Subspecific Differences Research Articles

Fauna and Bathymetry of Banks on Continental Shelf, Northwest Gulf of Mexico

Considerable new information has been obtained on the bathymetry and fauna of several calcareous banks on the continental shelf of the northwest Gulf of Mexico. A compilation of depths to tops and bases of 130 banks on the shelf revealed primary modes of depth occurrences at 9, 31, and 45 fathoms. These modes correspond with well developed terraces at the same depths on the banks studied in detail. Several of the banks were characterized by semi-ring depressions, steep central pinnacles, and flat terraces at several depths. The fauna collected on these banks at depths of between 24 and 31 fathoms are characteristic of intertidal depths in the West Indies and Caribbean. Many of the mollusks from these banks exhibited sub-specific differences from the species which have been collected from their normal range in the West Indies. Despite the existence of dead reef coral, no living forms were collected. Living lithothamnioids were common on all banks. Evidence suggests that the tops of these banks were in shallow intertidal waters at a time when over-all water temperatures were warmer than at present, and when populations of these faunas were continuous to the West Indies. As sea-level and hydrographic conditions changed, the original fauna became isolated and the corals which appear to form the primary organ c capping ceased their growth, leaving horizontal surfaces. The presence of large crystals of gypsum and inclusions of anhydrite from the flanks of one bank may have a bearing on the original topographic high at this place.

Speciation in the Mona Monkeys

In the course of investigations started in June, 1952, on the biology of the Gold Coast monkeys, the writer has made an attempt to plot the geographic distribution and limits of all the forms that include that country in their range. The results obtained indicate that the commonly accepted nomenclature of certain forms within the genera Cercocebus , Cercopithecus and Colobus fails to give a true picture of their specific or infraspecific status. The present investigations on the mona monkeys in the field have been sufficiently interesting to lead to a systematic study of the treatment of the entire mona group, Cercopithecus mona subspp. of Schwarz (1928 a , b ). Ideally, to gain an accurate idea of specific and subspecific differences, a single worker should study a group of related forms in their natural environment over the whole of their range. Such an opportunity rarely occurs in Africa, and it usually becomes necessary to apply what knowledge can be gained over a portion of the range to the group as a whole. Although the writer has been able to study only two of the eleven recognised forms of mona monkey in the field, he has found himself particularly fortunately placed geographically for the observation of species differentiation. The idea of species-structure thus formed would seem to be confirmed by supplementary museum work. Material .—Observations and collections of the forms Cercopithecus mona (Schreber) and of C. campbelli lowei Thomas have been made by the writer between Togoland in the East, and Guiglo, Ivory Coast, in the West. This area contains a belt of forest about six hundred miles long in which these monkeys are common. In addition, some scores of specimens have been kept in captivity in the Department of Zoology, University College of the Gold Coast, both for observation …

Genetic and morphological evidence for subspecific differences between Naples and Plymouth populations of Ophryotrocha puerilis.

INDIVIDUALS of Ophryotrocha until now classified as O. puerilis and collected in the Bay of Naples and at Plymouth breed normally, if kept in Naples water, under conditions described elsewhere1. The Naples and the Plymouth populations are unquestionably closely related and have the same chromosome number (2n = 8). However, cross-breeding between a Naples individual and a Plymouth individual has constantly resulted in embryos which degenerated at an early stage and were eaten by their parents.

So-called non-adaptive or neutral characters in evolution.

THE reaction that set in some thirty years ago against the facile assumption that all interspecific differences are adaptive was good but went too far. Several authors insisted that most specific and sub-specific differences were non-adaptive. More recently, Mayr1, while emphasizing the great importance of selection in speciation, considered that not all geographical variation is adaptive and, in particular, that most of the characters involved in polymorphism are completely neutral so far as survival value is concerned. Later2, he reversed this judgment on polymorphism.

Continuous and Discontinuous Variations and Their Inheritance in Peromyscus. III

1. In the preceding pages, the differences, structural and pigmental, which distinguish four geographical races of deer-mice are discussed in some detail. The pigmental differences relate to a considerable range of more or less independently varying characters, affecting both the intensity and the extensity of the pigment in the hair and skin. They are found to be, in a general way, correlated with certain elements of the physical environment, while the structural differences do not appear to be so correlated. 2. All of these differences, structural and pigmental, are found to be differences of degree, revealed through a comparison of mean or modal conditions rather than of individual animals. In comparing the less divergent of these races with one another, the frequency polygons, for any given character overlap broadly. 3. These subspecific differences, and even the minor differences which distinguish one narrowly localized subrace from the parent form, are found to be hereditary, as evidenced by their persistence when environmental conditions are interchanged. 4. The gradations, in certain of these characters by which individuals of the same race differ from one another are found to be strongly hereditary. 5. Hybrids between even the most divergent of these four races are predominantly intermediate in character, both in the F1 and the F2 generations. In both of these generations a wide range of variability is exhibited, which, however, is little if any greater in the F2 than in the F1. 6. In contrast to the sensibly continuous variation and sensibly blended inheritance shown in respect to these subspecific characters, is the behavior of certain "mutations.'' Here we meet with typical discontinuous variation, and inheritance of the strictly alternative or Mendelian type. It is insisted that the burden of proof rests upon those, who contend that these two types of variation and inheritance are reducible to a single category, that of discontinuity. Anything like a proof of this contention appears to be thus far lacking.

Continuous and Discontinuous Variations and Their Inheritance in Peromyscus

1. In the preceding pages, the differences, structural and pigmental, which distinguish four geographical races of deer-mice are discussed in some detail. The pigmental differences relate to a considerable range of more or less independently varying characters, affecting both the intensity and the extensity of the pigment in the hair and skin. They are found to be, in a general way, correlated with certain elements of the physical environment, while the structural differences do not appear to be so correlated. 2. All of these differences, structural and pigmental, are found to be differences of degree, revealed through a comparison of mean or modal conditions rather than of individual animals. In comparing the less divergent of these races with one another, the frequency polygons, for any given character overlap broadly. 3. These subspecific differences, and even the minor differences which distinguish one narrowly localized subrace from the parent form, are found to be hereditary, as evidenced by their p...