Wild Conditions Research Articles

CHROMOSOMAL FITNESS CHANGES IN EXPERIMENTAL POPULATIONS OFDROSOPHILA PERSIMILISFROM TIMBERLINE IN THE SIERRA NEVADA

Much of the evidence for the adaptive function of Drosophila chromosomal polymorphism has been derived from experimental population cage analysis. Observation of changes in relative frequencies of competing chromosomal arrangements over a short term of about eight to ten generations is usually sufficient to establish determinacy of outcome and the net adaptive, or fitness, values of the competing karyotypes (Wright and Dobzhansky, 1946; Dobzhansky, 1948b; Dobzhansky and Levene, 1951). However experimental populations once initiated evolve new genotypes. With a given initial genetic variance the random mating population will seek its optimum genetic equilibrium within the limits of a constant laboratory environment. Such an equilibrium may or may not be close to that characteristic of the wild population from which the genotypes were derived, depending on the cleverness of the investigator at duplication of the conditions upon which the equilibrium is contingent. Of course since most of the factors of the wild environment upon which the population's adaptation depends are virtually unknown, the investigator can never hope to approximate the wild conditions; consequently the laboratory conditions are novel to the species, yet they are not so extreme that the species' norm of reaction cannot permit reasonable survival and then adjustment of its gene pool. It is this adjustment which must be taken into account in any long term analysis. Presumably in short term studies the changes in relative frequencies of competing genotypes tell us the immediate re-

ZUGUNRUHE ACTIVITY IN CASTRATED BRAMBLINGS FRINGILLA MONTIFRINGILLA

Summary1. Zugunruhe, a condition of nocturnal activity in caged migratory birds that is generally held to be identical to premigratory restlessness in the wild, developed in the spring in captive castrated male Bramblings Fringilla montifringilla.2. Zugunruhe occurred in intact control birds about a week before it was recorded in castrates. Intact birds became restless each evening earlier than did the castrates.3. Nevertheless, the peaks of intensity in both castrate and intact birds occurred at the same time and coincided with the period during which the bulk of the wild population migrated to their northern breeding grounds.4. In intact birds Zugunruhe occurred during the initial period of seasonal gonad modification. It waned by the time of sperm‐production when, under wild conditions, the birds would have completed their journey to their distant breeding grounds.5. The data suggest that the seasonal phenomena of migratory unrest and gonad development occur independently of each other. The remote possibility that migration is influenced by extra‐testicular androgens is mentioned.

EXPERIMENTAL POPULATIONS OFDROSOPHILA PERSI-MILISFROM AN ALTITUDINAL TRANSECT OF THE SIERRA NEVADA

Populations of Drosophila pseudoobscura and D. persimilis throughout their respective distribution areas in western North America exhibit a very extensive and intricate pattern of gradients, or clines, in relative frequencies of the gene arrangements of the third chromosome -(Dobzhansky and Epling, 1944). These gradients may be very gradual over a wide area from north to south or west to east, or they may be rather steep in slope across an altitudinal transect of relatively short distance in a mountain range (Dobzhansky, 1948a). Within certain populations of D. pseudoobscura temporal fluctuations of less amplitude than the more extensive geographic differences have been observed (Dobzhansky, 1943, 1947a) while in some other populations of the same species long term trends were found (Dobzhansky, 1947b). It was by studying the behavior of these chromosomal types in artificial populations (Dobzhansky, 1947a, Wright and Dobzhansky, 1946) and later by statistical analysis of wild populations (Dobzhansky and Levene, 1948) that these gene arrangements were proved to have selective values and were shown to be-maintained at the observed frequencies by natural selection under both wild and artificial conditions. This information together with evidence of physiological differences between carriers of each arrangement -(Heuts, 1947b, 1948) leaves no doubt as to the importance of variation

Coprophagy in the Wild Rabbit

REPORTS of recent experiments by Madsen1 and Eden2 have shown refection to be a normal physiological process in the laboratory rabbit. A few observations collected by me, while studying the ecology and population dynamics of the wild rabbit, suggest that this process also occurs in natural conditions. From Eden's experiments, 54–82 per cent of faeces passed are shown to be normally refected, the advantage of the process to the rabbit being equivalent to chewing the cud. It is possible that there is a further ecological advantage, which operates under wild conditions.

Duck Protection Wasting America's Game Birds. "National Committee of One Hundred" Federal Power and Duck Bag Limits: Facts. A Study. National Association of Audubon Societies, Bulletin 6 Our Migratory Wild Fowl and Present Conditions Affecting Their Abundance

Duck Protection Wasting America's Game Birds. "National Committee of One Hundred" Federal Power and Duck Bag Limits: Facts. A Study. National Association of Audubon Societies, Bulletin 6 Our Migratory Wild Fowl and Present Conditions Affecting Their Abundance

Australasian Hispidae of the Genera Bronthispa and Promecotheca which destroy Coconut Palm Fronds

With the increasing demand for copra all over the world for the production of coconut oil, the cultivation of coconut palms has increased enormously during the last ten years in the Solomon Islands, New Britain, Papua, Samoa, and the New Hebrides, and large areas of virgin forest have been cleared and planted on regular scientific principles. In olden times most of the nuts were collected from the native plantations, where the palms were grown under almost wild forest conditions, arid were then more hardy and did not suffer to the same extent from insect pests as do the palms planted under modern conditions. It is probable that the increased food supply, represented in the fronds of the thousands of young coconut palms planted out, has been responsible for the enormous increase of a number of indigenous leafeating beetles, which, under the conditions previously prevailing, lived upon the wild coconut and other species of palms growing in the jungle. In addition to many insect pests allied to or identical with those known in Ceylon, India, and the Malay States, we have in these Eastern islands a number of leaf-destroyers in the small flattened beetles belonging to the family Hispidae. The larvae of these beetles feed either on the upper surface, or in the tissue of the leaf under the protection of which they finally pupate, so that one can sometimes obtain the whole life-history from the egg to the perfect insect in a single palm frond. The majority of these leaf beetles, which are causing so much damage in the coconut plantations, belong to the genus Protnecoiheca, Blanchard, and from what we know of the life-history of several species that have become serious pests, it is fairly safe to assume that the habits of all the species are similar.