May 18th, 2012
Reptiles are sexual animals and are the group that introduced internal fertilization to the vertebrate line. Thus, in a manner of speaking, they laid the foundation for the family unit in higher vertebrates, and from this came human society itself, with all its excitement and troubles. The ancestral amphibians deposited their eggs virtually naked in the water, and fertilized them by simply releasing sperm in the general vicinity. The hazards of such an informal operation to both sperm and egg are obvious. The reptilian egg, however, enters the world already fertilized, and packaged against a certain amount of environmental adversity. One need only compare the dozen or so eggs laid by the average lizard with the thousands laid by toads to see the great economy the new method has brought.
But even an egg with a shell is delicate. It can incubate successfully only within a narrow range of conditions of temperature, humidity and concealment. It is thus not surprising to find that a few reptiles have independently hit upon the recourse that we think of as one of the main attributes of the mammals – that of producing living young. All the live-bearing reptiles of modern times are lizards and snakes.
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May 14th, 2012
All reptiles practice internal fertilization. In all modern forms except the tuatara the male has an organ kept turned outside in, in the base of the tail, and everted through the opening of the cloaca during erection. In the tuatara the transfer of sperm is accomplished by bringing the genital openings into contact, as in birds. This was probably the method used by the ancestral reptiles – it is clear, in any case, that the penis had separate origin in turtles, crocodilians and mammals on the one hand, and in lizards and snakes on the other.
Thus, male lizards and snakes have not just one, but a pair of hollow structures called hemipenes, which make up their copulatory organs. Located as they are in the tail just behind the opening of the cloaca, the hemipenes often give the tail of the male a thicker, more gradually tapering contour than that of the female, and in many species the sexes can be distinguished by this difference. A groove that serves as a channel for the sperm extends from the opening of the sperm ducts along the inner wall (which is the outer wall during erection) of each hemipenis, and the surface may be pleated or set with spines that keep it in place on the oviduct of the female during mating. Either one of the hemipenes may be used, but only one, the one nearest to the female, is everted and protruded from the cloaca during erection, which is brought about by a combination of muscular action and distension of the walls with blood.
Among different reptiles fertilization is scheduled differently with respect to the time of nesting. In most species it seems to occur, as might be expected, just before the eggs are laid; but in some the sperm may live on in the reproductive tract of the female and continue to fertilize eggs months or even years after copulation has taken place. The longest known periods of such deferment of fertilization are four years for the diamondback terrapin of the southern United States, and five years in the case of the tropical American cat-eye snake. The green turtle, which evidently mates only in the sea off the nesting beach, often does so after the female has gone ashore and laid her eggs.
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May 9th, 2012
Reptiles fertilization is scheduled differently with respect to most species it seems to occur, as might be expected, were laid; but in some the sperm may live on and continue to fertilize eggs months or even years has taken place. The longest known periods of such deferment is four years for the diamondback terrapin of the south years in the case of the tropical American cat-eye snake. It is significant of the three reptiles which venture farthest north, even across the Arctic Circle, two- the European viper and the lizard Lacerta vivipara – bear their young alive. So does the slow worm (Anguis), another venturer into northern regions. The cold ground of those areas, no doubt, is not well suited to incubating eggs. Neither is water, so far as shelled eggs are concerned, which explains why most reptiles with strongly aquatic habits also bear their young alive.
Many of the live-bearing reptiles, however, belong to groups that have egg-laying members too. The skinks, the lacertas, the boids and the vipers are examples. There are even species that lay eggs in some parts of their ranges but bear live young in other parts. This suggests that their viviparity – as the ability to produce live young is called – is not so formal an undertaking as it is in mammals, and this is true. Some reptiles merely keep the eggs inside the body for varying periods up to and after hatching time. In others there are extensive, placentalike connections with the tissues of the maternal oviduct, and is used primarily for respiration. In a more advanced type the embryonic membranes, the chorion and allantois, interfold with maternal tissues and the embryo not only gets water and nourishment as well as oxygen, but conveniently has its excretory wastes taken away too. None of the live-bearing reptiles has dispensed with a big store of yolk as the main source of nourishment for the growing embryo.
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May 5th, 2012
In at least two races of lizards there appear to be no males at all,and young are evidently produced from unfertilized eggs. Such reproduction is known as parthenogenesis, or virgin birth. The most familiar case of parthenogenesis is that of the honey bee. The queen lays two kinds of eggs, some fertilized, some unfertilized. The unfertilized eggs produce the males, or drones; the fertilized eggs produce the workers. Ants, wasps and various other invertebrate animals sporadically or periodically reproduce by parthenogenesis. In some cases the parthenogenetic stage occurs at a time when conditions in the environment would make it difficult for the two sexes to meet for mating. How the two lizards evolved the practice, and why, is not clear. In some other species of lizards the females greatly outnumber the males and it is possible that this same phenomenon of parthenogenesis may normally alternate with bisexual reproduction.
Because the genitalia of male reptiles are internal, it is not always easy to tell the sexes apart. It takes a real expert, for instance, to determine the sex of a snapping turtle or alligator. However, in most species there are certain external features by which it is possible to distinguish the sexes of fully mature individuals. The two most obvious ones are size and coloration. There is no set rule about which sex may be the larger, but in many species it is the male that is bigger than the female. Where difference in color patterns exist, it is generally the male which has the more vivid coloration, as is usual in birds; but here again the situation is sometimes reversed. In some species the sexual coloration is a sort of nuptial dress, assumed for breeding and later abandoned.
Internal fertilization is a cooperative process, and to bring it about the sexes must find each other, and must be physiologically prepared for mating. Most if not all reptiles show some sort of courtship behavior by which the sex of a potential partner is determined, the coyness of the female is overcome, and a readiness to mate is generated in both members of the pair. Courtship often duplicates or blends with the expressions of rivalry and home defense between males, and since this whole complex of innate behavior is a hereditary part of the make-up of a species, it affords an interesting field for study.
The courtship of a number of different snakes and lizards is a case in point. Although there are clear similarities in behavior patterns among the two groups, it has been found that most lizards recognize the female visually, while snakes depend on odor, trailing the female with their noses as well as with the tongue and Jacobson’s organ. Male lizards put on quite a display among themselves – showing colored throat fans, erecting crests, arching their necks and affecting various gaits – but how much of this actually carries over into courtship is not surely known. Some of it, however, is brought to bear by the male on a prospective partner. When the female is thoroughly recognized as a female and her reticence overcome, the male lizard (like the males of some snakes) seizes her with his jaw, bends the base of his tail downward to maneuver the cloacal openings into contact, and insertion of one of the hemipenes is affected.
Turtles both aquatic terrapins and land tortoises, carry out varyingly elaborate courtships which may include butting and nipping of the female by the male, or his swimming backward in front of her, fluttering his claws beside her face, or stroking her cheeks with his elongate fingernails. Among some species of pond turtles and among sea turtles, courtship is accompanied by competitive behavior among males.
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May 1st, 2012
In some species a by-product of fighting between males is to augment their often fuzzy capacity to recognize the female at mating time. Experiments show that when breeding males of certain lizards approach another of their kind, their mode of sex recognition is not, as one would expect, to search for signs of femininity. Instead, the criteria seem wholly negative: if the challenged lizard fights back it is a male; if not, the only alternative is to regard it as a female lizard and make appropriate overtures.
In many cases the contests between males are carried out without physical contact. The same ends are accomplished are accomplished by various kinds of signals, posturings, and flashings of color patches, such as the throat fans of some lizards. The magnificent bellow of the American alligator, though not thoroughly understood, is partly a sexual call, but is partly used also as a territorial challenge.
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April 27th, 2012
In the pond in front of my house, during the mating season of the pond cooters, turtle heads are regularly seen in threes or fours. Off and on, for as long as two or three days at a time I have watched groups of these heads with a spotting scope, and while I could see little of what the bearers of the heads were actually doing, it did not seem to involve any very violent strife. The three heads simply stayed together in a restricted patch of water for a day or more at a time, and there were occasional outbreaks of splashing and finally, the back of one of the turtles would come out of the water, indicating that mating was taking place.
A similar thing occurs among the green turtles at their nesting ground on the coast of Costa Rica. Here, too, the observations made have been only in snatches, and whatever subtleties of courtship behavior are carried out have not been seen. But during the early part of the nesting season the turtles mate out in front of the beach a few hundred yards beyond the surf line. For the first week or so of the mating time there are large numbers of courtship groups involving two males and one female. Among sea turtles, mating is a strenuous process. Attempts of the male to mount the back of the female involve a great deal of thrashing and splashing of water. Once the male attains the position on the upper shell of the female, however, he remains firmly anchored by two huge claws on his front flippers which grip the fore edges of her shell, and by a strong horn at the tip of his tail which curls up under the back edge of her shell. The only time male turtles are seen on shore at the nesting ground is when a copulating pair is caught by a breaker and thrown onto the beach.
The courtship of the alligator is noisy and exciting. The bull bellows and exudes musk from glands on the throat and at the sides of the cloaca. When the female approaches, the two of them race about in wild circles, making a big wake that rocks the reeds and sends the fishes flying. The frogs stop singing and the waterfowl scream.
Closely related to courtship is rivalry and combative behavior among males. This sort of strife is not generally disorderly and injurious, but actually may serve a variety of useful purposes. It keeps the race physically on its toes, as it were, weeding out the weaker individuals as breeders. It brings about a distribution of territory, and thus lends order to both the reproductive process and the daily life of the individual. It establishes hierarchies of dominance and submission, and these again contribute harmony by forestalling more harmful untrammeled fighting. And just a courtship does, the fighting may help instigate glandular cycles involved in the mating process.
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April 23rd, 2012
All over the warm parts of the earth, crocodilians have been taken into religion and mythology. In many places the veneration is a sort of bribery, in which crocodiles are fed to gain their good will. Other cults carefully kill only crocodiles that have attacked people. At Lake Itasy in Madagascar a yearly proclamation is made announcing formally to the crocodiles that the evil ones among them – those which have killed someone during the past year – will be liquidated in their turn, and that all upright crocodiles should thus stay out of the way. In ancient Egypt, crocodiles were worshiped. Herodotus said that in parts of Egypt each household had a tame crocodile, which was fed daily, adorned with jewels and, when it died, embalmed and placed in a sacred repository. Crocodile mummies have been found in tombs. Crocodiles are still kept by fakirs near Karachi in Pakistan, and devout pilgrims buy goats which are cut up and fed to them.
All up and down the Americas reptiles were involved in the religions of the Indians in various ways. The most influential American reptile god – in this case a half-reptile god – was Quetzalcoatl, the feathered serpent and the “fair god” of the ancient Mexicans world: the quetzal and the rattlesnake. The quetzal is the resplendent trogon, the most striking of American birds.
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April 19th, 2012
Reptiles and people have always been important to each other. In the old days the relation was the natural give-and-take of ecology. Today we have the earth in hand, and in the lives of reptiles we loom much larger, while they count for less in ours. But in the time we lived together we were forever marked by these cool, dry creatures. Their sign is still on the human spirit all over the world, in their pervasion of mythology and religion.
In Judeo-Christian tradition the snake is generally assigned to an evil role. The temptation of Adam was instigated by the serpent; and besides getting original man expelled from the Garden of Eden, this turned the mind of the race toward procreation, which will likely one day make the world unfit for both men and snakes. There is some talk of the leviathan that ate Jonah being a crocodile instead of the whale it is usually thought to be, but this seems unlikely to me. A crocodile generally chops up its victuals too thoroughly for them to have much to say if they should ever get out again. A sort of backhanded intrusion of reptiles into Christian history was St. Patrick’s taking credit for the paleogeographic inequity of Ireland’s having no snakes. Actually the snakelessness of Ireland is pretty much the same sort of thing as the lack of elephants there, but I suppose the chance was just too good for St. Patrick’s public relations men to miss. I believe it is not generally known that someone once fetched a lot of snakes into Ireland in an effort to establish them there. I cannot say whether this was done idly or scientifically or in a spirit of iconoclasm. The Edinburgh New Philosophical Journal for April 1835 had only this to say of the event: “We have learned from good authority that a recent importation of snakes has been made into Ireland, and that at present they are multiplying rapidly within a few miles of St. Patrick’s tomb.”
Both turtles and snakes turn up repeatedly in Asiatic mythology. The third incarnation of Vishnu, the supreme god in the Hindu pantheon, was in the form of a turtle. At Vishnu’s suggestion the gods and demons set out to churn the ocean of milk to bring up the amrita, the liquor of immortality. They uprooted Mount Meru and set it in the sea as a churn staff. They somehow persuaded the great snake Vasuki to throw a half-hitch of his body around the staff and to let himself be used as a churn rope. Vishnu took the form of a big sea turtle and placed himself under the foot of the staff as a pivot base. There was some squabbling among gods and demons as tow which would pull the head end of the churn rope and which the ignoble afterend, but after a while they all fell to and churned for a thousand years. At one point the snake grew indisposed and threw up a terrible poison that came close to killing off all the gods, but Siva seized and swallowed it, and that is how his throat came to be blue. After other awesome vicissitudes the goblet of amrita finally came up, and likewise the comely Lakshmi, the goddess of beauty.
Another set of reptilian beings important in Indian mythology was a fabulous race of snakes, or half-snakes, often shown as put together of a human forepart with the back part normal snake. The males of these were called Nagas and their wives Naginas; and their natures were generally irresponsible and ornery. On the other hand, some Hindu snakes were beneficent. During the epochs of his cosmic rest – the times between his incarnations – Vishnu sleeps on the coils of the noble cobra Shesha, whose seven heads rise over the god as shade for his eon-long siesta. This is why Indians are kind to cobras.
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April 15th, 2012
The protection which the shelled egg gives to the developing embryo is its most obvious contribution to the survival of the species – but scarcely less important is the fact that when it hatches, it lets out into the world a tiny a tiny miniature of an adult, equipped from the beginning to make its own way in its environment. But to reach this perfected state the embryo needs a long period of development in the egg. Turtles like the snappers at left need two to three months; the primitive but specialized New Zealand tuatara needs more than a year. During these long incubations the eggs must be protected from predators and other dangers.
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April 11th, 2012
Compared to the simple eggs of fishes and amphibians, which are laid in water and often depend on it to bring fertilizing sperm to them, the reptile egg is a staggering innovation – the product of eons of development which started when the reptiles’ amphibian ancestors first took up internal fertilization. The alligator egg, with its embryo in a halfway stage of development, typifies the complexity of most reptile eggs. The embryo in the center is connected by an umbilical stalk to the primary food supply, the yellow yolk sac, and is encased in the amniotic sac, and envelope filled with fluid which leaves the embryo and cushions it from shock. The amniotic sac and yolk sac, in turn, are surrounded by still another envelope, the allantois, which in the early stages of development grows out from the embryo’s hind-gut. The allantois gets larger as the embryo grows and the yolk shrinks. It serves both as a storage bladder for uric acid, ammonia and other wastes, and as a conveyor for incoming oxygen and outgoing carbon dioxide. Another membrane, the chorion, encloses allantois, amniotic sac, yolk sac and embryo in a tough, resilient envelope closely associated with the eggshell itself. In crocodilians and turtles, the chorion contains egg white, or albumen, which serves to supply the embryo with water and probably some food.
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