Biogeographical modules and island roles: a comparison of Wallacea and the West Indies

Aim In order to advance our understanding of the assembly of communities on islands and to elucidate the function of different islands in creating regional and subregional distribution patterns, we identify island biogeographical roles on the basis of the distribution of the islands’ biota within the archipelago. We explore which island characteristics determine island biogeographical roles. Furthermore, we identify biogeographical subregions, termed modules. Location Wallacea in Indonesia, and the West Indies in the Caribbean Sea. Methods We use a network approach to detect island biogeographical roles and avian biogeographical modules. To designate the biogeographical role of an island, each island is assigned two coordinates, l and r. The position of an island in l–r space characterizes its role, namely as peripheral, connector, module hub, or network hub. Island characteristics are tested as predictors of l and r. Results Both Wallacea and the West Indies were found to be significantly modular and divided into four biogeographical modules. The four modules identified within Wallacea each contain all existing island roles, whereas no module in the West Indies represents all possible roles. Island area and elevation appeared to be the most important determinants of an island’s l score, while measurements of isolation essentially determined the r score. Main conclusions In both Wallacea and the West Indies, the geographic structuring into biogeographical modules corresponds well with our knowledge of past connections and contemporary factors. In both archipelagos, large, mountainous islands are identified as hubs and are thus responsible for faunal coherence within modules (module hubs) and across the entire archipelago (network hubs). We thus interpret these as source islands for the surrounding islands in their module (module hubs) or for the entire archipelago (network hubs). Islands positioned marginally in their module and distant from the mainland are identified as connectors or network hubs, behaving as sinks and stepping stones for dispersing species. Modularity and predictors of biogeographical roles are similar for Wallacea and the West Indies, whereas the build‐up of biogeographical modules and the assortment of roles depend on the spatial constellation of islands in each archipelago.     

Photoreactivation of pyrimidine dimers in the DNA of normal and xeroderma pigmentosum cells.

Photoproducts formed in the DNA of human cells irradiated with ultraviolet light (uv) were identified as cyclobuytl pyrimidine dimers by their chromatographic mobility, reversibility to monomers upon short wavelength uv irradiation, and comparison of the kinetics of this monomerization with that of authentic cis-syn thymine-thymine dimers prepared by irradiation of thymine in ice. The level of cellular photoreactivation of these dimers reflects the level of photoreactivating enzyme measured in cell extracts. Action spectra for cellular dimer photoreactivation in the xeroderma pigmentosum line XP12BE agree in range (300 nm to at least 577 nm) and maximum (near 400 nm) with that for photoreactivation by purified human photoreactivating enzyme. Normal human cells can also photoreactivate dimers in their DNA. The action spectrum for the cellular monomerization of dimers is similar to that for photoreactivation by the photoreactivating enzyme in extracts of normal human fibroblasts.     

Quantitative Caveats of Standard Immunohistochemical Procedures: Implications for Optical Disector�Cbased Designs

Immunohistochemistry is a ubiquitous technique in histology. Often, the goal of such studies is the quantification of some parameter associated with a particular antigen. When used correctly, the optical disector offers a statistically relevant approach to achieve this goal without bias from cell size, shape, or orientation. This three-dimensional counting probe is virtually embedded within the depth of the tissue section, thus avoiding sampling near the cut surfaces of the section, where cells are often lost during the cutting and subsequent processing steps. It follows that the probability that a cell could be immunolabeled should be equal throughout the section depth to correctly employ the optical disector. In this report, we demonstrate that parameters commonly used in immunohistochemistry often leave the middle of the section unlabeled. Furthermore, the degree of incomplete penetration varies among antibodies but can be overcome in some cases by extending the incubation time of the secondary antibody. The detection of this phenomenon in immunofluorescence preparations and the implications of these findings for quantitative stereology using the optical disector are discussed. (J Histochem Cytochem 58:577–584, 2010)     

The functional biogeography of species: biogeographical species roles of birds in Wallacea and the West Indies

Biogeographical systems can be analyzed as networks of species and geographical units. Within such a biogeographical network, individual species may differ fundamentally in their linkage pattern, and therefore hold different topological roles. To advance our understanding of the relationship between species traits and large‐scale species distribution patterns in archipelagos, we use a network approach to classify birds as one of four biogeographical species roles: peripherals, connectors, module hubs, and network hubs. These roles are based upon the position of species within the modular network of islands and species in Wallacea and the West Indies. We test whether species traits – including habitat requirements, altitudinal range‐span, feeding guild, trophic level, and body length – correlate with species roles. In both archipelagos, habitat requirements, altitudinal range‐span and body length show strong relations to species roles. In particular, species that occupy coastal‐ and open habitats, as well as habitat generalists, show higher proportions of connectors and network hubs and thus tend to span several biogeographical modules (i.e. subregions). Likewise, large body size and a wide altitudinal range‐span are related to a wide distribution on many islands and across several biogeographical modules. On the other hand, species restricted to interior forest are mainly characterized as peripherals and, thus, have narrow and localized distributions within biogeographical modules rather than across the archipelago‐wide network. These results suggest that the ecological amplitude of a species is highly related to its geographical distribution within and across bio geographical subregions and furthermore supports the idea that large‐scale species distributions relate to distributions at the local community level. We finally discuss how our biogeographical species roles may correspond to the stages of the taxon cycle and other prominent theories of species assembly.     

Differences in degradation lead to asynchronous expression of cyclin E1 and cyclin E2 in cancer cells

Cyclin E1 is expressed at the G₁/S phase transition of the cell cycle to drive the initiation of DNA replication and is degraded during S/G₂M. Deregulation of its periodic degradation is observed in cancer and is associated with increased proliferation and genomic instability. We identify that in cancer cells, unlike normal cells, the closely related protein cyclin E2 is expressed predominantly in S phase, concurrent with DNA replication. This occurs at least in part because the ubiquitin ligase component that is responsible for cyclin E1 downregulation in S phase, Fbw7, fails to effectively target cyclin E2 for proteosomal degradation. The distinct cell cycle expression of the two E-type cyclins in cancer cells has implications for their roles in genomic instability and proliferation and may explain their associations with different signatures of disease.     

Two distinct regions of calponin share common binding sites on actin resulting in different modes of calponin–actin interaction

Calponins are a small family of proteins that alter the interaction between actin and myosin II and mediate signal transduction. These proteins bind F-actin in a complex manner that depends on a variety of parameters such as stoichiometry and ionic strength. Calponin binds G-actin and F-actin, bundling the latter primarily through two distinct and adjacent binding sites (ABS1 and ABS2). Calponin binds other proteins that bind F-actin and considerable disagreements exist as to how calponin is located on the filament, especially in the presence of other proteins. A study (Galkin, V.E., Orlova, A., Fattoum, A., Walsh, M.P. and Egelman, E.H. (2006) J. Mol. Biol. 359, 478–485.), using EM single-particle reconstruction has shown that there may be four modes of interaction, but how these occur is not yet known. We report that two distinct regions of calponin are capable of binding some of the same sites on actin (such as 18–28 and 360–372 in subdomain 1). This accounts for the finding that calponin binds the filament with different apparent geometries. We suggest that the four modes of filament binding account for differences in stoichiometry and that these, in turn, arise from differential binding of the two calponin regions to actin. It is likely that the modes of binding are reciprocally influenced by other actin-binding proteins since members of the α-actinin group also adopt different actin-binding positions and bind actin principally through a domain that is similar to calponin's ABS1.     

Successful long-term cryopreservation of neonatal rat islet tissue

Neonatal rat pancreatic tissue was frozen to -196 degrees C using Me2SO as a cryoprotectant and a slow freezing rate to -70 degrees C followed by immersion in liquid nitrogen. Rapid thawing was used. Viability was demonstrated by successful transplantation to streptozotocin-induced diabetic recipients. Long-term preservation, up to 4 weeks, did not demonstrably affect viability. Cryopreservation techniques may afford a method for providing a diabetic recipient the opportunity to receive a large quantity of pooled islet tissue from well-matched donors.