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At least 505 records · Page 28Linked to original sources
PubMed1996

Comparative Earth history and Late Permian mass extinction.

The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.

Animals↗
PubMed2006

Geographic ranges, population structure, and ages of sexual and parthenogenetic snail lineages.

Asexual reproduction is thought to doom organisms to extinction due to mutation accumulation and parasite exploitation. Theoretical models suggest that parthenogens may escape the negative effects of conspecifics and biological enemies through escape in space. Through intensive sequencing of a mitochondrial DNA (mtDNA) and a nuclear intron locus in sexual and parthenogenetic freshwater snails (Campeloma), I examine three questions: (1) Are sexual mtDNA lineages more restricted geographically than parthenogenetic mtDNA lineages? (2) Are independent parthenogenetic lineages shorter lived than sexual lineages? and (3) Do parthenogens have higher intraindividual nuclear sequence diversity and form well-differentiated monophyletic groups as expected under the Meselson effect? Geographic ranges of parthenogenetic lineages are significantly larger than geographic ranges of sexual lineages. Based on coalescence times under different demographic assumptions, asexual lineages are short lived, but there is variation in clonal ages. Although alternative explanations exist, these results suggest that asexual lineages may persist in the short term through dispersal, and that various constraints may cause geographic restriction of sexual lineages. Both allotriploid and diploid Campeloma parthenogens have significantly higher allelic divergence within individuals, but show limited nuclear sequence divergence from sexual ancestors. In contrast to previous allozyme evidence for nonhybrid origins of diploid Campeloma parthenogens, cryptic hybridization may account for elevated heterozygosity.

Aging↗
PubMed1980

[Rubomycin complexing with copper (II)].

Complexing of rubomycin (H2R) with copper ions (II) in aqueous solutions was studied on the basis of fluorimetric and photometric measurements. H2R interacted with Cu (OH)+ to form the complex CuR with the molar extinction coefficient Ek = 4 . 96 . 10(3) and the stability 1g beta k = 5.54 +/- 0.09. The method of determining H2R in biological materials has been developed. It is based on the ability of the copper entering the complex to extinguish fluorexon luminescence in aqueous solutions.

Animals↗
PubMed1992

Structure-activity studies on the effects of atrial natriuretic peptide, brain natriuretic peptide and their analogs on fear-motivated learning behavior in rats.

Our previous studies have demonstrated that rat atrial natriuretic peptide (rANP 1-28) and porcine brain natriuretic peptide (pBNP 1-32) administered into the lateral brain facilitate the consolidation of a passive avoidance response and delay the extinction of an active avoidance response in fear-motivated learning in rats. To study the structure-activity relationships in the same learning processes, the effects of several fragments related to ANP and BNP were investigated following their intracerebroventricular administration to rats. The following peptides were studied: rANP 1-28, rANP 5-28, rANP 5-27, rANP 7-23 (ring), rANP 17-23, hANP 10-28, hANP 15-28, hANP 20-28, hANP 1-28, pBNP 1-32 and pBNP 7-32. The peptides were used in equimolar concentration. Two of the peptides studied, ANP 20-28 and ANP 17-23, were ineffective on the extinction of active avoidance behavior and on the consolidation of passive avoidance learning. They exhibited similar actions. The results showed that small fragments of ANP and BNP can carry the biological activity of ANP and BNP on the central nervous system (CNS). It is likely that the biological active center for ANP lies between amino acids 15 and 23 and it is suspected that the ring structure is not absolutely important for the CNS activity.

Amino Acid Sequence↗
PubMedDate not supplied

[Internal inhibition in rats after destruction of amygdaloid complex nuclei].

In experiments on male albino rats bilateral lesions of the basolateral amygdala (BLA) impaired extinction and differentiation of the food-procuring conditioned reflexes where as bilateral corticomedial (CMA) lesions had no effect on them. The BLA damage caused a significant impairment of the aversive stimuli discrimination but had no effect on the extinction of the conditioned avoidance reflex in a shuttle-box. The CMA lesions in both hemispheres led to attenuation of aversive stimuli discrimination and delay of avoidance extinction. The data obtained testify to the BLA dominant role in internal inhibition of the alimentary conditioned reflexes and the CMA dominant role in internal inhibition of avoidance conditioning and furthermore to the importance of BLA in the evaluation of the emotional significance and biological validity of the stimuli (reward or punishment).

Amygdala↗
PubMed1992

Selective form of an excitable membrane plasticity.

This work describes the change in an active electrogenesis of the command neurons responsible for defensive closure of a snail's pneumostome during elaborating, extinction and restoration of a classical conditioned defensive reflex to a tactile stimulus. Tactile stimulations applied to different parts of a snail's body served as a differential stimulus. As the biological value of a conditioned stimulus increases due to learning, the excitability of command neurons in response to conditioned stimulus rises. At the same time the neurons demonstrated a reduced excitability in response to a differentiating stimulus.

Animals↗
PubMed2001

Complexity and fragility in ecological networks.

A detailed analysis of three species-rich ecosystem food webs has shown that they display skewed distributions of connections. Such graphs of interaction are, in fact, shared by a number of biological and technological networks, which have been shown to display a very high homeostasis against random removals of nodes. Here, we analyse the responses of these ecological graphs to both random and selective perturbations (directed against the most-connected species). Our results suggest that ecological networks are very robust against random removals but can be extremely fragile when selective attacks are used. These observations have important consequences for biodiversity dynamics and conservation issues, current estimations of extinction rates and the relevance and definition of keystone species.

Ecosystem↗
PubMed2007

Going wild: what a global small-animal tracking system could do for experimental biologists.

Tracking animals over large temporal and spatial scales has revealed invaluable and spectacular biological information, particularly when the paths and fates of individuals can be monitored on a global scale. However, only large animals (greater than approximately 300 g) currently can be followed globally because of power and size constraints on the tracking devices. And yet the vast majority of animals is small. Tracking small animals is important because they are often part of evolutionary and ecological experiments, they provide important ecosystem services and they are of conservation concern or pose harm to human health. Here, we propose a small-animal satellite tracking system that would enable the global monitoring of animals down to the size of the smallest birds, mammals (bats), marine life and eventually large insects. To create the scientific framework necessary for such a global project, we formed the ICARUS initiative (www.IcarusInitiative.org), the International Cooperation for Animal Research Using Space. ICARUS also highlights how small-animal tracking could address some of the ;Grand Challenges in Environmental Sciences' identified by the US National Academy of Sciences, such as the spread of infectious diseases or the relationship between biological diversity and ecosystem functioning. Small-animal tracking would allow the quantitative assessment of dispersal and migration in natural populations and thus help solve enigmas regarding population dynamics, extinctions and invasions. Experimental biologists may find a global small-animal tracking system helpful in testing, validating and expanding laboratory-derived discoveries in wild, natural populations. We suggest that the relatively modest investment into a global small-animal tracking system will pay off by providing unprecedented insights into both basic and applied nature. Tracking small animals over large spatial and temporal scales could prove to be one of the most powerful techniques of the early 21st century, offering potential solutions to a wide range of biological and societal questions that date back two millennia to the Greek philosopher Aristotle's enigma about songbird migration. Several of the more recent Grand Challenges in Environmental Sciences, such as the regulation and functional consequences of biological diversity or the surveillance of the population ecology of zoonotic hosts, pathogens or vectors, could also be addressed by a global small-animal tracking system. Our discussion is intended to contribute to an emerging groundswell of scientific support to make such a new technological system happen.

Animal Migration↗
PubMed2006

The origin and early radiation of the therapsid mammal-like reptiles: a palaeobiological hypothesis.

The replacement of the basal synapsid pelycosaurs by the more 'mammal-like' therapsids in the Permian was an important event in the history of tetrapods because it initiated the eventual transition to the mammals. It is also an example of taxon replacement in the fossil record that is unusually amenable to explanation, based on a combination of analysis of the biological significance of the inferred character changes, with the stratigraphic, palaeogeographic and palaeoecological circumstances of the time. An hypothesis is presented in which the origin of the therapsids resulted from a correlated progression of character evolution leading to higher levels of metabolic activity and homeostatic regulation of the body. It was a response to the availability of a seasonally arid, savanna-like biome. The subsequent explosive radiation of therapsids was associated with habitat expansion made possible by the Mid-Permian development of geographical continuity between that biome and the temperate biomes. The final extinction of the pelycosaurs was a case of incumbent replacement by the new therapsid lineages.

Animals↗
PubMed2002

Molecular phylogeny and evolution of the extinct bovid Myotragus balearicus.

Myotragus balearicus was a dwarf artiodactyl endemic to the Eastern Balearic Islands, where it evolved in isolation for more than 5 million years before becoming extinct between 3640 and 2135 cal BC (calibrated years BC). Numerous unusual apomorphies obscure the relationship between Myotragus and the extant Caprinae. Therefore, genetic data for this species would significantly contribute to the clarification of its taxonomic position. In this study, we amplify, sequence, and clone a 338-base pair (bp) segment of the mitochondrial cytochrome b (cyt b) gene from a >9Kyr Myotragus subfossil from la Cova des Gorgs (Mallorca). Our results confirm the phylogenetic affinity of Myotragus with the sheep (Ovis) and the takin (Budorcas). In each tree, the Myotragus branch is long in comparison with the other taxa, which may be evidence of a local change in the rate of evolution in cyt b. This rate change may be due to in part to an early age of first reproduction and short generation time in Myotragus, factors that are potentially related to the extreme reduction in size of the adult Myotragus as compared to the other Caprinae.

Animals↗