Interspecific hybridization in the genus Hieracium s. str.: evidence for bidirectional gene flow and spontaneous allopolyploidization

Although reticulation has indisputably played an important role in the evolutionary history of the genus Hieracium s. str. (Asteraceae), convincingly documented cases of recent interspecific hybridization are very rare. Here we report combined evidence on recent hybridization between two diploid species, Hieracium alpinum and H. transsilvanicum. The hybrid origin of the plants from the Romanian Eastern Carpathians was supported by additive patterns of nuclear ribosomal DNA polymorphism (ITS), an intermediate position of hybrid plants in principal coordinate analysis based on amplified fragment length polymorphism phenotypes (AFLP), and additivity at one allozyme locus. Flow cytometric analyses and chromosome counting showed that two hybrids were diploid (2n~2x~18) while one was surprisingly tetraploid (2n=4x=36). To our knowledge, this is the first record of spontaneous polyploidization following interspecific crossing in the genus. Allozyme data, especially the presence of unbalanced heterozygosity at one locus, suggest the origin of this tetraploid via a triploid bridge with subsequent backcrossing to H. alpinum. According to PCR-RFLP analyses of the trnT-trnL intergenic spacer, all H. ×krasani hybrids examined had the H. alpinum haplotype while H. transsilvanicum served as a pollen donor. The hybrids occurred at the locality with abundant H. alpinum plants where paternal H. transsilvanicum was missing. Previously reported instances of interspecific hybridization between the same parental taxa showed an opposite direction of crossing and relative abundance of parental taxa. This suggests that the direction of hybridization might be influenced by the frequency of parental taxa at the localit

Intra-individual polymorphism in diploid and apomictic polyploid hawkweeds (Hieracium, Lactuceae, Asteraceae): disentangling phylogenetic signal, reticulation, and noise

<p>Abstract</p> <p>Background</p> <p><it>Hieracium </it>s.str. is a complex species-rich group of perennial herbs composed of few sexual diploids and numerous apomictic polyploids. The existence of reticulation and the near-continuity of morphological characters across taxa seriously affect species determination, making <it>Hieracium </it>one of the best examples of a 'botanist's nightmare'. Consequently, its species relationships have not previously been addressed by molecular methods. Concentrating on the supposed major evolutionary units, we used nuclear ribosomal (<it>ETS</it>) and chloroplast (<it>trnT</it>-<it>trnL</it>) sequences in order to disentangle the phylogenetic relationships and to infer the origins of the polyploids.</p> <p>Results</p> <p>Despite relatively low interspecific variation, the nuclear data revealed the existence of two major groups roughly corresponding to species with a Western or Eastern European origin. Extensive reticulation was mainly inferred from the character additivity of parental <it>ETS </it>variants. Surprisingly, many diploid species were of hybrid origin whilst several polyploid taxa showed no evidence of reticulation. Intra-individual <it>ETS </it>sequence polymorphism generally exceeded interspecific variation and was either independent of, or additional to, additive patterns accounted for by hybrid origin. Several <it>ETS </it>ribotypes occurred in different hybrid taxa, but never as the only variant in any species analyzed.</p> <p>Conclusion</p> <p>The high level of intra-individual <it>ETS </it>polymorphism prevented straightforward phylogenetic analysis. Characterization of this variation as additive, shared informative, homoplasious, or unique made it possible to uncover the phylogenetic signal and to reveal the hybrid origin of 29 out of 60 accessions. Contrary to expectation, diploid sexuals and polyploid apomicts did not differ in their molecular patterns. The basic division of the genus into two major clades had not previously been intimated on morphological grounds. Both major groups are thought to have survived in different glacial refugia and to have hybridized as a result of secondary contact. Several lines of evidence suggest the data is best explained by the presence of an extinct range of variation and a larger diversity of ancestral diploids in former times rather than by unsampled variation. Extinct diversity and extensive reticulation are thought to have largely obscured the species relationships. Our study illustrates how multigene sequences can be used to disentangle the evolutionary history of agamic complexes or similarly difficult datasets.</p

Discovery of the Northern Hemisphere hybrid Potamogeton ×salicifolius in the Pilbara region of Western Australia

The interspecific hybrid Potamogeton ×salicifolius (= P. lucens × P. perfoliatus), so far known only from several countries of Europe and a few countries of Asia, was discovered in Western Australia. Morphology of the Australian specimens fits the variation range of the Eurasian specimens. DNA sequencing confirmed the morphological identification as a hybrid P. lucens × P. perfoliatus and identified the former species as the maternal one. This identity is surprising because none of the parental species are known to occur in Western Australia and P. lucens currently even does not occur in the continent. Three possible explanations for the occurrence of P. ×salicifolius in Western Australia are discussed: its relictual occurrence from the time when both the parental species occurred there, long-distance dispersal of a hybrid seed from Eurasia and the remnant of local cultivation or intentional planting

Understanding, diagnosing, and treating Myalgic encephalomyelitis/chronic fatigue syndrome - State of the art: Report of the 2nd international meeting at the Charité fatigue center.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a devastating disease affecting millions of people worldwide. Due to the 2019 pandemic of coronavirus disease (COVID-19), we are facing a significant increase of ME/CFS prevalence. On May 11th to 12th, 2023, the second international ME/CFS conference of the Charité Fatigue Center was held in Berlin, Germany, focusing on pathomechanisms, diagnosis, and treatment. During the two-day conference, more than 100 researchers from various research fields met on-site and over 700 attendees participated online to discuss the state of the art and novel findings in this field. Key topics from the conference included: the role of the immune system, dysfunction of endothelial and autonomic nervous system, and viral reactivation. Furthermore, there were presentations on innovative diagnostic measures and assessments for this complex disease, cutting-edge treatment approaches, and clinical studies. Despite the increased public attention due to the COVID-19 pandemic, the subsequent rise of Long COVID-19 cases, and the rise of funding opportunities to unravel the pathomechanisms underlying ME/CFS, this severe disease remains highly underresearched. Future adequately funded research efforts are needed to further explore the disease etiology and to identify diagnostic markers and targeted therapies

Interspecific hybridization in the genus Hieracium s. str.: evidence for bidirectional gene flow and spontaneous allopolyploidization

Although reticulation has indisputably played an important role in the evolutionary history of the genus Hieracium s. str. (Asteraceae), convincingly documented cases of recent interspecific hybridization are very rare. Here we report combined evidence on recent hybridization between two diploid species, Hieracium alpinum and H. transsilvanicum. The hybrid origin of the plants from the Romanian Eastern Carpathians was supported by additive patterns of nuclear ribosomal DNA polymorphism (ITS), an intermediate position of hybrid plants in principal coordinate analysis based on amplified fragment length polymorphism phenotypes (AFLP), and additivity at one allozyme locus. Flow cytometric analyses and chromosome counting showed that two hybrids were diploid (2n ~ 2x ~ 18) while one was surprisingly tetraploid (2n = 4x = 36). To our knowledge, this is the first record of spontaneous polyploidization following interspecific crossing in the genus. Allozyme data, especially the presence of unbalanced heterozygosity at one locus, suggest the origin of this tetraploid via a triploid bridge with subsequent backcrossing to H. alpinum. According to PCR-RFLP analyses of the trnT-trnL intergenic spacer, all H. ×krasani hybrids examined had the H. alpinum haplotype while H. transsilvanicum served as a pollen donor. The hybrids occurred at the locality with abundant H. alpinum plants where paternal H. transsilvanicum was missing. Previously reported instances of interspecific hybridization between the same parental taxa showed an opposite direction of crossing and relative abundance of parental taxa. This suggests that the direction of hybridization might be influenced by the frequency of parental taxa at the locality

The endangered Florida pondweed (<i>Potamogeton floridanus</i>) is a hybrid: Why we need to understand biodiversity thoroughly

<div><p>Thorough understanding of biodiversity is a fundamental prerequisite for biological research. A lack of taxonomic knowledge and species misidentifications are particularly critical for conservation. Here we present an example of <i>Potamogeton floridanus</i>, the Florida Pondweed, an endangered taxon endemic to a small area in the Florida panhandle, whose taxonomic status remained controversial for more than a century, and all previous attempts to elucidate its identity have failed. We applied molecular approaches to tackle the origin of the mysterious taxon and supplemented them with morphological and anatomical investigations of both historical herbarium collections and plants recently collected in the type area for a comprehensive taxonomic reassessment. Sequencing of two nuclear ribosomal markers and one chloroplast non-coding spacer resulted in the surprising discovery that <i>P</i>. <i>floridanus</i> is a hybrid of <i>P</i>. <i>pulcher</i> and <i>P</i>. <i>oakesianus</i>, with the former being the maternal parent. The hybrid colony is currently geographically isolated from the distribution range of <i>P</i>. <i>oakesianus</i>. We show that previous molecular analyses have failed to reveal its hybrid identity due to inadequate nuclear DNA sequence editing. This is an example how the uncritical use of automized sequence reads can hamper molecular species identifications and also affect phylogenetic tree construction and interpretation. This unique hybrid taxon, <i>P</i>. <i>×floridanus</i>, adds another case study to the debate on hybrid protection; consequences for its conservation are discussed.</p></div

Comparison of the most relevant anatomical characters of <i>Potamogeton</i> ×<i>floridanus</i> and its parental species.

<p>Anatomical patterns of <i>P</i>. <i>oakesianus</i> and <i>P</i>. <i>pulcher</i> are based on observations of numerous samples as summarized in Ogden [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195241#pone.0195241.ref058" target="_blank">58</a>] and Wiegleb & Kaplan [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195241#pone.0195241.ref008" target="_blank">8</a>].</p

Placement of <i>P</i>. <i>floridanus</i> in phylogenetic trees.

<p>Bayesian consensus trees are shown with posterior probabilities above and bootstrap support of ML and MP analyses below branches (MP support in italics). <b>A</b>: The major ITS sequence of <i>P</i>. <i>floridanus</i> (M) corresponds to that of <i>P</i>. <i>pulcher</i>; a cloned sequence of the underrepresented ribotype of <i>P</i>. <i>floridanus</i> (x16) groups with <i>P</i>. <i>oakesianus</i>. <b>B</b>: The <i>P</i>. <i>floridanus</i> chloroplast haplotype corresponds to that of <i>P</i>. <i>pulcher</i> indicating the maternal origin of the hybrid. <b>C</b>: 5S-NTS sequences of the same species from Lindqvist et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195241#pone.0195241.ref033" target="_blank">33</a>] were included; they are indicated by GenBank accession numbers after species names. As in that study, <i>P</i>. <i>floridanus</i> groups with <i>P</i>. <i>oakesianus</i>, albeit without significant support. This placement is largely an artifact due to sequence polymorphisms (see text).</p