Chironomidae (Diptera) of peatlands in northwestern Ontario, Canada

Eighty-four species of Chironomidae were collected, using emergence traps, from three poor fens located in the Experimental Lakes Area (ELA) of northwestern Ontario. Of these, 37 were considered to be true peatland fauna. The majority (23) of the peatland species are new North American or Canadian records and, of these, 10 are previously undescribed. Numbers m⁻² yr⁻¹ emerging from the fens were similar to neighbouring lakes but biomass (mg) m⁻² yr⁻¹ emerging was much less, indicating the small average size of the fen chironomids. Emergence began in early May and was virtually completed by late July-early August in all three years of the study. Most of the emergence occurred early in the season. Eight species accounted for ≥90% of the emergence. Five of these, Gymnometriocnemus (R.) acigus Saeth., Doithrix villosa Saeth. and Subl., Pseudorthocladius (s.s.) destitutus Saeth. and Subl., P. (s.s.) curtistylus (Goetgh.), and Paramerina nr. smithae (Subl.) had univoltine life cycles and relatively stichronous emergences. Pseudosmittia forcipata (Goetgh.) was bivoltine, and Limnophyes minimus (Meig.) and Smittia nr. nudipennis Geotgh. had protracted emergence periods that made voltinism difficult to determine. Characteristic features of the chironomid fauna of peatlands at ELA are discussed. The general applicability of these features to peatlands, and needs for further research in these neglected but extensive Canadian habitats are considered.     

Effects of spring and autumn fires on the composition of Chionochloa rigida tussock grassland,New Zealand

Two areas of Chionochloa rigida tussock grassland on Flagstaff Hill were burnt in autumn and spring 1976, respectively. Plant species cover and frequency were recorded in 1977 and 1985. Initially, plant cover and frequency were lower, and the area of bare ground was greater, on the autumn burnt site. After nine years, cover and frequency values were similar for most species, and bare ground was rare, on both sites. Over this period, recovery in size of indigenous tussock-forming physiognomic dominants resulted in suppression of intertussock sub-shrubs, herbs and grasses that were initially favoured by reduction of competition after fire. Plant species most tolerant of fire have features that protect the meristem, for instance an underground perennating organ or dense tillering.     

Analysis of a tissue-specific enhancer: ARF6 regulates adipogenic gene expression.

The molecular basis of adipocyte-specific gene expression is not well understood. We have previously identified a 518-bp enhancer from the adipocyte P2 gene that stimulates adipose-specific gene expression in both cultured cells and transgenic mice. In this analysis of the enhancer, we have defined and characterized a 122-bp DNA fragment that directs differentiation-dependent gene expression in cultured preadipocytes and adipocytes. Several cis-acting elements have been identified and shown by mutational analysis to be important for full enhancer activity. One pair of sequences, ARE2 and ARE4, binds a nuclear factor (ARF2) present in extracts derived from many cell types. Multiple copies of these elements stimulate gene expression from a minimal promoter in preadipocytes, adipocytes, and several other cultured cell lines. A second pair of elements, ARE6 and ARE7, binds a separate factor (ARF6) that is detected only in nuclear extracts derived from adipocytes. The ability of multimers of ARE6 or ARE7 to stimulate promoter activity is strictly adipocyte specific. Mutations in the ARE6 sequence greatly reduce the activity of the 518-bp enhancer. These data demonstrate that several cis- and trans-acting components contribute to the activity of the adipocyte P2 enhancer and suggest that ARF6, a novel differentiation-dependent factor, may be a key regulator of adipogenic gene expression.     

Antigenic mapping of a human λ light chain: Correlation with three dimensional structure

Although the amino acid sequence and three-dimensional structure of human immunoglobulin light chains have been known for more than 15 years, the location of antigenic markers characteristic of chains has not been determined. Here, we use a set of synthetic overlapping peptides to completely model the sequence of the chain Mcg and test these for the binding or rabbit and goat antisera specific for chain determinants. We assess peptide contributions to -antigenic reactivity and also to identify a portion of C-region where conformational factors contribute to the antigenicity. Specific determinants occur both in the constant and variable (first and third framework) domains of the molecule. The fourth framework of the variable region, a segment specified by the joining gene, is also recognized and cross-reacts antigenically with the homologous region of T cell receptor chains. Major specific determinants are localized in the N- and C-terminal segments, which are linear and devoid of major conformational folding. Other segments that are strongly antigenic, such as the third framework of the V region (residue 78–93) and a segment of the constant region (residues 177–192), show strong conformational dependence in antigenicity.     

The effect of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus

Synopsis The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l^–1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg 0₂l^–1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg Oz l^–1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.     

The evolution of human chromosome 21: evidence from in situ hybridization in marsupials and a monotreme.

We have mapped five human chromosome 21 (HSA 21) markers in marsupials and a monotreme, two major groups of mammals that diverged from eutherians 130-150 and 150-170 million years before present (MYrBP), respectively. We have found that these genes map to two distinct autosomal sites, one containing SOD1/CBR/BCEI and the other containing ETS2/INFAR, in the marsupials Macropus eugenii and Sminthopsis macroura (which belong to orders that diverged 40-80 MYrBP), as well as in the monotreme Ornithorhynchus anatinus (the platypus). Since marsupials and monotremes diverged independently from eutherians, these data suggest that HSA 21 genes were originally located in two separate autosomal blocks. In another Sminthopsis species, SOD1 is linked to TRF (a marker on HSA 3q), suggesting that the ancestral SOD1/CBR/BCEI region also included HSA 3 markers. We suggest that these blocks became fused early in the eutherian evolution to form a HSA 3/21 chromosome, which has remained intact in artiodactyls, but has been independently disrupted in both the primate and rodent lineages.     

Statistical analysis of in situ hybridization data: Derivation and use of the Zmax test

There are many situations in which grain distributions resulting from in situ hybridization of radioactively labeled probes to unique genes should be subjected to a statistical analysis. However, the problems posed by analysis of in situ hybridization data are not straightforward, and no completely satisfying method is currently available. We have developed a procedure in which the major and any number of minor site(s) of hybridization may be specifically located and the significance of each tested. This Z_max procedure first tests the overall distribution for departure from randomness and then identifies significantly overlabeled whole chromosomes (or chromosome arms or other large segments), a process that may be repeated to pinpoint significantly overlabeled regions within these chromosomes. We describe in detail the derivation of the Z_max statistic, present tables of significant Z_max levels, and show with examples how Z_max is used in tests of significance of in situ hybridization data.