On head and body movements of flying flies

Head and body movements of flies (Musca domestica and Calliphora erythrocephala) have been studied during sustained flight. Two main points emerge from the analysis: a) Changes in body direction and head direction occur simultaneously in almost all cases. b) During visually guided flight active neck movements are initiated together and in the same direction of body movements. This does not hold in absence of a visual pattern (search). Implications of these findings with respect to the organization of the control system underlying head-body coordination in flies are briefly discussed.     

Ecophysiological investigations on lichens of the Negev desert

Summary Previous publications have reported on investigations of CO₂ exchange in the desert lichenRamalina maciformis both in its natural habitat in the Negev and in the laboratory. Utilizing laboratory data, net photosynthesis and dark respiration were expressed as mathematical functions of the most important environmental factors. Based on these relationships, a model is developed that allows one to predict CO₂ exchange of the plant. Input data are light intensity, temperature, and water content of the thallus, together with a measure of the rate of the seasonal change of photosynthetic and respiratory activity. The validity of the model is tested by comparing simulated daily courses of CO₂ uptake and release of the lichen with independent results of CO₂ exchange measurements conducted in the field during and after the condensation of dew. The sensitivity of the model is shown by simulating changes in the input data of temperature and water content of the lichen.This paper is dedicated to Dr. h.c. Oscar Klement on the occasion of his 80th birthday     

Modulation of intercellular adherens-type junctions and tyrosine phosphorylation of their components in RSV-transformed cultured chick lens cells.

Transformation of cultured chick lens epithelial cells with a temperature-sensitive mutant of Rous sarcoma virus (tsRSV) leads to radical changes in cell shape and interactions. When cultured at the restrictive temperature (42 degrees C), the transformed cells largely retained epithelial morphology and intercellular adherens junctions (AJ), whereas on switch to the permissive temperature (37 degrees C) they rapidly became fibroblastoid, their AJ deteriorated, and cell adhesion molecules (A-CAM) (N-cadherin) largely disappeared from intercellular contact sites. The microfilament system that was primarily associated with these junctions was markedly rearranged on shift to 37 degrees C and remained associated mainly with cell-substrate focal contacts. These apparent changes in intercellular AJ were not accompanied by significant alterations in the cellular content of several junction-associated molecules, including A-CAM, vinculin, and talin. Immunolabeling with phosphotyrosine-specific antibodies indicated that both cell-substrate and intercellular AJ were the major cellular targets for the pp60v-src tyrosine-specific protein kinase. It was further shown that intercellular AJ components serve as substrates to tyrosine kinases also in nontransformed lens cells, because the addition of a combination of vanadate and H2O2--which are potent inhibitors of protein tyrosine phosphatases--leads to a remarkable accumulation of immunoreactive phosphotyrosine-containing proteins in these junctions. This finding suggests that intercellular junctions are major sites of action of protein tyrosine kinases and that protein tyrosine phosphatases play a major role in the regulation of phosphotyrosine levels in AJ of both normal and RSV-transformed cells.     

Differential response to abiotic stress controls species distributions at biogeographic transition zones

Understanding range limits is critical to predicting species responses to climate change. Subtropical environments, where many species overlap at their range margins, are cooler, more light‐limited and variable than tropical environments. It is thus likely that species respond variably to these multi‐stressor regimes and that factors other than mean climatic conditions drive biodiversity patterns. Here, we tested these hypotheses for scleractinian corals at their high‐latitude range limits in eastern Australia and investigated the role of mean climatic conditions and of parameters linked to abiotic stress in explaining the distribution and abundance of different groups of species. We found that environmental drivers varied among taxa and were predominantly linked to abiotic stress. The distribution and abundance of tropical species and gradients in species richness (alpha diversity) and turnover (beta diversity) were best explained by light limitation, whereas minimum temperatures and temperature fluctuations best explained gradients in subtropical species, species nestedness and functional diversity. Variation in community structure (considering species composition and abundance) was most closely linked to the combined thermal and light regime. Our study demonstrates the role of abiotic stress in controlling the distribution of species towards their high‐latitude range limits and suggests that, at biogeographic transition zones, robust predictions of the impacts of climate change require approaches that account for various aspects of physiological stress and for species abundances and characteristics. These findings support the hypothesis that abiotic stress controls high‐latitude range limits and caution that projections solely based on mean temperature could underestimate species’ vulnerabilities to climate change.     

Mapping of distinct structural domains on microtubule-associated protein 2 by monoclonal antibodies

Monoclonal antibodies against microtubule-associated protein 2 (MAP2) were prepared and their specificity was verified by visualization of the antigens using the antibody overlay technique and by radioimmunoassay. MAP2 was cleaved by alpha-chymotrypsin to generate a series of high-molecular-mass fragments ranging between 270 and 140 kDa. The precursor-product relationship of these fragments was suggested from the rate of their appearance and from the analysis of the tryptic peptide map of each fragment. A group of monoclonal antibodies was found to react predominantly with the intact 270-kDa MAP2 molecule and a fragment having a mass of 240 kDa and to some extent with a 215-kDa fragment. Another group of monoclonal antibodies reacted with an antigenic determinant which was located on the 270-kDa molecule as well as on fragments as small as 140 kDa. None of the two groups of monoclonal antibodies reacted with the microtubule-binding domain of MAP2. These results suggest that one group of antibodies reacts with sites located at or dependent upon a terminal 60-kDa domain(s) distal to the microtubule-binding site of MAP2. The second group of antibodies, which can still bind to smaller proteolytic products, appear to be associated with the central region of the MAP2 molecule. Indirect immunofluorescence experiments with the antibody preparations indicated that at least some of the antigenic determinants are exposed when MAP2 is associated with microtubules in the cell body and neurite outgrowths of differentiated rat brain neuroblastoma B104 cells.     

HLA-DR+ CD38+ CD4+ T lymphocytes have elevated CCR5 expression and produce the majority of R5-tropic HIV-1 RNA in vivo

Percentages of activated T cells correlate with HIV-1 disease progression, but the underlying mechanisms are not fully understood. We hypothesized that HLA-DR(+) CD38(+) (DR(+) 38(+)) CD4(+) T cells produce the majority of HIV-1 due to elevated expression of CCR5 and CXCR4. In phytohemagglutinin (PHA)-stimulated CD8-depleted peripheral blood mononuclear cells (PBMC) infected with HIV-1 green fluorescent protein (GFP) reporter viruses, DR(-) 38(+) T cells constituted the majority of CCR5 (R5)-tropic (median, 62%) and CXCR4 (X4)-tropic HIV-1-producing cells (median, 61%), although cell surface CCR5 and CXCR4 were not elevated in this subset of cells. In lymph nodes from untreated individuals infected with R5-tropic HIV-1, percentages of CCR5(+) cells were elevated in DR(+) 38(+) CD4(+) T cells (median, 36.4%) compared to other CD4(+) T-cell subsets (median values of 5.7% for DR(-) 38(-) cells, 19.4% for DR(+) 38(-) cells, and 7.6% for DR(-) 38(+) cells; n = 18; P < 0.001). In sorted CD8(-) lymph node T cells, median HIV-1 RNA copies/10(5) cells was higher for DR(+) 38(+) cells (1.8 × 10(6)) than for DR(-) 38(-) (0.007 × 10(6)), DR(-) 38(+) (0.064 × 10(6)), and DR(+) 38(-) (0.18 × 10(6)) subsets (n = 8; P < 0.001 for all). After adjusting for percentages of subsets, a median of 87% of viral RNA was harbored by DR(+) 38(+) cells. Percentages of CCR5(+) CD4(+) T cells and concentrations of CCR5 molecules among subsets predicted HIV-1 RNA levels among CD8(-) DR/38 subsets (P < 0.001 for both). Median HIV-1 DNA copies/10(5) cells was higher in DR(+) 38(+) cells (5,360) than in the DR(-) 38(-) (906), DR(-) 38(+) (814), and DR(+) 38(-) (1,984) subsets (n = 7; P ≤ 0.031). Thus, DR(+) 38(+) CD4(+) T cells in lymph nodes have elevated CCR5 expression, are highly susceptible to infection with R5-tropic virus, and produce the majority of R5-tropic HIV-1. PBMC assays failed to recapitulate in vivo findings, suggesting limited utility. Strategies to reduce numbers of DR(+) 38(+) CD4(+) T cells may substantially inhibit HIV-1 replication.     

THE PONTIA DAPLIDICE-ED USA HYBRID ZONE IN NORTHWESTERN ITALY

The pierid butterflies Pontia daplidice and P. edusa, parapatrically distributed in southern Europe, have very similar morphologies and life histories, but show fixed differences at four allozyme markers. We sampled these allozymes in a 28-population transect north of Genoa in Italy, through the hybrid zone where these taxa meet. We used the numerical techniques developed for hybrid zone analysis to study the patterns of genetic differentiation and their underlying evolutionary causes. The hybrid zone is characterized by a very short and steep central region, flanked by broad tails of introgression extended up to 100 km in either direction. From mean two-locus disequilibium of D = 0.148 (maximum-likelihood two-unit support limits 0.139-0.153), and after accounting for minor differences in the center locations of the single-locus clines, which act to bias the dispersal estimate, we estimated a dispersal rate of σ = 4.4 (3.7-5.5) km/gen^1/2. The effective selection needed to maintain the steep central portion is strong, 0.47 < s? < 0.64, when combined over potential intrinsic (genetic background) and extrinsic (ecological) sources of selection. The clines in allozyme loci showed variation that was significantly different between the most divergent shapes, and the differences are attributable to different degrees of introgression on the edusa side of the zone. The average selection acting on individual allozyme loci was high at s_???e  1.5%, but because of the narrowness of the central region of the cline, we suspect that this estimate is somewhat biased by selection on loci closely linked to the allozyme markers. A common question for taxa that show fixed allozyme differences in parapatry is whether or not they are genetically isolated. A fairly general measure of genetic isolation across hybrid zones is the time, T, that it takes a neutral allele to cross the hybrid zone and recombine into the opposite genetic background, given by T = (β/σ)², where β is the barrier strength of the hybrid zone. Genetic isolation in the Pontia zone is weak, with T  25 generations for most allozyme markers. By this measure, populations of daplidice and edusa on opposite sides of the hybrid zone share more identical-by-descent alleles than do populations of phenotypically pure daplidice in, say, France and Morocco. Accordingly, we think it best for systematists to consider edusa as a well-marked subspecies of P. daplidice.