Is embryo abortion a post‐zygotic barrier to gene flow between Littorina ecotypes?

Genetic incompatibilities contribute to reproductive isolation between many diverging populations, but it is still unclear to what extent they play a role if divergence happens with gene flow. In contact zones between the "Crab" and "Wave" ecotypes of the snail Littorina saxatilis, divergent selection forms strong barriers to gene flow, while the role of post‐zygotic barriers due to selection against hybrids remains unclear. High embryo abortion rates in this species could indicate the presence of such barriers. Post‐zygotic barriers might include genetic incompatibilities (e.g. Dobzhansky–Muller incompatibilities) but also maladaptation, both expected to be most pronounced in contact zones. In addition, embryo abortion might reflect physiological stress on females and embryos independent of any genetic stress. We examined all embryos of >500 females sampled outside and inside contact zones of three populations in Sweden. Females' clutch size ranged from 0 to 1,011 embryos (mean 130 ± 123), and abortion rates varied between 0% and 100% (mean 12%). We described female genotypes by using a hybrid index based on hundreds of SNPs differentiated between ecotypes with which we characterized female genotypes. We also calculated female SNP heterozygosity and inversion karyotype. Clutch size did not vary with female hybrid index, and abortion rates were only weakly related to hybrid index in two sites but not at all in a third site. No additional variation in abortion rate was explained by female SNP heterozygosity, but increased female inversion heterozygosity added slightly to increased abortion. Our results show only weak and probably biologically insignificant post‐zygotic barriers contributing to ecotype divergence, and the high and variable abortion rates were marginally, if at all, explained by hybrid index of females

Genomic architecture of parallel ecological divergence : beyond a single environmental contrast

The study of parallel ecological divergence provides important clues to the operation of natural selection. Parallel divergence often occurs in heterogeneous environments with different kinds of environmental gradients in different locations, but the genomic basis underlying this process is unknown. We investigated the genomics of rapid parallel adaptation in the marine snail Littorina saxatilis in response to two independent environmental axes (crab-predation versus wave-action and low-shore versus high-shore). Using pooled whole-genome resequencing, we show that sharing of genomic regions of high differentiation between environments is generally low but increases at smaller spatial scales. We identify different shared genomic regions of divergence for each environmental axis and show that most of these regions overlap with candidate chromosomal inversions. Several inversion regions are divergent and polymorphic across many localities. We argue that chromosomal inversions could store shared variation that fuels rapid parallel adaptation to heterogeneous environments, possibly as balanced polymorphism shared by adaptive gene flow

Evolving inversions

Empirical data suggest that inversions in many species contain genes important for intraspecific divergence and speciation, yet mechanisms of evolution remain unclear. While genes inside an inversion are tightly linked, inversions are not static but evolve separately from the rest of the genome by new mutations, recombination within arrangements, and gene flux between arrangements. Inversion polymorphisms are maintained by different processes, for example, divergent or balancing selection, or a mix of multiple processes. Moreover, the relative roles of selection, drift, mutation, and recombination will change over the lifetime of an inversion and within its area of distribution. We believe inversions are central to the evolution of many species, but we need many more data and new models to understand the complex mechanisms involved

Using replicate hybrid zones to understand the genomic basis of adaptive divergence

Combining hybrid zone analysis with genomic data is a promising approach to understanding the genomic basis of adaptive divergence. It allows for the identification of genomic regions underlying barriers to gene flow. It also provides insights into spatial patterns of allele frequency change, informing about the interplay between environmental factors, dispersal and selection. However, when only a single hybrid zone is analysed, it is difficult to separate patterns generated by selection from those resulting from chance. Therefore, it is beneficial to look for repeatable patterns across replicate hybrid zones in the same system. We applied this approach to the marine snail Littorina saxatilis, which contains two ecotypes, adapted to wave-exposed rocks vs. high-predation boulder fields. The existence of numerous hybrid zones between ecotypes offered the opportunity to test for the repeatability of genomic architectures and spatial patterns of divergence. We sampled and phenotyped snails from seven replicate hybrid zones on the Swedish west coast and genotyped them for thousands of single nucleotide polymorphisms. Shell shape and size showed parallel clines across all zones. Many genomic regions showing steep clines and/or high differentiation were shared among hybrid zones, consistent with a common evolutionary history and extensive gene flow between zones, and supporting the importance of these regions for divergence. In particular, we found that several large putative inversions contribute to divergence in all locations. Additionally, we found evidence for consistent displacement of clines from the boulder–rock transition. Our results demonstrate patterns of spatial variation that would not be accessible without continuous spatial sampling, a large genomic data set and replicate hybrid zones

Homocysteine levels in pediatric renal transplant recipients.

Transplant Proc. 2003 May;35(3):1093-5. Homocysteine levels in pediatric renal transplant recipients. Mota C, Fonseca I, Santos MJ, Costa T, Faria MS, Henriques AC, Sarmento AM, Pereira E, Pereira M. Department of Paediatric Nephrology, Maria Pia Children's Hospital, R. da Boavista, 827, 4050-111, Porto, Portugal. [email protected] PMID: 12947872 [PubMed - indexed for MEDLIN

Linear And Nonlinear Dispersive Alfvén Waves In Two-ion Plasmas

A set of coupled nonlinear equations for dispersive Alfvén waves (DAWs) in nonuniform magnetoplasmas with two-ion species is derived by employing a multifluid model. The DAW frequency is assumed to lie between the gyrofrequencies of the light and heavy ion impurities. In the linear limit, a local dispersion relation (LDR) is derived and analyzed. The LDR admits a new type of DAW in two-ion plasmas. Furthermore, it is found that stationary solutions of the nonlinear mode coupling equations in two-ion plasmas can be represented in the form of different types of coherent vortex structures. The relevance of our investigation to space and laboratory plasmas is pointed out. © 1998 American Institute of Physics.5829472951Hasegawa, A., Uberoi, C., (1982) The Alfvén Wave, , National Technical Information Service, Springfield, VAPetviashvili, V.I., Pokhotelov, O.A., (1992) Solitary Waves in Plasmas and in the Atmosphere, , Gordon and Breach, Reading, Berkshire, UKMikhailovskii, A.B., (1992) Electromagnetic Instabilities in An Lnhomogeneous Plasma, , Hilger, Institute of Physics, Bristol, UKMikhailovskii, A.B., Lakhin, V.P., Aburdzhaniya, G.D., Mikahailovskaya, L.A., Onishenko, O.G., Smolyakov, A.I., (1984) Plasma Phys. Controlled Fusion, 29, p. 1Liu, J., Horton, W., (1986) J. Plasma Phys., 36, p. 1Yu, M.Y., Shukla, P.K., Stenflo, L., (1986) Astrophys. J., 309, pp. L63Chmyrev, V.M., Pokhotelov, O.A., Marchenko, V.A., Lazarev, V.I., Streltsov, A.V., Stenflo, L., (1988) Phys. Scr., 38, p. 841Shukla, P.K., Birk, G.T., Dreher, J., Stenflo, L., (1996) Plasma Phys. Rep., 22, p. 818Peterson, W.K., Yau, M.W., Whalen, B.A., (1993) J. Geophys. Res., 98, p. 11177Maslennikov, D.I., Mikhailenko, V.S., Stepanov, K.N., (1997) Fizika Plazmy, 23, p. 1088(1997) Plasma Phys. Rep., 23, p. 1007Elifomov, A.G., Galvao, R.M.O., Nascimento, I.C., Amarante-Segundo, G., (1997) Plasma Phys. Controlled Fusion, 39, p. 1151Shukla, P.K., Birk, G.T., Bingham, R., (1995) Geophys. Res. Lett., 22, p. 671Meiss, J.D., Horton, W., (1983) Phys. Fluids, 26, p. 990Stenflo, L., (1987) Phys. Fluids, 30, p. 3297Stenflo, L., (1994) Phys. Lett. A, 186, p. 133Stenflo, L., (1996) Phys. Lett. A, 222, p. 378Camevale, C.F., Vallis, G.K., (1990) J. Fluid Mech., 213, p. 549Dauxois, T., (1994) Phys. Fluids, 6, p. 162

Inversions and parallel evolution

Local adaptation leads to differences between populations within a species. In many systems, similar environmental contrasts occur repeatedly, sometimes driving parallel phenotypic evolution. Understanding the genomic basis of local adaptation and parallel evolution is a major goal of evolutionary genomics. It is now known that by preventing the break-up of favourable combinations of alleles across multiple loci, genetic architectures that reduce recombination, like chromosomal inversions, can make an important contribution to local adaptation. However, little is known about whether inversions also contribute disproportionately to parallel evolution. Our aim here is to highlight this knowledge gap, to showcase existing studies, and to illustrate the differences between genomic architectures with and without inversions using simple models. We predict that by generating stronger effective selection, inversions can sometimes speed up the parallel adaptive process or enable parallel adaptation where it would be impossible otherwise, but this is highly dependent on the spatial setting. We highlight that further empirical work is needed, in particular to cover a broader taxonomic range and to understand the relative importance of inversions compared to genomic regions without inversions

Green Functions for the Wrong-Sign Quartic

It has been shown that the Schwinger-Dyson equations for non-Hermitian theories implicitly include the Hilbert-space metric. Approximate Green functions for such theories may thus be obtained, without having to evaluate the metric explicitly, by truncation of the equations. Such a calculation has recently been carried out for various $PT$-symmetric theories, in both quantum mechanics and quantum field theory, including the wrong-sign quartic oscillator. For this particular theory the metric is known in closed form, making possible an independent check of these approximate results. We do so by numerically evaluating the ground-state wave-function for the equivalent Hermitian Hamiltonian and using this wave-function, in conjunction with the metric operator, to calculate the one- and two-point Green functions. We find that the Green functions evaluated by lowest-order truncation of the Schwinger-Dyson equations are already accurate at the (6-8)% level. This provides a strong justification for the method and a motivation for its extension to higher order and to higher dimensions, where the calculation of the metric is extremely difficult

Influência da qualidade dos materiais de reprodução na reflorestação com sobreiro

O sobreiro ocupa em Portugal cerca de 721000 ha o que corresponde a 21,5 % da área fl orestal nacional e 33% da área mundial (APCOR, 2005). A sua distribuição no território nacional traduz não só a sua adaptação a determinadas condições edafo-climaticas, mas tem sido condicionada por várias circunstancias, como o arroteamento, o fogo, o abuso do pastoreio, a exploração agrícola intensiva e as plantações fl orestais que contrariaram ou favoreceram a sua existência nesses locais (Natividade, 1950). A distribuição desta espécie é particularmente signifi cativa em zonas onde têm ocorrido acontecimentos climáticos graves e onde os níveis de desertifi cação humana são críticos. A fi leira da cortiça salienta-se por Portugal ocupar o primeiro lugar entre os países produtores, transformadores e exportadores de cortiça, correspondendo-lhe mais de metade da produção mundial desta matéria-prima. O nosso País é a origem de aproximadamente 60% das transacções de cortiça a nível mundial, valor que sobe para 80% quando nos referimos a transacções de produtos transformados. A nível nacional, o valor das exportações de cortiça representam aproximadamente 0,7% do PIB, 2,24% das exportações e correspondem a mais de 33% do conjunto das exportações de produtos fl orestais (APCOR, 2005). Para além da importância económica do sector corticeiro a nível nacional, o aumento da consciência e do interesse da sociedade nas questões ambientais, faz com que o montado de sobro seja reconhecido cada vez mais como um espaço fl orestal, de elevada biodiversidade, paisagísticamente único, que potencia micro-economias locais baseadas numa agricultura e pastorícia extensivas, interessante para outras actividades como o turismo rural e a caça. O sobreiro tem sido a espécie fl orestal que mais tem benefi ciado dos meios fi nanceiros disponibilizados aos proprietários fl orestais para a refl orestação no âmbito da aplicação das medidas de reforma da Política Agrícola Comum da UE, na arborização das terras agrícolas. Contudo, têm-se registado com frequência elevadas taxas de insucesso na arborização sendo a qualidade dos materiais florestais de reprodução (MFR) apontada como uma das causas. Neste trabalho abordaremos a a qualidade dos materiais de reprodução, considerando-a do ponto de vista genético e fisiológicoN/

Multi-walled carbon nanotubes as a platform for Immunoglobulin G attachment

Nanomaterials have been extensively used in different applications due to their peculiar characteristics and nanoscale dimensions. Among nanoparticles, carbon-based nanomaterials are becoming highly attractive for biomedical applications such as diagnosis, tissue engineering, drug delivery, and biosensing. The conjugation of carbon-based nanomaterials with antibodies combines the properties of these materials with the specific and selective recognition ability of the antibodies to antigens. The present work proposes a process intensification approach for immunoglobulin G (IgG present in rabbit serum) attachment on multi-walled carbon nanotubes (MWCNTs) in a single step. The effect of several parameters, namely MWCNTs external diameter, rabbit serum concentration, MWCNTs functionalization and pH value, on the IgG attachment yield was evaluated. The dilution of rabbit serum decreased other protein attachment, namely rabbit serum albumin (RSA), while increasing the IgG yield to 100%. The interaction mechanisms between IgG and MWCNTs were evaluated at pH 5.0 to 8.0. The protonation of IgG amino acids indicates that N-term are the most reactive amino acids in the antibody structure. The identification of the N-term reactivity at pH 8.0 allows to indicate a possible orientation of the antibody over the MWCNTs surface, described as “end-on”. Since the amount of RSA attached to MWNT decreased with the increase in serum dilution, the IgG orientation and amine activity was not affected. This orientation demonstrates that the IgG attachment over the surface of the MWCNTs could be an effective strategy to maintain the antigen recognition by the antibody, and to be used for biomedical applications.publishe