170,373 research outputs found
Genetic Basis of Self-Incompatibility in the Lichen-Forming Fungus Lobaria pulmonaria and Skewed Frequency Distribution of Mating-Type Idiomorphs: Implications for Conservation
No full textFungal populations that reproduce sexually are likely to be genetically more diverse and have a higher adaptive potential than asexually reproducing populations. Mating systems of fungal species can be self-incompatible, requiring the presence of isolates of different mating-type genes for sexual reproduction to occur, or self-compatible, requiring only one. Understanding the distribution of mating-type genes in populations can help to assess the potential of self-incompatible species to reproduce sexually. In the locally threatened epiphytic lichen-forming fungus Lobaria pulmonaria (L.) Hoffm., low frequency of sexual reproduction is likely to limit the potential of populations to adapt to changing environmental conditions. Our study provides direct evidence of self-incompatibility (heterothallism) in L. pulmonaria. It can thus be hypothesized that sexual reproduction in small populations might be limited by an unbalanced distribution of mating-type genes. We therefore assessed neutral genetic diversity (using microsatellites) and mating-type ratio in 27 lichen populations (933 individuals). We found significant differences in the frequency of the two mating types in 13 populations, indicating a lower likelihood of sexual reproduction in these populations. This suggests that conservation translocation activities aiming at maximizing genetic heterogeneity in threatened and declining populations should take into account not only presence of fruiting bodies in transplanted individuals, but also the identity and balanced representation of mating-type genes
Notes on Amandinea Petermannii Comb.nov. (Physciaceae) from Antarctica
No full textThe new combination Amandinea petermannii (Hue) Matzer, Mayrh. & Scheidegger; is proposed. The taxonomy, morphology, anatomy, chemistry, ecology and distribution of this lichen are discussed. Rinodina convoluta D. C. Lindsay is synonym of A. petermanni
Highly variable microsatellite markers for the fungal and algal symbionts of the lichen Lobaria pulmonaria and challenges in developing biont-specific molecular markers for fungal associations
No full textThe availability of highly variable markers for the partners of a fungal symbiosis enables the integrated investigation of ecological and evolutionary processes at the symbiotic level. In this article we analyze the specificity of the first and to date only microsatellite markers that had been developed for an epiphytic lichen (Lobaria pulmonaria). We used DNA extracts from cultures of the fungal and of the green algal symbionts of L. pulmonaria as well as total DNA extracts from related Lobaria species associated with the same algal partner, and got evidence that five of the previously described microsatellite markers, proposed to be fungus-specific, are indeed alga-specific. Hence, highly variable microsatellite primer sets available for both, the algal and the fungal symbionts of L. pulmonaria are now at our hands, which allow us to investigate so far unexplored biological processes of lichen symbionts, such as codispersal and coevolution. In a broader sense, our work evaluates and discusses the challenges in developing biont-specific molecular markers for fungi forming close associations with other organisms. © 2010 The British Mycological Society
C. Scheidegger Laemmle, Werkpolitik in der Antike: Studien zu Cicero, Vergil, Horaz und Ovid, Verlag C.H. Beck, Muenchen 2016 (collana Zetemata. Monographien zur klassischen Altertumswissenschaft)
No full textRecensione al volume di C. Scheidegger Lämmle, "Werkpolitik in der Antike. Studien zu Cicero, Vergil, Horaz und Ovid" (C.H. Beck, München 2016), in cui si esaminano le strategie degli autori latini di età tardorepubblicana e augustea, volte a creare collegamenti tra le proprie opere per assicurarne la trasmissione integrale
Microsatellite markers for Dictyochloropsis reticulata (Trebouxiophyceae), the symbiotic alga of the lichen Lobaria pulmonaria (L.)
No full textWe isolated and characterized eight microsatellite markers for Dictyochloropsis reticulata, the primary photosynthetic partner of the epiphytic lichen Lobaria pulmonaria. These are the first microsatellite loci reported for a lichen symbiotic alga. These polymorphic markers will be useful for investigating spatial genetic structure, biogeography and dispersal of this eukaryotic alga and will generally shed light on the coevolution of the green-algal lichen symbioses. © 2009 Springer Science+Business Media B.V
Long-term consequences of disturbances on reproductive strategies of the rare epiphytic lichen Lobaria pulmonaria: Clonality a gift and a curse
No full textThe effect of disturbance on symbiotic organisms such as lichens is particularly severe. In case of heterothallic lichen-forming fungi, disturbances may lead to unbalanced gene frequency and patchy distribution of mating types, thus inhibiting sexual reproduction and imposing clonality. The impact of disturbance on reproductive strategies and genetic diversity of clonal systems has so far received little attention. To infer the effects of disturbances on mating-type allele frequencies and population structure, we selected three populations in the Parc Jurassien Vaudois (Switzerland), which were affected by uneven-aged forestry, intensive logging and fire, respectively. We used microsatellite markers to infer genetic diversity, allelic richness and clonal diversity of the epiphytic lichen Lobaria pulmonaria and used L. pulmonaria-specific MAT1-1 and MAT1-2 markers to analyse the frequency and distribution of mating types of 889 individuals. Our study shows that stand-replacing disturbances affect the mating-type frequency and distribution, thus compromising the potential for sexual reproduction. The fire-disturbed area had a significantly lower genetic and genotypic diversity and a higher clonality. Furthermore, the majority of compatible mating pairs in this area were beyond the effective vegetative dispersal range of the species. We conclude that stand-replacing disturbances lead to lower chances of sex and symbiont reshuffling and thus have long-lasting negative consequences on the reproductive strategies and adaptive potential of epiphytic lichen symbioses
Vertical and horizontal photobiont transmission within populations of a lichen symbiosis
No full textLichens are widespread symbioses and play important roles in many terrestrial ecosystems. The genetic structure of lichens is the result of the association between fungal and algal populations constituting the lichen thallus. Using eight fungus- and seven alga-specific highly variable microsatellite markers on within-population spatial genetic data from 62 replicate populations across Europe, North America, Asia and Africa, we investigated the contributions of vertical and horizontal transmission of the photobiont to the genetic structure of the epiphytic lichen Lobaria pulmonaria. Based on pairwise comparisons of multilocus genotypes defined separately for the mycobiont and for the photobiont, we inferred the transmission mode of the photobiont and the relative contribution of somatic mutation and recombination. After constraining the analysis of one symbiont to pairs of individuals with genetically identical symbiotic partners, we found that 77% of fungal and 70% of algal pairs were represented by clones. Thus, the predominant dispersal mode was by means of symbiotic vegetative propagules (vertical transmission), which dispersed fungal and algal clones co-dependently over a short distance, thus shaping the spatial genetic structure up to distances of 20 m. Evidence for somatic mutation generating genetic diversity was found in both symbionts, accounting for 30% of pairwise comparisons in the alga and 15% in the fungus. While the alga did not show statistically significant evidence of recombination, recombination accounted for 7.7% of fungal pairs with identical algae. This implies that, even in a mostly vegetatively reproducing species, horizontal transmission plays a role in shaping the symbiotic association, as shown in many coral and other symbioses in nature. © 2012 Blackwell Publishing Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Constrained deep neural network architecture search for IoT devices accounting for hardware calibration
No full textDeep neural networks achieve outstanding results for challenging image classification tasks. However, the design of network topologies is a complex task, and the research community is conducting ongoing efforts to discover top-accuracy topologies, either manually or by employing expensive architecture searches. We propose a unique narrow-space architecture search that focuses on delivering low-cost and rapidly executing networks that respect strict memory and time requirements typical of Internet-of-Things (IoT) near-sensor computing platforms. Our approach provides solutions with classification latencies below 10 ms running on a low-cost device with 1 GB RAM and a peak performance of 5.6 GFLOPS. The narrow-space search of floating-point models improves the accuracy on CIFAR10 of an established IoT model from 70.64% to 74.87% within the same memory constraints. We further improve the accuracy to 82.07% by including 16-bit half types and obtain the highest accuracy of 83.45% by extending the search with model-optimized IEEE 754 reduced types. To the best of our knowledge, this is the first empirical demonstration of more than 3000 trained models that run with reduced precision and push the Pareto optimal front by a wide margin. Within a given memory constraint, accuracy is improved by more than 7% points for half and more than 1% points for the best individual model format
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