Dynamics of mtDNA introgression during species range expansion. Insights from an experimental longitudinal study

Introgressive hybridization represents one of the long-lasting debated genetic consequences of species range expansion. Mitochondrial DNA has been shown to heavily introgress between interbreeding animal species that meet in new sympatric areas and, often, asymmetric introgression from local to the colonizing populations has been observed. Disentangling among the evolutionary and ecological processes that might shape this pattern remains difficult, because they continuously act across time and space. In this context, long-term studies can be of paramount importance. Here, we investigated the dynamics of mitochondrial introgression between two mosquito species (Aedes mariae and Ae. zammitii ) during a colonization event that started in 1986 after a translocation experiment. By analyzing 1,659 individuals across 25 years, we showed that introgression occurred earlier and at a higher frequency in the introduced than in the local species, showing a pattern of asymmetric introgression. Throughout time, introgression increased slowly in the local species, becoming reciprocal at most sites. The rare opportunity to investigate the pattern of introgression across time during a range expansion along with the characteristics of our study-system allowed us to support a role of demographic dynamics in determining the observed introgression pattern

Genetic divergence in Northamerican freshwater planarians of the Dugesia dorotocephala group (Turbellaria, Tricladida, Paludicola)

The genetic differentiation between the members of the Dugesia (Girardia) dorotocephala group was analyzed by means of multilocus electrophoresis, and comared to that of another planarian secies, D. tahitiensis, also belonging to the subgenus Girardia. The species examined were: D. dorotocephala s.s (2n = 16), D. arizonensis (2n = 8), D. jenkinsae (2n = 8), and the above mentioned D. tahitiensis (2n = 16). The former three species inhabit North America, and show different proportion of fissiparous and sexual individuals; the latter species inhabits Polynesia and is fully asexual. A total of 11 enzyme loci were genetically analyzed: Mdh-1, Mdh-2, Zdh-1, Idh-2, G3pdh, Got-1, Ck, Pgm-2, Ada, Mpi, and Gpi. Low values of observed mean heterozygosity per locus (Ho) were found in the populations studied, ranging from 0 to 0.18 (average 0.08. In asexual populations (except that of D. tahitiensis) fixed heterozygosity was observered in all the individuals for 1 or 2 loci. The genetic divergence between the species examined is very high, with many loci showing discriminating alleles in different taxa (Nei's genetic distance varies from 0.871 to 1.759). The populations of D. dorotocehala s.s., on the contrary, appear to be genetically quite homogenous average D= 0.019), and the genetic distance values are apparently unrelated to their geographic location and to their way of reproduction. The genetic distance between D. tahitiensis, a species not included in the D. dorotocephala group and D. dorotocephala s.s. is 1.314 and hence similar to the D value between two members of;he dorotocephala group: D. dorotocephala and D. jenkinsae (D = 1.303). The genetic relationships among the populations studied were established by UPGMA cluster analysis and multidimensional scaling. The descendence of the North American species with 2n = 8 from a dorotocephala-like ancestor with 2n = 16 is considered. It is suggested that the latter, as well as a tahitiensis-like line, also having 2n = 16, have originated from a common ancestor by geographic isolation

Low microsatellite variation in Aphanius fasciatus from the Tarquinia Salterns

1 - The Tarquinia Salterns (Latium, central Italy) provided the opportunity to analyse the impact of environmental stress on the genetic structure of the resident population of the killifish Aphanius fasciatus. Indeed, after the salt production ceased in 1997, the salterns have undergone habitat degradation due to lack of maintenance. The ecological restoration carried out from 2003 to 2006 reverted the environmental conditions to those of ten years before. 2 - The temporal variation of the gene pool of the population of A. fasciatus inhabiting the Tarquinia Salterns was investigated using microsatellite markers in samples collected in 1998 and 2003. The results obtained showed a low genetic variability and a genetic homogeneity of the population, which appears not divided in sub-demes. 3 - Microsatellites revealed a surprisingly low level of genetic variability when compared to allozyme data obtained in previous studies. This is likely due to a difference in the time of response of the two markers to environmental degradation. Microsatellites would lose genetic variability earlier and faster because of their usually high polymorphisms. Conversely, allozymes would be more resistant to genetic erosion, being moderately variable markers. 4 - Selection probably contributed in maintaining allozyme polymorphism, while microsatellites, being neutral markers, did not benefit from the action of selection and lost diversity earlier and more rapidly. Accordingly, the population appeared subdivided in distinct demes based on allozyme data but spatially homogeneous following microsatellites results

Microfluidic cartridge with integrated array of amorphous silicon photosensors for chemiluminescence detection of viral DNA

Portable and simple analytical devices based on microfluidics with chemiluminescence detection are particularly attractive for point-of-care applications, offering high detectability and specificity in a simple and miniaturized analytical format. Particularly relevant for infectious disease diagnosis is the ability to sensitively and specifically detect target nucleic acid sequences in biological fluids. To reach the goal of real-life applications for such devices, however, several technological challenges related to full device integration are still to be solved, one key aspect regarding on-chip integration of the chemiluminescence signal detection device. Nowadays, the most promising approach is on-chip integration of thin-film photosensors. We recently proposed a portable cartridge with microwells aligned with an array of hydrogenated amorphous silicon (a-Si:H) photosensors, reaching attomole level limits of detection for different chemiluminescence model reactions. Herein, we explore its applicability and performance for multiplex and quantitative detection of viral DNA. In particular, the cartridge was modified to accommodate microfluidic channels and, upon immobilization of three oligonucleotide probes in different positions along each channel, each specific for a genotype of Parvovirus B19, viral nucleic acid sequences were captured and detected. With this system, taking advantage of oligoprobes specificity, chemiluminescence detectability, and photosensor sensitivity, accurate quantification of target analytes down to 70 pmol L-1 was obtained for each B19 DNA genotype, with high specificity and multiplexing ability. Results confirm the good detection capabilities and assay applicability of the proposed system, prompting the development of innovative portable analytical devices with enhanced sensitivity and multiplexed capabilities

No more time to stay ‘single’ in the detection of Anisakis pegreffii, A. simplex (s. s.) and hybridization events between them: a multi-marker nuclear genotyping approach

A multi-marker nuclear genotyping approach was performed on larval and adult specimens of Anisakis spp. (N = 689) collected from fish and cetaceans in allopatric and sympatric areas of the two species Anisakis pegreffii and Anisakis simplex (s. s.), in order to: (1) identify specimens belonging to the parental taxa by using nuclear markers (allozymes loci) and sequence analysis of a new diagnostic nuclear DNA locus (i.e. partial sequence of the EF1 α−1 nDNA region) and (2) recognize hybrid categories. According to the Bayesian clustering algorithms, based on those markers, most of the individuals (N = 678) were identified as the parental species [i.e. A. pegreffii or A. simplex (s. s.)], whereas a smaller portion (N = 11) were recognized as F1 hybrids. Discordant results were obtained when using the polymerase chain reaction–restriction fragment length polymorphisms (PCR–RFLPs) of the internal transcribed spacer (ITS) ribosomal DNA (rDNA) on the same specimens, which indicated the occurrence of a large number of ‘hybrids’ both in sympatry and allopatry. These findings raise the question of possible misidentification of specimens belonging to the two parental Anisakis and their hybrid categories derived from the application of that single marker (i.e. PCR–RFLPs analysis of the ITS of rDNA). Finally, Bayesian clustering, using allozymes and EF1 α−1 nDNA markers, has demonstrated that hybridization between A. pegreffii and A. simplex (s. s.) is a contemporary phenomenon in sympatric areas, while no introgressive hybridization takes place between the two species

Population structure of Atlantic swordfish (Xiphias gladius L. 1758) (Teleostea, Xiphiidae) using mitochondrial DNA analysis: implications for fisheries management

Recent studies on Atlantic swordfish (Xiphias gladius L. 1758) genetic structure have demonstrated significant heterogeneity but the precise boundary between populations remains to be identified. In this context, genetic diversity was investigated by PCR–RFLP analysis at the control region of mitochondrial DNA (D–loop) from 274 swordfish specimens collected from five different areas of the Atlantic Ocean. The analysis of molecular variance (AMOVA) showed that genetic variation was mainly due to differences within rather than between the studied areas. Additionally, the phylogenetic analysis did not show evident relationships among haplotypes from all areas. However, low but significant FST values were recorded when comparing Equatorial samples with those from the north central and north tropical Atlantic. These results do not support a need for changing the current management boundary for the Atlantic fishery. Key words: Xiphiidae, Swordfish, Xiphias gladius, Mitochondrial DNA, Genetic variability, Atlantic Ocean.Estudios recientes sobre la estructura genética del pez espada del Atlántico (Xiphias gladius L. 1758) han demostrado una heterogeneidad significativa, pero los límites precisos entre poblaciones no han sido identificados. En este contexto, la diversidad genética se ha investigado mediante análisis PCR–RFLP en la región control de ADN mitocondrial (bucle D) de 274 peces espada recolectados en cinco zonas diferentes del océano Atlántico. El análisis de la varianza molecular (AMOVA) mostró que la variación genética se debía a diferencias en cada zona y no entre las zonas estudiadas. Además, los análisis filogenéticos no muestran relaciones evidentes entre los haplotipos de todas las zonas. A pesar de ello, al comparar las muestras ecuatoriales con las de zonas más al norte, se obtienen valores de FST bajos pero significativos. Estos resultados indican que no es necesario cambiar los límites de las zonas de gestión para la pesquería del Atlántico. Palabras clave: Xiphiidae, Pez espada, Xiphias gladius, ADN mitocondrial, Variabilidad genética, Océano Atlántico.Recent studies on Atlantic swordfish (Xiphias gladius L. 1758) genetic structure have demonstrated significant heterogeneity but the precise boundary between populations remains to be identified. In this context, genetic diversity was investigated by PCR–RFLP analysis at the control region of mitochondrial DNA (D–loop) from 274 swordfish specimens collected from five different areas of the Atlantic Ocean. The analysis of molecular variance (AMOVA) showed that genetic variation was mainly due to differences within rather than between the studied areas. Additionally, the phylogenetic analysis did not show evident relationships among haplotypes from all areas. However, low but significant FST values were recorded when comparing Equatorial samples with those from the north central and north tropical Atlantic. These results do not support a need for changing the current management boundary for the Atlantic fishery. Key words: Xiphiidae, Swordfish, Xiphias gladius, Mitochondrial DNA, Genetic variability, Atlantic Ocea

On-chip detection performed by amorphous silicon balanced photosensor for lab-on chip application

In this paper we have integrated a two-channel microfluidic network, fabricated by molding two polydimethilsiloxane channels, with a balanced photodiode constituted by two series-connected amorphous silicon/silicon carbide n-i-p stacked junctions, deposited by Plasma Enhanced Chemical Vapor Deposition on a glass substrate. The structure takes advantage of the differential current measurement to reveal very small variations of photocurrent in a large background current signal suitable for biomedical application. The microfluidic network has been fabricated with dimensions of 3 cm × 2 mm × 150 μm (L × W × H) for each channel. The experiments have been carried out measuring the differential current in several conditions. All the experiments have been executed under a large background light intensity to reproduce realistic operating conditions in biomedical applications. We have found that the proposed device is able to detect the presence or absence of water flow in the channel and the presence of fluorescent marker. In particular, under identical channel conditions the differential current is at least a factor 60 lower that the current flowing in each diode

Differences in gene expression profiles of seven target proteins in third-stage larvae of anisakis simplex (Sensu stricto) by sites of infection in blue whiting (micromesistius poutassou)

The third-stage larvae of the parasitic nematode genus Anisakis tend to encapsulate in different tissues including the musculature of fish. Host tissue penetration and degradation involve both mechanic processes and the production of proteins encoded by an array of genes. Investigating larval gene profiles during the fish infection has relevance in understanding biological traits in the parasite’s adaptive ability to cope with the fish hosts’ defense responses. The present study aimed to investigate the gene expression levels of some proteins in L3 of A. simplex (s.s.) infecting different tissues of blue whiting Micromesistius poutassou, a common fish host of the parasite in the NE Atlantic. The following genes encoding for Anisakis spp. proteins were studied: Kunitz-type trypsin inhibitor (TI), hemoglobin (hb), glycoprotein (GP), trehalase (treh), zinc metallopeptidase 13 (nas 13), ubiquitin-protein ligase (hyd) and sideroflexin 2 (sfxn 2). Significant differences in gene transcripts (by quantitative real-time PCR, qPCR) were observed in larvae located in various tissues of the fish host, with respect to the control. ANOVA analysis showed that relative gene expression levels of the seven target genes in the larvae are linked to the infection site in the fish host. Genes encoding some of the target proteins seem to be involved in the host tissue migration and survival of the parasite in the hostile target tissues of the fish host

An all-glass microfluidic network with integrated amorphous silicon photosensors for on-chip monitoring of enzymatic biochemical assay

A lab-on-chip system, integrating an all-glass microfluidics and on-chip optical detection, was developed and tested. The microfluidic network is etched in a glass substrate, which is then sealed with a glass cover by direct bonding. Thin film amorphous silicon photosensors have been fabricated on the sealed microfluidic substrate preventing the contamination of the micro-channels. The microfluidic network is then made accessible by opening inlets and outlets just prior to the use, ensuring the sterility of the device. The entire fabrication process relies on conventional photolithographic microfabrication techniques and is suitable for low-cost mass production of the device. The lab-on-chip system has been tested by implementing a chemiluminescent biochemical reaction. The inner channel walls of the microfluidic network are chemically functionalized with a layer of polymer brushes and horseradish peroxidase is immobilized into the coated channel. The results demonstrate the successful on-chip detection of hydrogen peroxide down to 18 mu M by using luminol and 4-iodophenol as enhancer agent

Asymptomatic massive hypertriglyceridemia in an octogenarian.

Objective: To report the case of an 85-year-old man with asymptomatic massive hypertriglyceridemia (MHTG). Clinical Presentation and Intervention: Our case was a non-smoker, healthy 85-year-old Caucasian male, with no excessive alcohol intake and no evidence of an excessive sedentary lifestyle, body mass index = 23.2 kg/m2, BP = 125/85 mm Hg and plasma triglyceride (TG) >1,000 mg/dl. The MHTG was an incidental finding at the age of 70. He had no cardiovascular disease, xanthomas, xanthelasmas or keratic precipitate. During the last 15 years, his average TG plasma levels showed a significant variability independent of specific diet treatment and fibrate therapy. Liver ultrasound examination excluded hepatomegaly and fatty degeneration. Carotid artery ultrasound showed only intimal thickening in both carotid bifurcations. Conclusion: In this patient, MHTG had been silent for many years, with no evidence of coronary heart disease and liver fatty degeneration, both typical complications present in MHTG subjects with low high-density lipoprotein. Hence, this case must be considered as a rarity