The importance of immune gene variability (MHC) in evolutionary ecology and conservation

Genetic studies have typically inferred the effects of human impact by documenting patterns of genetic differentiation and levels of genetic diversity among potentially isolated populations using selective neutral markers such as mitochondrial control region sequences, microsatellites or single nucleotide polymorphism (SNPs). However, evolutionary relevant and adaptive processes within and between populations can only be reflected by coding genes. In vertebrates, growing evidence suggests that genetic diversity is particularly important at the level of the major histocompatibility complex (MHC). MHC variants influence many important biological traits, including immune recognition, susceptibility to infectious and autoimmune diseases, individual odours, mating preferences, kin recognition, cooperation and pregnancy outcome. These diverse functions and characteristics place genes of the MHC among the best candidates for studies of mechanisms and significance of molecular adaptation in vertebrates. MHC variability is believed to be maintained by pathogen-driven selection, mediated either through heterozygote advantage or frequency-dependent selection. Up to now, most of our knowledge has derived from studies in humans or from model organisms under experimental, laboratory conditions. Empirical support for selective mechanisms in free-ranging animal populations in their natural environment is rare. In this review, I first introduce general information about the structure and function of MHC genes, as well as current hypotheses and concepts concerning the role of selection in the maintenance of MHC polymorphism. The evolutionary forces acting on the genetic diversity in coding and non-coding markers are compared. Then, I summarise empirical support for the functional importance of MHC variability in parasite resistance with emphasis on the evidence derived from free-ranging animal populations investigated in their natural habitat. Finally, I discuss the importance of adaptive genetic variability with respect to human impact and conservation, and implications for future studies

Validation of internal reference genes for quantitative real-time PCR in a non-model organism, the yellow-necked mouse, Apodemus flavicollis

<p>Abstract</p> <p>Background</p> <p>Reference genes are used as internal standards to normalize mRNA abundance in quantitative real-time PCR and thereby allow a direct comparison between samples. So far most of these expression studies used human or classical laboratory model species whereas studies on non-model organism under in-situ conditions are quite rare. However, only studies in free-ranging populations can reveal the effects of natural selection on the expression levels of functional important genes. In order to test the feasibility of gene expression studies in wildlife samples we transferred and validated potential reference genes that were developed for lab mice (<it>Mus musculus</it>) to samples of wild yellow-necked mice, <it>Apodemus flavicollis</it>. The stability and suitability of eight potential reference genes was accessed by the programs BestKeeper, NormFinder and geNorm.</p> <p>Findings</p> <p>Although the three programs used different algorithms the ranking order of reference genes was significantly concordant and geNorm differed in only one, NormFinder in two positions compared to BestKeeper. The genes ordered by their mean rank from the most to the least stable gene were: <it>Rps18</it>, <it>Sdha</it>, <it>Canx</it>, <it>Actg1</it>, <it>Pgk1</it>, <it>Ubc</it>, <it>Rpl13a </it>and <it>Actb</it>. Analyses of the normalization factor revealed best results when the five most stable genes were included for normalization.</p> <p>Discussion</p> <p>We established a SYBR green qPCR assay for liver samples of wild <it>A. flavicollis </it>and conclude that five genes should be used for appropriate normalization. Our study provides the basis to investigate differential expression of genes under selection under natural selection conditions in liver samples of <it>A. flavicollis</it>. This approach might also be applicable to other non-model organisms.</p

Diverse MHC IIB allele repertoire increases parasite resistance and body condition in the Long-tailed giant rat (Leopoldamys sabanus)

<p>Abstract</p> <p>Background</p> <p>Genes of the major histocompatibility complex (MHC) code for key functions in the adaptive immune response of vertebrates and most of them show exceptionally high polymorphism. This polymorphism has been associated with the selection by diverse and changing parasite communities. We analysed MHC class IIB diversity, gastrointestinal parasite load and body condition in the wild ranging tropical rat <it>Leopoldamys sabanus </it>(Thomas, 1887) under natural selection conditions in a highly variable rainforest environment in Borneo to explore the mechanisms that maintain these high levels of genetic polymorphism.</p> <p>Results</p> <p>Allelic diversity was determined via SSCP and sequencing, and parasite screening was done through non-invasive faecal egg count. The detected alleles showed expected high levels of polymorphism and balancing selection. Besides a clear advantage for more diverse MHC genotypes in terms of number of alleles, reflected in better body condition and resistance against helminth infection, our data also suggested a positive effect of MHC allele divergence within an individual on these parameters.</p> <p>Conclusion</p> <p>In accordance with the heterozygote advantage hypothesis, this study provides evidence for an advantage of more diverse MHC genotypes. More specifically, the potential negative relation between individual allele divergence and number of parasite species is in line with the '<it>divergent allele advantage</it>' hypothesis.</p

Responses of five small mammal species to micro-scale variations in vegetation structure in secondary Atlantic Forest remnants, Brazil

<p>Abstract</p> <p>Background</p> <p>The Brazilian Atlantic Forest is highly endangered and only about 7% of the original forest remains, most of which consists of fragments of secondary forest. Small mammals in the Atlantic Forest have differential responses to this process of fragmentation and conversion of forest into anthropogenic habitats, and have varying abilities to occupy the surrounding altered habitats. We investigated the influence of vegetation structure on the micro-scale distribution of five small mammal species in six secondary forest remnants in a landscape of fragmented Atlantic Forest. We tested whether the occurrence of small mammal species is influenced by vegetation structure, aiming to ascertain whether species with different degrees of vulnerability to forest fragmentation (not vulnerable: <it>A. montensis</it>, <it>O. nigripes </it>and <it>G. microtarsus</it>; vulnerable: <it>M. incanus </it>and <it>D. sublineatus</it>; classification of vulnerability was based on the results of previous studies) are associated with distinct vegetation characteristics.</p> <p>Results</p> <p>Although vegetation structure differed among fragments, micro-scale distribution of most of the species was influenced by vegetation structure in a similar way in different fragments. Among the three species that were previously shown not to be vulnerable to forest fragmentation, <it>A. montensis </it>and <it>G. microtarsus </it>were present at locations with an open canopy and the occurrence of <it>O. nigripes </it>was associated to a low canopy and a dense understory. On the other hand, from the two species that were shown to be vulnerable to fragmentation, <it>M. incanus </it>was captured most often at locations with a closed canopy while the distribution of <it>D. sublineatus </it>was not clearly influenced by micro-scale variation in vegetation structure.</p> <p>Conclusion</p> <p>Results indicate the importance of micro-scale variation in vegetation structure for the distribution of small mammal species in secondary forest fragments. Species that are not vulnerable to fragmentation occurred at locations with vegetation characteristics of more disturbed forest, while one of the species vulnerable to fragmentation was found at locations with older forest characteristics. Results suggest that micro-habitat preferences may be an important factor influencing the capacity of small mammals to occupy altered habitats and, consequently, their vulnerability to forest fragmentation at a larger spatial scale.</p

Selection, diversity and evolutionary patterns of the MHC class II DAB in free-ranging Neotropical marsupials

<p>Abstract</p> <p>Background</p> <p>Research on the genetic architecture and diversity of the MHC has focused mainly on eutherian mammals, birds and fish. So far, studies on model marsupials used in laboratory investigations indicated very little or even no variation in MHC class II genes. However, natural levels of diversity and selection are unknown in marsupials as studies on wild populations are virtually absent. We used two endemic South American mouse opossums, <it>Gracilinanus microtarsus </it>and <it>Marmosops incanus</it>, to investigate characteristic features of MHC selection. This study is the first investigation of MHC selection in free-ranging Neotropical marsupials. In addition, the evolutionary history of MHC lineages within the group of marsupials was examined.</p> <p>Results</p> <p><it>G. microtarsus </it>showed extensive levels of MHC diversity within and among individuals as 47 MHC-DAB alleles and high levels of sequence divergence were detected at a minimum of four loci. Positively selected codon sites were identified, of which most were congruent with human antigen binding sites. The diversity in <it>M. incanus </it>was rather low with only eight observed alleles at presumably two loci. However, these alleles also revealed high sequence divergence. Again, positive selection was identified on specific codon sites, all congruent with human ABS and with positively selected sites observed in <it>G. microtarsus</it>. In a phylogenetic comparison alleles of <it>M. incanus </it>interspersed widely within alleles of <it>G. microtarsus </it>with four alleles being present in both species.</p> <p>Conclusion</p> <p>Our investigations revealed extensive MHC class II polymorphism in a natural marsupial population, contrary to previous assumptions. Furthermore, our study confirms for the first time in marsupials the presence of three characteristic features common at MHC loci of eutherian mammals, birds and fish: large allelic sequence divergence, positive selection on specific sites and trans-specific polymorphism.</p

Simple Screened Hydrogen Model of Excitons in Two-Dimensional Materials

We present a generalized hydrogen model for the binding energies ($E_B$) of excitons in two-dimensional (2D) materials that sheds light on the fundamental differences between excitons in two and three dimensions. In contrast to the well-known hydrogen model of three-dimensional (3D) excitons, the description of 2D excitons is complicated by the fact that the screening cannot be assumed to be local. We show that one can consistently define an effective 2D dielectric constant by averaging the screening over the extend of the exciton. For an ideal 2D semiconductor this leads to a simple expression for $E_B$ that only depends on the excitonic mass and the 2D polarizability $\alpha$. The model is shown to produce accurate results for 51 transition metal dichalcogenides. Remarkably, over a wide range of polarizabilities the expression becomes independent of the mass and we obtain $E_B^{2D}\approx3/(4\pi\alpha)$, which explains the recently observed linear scaling of exciton binding energies with band gap. It is also shown that the model accurately reproduces the non-hydrogenic Rydberg series in WS$_2$ and can account for screening from the environment.Comment: 5 page

Modelo para gestão do Curso de Tecnologia em Cerâmica da UNESC

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia de Produção.Este trabalho tem como objetivo principal desenvolver um modelo para gestão, com enfoque sistêmico, do curso de graduação de Tecnologia em Cerâmica da UNESC (Universidade do Extremo Sul Catarinense). Para tanto, a pesquisa explora sobre a educação superior no Brasil, cursos de tecnologia, abordagem sistêmica, qualidade nas instituições de ensino superior, bem como apresenta modelos de gestão para a educação. A construção de tal modelo ocorreu a partir de uma análise ambiental. Essa análise contou uma etapa de coleta de dados perceptivos e uma segunda etapa de coleta de dados evidentes. Na primeira, definiu-se quem participaria como especialista na idealização do modelo e quais elementos poderiam constituir-se como fatores importantes nessa proposta. Posteriormente, iniciou-se a fase de estruturação do modelo, que ocorreu a partir de entrevistas e encontros com os especialistas divididos em grupos. A análise de conteúdo e significado dos encontros, bem como o pré-modelo (Prêmio Malcolm Baldrige para Educação), forneceram a estrutura do modelo proposto. Essa estrutura, subdividida nos três ambientes organizacionais, macroambiente, ambiente da tarefa e ambiente interno, foi confrontada com fontes bibliográficas e complementada com aspectos relevantes. A partir disso, levou-se aos especialistas a proposta para adequação e aprovação. Devido à necessidade da avaliação do modelo e da situação atual da gestão do Curso de Tecnologia em Cerâmica, elaborou-se um questionário para diagnóstico, sendo esse aplicado a pessoas do curso e da IES em questão, verificando-se os pontos fortes e as oportunidades de melhoria da gestão do referido curso frente a tal proposta, bem como se avaliando a confiabilidade da pesquisa realizada. Dessa forma, obteve-se uma ferramenta que auxiliará a administração do Curso de Tecnologia em Cerâmica da UNESC na busca de uma gestão efetiva, eficaz e eficiente. Gestão essa que tem como propósito a melhoria da qualidade dos serviços prestados (ensino, pesquisa e extensão), sendo comprometida com o seu papel social. This study has as main objective to develop a management pattern of Tecnologia em Cerâmica Course, at UNESC (Universidade do Extremo Sul Catarinense) University with focusing on systematic. For that, this research approaches about Superior Teaching Institutions in Brazil, technologies courses, systemic approaches, quality in the universities, such as management patterns for the education shows. The construction of this pattern occurred from this an ambient analysis, which it had, two steps: in the first one there were perceptive data collections and the second one there were evident data collections. In the first collect, it was defined who would participate as specialist on pattern idealization and what elements could be constituted as important factors in this proposal. After that, it began the structuring of the pattern period which occurred from interviews and meetings with these specialists divided in groups. The content and meaning analysis of these meetings, besides the pre-pattern (Malcolm Baldrige National Quality Program) gave the structure of a suggested pattern. This structure is subdivided in three organizational ambients: macroambient, work ambient and internal ambient, and it was compared to bibliographies searches and complemented with important aspects. From that, it was led the proposal to the specialists for they settle and approve. Due to the need of pattern evaluation and the current situation of management in Tecnologia em Cerâmica Course, it was elaborated a questionary like a way to diagnose and it was applied to people who are relationed to this course and the Superior Teaching Instituition in focus. The objective of this diagnosis was verify the positive points and the opportunities to be better this course management in face this proposal, besides to evaluate trustfully of the research done. This way, it was obtained a tool that will be very important for the management of Tecnologia em Cerâmica Course of UNESC in search of an effective, efficacious and efficient Management. The last one has as purpose a better quality of offered services (teaching, research and extension) compromised with its social role