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Results for “Evolution of cooperation”

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PubMed2005

Sexual cooperation: mating increases longevity in ant queens.

Divergent reproductive interests of males and females often cause sexual conflict . Males of many species manipulate females by transferring seminal fluids that boost female short-term fecundity while decreasing their life expectancy and future reproductivity . The life history of ants, however, is expected to reduce sexual conflict; whereas most insect females show repeated phases of mating and reproduction, ant queens mate only during a short period early in life and undergo a lifelong commitment to their mates by storing sperm . Furthermore, sexual offspring can only be reared after a sterile worker force has been built up . Therefore, the males should also profit from a long female lifespan. In the ant Cardiocondyla obscurior, mating indeed has a positive effect on the lifetime reproductive success of queens. Queens that mated to either one fertile or one sterilized male lived considerably longer and started laying eggs earlier than virgin queens. Only queens that received viable sperm from fertile males showed increased fecundity. The lack of a trade-off between fecundity and longevity is unexpected, given evolutionary theories of aging . Our data instead reveal the existence of sexual cooperation in ants.

Animals↗
PubMed2000

The population genetics of ecological specialization in evolving Escherichia coli populations.

When organisms adapt genetically to one environment, they may lose fitness in other environments. Two distinct population genetic processes can produce ecological specialization-mutation accumulation and antagonistic pleiotropy. In mutation accumulation, mutations become fixed by genetic drift in genes that are not maintained by selection; adaptation to one environment and loss of adaptation to another are caused by different mutations. Antagonistic pleiotropy arises from trade-offs, such that the same mutations that are beneficial in one environment are detrimental in another. In general, it is difficult to distinguish between these processes. We analysed the decay of unused catabolic functions in 12 lines of Escherichia coli propagated on glucose for 20,000 generations. During that time, several lines evolved high mutation rates. If mutation accumulation is important, their unused functions should decay more than the other lines, but no significant difference was observed. Moreover, most catabolic losses occurred early in the experiment when beneficial mutations were being rapidly fixed, a pattern predicted by antagonistic pleiotropy. Thus, antagonistic pleiotropy appears more important than mutation accumulation for the decay of unused catabolic functions in these populations.

Adaptation, Physiological↗
PubMed2002

Paternity-parasitism trade-offs: a model and test of host-parasite cooperation in an avian conspecific brood parasite.

Efforts to evaluate the evolutionary and ecological dynamics of conspecific brood parasitism in birds and other animals have focused on the fitness costs of parasitism to hosts and fitness benefits to parasites. However, it has been speculated recently that, in species with biparental care, host males might cooperate with parasitic females by allowing access to the host nest in exchange for copulations. We develop a cost-benefit model to explore the conditions under which such host-parasite cooperation might occur. When the brood parasite does not have a nest of her own, the only benefit to the host male is siring some of the parasitic eggs (quasi-parasitism). Cooperation with the parasite is favored when the ratio of host male paternity of his own eggs relative to his paternity of parasitic eggs exceeds the cost of parasitism. When the brood parasite has a nest of her own, a host male can gain additional, potentially more important benefits by siring the high-value, low-cost eggs laid by the parasite in her own nest. Under these conditions, host males should be even more likely to accept parasitic eggs in return for copulations with the parasitic female. We tested these predictions for American coots (Fulica americana), a species with a high frequency of conspecific brood parasitism. Multilocus DNA profiling indicated that host males did not sire any of the parasitic eggs laid in host nests, nor did they sire eggs laid by the parasite in her own nest. We used field estimates of the model parameters from a four-year study of coots to predict the minimum levels of paternity required for the costs of parasitism to be offset by the benefits of mating with brood parasites. Observed levels of paternity were significantly lower than those predicted under a variety of assumptions, and we reject the hypothesis that host males cooperated with parasitic females. Our model clarifies the specific costs and benefits that influence host-parasite cooperation and, more generally, yields precise predictions about expected levels of host male paternity. These predictions will enable a more rigorous assessment of field studies designed to test adaptive hypotheses of host-parasite cooperation.

Animals↗
PubMed2002

Dynamics of Pleistocene population extinctions in Beringian brown bears.

The climatic and environmental changes associated with the last glaciation (90,000 to 10,000 years before the present; 90 to 10 ka B.P.) are an important example of the effects of global climate change on biological diversity. These effects were particularly marked in Beringia (northeastern Siberia, northwestern North America, and the exposed Bering Strait) during the late Pleistocene. To investigate the evolutionary impact of these events, we studied genetic change in the brown bear, Ursus arctos, in eastern Beringia over the past 60,000 years using DNA preserved in permafrost remains. A marked degree of genetic structure is observed in populations throughout this period despite local extinctions, reinvasions, and potential interspecies competition with the short-faced bear, Arctodus simus. The major phylogeographic changes occurred 35 to 21 ka B.P., before the glacial maximum, and little change is observed after this time. Late Pleistocene histories of mammalian taxa may be more complex than those that might be inferred from the fossil record or contemporary DNA sequences alone.

Animals↗
PubMed1999

Management of celiac disease.

Celiac disease (CD), perceived as a rare cause of chronic diarrhea three decades ago, was diagnosed as a cause of diarrhea in 60 (7.5%) post weaned children among 800 cases of chronic diarrhea. The diagnosis was established on the basis of a detailed clinical history, histopathological studies on small bowel mucosa and a complete recovery on gluten free diets. Thirty four children were followed up for a period of 0.3 to 8.2 years (mean 3.45 +/- 2.28). Catch up growth was seen in all. A rapid gain in height and weight was observed in first year following exclusion of gluten from the diet. However, on subsequent follow up, flattening of growth curve was seen in 9 subjects which was attributed to non-compliance of gluten free diets and dietary inadequacies. Strict dietary compliance is difficult to adhere to with wheat being a staple cereal in India. Other factors affecting compliance include lack of awareness and non availability of gluten free diets as well as contamination of other items with wheat at grocery shops. A few cases may present as celiac crisis which is a medical emergency requiring aggressive management including use of corticosteroids to improve survival in this otherwise life threatening situation. Effective management of CD requires intense family cooperation as well as concerted national efforts to provide these patients easy access to gluten free diets. The evolution of Celiac Societies, and widespread dissemination of knowledge through all available media will greatly help in management of patients with this chronic disease.

Celiac Disease↗
PubMed2000

Rapid evolution of NK cell receptor systems demonstrated by comparison of chimpanzees and humans.

That NK cell receptors engage fast-evolving MHC class I ligands suggests that they, too, evolve rapidly. To test this hypothesis, the structure and class I specificity of chimpanzee KIR and CD94:NKG2 receptors were determined and compared to their human counterparts. The KIR families are divergent, with only three KIR conserved between chimpanzees and humans. By contrast, CD94:NKG2 receptors are conserved. Whereas receptors for polymorphic class I are divergent, those for nonpolymorphic class I are conserved. Although chimpanzee and human NK cells exhibit identical receptor specificities for MHC-C, they are mediated by nonorthologous KIR. These results demonstrate the rapid evolution of NK cell receptor systems and imply that "catching up" with class I is not the only force driving this evolution.

Animals↗
PubMed2004

Cytonuclear coevolution: the genomics of cooperation.

Without mitochondria we would be in big trouble, and there would be a global biological energy crisis if it were not for chloroplasts. Fortunately, genomic evolution over the past two billion years has ensured that the functions of these key organelles are with us to stay. Whole-genome analyses have not only proven that mitochondria and chloroplasts are descended from formerly free-living bacteria, but have also shown that it is difficult to define eukaryotes without reference to the fusion and coevolution of host and endosymbiont genomes. Here, we review how the macro- and microevolutionary insights that follow from the genomics of cytonuclear interactions are uniting molecular evolution, structural proteomics, population genetics and problems in aging and disease. Our goals are to clarify the coevolutionary events that have governed nuclear and organelle evolution, and to encourage further critical analyses of these interactions as problems in the study of co-adapted gene complexes.

Journal Article↗
PubMed2000

Digression on chemical electromagnetic field effects in membrane signal transduction--cooperativity paradigm of the acetylcholine receptor.

There is ongoing public concern on potential hazards and risks of even small electromagnetic fields (EMFs) such as those emanating from electrical appliances. Evolution and persistence of life in the natural geofields and basic scientific experience in using technical EMFs (F) suggest that, in general, living matter is remarkably stable against external field perturbations within the technical safety limits of the EM field strengths. Besides the trivial primary effects of EMF on ionic charges and dipolar matter, it is explicitly elaborated that cellular biochemical reactivity and channel transport processes are field dependent. However, equilibrium (K) and rate (k) constants are only sensitive to F if the reaction moments deltaM are finite, as seen in the general van't Hoff relationship d ln K/dF = deltaM/RT. Indeed, it is the difference (deltaM) in the electric or magnetic moments (M), representing the difference in the field forces on the reaction partners, that determines the extent of the field-induced transitions, say from an inactive conformer of a macromolecule to an active one. If small EM fields, which locally can only cause small shifts in K and k, are to become effective for chemical reactivity, amplification is required. A widely encountered concept of chemical amplification is structural, and thus functional, cooperativity, realized in many biopolymers. The cooperation of n units of such a polymer yields a larger deltaM(n)= ndeltaM and exponentially increases the field sensitivity of the overall equilibrium constant K(n) = Kn. Using the acetylcholine receptor protein as an example for signal amplification by structural cooperativity, explicit proposals are specified for the presumed amplification of small local field effects on proteins of the classical signal transduction cascades. Electric membrane field amplification by interfacial polarization in external fields is discussed in the context of using electric field pulses to transiently permeabilize cells and tissue for the direct transfer of effector substances and genes in cancer and gene therapy.

Cell Membrane↗
PubMed1995

An evolutionary perspective on signaling in behavior and immunology.

Signaling and communication are important at different levels of biological organization. Signals exchanged between cells of the immune system initiate and coordinate the immune response; signals exchanged between individuals often coordinate social behavior. Behavioral ecologists interested in the evolution and functional design of signals exchanged between individuals have produced a theory of signaling and communication that stresses the importance of cooperation and conflict; if a conflict of interest between signaler and receiver is great enough, signals evolve towards greater reliability. We suggest that the application of signaling system theory to signals exchanged between cells within an individual will allow for a better understanding of immunity and intra-individual communication in general, with potential for novel approaches to the treatment of disease.

Allergy and Immunology↗