Antarctic Futures: An Assessment of Climate-Driven Changes in Ecosystem Structure, Function, and Service Provisioning in the Southern Ocean

In this article, we analyze the impacts of climate change on Antarctic marine ecosystems. Observations demonstrate large-scale changes in the physical variables and circulation of the Southern Ocean driven by warming, stratospheric ozone depletion, and a positive Southern Annular Mode. Alterations in the physical environment are driving change through all levels of Antarctic marine food webs, which differ regionally. The distributions of key species, such as Antarctic krill, are also changing. Differential responses among predators reflect differences in species ecology. The impacts of climate change on Antarctic biodiversity will likely vary for different communities and depend on species range. Coastal communities and those of sub-Antarctic islands, especially range-restricted endemic communities, will likely suffer the greatest negative consequences of climate change. Simultaneously, ecosystem services in the Southern Ocean will likely increase. Such decoupling of ecosystem services and endemic species will require consideration in the management of human activities such as fishing in Antarctic marine ecosystems.

Global biogeographic patterns in bipolar moss species

A bipolar disjunction is an extreme, yet common, biogeographic pattern in non-vascular plants, yet its underlying mechanisms (vicariance or long-distance dispersal), origin and timing remain poorly understood. Here, combining a large-scale population dataset and multiple dating analyses, we examine the biogeography of four bipolar Polytrichales mosses, common to the Holarctic (temperate and polar Northern Hemisphere regions) and the Antarctic region (Antarctic, sub-Antarctic, southern South America) and other Southern Hemisphere (SH) regions. Our data reveal contrasting patterns, for three species were of Holarctic origin, with subsequent dispersal to the SH, while one, currently a particularly common species in the Holarctic (Polytrichum juniperinum), diversified in the Antarctic region and from here colonized both the Holarctic and other SH regions. Our findings suggest long-distance dispersal as the driver of bipolar disjunctions. We find such inter-hemispheric dispersals are rare, occurring on multi-million-year timescales. High-altitude tropical populations did not act as trans-equatorial 'stepping-stones', but rather were derived from later dispersal events. All arrivals to the Antarctic region occurred well before the Last Glacial Maximum and previous glaciations, suggesting that, despite the harsh climate during these past glacial maxima, plants have had a much longer presence in this southern region than previously thought.

Verbal memory declines more in female patients with Parkinson's disease: the importance of gender-corrected normative data

BACKGROUND

Data on gender-specific profiles of cognitive functions in patients with Parkinson's disease (PD) are rare and inconsistent, and possible disease-confounding factors have been insufficiently considered.

METHOD

The LANDSCAPE study on cognition in PD enrolled 656 PD patients (267 without cognitive impairment, 66% male; 292 with mild cognitive impairment, 69% male; 97 with PD dementia, 69% male). Raw values and age-, education-, and gender-corrected Z scores of a neuropsychological test battery (CERAD-Plus) were compared between genders. Motor symptoms, disease duration, l-dopa equivalent daily dose, depression - and additionally age and education for the raw value analysis - were taken as covariates.

RESULTS

Raw-score analysis replicated results of previous studies in that female PD patients were superior in verbal memory (word list learning, p = 0.02; recall, p = 0.03), while men outperformed women in visuoconstruction (p = 0.002) and figural memory (p = 0.005). In contrast, gender-corrected Z scores showed that men were superior in verbal memory (word list learning, p = 0.02; recall, p = 0.02; recognition, p = 0.04), while no difference was found for visuospatial tests. This picture could be observed both in the overall analysis of PD patients as well as in a differentiated group analysis.

CONCLUSIONS

Normative data corrected for gender and other sociodemographic variables are relevant, since they may elucidate a markedly different cognitive profile compared to raw scores. Our study also suggests that verbal memory decline is stronger in women than in men with PD. Future studies are needed to replicate these findings, examine the progression of gender-specific cognitive decline in PD and define different underlying mechanisms of this dysfunction.

Cenozoic climate change and diversification on the continental shelf and slope: evolution of gastropod diversity in the family Solariellidae (Trochoidea)

Recent expeditions have revealed high levels of biodiversity in the tropical deep-sea, yet little is known about the age or origin of this biodiversity, and large-scale molecular studies are still few in number. In this study, we had access to the largest number of solariellid gastropods ever collected for molecular studies, including many rare and unusual taxa. We used a Bayesian chronogram of these deep-sea gastropods (1) to test the hypothesis that deep-water communities arose onshore, (2) to determine whether Antarctica acted as a source of diversity for deep-water communities elsewhere and (3) to determine how factors like global climate change have affected evolution on the continental slope. We show that although fossil data suggest that solariellid gastropods likely arose in a shallow, tropical environment, interpretation of the molecular data is equivocal with respect to the origin of the group. On the other hand, the molecular data clearly show that Antarctic species sampled represent a recent invasion, rather than a relictual ancestral lineage. We also show that an abrupt period of global warming during the Palaeocene Eocene Thermal Maximum (PETM) leaves no molecular record of change in diversification rate in solariellids and that the group radiated before the PETM. Conversely, there is a substantial, although not significant increase in the rate of diversification of a major clade approximately 33.7 Mya, coinciding with a period of global cooling at the Eocene-Oligocene transition. Increased nutrients made available by contemporaneous changes to erosion, ocean circulation, tectonic events and upwelling may explain increased diversification, suggesting that food availability may have been a factor limiting exploitation of deep-sea habitats. Tectonic events that shaped diversification in reef-associated taxa and deep-water squat lobsters in central Indo-West Pacific were also probably important in the evolution of solariellids during the Oligo-Miocene.

The biodiversity of the deep Southern Ocean benthos

Our knowledge of the biodiversity of the Southern Ocean (SO) deep benthos is scarce. In this review, we describe the general biodiversity patterns of meio-, macro- and megafaunal taxa, based on historical and recent expeditions, and against the background of the geological events and phylogenetic relationships that have influenced the biodiversity and evolution of the investigated taxa. The relationship of the fauna to environmental parameters, such as water depth, sediment type, food availability and carbonate solubility, as well as species interrelationships, probably have shaped present-day biodiversity patterns as much as evolution. However, different taxa exhibit different large-scale biodiversity and biogeographic patterns. Moreover, there is rarely any clear relationship of biodiversity pattern with depth, latitude or environmental parameters, such as sediment composition or grain size. Similarities and differences between the SO biodiversity and biodiversity of global oceans are outlined. The high percentage (often more than 90%) of new species in almost all taxa, as well as the high degree of endemism of many groups, may reflect undersampling of the area, and it is likely to decrease as more information is gathered about SO deep-sea biodiversity by future expeditions. Indeed, among certain taxa such as the Foraminifera, close links at the species level are already apparent between deep Weddell Sea faunas and those from similar depths in the North Atlantic and Arctic. With regard to the vertical zonation from the shelf edge into deep water, biodiversity patterns among some taxa in the SO might differ from those in other deep-sea areas, due to the deep Antarctic shelf and the evolution of eurybathy in many species, as well as to deep-water production that can fuel the SO deep sea with freshly produced organic matter derived not only from phytoplankton, but also from ice algae.

Molecular contacts between nebulin and actin: cross-linking of nebulin modules to the N-terminus of actin

Nebulin, a giant actin binding protein, coextends with actin and is thought to form a composite thin filament in the skeletal muscle sarcomere. To understand the molecular interactions between nebulin and actin, we have applied chemical cross-linking techniques to define molecular contacts between actin and ND8, a two-module nebulin fragment that promotes actin polymerization and inhibits depolymerization by binding to both G- and F-actin. The formation of a 1:1 complex with a dissociation constant of 4.9 microM between ND8 and G-actin was demonstrated by fluorescence titration of dansyl-ND8 with G-actin. Treatment with a zero-length cross-linker, l-ethyl-3-[3-(dimethylamino) propyl]carbodiimide (EDC), cross-linked the ND8-G-actin complex covalently without impairing actin's ability to polymerize. End-labeling Western blot and sequence and mass analyses of purified conjugated peptides revealed the cross-linking between lysine 5 of ND8 and the two N-terminal acidic residues of G-actin. Similarly, we have shown by end-labeling that cross-linking of ND8 to F-actin occurred at the N-terminus of actin protomer. The binding of nebulin to the N-terminus of actin is likely to be significant in its ability to affect actin polymerization. Furthermore, the association of nebulin modules with the actin N-terminus in subdomain 1 supports the hypothesis that nebulin wraps around the outer edges of actin filaments where Sl, tropomyosin, and several actin binding proteins are known to interact.

Stoichiometry of subunits and heme content of hemoglobin from the earthworm Lumbricus terrestris

The extracellular hemoglobin (Hb) of the earthworm, Lumbricus terrestris, has four major O2-binding chains, a, b, c (forming a disulfide-linked trimer), and d ("monomer"). Additional structural chains, "linkers," are required for the assembly of the approximately 200-polypeptide molecule. The proportion of linker chains had been reported to be one-third of the total mass on the basis of densitometry of Coomassie Blue-stained SDS-gels. Reverse-phase high performance liquid chromatography (HPLC), however, gave 16.3% linkers on the basis of both 220-nm absorbance and amino acid analysis (Ownby, D. W., Zhu, H., Schneider, K., Beavis, R. C., Chait, B. C., and Riggs, A. F. (1993) J. Biol. Chem. 268, 13539-13547). The subunit proportions have now been redetermined by SDS capillary electrophoresis as a test of the HPLC results. The electrophoresis, monitored at 214 nm, avoided the use of Coomassie Blue and provided results identical with those obtained by HPLC. Capillary electrophoresis monitored at both 214 and 415 nm was used to show that linker chains do not bind heme. Heme content has been found to be 2.9% by determination of hemin, amino acid analysis and dry weight. Measurement of the rate of hemin loss from oxidized L. terrestris Hb shows that high rates of loss can account for values of heme content significantly below 2.9% (or 0.26% iron).

The GTP-binding peptide of beta-tubulin. Localization by direct photoaffinity labeling and comparison with nucleotide-binding proteins

The binding site of the guanine moiety of GTP on beta-tubulin was located within the peptide consisting of residues 63-77, AILVDLEPGTMDSVR. The result was obtained using direct photoaffinity labeling, peptide sequencing, and limited proteolysis. Peptides were identified by end-labeling with a monoclonal antibody against beta-tubulin whose epitope was located between 3 and 4 kDa from the C terminus. The sequence of the GTP-binding site is consistent with predictions from other GTP-binding proteins such as elongation factor Tu or ras p21.