Phase Of Rapid Increase Research Articles

Regulation of alkaline phosphatase in human skin fibroblasts.

SummaryThe specific activity of alkaline phosphatase in human diploid skin fibroblasts in tissue culture increased following addition of prednisolone, hydrocortisone, and cortisone. Estradiol-17β, testosterone, and progesterone had no significant effect on induction of alkaline phosphatase in the same tissue culture system. Using prednisolone-21-phosphate (10–5 to 10–8M), we have shown that the phase of rapid increase in enzyme activity is linear with respect to time and that the rate of increase is dependent on concentration of the hormone. Maximal rate of induction occurred at a 10–6M concentration of prednisolone-21-phosphate. Evidence from our in vitro system indicates that the activity of alkaline phosphatase in regenerating connective tissue may be effectively regulated by physiological levels of adrenal glucocorticoids present in plasma.We sincerely thank Miss M. Gail Hawkins and Mr. Boyd R. Switzer for assistance in this work.

The Exploitation and Conservation of Resources by Populations of Insects

The idea that many animal populations have intrinsic mechanisms which prevent them from becoming so large as to induce population crashes through shortage of resources is widespread among vertebrate ecologists. Wynne-Edwards (1962, 1965) has presented a large volume of evidence, much of it circumstantial and anecdotal, that the explanation of the apparent rarity of many vertebrates lies not directly in environmental influences such as weather or immediate shortage of food but in social interactions which increase the death-rate or decrease the birth-rate before obvious crowding sets in. Various laboratory studies (e.g. Strecker & Emlen 1953; Terman 1965; see also a review by Christian & Davis 1964) have tended to support this contention. Chitty (1960) suggested that time and selection against genotypes present in the phase of rapid increase could also lead to the limitation of local populations. The existence of such self-restraining mechanisms has been convincingly demonstrated for only a relatively small number of vertebrate species and, in some of these, environmental changes may upset the regulation (Davis 1953). But, because populations of many invertebrates, particularly pest-insects, undergo spectacular rises and falls from season to season and year to year, hypotheses of selfregulation have not been so popular with students of invertebrate ecology. A laboratory study of Tribolium (Brereton 1962) suggests that a self-restraining mechanism exists in this species, and Wellington (1964) has given evidence that in Malacosoma genetic deterioration of local populations through differential emigration of the more active and hardy individuals can account for limitation of local populations even though the environment remains favourable. The present paper supports the idea that the nature and importance of intrinsic regulatory mechanisms may depend on the degree to which the size of an animal population is capable of influencing the quantity of limiting resources available to later generations. A number of accounts by other workers are examined from this point of view and new work is presented on the importance of the pattern of population-dispersion in the use and conservation of food by two contrasted species, Dacus tryoni Frogg. (Diptera, Trypetidae) and Cactoblastis cactorum Berg. (Lepidoptera, Phycitidae).

Seasonal Changes in Survival in Mixed Populations of Two Species of Vole

This paper describes the last of a series of field trials designed to discover the factors preventing unlimited increase in the numbers of the short-tailed vole (Microtus agrestis). The present study may be regarded as a pilot test of the hypothesis that 'a decline in numbers is a necessary consequence of the selective action of hostility against the genotypes present during the phase of rapid increase' (Chitty & Phipps 1961). Here we describe findings which, for the first time in the course of these investigations, did not compel us to modify our initial point of view. Unfortunately they did not enable us to establish it either, since they merely confirmed that further progress was impossible without critical studies of behaviour and genetics. One such study on behaviour has since been performed by Sadleir (1965), using the deermouse Peromyscus maniculatus. The eliminative procedures used in earlier studies are described in the first paper in the series (Chitty 1952, especially pp. 535-7), and in later papers also; but because some people still believe in the ideas thus discarded we shall summarize the events that led up to the present study-references and reviews are given by Chitty (1960), Newson & Chitty (1962), Barnett (1964) and Krebs (1964). An assumption that is essential to the whole argument is that these studies are concerned with a single phenomenon, i.e. that the population changes are not mere changes in numbers but are associated with diagnostic events. These other events include variations in mean adult body weight, differences in survival rates between juveniles and adults, and between males and females, together with such less constant features as a tendency for fluctuations to recur every 4 years and to be synchronous with those in neighbouring populations. Given a recognizable class of events and enough comparable instances we can eliminate as not sufficient all factors which are sometimes present when the phenomenon is absent, and as not necessary all factors which are absent when the phenomenon is present. (One does not, of course, reach the absurd conclusion that factors so eliminated play no part in producing numerical differences of other kinds.) Prior to 1959 the more obvious explanations had been rejected for reasons explained by Elton (1942) and subsequent workers. On the positive side it was known that: (a) populations were qualitatively different at different stages of abundance; (b) declines continued for one or more generations after peak densities had been passed; (c) individuals from rapidly declining populations survived well in captivity; and (d) some but not all of these individuals reached high body weights in captivity, whereas none did in the field. The present hypothesis is consistent with these findings and, though not known to be true, has the merit of being highly testable, since falsifying instances can be looked for in other species (Chitty 1964, 1965). As shown in the following account it also offers a possible explanation for otherwise puzzling changes in survival. The nearest alternative explanation is that of Christian & Davis (1964), who believe that there are 'endocrine mechanisms which have the prolonged effects necessary to * Present address: Department of Zoology, University of British Columbia, Vancouver 8, B.C., Canada.

Cytochemical evidence for the nature of herpes simplex inclusion bodies.

The experiments reported below were designed to test the notion that viral inclusion bodies represent virus colonies and that the inclusion bodies undergo a phase of rapid increase of virus material (and of the enzymatic activities with which it may be associated) followed by a phase of decline. The work was based on the assumption that virus particles of most animal virus diseases contain DNP (desoxyribonucleoproteins). Herpetic inclusion bodies, in different stages of their development, have accordingly been examined by cytochemical methods for their DNP content and for selected enzymatic activities.