The two North Atlantic eel species, the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata), spawn in partial sympatry in the Sargasso Sea, providing ample opportunity to interbreed. In this study, we used a RAD (Restriction site Associated DNA) sequencing approach to identify species-specific diagnostic single-nucleotide polymorphisms (SNPs) and design a low-density array that combined with screening of a diagnostic mitochondrial DNA marker. Eels from Iceland (N=159) and from the neighboring Faroe Islands (N=29) were genotyped, along with 94 larvae (49 European and 45 American eel) collected in the Sargasso Sea. Our SNP survey showed that the majority of Icelandic eels are pure European eels but there is also an important contribution of individuals of admixed ancestry (10.7%). Although most of the hybrids were identified as F1 hybrids from European eel female × American eel male crosses, backcrosses were also detected, including a first-generation backcross (F1 hybrid × pure European eel) and three individuals identified as second-generation backcrosses originating from American eel × F1 hybrid backcrosses interbreeding with pure European eels. In comparison, no hybrids were observed in the Faroe Islands, the closest bodies of land to Iceland. It is possible that hybrids show an intermediate migratory behaviour between the two parental species that ultimately brings hybrid larvae to the shores of Iceland, situated roughly halfway between the Sargasso Sea and Europe. Only two hybrids were observed among Sargasso Sea larvae, both backcrosses, but no F1 hybrids, that points to temporal variation in the occurrence of hybridization.
Elucidating barriers to gene flow is important for understanding the dynamics of speciation. Here we investigate pre- and post-zygotic mechanisms acting between the two hybridizing species of Atlantic eels: Anguilla anguilla and A. rostrata. Temporally varying hybridization was examined by analyzing 85 species-diagnostic single-nucleotide polymorphisms (SNPs; FST ?0.95) in eel larvae sampled in the spawning region in the Sargasso Sea in 2007 (N=92) and 2014 (N=460). We further investigated whether genotypes at these SNPs were nonrandomly distributed in post-F1 hybrids, indicating selection. Finally, we sequenced the mitochondrial ATP6 and nuclear ATP5c1 genes in 19 hybrids, identified using SNP and restriction site associated DNA (RAD) sequencing data, to test a previously proposed hypothesis of cytonuclear incompatibility leading to adenosine triphosphate (ATP) synthase dysfunction and selection against hybrids. No F1 hybrids but only later backcrosses were observed in the Sargasso Sea in 2007 and 2014. This suggests that interbreeding between the two species only occurs in some years, possibly controlled by environmental conditions at the spawning grounds, or that interbreeding has diminished through time as a result of a declining number of spawners. Moreover, potential selection was found at the nuclear and the cytonuclear levels. Nonetheless, one glass eel individual showed a mismatch, involving an American ATP6 haplotype and European ATP5c1 alleles. This contradicted the presence of cytonuclear incompatibility but may be explained by that (1) cytonuclear incompatibility is incomplete, (2) selection acts at a later life stage or (3) other genes are important for protein function. In total, the study demonstrates the utility of genomic data when examining pre- and post-zyotic barriers in natural hybrids.
Notes
Cites: Genetics. 2003 Aug;164(4):1567-8712930761
Cites: Science. 2009 Feb 6;323(5915):737-4119197053
Cites: Mol Ecol. 2013 Apr;22(7):1763-7623216918
Cites: Genetics. 2000 Jun;155(2):945-5910835412
Cites: Evolution. 2006 Jul;60(7):1372-8116929654
Cites: Science. 2007 Aug 17;317(5840):910-417702935
OBJECTIVE: To examine the relationship between autoimmunity and extranodal lymphocytic infiltrates in different lymphoproliferative disorders with immunoglobulin alterations. SUBJECTS AND DESIGN: A clinical review combined with a retrospective cohort study of 380 patients, 28 with monoclonal gammopathy of undetermined significance, three with common variable immunodeficiency, 147 with chronic lymphocytic leukaemia, 57 with Waldenstr?m's macroglobulinaemia and 145 with non-Hodgkin's malignant lymphoma. SETTING: A university hospital and The State Serum Institute in Copenhagen. INTERVENTION: Clinical examination of each patient with special attention to chronic inflammatory and autoimmune manifestations. Biopsies were taken from non-infectious infiltrates, some of which were additionally tested with PCR analysis for gene rearrangements. Serological screening with a test battery for various autoantibodies was used in combination with techniques for the detection of M-components and monoclonal B-cell proliferation. MAIN OUTCOME MEASURES: Clinical and/or serological autoimmune manifestations, M-component and other immunoglobulin alterations, and inflammatory tissue changes were studied in patients with chronic inflammatory, polyclonal or oligoclonal pseudolymphomas and in monoclonal, malignant extranodal lymphomas. RESULTS: In 380 consecutive patients, 49 (12.9%) had extranodal manifestations, of whom 47 also had autoimmune manifestations. Nearly half of the 47 patients had more than one autoimmune manifestation. There was a strong correlation between clinical signs and corresponding autoantibodies such as anti-SSA and -SSB antibodies in Sj?gren's syndrome (10 cases), antithyroid peroxidase antibodies in thyroiditis and Graves' disease (10 cases), and parietal cell antibodies in gastric ulcers with maltoma (12 cases). Clinical and serological signs of autoimmunity correlated strongly with female sex (34, 72% women; and 13, 28% men) and with immunoglobulin alterations. CONCLUSIONS: To our knowledge this is the first systematic review of B-lymphoproliferative and autoimmune disorders indicating that pseudolymphoma and malignant lymphomas, including maltomas, may develop in the context of a permanent autoantigenic drive.
One hundred consecutive autologous stem cell transplants are reported: Non-Hodgkin's lymphoma 51 cases, Hodgkin's disease 27 cases, acute leukaemia 14 cases, multiple myeloma seven cases and chronic myeloid leukaemia one case. Most patients were in their second or later remission. The overall three-year survival for all patients was 60% and the three-year disease-free survival was 50% for lymphoma patients and 30% for acute leukaemia patients. The dominant source of stem cells was bone marrow during 1993, but from 1994 it has been peripheral blood, now totalling 33 cases. There were 12 toxic deaths, all among patients who were heavily treated before bone marrow harvest and transplantation. The patients transplanted with blood stem cells had significantly shorter duration of pancytopenia, and hospital stay, but their disease-free survival was not longer than that of a comparable group of bone marrow transplanted patients. Six patients were transplanted with purified CD34+ cells (selected by avidity column (Ceprate (R)), and had duration of thrombocytopenia and hospital stay similar to the patients transplanted with unmanipulated blood stem cells, but slightly longer duration of neutropenia. We conclude that high-dose therapy with autologous stem cell transplantation in not too heavily pretreated patients is a safe procedure irrespective of the source of stem cells.
To ascertain whether the microbiological etiology of bacteremia among patients with hematological malignancies has changed in Denmark, the species distribution of clinically relevant blood culture isolates from the Hematological Department at Rigshospitalet, Copenhagen in 1990 was compared with 2 previous studies (1970-72; 1981-85). In addition, time trends of the etiology of bacteremia among hematological patients in Copenhagen (eastern Denmark) and in Arhus (western Denmark) were compared. In contrast to many other studies, a significant increase in the proportion of Gram-negative aerobes was observed in Copenhagen (from 43% in 1981-85 to 55% in 1990; p
Five hundred and fifty consecutive patients with newly diagnosed B-CLL have been registered and classified in a Danish multicenter study. The study includes a protocol for primary treatment of patients in stage B or C (at diagnosis or after demonstrated progression), below 76 years of age, and without complicating serious disease. Until now 144 such patients have been randomized to either prednisolone (PRD) plus chlorambucil (CLB) 5 days every 4 weeks or monthly intensive CHOP treatment. Twenty-nine percent of the treated patients achieved CR on PRD + CLB versus 63% on CHOP (p less than 0.005). No response was found in 29% versus 18%, respectively (NS). A significant difference in survival between patients achieving CR, PR and NR was also demonstrated, whereas to date no difference in survival could be demonstrated between the two regimens. The toxicity was limited, and only 2 treatment-related deaths occurred in approximately 700 CHOP treatment series.
In the period 1984-1987, 500 consecutive, newly diagnosed patients with chronic lymphocytic leukaemia (CLL) have been registered in the still open Danish CLL2-study. As part of patient work-up, the immunological phenotype was established in all patients by immunofluorescence microscopy, and in 458 patients also by flow cytometry, with a panel of polyclonal and monoclonal antibodies. The majority of cases exhibited a CD5-pos, SmIgMD-pos phenotype with faint SmIg-fluorescence, and there is as yet no significant difference in survival between SmIgD-pos and SmIgD-neg cases. Seventy cases were FMC7-pos, a marker associated with a higher B-cell differentiation, and this was significantly correlated with stronger SmIg fluorescence intensity and splenomegaly (Rai stage II). The survival of the FMC7-pos patients was not significantly different from that of the FMC7-neg. Thus, in this preliminary phenotype analysis of the first 500 patients in the CLL2 study, no important prognostic subgroups were detected, although this might be due to the still short observation time (median observation time 532 days).
We investigated how population changes and fluctuations in the pink-footed goose might have been affected by climatic and anthropogenic factors. First, genomic data confirmed the existence of two separate populations: western (Iceland) and eastern (Svalbard/Denmark). Second, demographic inference suggests that the species survived the last glacial period as a single ancestral population with a low population size (100-1,000 individuals) that split into the current populations at the end of the Last Glacial Maximum with Iceland being the most plausible glacial refuge. While population changes during the last glaciation were clearly environmental, we hypothesize that more recent demographic changes are human-related: (1) the inferred population increase in the Neolithic is due to deforestation to establish new lands for agriculture, increasing available habitat for pink-footed geese (2) the decline inferred during the Middle Ages is due to human persecution and (3) improved protection explains the increasing demographic trends during the 20th century. Our results suggest both environmental (during glacial cycles) and anthropogenic effects (more recent) can be a threat to species survival. This article is protected by copyright. All rights reserved.
We investigated how population changes and fluctuations in the pink-footed goose might have been affected by climatic and anthropogenic factors. First, genomic data confirmed the existence of two separate populations: western (Iceland) and eastern (Svalbard/Denmark). Second, demographic inference suggests that the species survived the last glacial period as a single ancestral population with a low population size (100-1,000 individuals) that split into the current populations at the end of the last glacial maximum with Iceland being the most plausible glacial refuge. While population changes during the last glaciation were clearly environmental, we hypothesize that more recent demographic changes are human-related: (1) the inferred population increase in the Neolithic is due to deforestation to establish new lands for agriculture, increasing available habitat for pink-footed geese, (2) the decline inferred during the Middle Ages is due to human persecution, and (3) improved protection explains the increasing demographic trends during the 20th century. Our results suggest both environmental (during glacial cycles) and anthropogenic effects (more recent) can be a threat to species survival.
Feral animals represent an important problem in many ecosystems due to interbreeding with wild conspecifics. Hybrid offspring from wild and domestic parents are often less adapted to local environment and ultimately, can reduce the fitness of the native population. This problem is an important concern in Norway, where each year, hundreds of thousands of farm Atlantic salmon escape from fish farms. Feral fish outnumber wild populations, leading to a possible loss of local adaptive genetic variation and erosion of genetic structure in wild populations. Studying the genetic factors underlying relative performance between wild and domesticated conspecific can help to better understand how domestication modifies the genetic background of populations, and how it may alter their ability to adapt to the natural environment. Here, based upon a large-scale release of wild, farm and wild x farm salmon crosses into a natural river system, a genome-wide quantitative trait locus (QTL) scan was performed on the offspring of 50 full-sib families, for traits related to fitness (length, weight, condition factor and survival). Six QTLs were detected as significant contributors to the phenotypic variation of the first three traits, explaining collectively between 9.8 and 14.8% of the phenotypic variation. The seventh QTL had a significant contribution to the variation in survival, and is regarded as a key factor to understand the fitness variability observed among salmon in the river. Interestingly, strong allelic correlation within one of the QTL regions in farmed salmon might reflect a recent selective sweep due to artificial selection.
