Research plan for the Panther
Chameleon Furcifer pardalis
in
Background
The panther chameleon Furcifer
pardalis is one of the more spectacular natural treasures that one is likely
to encounter while touring the agricultural countryside and villages of coastal
northern
Over the past few decades much has been learned about their natural history. Adult panther chameleons breed during the warm, rainy, summer months, females producing from one to several clutches of one- to two-dozen eggs buried deep in the ground. After a long (up to a year) incubation period the hatchlings emerge, grow rapidly and mature at as early an age as 6 months, although males may take up to a year to reach full size. While males can exceed five years of age in captivity, most wild panther chameleons probably survive only one or two years after maturity. They feed mostly on terrestrial invertebrates but have been observed to eat small vertebrates, including juveniles of their own species, and, rarely, plant material. On sunny days they behaviorally adjust their body temperature to about 30 degrees C, but on overcast days they carry out their activities with a body temperature that closely matches that of their surroundings. During the breeding season males are strongly territorial and will threaten an intruding male with open-mouth posturing, color change (in some populations) and chase followed by attack, if necessary. Staging an encounter makes for spectacular photo-opportunities for eco-tourists, but one must take care not to allow combat which can result in severe injury or death to the combatants. Using a mirror to simulate intrusion and elicit display sometimes works just as effectively.
While panther chameleons are hardy captives, they were initially difficult to breed successfully in captivity due to poor ultraviolet light environments for females. Ultraviolet (UV) light from the sun is known to produce vitamin D in the skin of many vertebrates including ourselves and panther chameleons. UV-induced vitamin D serves as a hormone in the body to help regulate calcium-phosphorus balance in the body. Its chief function is to stimulate the uptake of calcium from the gut and inhibit calcium reabsorption from bone. In short without adequate vitamin D from either UV exposure or dietary intake females cannot provide enough vitamin D to their eggs to enable the developing embryos to form their skeletons. Their eggs fail to hatch.
An important discovery made in the last few years was that females seem to be able to sense their internal vitamin D-condition, perceive an external UV source and voluntarily expose themselves to that source when they are vitamin D deficient. Alternatively, they choose to avoid high UV sources when they are vitamin D sufficient. In short they seem able to “photo-regulate” their vitamin D condition much like many lizards thermoregulate their body temperature by shuttling between heat sources and heat sinks in their environment. Prior to our studies no vertebrate had been shown to possess this “vitamin D-UV photo-regulation” ability. Certainly we don’t! Our most recent research has shown that other lizard species besides the panther chameleon may possess this same ability, so it may be an adaptive mechanism for lizards in general.
All of the research on panther chameleons leading to the discovery outlined above has been conducted in the laboratory. There are missing pieces of information regarding the UV environment of panther chameleons in nature that can be rapidly filled in a few days by an eco-tour group and will increase our understanding of this phenomenon. We know that the UV requirement of reproducing adult females and juveniles is greater than that of adult males in captivity. Are the UV environments of adult breeding females and juveniles higher than those of adult males in nature? We know what the optimum dose of UV is for breeding females in captivity to ensure good hatching success. Because females in captivity seem willing and able to expose themselves to the amount of UV necessary, we need to see if UV exposures in the field are similar to those predicted from our laboratory studies. Something that we have not learned either in captivity or in nature is how females balance their need for UV exposure with their need for thermal exposure. The sun produces both heat (infrared radiation or IR) and UV. In open habitats these two irradiances are highly correlated, i.e., bright sunny spots are high in all light irradiances, including IR and UV. However in filtered sunlight IR and UV radiation become somewhat dissociated. Must females and juveniles with their higher UV requirements tolerate higher body temperatures than adult males or can they dissociate these to the extent that they can obtain higher UV exposure but maintain the same body temperature? With some simple observations and measurements in the field we can answer these questions.
Procedures
Our objectives will be to search the vegetation for chameleons between the hours of 0800 and 1400. While our focus will be panther chameleons, data for any species will be valuable. For every animal encountered we will record the following data in the following sequence:
2. subjective assessment of sun exposure when spotted (full sun, partial sun, shade). Noticeably darkened coloration of the animal should be recorded.
3. time and cloud-cover conditions when spotted (sunny, filtered sun, overcast)
4. activity when spotted (sitting, moving, feeding, courting, displaying to same-sex individual etc.)
5. flank temperature (both sides of animal ) taken using a remote-sensing laser temperature gun.
6. UVB exposure where first spotted using Solartech 6.2 UVB meter (three readings- vertical, horizontal, pointing toward sun)
7. visible light exposure where first spotted using light meter (same three readings as for UVB)
*** steps 1-7 should be completed in less than 3 minutes, if possible***
8. at this point animal can be photographed, observed manipulated (e.g. fed, shown mirror etc.)
9. SVL, mass, cloacal temperature. Animal will be captured, measured with a meter stick or ruler and weighed with a Pesola spring scale. Cloacal temperature will be taken with a Miller-Weber quick-reading thermometer but only if step 8 is minimized and/ or there is no reason to think that the animal has substantially changed its thermal environment.
10. animal will be released at site of capture.
11. after a brief training period, at least two crews working independently will be formed and work simultaneously.