A collaborative study from the Indian Institute of Science, Bangalore, and other institutes, found that agamid lizards display rapid colour change in different contexts, including thermoregulation, communication, and stress. The massive range of colours in these species opens up new questions on the whys, hows, and whens of this colour change.
In a world painted with a stunning palette of colours, nature’s creatures showcase a mesmerising array of hues that never fail to captivate our senses. From the iridescence of a peacock’s feathers to the vibrant tones of a Siamese fighter fish’s fins, the animal kingdom’s diversity of colours knows no bounds. Among this kaleidoscope of hues, some creatures possess an extraordinary talent: the ability to change the colour of their body parts.
Chameleons, the renowned masters of colour change, have long fascinated scientists and enthusiasts alike with their remarkable skill. However, hidden within the vast Asian landscape, another group of creatures possesses this awe-inspiring ability – the agamid lizards, a highly diverse family of lizards in India.
In this recent study led by Maria Thaker, Associate Professor, Indian Institute of Science, Bangalore, the authors found that although male and female agamid lizards show stark differences in colours, with the males displaying more colours, the extent of rapid colour change in male agamids is unrelated to overall sexual dichromatism – the difference in colouration between sexes.
Across the animal kingdom, it is typical to have colourful males and less vibrant females. This allows males to manifest a body of a competent fighter, looking desirable to females, while females, with their dull looks, can remain unnoticeable to predators. Animals can also change colours to control their body temperature, communicate, catch prey, or evade predators. This dynamic change in colour occurs within seconds to minutes.
In this study, the researchers used six species of agamid lizards, grouping them into three closely related pairs. Although the researchers provided the lizards with different temperatures, stresses, and other cues to mimic the actual scenario in the lab and tried to record the dynamic colour changes they observed, they found it challenging to get them to reveal all the colours they displayed in the wild. “It’s genuinely hard to get a lizard to court in the lab!” chuckled Thaker.
To understand the connection between sexual dichromatism and colour change, the researchers evaluated the colour volume occupied by males and females of each species in a lizard-vision colour space. This allowed them to estimate the degree of sexual dichromatism based on the non-overlapping colour volumes between males and females.
While it was anticipated that species with high levels of sexual dichromatism would exhibit greater individual colour change, the findings did not align with this hypothesis. The extent of colour change in males varied between species and among different body regions within a species.
Anuradha Batabyal, Assistant Professor, FLAME University, Pune, who is also the first and corresponding author of the study, believes that agamids have been overlooked for research on colour change. This study provides a platform to look at this colour change from different angles, Batabyal elaborated,
Behavioural ecologists can study what kinds of behaviour leads to this colour change, then you can have a molecular biology perspective on how these colours are produced, and how fast this change happens, which genes are controlling this [trait], how is this developed, and also these big evolutionary questions like, why such colouration, what kind of selection pressures are acting, or when have these colours evolved in the lineage of lizards.
Divya Uma, Assistant Professor, Azim Premji University, Bangalore, who studies colour change in spiders, and is not associated with the study, said, “The number of agamids tested in the paper is rather less, but quantifying dynamic colour change is very difficult, as colour change happens within seconds. Also, carrying out these experiments under field conditions is quite a challenging task”. As the colours in agamids are produced by both pigments and structural colours, she thinks it would be interesting to check how they contribute to colour change in each context. Furthermore, her interests lie primarily in discovering “Whether these lizards get habituated and show less colour change if the social context (stress, predator, etc.) persist for longer periods.”
Acknowledging the smaller sample sizes for this study, Thaker mentioned,“It was a way to start thinking about a hypothesis, and not the final or definite answer.” This exploratory study has intrigued her group to continue the work with more lizards to develop an evolutionary map of the extent of colour change in agamids across different contexts.