Vegetation types and patterns in Senegal based on multivariate analysis of field and NOAA-AVHRR satellite data

Abstract. Woody vegetation was studied in 44 sites in Senegal. Species composition and density were analysed with TWINSPAN and Canonical Correspondence Analysis; 16 vegetation types were defined. A supervised, multispectral and multitemporal classification of day and night, dry season NOAA-AVHRR imagery was used to identify their distribution with a classification accuracy ranging from 60–100%.     

Are Research Schools Necessary? Contrasting Models of 20th Century Research at Yale Led by Ross Granville Harrison, Grace E. Pickford and G. Evelyn Hutchinson

This paper compares and contrasts three groups that conducted biological research at Yale University during overlapping periods between 1910 and 1970. Yale University proved important as a site for this research. The leaders of these groups were Ross Granville Harrison, Grace E. Pickford, and G. Evelyn Hutchinson, and their members included both graduate students and more experienced scientists. All produced innovative research, including the opening of new subfields in embryology, endocrinology and ecology respectively, over a long period of time. Harrison's is shown to have been a classic research school; Pickford's and Hutchinson's were not. Pickford's group was successful in spite of her lack of department or institutional position or power. Hutchinson and his graduate and post-graduate students were extremely productive but in diverse areas of ecology. His group did not have one focused area of research or use one set of research tools. The paper concludes that new models for research groups are needed, especially for those, like Hutchinson's, that included much field research.     

Calcitriol Prevents RAD51 Loss and cGAS‐STING‐IFN Response Triggered by Progerin

Hutchinson Gilford progeria syndrome (HGPS) is a devastating accelerated aging disease caused by LMNA gene mutation. The truncated lamin A protein produced “progerin” has a dominant toxic effect in cells, causing disruption of nuclear architecture and chromatin structure, genomic instability, gene expression changes, oxidative stress, and premature senescence. It was previously shown that progerin‐induced genomic instability involves replication stress (RS), characterized by replication fork stalling and nuclease‐mediated degradation of stalled forks. RS is accompanied by activation of cGAS/STING cytosolic DNA sensing pathway and STAT1‐regulated interferon (IFN)‐like response. It is also found that calcitriol, the active hormonal form of vitamin D, rescues RS and represses the cGAS/STING/IFN cascade. Here, the mechanisms underlying RS in progerin‐expressing cells and the rescue by calcitriol are explored. It is found that progerin elicits a marked downregulation of RAD51, concomitant with increased levels of phosphorylated‐RPA, a marker of RS. Interestingly, calcitriol prevents RS and activation of the cGAS/STING/IFN response in part through maintenance of RAD51 levels in progerin‐expressing cells. Thus, loss of RAD51 is one of the consequences of progerin expression that can contribute to RS and activation of the IFN response. Stabilization of RAD51 helps explain the beneficial effects of calcitriol in these processes.     

Transient introduction of human telomerase mRNA improves hallmarks of progeria cells

Hutchinson–Gilford progeria syndrome (HGPS) is characterized by accelerated senescence due to a de novo mutation in the LMNA gene. The mutation produces an abnormal lamin A protein called progerin that lacks the splice site necessary to remove a farnesylated domain. Subsequently, progerin accumulates in the nuclear envelope, disrupting nuclear architecture, chromatin organization, and gene expression. These alterations are often associated with rapid telomere erosion and cellular aging. Here, we further characterize the cellular and molecular abnormalities in HGPS cells and report a significant reversal of some of these abnormalities by introduction of in vitro transcribed and purified human telomerase (hTERT) mRNA. There is intra‐individual heterogeneity of expression of telomere‐associated proteins DNA PKcs/Ku70/Ku80, with low‐expressing cells having shorter telomeres. In addition, the loss of the heterochromatin marker H3K9me3 in progeria is associated with accelerated telomere erosion. In HGPS cell lines characterized by short telomeres, transient transfections with hTERT mRNA increase telomere length, increase expression of telomere‐associated proteins, increase proliferative capacity and cellular lifespan, and reverse manifestations of cellular senescence as assessed by β‐galactosidase expression and secretion of inflammatory cytokines. Unexpectedly, mRNA hTERT also improves nuclear morphology. In combination with the farnesyltransferase inhibitor (FTI) lonafarnib, hTERT mRNA promotes HGPS cell proliferation. Our findings demonstrate transient expression of human telomerase in combination with FTIs could represent an improved therapeutic approach for HGPS.     

The regulatory roles of T4 and T8 subsets in tetanus toxoid-induced in vitro immunoglobulin production

A new mitogenic system for in vitro immunoglobulin production induced by tetanus toxoid is presented and the role of T4 and T8 subsets in tetanus toxoid-induced in vitro immunoglobulin production is investigated. Purified T, T4, T8, and B cells from normal individuals previously immunized but not boosted with tetanus toxoid were cultured in helper and suppressor assays and the number of immunoglobulin-secreting cells were enumerated after culture using a hemolytic plaque assay. The regulatory roles of T4 and T8 cells in this tetanus toxoid system were compared with the role of these subsets after pokeweed mitogen stimulation. Although most of the immunoglobulin produced in the tetanus toxoid system was polyclonal, there were differences in the time course, the magnitude of the responses, the radiosensitivity of the subsets, and optimal T- to B-cell ratios for immunoglobulin production which distinguish the tetanus toxoid and pokeweed mitogen systems.     

Litter fall and nutrient dynamics in a Nigerian rain forest seven years after a ground fire

Abstract. Seasonal litter fall and mineral element content (N, P, Ca, Mg, K) of regrowth forest communities at the base and on the slope of an inselberg in Ile-Ife, Nigeria, were studied 7 yr after a ground fire ravaged the forest. Litter fall (tha^?1 yr^?1) was 4.6 (total), 4.2 (leaf), 0.3 (small wood < 2.5 cm diameter) and 0.1 (reproductive parts: fruits and flowers) in the base community and 6.4 (total), 5.4 (leaf), 0.9 (small wood) and 0.1 (reproductive parts) in the slope community. There was significant monthly variation in litter fall in the two communities with lowest amount of litter recorded during the wettest months of the year (May - August) and the highest amount during the dry season. Significant monthly variation (P<0.05) in Ca, Mg and K concentration in leaf litter and for Mg (P < 0.01) in fruit litter occurred, with the lowest concentration recorded during the wettest months (May-August). In leaf and wood litter the order of mineral element concentration was Ca>N>K> Mg > P while in fruit litter it was N > K > Ca > Mg > P. Quantities of mineral element (kg ha^-1 yr¹) returned to the soil via litterfall were N: 66; P: 4; Ca: 97; Mg: 15; K: 45 in base forest, and N: 112; P: 5; Ca: 142; Mg: 20; K: 66 in slope forest. Through leaf litter >88.5% of these elements was returned into the two communities, through wood > 4.0% and through reproductive organs > 0.3%. The order of quantities of these elements returned in leaf and wood litter was Ca > N > K > Mg > P, in fruit litter N ～ K > Ca > Mg > P. Significant monthly variation in the amounts of the various elements returned were recorded in leaf litter, but not in wood and fruit litter. The lowest amount of various elements was returned during the wettest months (May-August) which coincided with the period of the lowest element concentration and litter fall.     

A test for spatial relationships between neighbouring plants in plots of heterogeneous plant density

Abstract. Maps of plant individuals in (x, y) coordinates (i.e. point patterns) are currently analysed through statistical methods assuming a homogeneous distribution of points, and thus a constant density within the study area. Such an assumption is seldom met at the scale of a field plot whilst delineating less heterogeneous subplots is not always easy or pertinent. In this paper we advocate local tests carried out in quadrats partitioning the plot and having a size objectively determined via a trade‐off between squared bias and variance. In each quadrat, the observed pattern of points is tested against complete spatial randomness (CSR) through a classical Monte‐Carlo approach and one of the usual statistics. Local tests yield maps of p‐values that are amenable to diversified subsequent analyses, such as computation of a variogram or comparison with co‐variates. Another possibility uses the frequency distribution of p‐values to test the whole point pattern against the null hypothesis of an inhomogeneous Poisson process. The method was demonstrated by considering computer‐generated inhomoge‐neous point patterns as well as maps of woody individuals in banded vegetation (tiger bush) in semi‐arid West Africa. Local tests proved able to properly depict spatial relationships between neighbours in spite of heterogeneity/clustering at larger scales. The method is also relevant to investigate interaction between density and spatial pattern in the presence of resource gradients.     

Relative effects of climate change, isolation and competition on body-size evolution in the Japanese field mouse, Apodemus argenteus

Aim This paper examines body size variation in both recent and Quaternary populations of the Japanese field mouse Apodemus argenteus in order to assess the relative effects on body size of climate change, isolation and competitive interactions with its congeneric A. speciosus. Both temporal (since the Last Glacial Maximum, LGM) and spatial (over the Japanese archipelago) scales are considered. Location The small field mouse is widespread in Japan, and the specimens examined were collected from 10 localities on islands of widely differing area (from 4 km² to 230,510 km²) and at latitudes ranging from 30.3° N to 45.1° N. Methods The effects of geographical factors such as latitude and island area on the size variation of A. argenteus were investigated, using the lower incisor size. In addition, the size of some specimens from two Quaternary localities was compared with the size of the extant specimens. Evolutionary rates of size change since the LGM were calculated in darwins. Hutchinson size ratios were used to examine the pattern of variation of the size segregation between the two Japanese field mice, A. argenteus and A. speciosus, in relation to time and space. Results There was a negative relationship between size and latitude among living A. argenteus populations. In addition, there was no effect of island area on body size, especially at higher latitudes. At lower latitudes, A. argenteus were larger on smaller islands, although this trend was not statistically significant. Quaternary specimens of A. argenteus were smaller in size than their living representatives. The interspecific size ratio between the two Japanese Apodemus was larger on smaller islands and at higher latitudes, and there has been a decrease in the size ratio between the two Apodemus since the LGM. Lastly, in accordance with the theory of character displacement, the small A. argenteus was larger in allopatry than in sympatry, whereas the large A. speciosus was smaller in allopatry than in sympatry. Main conclusions These results indicate that A. argenteus does not conform to Bergmann's rule or to the island rule. The variation in size for the small Japanese field mouse at both spatial and temporal scales may be related to climate change, with an additional effect of competition with the large field mouse, especially on smaller islands. The size convergence between the two Japanese Apodemus observed over the last 21,000 years may be explained by the diminution of available food resources due to the reduction of land mass areas following the LGM. It may also be the result of an evolution towards an optimal body size; a hypothesis previously proposed to explain the evolution of body size in island mammals. Lastly, the evolutionary rates of body size calculated for A. argenteus since the LGM are typical of rates calculated for other Quaternary mainland mammals, thus suggesting that the evolution in this species was not particularly rapid, as is often thought for island mammals.     

Differences between banded thickets (tiger bush) at two sites in West Africa

Abstract. This paper deals with the influence of edaphic conditions on the spatial structure of banded thickets or tiger bush (brousse tigrée). It is based on two sites in West Africa, with similar climatic conditions but located on contrasting substrates. The spatial structure was described with standardized characteristics including thicket spacing, thicket/inter‐thicket contrast, upslope/downslope asymmetry and species zonation throughout the vegetation band. Recruitment and senescence features of woody stands were emphasized in order to understand current dynamics. Data were collected on transects oriented perpendicular to the contours and so to the thickets as well. A standardized analytical procedure was applied to data from both sites to ensure consistent and thorough delineation of thickets. The overall periodicity of thickets, the woody flora and the dominant species Combretum micranthum were similar at the two sites. However, thicket spacing, thicket/inter‐thicket contrast and upslope/downslope floristic asymmetry of the thickets were higher in the less favourable site. Also seedlings were less abundant, with a greater dependence on pre‐existing thickets. Not all banded vegetation systems show sharp contrasts and are strongly asymmetric, since such characteristics are likely to be reinforced by adverse environmental conditions. As a consequence, current dynamics may be more diverse than expected. Quantified inter‐site comparisons can greatly help to classify African banded vegetation systems and to discuss potential dynamic outcomes.