Use of tree rings to study the effect of climate change on trembling aspen in Québec

In this paper, we present a new approach, based on a mixed model procedure, to quantify the tree‐ring‐based growth‐climate relationship of trembling aspen along a latitudinal gradient from 46 to 54 °N in eastern Canada. This approach allows breaking down the growth response into general intersite and local climatic responses, and analyzing variations of absolute ring width as well as interannual variations in tree growth. The final model also integrates nonclimatic variables such as soil characteristics and the occurrence of insect outbreaks into the growth predictions. Tree level random effects on growth were important as intercepts but were nonsignificant for the climatic variables, indicating that a single climate–growth relationship was justified in our case. The response of tree growth to climate showed, however, a strong dependence on the spatial scale at which the analysis was performed. Intersite variations in tree growth were mostly dependent on variations in the thermal heat sum, a variable that showed low interannual and high intersite variation. When variation for a single site was analyzed, other variables showed up to be important while the heat sum was unimportant. Finally, future growth under six different climate change scenarios was simulated in order to study the potential impact of climate change. Results suggest only moderate growth increases in the northern portion of the gradient and a growth decrease in the southern portion under future climatic conditions.     

Soil carbon stocks,deforestation and land‐cover changes in the Western Ghats biodiversity hotspot (India)

Habitat loss and soil organic carbon (SOC) stock variations linked to land‐cover change were estimated over two decades in the most densely populated biodiversity hotspot in the world, in order to assess the possible influence of conservation practices on the protection of SOC. For a study area of 88 484 km², 70% of which lie inside the Western Ghats Biodiversity Hotspot (WGBH), land‐cover maps for two dates (1977, 1999) were built from various data sources including remote sensing images and ecological forest maps. SOC stocks were calculated from climatic parameters, altitude, physiography, rock type, soil type and land‐cover, with a modelling approach used in predictive learning and based on Multiple Additive Regression Tree. The model was trained on 361 soil profiles data, and applied to estimate SOC stocks from predictor variables using a Geographical Information System (GIS). Comparison of 1977 and 1999 land‐cover maps showed 628 km² of dense forests habitat loss (6%), corresponding to an annual deforestation rate of 0.44%. This was found consistent with other studies carried out in other parts of the WGBH, but not with FAO figures showing an increase in forest area. This could be explained by the different forest definitions used, based on ecological classification in the former, and on percentage tree cover in the latter. Unexpectedly, our results showed that despite ongoing deforestation, overall SOC stock was maintained (～0.43 Pg). But a closer examination of spatial differences showed that soil carbon losses in deforested areas were compensated by sequestration elsewhere, mainly in recent plantations and newly irrigated croplands. This suggests that more carbon sequestration in soils could be achieved in the future through appropriate wasteland management. It is also expected that increasing concerns about biodiversity loss will favour more conservation and reinforce the already prevailing protective measures, thus further maintaining C stocks.     

HIV-1 Vpu disarms natural killer cells

Natural killer (NK)-cell killing of virus-infected cells is regulated in part by the engagement of activation and coactivation receptors. In this issue of Cell Host & Microbe, Shah et?al. (2010) demonstrate that HIV-1 protects infected cells from NK-cell-mediated killing by hindering NK-cell degranulation through downmodulation of NTB-A coactivation receptor ligands by the Vpu accessory protein.     

A pivotal role for CXCL12 signaling in HPV-mediated transformation of keratinocytes: clues to understanding HPV-pathogenesis in WHIM syndrome

The WHIM syndrome, which features high susceptibility to human papillomavirus (HPV) infection, is a rare immunodeficiency associated with autosomal dominant heterozygous mutations of the CXCR4 chemokine receptor. CXCL12 and its receptors, CXCR4 and CXCR7, are linked to tumorigenesis, and we reported that abnormal expression of CXCL12 in epidermal keratinocytes correlates with HPV infection. However, the HPV-related pathologies observed in WHIM patients remain mechanistically unexplained. We show that keratinocytes immortalized by oncogenic HPV16 or HPV18 upregulate CXCL12 and its receptors in a manner dependent upon expression of the viral proteins E6 and E7. Autocrine signaling activated by CXCL12-engagement of its receptors controls motility and survival of the infected cells. Strikingly, expression of a WHIM syndrome-related gain-of-function CXCR4 mutant confers transforming capacity to HPV18-immortalized keratinocytes. These results establish a pivotal role for CXCL12 signaling in HPV-mediated transformation and provide a mechanistic basis for understanding HPV pathogenesis in WHIM syndrome.     

Why do some species in arid lands increase under grazing? Mechanisms that favour increased abundance of Maireana pyramidata in overgrazed chenopod shrublands of South Australia

While the abundance of some plant species decreases under high grazing intensity, others become more abundant. Release from competition by decreaser species contributes to this pattern in mesic systems, but this may not be the case in xeric systems where competition may be less intense. Here we examine three mechanisms that may be involved: (i) increased recruitment and growth because of soil changes produced by grazing, for example, increased soil nutrient availability through dung accumulation; (ii) increased recruitment favoured by the breaking up of the lichen crust; and (iii) reduced competition because of the decline of decreaser species. We used field and glasshouse experiments to determine the possible contribution of these mechanisms to the increase of the chenopod Maireana pyramidata around a watering point in a chenopod shrubland of South Australia. There was no evidence of nutrient accumulation close to the watering point, and while seedlings of M. pyramidata responded to nutrient addition, their growth was the same in soil collected from areas with different grazing intensity. While a broken lichen crust increased the emergence of both M. pyramidata and the decreaser Atriplex vesicaria, the effect was larger for the former. We found no competition between seedlings of the two species or between juveniles of A. vesicaria and seedlings of M. pyramidata in glasshouse experiments. Adult plants of both A. vesicaria and M. pyramidata produced similar growth reduction in seedlings of M. pyramidata. Furthermore, a field removal experiment failed to detect any competitive effect of A. vesicaria on M. pyramidata. Our data indicate that the disintegration of the soil crust by grazer activities can be a major factor controlling floristic changes in overgrazed rangelands. These results imply that factors that control establishment may be more important than competition in shaping shrub population dynamics in these systems. Ground surface itself can affect establishment opportunities, and this should be taken into account in management and restoration efforts in arid lands.     

Host infestation patterns of the massive liana Hydrangea serratifolia (Hydrangeaceae) in a Chilean temperate rainforest

As competition from lianas reduces fitness of host trees, lianas could influence community composition and structure if potential host species differ in susceptibility to infestation. We quantified infestation frequencies of Chilean temperate rainforest tree species by the massive liana Hydrangea serratifolia (H. et A.) F. Phil (Hydrangeaceae), which climbs using adhesive adventitious roots, and examined relationships with host light requirements and stem diameter. We recorded presence or absence of H. serratifolia in a random sample of 515 trees ≥10 cm diameter. Fifty‐four per cent of trees were infested by at least one individual of H. serratifolia. Although there was significant interspecific variation in infestation frequency, this variation was not systematically related to light requirements of host tree species. Probability of infestation increased with diameter for most host tree species, and old trees were found to be infested by a wide range of liana size classes, including some stems <2 cm diameter. This evidence supports the proposal that lianas which attach by adhesive roots can colonize host stems of any size.     

Environmental controls and patterns of cumulative radial increment of evergreen tree species in montane,temperate rainforests of Chiloé Island,southern Chile

We investigated the local environmental controls on daily fluctuations of cumulative radial increment and cambial hydration of three dominant, evergreen tree species from montane, Coastal rainforests of Chiloé Island, Chile (42° 22′ S). During 2 years (1997–1998 and 1998–1999) we recorded hourly cumulative radial increments using electronic band dendrometers in the long‐lived conifer Fitzroya cupressoides (Cupressaceae), the evergreen broad‐leaved Nothofagus nitida (Nothofagaceae), and the narrow‐leaved conifer Podocarpus nubigena (Podocarpaceae). We also measured soil and cambial tissue hydration using capacitance sensors, together with air and soil temperature and rainfall during the period of the study. In addition, we collected cores of these tree species to evaluate how dendrometer measurements reflect annual tree ring width. One‐year long daily time series of cumulative radial increments suggests that radial growth of Fitzroya cupressoides was initiated slowly in early spring, with a maximum in early summer. Multiple regressions showed positive relations between daily precipitation and radial index (i.e. the difference in cumulative radial increment of two consecutive days) in the three species. According to path analysis there was a significant direct effect of changes in tree hydration on radial index of the three focal species. In emergent, pioneer species such as Nothofagus and Fitzroya, radial index was negatively affected by changes in maximum air temperature and photosynthetically active radiation, probably because of high evapotranspiration demand on warm sunny days. The shade‐tolerant species Podocarpus nubigena was positively affected by photosynthetically active radiation. Our diel scale findings support the use of tree ring widths for reconstructing past climate in these southern temperate forests and provide evidence that rainforest trees may be highly sensitive to future declines in rainfall and temperature increases during summer.     

What is “functional impairment”? Disentangling disability from clinical significance

The formulation of disability (or “functional impairment”) is currently not operationalized in either the ICD or the DSM. In the DSM system, making a diagnosis depends on a conjoint assessment of symptoms and functioning, whereas the ICD keeps the disability construct separate from the diagnosis of mental disorders. We need an internationally agreed conceptualization between ICD and DSM in terms of better operationalization of disease and disability components. No functioning or disability should appear as part of the threshold of the diagnosis in either system.     

Sex‐specific evolution of bite performance in Liolaemus lizards (Iguania: Liolaemidae): the battle of the sexes

Although differential selective pressures on males and females of the same species may result in sex‐specific evolutionary trajectories, comparative studies of adaptive radiations have largely neglected within‐species variation. In this study, we explore the potential effects of natural selection, sexual selection, or a combination of both, on bite performance in males and females of 19 species of Liolaemus lizards. More specifically, we study the evolution of bite performance, and compare evolutionary relationships between the variation in head morphology, bite performance, ecological variation and sexual dimorphism between males and females. Our results suggest that in male Liolaemus, the variation in bite force is at least partly explained by the variation in the degree of sexual dimorphism in head width (i.e. our estimate of the intensity of sexual selection), and neither bite force nor the morphological variables were correlated with diet (i.e. our proxy for natural selection). On the contrary, in females, the variation in bite force and head size can, to a certain extent, be explained by variation in diet. These results suggest that whereas in males, sexual selection seems to be operating on bite performance, in the case of females, natural selection seems to be the most likely and most important selective pressure driving the variation in head size. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 461–475.     

Genetic and morphological differentiation of the mangrove crab Perisesarma guttatum (Brachyura: Sesarmidae) along an East African latitudinal gradient

The genetic structure and morphometric differentiation of mangrove crab Perisesarma guttatum populations were examined among shelf connected locations along a latitudinal gradient on the East African coast. Over 2200 specimens were sampled from 23 mangrove sites for geometric morphometrics analysis. Population genetic analyses of mitochondrial cytochrome c oxidase subunit I (COI) DNA sequences were used to evaluate connectivity among populations. A total of 73 haplotypes were detected, and almost no haplotypes were found in common between two highly supported phylogeographic clades: southern Mozambique (Inhaca Island and Maputo Bay) and a northern clade that included north Mozambique, Tanzania and Kenya. These two clades were identified based on the species' populations pairwise genetic differentiation and geographical location. Φ_ST values were considerably high between the two clades, indicating the presence of significant population genetic structure between Kenya and South Mozambique. However, each clade was composed of genetically similar populations along the latitudinal gradient, and no significant population structure was found within each clade because the Φ_st values were not significant. The morphometric analysis corroborated the division into two clades (i.e. Inhaca Island/Maputo Bay and northern populations) and also detected less shape variation among populations that were few kilometres apart. The significant spatial genetic structuring between the southern and the northern populations of P. guttatum along the geographic gradient under study, combined with morphological differences, suggests that these populations may be considered as cryptic species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 28–46.