Development of the deep‐sea viviparous quill worm Leptoecia vivipara (Hyalinoeciinae,Onuphidae, Annelida)

Development of Leptoecia vivipara, a brooding deep‐sea onuphid polychaete with a circum‐Antarctic distribution, was studied using light microscopy, scanning and transmission electron microscopy, and histology. All specimens examined were brooding viviparous females or juveniles; no male gametes were detected. Anterior segments of juvenile and adult worms bore paired compact ovaries with clusters of vitellogenic oocytes. In adults, the mid‐body region formed a chamber containing up to 12 offspring at different stages of development, from oocyte to 13 chaetigers. Mature oocytes freely floated in the coelomic fluid, while embryos and juveniles were enclosed in peritoneal envelopes. Chaetal replacement in juveniles and the morphology of the provisional maxillae are described. Leptoecia vivipara is argued to be a progenetic species with juvenile‐like external morphology and accelerated sexual maturation. These traits may have arisen as adaptations to epibenthic life in a high‐latitude deep‐sea environment affected by seasonal pulses of organic matter.     

Reactive oxygen species and the Antarctic macroalgal wound response

Reactive oxygen species (ROS) are commonly produced by algal, vascular plant, and animal cells involved in the innate immune response as cellular signals promoting defense and healing and/or as a direct defense against invading pathogens. The production of reactive species in macroalgae upon injury, however, is largely uncharacterized. In this study, we surveyed 13 species of macroalgae from the Western Antarctic Peninsula and show that the release of strong oxidants is common after macroalgal wounding. Most species released strong oxidants within 1 min of wounding and/or showed cellular accumulation of strong oxidants over an hour post‐wounding. Exogenous catalase was used to show that hydrogen peroxide was a component of immediate oxidant release in one of five species, but was not responsible for the entire oxidative wound response as is common in vascular plants. The other component(s) of the oxidant cocktail released upon wounding are unknown. We were unable to detect protein nitration in extracts of four oxidant‐producing species flash frozen 30 s after wounding, but a role for reactive nitrogen species such as peroxynitrite cannot be completely ruled out. Two species showed evidence for the production of a catalase‐activated oxidant, a mechanism previously known only from the laboratory and from the synthetic drug isoniazid used to kill the human pathogen Mycobacterium tuberculosis. The rhodophyte Palmaria decipiens, which released strong oxidants after wounding, also produced strong oxidants upon grazing by a sympatric amphipod, suggesting that oxidants are involved in the response to grazing.     

Chemical mediation of mutualistic interactions between macroalgae and mesograzers structure unique coastal communities along the western Antarctic Peninsula

Hard bottom communities along the western Antarctic Peninsula region are dominated by thick macroalgal forests, which support high densities of mesograzers, particularly amphipods, and also numerous gastropods. The macroalgae are chemically defended from consumption by the mesograzers and other herbivores and they provide the mesograzers a chemically defended refuge from predation by omnivorous fish. The macroalgae benefit in return because the mesograzers remove epiphytic algae from them. Since these two assemblages are major components of the community, this can be viewed as a community‐wide mutualism. Most subcomponents of these interactions have also been documented in lower latitude communities and the similarities and differences between the communities in Antarctica and in other regions are discussed.     

Influence of reproductive output on divorce rates in polar seabirds

The high occurrence of social monogamy in birds has led to questions about partner fidelity, or the perennial nature of monogamy from one breeding season to another. Despite the evolutionary advantages of partner fidelity, divorce occurs among 95% of bird species. We aimed to describe patterns of divorce and partner fidelity in five seabird species breeding in Arctic and Antarctic regions and investigated the influence of breeding status on pair bond maintenance. For four out of the five species considered, we observed low divorce rates (respectively 1.9%, 3.3%, 2.5%, and 0.0% for Brünnich''s guillemot, glaucous gull, Antarctic petrel, and south polar skua), while the divorce rate was much higher (19.1%) for the black‐legged kittiwake. For kittiwakes, the divorce rate was lower for pairs that managed to raise their chick to 15 days of age, while the effect of breeding success on divorce in the four other species could not be tested due to the rareness of divorce events. Our results emphasize the potentially large temporal (interannual) variations that should be taken into account in understanding divorce and partner fidelity in seabirds.     

Microbial mats of twenty-six lakes from Potter Peninsula,King George Island,Antarctica

The taxonomic composition and ecology of microbial mats were investigated in 26 lentic environments of Potter Peninsula (King George Island, Antarctica) during the summer of 1995/96. These have different limnological characteristics according to the location of the basins. Among the 139 algal taxa registered, 10 are new records for Antarctica. Bacillariophyceae was the dominant class in terms of species richness, followed by the Cyanobacteria and Chlorophyceae. TWINSPAN classification was used to describe six epilithic algal assemblages; Canonical Correspondence Analysis ordination showed that soluble reactive phosphorus, phytoplanktonic chlorophyll a concentration and conductivity were the main sources for the variation in the data.     

Microbiota within the perennial ice cover of Lake Vida, Antarctica

Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.     

海南和台湾蕨类植物多样性及其大陆性特征

海南和台湾是我国南部和东部两个最重要的大陆性岛屿,具有极为丰富的蕨类植物多样性。特有现象揭示着植物区系和植物多样性的历史,间断分布揭示着与邻近或相关植物区系的联系;特别是在岛屿地区,这种现象和意义尤其明显。海南有蕨类植物区系55科、135属、466种,其中特有种有32种,台湾蕨类植物区系57科、142属、599种,其中特有种达66种。在海南与台湾两地,有共有属104属,共有种仅有176种。台湾海峡出现始于晚白垩世,持续至第四纪;琼州海峡出现于早第四纪,因此,两地的特有现象远少于种子植物(台湾有801种,海南有501种),原因与蕨类植物具有更广的散布性相关,而且在被子植物中起重要作用的物种生物学障碍(机制)在蕨类是缺乏的;形态学的、生殖生物学特征导致蕨类植物具有较缓慢的物种演化历史和较低的灭绝率(Smith,1972)。海南和台湾蕨类植物区系的比较还表明,地理位置和海拔高度对植物区系的物种分化和物种多样性产生了极大的影响。     

Responses of Antarctic Iridaea cordata (Rhodophyta) tetraspores exposed to ultraviolet radiation

In Antarctica ozone depletion is highest during spring, coinciding with the reproduction of many seaweed species. Propagules are the life-stage of an alga most susceptible to environmental perturbations. Therefore, fertile thalli of Iridaea cordata (Turner) Bory (Rhodophyta) were collected in the eulittoral of King George Island (Antarctica) to examine spore susceptibility to ultraviolet radiation (UVR). In the laboratory, freshly released tetraspores were exposed to photosynthetically active radiation (PAR) (400–700 nm), PAR+UV-A (320–700 nm) or PAR+UV-A+UV-B (280–700 nm). Photosynthetic efficiency was measured during 1–8 h of exposure and after 48 h of recovery. Additionally, mycosporine-like amino acids (MAAs) and DNA damage were determined. Saturating irradiance of photosynthesis of freshly released tetraspores was 57 µmol photons m⁻² s⁻¹. Exposure to increasing fluence of PAR reduced photosynthetic efficiency. UVR further decreased the photosynthetic efficiencies of the tetraspores but spores were able to recover completely after UVR exposure and 2 days post-cultivation under low PAR. DNA damage was minimal and lesions were effectively repaired under photoreactivating light. Concentrations of the MAAs shinorine and palythine were higher in tetraspores treated with UVR than in spores only exposed to PAR. Generally, the tetraspores show a good UV tolerance. This flexible response of the tetraspores of this species to changing radiation conditions enables the alga to grow along a considerable depth gradient from the sublittoral to the eulittoral where they can be exposed to enhanced UVBR under conditions of stratospheric ozone depletion.     

DGGE fingerprinting of bacteria in soils from eight ecologically different sites around Casey Station,Antarctica

Bacterial community structures in soils collected from eight sites around Casey Station, Antarctica, were investigated using denaturing gradient gel electrophoresis (DGGE) of amplified 16S rRNA gene fragments. Higher bacterial diversity was found in soils from protected or relatively low human-impacted sites in comparison to highly impacted sites. However, the highest diversity was detected in samples from Wilkes Tip, a former waste disposal site that has been undisturbed for the last 50 years. Comparison of community structure based on non-metric multidimensional scaling plots revealed that all sites, except the hydrocarbon-contaminated (oil spill) site, were clustered with a 45% similarity. A total of 23 partial 16S rRNA gene sequences were obtained from the excised DGGE bands, with the majority of the sequences closely related to those of the Cytophaga–Flexibacter–Bacteroides group. No significant correlation was established between environmental variables, including soil pH, electrical conductivity, carbon, nitrogen, water content and heavy metals, with bacterial diversity across the eight study sites.