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Brains and Brawn: Dominant lizards are better learners!

By Fonti Kar

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 whether dominant and subordinate eastern water skinks differ in their ability to learn from one and other (social learning). Previous work has shown in this species that young skinks tend to learn from older skinks, but age and dominance status and body size are inherently confounded. In other words, the age-dependent pattern may actually reflect a dominance effect, whereby young and therefore subordinate skinks tend to learn from older, dominant lizards.

In order to disassociate these confounding factors, we matched skinks closely in size and therefore age and allowed them to fight to determine their dominance statuses (Fig. 1). Winners of this fight was considered ‘dominant’, while the loser was considered ‘subordinate’. We then divided our skink pairs into two treatment groups, a ‘control’ group, where a skink watched their status counterparts do nothing and a ‘social learning’ group, where a skink was able to watch their status counterpart solve a foraging task e.g. a subordinate skink was able to watch a dominant skink, while a dominant skink was able to watch a subordinate skink (Fig. 2).

Control and social learning group set up. The control group watched their status counterparts do nothing. While the social learning group watched their status counterparts solve a task before receiving the task themselves

We gave the lizards two foraging tasks. In the first task, the lizards had to learn from their status counterparts how to learn to flip a blue lid to access a worm and ignore a white lid (association task). In the second task, the lizards had to unlearn the blue lid-worm association and learn to flip the white lid for the worm (reversal task). We then recorded how many trials it took for skinks to learn these tasks.

In the association task, skinks had to learn to flip the blue lid to access food. They then had to unlearn this association in the reversal task and learn to flip the white lid. See video below!

 

To our surprise, lizards did not seem to learn from the other lizard but instead relied on their own trial-and-error learning abilities. This was consistent for both dominant and subordinate lizards. We also found that dominant lizards learnt faster compared to subordinate lizards.

These results tell us a few neat things about social learning in the eastern water skink. Firstly, skinks were closely matched in size but they didn’t seem to learn from watching another skink. This seems to suggest that skinks may not want to learn from an individual of similar age and actually this may actually impede learning. Secondly, dominant individuals learnt faster compared to subordinate skinks implies that dominant skinks may be less prone to the stress associated with learning in the presence of another skink or they may indeed have both brains and brawn.

For more information, check out the paper published in Animal Cognition here

Meta-analysis on reptile developmental plasticity

It’s been many years in the making with Lisa Schwanz and Vaughn Stenhouse, but finally our utterly massive meta-analysis on the role of incubation temperatures on phenotypic variability and survival is finally out in Biological Reviews! We collated effect sizes from 92 different species across all major reptile orders taken from 175 different studies that manipulated incubation temperatures! Extracting all these data was no small task, but has lead to some important insights that have implications for our understanding of how climate change will affect reptiles and the role of early thermal environments more generally on developmental plasticity in reptiles.

There are lots of new stuff in the paper but a pretty graph (only one so as not to spoil anything) and the major conclusions are summarised below!

(1) The magnitude of the phenotypic effect of incubation temperature is moderate to large across orders, trait categories and ages. There is no evidence that this effect is substantially larger in any single order of reptiles, although data are sparse for Rhynchocephalia (a species-poor order) and Crocodilia.

(2) Effects of incubation temperature can persist for many months post-hatching. Sampling is poor for ages >1 year, thus more data would be useful in increasing our confidence in the persistence of effects.

(3) The effect of temperature on incubation duration is much stronger than on any other trait category. Survival also stands out with particularly strong effect sizes, while the relative strength of other trait categories varies in ways that compels more detailed comparison of reaction norms.

(4) Temperature fluctuations in the incubation environment potentially decrease the phenotypic effect of different mean temperatures, particularly when the temperature differences between treatments are large (although not significantly). More data are needed from fluctuating temperature regimes to assess more rigorously whether this tendency is real, and to quantify the impact of increasing fluctuation.

(5) On average, increased temperature changes lead to greater phenotypic effects. Despite expectations that the exact impact of warming incubation temperatures will depend on the trait studied and the shape of the reaction norm, we can say that, on average, nest temperatures that increase by 4°C would have a greater impact on nearly all phenotypes than would an increase of 2°C.

(6) The effect of increased incubation temperature depends on the temperatures experienced (mid-temperature), and this dependence varies according to trait type. Survival, morphology and performance were affected more strongly at extreme temperatures compared to intermediate temperatures indicating that increasingly warmer nest temperatures will accelerate change in these traits. Thus, collecting phenotypic data from extreme incubation temperatures is important.

Figure 1 – An example of how the average temperatures of pairwise treatments and their temperature difference impact the magnitude of effect for incubation duration.

(7) Substantial variation in the magnitude and direction of the phenotypic effects of incubation temperature remain unexplained. Future research should quantify the shape of the reaction norm to explore interspecific variation along with how parental and/or ecological effects might mediate responses.

If you want to find out more have a read of the paper!

 

Skinks and Ladders: A family-living lizard’s learning ability is not affected by their home environment

by Julia Riley

tree-skink_mom-and-juveniles

We have found that the learning ability of the Tree Skink, a lizard that lives with family, is not linked to growing up with others. These lizards were able to learn to navigate a complex spatial maze whether they lived by themselves or with a ‘roomate’.

 This result was surprising because previous studies have shown that for social animals, like humans, rats, rhesus macaques, and chickens, being removed from social contact during development, negatively affects how they grow up. Individuals raised alone are more fearful, anxious, more sedentary, less social, and have a harder time learning. Yet, no one has studied how being raised away from from the social group affects growth in other, less-obvious, social animals – like reptiles.

 Australian Tree Skinks (Egernia striolata) are a common lizard found throughout southeastern Australia. In the wild, these lizards are often found in family groups – most often parent(s) and offspring are found together. However, each lizard varies in how social they like to be – there are loners, lizards that tend to spend most of their time alone, and social butterflies, lizards that are always found with other lizards. Their variable social nature make the Australian Tree Skink a desirable species to study how a social environment can affect their behaviour during development.

 Myself and my PhD supervisor, Martin Whiting, from Macquarie University’s Department of Biological Sciences teamed up with Dan Noble from the University of New South Wales in Sydney and Richard Byrne from the University of St. Andrews in Scotland to conduct these first examinations of how social environment can affect lizard learning ability.

 We raised Tree Skinks alone, or paired with another juvenile from just after birth until they were about a year in age. Then we presented each lizard with a complex spatial maze – each lizard had to navigate a set of five ladders and three ledges to access a food reward. Only 2 of the 5 ladders were climbable, and we measured how long it took each lizard to learn the correct path.

Our study’s findings, published in Animal Cognition, were unexpected! Unlike social mammals and birds, we found no evidence that the social environment they were raised in affected their learning ability – almost the exact same number of skinks from each treatment learnt this complex task!

 We think there are key reasons for this unexpected result, Tree Skinks naturally vary in their individual sociability, so growing up alone may be a normal option in the wild and is less stressful for them. Alternatively, the presence of a parent while growing up (which we did not measure) may be what affects development of tree skink learning ability.

 Article reference: Riley, JL., Noble, DWA., Byrne, RW., Whiting, MJ. 2016. Does social environment influence learning ability in a family-living lizard? Animal cognition. (doi:10.1007/s10071-016-1068-0)