Standing’s Day Gecko… Why Not Night?

 

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Standing’s Day Gecko at Lincoln Park Zoo.

The Standing’s Day Gecko, Phelsuma standingi, was named after Herbert F. Standing, a paleontologist, author and medical missionary in Madagascar, as well as after the Dutch Physician Murk van Phelsum. But why has this gecko gained the name Standing’s Day gecko and not Standing’s Night gecko? This gecko, unlike other members of its family Gekkonidae, is a diurnal species. Although active during the day, there have been limited observations of the behavior of these animals in the wild due to their population decline. Phelsuma standingi has the status Vulnerable according to The IUCN Red List of Threatened Species mainly due to over exploitation by the pet trade (which also uses the common name Banded Day Gecko) as well as habit destruction by humans. They appeal to the pet trade with their large size, tolerance of more arid conditions and ability to thrive in less dense vegetation than other species of geckos. In captivity, Standing’s Day Geckos have been known to live up to 15 years or more!

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Photo Taken at Lincoln Park Zoo.

 

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The Standing’s Day Gecko is endemic to a small portion of Southwest Madagascar where its arboreal lifestyle is supplemented with an omnivorous diet, which ranges from fruit and small invertebrates to small lizards. The geckos particularly thrive in dry thorn forests. Living in pairs, the geckos reach sexual maturity after just one year. It has been shown that males are highly territorial against other males. Females are aggressive to other females although less frequently than the male-male interaction.

How can one tell the difference between a male and a female or even a juvenile and an adult? It is all in the coloration and patterns on their skin. All Standing’s Day Geckos have a speckled grey-brown pattern the entire length of their body.  Juveniles can be distinguished by yellow bands on their neck that fade to a lighter color as they continue down their backs. Adults are characterized by bright green or turquoise heads and tails. However, there are many variations in the brightness of the geckos coloration. Adult Standing’s Day Geckos can reach up to 28 cm or 11 in in length!

As a sexually dimorphic species, males can be distinguished by bulges on their abdomen which are hemipenes stored under the skin, a characteristic of the order Squamata. Females are distinguishable by their pronounced chalk sacs on their necks which they use to store calcium. Calcium is critical for the formation of healthy egg shells during reproduction. Fertilization of the eggs is internal through one of the two male hemipenes. As members of the class Reptilia, Phelsuma standingi lay amniotic eggs that hatch after about 2 months.

One unique aspect of gecko anatomy is they lick their eyes! Instead of eyelids, the geckos have a membrane that completely encloses their eye. To keep the eyes moist and clean the geckos extend their tongue and completely coat their eye in saliva. Gross! The gecko’s eyes are also stationary in the eye sockets with a fixed lens that adjusts to different levels of light. Diurnal species of geckos, such as Phelsuma standingi, eyes contain both the rod and cone system, the same that is present in humans. It is proposed that nocturnal geckos evolved from diurnal species which had lost the eye rods. Nocturnal geckos then developed highly modified cone systems to better process low lighting.

A second unique aspect of gecko anatomy is the adhesive abilities of their feet! The Standing’s Day Gecko’s toe pads contain many individual setae, or hair like structures, which are arranged in lamellae, ridge like structures that have spaces between them.

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Close up of a geckos foot showing the setae arranged to form the lamella.

The toe pads attach to surfaces using the properties of Van der Waals’ forces (attractive or repulsive forces between molecules that do not arise from ionic or covalent bonds). Therefore, the geckos do not depend on fluids for adhesion; this allows the Standing’s Day Gecko to climb effectively in its arid habitat. The mechanism for unsticking it’s toes is simple. The geckos curl their toes in breaking the interactions of the toe pads and the surface allowing them to move forward. The toe pads are even self-cleaning every few steps, ensuring proper adhesion. Scientists are very interested in developing a setae and lamella synthetic adhesive to benefit how we assemble computer chips as well as developing micro-surgeries on humans.

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