Genetic and environmental determinants of dental occlusal variation in twins of different nationalities

We have compared 10 occlusal traits in 358 monozygous and dizygous twin pairs in 4 different samples and estimated genetic variances for these features. Variable and frequently nonsignificant genetic variance was noted across samples for incisal overbite and overjet, sagittal molar relationship, posterior crossbite, and rotations and displacements of anterior teeth. Heritability estimates (when appropriately calculated) were low in magnitude (0-40%) and erratic, emphasizing the importance of environmental influences on occlusal variation and the variability of apparent genetic determinants with respect to the environment or population in which they are measured.     

Stream flow and predation effects on the spatial dynamics of benthic invertebrates

Field experiments were carried out to determine the influence of predation and prey movements on the accumulation of prey in enclosures. Experimental enclosures permitted exchange of prey with the benthos, but not of the large, predatory larvae of the caddisfly, Plectrocnemia conspersa (Curtis). Unseasonally heavy rainfalls during the experiment resulted in high flows and enabled us to examine the effects of a major, abiotic disturbance on invertebrate spatial dynamics. Prey colonization rates of cages without predators were determined in nine 24 h periods. Colonization rates increased exponentially with flow and were species-specific, depending on dispersal behaviour. Prey accumulation and predator impacts were measured in cages, with and without P. conspersa larvae, placed in the stream for 1, 2 or 3 weeks. Prey densities in cages increased with exposure time, but increases were not gradual and depended on flow regime. Flow was reduced within cages and they accumulated large numbers of invertebrates during high discharge. Analogous, naturally occurring refugia in the stream channel could be important for the recovery of lotic communities after major disturbances. Overall, prey densities were lowest in cages with predators. For fast colonizers, predation effects were detectable early in the experiment, but quickly obscured thereafter by continuous exchange of prey. For slow colonists, predation effects were detectable later, but persisted longer. Consumption rates for P. conspersa varied with prey density and flow regime. We suggest that the spatial dynamics of benthic invertebrates, especially as they are influenced by stochastic events, are important in understanding and detecting predation effects in stream communities.     

Lignin peroxidase oxidation of Mn2+ in the presence of veratryl alcohol, malonic or oxalic acid, and oxygen

Veratryl alcohol (3,4-dimethoxybenzyl alcohol) appears to have multiple roles in lignin degradation by Phanerochaete chrysosporium. It is synthesized de novo by the fungus. It apparently induces expression of lignin peroxidase (LiP), and it protects LiP from inactivation by H2O2. In addition, veratryl alcohol has been shown to potentiate LiP oxidation of compounds that are not good LiP substrates. We have now observed the formation of Mn3+ in reaction mixtures containing LiP, Mn2+, veratryl alcohol, malonate buffer, H2O2, and O2. No Mn3+ was formed if veratryl alcohol or H2O2 was omitted. Mn3+ formation also showed an absolute requirement for oxygen, and oxygen consumption was observed in the reactions. This suggests involvement of active oxygen species. In experiments using oxalate (a metabolite of P. chrysosporium) instead of malonate, similar results were obtained. However, in this case, we detected (by ESR spin-trapping) the production of carbon dioxide anion radical (CO2.-) and perhydroxyl radical (.OOH) in reaction mixtures containing LiP, oxalate, veratryl alcohol, H2O2, and O2. Our data indicate the formation of oxalate radical, which decays to CO2 and CO2.-. The latter reacts with O2 to form O2.-, which then oxidizes Mn2+ to Mn3+. No radicals were detected in the absence of veratryl alcohol. These results indicate that LiP can indirectly oxidize Mn2+ and that veratryl alcohol is probably a radical mediator in this system.     

Occlusal variation in Australian aboriginals

Variation of dental occlusion around established norms has frequently been related to industrialized or modernized life habits. This tendency has been tested among samples (n = 48) of older (originally nomadic) and younger (settled and rationed) Australian Aboriginals. Although significant differences are found in incisor relation traits, tooth malalignment, and relative arch breadth, these are slight compared to some other studies of peoples undergoing one-generation dietary westernization. Reasons for this might relate to concomitantly subtle differences in diet or masticatory habits, genetic buffering, attrition gradient, tooth size, biased sampling according to tooth retention, or fluoride in water supplies.     

Concepts of occlusion: Australian evidence

Longitudinal studies of aboriginal children over a 20-year period have drawn attention to the wide variation in morphological features of the dentition and the way in which occlusal relationships develop. This paper summarizes some important determinants of optimal occlusal development, namely, tooth size relationships within and between dentitions, the patterns of alveolar growth, and tooth migrations during the transition from primary to permanent teeth and the nature of growth changes in the dental arches. Dental occlusion constantly changes throughout life in response to changing functional requirements. Observations limited to cross-sectional material provide an incomplete, and sometimes misleading, concept of dental occlusion and masticatory function.     

Induction of congenital anomalies in offspring of female mice exposed to varying doses of X-rays

Female mice were exposed to varying absorbed doses (108–504 rad) of X-rays and mated at different intervals after irradiation (1–7, 8–14, 15–21 and 22–28 days). Uterine contents were examined at late pregnancy in order to detect early fetal deaths (dominant lethality) and malformations in the live fetuses.Two trends were apparent from data on abnormal fetuses. At each weekly interval, the incidence of abnormalities tended to rise with increase in dose, and, at any given dose, the incidence tended to increase with time after irradiation. Dwarfism and exencephaly were the two most common malformations found.The changes in incidence of dominant lethality and of abnormal fetuses with time and with dose follow each other closely, the highest incidence for both being reached in week 3 (59±4.7% for dominant lethals and 12.5±3.1% for abnormal fetuses, after 504 rad) indicating increased radiosensitivity of less mature oocytes. These results parallel those obtained from known genetic effects reported by other workers and suggest that testing for incidence of congenital malformations among offspring of treated animals may prove a useful means of assessing genetic hazards of radiation of chemicals.     

On the defence strategy of Physa fontinalis (L.), a freshwater pulmonate snail

Summary Physa fontinalis (L.) gives a characteristic, chemically mediated escape response when stimulated by the majority of British leeches and flatworms. The snail responds rapidly and consistently to contact with all the molluskivorous leeches but also to three species which may be considered harmless. However, no response was given to Erpobdella octoculata, the most abundant and widespread of the harmless leeches. The flatworms generally evoked less strong reactions. The adaptive significance of the pattern of responsiveness is discussed. A weaker shell-shaking response is elicited in conspecifics and it is shown that this antisocial behaviour leads to a relatively spaced-out dispersion pattern. A possible adaptive advantage is the reduction of risk of detection by shell-crushing fish predators, to which the snails are otherwise extremely vulnerable.     

Combination v. sequential therapy with melphalan, 5-fluorouracil and methotrexate for advanced ovarian cancer.

The results of a national clinical trial to compare combination and sequential chemotherapy for stage III or IV ovarian cancer are reported. Of the 253 patients from 16 centres across Canada who were admitted to the trial 13 were excluded from the analysis. All the patients were observed for 2 to 5 years from entry into the trial. There were no differences in response to therapy or in survival between the patients treated with melphalan followed by 5-fluorouracil and then by methotrexate in high dosage and the patients treated with the same agents in combination. Patients with minimal residual disease after resection of stage III ovarian cancer had a good prognosis. Other favourable prognostic factors were age (less than 55 years), performance status (90% or 100% on the Karnofsky scale) and histologic grade of the tumour.