Palynological indications of environmental changes during the Late Cretaceous–Eocene on the southern continental margin of Laurasia, Xizang (Tibet)

A palynostratigraphic and palynofacies study of a geological section at Cuojiangding in Zhongba County has provided a basis for discussing the palaeoenvironmental evolution of the southern continental margin of Laurasia in Xizang (Tibet) towards the end of the Cretaceous Period and during the Paleogene. It is the only record of fossil spores and pollen grains from collision- and convergence-related sediments close to the major Yarlung Zangbo Suture. Deposits of the Padana Formation at the base of the section through the Qubeiya, Quxia, and Jialazi formations to the Rujiao Zangbo Conglomerate at the top are considered to range in age from Santonian to Eocene or possibly Oligocene. During this period the India plate collided with, and continued to push against, Laurasia plate. Two spore and pollen zones and three palynofacies types are recognized. These are correlated with two transgressive–regressive cycles associated with the collision, periods of geologically rapid uplift being reflected by the molasse-like sediments of the upper Quxia Formation and the Rujiao Zangbo Conglomerate, which accumulated during the Late Paleocene and Eocene–Oligocene respectively. The first regression led to intermittent subaerial exposure and erosion of the Cuojiangding area. The second ended the marine history of the area and led first to the development of swamps in a subtropical climate, now preserved in the coal-bearing Qiuwu Formation, and later to the development of mountainous terrain, with a cooler climate at higher elevations.     

Growth response of Sabina tibetica to climate factors along an elevation gradient in south Tibet

We examine the climate significance in tree-ring chronologies retrieved from Sabina tibetica Kom. (Tibetan juniper) at two sites ranging in elevation from 4124 to 4693 m above sea level (a.s.l.) in the Namling region, south Tibet. The study region is under the control of semi-arid plateau temperate climate. The samples were grouped into high- and low-elevation classes and standard ring-width chronologies for both classes were developed. Statistical analysis revealed a decreasing growth rate yet increasing chronology reliability with increasing elevation. Overall, correlation analyses showed that radial growth in S. tibetica at the study sites was controlled by similar climatic factors, regardless of elevation; these factors comprised early winter (November) and early summer (May–June) temperatures as well as annual precipitation (July–June). Slight differences in the correlation between tree growth along the elevation gradient and climate variables were examined. The correlations with early winter temperature varied from significantly positive at the low-elevation site to weakly positive at the high-elevation site, whereas the correlations between radial growth and early summer temperature increased from weakly negative at the low-elevation sites to strongly negative at the high-elevation sites. The abundant precipitation through the year may have masked variations in tree growth on different elevation aspects. Our results will aid future dendroclimatological studies of Namling tree rings in south Tibet and demonstrate the potential of S. tibetica Kom. for improving our understanding of environmental impacts on tree growth.     

An ecological study of soils in the highlands of western Tibet II. Vertical change from 3900 m to 5450 m in elevation

Two kinds of soil study were carried out in the south-western Tibet region of China. Changes in soil properties with elevation were examined from the snout of a glacier at 5450 m above sea level down to a village (Burang) at 3900 m. The area close to the glacier was devoid of vegetation, probably because of the coldness. With a decrease in elevation, the landscape changed from desert to sparseArtemisia steppe, and below 4750 m, to a thorn-bush steppe dominated byCaragana spp. which continued down to the village (where the annual precipitation was 169 mm). Organic C, total N and cation exchange capacity (CEC) all increased with decreasing elevation down to 4700 m due to the increase in warmth, but the parameters decreased below 4700 m, reflecting the increase in aridity. Almost no carbonate was detected in areas above 4700 m, but below this elevation it increased exponentially, also reflecting the increase of aridity. Available P tended to decrease with both the decrease in elevation and the increase in carbonate. The vertical distribution of soil parameters was investigated in the soil profiles of dry and wet plots at 4700 m. Organic C, total N, and CEC decreased with increasing soil depth. Their values were higher in the dry plot than in the wet plot. In the dry plot, carbonate increased with depth. Total P was found to be similar in both the wet and dry plots, but there was less available P in the soil of the dry plot, reflecting the abundance of calcium carbonate.     

Molecular evidence for an Asian origin of monitor lizards followed by Tertiary dispersals to Africa and Australasia

Monitor lizards are emblematic reptiles that are widely distributed in the Old World. Although relatively well studied in vertebrate research, their biogeographic history is still controversial. We constructed a molecular dataset for 54 anguimorph species, including representatives of all families with detailed sampling of the Varanidae (38 species). Our results are consistent with an Asian origin of the Varanidae followed by a dispersal to Africa 41 (49-33) Ma, possibly via an Iranian route. Another major event was the dispersal of monitors to Australia in the Late Eocene-Oligocene 32 (39-26) Ma. This divergence estimate adds to the suggestion that Australia was colonized by several squamate lineages prior to the collision of the Australian plate with the Asian plate starting 25 Ma.     

Sinopaninae and Arfianinae (Hyaenodontida,Mammalia) from the Early Eocene of Europe and Asia; evidence for dispersal in Laurasia around the Paleocene/Eocene boundary and for an unnoticed faunal turnover in Europe

Hyaenodontida are represented in Europe by three subfamilies: Proviverrinae, Arfianinae and Sinopaninae. Here, we review all the specimens of Arfianinae and Sinopaninae known to date in Europe and Asia. A new Galecyon species is erected: Galecyon gallus nov. sp. We discuss the taxonomic position of the two Asian hyaenodontidans Anthracoxyaena palustris and Arfia langebadreae; the genus Anthracoxyaena is synonymized with Arfia. The analysis of the European and Asian arfianines and sinopanines provides new data concerning the dispersals and faunal events that occurred during the Early Eocene in Laurasia. The Arfianinae and Sinopaninae appeared in Europe around the Paleocene/Eocene boundary (reference-level MP7). The sinopanines are widespread in Europe; they are known in Dormaal (Belgium, reference-locality of the level MP7), Rians, Soissons, Pourcy, Try, Le Quesnoy (France), and Abbey Wood (England). The analysis of the paleogeographic distribution of all Oxyaenodonta and Hyaenodontida at and after the MP7 supports the existence of two European provinces: the North Province and Mesogean Province. We show that the Arfianinae and Sinopaninae rapidly disappeared from Europe; they are unknown in Avenay (reference-locality of the level MP8+9) and younger localities. Their disappearance from Europe is synchronous with that of the Oxyaenodonta. These observations support the existence of a faunal turnover, which occurred between the reference-levels MP7 (Dormaal) and MP8+9 (Avenay). The hypothesis of a dispersal from Europe to North America during the Paleocene-Eocene transition for the Arfianinae and Sinopaninae is supported. Moreover, the study of Arfianinae supports a dispersal from Europe to Asia around the P/E boundary, followed by a short period of endemic evolution. However, our study does not support a close relationship between Arfia and the “Arfia-like South Asian Proviverrinae” (Kyawdawia, Indohyaenodon, Paratritemnodon and Yarshea).     

Immunological evidence for an allatostatin-like neuropeptide in the central nervous system of Schistocerca gregaria,Locusta migratoria and Neobellieria bullata

Methanolic brain extracts of Locusta migratoria inhibit in vitro juvenile hormone biosynthesis in both the locust L. migratoria and the cockroach Diploptera punctata. A polyclonal antibody against allatostatin-5 (AST-5) (dipstatin-2) of this cockroach was used to immunolocalize allatostatin-5-like peptides in the central nervous system of the locusts Schistocerca gregaria and L. migratoria and of the fleshfly Neobellieria bullata. In both locust species, immunoreactivity was found in many cells and axons of the brain-retrocerebral complex, the thoracic and the abdominal ganglia. Strongly immunoreactive cells were stained in the pars lateralis of the brain with axons (NCC II and NCA I) extending to and arborizing in the corpus cardiacum and the corpora allata. Although many neurosecretory cells of the pars intercerebralis project into the corpus cardiacum, only 12 of them were immunoreactive and the nervi corporis cardiaci I (NCC I) and fibers in the nervi corporis allati II (NCA II) connecting the corpora allata to the suboesophageal ganglion remained unstained. S. gregaria and L. migratoria seem to have an allatostatin-like neuropeptide present in axons of the NCC II and the NCA I leading to the corpus cardiacum and the corpora allata. All these data suggest that in locusts allatostatin-like neuropeptides might be involved in controlling the production of juvenile hormone by the corpora allata and, perhaps, some aspects of the functioning of the corpus cardiacum as well. However, when tested in a L. migratoria in-vitro juvenile hormone-biosynthesis assay, allatostatin-5 did not yield an inhibitory or stimulatory effect. There is abundant AST-5 immunoreactivity in cell bodies of the fleshfly N. bullata, but none in the CA-CC complexes. Apparently, factors that are immunologically related to AST-5 do occur in locusts and fleshflies but, the active protion of the peptide required to inhibit JH biosynthesis in locusts is probably different from that of AST-5.     

Spectroscopic evidence for the presence of an iron-sulfur center similar to Fx of Photosystem I inHeliobacillus mobilis

Treatment of membranes ofHeliobacillus mobilis with high concentrations of the chaotropic agent urea resulted in the removal of the iron-sulfur centers F_A and F_B from the reaction center, as indicated by EPR spectra under strongly reducing conditions. In urea-treated membranes, transient absorption measurements upon a laser flash indicated a recombination between the photo-oxidized primary donor P798⁺ and a reduced acceptor with a time constant of 20 ms at room temperature. Benzylviologen, vitamin K-3 and methylene blue were found to accept electrons from the reduced acceptor efficiently. A differential extinction coefficient of 225–240 mM^–1 cm^–1 at 798 nm was determined from experiments in the presence of methylene blue. Transient absorption difference spectra between 400 and 500 nm in the presence and absence of artificial acceptors indicated that the electron acceptor involved in the 20 ms recombination has an absorption spectrum similar to that of an iron-sulfur center. This iron-sulfur center was assigned to be analogous to F_X of Photosystem I. Our results provide evidence in support of the presence of F_X in heliobacteria, which was proposed on the basis of the reaction center polypeptide sequence (Liebl et al. (1993) Proc. Natl. Acad. Sci. USA 90: 7124–7128). Implications for the electron transfer pathway in the reaction center of heliobacteria are discussed.     

Inter-species hybridization among Neotropical cats of the genus Leopardus, and evidence for an introgressive hybrid zone between L. geoffroyi and L. tigrinus in southern Brazil

Natural hybrid zones between distinct species have been reported for many taxa, but so far, few examples involve carnivores or Neotropical mammals in general. In this study, we employed mitochondrial DNA (mtDNA) sequences and nine microsatellite loci to identify and characterize a hybrid zone between two Neotropical felids, Leopardus geoffroyi and L. tigrinus, both of which are well-established species having diverged from each other c. 1 million years ago. These two felids are mostly allopatric throughout their ranges in South America, with a narrow contact zone that includes southern Brazil. We present strong evidence for the occurrence of hybridization between these species and identify at least 14 individuals (most of them originating from the geographical contact zone) exhibiting signs of interspecific genomic introgression. The genetic structure of Brazilian L. tigrinus populations seems to be affected by this introgression process, showing a gradient of differentiation from L. geoffroyi correlated with distance from the contact zone. We also corroborate and extend previous findings of hybridization between L. tigrinus and a third related felid, L. colocolo, leading to an unusual situation for a mammal, in which the former species contains introgressed mtDNA lineages from two distinct taxa in addition to its own.     

Direct evidence for the nature of the binding of mitochondria to microtubules in ovarian nutritive tubes of an hemipteran insect

Interactions between mitochondria and microtubules have been investigated in the nutritive tubes that link the nurse cells to the oocytes in ovarioles of the hemipteran insect, Notonecta. The nutritive tubes comprise large numbers of microtubules, which can be dissected manually from ovarioles. This approach, which retains the intrinsic components of the system, has allowed the in vivo interactions between the microtubules and mitochondria, which are also present in the nutritive tubes, to be studied directly. Static binding occurred between mitochondria and microtubules, and investigations of its nucleotide and salt-sensitivities have indicated its microtubule-associated protein (MAP)-dependency. Received: 30 September 1996 / Accepted: 1 February 1997     

Factors controlling the distribution of Marenzelleria cf. viridis, Pygospio elegans and Streblospio shrubsoli (Polychaeta: Spionidae) in the southern Baltic Sea, with special attention for the response to an event of hypoxia

The large-scale distribution patterns of the estuarine spionid polychaetes Marenzelleria cf. viridis, Pygospio elegans, and Streblospio shrubsoli were studied in the Pomeranian Bay (southern Baltic Sea) at 20 stations in April 1993 and their relationship with hydrographic factors and sediment composition investigated. The densities of M. cf. viridis and S. shrubsoli decreased rapidly with increasing distance offshore. A corresponding decrease in phytoplankton concentration offshore is suggested as the main cause for the observed spatial patterns. P. elegans was more evenly distributed. At 10 selected stations further samples were collected between April 1993 and July 1996 to study the response of abundance and biomass of the three polychaetes to changes in environmental conditions and to investigate interspecific interactions within the macrofauna. Salinity, pelagic food supply, and sediment parameters did not change. At three of these stations redox potential of the sediment and macrofauna composition were affected by an unusual hypoxic/anoxic event in July/August 1994. All three spionid species were able to survive moderate seasonal hypoxic conditions, but died after exposure to severe anoxia. Special attention was focused on the re-establishment of the spionids. The rate with which M. cf. viridis and P. elegans re-colonised defaunated stations varied between a few weeks and two years. These differences in rate of re-establishment were attributed to the distance from undisturbed recruitment areas, and to the severity of the oxygen deficiency. Increasing densities of P. elegans and S. shrubsoli after the hypoxic event coincided with a reduced abundance of the bivalve Mya arenaria, suggesting a negative interspecific interaction.     

Bioinformatics evidence for the transfer of mycosporine-like amino acid core (4-deoxygadusol) synthesizing gene from cyanobacteria to dinoflagellates and an attempt to mutate the same gene (YP_324358) in Anabaena variabilis PCC 7937

We have identified a homologue of 4-deoxygadusol (core of mycosporine-like amino acids) synthesizing gene (ZP_05036788) from Synechococcus sp. PCC 7335 that was found to have additional functionally unknown N-terminal domain similar to homologues from dinoflagellates based on the ClustalW analysis. Phylogenetic analysis revealed that Synechococcus sp. (ZP_05036788) makes a clade together with dinoflagellates and was closest to the Oxyrrhis marina. This study shows for the first time that N-terminal additional sequences that possess upstream plastid targeting sequence in Heterocapsa triquetra and Karlodinium micrum were already evolved in cyanobacteria, and plastid targeting sequence were evolved later in dinoflagellates after divergence from chloroplast lacking Oxyrrhis marina. Thus, MAAs synthesizing genes were transferred from cyanobacteria to dinoflagellates and possibly Synechococcus sp. PCC 7335 acted as a donor during lateral gene transfer event. In addition, we also tried to mutate 4-deoxygadusol synthesizing gene (YP_324358) of Anabaena variabilis PCC 7937 by homologous recombination, however, all approaches to get complete segregation of the mutants from the wild-type were unsuccessful, showing the essentiality of YP_324358 for A. variabilis PCC 7937.