Viral Infection Spreading and Mutation in Cell Culture

A new model of viral infection spreading in cell cultures is proposed taking into account virus mutation. This model represents a reaction-diffusion system of equations with time delay for the concentrations of uninfected cells, infected cells and viral load. Infection progression is characterized by the virus replication number Rv, which determines the total viral load. Analytical formulas for the speed of propagation and for the viral load are obtained and confirmed by numerical simulations. It is shown that virus mutation leads to the emergence of a new virus variant. Conditions of the coexistence of the two variants or competitive exclusion of one of them are found, and different stages of infection progression are identified.

Spatial scales of competition and a growth-motility tradeoff interact to determine bacterial coexistence

The coexistence of competing species is a long-lasting puzzle in evolutionary ecology research. Despite abundant experimental evidence showing that the opportunity for coexistence decreases as niche overlap increases between species, bacterial species and strains competing for the same resources are commonly found across diverse spatially heterogeneous habitats. We thus hypothesized that the spatial scale of competition may play a key role in determining bacterial coexistence, and interact with other mechanisms that promote coexistence, including a growth-motility tradeoff. To test this hypothesis, we let two Pseudomonas putida strains compete at local and regional scales by inoculating them either in a mixed droplet or in separate droplets in the same Petri dish, respectively. We also created conditions that allow the bacterial strains to disperse across abiotic or fungal hyphae networks. We found that competition at the local scale led to competitive exclusion while regional competition promoted coexistence. When competing in the presence of dispersal networks, the growth-motility tradeoff promoted coexistence only when the strains were inoculated in separate droplets. Our results provide a mechanism by which existing laboratory data suggesting competitive exclusion at a local scale is reconciled with the widespread coexistence of competing bacterial strains in complex natural environments with dispersal.

Trophic relationships among three species of ornamental fish from the region of Lake Amanã, Amazon

The present study objectified to evaluate the trophic relationships and the possible aggressive mimicry involving Carnegiella strigata, Carnegiella marthae and Gnathocharax steindachneri, in lowland forest streams. Samplings occurred in November 2002, March and August 2003 in Amanã Sustainable Development Reserve (ASDR). The total of 943 fish was caught, being 79.43% of C. marthae, 3.18% of C. strigata and 17.39% of G. steindachneri. Stomach contents, degree of stomach repletion, relative volume and frequency of occurrence of food items were evaluated. Thirteen food items were identified, and the presence of terrestrial and aquatic insects indicates the high dependence of these species and the flooded forest. Low feeding overlap was observed between Carnegiella strigata and C. marthae compared to Gnathocharax steindachneri. However, the overlap between the two Carnegiella species was relatively high, which could explain the low frequency of syntopic occurrence among these species, suggesting a possible case of competitive exclusion.

Comparison of the Floristic Composition and Diversity of Two Wetlands in Ethiopian

The main purpose of this study was to determine and compare the floristic composition and diversity indices of Washa and Borale Wetlands, located in Central Ethiopian. As revealed in the result, 74 species belonging to 26 families, and 57 genera were identified. Asteraceae and Poaceae were the most dominant families contributing 24.56% and 14.04% to the total genera, and 20.27% and 16.22% to the total species identified, respectively. Of the total, about 92% plant species were herbs, whereas 1% was climber, the least one. The alpha diversity of the Washa and Borale wetlands were 51 and 64, respectively. The average richness of the Washa and Borale wetlands were 12.3 ±0.91, and 15.35 ± 0.89, respectively. Likewise, the Shannon diversity (H’) and evenness (E) of Washa and Borale sites were 2.24 and 0.87, and 2.67 and 0.97 respectively. Accordingly, based on their average values, the diversity, evenness and richness indices were higher in Borale than Washa sites, and showed significance difference between the two wetlands (P < 0.05). Likewise, in both sites, especially in Borale, the majority of the species were native, annual and upland, implying the suitability of the wetlands to these native, but to annual and upland invaders due to the ecological and hydrological modifications of the wetlands, and competitive exclusion of the native aquatic plants by upland annual plants. Generally, many of the wetlands’ species were annual and upland invaders. Hence, in-situ and ex-situ strategic plans are required for restoring the wetlands via giving priority.

The Ecological Interpretation of Unbiased Estimator for the Taxonomic Ratio: Different Approaches for Local and Regional Flora

Taxonomic ratio in an ecological context is considered as an indicator of the level of competitive exclusion. In spite of more than a century of discussions on taxonomic ratio, the problem of finding an unbiased estimator for flora characterisation remains unsolved. The traditional form of taxonomic ratio (species/genus or species/families ratio) is biased, which depends on the area of territory for which the floral composition was established. This circumstance makes the taxonomic ratio an inadequate characteristic of the flora. To solve the problem of finding an unbiased estimator for the taxonomic ratio, we have combined two fundamental ecological generalisations. The first is that species that belong to the same genus usually live in similar habitats and have similar morphological features. The struggle for life between species from the same genus is, therefore, more intense than between species from different genera. The second is species–area relationship. We have considered the problem of finding an unbiased taxonomic relationship using the Arrhenius curves to fit species–area relationships. This combination allowed us to find a form of unbiased taxonomic relationship. The example of Cyanophyceae flora shows that this indicator is closely related to a wide range of ecological and biogeographical characteristics of vegetation. The residual of the linear equation of dependence of the logarithm of the number of species on the logarithm of the number of genera is an unbiased indicator of the taxonomic relation, which is independent of the number of genera (or number of families) and the sampling size (or area). An unbiased taxonomic relationship is a characteristic of regional flora, which depends on a wide range of its ecological and biogeographical features.

Effects of Vertical Spatial Overlap on Phytoplankton Diversity under Experimentally Altered Lake Stratification Regimes

In phytoplankton communities, competitive exclusion might occur when functionally similar species are impeded from regulating their positions along light and nutrient gradients to reduce niche overlap. Greater spatial overlap (SO) between species due to water column mixing could thus promote competitive exclusion, reducing community taxonomic diversity. However, greater SO could also promote coexistence of functionally different taxa. Using data from a whole-lake experiment, we investigated the effects of SO and other relevant environmental factors on phytoplankton diversity across the water columns of lake basins with different thermocline manipulations. We estimated SO using an in situ fluorometer, and overall community diversity microscopically. Using structured equation models, we estimated directional relationships between phytoplankton diversity, SO, the lake physical structure and the zooplankton community. No significant effect of SO on phytoplankton taxonomic diversity was observed, but higher SO was associated with greater functional diversity. Change in lake physical structure and in the zooplankton community also affected diversity, with a negative response to increased top-down interactions. Overall, despite the fact that the alteration of water column stratification structure and top-down interactions were stronger drivers of phytoplankton diversity in our system, some effect of spatial overlap on the outcome of inferred competitive interactions were observable.

Flower morphological differentiation and plant-pollinator interactions among sympatric Aframomum species (Zingiberaceae) with floral trumpet type in the tropical African rainforest

Background and aims – Diversification in plant-pollinator interactions based on floral diversity is potentially a mechanism of coexistence in angiosperms. However, besides high floral diversity, some genera seemingly exhibit the same floral type in many of their species. This contradicts some expectations of competitive exclusion. We thus tested on a finer flower morphological scale whether five sympatric Aframomum species (61 spp., Zingiberaceae) in southeastern Gabon exhibiting the same general floral type (trumpet) were differentiated, and whether this resulted in different “pollinator niches”.Material and methods – We carried out a detailed survey measuring 18 flower morphological parameters as well as nectar volume (μl) and sugar concentration (% Brix) on five flowers per species and locality. Furthermore, we observed inflorescence phenology and pollinator activity from 8 am to 4 pm for 12 to 50 hours per species and conducted pollinator exclusion experiments.Key results – This study proves fine-scale flower morphological and resource differentiation within the trumpet floral type. Pollination-relevant parts of the flowers, however, remain constant across species. Our pollinator observations reveal the same broad bee pollinator spectrum for all observed simultaneously flowering sympatric species.Conclusion – As we could not detect a pollinator-based differentiation in the studied sympatric Aframomum species we assume that species boundaries developed randomly by genetic drift during geographic isolation in the past. The trumpet floral type and its pollinator guild, however, were maintained due to similar selection pressures in comparable habitats during isolation and are potentially an advantage for increased pollinator attraction through co-flowering.

Ccp1-Ndc80 switch at the N terminus of CENP-T regulates kinetochore assembly

Kinetochores, a protein complex assembled on centromeres, mediate chromosome segregation. In most eukaryotes, centromeres are epigenetically specified by the histone H3 variant CENP-A. CENP-T, an inner kinetochore protein, serves as a platform for the assembly of the outer kinetochore Ndc80 complex during mitosis. How CENP-T is regulated through the cell cycle remains unclear. Ccp1 (counteracter of CENP-A loading protein 1) associates with centromeres during interphase but delocalizes from centromeres during mitosis. Here, we demonstrated that Ccp1 directly interacts with CENP-T. CENP-T is important for the association of Ccp1 with centromeres, whereas CENP-T centromeric localization depends on Mis16, a homolog of human RbAp48/46. We identified a Ccp1-interaction motif (CIM) at the N terminus of CENP-T, which is adjacent to the Ndc80 receptor motif. The CIM domain is required for Ccp1 centromeric localization, and the CIM domain–deleted mutant phenocopies ccp1Δ. The CIM domain can be phosphorylated by CDK1 (cyclin-dependent kinase 1). Phosphorylation of CIM weakens its interaction with Ccp1. Consistent with this, Ccp1 dissociates from centromeres through all stages of the cell cycle in the phosphomimetic mutant of the CIM domain, whereas in the phospho-null mutant of the domain, Ccp1 associates with centromeres during mitosis. We further show that the phospho-null mutant disrupts the positioning of the Ndc80 complex during mitosis, resulting in chromosome missegregation. This work suggests that competitive exclusion between Ccp1 and Ndc80 at the N terminus of CENP-T via phosphorylation ensures precise kinetochore assembly during mitosis and uncovers a previously unrecognized mechanism underlying kinetochore assembly through the cell cycle.