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PubMed2005

Ecology: is speciation driven by species diversity?

Emerson and Kolm show that the proportion of species endemic to an island is positively related to its species richness and, assuming that endemism indexes speciation rate, they infer that greater species diversity accelerates diversification. Here we demonstrate that the same correlation between species richness and percentage endemism can arise even if within-island speciation is negligible, particularly when both endemism and species richness depend on attributes of islands (such as area) that influence the average age of resident populations. Island biogeography theory indicates that, where the average time to extinction is relatively long, diversity increases through colonization, irrespective of whether new species are formed; at the same time, islands on which populations persist for longer accumulate more endemic species as local populations differentiate and populations on neighbouring islands become extinct. We therefore suggest that species richness and endemism are correlated fortuitously owing to their mutual dependence on the life spans of populations on islands, which is unrelated to speciation itself.

Animals↗

PubMed2003

Geographic range size, life history and rates of diversification in Australian mammals.

What causes species richness to vary among different groups of organisms? Two hypotheses are that large geographical ranges and fast life history either reduce extinction rates or raise speciation rates, elevating a clade's rate of diversification. Here we present a comparative analysis of these hypotheses using data on the phylogenetic relationships, geographical ranges and life history of the terrestrial mammal fauna of Australia. By comparing species richness patterns to null models, we show that species are distributed nonrandomly among genera. Using sister-clade comparisons to control for clade age, we then find that faster diversification is significantly associated with larger geographical ranges and larger litters, but there is no evidence for an effect of body size or age at first breeding on diversification rates. We believe the most likely explanation for these patterns is that larger litters and geographical ranges increase diversification rates because they buffer species from extinction. We also discuss the possibility that positive effects of litter size and range size on diversification rates result from elevated speciation rates.

Animals↗

PubMed2003

Sexual selection affects local extinction and turnover in bird communities.

Predicting extinction risks has become a central goal for conservation and evolutionary biologists interested in population and community dynamics. Several factors have been put forward to explain risks of extinction, including ecological and life history characteristics of individuals. For instance, factors that affect the balance between natality and mortality can have profound effects on population persistence. Sexual selection has been identified as one such factor. Populations under strong sexual selection experience a number of costs ranging from increased predation and parasitism to enhanced sensitivity to environmental and demographic stochasticity. These findings have led to the prediction that local extinction rates should be higher for speciespopulations with intense sexual selection. We tested this prediction by analyzing the dynamics of natural bird communities at a continental scale over a period of 21 years (1975-1996), using relevant statistical tools. In agreement with the theoretical prediction, we found that sexual selection increased risks of local extinction (dichromatic birds had on average a 23% higher local extinction rate than monochromatic species). However, despite higher local extinction probabilities, the number of dichromatic species did not decrease over the period considered in this study. This pattern was caused by higher local turnover rates of dichromatic species, resulting in relatively stable communities for both groups of species. Our results suggest that these communities function as metacommunities, with frequent local extinctions followed by colonization. Anthropogenic factors impeding dispersal might therefore have a significant impact on the global persistence of sexually selected species.

Animals↗

PubMed1991

Signal convergence on protein kinase A as a molecular correlate of learning.

The response of a reaction network composed of protein kinase A, calpain, and protein phosphatase to transient cAMP and Ca2+ signals was studied. An essential feature of signal convergence is that the regulatory subunit of cAMP-dissociated protein kinase A undergoes limited proteolysis by the Ca(2+)-activated proteinase calpain. A dynamic model of this system based on kinetic differential equations was built and simulated by computer. The system shows analogies to typical features of associative learning such as acquisition, contiguity detection, extinction, and memory decay, suggesting that these biochemical reactions may be part of the molecular mechanism of learning in Drosophila.

Calpain↗

PubMed1998

Spatially induced speciation prevents extinction: the evolution of dispersal distance in oscillatory predator-prey models.

In a discrete-generation, individual-oriented model of predator-prey interactions that exhibits oscillations, we show that the self-structuring of the populations into spiral waves induces a selection pressure for ever-increasing dispersal distances in both populations. As the dispersal distances increase, the sizes of the spatial patterns increase, until they are too large to fit into the limited space. The patterns are then lost and the predators go extinct. This scenario, is, however, not the only outcome. A second selection pressure induced by the spatial boundary can cause reduction of the dispersal distances. Depending on the relative strengths of the two selection pressures, the predators and prey may speciate to give coexistence between short-dispersing boundary quasi-species and far-dispersing spiral quasi-species. Now, when pattern loss occurs, the predators switch to predating on the boundary prey quasi-species and do not go extinct. Also, if the populations reproduce sexually, local gene flow can inhibit the evolution of increasing dispersal distances, and hence the spatial patterns are not lost. Speciation and coexistence can also occur in the sexually reproducing species.

Biological Evolution↗

PubMed2005

Forest fragmentation effects on patch occupancy and population viability of herbaceous plant species.

Habitat fragmentation is one of the major threats to species diversity. In this review, we discuss how the genetic and demographic structure of fragmented populations of herbaceous forest plant species is affected by increased genetic drift and inbreeding, reduced mate availability, altered interactions with pollinators, and changed environmental conditions through edge effects. Reported changes in population genetic and demographic structure of fragmented plant populations have, however, not resulted in large-scale extinction of forest plants. The main reason for this is very likely the long-term persistence of small and isolated forest plant populations due to prolonged clonal growth and long generation times. Consequently, the persistence of small forest plant populations in a changing landscape may have resulted in an extinction debt, that is, in a distribution of forest plant species reflecting the historical landscape configuration rather than the present one. In some cases, fragmentation appears to affect ecosystem integrity rather than short-term population viability due to the opposition of different fragmentation-induced ecological effects. We finally discuss extinction and colonization dynamics of forest plant species at the regional scale and suggest that the use of the metapopulation concept, both because of its heuristic power and conservation applications, may be fruitful.

Biodiversity↗

PubMed1986

[A special comparative pathology].

In twenty-nine years, teaching of the subject 'Nosology of Exotic Animals' has acquired a specific content and taken on a structural form. A sort of 'clinical pathology' developed, which yielded many fruits. The Department of Nosology of Exotic Animals stood up for the conservation of animals in danger of becoming extinct by stimulating breeding of these animals. Various methods are used in comparative nosology. Not only clinical processes but also species of animals and pathological reaction patterns are compared. As regards education, an approach from the point of view of pathology is essential for the time being in transmitting the understanding of processes of disease, based on morbid-anatomical and patho-biological findings. Future scientific developments are mainly anticipated in teaching on the subject of small companion animals, knowledge of the nosology of laboratory animals, animals in zoological gardens and those living in the wild. Studies will be partly on research level; they will, however, take the form of setting up special projects wherever possible.

Animal Population Groups↗

PubMed2006

The efficient interaction of indirect reciprocity and costly punishment.

Human cooperation in social dilemmas challenges researchers from various disciplines. Here we combine advances in experimental economics and evolutionary biology that separately have shown that costly punishment and reputation formation, respectively, induce cooperation in social dilemmas. The mechanisms of punishment and reputation, however, substantially differ in their means for 'disciplining' non-cooperators. Direct punishment incurs salient costs for both the punisher and the punished, whereas reputation mechanisms discipline by withholding action, immediately saving costs for the 'punisher'. Consequently, costly punishment may become extinct in environments in which effective reputation building--for example, through indirect reciprocity--provides a cheaper and powerful way to sustain cooperation. Unexpectedly, as we show here, punishment is maintained when a combination with reputation building is available, however, at a low level. Costly punishment acts are markedly reduced although not simply substituted by appreciating reputation. Indeed, the remaining punishment acts are concentrated on free-riders, who are most severely punished in the combination. When given a choice, subjects even prefer a combination of reputation building with costly punishment. The interaction between punishment and reputation building boosts cooperative efficiency. Because punishment and reputation building are omnipresent interacting forces in human societies, costly punishing should appear less destructive without losing its deterring force.

Cooperative Behavior↗

PubMed2006

Sequence-based species delimitation for the DNA taxonomy of undescribed insects.

Cataloging the very large number of undescribed species of insects could be greatly accelerated by automated DNA based approaches, but procedures for large-scale species discovery from sequence data are currently lacking. Here, we use mitochondrial DNA variation to delimit species in a poorly known beetle radiation in the genus Rivacindela from arid Australia. Among 468 individuals sampled from 65 sites and multiple morphologically distinguishable types, sequence variation in three mtDNA genes (cytochrome oxidase subunit 1, cytochrome b, 16S ribosomal RNA) was strongly partitioned between 46 or 47 putative species identified with quantitative methods of species recognition based on fixed unique ("diagnostic") characters. The boundaries between groups were also recognizable from a striking increase in branching rate in clock-constrained calibrated trees. Models of stochastic lineage growth (Yule models) were combined with coalescence theory to develop a new likelihood method that determines the point of transition from species-level (speciation and extinction) to population-level (coalescence) evolutionary processes. Fitting the location of the switches from speciation to coalescent nodes on the ultrametric tree of Rivacindela produced a transition in branching rate occurring at 0.43 Mya, leading to an estimate of 48 putative species (confidence interval for the threshold ranging from 47 to 51 clusters within 2 logL units). Entities delimited in this way exhibited biological properties of traditionally defined species, showing coherence of geographic ranges, broad congruence with morphologically recognized species, and levels of sequence divergence typical for closely related species of insects. The finding of discontinuous evolutionary groupings that are readily apparent in patterns of sequence variation permits largely automated species delineation from DNA surveys of local communities as a scaffold for taxonomy in this poorly known insect group.

Animals↗

PubMed1987

[Anti-amnesic effect of prolyl endopeptidase inhibitors in mice].

Based on the results of a previous report that prolyl endopeptidase (PPCE) inhibitors facilitated the acquisition of active avoidance response and retarded the extinction of the response, further studies were made on the effect of PPCE inhibitors on learning and the memory process. Using mice, tests were performed both in the light-dark discrimination Y-maze task and the lever-press task of the water reinforcement schedule, and mice were also tested in the acquisition and retention of one-trial "step-through" passive avoidance task. The effect of PPCE inhibitors were investigated both in control and electroconvulsive shock- or scopolamine-induced amnesic animals. Z-Pro-p, the most potent inhibitor among 5 compounds tested in this study, and arginine vasopressin (AVP) facilitated the learning process and retarded the extinction of the acquired response in all tests. Suc-Pro-p was also effective in the Y-maze and passive avoidance test. Thus, the effect of the test compounds were parallel with their in vitro activities as PPCE inhibitor. These results suggest that the anti-amnesic effect of PPCE inhibitors is partially attributable to their effect on the breakdown of the biologically active peptides which are involved in the memory process, such as AVP, in the brain.

Amnesia↗

PubMed1991

Vector population responses to control interventions.

In 1981, Kenyan authorities attempted eradication of tsetse (Glossina pallidipes) from the Lambwe valley, by sequential aerial spraying of endosulfan. Fly populations were reduced by over 99.9% in the main habitats, but recovered to their original levels within one year. In 1986, an Argentine research team attempted local elimination of domestic Triatominae (Triatoma infestans) in an area of Santiago del Estero. House infestation rates were reduced to an apparent zero, but recovered to pre-control levels in two years. In Sri Lanka, a combination of mosquito control with active case detection and treatment reduced malaria incidence to just 17 cases in 1964. Interruption of the programme then saw case incidence return to over 500,000 by 1969. These three examples-from African trypanosomiasis, South American Chagas disease and malaria-all illustrate the same process. Vector populations, infestation rates, and rates of disease transmission, can be reduced. The real problem is not in achieving the initial reduction, but in subsequently either driving the disease to extinction or maintaining it below acceptable levels. And this problem takes us beyond the simple analysis of interventions, into the complex realms of population behaviour set in its political, social and economic context. It seems that we have been too rarely concerned to plan and implement the long term surveillance and selective interventions that are required to translate initial gains into real success. In biological terms, we tend to ignore the complexity and robustness of vector populations and disease transmission cycles, especially their varied capacity to recover from interference. Moreover, in socio-political terms, a reduced problem-even one representing potential for future catastrophe-tends to claim less priority than present problems, even though premature redeployment of resources may abnegate gains already achieved. The problem is strongly compounded by methods of economic analysis where the benefits of avoiding future problems are strongly discounted in favour of short-term temporary gains. This paper seeks to open discussion on these long-term planning issues.

Animals↗

PubMed2000

Ecological symmetry breaking can favour the evolution of altruism in an action-response game.

The evolution of altruistic behaviour is studied in a simple action-response game with a tunable degree of conflict of interest. It is shown that for the continuous, mixed-medium approach no stable polymorphism favours altruism. Ecological dynamics are explored with the addition of a spatial dimension and a local energy variable. A continuous spatial model with finite local range does not introduce any substantial difference in the results with respect to the level of altruism. However, the model illustrates how ecological coupling may lead to the formation of stable spatial patterns in the form of discrete and isolated clusters of players as a consequence of inverse density dependence. A discrete, individual-based model is built in which local interactions are also modelled as occurring within a finite neighbourhood of each individual and spatial positions are not restricted as in lattice models. This model shows substantially different results. A high level of altruism is observed for low (but positive) degrees of conflict and this level decreases linearly for higher degrees of conflict. The evolution of altruism is explained by studying the broken symmetries introduced by the spatial clusters themselves, mainly between their central and peripheral regions which, in combination with the discrete and the stochastic nature of the model, result in the stabilization of strategies in which players behave altruistically towards the same type. As a consequence of the activity of the players, energy resources at the centre of an altruistic cluster are very depleted; so much so that, for low conflict, fitter non-altruistic mutants may initially invade only to become locally extinct due to their less efficient use of energy as their numbers increase. In peripheral regions invader may subsist; however, for geometrical reasons long-lasting genealogies tend to originate only at the centre of a cluster.

Altruism↗

PubMed1979

Photoreaction center of photosynthetic bacteria. 1. Further chemical characterization of the photoreaction center from Rhodospirillum rubrum.

The photoreaction center from Rhodospirillum rubrum contains about 90% protein, 6% pigment, mere traces of lipids, and no cytochromes. It also contains at least 1 mol of ubiquinone and 1 iron atom per mol. Its three-component polypeptide chains were isolated by preparative electrophoresis, and their molar stoichiometry was established as 1:1:1. The amino acid composition of the photoreaction center from strain S1 and from its subunits is reported. The protein as a whole contains about 65% nonpolar residues, and the degree of hydrophobicity of its subunits is alpha less than beta less than gamma. The minimal molecular weight based on the extinction coefficient and on the amino acid content is 90 000. This corresponds to a half-cystine mole number of 6.

Amino Acids↗

PubMed2005

Cycles in fossil diversity.

It is well known that the diversity of life appears to fluctuate during the course of the Phanerozoic, the eon during which hard shells and skeletons left abundant fossils (0-542 million years ago). Here we show, using Sepkoski's compendium of the first and last stratigraphic appearances of 36,380 marine genera, a strong 62 +/- 3-million-year cycle, which is particularly evident in the shorter-lived genera. The five great extinctions enumerated by Raup and Sepkoski may be an aspect of this cycle. Because of the high statistical significance we also consider the contributions of environmental factors, and possible causes.

Biodiversity↗

PubMed2003

Killer-sensitive coexistence in metapopulations of micro-organisms.

Many micro-organisms are known to produce efficient toxic substances against conspecifics and closely related species. The widespread coexistence of killer (toxin producer) and sensitive (non-producer) strains is a puzzle calling for a theoretical explanation. Based on stochastic cellular automaton simulations and the corresponding semi-analytical configuration-field approximation models, we suggest that metapopulation dynamics offers a plausible rationale for the maintenance of polymorphism in killer-sensitive systems. A slight trade-off between toxin production and population growth rate is sufficient to maintain the regional coexistence of toxic and sensitive strains, if toxic killing is a local phenomenon restricted to small habitat patches and local populations regularly go extinct and are renewed via recolonizations from neighbouring patches. Pattern formation on the regional scale does not play a decisive part in this mechanism, but the local manner of interactions is essential.

Ecosystem↗

PubMed2002

Accumulation of deleterious mutations: additional Drosophila melanogaster estimates and a simulation of the effects of selection.

We report an assay of egg-to-adult viability in full-sibling mutation accumulation (MA) lines derived from a completely homozygous population of Drosophila melanogaster and maintained for 210 generations. A simultaneous evaluation was also made of a large population derived from the same origin and maintained as a control for the same period. We also present computer simulations to explore the possible decline in viability of the control population due to mutation accumulation and the possible effect of selection within and between MA lines. For this purpose, we used two mutational models independent from the data analyzed and based on radically different assumptions. The first model implies a large number of mutations of small effect, whereas the second implies a much smaller number of mutations with much larger effects. The observed rate of decline in mean viability was very small but significant (0.077%). The rate of increase in among line variance (0.189 x 10(-3)) was similar to those obtained previously in the same lines. The simulation results indicated that a model of many mutations of small effect is incompatible with the evolution of the mean viability of the control and MA lines over generations, the distribution of line means after 210 generations of mutation accumulation, and the pattern of line extinction over generations. Basically, this model predicted a large drop in viability, both in the control and particularly the MA lines, that is not observed empirically. It also predicted a rate of line extinction too low in the early generations and too high in the later ones. In contrast, the model based on few mutations of large effect was generally consistent with all the observations.

Animals↗

PubMed2006

The impact of increased environmental stochasticity due to climate change on the dynamics of asiatic wild ass.

Theory proposes that increased environmental stochasticity negatively impacts population viability. Thus, in addition to the directional changes predicted for weather parameters under global climate change (GCC), the increase in variance of these parameters may also have a negative effect on biodiversity. As a case study, we assessed the impact of interannual variance in precipitation on the viability of an Asiatic wild ass (Equus hemionus) population reintroduced in Makhtesh Ramon Nature Reserve, Israel. We monitored the population from 1985 to 1999 to determine what environmental factors affect reproductive success. Annual precipitation during the year before conception, drought conditions during gestation, and population size determined reproductive success. We used the parameters derived from this model to assess population performance under various scenarios in a Leslie matrix type model with demographic and environmental stochasticity. Specifically, we used a change in the precipitation regime in our study area to formulate a GCC scenario and compared the simulated dynamics of the population with a no-change scenario. The coefficient of variation in population size under the global change scenario was 30% higher than under the no-change scenario. Minor die-offs (> or = 15%) following droughts increased extinction probability nearly 10-fold. Our results support the idea that an increase in environmental stochasticity due to GCC may, in itself, pose a significant threat to biodiversity.

Animals↗

PubMed2004

Species coextinctions and the biodiversity crisis.

To assess the coextinction of species (the loss of a species upon the loss of another), we present a probabilistic model, scaled with empirical data. The model examines the relationship between coextinction levels (proportion of species extinct) of affiliates and their hosts across a wide range of coevolved interspecific systems: pollinating Ficus wasps and Ficus, parasites and their hosts, butterflies and their larval host plants, and ant butterflies and their host ants. Applying a nomographic method based on mean host specificity (number of host species per affiliate species), we estimate that 6300 affiliate species are "coendangered" with host species currently listed as endangered. Current extinction estimates need to be recalibrated by taking species coextinctions into account.

Animals↗