Showing papers in "The American Naturalist in 1931"

A Preliminary Report on Some Chromosome Alterations by X-Rays in Crepis

Abstract: 2. Dislocatiows: Rearrangement of chromosome material without any alteration in the total mass of the nucleus. Here should be classified various alterations known to occur spontaneously, such as attachment, duplication, translocation, fragmentation, etc. 3. Transformzations: Alteration of the morphological characters of the chromosomes invariably connected with a change of the total mass of the nucleus, although often affecting different chromosomes independently. Transformation is believed to have occurred in course of the evolution of the Crepis species, which in most cases markedly differ in the sizes and shapes of their individual chromosomes. 4. Novations: A presumed phenomenon of formation of the chromosomes de novo, which was called to account for some apparently otherwise inexplicable cases of appearance of nsew large "V-shaped" chromosome structures. As will be shown in the following, this last type should very probably be merged with dislocations.

Inheritance in Nicotiana tabacum. XI. The Fluted Assemblage

Abstract: 1. By loss of an F-chromosome, probably as a consequence of occasional non-conjunction, N. tabacum var. purpurea produces the monosomic, fluted. 2. When selfed, fluted has produced as further variants the distinctive recessive types, coral and mammoth, both of which have been established in pure lines. 3. From crosses with fluted, both coral and mammoth have been shown to be due to secondary modification of the F-chromosome. 4. Coral and mammoth, when crossed with normal or with each other, produce hybrids of the normal type, which; however, exhibit frequent non-conjunction of the F-chromosomes. 5. By reason of this non-conjunction, F2 and other derivative populations from these crosses contain some haplo-F and triplo-F individuals in addition to the expected classes of offspring. 6. Hybrids of coral with mammoth apparently exhibit no crossing-over between the two modified F-chromosomes. 7. Some of the F2 populations of coral X normal segregated for a recessive pale sterile type, which owes its sterility ...

Chick Mortality and Sex-Ratio in the Domestic Fowl

Abstract: IT is a well-known fact that in man during childhood male mortality is higher than female mortality. This greater male mortality is responsible for a gradual decline of the sex-ratio from birth to puberty. It appears that no observations have been made as yet concerning the relation between postnatal mortality and sex-ratio in the domestic fowl. Since such information aside from its immediate interest may be of theoretical value for the explanation of selective mortality in general, we have undertaken to analyze the mortality rec-' ords for the first two months after hatching of the chicks, which at this station were hatched for experimental purposes during the years 1922 to 1930. Approximately 19,100 chicks were hatched during this nine-year period. About 9,500 chicks out of this total belonged to a large number of crosses which were made for the genetic analysis of various morphological characters, while the remaining 9,600 chicks were Single Comb White Leghorns-. The Leghorn chicks belonged to inbreeding experiments carried out by Dr. L. C. Dunn and were partly derived from brother by sister or half-brother by sister matings and partly from crosses between unrelated individuals. In tabulating the death records all cases of accidental death (due to crowding, predatory enemies, drowning, and so on) were omitted; these amounted to approximately 5 per cent. of the total mortality. There was also a small number of chicks which could not be sexed because they had lost their identification bands or were decomposed before they were found. Most of the chicks were hatched during March, April and May. There were some small hatches, however, which came off in January

Notes on Differential Growth

Abstract: A number of numerical data found in the literature have been analysed in relation to the idea of differential growth-ratios and growth-gradients. The following chief results have been obtained. (A) Crustacean abdomens (1) The female abdomen of Pinnotheres (data of Atkins) has, both for breadth and length, a steep growthgradient with growth-center in the terminal segment. The growth-gradient for length is at a lower absolute level than that for breadth, but is steeper. The size at which this rapid differential growth begins appears to vary by at least one instar. (2) The female abdomen of Telmessus (data of Sasaki) has a much flatter growth-gradient (only determined for breadth) with growth-center in the subterminal (6th) segment. The corresponding growthgradient for the male abdomen is still flatter, with growth-center between the 4th and 5th segments. (B) Negatively heterogonic Crustacean limbs The Racing Crab Ocypoda (data of Cott) shows a negative heterogony of its walking limbs, whereas its chela is i...

Chromonemata in Somatic and Meiotic Mitoses

Abstract: With increasing knowledge of the generic differences it becomes increasingly difficult o picture just how such differences may have arisen; as modifications of some common basis; or derivation of one genus from the other, since geographical distribution leaves little doubt that Cambarus is the llewNest genus of crayfish. The existence of a sperm receptacle in Camtbarats i apparently correlated with all economy of sperms, since the numbers used for one egg-layincg are much smaller than in Potat)mtobits, where the spermatophores are scattered and not concentrated within a. small receptacle; moreover, the central position of the receptacle seems better to assure the contact of the sperm withl the issuing eggs than the wide spreading of the sperniatophores o01 the outside of the shell, since the eggs tend to glide along the middle line, though emergillo right and left. It is then possible to regard the invention of the sperm receptacle as a gain in economy and a useful improvement hat might, conceivably, be of some moment to the race hence natural selection might have had a hand in its preservation. In brief, the accuracy of aim in sperm transfer may have enabled Camitbarus to avoid some of the loss of materials caused by the scattering methods of Potamobius. Other characters of these two genera, such as the slight differences in nuiibers of gills and the numbers of arms of the sperms, can scarcely be thought of as in themselves of any survival value, and raise the question whether we shall regard this whole complex of secondary sexual organs and their functions as arising from unknown variations ill supposed genes producing results in jcart seemingly significantly useful. Pending experimentation we remain quite ignorant of any explanation of the causes for such generic differences as those separating Pota'inobius and Cambaruts. E. A. A NDREWS

Chromosome Structure in Drosophila

Abstract: Schwemmle, J. 1926. "'Vergleichend zytologische Untersuchungen an Onograceen. Die Reduktionsteilung von Eucharidium concinnum," Jahrb. wiss. Bot., 65: 778-818. Shull, G. H. 1923a. 'Linkage with Lethal Factors the Solution of the Oenothera Problem," Eugenics, Genetics and the Family, 1: 87-99. 1923b. 'Further Evidence of Linkage with Crossing-over in Oenothera,'' Genetics, 8: 154-167. Weier, T. E. 1930. "'A Comparison of the Meiotic Prophases in Oenothera Lamarciciana and Oenothera Hookeri," Cellule, 39: 271-306.

The Weight-Length Relationship of the Shells of the Hawaiian Pearl Oyster, Pinctada sp.

Abstract: SINCE the formulation of Spencer's "cube law" (1872) stating that the weights of the organisms increase as the cubes of their dimensions, numerous attempts were made to apply this relation to various animals and to fit the observed and calculated data to a simple formula, W aL3, where W is weight, L is length and a is a constant dependent on the unit of measure and the organism studied. This simple formula was often used in a study of growth and in comparing the weight-length factors, a W of various food fishes. An extensive and widely L' scattered bibliography on the subject compiled by Clark (1928) can be found in her paper on the weight-length relationship of the California sardine. Although the application of a "cube law" gave satisfactory results for fishery studies (Hensen, 1899; Heincke, 1908; Johnstone, 1914), its validity and theoretical significance for the interpretation of the relation between growth and form has been but little studied. In 1916 Hecht, accepting the cube law as representing the true relation between the weight and the length, came to the conclusion that in the organisms in which growth is uniform but unlimited (indeterminate) the form of the individual is laid down very early in life and is adhered to throughout its period of growth which lasts for the rest of its life (fishes, bivalve mollusc Dosinia), whereas in the organisms with determinate growth (man) the form is continually changing during the period of growth. In the latter case when the form becomes constant the growth ceases. In recent years Huxley (1924, 1927) has developed this idea more

Size Groups and their Characteristics in the Salamander Hemidactylium scutatum (Schlegel)

Abstract: 1. Evidence has been presented in favor of the view that Hemidactylium attains sexual maturity near the end of its third season of life, i.e., when it is approximately two and a third years old. 2. Juveniles in their first autumn can be recognized by their small size (about 26 to 41 millimeters of total length) and by their short tails (less than the length of the body measured to the posterior insertion of the hind leg). There is practically no difference in length between the sexes at this age, but the mean for the females is slightly, perhaps significantly, greater than that for the males. 3. Juveniles in their second autumn are distinctly longer than the yearlings, but as a group they overlap in length the shorter portion of the adult group. The females average about four millimeters longer than the males. The relative length of the tail is not significantly different between the sexes at this age. It is distinctly different, however, from that of the yearlings, for it is nearly always longer than the...

Linkage in Size Inheritance

Abstract: An analysis of the data on the back-cross generation of a mouse interspecific cross between large Mus musculus, with three recessive color characters, and small Mus bactrianus, with the three dominant allelomorphs, has indubitably shown an association in heredity between factors productive of a large size in several quantitative characters and a recessive qualitative character, brown coat color. Thus, the fact that size in mice is influenced by chromosomal genes can scarcely be questioned any longer. To a lesser extent factors linked with dilution also affect size in certain characters.

The Effects of Increasing X-Ray Voltages on the Production of Lethal Mutations in Drosophila melanogaster

Abstract: (1) Sex-linked lethal mutations furnish good material for a quantitative analysis of the mutation process. (2) When the intensity of the X-ray beam is increased by raising the voltage over a range of 40 to 99 kilovolts, the number of mutations is increased accordingly. Taking the amount of ionization in air as a measure, the mutation rate seems to vary approximately in direct proportion to the intensity. (3) There is some evidence that gene mutations are due not to a number of causes, but to one, the beta particle, and that it is because X-rays and radium both produce beta radiation that they are successful agents in inducing gene mutations in the laboratory. Similarly, it is suggested that some kind of earth radiation producing beta particles may be responsible for mutant types in nature. Recent measurements by Muller and MottSmith (1930), however, seem to indicate that natural radioactivity is far "inadequate to explain the frequency of 'natural' mutations."

Chromosome Number in Species of Peanut, Arachis

Abstract: Normal appearing pollen is formed. According to Bailey (1930) \"the plant cultivated under this name is apparently a hybrid between P. bifida and P. subulata.\" I was unable to count the chromosomes of P. stellaria. During the summer of 1930 attempts were made to cross Phlox paniculata reciprocally with Phlox drummondi. Approximately sixty crosses were made each way. The crosses in which P. drummondi was used as the female parent resulted in three weak-appearing sets. These matured into capsules devoid of seed. No sets were secured from the reciprocal. In the spring of 1931 attempts were made to cross Phlox divaricata reciprocally with Phlox drumminondi. Forty crosses were made using the former as the female parent. Twenty-six sets resulted. From these twenty-three normal appearing seed were secured. Many of the capsules contained only one seed, or no seed, or seeds that were shriveled. No sets were obtained from thirty-f our reciprocal crosses.

The Yaquina Oyster Beds of Oregon

Abstract: 1. The Yaquina oyster beds of Oregon are located in that portion of the Yaquina River lying mainly in the vicinity of Oysterville, beginning approximately six miles below the town of Toledo and extending for nearly three miles in the direction towards Newport. 2. The oyster beds are limited in area, comprising no more than 135 acres at the most. The large bulk of the oysters consists of the native Pacific species, Ostrea lurida Carpenter. There have also been numerous plantings of the Atlantic oyster, Ostrea virginica Gmelin, but with few exceptions these have not acclimated themselves to their new locations in the Yaquina region. 3. The Yaquina River is an exceedingly narrow and shallow stream carrying a large amount of sediment and debris. Inasmuch as this suspended material settles on the oyster beds, it becomes absolutely necessary for the oystermen to keep constant watch over their beds and give them the very best of care and cultivation. 4. The salinity and food in the vicinity of the oyster beds ar...

Genetic Non-Disjunctional Forms in Drosophila

Abstract: This paper presents an analysis of the type parents and atypical forms found within a special stock of Drosophila melanogaster. The anatomical changes observed in the abnormal individuals of this stock consist very largely in over or under growth of the organs, especially those of the reproductive system, bristles and wings. They involve alterations in the testes, ovaries, paragonia, vas deferens, ejaculatory sac, oviduct, spermathecae, parovaria, ventral receptacle and uterus, as well as the external genitalia, sex-combs, clasper plates and anal plates. Fertility is reduced. The duration of life is shortened. Bristles are reduced and wings cut. These forms appear sporadically within a certain family or its near relatives. The ratio of the abnormal individuals to normal varies anywhere from I in 26 to I in 100. Profound alterations are found within the cells of these abnormal individuals. The chromosomes are increased in number, 12 chromosomes instead of 8 being ordinarily found in the cells. The anatomic...

Do Earthworms Grow by Adding Segments

Abstract: 1 This investigation was undertaken and completed at Ohio State University. 2 Pearl, R., and Fuller, WV. N., I'Variation and Correlation in the Earthworm," Biometrica, 1905-06, 4, 213-229. Up to a certain age at least, Lrmbriicus adds somnites at the posterior end of the body with growth. It is clear . . . that the great extent of the total range in the variation in this character arises from the presence of a comparatively small number of individuals with few somites which unduly extend the lower end of the range. It seems reasonably certain from what we know of the method of growth in the earthworm that if this sample of worms could have been allowed to go on growing the range of variation in total number of sonlites would have steadily decreased with lapse of time. The fact that there is no apparent tendency towards extreme extension of the range at the upper end indicates that the bulk of the worms included in the sample have either completed the process of adding somites or at least that the process is going on very slowly if at all. ... The conclusion, that the earthworm is more variable in length than in number of somites, may seem at first sight paradoxical. But it is really no more so than to conclude, what is very obviously the fact, that man is more variable in respect to sitting height than in respect to number of vertebrae. It simply indicates that in the earthworm we have two kinds of growth occurring together: one the addition of somites, the other increase in size of the individual somites. That these two kinds of growth are acting together' will be clear when the correlation surface between total number of somites and length of body is examined (p. 218). It is seen at once by mere inspection that the relationship between the two characters is not the same in all parts of the correlation table. Thus the worms in the two lowest length classes (i.e.. from 10 to 15 cm in lenotlf)

On the nature of size factors in mice.

Abstract: Data on quantitative characters, derived from a mouse species cross, have shown that the F1 means fall into two general classes: one in which the means are intermediate between those of the two parent species and the other in which they equal or surpass the larger parent. In general, external dimensions (body length, tail length) and weight fall into the first; while skeletal dimensions fall into the second. Humerus length, however, is intermediate. These results make it appear probable that not all size characters are equally subject to the influence of general factors. Coefficients of correlation were computed for various pairs of characters and disclosed significant differences. Femur and tibia are more closely correlated than is either with skull length. These two leg bones in mice, as well as in rabbits, are apparently largely influenced by common factors. Sex differences were found in the degree of correlation between various pairs. In general, females present higher coefficients than males perhaps ...

Sex Dimorphism and Schooling Behavior Among Fishes

Abstract: IN a previous paper' the writer has attempted to show how the psychological mechanism involved in the aggregation and maneuverings of individual fishes in schools may probably be explained as composed of a very simple set of purely automatic reactions. Greater difficulties are met with in an endeavor to explain the phylogenetic or ontogenetic origins of these reactions. It is not a prior inconceivable that they should properly be regarded as manifestations of ontogenetically acquired habits, but their early appearance ill the life of the individuals and their more or less fixed relationship to definite systematic groups of fishes indicate the probability of their being based upon the phylogenetically developed, inheritable, nervous and morphological orgaiiization of the species after the manner of tropisms and sex instincts. With our present inadequate knowledge of the physical background for instinicts and nervous reactions, it is impossible to attempt any direct explanation for the evolution of the schooling "'complex,'" unless the theory of phylogenetic adaptation according to the requirements of the organism be dogmatically adopted as a necessary axiom of biology. But, granting the evolution of the schooling instinct as an inexplicable quality in the nervous organization of many fishes, we may be able to determine some of the factors influencing its varying degrees of manifestation in the different systematic or biological groups, by studying the relation-

Cyto-Genetics and the Species Concept

Abstract: ONE'S concept of species must necessarily involve one's point of view concerning fundamental questions such as the following: Do species really exist? If so how do they originate ? And how may species be recognized ? For the sake of brevity I shall assume that my audience accepts the evidence from the ever-increasing body of experience in classifying animals and plants, which certainly indicates that species do exist and that they are really natural groups of individual organisms. That is to say, with organisms in which large numbers of individuals have been thoroughly studied, the experience of many students of classification goes to show that really distinct groups of individuals have existed and do exist; that while the individuals within a group are not all alike and may differ almost endlessly and even strikingly in certain details, yet they resemble one another more than they resemble the individuals of any other group; also that the groups existing in a given time-plane usually differ from one another in numerous characteristics and are separated by definite gaps, marked by physiological and ecological divergence if not by constant morphological features, except in some cases where natural hybrids occur. Along with a certain range of variation to

The Antiquity of Insect Structures

Abstract: ANY,.y warm night in summer time, one may observe those minute Diptera lkowTn as punkies, which are so small that they pass without difficulty through the mi1osquito screen. Melere specks to the naked eye, they are nevertheless more complicated than any automobile, more efficient in flying than any aeroplane. They have muscles, nerves, a blood system, connective tissue, a reproductive system, and a marvelously complex exoskeleton. Their kind existed millions of years before man developed, and who can say that they may not continue to flourish after hie has disappeared? Such marvelous little machines are of enormous antiquity, coming clown through the ages in variously modified types, but with surprisingly little change in essential characters. We are all interested in diversity, iii progress, in evolution. But it is useful to consider also the stability of living things, the extraordinary fact that in them the most complex chemical substances known retain through vast ages their essential identity. The mammals, which have undergone so many remarkable developments during Tertiary time, are really exceptional. The lower vertebrates, and especially the invertebrates and plants, show a much slower rate of evolution, though it is possible or probable that they too had their time of rapid evolution in the remote past. Considering all the evidence, we are inclined to formulate some general statements, thus: (1) The rate of evolution in any large group is not uniform; there are periods of relative stability, and periods of comparatively rapid change. (2) Tertiary time has seen rapid change in the mainmalia, but not in the insects, mollusks or flowering plants.

Chromosome Numbers in Phlox

Abstract: ture, hence it is scarcely possible that the reproductive system is determined still later. It appears practically certain, therefore, that the second possible explanation of my earlier experiments must be abandoned. The first and third, one of them consistent with Goldschmidt's theory of intersexes, the other not, remain as possibilities. It is hoped that the more complete study of intermediates which is in progress will throw light on the relative values of these two explanations. A. FRANKLIN SHULL

Intergeneric Hybrids between Gossypium and Thurberia

Abstract: THE genera Thurberia and Gossypium are referred by Benthaam and Hooker to the same tribe (Hibisceae) of the natural order Malvaceae. The chromosome number of the so-called Arizona wilcotton, Thurberia thespesioicles A. Gray, has beei determined by Dr. A. E. Longley (personal communication) as 13. The correctness of this number, which is the same as that of the cultivated Asiatic cottons, G. stocksii, and the wild Mexican cotton, G. Davidsonii, has been verified in this laboratory by J. E. Plans in acetocarmine preparations. Thurberia thespesioicles is morphologically very similar to Gossypium)-i, and indeed was described by J. Miers (Jour. Bot., xxxl, 330) as G. lanceoefornte. Seeds of this species were obtained from Arizona through the kindness of Dr. T. Kearney and the resulting plants proved to be moderately well adapted to Trinidad conditions. Attempts have been made to hybridize Thurberia with other species of Gossypium, and success has been attained in three instances.

Experimentally Induced Alterations of the Morphology of Chromosomes

Abstract: except the cellar bristle number and the number of rows of acrostical hairs. In these latter instances the relationship is reversed, although bar still retains its intermediate place. Incidentally, in working with the forked and straight-bristled strains certain differences were noted between them. The conclusions to be drawn from these observations may be summed up as follows: (1) The somatic effect of the bar gene is primarily a reduction in facet number; (2) when this effect is doubled, as in ultra-bar, the facet number is again appreciably reduced; (3) head width, haltere length, thoracic length, wing length and width, and size of the median ocellus are directly correlated with the facet count; (4) while the number of rows of acrostical hairs and the cellar hair number are in inverse relationship; (5) in almost every respect the forked bristled flies are smaller than those with the straight bristles; (6) proof of the wide-spread somatic effects produced by a single gene change is shown by the fact that observations made upon either the forked or straight-bristled strain are substantiated by similar observations upon the other.

The Cytological Basis of Mutations

Abstract: The term mutation should be used in a generic sense to include inherited changes of any kind in the germplasm. Various types of mutations, such as trisomics, polyploids, translocations and gene mutations, can then be classified. The remarkable constancy in the structural arrangement and spatial relationships of the elements making up the germinal material under normal conditions is emphasized. The term catenation is proposed for the linkage of chromosomes in a ring or chain, now known to occur in a number of plants. The causes of catenation, especially in Oenothera, are discussed, and the theory of hybridization combined with some translocations between non-homologous chromosomes is supported. The present cytological evidence for parasynapsis in Oenothera is not regarded as satisfactory, although if parasynapsis occurred it would afford a basis for much at least of the chromosome ring formation in Oenothera.

The Effects of Selection on Eye and Foot Abnormalities Occurring Among the Descendants of X-Rayed Mice

Abstract: IN 1921 the writer and Bagg discovered certain abnormalities of the eyes aiid feet in mice. These particular genetic abnormalities have occurred only among the descendants of certain animals which as adults (non-pregnant females ancd males) were treated with light doses of X-rays over the whole body. A series of papers dealing with the various abnormalities from genetic ancd anatomical points of view are included in the bibliography of this note. The object of the preseiit communication is to record the results of selection within the abnormal race as it is at present being carried on. It should be recalled that whereas Bagg has at present aiiimals descended without an outcross from the original abnormials, the mice which provide the primary data incorporated in this note are the result of either oiie or two outcrosses wNNith a normal albino race followed by close (brother to sister) inbreeding and, in certain of the lines, selection of the abnormal individuals as parents. The ancestry of most of these

Internal Factors Affecting Discontinuity between Species

Abstract: MAY I preface mny, remarks by repeating mnyconviction that the species problem is a problem and that as one of the fundamental problems of biology it is worthy of study as an end in itself and not as a mere corollary to work in ecology, systematics or genetics\" Not until a fairly large number of species have been carefully and methodically studied over their entire range shall we be able to discuss the problem intelligently. Aside from the work on cultivated plants by AYavilov and his associates, there are not even complete mnorphological surveys of any of the higher plants. For what species can the following simple questions be answered: What is its actual distribution? Does it grow in different situations in different parts of its range? What, for some easily measured character such as height or flower size, are the largest and smallest values for the species, what the average for the species as a whole? Do the values for different localities depart significantly from the mean of the species? Over what part of its range is it the most variable, over what part the least? lAre there distinctive color forms and if so what is their comiparative frequency in different localities ? Are there any geographical regularities in the distribution of such conspicuous characters as hairiness, prostrate habit, etc., and if so, are they paralleled in other species having approximately the same distribution? For the past six years I have been attempting to gather data which would answer just such questions. I have been studying a few species of Iris, the genus Aquilegia and several species of Aster. While the work is far

A Mutual Translocation Involving the Fourth and the X-Chromosomes of Drosophila

Abstract: (1) The wm5vf stock of Drosophila melanogaster contains a mutual translocation of X and IV, produced by x-ray. (2) The X-chromosome is broken between white and facet; the left end is attached to the IV. (3) The IV-chromosome is broken between eyeless and bent and the eyeless (left) part is attached to the right portion of the broken X. Bent is located on the spindle fiber (right end) portion of the IV. (4) Non-disjunction of IV occurs very frequently in this stock. (5) A gene, the double dose of which is important for viability, is located in the left (eyeless) end of the IV.