Ecological Disadvantage Research Articles

Trubnikov G.A. Chronic bronchitis in conditions of ecological disadvantage. - Astrakhan, Astrakhan State Medical Academy Press, 1996, 180 p.

The monograph of Professor G.A. Trubnikov, Astrakhan Medical Academy, as well as his act speech, which was pronounced at the ceremonial meeting of the Academy on 20.11.1996 on the occasion of the 78th anniversary of the famous medical institution, reveals the basis of the new direction of the clinic of internal diseases - pulmonology ecology.

The Effects of Neighborhood Disadvantage on Adolescent Development

A conceptual framework for studying emerging neighborhood effects on individual development is presented, identifying specific mechanisms and processes by which neighborhood disadvantage influences adolescent developmental outcomes. Using path analyses, the authors test the hypothesis that these organizational and cultural features of neighborhoods mediate the effects of ecological disadvantage on adolescent development and behavior; they then estimate the unique contribution of neighborhood effects on development using hierarchical linear modeling (HLM). The study involves samples of neighborhoods from two sites, Chicago and Denver. The analyses support the hypothesis that the effects of ecological disadvantage are mediated by specific organizational and cultural features of the neighborhood. The unique influence of neighborhood effects is relatively small, but in most cases these effects account for a substantial part of the variance explained by the HLM model.

High incidence of malocclusion in an isolated population of the red fox (Vulpes vulpes) in the Netherlands

Out of 72 fox skulls (Vulpes vulpes L.) collected in the North Holland Dune Reserve (NHD) between 1979 and 1985, 12 (16.7%) skulls showed a pronounced protrusion of the maxillary incisors over the mandibular incisors. Comparison of dimensions of affected and normal skulls revealed that this protrusion was the effect of a shortening of the front part of the mandibles. The mode of inheritance of this aberration is thought to be under recessive monogenetic control. This was deduced from the family relations between individual foxes radio‐collared or earmarked during five years of ecological research, and from the clear bimodal distribution in mandible length. The high incidence of the aberration can be explained by the history of the fox population in the NHD. Before 1968 the NHD was not inhabited by foxes as a result of its ecological isolation. It is rumoured that in that year four cubs, probably from one litter, were set free. It is believed, therefore, that the present population has originated from a small and isolated gene pool. Compared to normal foxes, affected animals are likely to be at an ecological disadvantage. Hence it is expected that the incidence of the aberration will decline in the future, since the population density reached a stable maximum around 1982 and the selective forces against the aberration will presumably be stronger now than during the phase of rapid population growth.

Environmental influences on mountain gorilla time budgets.

Data on the time budgets of mountain gorillas (Gorilla gorilla beringei) were collected during field studies in the Virunga Volcanoes region of Rwanda and Zaire. Focal sampling was used to determine the proportion of time that individuals of different age/sex classes spent in several mutually exclusive activity states. The gorillas spent the majority of daylight hours feeding; most of the rest of the day was devoted to resting, with little time spent moving or engaged in social activity. The time budget varied among the different subhabitats used by the gorillas, and the gorillas satisfied subsistence needs more quickly when in areas where food was more abundant and/or of better nutritional quality. Silverbacks spent more time feeding than all other age/sex classes, but age/sex class differences were not great. All age/sex classes responded to variability in habitat quality in similar fashion. Unlike the case for many other primates, there was no significant seasonal variation in time budgets. There was a direct relationship between group size and time spent feeding, although variation in relation to group size was lower than that in relation to variation in habitat quality. These results are consistent with the relationship of feeding time to body size in primates. They are also consistent, with other evidence that social foraging entails a cost to gorilla females, but that this cost is low in comparison to those faced by many other primates. Permanent association with males apparently offers little ecological disadvantage to females, who are likely to be more than compensated by mutualistic benefits.

Die ökologische Benachteiligung südamerikanischer feuchttropischer Tieflands- gegenüber Gebirgslebensräumen

Die ökologische Benachteiligung südamerikanischer feuchttropischer Tieflands- gegenüber Gebirgslebensräumen

Acquired cycloheximide resistance inNeurospora crassa andSclerotium rolfsii

Acquired resistance to the antibiotic cycloheximide developed byNeurospora crassa andSclerotium rolfsii was studied. Both the fungi gained certain level of tolerance to the antibiotic just after a single exposure and by serial transfers could adapt to the several-fold initial inhibitory dosage. Cycloheximide-resistance in both the cases was not a stable characteristic and was lost gradually on serial transfers in fungicide-free media. The resistant strains of both the fungi showed poor growth and decreased sporulation or sclerotia formation in fungicide-free media.Sclerotium rolfsii developed cross-resistance to Difolatan but not to Polyoxin-D, Hinosan and Bayleton. The cycloheximide-resistance inSclerotium rolfsii was probably due to the conversion of cycloheximide into isocycloheximide which is a less toxic structural analog, as revealed by thin layer chromatographic studies of culture filtrates of resistant and sensitive strains. The resistant strain ofSclerotium rolfsii retained its pathogenicity to tomato, mustard and chilli seedlings. However, the loss of sclerotia forming capacity and the instability of the acquired resistance trait may prove to be of ecological disadvantage to the resistant strain.

Plasmid-mediated susceptibility to intestinal microbial antagonisms in Escherichia coli.

Self-transferable plasmid pIP1100 confers to Escherichia coli an unusually high level of resistance (1 to 2 mg/ml) to erythromycin by production of an erythromycin esterase. The effect of pIP1100 on the destiny of E. coli strains in the intestines of gnotobiotic mice was studied. In germfree mice, pIP1100 was efficiently transferred to a plasmid-free E. coli recipient. Intestinal counts of the donor, the recipient, and the transconjugants were greater than 8.5 log CFU/g of feces. When erythromycin was added to the diet of the mice, counts of the plasmid-bearing strains were only slightly lowered and partial inactivation of erythromycin was observed in the feces. Transfer of pIP1100 also occurred in human-flora-associated mice. In this model all the E. coli strains were subject to microbial antagonisms caused by the anaerobic components of the flora. However, strains harboring pIP1100 were strongly inhibited (less than 2.5 log CFU/g of feces), whereas their plasmid-free counterparts persisted at much higher population levels (greater than 5.2 log CFU/g of feces). The ecological disadvantage conferred by pIP1100 to E. coli when a complex human flora was concomitantly present in the intestine of the mice persisted during erythromycin administration. These results provide an explanation for the low incidence of isolation of highly erythromycin-resistant E. coli strains despite the extensive use of the antibiotic.

A microecological approach to larch canker biology

In a comprehensive study of the microflora of larch cankers, it was shown that Trichoscyphella willkommii (Hart.) Nannf. was the only fungus consistently associated with canker extension tissue. A total of eighty-three other fungal species was isolated from 208 cankers and a sequential colonization of cankers by these fungi was demonstrated. The spread within the canker of other species coincided with disappearance of T. willkommii. The four most frequently isolated canker invading fungi, Cryptosporiopsis abietina, Zalerion arboricola, Tympanis laricina and a Phialophora sp. were shown to be able to replace T. willkommii in bark blocks, while Z. arboricola and Phialophora sp. brought about the death of its hyphae on agar plates. Inoculation of the four species either into branch lesions in which T. willkommii was established, or jointly with T. willkommii into new incisions, showed that lesion extension was markedly decreased in their presence. It was suggested that the natural healing of larch cankers is largely initiated because T. wilkommii is placed at an ecological disadvantage through having to compete with other fungi.

Development of the nitrogen-fixing system in legumes

It seems probable that Rhizobium was originally a free-living soil organism with the ability to produce nitrogenase, and this enzyme was the source of the nodular nitrogenase. Where the genetic information for leghaemoglobin formation came from is much more a matter for speculation. In the course of natural selection for competence to survive and multiply in soil as a saprophyte between legume-sheltered phases, nitrogen fixation probably became an ecological disadvantage to Rhizobium in its earlier form. Complete repression of the nitrogenase by a system which today is only derepressed by particular compounds in the legume is unlikely, mainly because constitutive mutants would be expected and have not apparently been found. It appears quite likely that part of the genetic information for the nitrogenase system became “banked”, as it were, with the plant. As a direct result of this transfer, the two partners became dependent on their symbiosis for the production of nitrogenase. The mechanism of the return to the bacteroid of the necessary information or its products can only be guessed at in the light of very meagre information. Mechanisms dependent on DNA transfer, either as a chromosome modification or as an episomal addition, are complicated because the added information must be eliminated from each cell which acquires it. On the other hand, transmission of mRNA to the bacterial ribosomes, or of a ready-made protein or part thereof, appears far more probable. Complementation between protein parts synthesized by the plant and by the bacterium could explain the degrees of effectiveness found in symbioses of one plant with several bacterial strains, or of one bacterial strain with several different plants. Many of the possible mechanisms considered here can be examined experimentally. The existence of episomal DNA should be readily detected, protein differences between Rhizobium from laboratory culture and its corresponding bacteroid forms can be explored, and the use of two bacterial strains with two legume hosts may indicate the controlling system for the various enzymatic components of nitrogenases.