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PubMed2001

Emotion-related learning in individuals prenatally exposed to alcohol: an investigation of the relation between set shifting, extinction of responses, and behavior.

The association between deficits in emotion-related learning, conceptual set shifting, and behavioral problems was investigated in individuals with substantial prenatal alcohol exposure. Twenty subjects with confirmed prenatal alcohol exposure (10 of whom were diagnosed as having Fetal Alcohol Syndrome) and 20 normal controls matched for age, gender, and ethnic background participated. The two groups were administered a battery of tests including two tests of emotion-related learning (visual discrimination reversal and extinction of reward-response associations), tests of conceptual set shifting and intellectual ability, and behavioral measures. The alcohol-exposed group made fewer reversals than the control group in visual discrimination reversal and exhibited more variability in extinction. These group differences remained significant after controlling for intellectual ability and conceptual set shifting. Variability in extinction and two measures of set shifting, perseverative errors on the Wisconsin Card Sorting Test and omission errors on reversal learning, were found to be robust predictors of parent-rated behavioral problems.

Adolescent↗
PubMed1999

Somatosensory extinction for meaningful objects in a patient with right hemispheric stroke.

Implicit, high level processing of extinguished objects has often been described in the visual modality. In the tactile domain, however, research on this topic is meagre and it is still uncertain whether processing of tactually presented stimuli can be affected by the same attentional disorders as visual stimuli. In this paper we describe a patient, ENM, with visual neglect and light touch extinction who, in a naming task of objects presented in the tactile modality, simultaneously to both hands, showed extinction for left hand objects. He was, nevertheless, able to make above chance Same/Different judgements on the two stimuli. We also tested two neurologically intact subjects who performed the test wearing a ski-glove on the left hand to impair the recognition of left hand objects. In these subjects, Same/Different judgements were at chance level when recognition rate was as low as that found in patient ENM. This happened when either the objects, although sharing the same name were different in shape (conditions Same-Different) or when the two objects were different with respect to the category name but were actually physically similar (conditions Different-Similar). However, when the objects were either identical or completely different, i.e., in a condition where judgement could be based simply on the physical analysis of the object shape (condition Same Identical and Different Dissimilar), their Same/Different judgements were above chance, despite the tactual deficit. Our conclusion was that patient ENM showed implicit recognition of left hand objects, at least in the Same Different and in the Different-Similar conditions, whereas, in the same conditions, normal subjects with an artificial sensory impairment did not. Our results also show that Same/Different judgements may be, in some conditions, less demanding than naming tasks, as suggested by Farah et al. Furthermore, patient ENM performed the test both with uncrossed and crossed hands. We found that extinction always affected the hand contralateral to the brain damage, although there was a tendency for a decrement of the ipsilesional hand performance in the crossed condition. We discuss these findings with reference to the most recent theories on the existence of a body centered spatial frame of reference.

Aged↗
PubMed2000

Faces call for attention: evidence from patients with visual extinction.

Three patients with left spatial neglect and visual extinction from right brain damage were studied to determine whether faces are privileged in summoning attention. In a first experiment, either a face, a name, or a meaningless shape were briefly presented in the right, left or both visual hemifields. On bilateral trials, all patients extinguished a left-side face much less often than a left-side name or a left-side shape. Conversely, they extinguished a left-side shape more often when it was accompanied by a right-side face rather than a right-side name. In a second experiment, either a face or a scrambled face could appear in the right, left or both hemifields. Again, on bilateral trials, a left-side face was less likely to be missed than a scrambled one. These results suggest an advantage of faces in capturing attention and overcoming extinction, which may be related to their special biological and social value, or to the very efficient and automatic operation of specific perceptual processses that extract facial organization in extrastriate visual areas. These findings also demonstrate that the distribution of spatial attention and extinction can be modulated by the relevance of visual stimuli. This implies that substantial analysis and categorization may take place in the visual system before information from the contralesional field is selected for, or excluded from, attentive vision.

Aged↗
PubMed2000

Axis-based grouping reduces visual extinction.

We examined the effects on extinction of grouping by collinearity of edges and grouping by alignment of internal axes of shapes, in a patient (GK) with simultanagnosia following bilateral parietal brain damage. GK's visual extinction was reduced when items (equilateral triangles and angles) could be grouped by base alignment (i.e., collinearity) or by axis alignment, relative to a condition in which items were ungrouped. These grouping effects disappeared when inter-item spacing was increased, though factors such as display symmetry remained constant. Overall, the results suggest that, under some conditions, grouping by alignment of axes of symmetry can have an equal beneficial effect on visual extinction as edge-based grouping; thus, in the extinguished field, there is derivation of axis-based representations from the contours present.

Agnosia↗
PubMed2003

Extinction risk to bird populations caused by DDT exposure.

The impact of toxic chemicals on wild animals and plants can be quantified in terms of the enhanced risk of population extinction. To illustrate a method for doing this, we estimated such impact for two bird species: herring gull (Larus argentatus) in Long Island, NY, and sparrowhawk (Accipiter nisus) in eastern England, when they were exposed to DDT (p,p(')-dichlorodiphenyltrichloroethane) and its metabolites (called DDTs). The method we used is based on a formula of the mean time to population extinction derived for a stochastic differential equation (the canonical model). The intrinsic rate of natural population growth was estimated from an exponentially growing population, and the intensity of the environmental fluctuation was estimated from the magnitude of population size fluctuation. The effect of exposure to DDTs in reducing the population growth rate was evaluated based on an age-structured population model, by assuming that age-specific fertility is density-dependent and sensitive to DDTs exposure, but age-specific survivorship is not. The results are expressed in terms of the risk equivalent--the decrease in carrying capacity K that causes the same enhancement of extinction risk as chemical exposure at a given level. The risk equivalent can be used in mitigation banking.

Animals↗
PubMed2003

Ecological risk assessment of pollutant chemicals: extinction risk based on population-level effects.

The extinction probability is one of the most useful endpoints that are utilized in conservation biology. A parallel approach is advocated for the ecological risk assessment of chemical pollutants. The presented framework estimates extinction probability induced by pollutant chemicals in order to evaluate ecological hazards of pollution, and is applicable to any biological community (aquatic or terrestrial). The analytical framework, which is based on stochastic population dynamics theory, is briefly explained. The extinction risk estimation is feasible if ecotoxicological data concerning pollutant effects on population growth rate of organisms (the intrinsic rate of natural increase), and if environmental exposure concentration is provided. Tentative risk estimation was made for some agrochemicals and surfactants on zooplankton populations (Daphnia) as target organisms.

Agriculture↗
PubMed2000

Training history affects magnitude of spontaneous recovery from extinction of appetitive conditioned responding.

Three experiments examined spontaneous recovery from extinction of appetitive conditioned responding (CR) as a function of training history. Rats first received reinforced and non-reinforced conditioning trials. Groups of rats were equated for total number of reinforced trials but differed in the number of non-reinforced trials, or in the order of reinforced and non-reinforced trials. CR was then extinguished in all groups. Subsequently, the extent of recovery of CR was assessed in a test session performed either 1 or 17 days after the last extinction session. After a 17-day delay, rats that had received all reinforced trials immediately prior to the first extinction session showed stronger recovery than did rats having received all reinforced trials at the beginning of training, or interspersed among non-reinforced trials. No significant spontaneous recovery was observed after a 1-day test delay. These results, which may be of clinical relevance with respect to relapse after therapy, are explained in terms of the training schedules generating differences in strength of inhibitory associations, and a relatively long, but not a short, test delay attenuating these associations.

Journal Article↗
PubMed2001

Reinstatement of acquisition performance by the presentation of the outcome after extinction in causality judgments.

Two experiments were conducted with the aim of exploring reinstatement after extinction using a causality judgment task in human beings. In Experiment 1, participants learned first that a fictitious medicine produced a side-effect. The medicine was then presented in extinction. Re-exposure to the side-effect by itself before the test reinstated acquisition performance. Reinstatement was greater when exposure took place in the test context than when it took place in a different context. Experiment 2 replicated reinstatement in a situation that ensured equivalent extinction for the different groups before the test.

Journal Article↗
PubMed2000

Molecular mechanisms of extinction: old findings and new ideas.

Fusion experiments between somatic cells have been used for a long time as a means to understand the regulation of gene expression. In hybrids between differentiated cells such as hepatocytes or lymphocytes and undifferentiated cells such as fibroblasts a phenomenon called extinction has been described. In such hybrids expression of cell-specific genes derived from the more differentiated parental cell is selectively turned off (extinguished), whereas genes expressed from both cells like housekeeping genes remain active after fusion. Study of the molecular basis of extinction of the liver-specifically expressed tyrosine aminotransferase gene and of the B-cell-specifically expressed immunoglobulin genes has revealed that in hybrids the transcriptional program of the differentiated cells is reset. This is accompanied by a loss of expression or activity of many of the regulatory molecules that were operating in the differentiated cells. In the light of new insights in eukaryotic gene regulation we speculate that molecular mechanisms such as chromatin remodelling, recruitment to heterochromatin or subnuclear localization could underly the extinction process.

Animals↗
PubMed1989

Inhibition by diazepam of the effect of additional training and of extinction on the retention of shuttle avoidance behavior in rats.

Rats were submitted to a training and a test session in a shuttle avoidance task. In some groups, a second training session was interpolated 2 or 24 hr after the first session. In others, a session of extinction was interpolated 2 or 24 hr after the training session. When the interpolated task was 2 hr after training, training-test interval was 24 hr. When the interpolated task was 24 hr after training, training-test interval was 48 hr. The additional training enhanced, and the extinction depressed, retention test performance. Diazepam, given 30 min prior to the first (or only) training session enhanced the performance of avoidance responses in that session but inhibited it in the subsequent retention test. Diazepam given 90 min after training had no effect on retention. Diazepam given 30 min prior to either the additional training session or the extinction session did not affect performance in that session but cancelled their effects on retention test performance. The effects are related to the previously described prevention by diazepam of interfering effects on memory.

Animals↗
PubMed1993

Chaos reduces species extinction by amplifying local population noise.

In the mid-1970s, theoretical ecologists were responsible for stimulating interest in nonlinear dynamics and chaos. Ironically, the importance of chaos in ecology itself remains controversial. Proponents of ecological chaos point to its ubiquity in mathematical models and to various empirical findings. Sceptics maintain that the models are unrealistic and that the experimental evidence is equally consistent with stochastic models. More generally, it has been argued that interdemic selection and/or enhanced rates of species extinction will eliminate populations and species that evolve into chaotic regions of parameter space. Fundamental to this opinion is the belief that violent oscillations and low minimum population densities are inevitable correlates of the chaotic state. In fact, rarity is not a necessary consequence of complex dynamical behaviour. But even when chaos is associated with frequent rarity, its consequences to survival are necessarily deleterious only in the case of species composed of a single population. Of course, the majority of real world species (for example, most insects) consist of multiple populations weakly coupled by migration, and in this circumstance chaos can actually reduce the probability of extinction. Here we show that although low densities lead to more frequent extinction at the local level, the decorrelating effect of chaotic oscillations reduces the degree of synchrony among populations and thus the likelihood that all are simultaneously extinguished.

Ecology↗
PubMed1985

The fixation of chromosomal rearrangements in a subdivided population with local extinction and colonization.

The fixation of major chromosomal rearrangements with a heterozygote disadvantage is modelled as a simple example of Wright's shifting balance process of evolution in a strongly subdivided population. Chromosomal mutations with an inferior heterozygote become fixed in a local population (or deme) by random genetic drift and spread by migration and colonization. Wright postulated a process of selective diffusion in which the numbers of emigrants and colonizers dispersed from a deme increase with the mean fitness of individuals in it. The present models show that interdeme selection during the spread of a mutation depends more on the capacity of the mutant to invade and become established in other demes than on selective diffusion, unless there is rapid local extinction and colonization. The intensity of interdeme selection is reduced by random local extinction and colonization, and when these processes are rapid (with no selective diffusion) the expected fixation rate of spontaneous mutations with a heterozygote disadvantage approaches that in a single isolated deme. Local extinction and colonization, and selection on the homozygotes, accelerate the spread of chromosomal mutations which are destined to be fixed.

Animals↗
PubMed2003

Extreme reversed sexual size dimorphism in the extinct New Zealand moa Dinornis.

The ratite moa (Aves; Dinornithiformes) were massive graviportal browsers weighing up to 250 kg (ref. 1) that dominated the New Zealand biota until their extinction approximately 500 yr ago. Despite an extensive Quaternary fossil record, moa taxonomy remains problematic and currently 11 species are recognized. Three Dinornis species were found throughout New Zealand and differed markedly in size (1-2 m height at back) and mass (from approximately 34 to 242 kg). Surprisingly, ancient mitochondrial DNA sequences show that the three species were genetically indistinguishable within each island, but formed separate North and South Island clades. Here we show, using the first sex-linked nuclear sequences from an extinct species, that on each island the three morphological forms actually represent just one species, whose size varied markedly according to sex and habitat. The largest females in this example of extreme reversed sexual size dimorphism were about 280% the weight and 150% the height of the largest males, which is unprecedented among birds and terrestrial mammals. The combination of molecular and palaeontological data highlights the difficulties of analysing extinct groups, even those with detailed fossil records.

Animals↗
PubMed2004

Microbialite resurgence after the Late Ordovician extinction.

Microbialites, including biogenic stromatolites, thrombolites and dendrolites, were formed by various microbial mats that trapped and bound sediments or formed the locus of mineral precipitation. Microbialites were common and diverse during the Proterozoic, but declined in abundance and morphological diversity when multicellular life diversified during the Cambrian Radiation. A second decline occurred during the Ordovician Radiation of marine animals, and from then until the present microbialites have been confined largely to high-stress environments where multicellular organisms are rare. The microbialite declines in the Phanerozoic are attributed to disruption of the mats by animals. A resurgence of stromatolite abundance and size during reduced animal diversity after the Permian extinction has been documented anecdotally. Here we show, with statistical support, that a microbialite resurgence also occurred after the Late Ordovician extinction event in western North America. The resurgences were associated with loss of mat-inhibiting animals, providing insights into shallow-water community structures after extinction events.

Animals↗
PubMed2004

Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth.

The extinction of the many well-known large mammals (megafauna) of the Late Pleistocene epoch has usually been attributed to 'overkill' by human hunters, climatic/vegetational changes or to a combination of both. An accurate knowledge of the geography and chronology of these extinctions is crucial for testing these hypotheses. Previous assumptions that the megafauna of northern Eurasia had disappeared by the Pleistocene/Holocene transition were first challenged a decade ago by the discovery that the latest woolly mammoths on Wrangel Island, northeastern Siberia, were contemporaneous with ancient Egyptian civilization. Here we show that another spectacular megafaunal species, the giant deer or 'Irish elk', survived to around 6,900 radiocarbon yr bp (about 7,700 yr ago) in western Siberia-more than three millennia later than its previously accepted terminal date-and therefore, that the reasons for its ultimate demise are to be sought in Holocene not Pleistocene events. Before their extinction, both giant deer and woolly mammoth underwent dramatic shifts in distribution, driven largely by climatic/vegetational changes. Their differing responses reflect major differences in ecology.

Animals↗
PubMed2006

New carbon dates link climatic change with human colonization and Pleistocene extinctions.

Drastic ecological restructuring, species redistribution and extinctions mark the Pleistocene-Holocene transition, but an insufficiency of numbers of well-dated large mammal fossils from this transition have impeded progress in understanding the various causative links. Here I add many new radiocarbon dates to those already published on late Pleistocene fossils from Alaska and the Yukon Territory (AK-YT) and show previously unrecognized patterns. Species that survived the Pleistocene, for example, bison (Bison priscus, which evolved into Bison bison), wapiti (Cervus canadensis) and, to a smaller degree, moose (Alces alces), began to increase in numbers and continued to do so before and during human colonization and before the regional extinction of horse (Equus ferus) and mammoth (Mammuthus primigenius). These patterns allow us to reject, at least in AK-YT, some hypotheses of late Pleistocene extinction: 'Blitzkrieg' version of simultaneous human overkill, 'keystone' removal, and 'palaeo-disease'. Hypotheses of a subtler human impact and/or ecological replacement or displacement are more consistent with the data. The new patterns of dates indicate a radical ecological sorting during a uniquely forage-rich transitional period, affecting all large mammals, including humans.

Animals↗
PubMed2003

Inbreeding depression in fecundity and inbred line extinction in the bulb mite, Rhizoglyphus robini.

This study investigated the magnitude of inbreeding depression in fecundity, and whether the depression is purged during six generations of sib mating in the bulb mite, Rhizoglyphus robini. The progeny resulting from a single generation of brother-sister mating suffered significant inbreeding depression in fecundity. During the following six generations of continuous sib-mating, 58% lines were lost, 45% because of sterility and 13% because of preadult mortality. The lines were then outcrossed, and their inbreeding depression compared with that of the base population. The inbreeding depression for the outcrossed population was 0.15, and for the base population 0.19, but the difference was not significant. The lack of significant purging of inbreeding depression indicates that it was caused either by detrimental genes of small effect, or by the breaking down of overdominant relations between alleles. However, the large proportion of extinct lines points to the former mechanism as a predominant cause of inbreeding depression. Theory predicts that the probability of line extinction with inbreeding increases with its load of mutations. If phenotypic variation in fecundity was partly because of differences in numbers of mutations carried by individuals, the fecundity of the line founder could be expected to correlate with the probability that the line derived from it will survive long-term inbreeding. Indeed, fecundity of founder females was significantly associated with line survival, which suggests that line extinction rate may be used as a method to study individual mutational loads, for example, in studies of sexual selection.

Animals↗
PubMed1997

Molecular evidence for an extinct parent of the tetraploid species Microseris acuminata and M. campestris (Asteraceae, Lactuceae).

To determine the origin of the tetraploid annuals Microseris campestris and M. acuminata, chloroplast RFLP, RAPD and ITS sequence variability among nine populations of the two polyploids and 14 populations of the diploid annuals M. elegans and M. douglasii have been surveyed. Previously described variable chloroplast restriction sites infer M. douglasii as the possible maternal parent of both tetraploid species. However, the chloroplast genome typical for M. douglasii has now also been found in some plants of M. elegans. RAPD analysis revealed 172 polymorphic DNA markers that defined all four species as genetically distinct groups, but demonstrated closer associations between M. douglasii and M. acuminata, and between M. elegans and M. campestris. Sequencing of the ITS-1 and ITS-2 region yielded 73 phylogenetically informative sites. Thirty basepair mutations separated the annual Microseris species from the outgroup, Uropappus lindleyi. The putative interspecific allotetraploid M. campestris contained only one type ITS sequence that, on the basis of eight synapomorphic substitutions was derived from M. elegans. The single ITS of M. acuminata shares six common sites with M. douglasii. Surprisingly, six sites were synapomorphic for the two tetraploids, M. campestris and M. acuminata, suggesting recombination within the ITS of both species with that of a common, now extinct, parental taxon, possibly the donor of the M. douglasii type chloroplasts found in both tetraploids. These results confirm the interpretation of M. campestris as derived from M. douglasii (extinct population) and M. elegans, and resolve the unknown origin of M. acuminata as an intraspecific hybrid between two very distinct populations of M. douglasii, one of them the same extinct M. douglasii form that contributes to M. campestris.

Base Sequence↗