Is subarctic forest advance able to keep pace with climate change?

Recent climate warming and scenarios for further warming have led to expectations of rapid movement of ecological boundaries. Here we focus on the circumarctic forest-tundra ecotone (FTE), which represents an important bioclimatic zone with feedbacks from forest advance and corresponding tundra disappearance (up to 50% loss predicted this century) driving widespread ecological and climatic changes. We address FTE advance and climate history relations over the 20th century, using FTE response data from 151 sites across the circumarctic area and site-specific climate data. Specifically, we investigate spatial uniformity of FTE advance, statistical associations with 20th century climate trends, and whether advance rates match climate change velocities (CCVs). Study sites diverged into four regions (Eastern Canada; Central and Western Canada and Alaska; Siberia; and Western Eurasia) based on their climate history, although all were characterized by similar qualitative patterns of behaviour (with about half of the sites showing advancing behaviour). The main associations between climate trend variables and behaviour indicate the importance of precipitation rather than temperature for both qualitative and quantitative behaviours, and the importance of non-growing season as well as growing season months. Poleward latitudinal advance rates differed significantly among regions, being smallest in Eastern Canada (~10 m/year) and largest in Western Eurasia (~100 m/year). These rates were 1-2 orders of magnitude smaller than expected if vegetation distribution remained in equilibrium with climate. The many biotic and abiotic factors influencing FTE behaviour make poleward advance rates matching predicted 21st century CCVs (~103 -104  m/year) unlikely. The lack of empirical evidence for swift forest relocation and the discrepancy between CCV and FTE response contradict equilibrium model-based assumptions and warrant caution when assessing global-change-related biotic and abiotic implications, including land-atmosphere feedbacks and carbon sequestration.

Elastohydrodynamic Scaling Law for Heart Rates.

Animal hearts are soft shells that actively pump blood to oxygenate tissues. Here, we propose an allometric scaling law for the heart rate based on the idea of elastohydrodynamic resonance of a fluid-loaded soft active elastic shell that buckles and contracts axially when twisted periodically. We show that this picture is consistent with numerical simulations of soft cylindrical shells that twist-buckle while pumping a viscous fluid, yielding optimum ejection fractions of 35%-40% when driven resonantly. Our scaling law is consistent with experimental measurements of heart rates over 2 orders of magnitude, and provides a mechanistic basis for how metabolism scales with organism size. In addition to providing a physical rationale for the heart rate and metabolism of an organism, our results suggest a simple design principle for soft fluidic pumps.

Quantitative flow analysis of swimming dynamics with coherent Lagrangian vortices.

Undulatory swimmers flex their bodies to displace water, and in turn, the flow feeds back into the dynamics of the swimmer. At moderate Reynolds number, the resulting flow structures are characterized by unsteady separation and alternating vortices in the wake. We use the flow field from simulations of a two-dimensional, incompressible viscous flow of an undulatory, self-propelled swimmer and detect the coherent Lagrangian vortices in the wake to dissect the driving momentum transfer mechanisms. The detected material vortex boundary encloses a Lagrangian control volume that serves to track back the vortex fluid and record its circulation and momentum history. We consider two swimming modes: the C-start escape and steady anguilliform swimming. The backward advection of the coherent Lagrangian vortices elucidates the geometry of the vorticity field and allows for monitoring the gain and decay of circulation and momentum transfer in the flow field. For steady swimming, momentum oscillations of the fish can largely be attributed to the momentum exchange with the vortex fluid. For the C-start, an additionally defined jet fluid region turns out to balance the high momentum change of the fish during the rapid start.

Energy landscapes shape animal movement ecology.

The metabolic costs of animal movement have been studied extensively under laboratory conditions, although frequently these are a poor approximation of the costs of operating in the natural, heterogeneous environment. Construction of "energy landscapes," which relate animal locality to the cost of transport, can clarify whether, to what extent, and how movement properties are attributable to environmental heterogeneity. Although behavioral responses to aspects of the energy landscape are well documented in some fields (notably, the selection of tailwinds by aerial migrants) and scales (typically large), the principles of the energy landscape extend across habitat types and spatial scales. We provide a brief synthesis of the mechanisms by which environmentally driven changes in the cost of transport can modulate the behavioral ecology of animal movement in different media, develop example cost functions for movement in heterogeneous environments, present methods for visualizing these energy landscapes, and derive specific predictions of expected outcomes from individual- to population- and species-level processes. Animals modulate a suite of movement parameters (e.g., route, speed, timing of movement, and tortuosity) in relation to the energy landscape, with the nature of their response being related to the energy savings available. Overall, variation in movement costs influences the quality of habitat patches and causes nonrandom movement of individuals between them. This can provide spatial and/or temporal structure to a range of population- and species-level processes, ultimately including gene flow. Advances in animal-attached technology and geographic information systems are opening up new avenues for measuring and mapping energy landscapes that are likely to provide new insight into their influence in animal ecology.

Differential response of the homoploid hybrid species Iris nelsonii (Iridaceae) and its progenitors to abiotic habitat conditions.

PREMISE OF THE STUDY: Homoploid hybrid speciation involves the evolution of reproductive isolation between a hybrid lineage and its progenitors without a change in chromosome number. Ecological divergence presumably plays a large role in the stabilization of hybrid lineages, as all homoploid hybrid species described to date are reported to be ecologically divergent from their progenitors. However, the described ecological divergence in most systems is anecdotal and has not been empirically tested. METHODS: We assessed the vegetative response of Iris nelsonii, a homoploid hybrid species, and its three progenitor species, I. brevicaulis, I. fulva, and I. hexagona, to different abiotic conditions (i.e., varied sunlight availability and flooding conditions) that largely characterize the habitats of these four species in their natural habitats in Louisiana, USA. KEY RESULTS: The species differed in their responses to the water-level treatment for many of the response variables, including rhizome weight, ramet growth, plant height, and two principal components used to characterize the data. The species differed in their response to the light-level treatment for root allocation and the principal component used to characterize plant size. Iris nelsonii significantly differed from its progenitors, including its most closely related progenitor species, in response to many of the treatments. CONCLUSIONS: The differential response to abiotic habitat conditions of I. nelsonii suggests that this species is ecologically divergent from its progenitor species.

T cells compete for access to antigen-bearing antigen-presenting cells.

These studies tested whether antigenic competition between T cells occurs. We generated CD8(+) T cell responses in H-2(b) mice against the dominant ovalbumin epitope SIINFEKL (ova8) and subdominant epitope KRVVFDKL, using either vaccinia virus expressing ovalbumin (VV-ova) or peptide-pulsed dendritic cells. CD8(+) T cell responses were visualized by major histocompatibility complex class I-peptide tetrameric molecules. Transfer of transgenic T cells with high affinity for ova8 (OT1 T cells) completely inhibited the response of host antigen-specific T cells to either antigen, demonstrating that T cells can directly compete with each other for response to antigen. OT1 cells also inhibited CD8(+) T cell responses to an unrelated peptide, SIYRYGGL, providing it was presented on the same dendritic cells as ova8. These inhibitions were not due to a more rapid clearance of virus or antigen-presenting cells (APCs) by the OT1 cells. Rather, the inhibition was caused by competition for antigen and antigen-bearing cells, since it could be overcome by the injection of large numbers of antigen-pulsed dendritic cells. These results imply that common properties of T cell responses, such as epitope dominance and secondary response affinity maturation, are the result of competitive interactions between antigen-bearing APC and T cell subsets.

Evidence of DNA bending in transcription complexes imaged by scanning force microscopy.

Complexes of Escherichia coli RNA polymerase with DNA containing the lambda PL promoter have been deposited on mica and imaged in air with a scanning force microscope. The topographic images reveal the gross spatial relations of the polymerase relative to the DNA template. The DNA appears bent in open promoter complexes containing RNA polymerase bound to the promoter and appears more severely bent in elongation complexes in which RNA polymerase has synthesized a 15-nucleotide transcript. This difference could be related to the conformational changes that accompany the maturation of open promoter complexes into elongation complexes and suggests that formation of the elongation complex involves a considerable modification of the spatial relations between the polymerase and the DNA template.

HeLa cultures defined.

A list is presented of references to all known publications on properties which have served to relate strains of HeLa cells to each other as well as to indict other purported human cell lines as HeLa cell contaminants. Eleven additional cell lines not previously indicted are described. When they exhibit (i) type A (fast) mobility for glucose-6-phosphate dehydrogenase, (ii) phosphoglucomutase type 1 at locus 1 and locus 3, (iii) absence of a Y chromosome by fluorescent staining, and (iv) possession of a complex of trypsin-Giemsa banded marker chromosomes present in known HeLa cells, then cell substrates regardless of designation should be considered de facto strains of HeLa.

Inter- and intraspecies contamination of human breast tumor cell lines HBC and BrCa5 and other cell cultures.

It is shown that the two most recently reported cell lines derived from malignant human breast tissue, HBC and BrCa5 are, respectively, rat and HeLa cell contaminants. The incidence of inter- and intraspecies contamination among 279 cell cultures from 45 laboratories in an 18-month survey is also presented.

Banded marker chromosomes as indicators of intraspecies cellular contamination.

Chromosome banding revealed marked chromosomes characteristic of HeLa cells in cultures designated HEK, HEK/HRV, HBT-3, HBT-39B, MA160, and a strain of SA-4TxS-Husa(1). Ohter HeLa cell characteristics found were glucose-6-phosphate dehydrogense type A mobility and lack the Y chromosome. Conventional chromosome analysis and immunological and enzymatic technique serve to monitor species specificity and racial origin of the donor. Chromosome banding, however, can monitor intralinear karyotype peculiarity and its evolution during long-term cultivation.

Cross-contamination of cells in culture.

Lists are presented of references to all known publications describing cell properties that serve to characterize (i) known strains of HeLa and purported human cell lines indicated as HeLa contaminants, (ii) strains of human cell lines contaminated with human but non-HeLa cells, and (iii) strains of cells contaminated by cells from one or more other species. Frequencies of cell cross-contaminations are cited and references are presented to relatively simple techniques that could serve to detect such contamination.

Establishment of a cell line with associated Epstein-Barr-like virus from a leukemic orangutan.

An Epstein-Barr virus like herpesvirus has been isolated from a lymphoid cell line derived from an orangutan with spontaneous myelomonocytic leukemia. Herpesvirus has not previously been isolated from this species of higher ape.

In rats gestational iron deficiency does not change body fat or hepatic mitochondria in the aged offspring.

Mitochondrial dysfunction and resulting changes in adiposity have been observed in the offspring of animals fed a high fat (HF) diet. As iron is an important component of the mitochondria, we have studied the offspring of female rats fed complete (Con) or iron-deficient (FeD) rations for the duration of gestation to test for similar effects. The FeD offspring were ~12% smaller at weaning and remained so because of a persistent reduction in lean tissue mass. The offspring were fed a complete (stock) diet until 52 weeks of age after which some animals from each litter were fed a HF diet for a further 12 weeks. The HF diet increased body fat when compared with animals fed the stock diet, however, prenatal iron deficiency did not change the ratio of fat:lean in either the stock or HF diet groups. The HF diet caused triglyceride to accumulate in the liver, however, there was no effect of prenatal iron deficiency. The activity of the mitochondrial electron transport complexes was similar in all groups including those challenged with a HF diet. HF feeding increased the number of copies of mitochondrial DNA and the prevalence of the D-loop mutation, however, neither parameter was affected by prenatal iron deficiency. This study shows that the effects of prenatal iron deficiency differ from other models in that there is no persistent effect on hepatic mitochondria in aged animals exposed to an increased metabolic load.

Biophysical studies of T-cell receptors and their ligands.

Recently developed methodologies for the production of the soluble extracellular domains of alpha beta TCRs have allowed several biophysical characterizations. The thermodynamic and kinetic parameters associated with specific ligand interactions between the TCR and MHC-peptide complexes, as well as superantigens, are now being established. Crystallographic studies of isolated TCR fragments have yielded the structures of a V alpha domain and the two extracellular domains of a beta-chain. These investigations are beginning to allow a new visualization of antigen recognition and T-cell activation processes.

Genomic-scale analysis of gene expression in resting and activated T cells.

Recent advances in gene array technology and isolation of lymphocytes now allow comprehensive analysis of gene expression in many different types of T cells. So far only a few sets of results have been published. However it is already clear that these analyses provide accurate measurements of gene expression in T cells. This technology offers the first opportunity to examine global and subtle changes in gene expression in response to specific stimuli.

Oncofetal antigen-I: distribution in human tumors.

Oncofetal antigen-I (OFA-I) is a human tumor-associated fetal antigen that cross-reacts with fetal brain. The biological distribution of this antigen was studied in a variety of histologic types of human tumors and normal tissues. A total of 170 human tumors and 89 normal tissues obtained from biopsied and autopsied specimens were tested by immune adherence absorption assay. The antigen was most prevalent in malignant melanomas (82%); next in order of incidence were lung carcinomas (71%), sarcomas (61%), brain tumors (58%), and breast carcinomas (53%). However, OFA-I was found in only 15% of gastrointestinal tumors. The four hepatoma specimens tested were negative for OFA-I. OFA-I was also present in metastases and normal-appearing tissues of patients with OFA-I positive tumors but was not found in normal tissues from noncancer patients. These studies demonstrated that OFA-1 is widely distributed among human tumors. It appears to be more prevalent in tumors of ectodermal and mesodermal origin.

Tumorigenicity of human malignant lymphoblasts: comparative study with unmanipulated nude mice, antilymphocyte serum-treated nude mice, and X-irradiated nude mice.

The ability of unmanipulated, antilymphocyte serum (ALS)-treated, and X-irradiated nude BALB/c female mice (in their 13th backcross generation) to serve as hosts for 10 human lymphoblastoid cell lines as well as for peripheral blood lymphocytes from healthy humans was compared. The 10 lymphoma lines included 7 previously characterized and reported in the literature. Significant differences with respect to both latency period for tumor appearance and success rate for tumor transplantation were detected among the 3 experimental groups. The unmanipulated mice were poor recipients for lymphoma heterotranplants, and tumors were produced in only two instances. In contrast, 6 tumor lines were successfully transplanted in mice inoculated with ALS, and all 10 lines were successfully transplanted in X-irradiated recipients. Although tumors were readily produced in ALS-treated and X-irradiated mice, no gross or histologic evidence of focal or distant metastases was apparent. Human lymphoblastoid cells were recultured, essentially unchanged, from the heterotransplants from 6 of 7 tumors tested. Although the tumor line HT 1460, originally from a human lymphoma, was successfully transplanted in all 3 groups, only mouse cells were recultured. The use of X-irradiation, rather than ALS, to immunosuppress nude mice offers a more standardized method for heterotransplanting human tumor cell lines and permits ready comparisons between laboratories. Furthermore X-radiation permits transplantation and subsequent study of lymphoblastoid tumors that are otherwise difficult to successfully transplant in nude mice.

Epithelial cell cultures from normal and cancerous human tissues.

Thirty epithelial cell strains were isolated from human carcinomas and normal epithelial tissues by collagenase digestion and selective removal of fibroblasts with trypsin-Versene. Most strains were obtained from metastatic carcinomas or epithelia of the urinary and intestinal tracts. The success rate for growth of both neoplastic and normal tissues (excluding skin) was 38%. Six of these strains showed gross morphologic and chromosome changes typical of malignant cells. Nine resembled normal epithelium. The other 15 exhibited some degree of morphologic change from normal.

Human bladder carcinoma: characterization of two new tumor cell lines and search for tumor viruses.

Two newly established human bladder carcinoma cell lines, designated HT-1197 and HT-1376, were characterized. Cells of both cultures exhibited fine structural microvilli and tonofibrils indicative of their epithelial origin. In addition, desmosomes were also present in HT-1197. Marker chromosomes present in HT-1197 and HT-1376 distinguished these from each other and from other known human tumor cell lines. Both cultures grew in soft agar, induced fibrinolytic activity, and were tumorigenic in mice and hamsters. No type C or other virus expression was detected in these cell lines nor in other human urothelial tumors tested.

Two syngeneic cell lines from human breast tissue: the aneuploid mammary epithelial (Hs578T) and the diploid myoepithelial (Hs578Bst) cell lines.

We characterized two human cell lines (Hs578T and Hs578Bst), which provide several unique features that should be useful in the study of breast disease. Hs578T, derived from a carcinosarcoma, is epithelial in origin. Hs578Bst, established from normal tissue peripheral to the tumor, is myoepithelial in origin. This is the first report of companion cell lines, one malignant and one normal, established from the same organ.