Our most recent paper, co-author with Leo Fleishman, and recently published on Functional Ecology “Whydo Anolis lizard dewlaps glow? An analysis of a translucent visual signal” is a prime example of this approach, in which detailed observations of an organism's general ecology are examined within a theoretical framework to yield novel hypotheses: what I called Experimental Natural History.
In the case of this paper the observation happened a long time. So long, that at the time I was a graduate student finishing my work and getting ready to move to Leo’s lab. I was in Cuba collecting data on the ecology of anoles, particularly the community of anoles at Soroa. While at Soroa, I filmed the display of a few species of anoles, including A. homolechis. Anolis homolechis is found in partially shaded forest and has a white dewlap. As shown by the video, the dewlap of A. homolechis appears to “glow.” This effect is so dramatic that the dewlap stands out against the background, giving the impression that it is a light source.
Video of a male Anolis homolechis
When I showed the above video to Leo, he was so impressed that he suggested that we should evaluate the possibility of “fluorescence”, that is, the short wavelengths striking the dewlap were being absorbed and re-emitted as longer wavelengths, thus giving it the perception of a “light bulb”. To make a long story short, that was not the case, and in the process of testing this idea I learned that although lasers are commonly described as monochromatic they are not. In the majority of the cases laser also emit a longer wave peak.
This was the end of the potential “fluorescence” effect, but not the end of our quest to understand the mechanism by which dewlaps are able to appear so bright, and if those mechanisms have potential consequences in the ability of the receiver to detect the signal. We conducted a second experiment, showing that light geometry highly contribute to this effect. Below is an illustration of our gadget to test this effect. Basically we simulate the "sun" striking the dewlap from different angles and measured, from the front of the dewlap (reflection) and back of the dewlap (transmission) and measured the radiance spectrum of the dewlap A pdf of the paper entitled "Illumination geometry, detector position and objective determination of animal signal colours in natural light" can be found here. As a side note, this paper is somewhat technical, yet is packed with ideas and a must read for those interested in visual ecology.
|Schematic of our gadget to evaluate the effect of light geometry |
on dewlap reflectance and transmission
|Male Anolis lineatopus from Jamaica. Note how the dewlap coloration is dominated by light striking the dewlap from the back, that is, the dewlap is scattering the light rays in all directions to appear "translucent"|
|Two of the panels of figure 4|
As a naturalist I hope this paper illustrates the value of natural history. Moreover, it give you a taste of what I called “Experimental Natural History” when observations of an organism's ecology are examined within a theoretical framework, usually by integrating multiple fields, to yield novel hypotheses. If lucky, those novel hypotheses can open new areas for further studies. In this case, transmission is not limited to dewlaps, other signal structures such as fish fin, insect wings, and feathers are also capable of transmitting light. How important is transmission for the efficacy of those signals remains an open question waiting to be tested.