Introduction to Lizard Breeding
Table of Contents
Many lizard fanciers will want to get their lizards to breed. On the one hand, successful breeding is reassurance that you have created optimal living conditions for the animals, for if the conditions are not right, you will certainly be unsuccessful. On the other hand, by raising healthy offspring, you contribute to the conservation of lizards living in the wild.
The Lizard Parent
As a rule you need a breeding pair if you are going to try to breed, but sometimes it can happen that you acquire a pregnant female. Care of this female requires meticulous attention because the capture, transport, and changes of environment and climate are particularly damaging to a pregnant animal; successful egg-laying will only occur under the best possible environmental conditions.
Most lizard-keepers are not acquainted with the phenomenon that can occur in some lizard populations: unisexual reproduction (parthenogenesis); it is considered an exception. Therefore the lizard-keeper must become concerned with distinguishing between male and female.
Determination of Gender
For lizards with distinct dimorphism, that is with visible distinctions between male and female, determining sex by external markings of mature animals is easy. It is more difficult or impossible with the young animals of these species, for instance the Canary Island lizard and Weber's sailing lizard. With the beginning of sexual maturity, the males of some species of lizards grow flaps of skin or combs of varying sizes on their heads, throats, backs, or tails. In other groups the males, always or only during the mating season, are of a noticeably brighter color than the female. Constant and clearly visible marks of difference are the two large scales behind the cloaca of male anoles, the anal or preanal pores of geckos, and the thigh or femoral pores of the agamas, and most iguanid species. Preanal or femoral pores — in some genera both — are mostly present in males but are also observable in the females of some species, although always significantly less noticeable. For definite determination, lizards of about the same size or about the same age should be available for comparison.
Much experience enables a lizard fancier to determine sex from skull proportions and length, breadth, or circumference of the root of the tail. Lizard-keepers who would like to know more about this should learn from an experienced lizard-keeper.
Modes of Determining Gender
With many lizards, sex determination is only possible through the use of a probe. How to hold the probe is difficult to describe and would be a digression in this book. The examination requires a great deal of experience and empathetic concern, so that for the first time you should have the counsel and help of an experienced lizard-keeper. You may contact other lizard fanciers through the various lizard-fanciers organizations.
Prerequisites for Mating
Unfortunately, possession of definitely identified, optimally cared-for males and females does not guarantee successful mating; the stimulation of sexual instinct is the deciding factor. Climate is an important trigger. It plays a great role, especially with the lizards who live in the climatically moderate zones of the northern and southern hemispheres of our earth. As soon as the dark, cold winter months are over, these lizards begin the mating period immediately after leaving winter quarters. In the areas near the equator, the unbearably hot time of the year can induce a resting phase. To make triggering of the sexual drive possible in the terrarium, you must be able to control the climate effectively. Thus it is essential that you know as much as possible about the origins of the lizards and their climate needs.
Many forms of courtship are observable at mating time. Iguanas present their dewlap while nodding their heads. Agamas also nod their heads and “wave” at the same time — that is, they execute a circular horizontal movement with a front leg. Male anoles woo a female with a quick nodding of the head.
The lizards may take almost no nourishment during the courtship period, in spite of their activity, but there is no cause for worry if they have been as well nourished as possible beforehand. Eating will follow later and often at an above-average rate for the female, who should be left along during this period, because the production of eggs demands an above-average supply of energy.
The intromittent sexual organs of male reptiles are concealed in the external opening of the cloaca, which is covered by the transverse flaplike vent in all lizards. Male lizards possess paired organs called hemipenes which lie within sheaths in the ventral portion of the tail. Each hemipenis is connected to a testicle by a tubular vas deferens. The testicles are located within the body cavity and lie near the kidneys.
It is anatomically impossible for male lizards to mount for copulation as do the mammals. They approach the female from the side; the males of many lizard species bite the neck of the female and try to maneuver the cloaca as close as possible to that of the female. Then the hemipenis that is nearest to the opening of the female's cloaca is erected. The hemipenes of the various species of lizards, which are creased or grooved in a variety of ways that are type-specific to each species, are provided with thorns or barbs, thus making possible secure binding during mating. The sperm flows through the tube-shaped penis in a channel along the hemipenis to the cloaca of the female. There it enters the oviducts where fertilization occurs. With some reptiles, sperm can be stockpiled by the female so that fertilization of late-maturing eggs can still take place after months or years.
As the day of egg-laying nears, the female will inspect the ground surface and dig holes in many places. She will do it as often and as long as it takes until one of these test holes meets with her approval; then egg-laying begins. In most cases the eggs must be transferred to an incubator. But this should not be done before the female has finished laying her eggs and has covered over the nest hole again. Any intervention too soon is a disturbance and can result in discontinuance of the laying and may cause a laying emergency as a consequence!
Transferring the Eggs to the Incubator
An incubator is necessary for brooding the eggs (maturing or incubation). It should have been set up during the courtship period and be standing ready. A discarded aquarium or a small refrigerator that no longer works are suitable for use as incubators. A thermostatically controlled heat source (a heating cable, heat lamp, or incandescent bulb) must be installed inside. You will find details of incubator temperature and length of incubation in the descriptions of the lizards in the last chapter. Before transferring the eggs, you must be sure that the proper temperature has been reached and that it can be maintained constantly.
You need a container for the clutch of eggs — a refrigerator box is best for this. It should be filled with vermiculite, mica that has been fired to become heat-resistant (available in pet and garden shops). Vermiculite comes in various grain sizes; the best mixture is vermiculite No. 3 VET mixed with water in a proportion ranging from 1:1.5 parts to 1:2 parts by weight. This gives you a material of the proper dampness, which will remain that way in the closed refrigerator container.
Transferring the Eggs
After the egg-laying is completed, carefully uncover the nest hole and remove the clutch. Unearthing must be undertaken with special care because the eggs of most lizards have a flexible shell, something like a soft plastic — only that of most geckos is hardened by deposited calcium. You must also be careful not to change the position of the eggs while removing them. In nature, in contrast to birds, reptile eggs are not moved again after they are laid; the embryo is fixed and may be smothered by the yolk supply if the position of the egg is later changed. After the eggs are settled into the incubating medium, the box is closed so that a minimal amount of air circulation is possible, and then it is placed in the incubator. If you are using vermiculite as a hatching medium, the often-recommended examination and removal of unfruitful eggs is not necessary. Such measures only cause damage, particularly as experience has shown that healthy eggs are not harmed by dead ones. Also unnecessary is the so-frequently recommended evaporation of water to maintain a high level of relative humidity in the incubator. In a closed refrigerator container the desired humidity is maintained!
The Young Animal
How long the eggs remain in the incubator depends on the species of lizard. The maturation time, the length of time between egg-laying and hatching, can vary widely. For instance, with monitor lizards it requires up to 120 days, whereas it is only 50 days for the Madagascar gecko. To free itself from the egg, the hatchling uses its egg tooth to rip open the shell. This is a tooth, located forward on the premaxillary bone, which grows in most lizard embryos and falls out a few days after hatching. After hatching, the young lizards are placed in a separate terrarium, arranged appropriately for the species of lizard. In the “parental” terrarium they would be in danger of attack and resulting fatal bites from the parent animals. The newly hatched lizards must slowly become used to the climate of the parent animals after the regular temperature of the incubator. There is no reason to keep them warmer. Any unnecessarily higher temperature — especially the failure to lower the temperature at night — does certainly allow the young to grow more quickly, but the negative consequences also show quickly. The calcium cannot be maintained and rickets or other metabolic bone diseases result; also vitamin B complex deficiencies may develop, convulsive trembling results, and soon the promising offspring have become miserable objects of pity. Ultraviolet irradiation is required for the successful raising of many lizards. Even the smallest nurturing cage must therefore have a covering of wire screening so that as much of the UV light as possible will reach the lizards. As mentioned earlier, some shade must be provided.
The time at which food is first taken can vary widely indeed. Whereas skinks take their first food soon after birth, the reserves of some species can last for as long as a few weeks. You should not lose patience and resort to force-feeding; this in combination with the psychic stress will worsen the general health of the young lizard, thus endangering its chances of hardiness in the future. Food for young lizards must be rich in variety and prepared with utmost care, and the calcium and vitamin supply especially should not be neglected.
The form of reproduction that is described in the foregoing paragraphs is called oviparity. This means that the development of the embryo takes place in the egg outside the mother's body. But in some lizards there occurs another type of reproduction, livebearing ovoviviparous. In ovoviviparity, the embryo development takes place within the mother's body, albeit in a thin-skinned egg; therefore, for the most part, there is no connection to the circulation of the mother. There is also still another form of embryonic development, for example in some Australian skinks and in the desert night lizard, Xantusia vigilis, in whom the nourishment is partially supplied by the mother's metabolism. In the ovoviviparous lizards the young lizards hatch out of the egg membrane before, during, or immediately after the mother has laid the egg. Sometimes she eats the unfruitful egg right then. The mother does not nurture the freshly hatched lizards; on the contrary, very often they are in grave danger from the parent animals.
The live-born young animals should be raised in the terrarium in the same way as the incubator-hatched ones.