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Article: Leopard Geckos
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Leopard Geckos
written by Cheong Kar Wai

Introduction

The leopard gecko (Eublepharis macularius) is a member of Eublepharidae, a primitive gecko family that includes the fat tail gecko Hemitheconyx caudicinctus from Africa, the genus Coelonyx from Southwestern USA and the cat gecko Aeluroscalabotes felinus from Southeast Asia. They share similar features that differentiate them from typical geckos. Firstly they lack specialized toe pads as in typical geckos, therefore they cannot climb smooth vertical surfaces such as walls, although they can climb rough surfaces to some extent. Secondly they have movable eyelids which the typical gecko does not have. However, they have one common characteristic of geckos, the ability to break their tails off. This is called autotomy, and is a defense mechanism used when confronted by predators in the wild. The tail is annulated, meaning the sections are segmented and are able to break off at any point along the tail length. Upon breaking, the specialized blood vessels immediately seal up, so very little bleeding is seen. At this time, the gecko will have to eat plenty of food to regain the lost stored energy in the tail. After a few weeks, a new tail will grow back but the shape will be different from that of the original tail (Bartlett and Bartlett, 1999).

Leopard geckos are native to Pakistan and India, where they live in the desert grasslands that resemble the hot and dry conditions of savannahs. During the day they hide in empty burrows dug by rodents and other creatures, and under rocks or bushes, only coming out at night to hunt for prey such as crickets and grasshoppers (Nickerson, 1997-2006). The average length of a fully grown leopard gecko is approximately 7 to 10 inches. The males are bigger than the females and have a heavier built. In addition, they have large femoral pores and hemipenal bulges on their tail bases. Babies are banded without spots. As they grow older, the bands disperse and depending on the type of morph/patterning, the amount of spots will gradually appear until they reach adult stage (Bartlett and Bartlett, 1999).

Vision and hearing

The vision of a leopard gecko is a complex combination of biological components. Basically a leopard gecko eye, like that of other nocturnal reptiles, has a large pupil and cornea. By the help of ciliary and annular muscles, the pupil can contract and expand in respond to different light levels. In addition, geckos share a common trait with other reptiles in that their retinas contain photoreceptors that are able to detect different wavelengths, including that of UV, so allowing them to have a colour vision (Kaplan, 2003).

Hearing in reptiles has been and still in research. Different reptiles show varying degrees of being able to detect sounds and vibrations. Many have a typical tympanic membrane which in geckos, for example, is located deep in the head. The function is simple, when sound reaches the membrane, it causes certain vibrations which are transferred by the interconnecting muscles called stapes which then transfer the vibrations to the inner ear cavity which includes the fluid-filled cochlear duct and then to the sensory clusters which then passes the impulse to the brain along the auditory nerve (Kaplan, 2003).

Body language

Their hunting methods are interesting to observe. The gecko first watches from a distance as the prey crosses its vision. When it has a clear focus on the target, it advances slowly, like a cat, lifting one leg and holding its posture still before carefully stepping forward. At the same time, its tail waves slowly from left to right like a flag (Bartlett and Bartlett, 1999). When it is within reach, excitation from the impulse in the central nervous system produces involuntary movement of the tail muscles, so that the tail vibrates before the gecko lunges forward. It may take only a split second but sometimes it may miss the prey item. Body language plays an important role in breeding behaviour as well. In breeding females, the tail is held high up and moved from side to side to indicate receptiveness in mating. Males display a waggling of only the tail tip as a sign of being interested to mate with the females (Smith, 2004).

Sounds

Vocalization is also an important part of leopard gecko behaviour. A hatchling or juvenile, when threatened will emit a screeching sound, which some owners compare to a boiling kettle which will scare off the potential enemy. Adults, if handled roughly, will make low squeaks, like a door creaking. Clicking, chirping and squeaking sounds are normally made in territory fights (Smith, 2004). However to the observations made by different leopard gecko keepers, these sounds are only made by some, not all, leopard geckos.

Sex determination

Another unique nature of leopard gecko morphology is that the sex is determined by the temperature at which the eggs are kept during the incubation period rather than genetically. This is because certain species of reptiles like the leopard gecko do not have the normal X and Y chromosomes that determine sex in most animals (Crews, 2003). The parameters are as follows:

1.      At temperature ranges of between 28.9 oC and 30.6 oC, both sexes will be produced (Bartlett and Bartlett, 1999).

2.      At temperatures below 28.3oC, high proportion of females to males will be produced (Bartlett and Bartlett, 1999).

3.      At temperatures above 31oC, high proportion of males to females will be produced (Bartlett and Bartlett, 1999).

However, if the eggs are incubated at temperatures above 32 oC, females are again produced. These are called superfemales, because they are large and highly aggressive, and act like males, therefore are unsuitable for future breeding (Crews, 2003).


Leopard geckos as pets

Due to their docile, calm behaviour, leopard geckos are a favourite beginner lizard for those new in keeping reptiles. It is not until the mid 90s that serious breeders from around the world began importing wild specimens from Pakistan and India (Nickerson, 1997-2006) and currently there are more than twelve morphs in the exotic pet market of countries such as the UK, North America, and Canada. The oldest morphs initially appeared around 1994 where high yellow and jungle leopard geckos were produced from wild stock. Selective breeding for size and carefully planned genetics were implemented until in 1997 the first albino geckos came into the market, and several years later saw newer morphs such as blizzards, leucistic, tangerine and their sub morphs, as well as one of the latest 2004 morphs, the Mack Snow. It is very interesting to anticipate a new morph from a batch of hatchlings because they are rare and randomly produced with each clutch.

Due to the sensitive nature of leopard geckos, like other reptiles, one must ensure the gecko does not struggle or placed in an uncomfortable position while being handled. If it does, chances are that the gecko may regard the handler as a threat and may by instinct drop its tail to escape. Hatchling and juvenile leopard geckos are more skittish and do not respond well to handling. While this may seem frustrating to the owner, according to many herpetologists, being fast moving and elusive is Natures way of ensuring survival. In addition, potential predators are viewed as attacking from above, like birds and larger animals therefore, approaching it and grasping it from above will result in an unhappy, wriggling gecko (Bartlett and Bartlett, 1999).

In breeding projects, temperature is also the main cause of other abnormal occurrences that affect leopard gecko development during incubation aside from being a sex determinant. Inappropriate incubation temperatures cause deformities in body structure such as missing or twisted limbs, missing tail segments, runts, kinked tails, and other extreme conditions. Genetic defects may also play a factor, although it is minor and thus sometimes negligible.

However slow it may seem, the rest of the world is already beginning to catch up on keeping these beautiful reptilian masterpieces as living collections and running their own breeding projects. Therefore, in view of the increasing number of potential keepers and breeders it is important for leopard geckos to be understood as much as possible in terms of behaviour and husbandry so they can be truly appreciated and receive proper respect and treatment in captivity.

References

Bartlett, R.D.; Bartlett, P. (1999) Reptile Keepers Guides  Leopard and Fat Tailed Geckos Barrons Publishing, New York, U.S.A.

Crews, D. (2003) Sex determination  Where environment and genetics meet, Evolution and Development; Vol. 5; Iss.1, pg.50 -55.

Kaplan, M. (2003) Reptile Hearing,
http://www.anapsid.org/reptilehearing.html
date accessed: 1/7/06.

Nickerson, C. (1997-2006) Leopard Geckos,
http://members.aol.com/msnick1/leopardgeckos.html
date accessed: 1/7/06.

Smith, P. (2004) Leopard Gecko Behaviour
http://www.thegeckospot.com/leocareindex3.html
date accessed: 30/6/06.

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