1,721,066 research outputs found
Computer simulations of kin selection
No full textThe theory of kin selection is central to the understanding of social evolution. Recent theoretical work suggests a limitation on the action of kin selection in structured populations. The first such limit involves a specialized population structure, termed "budding viscosity," common to social insects, in which new groups are formed by fission with no individual dispersal. An argument based on the separation of kin selection dynamics into among and within group components suggests that kin selection cannot operate in this structure. However, stochastic computer simulations show that random variation among daughter groups can supply the needed among-groups variation and allow kin selection to proceed. The second limit on kin selection involves simple population viscosity, in which individuals disperse limited distances and so are related to their neighbors. Altruism toward neighbors, favored by kin selection, is opposed by local competition. Computer simulation confirms this limitation and shows that some form of specific kin recognition is required to favor the evolution of altruism by kin selection. All applications of kin selection require a measure of genetic relatedness; a computer program for calculating this statistic from genetic data on natural populations is described
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Conflict and cooperation in the tropical wasp, Parachartergus colobopterus, and the chimeric multicellular organism, Dictyostelium discoideum
No full textSeveral transitions to higher levels of biological organization have punctuated the history of life. These transitions occur when cooperative alliances lead to the integration of non-identical partners into more complex wholes. Yet there is inevitable conflict within these cooperative alliances. In the following chapters I investigate reproductive conflicts of interest between cooperators within insect societies and chimeric multicellular organisms. In the first chapter I show that in the tropical wasp, Parachartergus colobopterus, workers use aggression toward totipotent, emerging females to influence the reproductive future of the latter. By doing this workers resolve conflict over who reproduces in accord with their collective interests. In the second chapter I show that environmental heterogeneity can affect the outcome of conflict between co-aggregating clonal lineages of Dictyostelium discoideum. This helps account for the coexistence of cheaters and victims in natural populations of D. discoideum
Reproductive conflicts in the social wasp, Eustenogaster fraterna, and in the social amoeba, Dictyostelium discoideum
No full textMy dissertation encompasses three studies of social behavior. Two explore the reproductive conflicts that occur between cooperating individuals. I examine conflict at two levels: within colonies of the social wasp, Eustenogaster fraterna, and within chimeric multicellular organisms formed by the social amoeba, Dictyostelium discoideum. The third project investigates the occurrence of sexual reproduction in a natural population of D. discoideum.
Eustenogaster fraterna belongs to the basal eusocial family of stenogastrine wasps. Colonies are small averaging only 2.7 adult females but only one mated female. I examined the reproductive and genetic structure of 18 colonies by genotyping all within-colony individuals and assessing the ovarian development of females. My results show that 85% of females were potential reproducers. Adult females were not related as full sisters. Some brood could not be assigned to any of the adult females, suggesting that subordinate females could inherit the nest and replace the dominant female.
D. discoideum live as free-living, single cells, but when starved they aggregate to form a multicellular fruiting body. Genetically distinct clones of D. discoideum co-aggregate to form genetic chimeras. 20% of cells form the stalk of the fruiting body and die, while others become reproductive spores. One clone can exploit the other by contributing less than its proportional share to the sterile stalk. I investigated whether cheating is a strategy dependent on the relative proportion of the clones aggregating. In a chimera, a rare clone could benefit by avoiding forming the stalk because it is less related to the reproductive part. My results do not support the frequency-dependence strategy.
I investigated the occurrence of sexual reproduction in a natural population of D. discoideum, using the approach of estimating linkage disequilibrium in the population at one site. My results show that recombination does occur and is due to sexual reproduction not to parasexuality.
In sum, conflicts within societies can be mitigated. E. fraterna workers gain insurance advantages by obtaining indirect genetic benefits or inheritance of work force. D. discoideum clones gain cheating advantages either when rare or common in the aggregation. Recombination yields novel genotypes; this might increase the complexity of interactions between co-aggregating clones
Evolutionary conflict in chimeras of the social amoeba, Dictyostelium discoideum
No full textMolecular biologists have extensively studied Dictyostelium discoideum and consider it a model organism for the study of cellular differentiation but paradoxically many aspects of the natural life and evolution of this organism are unknown. My study demonstrates there is high clonal diversity in nature and that different clones coexist in the same small soil sample. Thus, amoebae with different genotypes can join in the same multicellular organism making a genetic chimera in nature. I also show that a linear dominance hierarchy describes the interactions of genetically distinct clones in competition for survival in the multicellular stage. In fact, during this stage the amoebae differentiate into different types of cells allowing the pseudoplasmodium to form a fruiting body consisting of two principle cell types: the spore and the stalk cells. The formation of the fruiting body probably guarantees a better survival and dispersion of the spore but requires the death of 20% of the cells that initially comprise the pseudoplasmodium that differentiate into the stalk and the basal disc. Contributions of two clones in a chimera to spore and stalk are often unequal, with one clone taking advantage of the other's stalk contribution. To assess whether there was a hierarchy of exploitation among clones, I competed all possible pairs among seven clones. I found a clear linear hierarchy with one clone being most dominant, and the bottom clone losing in competition to all the others. The hierarchy at an earlier stage, evaluated with prespore and prestalk cells in the slug, was not as clear. These results suggest that there is a single principal mechanism for differential contribution to the spore and that it involves more than spore/stalk competition.
My results legitimate the use of chimeric D. discoideum as a model organism for the investigation of issues relating to coexistence and conflict between cells during organismal development and thus as a simple model for the relationship between social organisms
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Fitness consequences of genetic and phenotypic chimeras in the social amoeba, Dictyostelium discoideum
No full textMulticellular organisms regularly eliminate unfit or harmful cells in the process of normal development. This high level of cooperation is maintained because all cells within the organism are genetically identical and thus, have the same evolutionary interests. However, there are some multicellular organisms that develop not from a single cell but from many individuals. In the case of the social amoebae, Dictyostelium discoideum, the usually solitary amoebae aggregate with nearby cells when starving to form a motile, multicellular slug that migrates to the soil surface and forms a fruiting body consisting of a bail of spores held aloft by a stalk of dead cells. These aggregations may be a mix of genetically identical individuals or of multiple clones, called genetic chimeras. Within chimeras, a conflict may arise over which cells contribute to the reproductive spores versus the dead stalk. Previous work on D. discoideum has shown that uniclonal slugs migrate further than chimeric slugs of the same size across agar. Here we test whether this resuits in a fitness cost under more natural conditions. We examined migration of slugs across decaying leaves and soil as well as migration up through layers of these substrates, closely reflecting the natural migration of D. discoideum slugs in the wild. In most trials, chimeras performed worse than single clones. Thus, chimerism in D. discoideum should produce a fitness cost likely to be important in nature. Since D. discoideum readily mixes with multiple clones, the potential for conflict is high. Diverging evolutionary interests in chimeras could influence adaptive strategies for filling the spore and stalk roles. Here we explore the strategy for filling these roles in phenotypic chimeras, mixes of cells differing only in physical condition. We explore the fitness of D. discoideum spores and found that cells with better prospects tend to represent the subsequent generations. However, we also found that D. discoideum amoebae did not respond to the condition of cells with which they aggregate. Our results indicate that, within a genetically identical population, the differentiation of spore and stalk roles is a competition based on the condition of the individual cells
Evolution of trinucleotide microsatellite sequence variation across the Polistinae, a social wasp subfamily
No full textI examined sequences of 3 microsatellite loci that were derived from Polistes bellicosus investigated their evolution in 78 species from four tribes in the Polistinae subfamily of wasps. I found that the basic repeat structure of the microsatellite repeat region at these three loci was conserved across species at the subgenus level. Besides changes in the number of repeats, base substitutions were the dominant mutations in the repeat regions. The tribe from which the loci were isolated had longer repeat regions and more perfect repeats that the tribes at the same loci. At microsatellite flanking regions, I found that a high proportion of insertions duplicated 1-4 bases of their preceding sequences. Microsatellite repeats may originate from these such little insertions
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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