Evidence for association of chromosomal form and development time from complex clines and geographic races in the grasshopper Caledia captiva (Orthoptera: Acridadae)

Evidence for an association between chromosomal form and development time in the grasshopper Caledia captiva (F.) was obtained through comparison of two geographic taxa and analysis of a complex latitudinal cline within one of the taxa. Northern populations of the Moreton taxon possess a metacentric genome and are slow-developing. In contrast, the Torresian taxon, distributed throughout northern, coastal Australia, a region of pronounced seasonality in rainfall, and southern populations of the Moreton taxon, which inhabit a region of pronounced seasonality in temperature, Soth have an acrocentric genome and are fast-developing. The convergence of chromosomal form and development time between Torresian and southern Moreton populations appears to be driven by convergence in life history. Seasonality limits grasshoppers to one generation per year and favours fast development. The transition between relatively acrocentric southern Moreton populations and relatively metacentric northern Moreton populations is gradual but not monotonic. Instead, a shift to a bivoltine life history in the middle of the transect occurs and is associated with shifts in both development time and chromosomal form. These results imply an adaptive role for chromosomal form, although the causative link between chromosomal variation and variation in development time remains to be established.     

Influence of excess nitrogen deposition on a white spruce (Picea glauca) stand in southern Alaska

Excess N delivered to forest ecosystems has been shown to alterinternal ecosystem biogeochemical cycles, contribute to forestdecline, and negatively affect the health of receiving waters.In the vicinity of the Nikiski Industrial Complex, Kenai Peninsula,Alaska, there has been recent concern about the influence ofNH3 emissions that have occurred for over twodecades on local soils and vegetation. The study site representedan opportunity to examine the influence of elevated N depositionon a northern coniferous ecosystem in an area with a low backgroundof N deposition. Overstory vegetation in the area is dominated bywhite spruce (Picea glauca Moench. Voss) and paper birch (Betulapapyrifera Marsh.). Mortality of both species has occurred adjacent(<2 km) to the industrial complex. Average annual Ndeposition rates ranged from 0.7 to 21.0 kg ha-1 y-1in the area, with the highest rates closest to the complex. Sulfatedeposition at the site was low. Due to the high NH3deposition, precipitation near the complex was less acidic thanprecipitation in general; bulk precipitation pH ranged from 5.51to 7.06. Within 1.80 km of the facility there was an increase inKCl- and resin- extractable soil NH4+ andNO3- in the O horizon, and a decrease in soil pHcompared to soils further from the facility. Spruce near thefacility had chlorotic foliage and thinning crowns, higherconcentrations of N, but lower foliar Ca and Mg. Foliar Mglevels approached deficiency levels, but foliar Ca was wellabove reported deficiency levels at all sites. Both Mg:N andCa:N ratios, however, suggest nutrient imbalances in the highN deposition zone. Canopy death and fertilization by N appearto have encouraged growth of the native bluejoint grass. Thepresence of elevated NO3- in O horizon soilextracts, elevated NO3- in resin bags placed betweenthe O and E horizons, and nutritional imbalances in the foliagesuggest that N saturation may be occurring in soils adjacent to thefacility.     

Mapping of the genes for rat endothelin receptor type A (ETAR) and type B (ETBR) to chromosomes 19 and 15 respectively

Chromosomal assignments of the genes for rat endothelin receptor type A (ET_AR) and type B (ET_BR) were performed by analysing somatic cell hybrid DNAs with the polymerase chain reaction (PCR) using primers specific for rat ET_AR and ET_BR genes. The genes for ET_AR and ET_BR were assigned to rat chromosomes 19 and 15 respectively.     

Effect of cryopreservation on the frequency of chromosomal abnormalities and sex ratio in human sperm

The effects of cryopreservation on the frequency and type of chromosomal abnormalities in human sperm were investigated. Employing a technique that enables direct visualization of human sperm chromosomes following in vitro penetration of hamster oocytes, sperm samples from 10 normal men were examined before and after freezing in liquid nitrogen. A total of 1,960 sperm karyotypes were analyzed, 1,132 before freezing and 828 after freezing. There was no significant difference in the frequency of structural chromosomal anomalies (10.5% prefreeze vs. 8.5% postfreeze), but there was a significant decrease in the frequency of numerical abnormalities (5.2% prefreeze vs. 3.0% postfreeze). However, there was a large excess of hypohaploid complements compared with hyperhaploid complements, suggesting that the hypohaploid complements were caused by technical artefact. A conservative estimate of aneuploidy, derived by doubling the hyperhaploid frequencies, did not differ before (0.4%) and after (0.4%) freezing. There was no evidence for interdonor variability in response to sperm cryopreservation for total chromosomal abnormalities, structural abnormalities, and sex ratios. The sex ratios were also not affected by cryopreservation and did not differ significantly from the theoretical 50%. It is concluded that cryopreservation does not affect the frequencies of chromosomal abnormalities or alter the sex ratio in human sperm, provided that an adequate cryoprotective buffer and freezing system is employed.     

Partition of Genetic Variance for Sub-Populations

The variance between and within backcrosses of two populations is partitioned on the base of (I) multinomially distributed numbers of effects of specific chromosomes taking (II) recombination into account and on the base of (III) normally distributed sums of gene effects. The method of estimation makes use of a specific structure of data with backcross parents taken from different generations of random mating reproduction of crosses between the two populations.     

The Propensity Score in the Analysis of Therapeutic Studies

A method for reducing bias in observational studies proposed by ROSENBAUM and RUBIN (1983, 1984) is discussed with a view to applications in studies designed to compare two treatments. The data are stratified on a function of covariates, called the propensity score. The propensity score is the conditional probability of receiving a specific treatment given a set of observed covariates. Some insight into how this kind of stratification works in theory is given. Within strata, the treatment groups are comparable with respect to the distribution of covariates incorporated into the score, hence a corresponding stratified analysis can be considered. The method is different from other strategies in that the sub-classes are not intended to comprise patients with similar prognosis. In practice, estimated grouped scores are used. Problems concerning the interpretation of the proposed stratified approach are illustrated by an application in oncology, and the results are compared to those from an analysis in a standard regression model.     

Measures of Imbalance for Higher Order Designs

In this paper we consider a generalization of the measures of imbalance given by AHRENS and PINCUS (1981) considering the cases: m-fold hierarchical model and m-way classification model in order to quantify the degree of imbalance in an unbalanced design. These measures of imbalance satisfy the same properties as those for the one-way classification model.