590 Tiere (Zoologie)
Refine
Year of publication
Document Type
- Article (3811)
- Part of Periodical (2377)
- Book (107)
- Review (82)
- Doctoral Thesis (71)
- Periodical (20)
- Preprint (20)
- Contribution to a Periodical (14)
- Report (8)
- Diploma Thesis (7)
- Conference Proceeding (6)
- Other (6)
- Part of a Book (5)
- Working Paper (1)
Language
- English (4118)
- German (1974)
- French (220)
- Spanish (78)
- Multiple languages (52)
- Italian (27)
- Latin (23)
- dut (17)
- Portuguese (10)
- Danish (5)
Is part of the Bibliography
- no (6535)
Keywords
- taxonomy (716)
- new species (433)
- morphology (161)
- distribution (120)
- biodiversity (85)
- Odonata (84)
- systematics (82)
- phylogeny (63)
- Taxonomy (61)
- Neotropical (58)
Institute
- Extern (331)
- Biowissenschaften (248)
- Institut für Ökologie, Evolution und Diversität (157)
- Senckenbergische Naturforschende Gesellschaft (139)
- Biodiversität und Klima Forschungszentrum (BiK-F) (79)
- Medizin (48)
- Präsidium (24)
- Biochemie und Chemie (10)
- Geowissenschaften (7)
- Exzellenzcluster Makromolekulare Komplexe (4)
Shaped by some of the most dramatic tectonic events of the Cenozoic, the parts of southern and eastern Asia that have become known as the Oriental faunal region comprise vast areas of great geological complexity and ecological diversity. One of the four major groups of terrestrial elapid snakes in this region is the genus Bungarus. These nocturnal and predominantly ophiophagous snakes are widely known as kraits and are an important cause of snakebite mortality throughout their wide range that extends from Afghanistan to Vietnam and eastern China, and south to the Indonesian islands of Java and Bali. Although present on Borneo, kraits have not been found on any island of the Philippines, nor on Lesser Sunda Islands east of Bali. Despite their medical significance and the great importance of Bungarus toxins as tools in neuropharmacology, krait systematics and taxonomy have remained largely unstudied. Twelve species of Bungarus were recognized at the beginning of the present study. Many of these are rare in collections, and most aspects of their biology are unknown. While some species are highly distinct, most kraits are conservative morphologically, rendering molecular methods invaluable for the study of their diversity and biogeography. This study is the first to address the relationships within Bungarus and the historical biogeography of kraits based on molecular evidence. I inferred phylogeographic relationships based on analyses of new nucleotide sequences of the entire mitochondrial cytochrome b gene of 51 kraits and partial NADH dehydrogenase subunit 4 sequences of 40 kraits which I analyzed together with a representative sample of 32 published elapid and non-elapid outgroup taxa using Bayesian, maximum-likelihood, maximum-parsimony and neighbor-joining methods. I then used the recovered phylogeny to investigate the evolution of selected morphological characters and, together with collections-based geographical distribution information, in dispersal-vicariance analyses with models of variable taxonomic and biogeographic complexity. The phylogenetic analyses demonstrate that the current taxonomy of kraits does not adequately represent either the relationships or the genetic diversity in this genus. In contrast, I identified monophyletic groups that are congruent with recognized biogeographic units as well as extensive ecomorph evolution and morphologically cryptic speciation. The following additional conclusions are collectively supported by the mitochondrial phylogeny and morphological as well as biochemical synapomorphies: (1) Kraits are monophyletic with respect to the remaining taxa of the Elapidae; (2) Bungarus flaviceps and Bungarus bungaroides form the monophyletic sister clade of a clade formed by B. fasciatus, black-and-white-banded, and uniformly black taxa; (3) the remaining taxa are divisible into two sister clades, the South Asian species (Bungarus sindanus (Bungarus caeruleus, Bungarus ceylonicus)) vs. Himalayan, Burmese, Southeast and East Asian taxa; (4) within the latter, Burmese taxa form the sister clade to Southeast and East Asian taxa; (5) the widespread and medically significant species Bungarus candidus and Bungarus multicinctus are paraphyletic. The results of this study highlight the importance of vicariant geological events and sea level fluctuations for the cladogenesis of kraits. Events of particular importance in the evolution of kraits include the uplift of the Indo-Burman ranges (Arakan-Naga Hills) which separated black-and-white banded kraits in India and Southeast Asia, and the uplift of mountain ranges in Yunnan, China (e.g., the Gaoligong Shan), which coincided with lineage separation in two distantly related clades of kraits. Alternating dispersal and vicariance events due to Pleistocene climatic and sea level changes have caused complex phylogeographic patterns in kraits in Southeast Asia. Zones of contact between closely related evolutionary lineages of the B. candidus complex are identified in Thailand, Vietnam, and southern China (Hainan). Within this complex, two main clades are revealed. One includes populations from the Southeast Asian mainland and is in contact with B. multicinctus in southern China. The other consists of populations from Thailand, southern Vietnam, Java, and Bali. The phylogeny as well as genetic distances suggest a scenario in which a Pleistocene southward dispersal of B. candidus to Sumatra, Java, and Bali during times of low sea levels was temporarily interrupted by vicariant events (rising sea levels, especially flooding of the Malacca Strait between Sumatra and the Malay Peninsula, and of the Bali Strait between Java and Bali). In this context, the close phylogenetic relationship between haplotypes from southern Vietnam and those from Java and Bali suggests that "southern" B. candidus dispersed directly via colonization of the widely receded South Chinese Sea, and not by taking a detour via the Malay Peninsula and Thailand, which were already inhabited by other populations of B. candidus. Using these phylogenetic estimates as the framework for a study on the diversity and evolution of krait venom components, I applied biochemical and molecular genetic approaches to identify and quantify polypeptide and protein toxins in krait venom, focusing on the distribution and molecular evolution of alpha-bungarotoxin, an irreversible competitive antagonist of nicotinic acetylcholine receptors with an exceptionally high applied significance as a receptor probe. I was specifically interested in the medically relevant question of intraspecific and interspecific variability in toxin diversity, and whether receptor-binding postsynaptic toxins evolve at rates different from those of presynaptic neurotoxins like beta-bungarotoxin, which act by destroying the nerve terminal and are believed to exhibit hypervariable functional diversification due to an accelerated mode of molecular evolution. In the context of this question, I isolated and purified the major lethal neurotoxins from B. candidus venoms by sequential steps of liquid chromatography for structural and functional characterization studies. Cloning and sequence analysis of toxin-coding genomic DNAs showed that the gene encoding the alpha-bungarotoxin alanine-31 variant, originally isolated from B. multicinctus venom, is widely present and highly conserved in multiple populations of B. candidus and is expressed as the principal postsynaptic neurotoxin at least in Javan B. candidus. In addition to the widespread presence of genomic DNAs encoding the alpha-bungarotoxin alanine-31 variant, the present study also revealed the partial genes of three novel alpha-bungarotoxin isoforms in addition to the previously known alanine-31 and valine-31 variants, all of which share an invariant exon 3 coding region. While alpha-bungarotoxin is the principal postsynaptic neurotoxin of Taiwanese B. multicinctus and Javan B. candidus, the main postsynaptic neurotoxin of Thai B. candidus both by quantity and lethality was a novel polypeptide of similar toxicity with a mass of 8030 Da and 73 amino acid residues, whose characterization at the genetic and protein levels revealed a novel subgroup of krait neurotoxins, here named alpha-delta-bungarotoxins and represented by four sequences from Bungarus caeruleus and B. candidus. alpha-delta-Bungarotoxins share high sequence homology with alpha-bungarotoxins but the purified, 8030 Da alpha-delta-bungarotoxin-1 exhibits only reversible, low affinity binding to nicotinic receptors and high site-selectivity for the acetylcholine binding site at the alpha-delta-subunit interface of the receptor. These properties render alpha-delta-bungarotoxin not only the first snake long-chain neurotoxin with reversible binding and binding-site selectivity, but also an exciting natural tool with which to address structure-function relationships at the subunit interfaces of the human receptor. The results of comparisons of the number of non-synonymous nucleotide substitutions per nonsynonymous site (dN) to the number of synonymous nucleotide substitutions per synonymous site (dS) strongly suggest that positive selection is acting on exon 2 of the alpha-bungarotoxin and probably also of the alpha-delta-bungarotoxin genes. In addition, the numbers of nucleotide substitutions per site of intron (dI) compared to the dS value of the toxin-coding exon regions provide strong evidence for accelerated molecular evolution in exon 2 of alpha-delta-bungarotoxins —whose value of dI is only one-eighth of the value of dS—whereas the hypothesis of accelerated evolution is rejected for 13 unique genomic DNAs encoding five alpha-bungarotoxin isoforms from B. candidus and B. multicinctus....
1. Ein junger männlicher Steinmarder lernte in kurzer Zeit das Öffnen einer Schiebetür. Vor die Aufgabe gestellt, einen diese Tür verschließenden Riegel zu drehen, versagte er. Auch eine sekundäre Lösung, die auf dem Wege über eine Passivdressur angestrebt wurde, erfolgte nicht, ebensowenig wurde eine optische Orientierung auf Grund der Riegelstellung beobachtet. 2. Kleine Umwege in horizontaler und vertikaler Richtung wurden gut, in primärer Bewältigung der Aufgabe, genommen. 3. Eine einfache Ortsdressur (auf einen der Ecktöpfe einer dargebotenen Reihe von vier gleichen Töpfen) wurde unter Benutzung olfaktorischer Hilfen in kurzer Zeit zu dem gewünschten Erfolg gebracht. Eine kompliziertere Ortsdressur (Wahl des zweiten Topfes von links aus einer Reihe von fünf gleichen Töpfen) führte, bei strenger Vermeidung olfaktorischer Orientierungsmöglichkeiten, erst nach einer größeren Anzahl (etwa 220) Versuchen zum Ziele. Die Erlernung erfolgte auf Grund kinästhetischer, vor allem aber optischer Reize. Der Vorgang der optischen Gliederung der Reihe konnte genau festgestellt werden. 4. Ein mehrjähriger Iltisrüde wurde hinsichtlich der sich aus allgemeinen anatomischen und biologischen Unterschieden ergebenden Eigenheiten im psychischen Verhalten beobachtet und untersucht. Es ergaben sich bei einem Vergleich mit dem Steinmarder eine Reihe wichtiger artspezifischer Differenzen, die sich zumeist auf den Unterschied Bodentier-Klettertier zurückführen ließen. 5. Auch der Iltis lernte das Öffnen einer Schiebetür. Im horizontalen Umwegversuch wurden recht gute primäre, vor allem aber auch sekundäre Lösungen festgestellt. Auf Grund der sekundären Lösungen wird eine starke Entwicklung des kinästhetischen Sinnes angenommen. 6. Eine Helligkeitsdressur bei alternativer Wahl scheiterte an der Unmöglichkeit, die hauptsächlich auf der Intensität der kinästhetischen Empfindungen beruhenden Tendenzen einer ortsbedingten Wahl auszuschalten. 7. Eine multiple Ortsdressur, der des Steinmarders entsprechend, gelang, obwohl durch Hinzunahme von insgesamt vier neuen Aufstellungsarten die Aufgabe für den Iltis nicht unbedeutend erschwert wurde. Die große Bedeutung des Ortskriteriums für das Tier wurde im Verlaufe dieser Versuche besonders deutlich und konnte exakt nachgewiesen werden. 8. Eine Helligkeitsdressur bei multipler Wahl gelang. Ebenso konnte bei einer Rot-Blaudressur Blauwahl erreicht werden. 9. Im Anschluß an die vorhergehende Dressur kam Blauwahl nunmehr auch bei Anwendung der Alternativmethode zustande. 10. Es konnte gezeigt werden, daß die in 8 und 9 dargestellten Resultate auf Grund einer helligkeits-, nicht farb-bedingten Orientierung zustande kamen. Färb- und Graupapiere, die dem zur Dressur verwandten Heringschen Blau Nr. 12 helligkeitsverwandt waren, wurden mit diesem verwechselt. Dieser Befund läßt den Schluß auf das Vorhandensein einer Farbenschwäche oder Farbenblindheit zu. 11. Es wurde festgestellt, daß der Iltis sowohl in orts- als auch in helligkeitsbedingter Wahl sich nach relativen Kriterien richtete.