dimension, we change to the second previously unimportant colour dimension. This means that lizards have to stop paying attention to the shapes and instead find out which colour is rewarded. Extra-dimensional shifts are considered harder than reversals. Our lizards were able to learn during the extra-dimensional shift. However, unlike humans and non-human primates, they did not take longer compared to the intra-dimensional acquisition. They also did not generalise stimuli into colours and shapes but instead, most likely viewed each cue card as a single stimulus and learned which two were associated with the reward.

Figure 4. Graphical abstract. Order of stimulus presentation during the eight stages of the discrimination learning experiment. Lizards were able to successfully learn in all stages of the experiment.

So what do our results tell us about tree skink behavioural flexibility? First of all, they are definitely flexible to some degree because they performed well in the reversal stages. Unfortunately, our experiment does not tell us how exactly they perceive dimensions and why they learned so fast in the extra-dimensional shift. Our experiment is, however, a first step towards better understanding learning in lizards and how intelligence developed during the course of evolution.

Download the PDF here or e-mail us for one.

Szabo, B., Noble, D. W. A., Byrne, R. W., Tait, D. S., & Whiting, M. J. (2018). Subproblem learning and reversal of a multidimensional visual cue in a lizard: evidence for behavioural flexibility? Animal Behaviour, 144, 17-26. doi: https://doi.org/10.1016/j.anbehav.2018.07.018

Here is the abstract:
Behavioural flexibility, the ability to adjust behaviour to environmental change by adapting existing skills to novel situations, is key to coping with, for example, complex social interactions, seasonal changes in food availability or detecting predators. We tested the tree skink, Egernia striolata, a family-living skink from eastern Australia, in a set-shifting paradigm of eight colour/shape discriminations including reversals, an intradimensional acquisition of a new colour/shape and extradimensional shift from colour to shape (and vice versa). Skinks could learn to discriminate between colour/shape pairs and reverse this
initial stimulusereward association; however, they showed no significant decrease in the probability of making a correct choice in the extradimensional shift suggesting that they did not form an attentional set. Subjects appear to have learnt each stage as a new problem instead of generalizing stimuli into specific dimensions (set formation). In conclusion, tree skinks solved a discrimination reversal by focusing their attention towards visual stimuli and flexibly adjusting their choice behaviour accordingly. These lizards learned to use multidimensional visual stimuli to find a food reward but did not generalize stimuli into dimensions. Furthermore, this study is the first to test for set shifting in a lizard species and
thereby allows us to extend set-shifting theory to a new taxon for comparison with primates, rodents, a bird and a turtle.

Come on a tour of The Lizard Lab

This is a behind-the-scenes video tour of the lab. We will show you our research facilities, some of our study animals, and our lizard enclosures. This video was entirely put together by Cooper Van De Wal. Cooper is a student at Macquarie and volunteers in the lab. He also has his own, highly successful . . . → Read More: Come on a tour of The Lizard Lab

Tree skinks go to school: The complexities of social learning in lizards

By: Fonti Kar & Julia Riley

“Never study an animal that is smarter than you” – Dr Martin Whiting

An adult female tree skink after performing the discrimination task we used to quantify their learning ability – she successfully removed the blue lid from this dish and accessed the food reward . . . → Read More: Tree skinks go to school: The complexities of social learning in lizards

Up for a fight or doing a runner, for a lizard it could be in their genes

Animals often instinctively assess their environment, and display innate behavioural responses. For example, many newly born reptiles and fish know how to respond to predators – knowing when to “fight” and when to “flee” – right after hatching out of their eggs! Innate behavioural responses, especially in times of peril, may be the difference . . . → Read More: Up for a fight or doing a runner, for a lizard it could be in their genes

The Bluetongue interviews

There was some interest in our recent paper on bluetongue lizards (blueys) and why they have this amazing blue tongue, which is actually a UV-blue tongue. (See our previous blog post.)

Here is an interview from ABC news:

Helen Shield interviews Martin Whiting on ABC radio, Hobart (nation wide). 11 June 2018. http://whitinglab.com/wp-content/uploads/2018/06/ABC_radio_11.6.2018-1.mp3

. . . → Read More: The Bluetongue interviews

Why blue tongue? A potential deimatic display has been uncovered in blue-tongue skinks

An enduring question among fans of blue-tongue lizards is why the blue tongue? Why have such an outrageously coloured tongue, given that the vast majority of lizards have a regular old pink tongue? Blueys (bluetongue skinks) are something of an Australian icon. They are part of Australian folklore and most Australians have encountered them . . . → Read More: Why blue tongue? A potential deimatic display has been uncovered in blue-tongue skinks

Dispatches from the field: new adventures with endangered crocodile lizards and oriental garden lizards

It’s been a very busy year, which explains why I am only now writing this blog post from my trip to China earlier this year (May-June). I had the amazing opportunity of seeing one of the world’s most endangered lizards—the crocodile lizard (Shinisaurus crocodilurus), in the wild, and working with one of the largest . . . → Read More: Dispatches from the field: new adventures with endangered crocodile lizards and oriental garden lizards

Turn up the colour: male frogs use bright colours to avoid confusion at the pond

Imagine being a frog during the chaos of the breeding season and navigating the gathering crowds around the pond. How do you know who might be a suitable mate let alone whether they are male or female? One solution is colour. If one sex, typically males, is able to turn on some bright colour . . . → Read More: Turn up the colour: male frogs use bright colours to avoid confusion at the pond

Brains and Brawn: dominant lizards are better learners too!

Note: this blog post is republished from Fonti’s web site

Dominant individuals tend to have greater monopoly over food and mates and therefore have more offspring compared to subordinate individuals. Are these successes attributed to greater cognitive ability? Or are dominant individuals just better at freeloading from their clever subordinate counterparts?

We investigated . . . → Read More: Brains and Brawn: dominant lizards are better learners too!

PhD opportunity – visual ecology of lizards

We are looking for a highly motivated and suitably qualified candidate to conduct a PhD program of research on reptile visual ecology, commencing in 2017.

The successful applicant will be guided to develop a project to investigate the visual performance and ecological adaptations of a range of lizard species with differing life history traits. . . . → Read More: PhD opportunity – visual ecology of lizards