Desert Mammals Research Articles

Water content in the tissues of desert animals.

WHEN studying Gerbillus piramidum and Jaculus jaculus, Khalil and Abdel-Messeih1 claimed that the tissues of desert mammals contained less water than did those of non-desert ones. Several other workers (for example, the Schmidt-Nielsens2) found that desert animals lost less water through their skins. The data obtained by Khalil and Abdel-Messeih1 suggest that the low water content in the tissues of desert animals (including the skin) contributes to the decreased loss in water and thus represents an important adaptation of animals to the environmental conditions of the desert.

Some Fabulous Beasts

MOST people have heard of dragons, mermaids, phoenixes and unicorns, and probably of griffins and basilisks. What is surprising is the number of other imaginary animals that have been written about, and largely believed in, in Europe since the Dark Ages. I have a list, by no means exhaustive compiled mainly from English references and entirely omitting immediate sources outside Europe which contains about 140 names of animals, birds, reptiles and fishes which do not exist in nature, from abath to zitiron and from avanc to ypotryll. I say names, because the number of imagined beasts is only exceeded by the multiplicity of the names that have been applied to them. Frequently one finds several names for what is apparently the same creature, and nearly as often there is doubt about whether a different name denotes a slightly different idea. A monoceros, for instance, may clearly be exactly the same as a unicorn, the two words being the Greek and Latin for 'one-horned'; and a centaur is apparently very similar to a sagittary; but on the other hand all centaurs or onocentaurs are not alike: some have four legs as well as two arms whereas others, according to illustrations, have only four limbs altogether two arms and two hind legs and very much off-balance they look. The names themselves in their English forms often sound outlandish, and of course their derivations may lead one back a good part of the way towards the origins of the animals. To take one of the most familiar of all the dragon: there was a Greek word 'dracon', meaning 'a large snake', which was adopted through Latin into English and used in bestiaries and similar works in the sense of 'snake' from the thirteenth century onwards. Meanwhile the Greek and Latin words had been used, in the Septuagint and the Vulgate, to translate a Hebrew word which may have denoted, apparently, either a desert mammal such as the jackal or a large water-creature such as a whale, shark or crocodile. Perhaps this s 273

Water Economy of the Dorcas Gazelle

ALTHOUGH the physiology of the camel, kangaroo-rat, jerboa and various domestic animals of desert regions has been examined in some detail1,2, nothing is known of the heat and water relations of that most typical desert mammal, the gazelle. It has occasionally been suggested that gazelles may be able to live indefinitely on dry food without water, like desert rodents, but no experiments have been made to determine if this is true or whether, like camels, they need to drink. For this reason an investigation of the water economy of the Dorcas gazelle, Gazella dorcas dorcas (L.) is now being pursued here.

Some Aspects of Adaptation in Desert Mammals

Some Aspects of Adaptation in Desert Mammals

Tissue constituents of reptiles in relation to their mode of life—II. Lipid content

Abstract 1. 1. Lipid content of different tissues of Crocodylus niloticus, Tropidonotus tessellatus, Coluber florulentus, Chalcides ocellatus, Varamus griseus and Testudo leithii was determined under normal conditions of feeding. 2. 2. It was found that the tissues of different reptiles examined, as regards their lipid content, can be classified into three categories: (a) Nervous tissue with more or less constant values of lipid content in the different orders of reptiles examined in spite of their variation in habitat. (b) Liver with variable amounts of lipids irrespective of the habitat of the animal. (c) Rest of tissues being more fatty in desert reptiles than in semidesert or amphibious representatives examined. 3. 3. It was assumed that stored fat in tissues and in fat bodies in the desert lizards such as V. griseus act as a source of energy and of water, contrary to what has been assumed for desert mammals.

Endocrine factors in the water metabolism of the desert mammal, G. gerbillus.

IN RECENT years attention has been called to some of the mechanisms which allow the survival of various species of mammals in the hot and waterless circumstances of the desert. In 1947-48, the Schmidt-Nielsens (K. Schmidt-Nielsen, and B. Schmidt-Nielsen, 1952) were able to work out a water balance for several species of mammals living in the desert ofsoutheastern Arizona. In the laboratory, these animals were given no water per se. They derived water from the moisture content of their dry grain diet (about 5% water) and from its water of metabolism. On the deficit side, water loss occurred in the urine and by evaporation from the lungs. The loss from sweat and in the feces appeared to be negligible. Probably the most important aspect of their water account is their conservation of water by excreting a highly concentrated urine. Several species of desert mammals have been reported to produce specimens of urine with urea concentration of 3 to 4 M/L., and an electrolyte content equivalent to 1.2 to 1.5N NaCl...

The Stability of Subspecific Characters Under Changed Conditions of Environment

(I) Mice belonging to the subspecies Peromyscus maniculatus sonoriensis, from the Mojave Desert, were reared for more than eight years at La Jolla, the resulting stock representing a minimum of seven and a maximum of twelve or more generations. During this period, they did not, in respect to any single measured character, undergo a modification in the direction of the La Jolla subspecies, gambeli. On the contrary, the mice of the later generations were in some regards less like gambeli than were their ancestors trapped in the desert. (II) Mice belonging to the subspecies P. m. rubidus, from the northwest coast of California, were reared at La Jolla for six years, the resulting stock (with a very few exceptions) representing a minimum of four and a maximum of six or seven generations. Here again, the slight differences between the ancestral stock and its descendants were not such as to indicate a modification in the direction of the local race. As in the case of sonoriensis, the mice of the later generations of rubidus were, on the whole, less like gambeli than were their wild ancestors from Humboldt County. (III) Comparing the two introduced strains, sonoriensis and rubidus, there was no tendency towards convergence, under the influence of a common environment. To judge from the samples at our disposal, there was actually a slight divergence in respect to all but one of characters which were measured. (IV) The nature of these slight differences between the transplanted and ancestral series of a given race renders it highly improbable that they have been due to changed climatic conditions. To some extent, they are known to be the results of captivity, irrespective of climate. (V) Subjection of deer-mice of several strains to an atmosphere of high temperature and very low relative humidity gave conflicting results. In P. maniculatus dubius the dry-room animals were, on the whole, noticeably paler than the control, while in the gray juvenile pelage. This difference was not invariable, however, and the numbers were not sufficient to furnish decisive evidence of such a change. In any case, this initial difference in shade disappeared with the assumption of the second pelage, while the difference was actually reversed in later pelages, the dry-room animals now being somewhat darker. Such an effect, of course, was quite unexpected, in view of the prevailingly pale coloration of desert mammals. But, in judging these results, the almost pathological character of the dry-room animals must be taken into account. In mice of certain other races, on the contrary, no differences were noted between the experimental and control series, either in the juvenile or later pelages. (VI) On the whole, one can not fail to be impressed by the comparative stability of these various races of mice under very marked alterations in the physical environment. As regards color characters, such almost wholly negative results are not in agreement with those of certain other experimenters who have reported pronounced color changes in animals, following considerable changes in atmospheric humidity. Nor do the present results afford any support for the view held by certain zoologists that the differences between geographic races or subspecies are purely "somatic" and therefore nonhereditary. Regarding the more difficult question whether climatic influences may not have a cumulative effect in the course of sufficiently great periods of time, our views must at present be decided by considerations of a taxonomic and distributional nature rather than by any available experimental evidence.