Why do male peninsular rock agamas have multiple displays?
Amidst the scrub of Rishi Valley, Andhra Pradesh, ecologists spied through their binoculars, murmured on voice recorders, and marked the locations of those they watched using a GPS. Why did they act like secret agents? Well, they were busy observing peninsular rock agamas. But what for? Let’s find out.
A multifarious puzzle
Peninsular rock agamas are found on large rocks in parts of peninsular India. Males are about as long as a big shoe and can be brightly coloured during the mating season. They communicate with other males and females using various body movements, such as head bobs and push-ups (please refer to the pictures). Interestingly, they even change their body colour (from pale yellow to bright yellow and even bright orange) within seconds to communicate!
A male communicating using head movements called 'head bobs'!
A male showing off by performing 'push-ups'!
Males can change colours within seconds!
Here, colour on the side changes from red to jet black and that on the top changes from yellow to bright orange (Duration of the original video is approx. 5 mins)
However, such displays and signals can be costly. For example, it’s easier for predators to spot brightly coloured and moving prey, and a conspicuous signal can take up precious energy. When there are more signals, there are probably more costs. So why do these males communicate with so many signals?
This is exactly what Dr. Shreekant Deodhar and Prof. Kavita Isvaran from CES (IISc, Bangalore) wanted to find out. On reviewing the literature, the researchers put forward two possible reasons as to why males might use a variety of signals to communicate. First, they speculated that males may have multiple signals to send different messages to different receivers. That is, they might communicate with other females (potential mates), other males (potential competitors), and predators using different signals. Second, they speculated that many signals together might convey a message more strongly to the same audience by reinforcing it.
Detectives in the field
To understand why these lizards have so many phenomenal signals, the researchers selected a suitable, relatively undisturbed site in the Eastern Ghats of India (in Andhra Pradesh). At the beginning of the breeding season (May 2013), wild males were caught, and four coloured beads of different combinations were attached to their tails to help identify each individual. The lizards were released where they were caught within 15 minutes. Over the next few months (until September), the researchers spent long hours regularly monitoring the identified males using a carefully designed protocol. They watched the males through binoculars and recorded their behaviours by taking notes on voice recorders. Crucially, they took note of how many females or other males were around the male they were observing, and whether there were any predators.
A male tagged with different coloured beads for individual identification
Many hued findings
Careful analysis of many hours of data helped the researchers solve the puzzle of why males have multiple displays. The researchers found that males change their colour to bright orange/crimson on the back and jet black on the sides in the presence of females! In female company, they also increase their use of body movement signals (like push-ups and head bobs). This is probably to show off their abilities to females to be chosen as mates. This strongly suggests that male agamas use multiple signals to better convey the same message to one audience by reinforcing it.
Males turn bright orange in the presence of females!
Interestingly, many of the signals directed at females are reduced in the company of predators. As mentioned earlier, being conspicuous comes at the cost of being eaten, which is why males aren’t bright orange around predators!
They aren’t bright orange around other males either. In male company, they change colour to yellow on the back and red on the sides. Since this signal isn’t directed at females, it shows limited support that males also use multiple signals to convey different messages to different recipients!
Males turn yellow on the back and red on the sides when there are males around!
But since most signals are directed at females, what is the relationship between those signals and how many descendants a male has? It turns out that males which signalled the most to females had more females in their territory, and were around for longer. This means that males who signal more are likely to get more opportunities to mate and thus have more descendants than males which signal less!
In conclusion, multiple signals are advantageous to male peninsular rock agamas. They improve their chances of attracting females, and they allow them to communicate with other males as well. Consequently, the significance of this study is that some animals can afford to use multiple signals despite the costs; the benefit of having more descendants is large enough. Furthermore, the phenomenon of multiple signals isn’t limited to peninsular rock agamas alone but can be found among a large number of animals across the animal kingdom. This study illustrates the biological roles of multiple signals, in general, may play.
But by no means is this the final word on male agama signalling. Soon we’ll share another article which zooms in on colour in particular - so stay tuned!
Deodhar, Shreekant, and Kavita Isvaran. "Why do males use multiple signals? Insights from measuring wild male behaviour over lifespans." Frontiers in Ecology and Evolution 6 (2018): 75. Link to the original paper: https://www.frontiersin.org/articles/10.3389/fevo.2018.00075/full
The article is written primarily by Prahlad Saldhana