Distribution of \u3ci\u3ePelecinus Polyturator\u3c/i\u3e in Wisconsin (Hymenoptera: Pelecinidae), With Speculations Regarding Geographical Parthenogenesis

The geographical distribution of Pelecinus polyturator in Wisconsin is summarized. Only five males have been recorded; a recently collected male from the University of Wisconsin Field Station in Ozaukee County represents the first male collected in the state in over 40 years. Speculations on the possible significance and implications of geographical parthenogenesis relative to Pelecinus are offered

Geographical parthenogenesis

Diese Dissertation hat zum Ziel, das Phänomen der geographische Parthenogenese (GP) zu verstehen. GP bedeutet, dass sexuelle und asexuelle Populationen desselben Artkomplexes nicht die gleiche geographische Verbreitung aufweisen. Im allgemeinen besetzen asexuelle Populationen höhere Lagen und Breitengrade, und sind weiter verbreitet. Geographische Parthenogenese kombiniert verschiedene Aspekte, die für das Verständnis der Verbreiungsmuster betrachtet werden müssen: das Repoduktion-System, Polyploidisierung, genetische Diversität und die Fähigkeit zur Kolonisierung. Die alpine Art Ranunculus kuepferi ist als Modell zum Studium der geographischen Parthenogenese geeignet, da polyploide, asexuelle Populationen im gesamten Alpengebiet weit verbreitet sind, während die diploiden sexuellen Populationen auf glaziale Refugien beschränkt sind. Ich habe verschiedene Formen der Reproduktion und die Stabilität der Zytotypen mittels Flow Cytometry (FC) und Durchflusszytometrie an Samen (FCSS) untersucht. Die Herkunft der Polyploidisierung und die genetische Vielfalt der Populationen wurde mit molekular-biologischen Methoden, mit Amplified Fragment Length Polymorphism (AFLPs; dominante Marker) und Mikrosatelliten (SSR; kodominanten Marker) analysiert. Diese Studien wurden an 60 Populationen aus dem ganzen Verbreitungsgebiet dieser Art durchgeführt. All diese Marker haben dazu beigetragen, Aufschluss über die genetische Struktur und den Einfluss der Reproduktion auf die Entstehung von geographischer Parthenogenese zu erhalten. Die drei Kapitel der Arbeit behandeln die verschiedenen Aspekte wie folgt: Die Stabilität der Zytotypen wurde mittels FC, der Fortpflanzungsmodus mittels FCSS bestimmt. Diese Analyse ergab, dass die diploiden Populationen stabil und voll sexuell bleiben. Triploide individuen kommen in der Kontaktzone vor und sind ein Produkt von Rückkreuzungen zwischen diploiden und tetraploiden Populationen. Außerhalb der Kontaktzone weisen in tetraploiden Populationen c. 30% der Samen triploide Embryos auf, aber triploide erwachsene Pflanzen treten nur einmal im ganzen tetraploiden Verbreitungsgebiet auf. Die Mehrheit der Tetraploiden behält eine stabile Ploidiestufe mittels gametophytischer Apomixis, wobei die Bildung des Endosperms entweder pseudogam oder autonom erfolgt. Einige wenige Prozent der Samen der tetraploiden Pflanzen sind auf sexuellem Weg entstanden. Polyploidisierung kann eine Erklärung geben, warum Apomixis in der Art Ranunculus kuepferi entstanden ist. Die autopolyploide Herkunft der Tetraploiden wurde mittels Bayesian-Analyse der Populations-Struktur (BAPS) Analyse der SSRs nachgewiesen. Damit konnte gezeigt werden, dass die tetraploiden aus diploiden Populationen ohne den Beitrag eines anderen Genoms entstanden sind. Die tetraploiden entstanden mehrfach von diploiden Populationen, da sie fast keine genetischen Unterschiede und nur wenige neue SSRs-Allele zeigen. AFLPs bestätigen in einer Neighbor Joining Analyse, dass diploide und tetraploide Populationen den gleichen Gen-Pool aufweisen. Daher ist der geographische Erfolg der Apomikten nicht auf den Beitrag eines neuen Genoms zurückzuführen, wie es in Allopolyploiden anzunehmen ist. Apospory scheint die Probleme in der Meiose, die durch Multivalentbildung verursacht wird, zu überwinden, was vom Vorkommen von Genotypen mit multiple Allelen in den SSR Loci angenommen werden kann. Diese ungewöhnliche Kombination von Autopolyploidie und Aposporie stabilisiert das Reproduktionssystem und damit die Ploidiestufe. Die Auswirkung von Reproduktionssystem und der genetischen Diversität der Populationen wurden durch die Verwendung von AFLPs und SSRs untersucht. Tetraploide Populationen von Ranunculus kuepferi haben die Selbst-Inkompatibilität verloren, wodurch pseudogame Selbstbestäubung ermöglicht wird, während die diploiden selbst-inkompatibel bleiben. Daher können Apomikten leichter neue Populationen, potentiell sogar mit einem einzigen Samen gründen, und zeigen damit eine bessere Fähigkeit zur Kolonisierung. Eine BAPS Analyse der AFLP Daten bestätigt, dass die Apomikten populationsspezifische Gen-Pools aufweisen, die wahrscheinlich auf mehrfache Gründer-Effekte zurückzuführen sind. Diploide sexuelle Populationen hätten den Vorteil einer höheren genetischen Vielfalt durch Rekombination. Mein Ergebnis zeigt eine genetische Diversität, die typisch für sexuelle auskreuzende Arten ist. Die tetraploiden Apomikten weisen jedoch ein gleiches Ausmaß genetischer Diversität hinsichtlich Heterozygotie und der Fst Werte auf; außerdem zeigen sie keine Klonalität. Genetische Vielfalt wird über fakultative Apomixis beibehalten und ermöglicht die weite Verbreitung der Tetraploiden. Die tetraploiden Populationen profitieren von Vorteilen beider Reproduktions-Systeme (besser Kolonisierungsfähigkeit und genetische Vielfalt), und sind damit effizienter als die diploiden, ein großes Verbreitungsgebiet zu besiedeln.This doctoral thesis aims at understanding geographical parthenogenesis, which means that sexual and asexual populations of the same species complex do not share the same distribution area. In general, asexuals occupy higher altitudes and latitudes and are more widespread. Geographical parthenogenesis combines different aspects that need to be considered for understanding the pattern: the reproduction system, poly-ploidisation events, genetic diversity, and colonization ability. The alpine species Ranunculus kuepferi is a model for studying geographical parthenogenesis, since polyploid, putative asexual populations are widespread throughout the Alps, while diploids sexual are confined to small refugial areas. I investigated different modes of reproduction and stability cytotypes via Flow Cytometry (FC) and Flow Cytometric Seed Screening (FCSS) in seeds. The origin of polyploidisation and genetic diversity of populations was analyzed with molecular methods, by using Amplified Fragment Length Polymorphism (AFLPs; dominant marker) and microsatellites (SSRs; codominant marker). These studies were conducted on 60 populations out of the whole distributional range of the species. All these markers helped to reveal the population genetic structure and the importance of modes of reproduction for the evolution of geographical parthenogenesis. The three chapters of the thesis treat the different aspects as follows: Cytotype stability for each ploidy level was assessed over the distribution area with FC, and the mode of reproduction was determined via FCSS. This analysis revealed that diploids remain stable and fully sexual. Triploids in the contact zone are a product of backcrossing between diploids and tetraploids. Outside the contact zone, 30% of the seed display triploid embryos in tetraploid populations, but triploid adult plants occur only once in the whole tetraploid area. The majority of tetraploids maintain a stable ploidy level via gametophytic apomixis with either pseudogamous or autonomous endosperm formation. However, a few percent of seeds of tetraploids are formed in the sexual way. Polyploidization events may give an explanation why apomixis originated in the species Ranunculus kuepferi. Evidence for an autopolyploid origin of the tetraploids was presented by Bayesian Analysis of Populations Structure (BAPS) analysis of SSRs, which showed that tetraploids originated from diploids without the contribution of another genome. Tetraploids obviously originated several time from diploids since they show almost no divergence and only few new alleles in SSRs are present in tetraploids. AFLPs show in a Neighbor Joining analysis that diploids and tetraploids share the same gene pool. Therefore, geographical success of apomicts does not result from genomic novelty, which could be predicted in allopolyploids. Apospory seems to help to overcome the problems occurring in unbalanced meiosis caused by multivalent formation, which can be assumed from genotypes exhibiting multiple allelism in SSR loci. This uncommon combination of autopolyploidy and apospory stabilizes the reproductive system and hence the ploidy level. Effects of breeding system and genetic diversity of populations were further studied by using AFLPs and SSRs. Tetraploids of Ranunculus kuepferi have a breakdown of the self-incompatibility system, allowing for pseudogamous selfing, whereas diploids remain self-incompatible. Therefore, apomicts can easily establish new populations, potentially with a single seed, and thus they have superior colonization ability. A BAPS analysis of AFLP data confirms populations-specific gene pools in apomicts which have probably resulted from multiple founder events. Diploids ought to have the advantage of higher genetic diversity via recombination, as our result show a genetic diversity typical for sexual outcrossers. However, tetraploids show the same level of diversity with respect to heterozygosity and Fst values, as well as they exhibit no clonality. Genetic diversity is maintained via facultative apomixis and allows maintenance of the widespread distribution pattern of tetraploids. Tetraploids profit from the best of both reproductive systems (better colonization ability and genetic diversity), and therefore they are more efficient than the diploids to spread over the major distribution area

Diversity in the Reproductive Modes of European Daphnia pulicaria Deviates from the Geographical Parthenogenesis

10 páginas, 5 figuras, 3 tablas.Background: Multiple transitions to obligate parthenogenesis have occurred in the Daphnia pulex complex in North America. These newly formed asexual lineages are differentially distributed being found predominantly at high latitudes. This conforms to the rule of geographical parthenogenesis postulating prevalence of asexuals at high latitudes and altitudes. While the reproductive mode of high-latitude populations is relatively well studied, little is known about the reproduction mode in high altitudes. This study aimed to assess the reproductive mode of Daphnia pulicaria, a species of the D. pulex complex, from high altitude lakes in Europe. Methodology/Principal Findings: Variation at eight microsatellite loci revealed that D. pulicaria from the High Tatra Mountains (HTM) had low genotype richness and showed excess of heterozygotes and significant deviations from Hardy- Weinberg expectations, and was thus congruent with reproduction by obligate parthenogenesis. By contrast, populations from the Pyrenees (Pyr) were generally in Hardy-Weinberg equilibrium and had higher genotypic richness, suggesting that they are cyclic parthenogens. Four lakes from lowland areas (LLaP) had populations with an uncertain or mixed breeding mode. All D. pulicaria had mtDNA ND5 haplotypes of the European D. pulicaria lineage. Pyr were distinct from LLaP and HTM at the ND5 gene. By contrast, HTM shared two haplotypes with LLaP and one with Pyr. Principal Coordinate Analysis of the microsatellite data revealed clear genetic differentiation into three groups. HTM isolates were intermediate to Pyr and LLaP, congruent with a hybrid origin. Conclusion/Significance: Inferred transitions to obligate parthenogenesis have occurred only in HTM, most likely as a result of hybridizations. In contrast to North American populations, these transitions do not appear to involve meiosis suppressor genes and have not been accompanied by polyploidy. The absence of obligate parthenogenesis in Pyr, an environment highly similar to the HTM, may be due to the lack of opportunities for hybridization.Peer reviewe

Effects of cold stress on reproductive biology and epigenetic profiles of the alpine plant Ranunculus kuepferi (Ranunculaceae)

Alpine habitats are shaped by harsh abiotic conditions and cold climates. Plant life in such habitats is challenging, as environmental influence can alter the conditions for development and reproduction. More specifically, phenotypic plasticity of morphological traits can be influenced by temperature stress. Temperature stress can also affect epigenetic and gene expression profiles, which may have an impact on acclimation and adaptation of the species. Polyploidy seems to affect the DNA methylation profiles, while distribution patterns suggest that it could be advantageous under cold conditions. Nevertheless, little is known about non -model plants, whether temperature stress can induce methylation changes depending on the cytotypes of the individuals, to what extent a treatment shift can induce epigenetic responses and how they are depicted in phenotypic plasticity and reproduction of the species. Furthermore, it remains vague how cold stress is translated in gene expression changes under different cytotypes and how such a putative response is framed through gene set pathways and epigenetic control. The perennial alpine plant Ranunculus kuepferi was utilized to investigate the correlations of cold stress with polyploidy, mode of reproduction, phenotypic plasticity, epigenetics, gene expression and geographical parthenogenesis . The species is mainly found in the wild with diploid and autotetraploid cytotypes, which are mostly sexual and facultative apomicts, respectively. Diploid and autotetraploid individuals were placed in two climate chambers and exposed to cold (+7°C day/+2°C night, -1°C cold shocks for three nights per week) and warm (control) (+15°C day/+10°C night) temperature treatments in climate growth chambers for four consecutive flowering periods and shifted from one condition to the other after the first flowering period. Methylation-sensitive amplified fragment- length polymorphism markers were applied for the first two years, to screen possible genome-wide methylation alterations triggered by temprerature treatments and treatment shifts. For the second year of t emperature treatments, morphological traits (height, leaves and flowers) and the proportion of well- developed seeds were measured as fitness indicators, while flow cytometric seed screening (FCSS) was utilized to determine the reproduction mode. Subsequently, comparisons with patterns of methylation-sensitive amplified fragment- length polymorphisms (MS-AFLPs/MSAPs) regarding the same year of treatment were conducted. Finally, for the last year of treatment, both cytotypes were investigated for their gene expression profiles via transcriptome sequencing and qRT-PCR. The datasets were analyzed for four predefined groups with respect to treatment (Cold/Warm) and ploidy level (Diploid/Tetraploid). DNA methylation profiles showed temperature sensitivity and propose a ploidy effect for both years of analysis. Likewise, the treatment shift had an impact on both cytotypes, resulting in significantly less epiloci, regardless of the shift’s direction. Such correlations of ploidy level and epigenetic profiles may reflec t DNA methylation dynamics during cold acclimation. The AMOVA results are in line with the hypothesis of cold stress influencing the epigenetic patterns, while they also depict the DNA methylation dynamics of tetraploids, as a response to temperature treatment shift. Concerning the phenotypic plasticity of the species under temperature treatments, the potential of acclimation under environmental conditions is underlined, as diploids grow better under warm conditions and tetraploids perform better in cold treatments, while the expressed morphological traits are linked with epigenetic patterns. Moreover, cold stress reduced the reproduction fitness but did not induce apomixis in diploid individuals. These results confirm the different niche preferences of cytotypes in natural populations and empower the geographical parthenogenesis scenario, which is previously proposed for the species. Cold acclimation of the cytotypes is further indicated by gene expression profiles. Overall, diploid individuals altered more gene set pathways than tetraploid ones, and suppressed pathways involved in ion/cation homeostasis. Gene Set Pathways mostly activated under tetraploids are related to cell wall and plasma membrane. Thus, tetraploids seem to be better acclimated to cold conditions, enabling them to colonize colder climatic areas in the Alps. Finally, an epigenetic background for gene regulation in response to temperature conditions is indicated.2022-01-2

Geographical parthenogenesis, genome size variation and pollen production in the arctic-alpine species Hieracium alpinum

Hieracium alpinum L. (Asteraceae) is an arctic-alpine species distributed throughout Europe with both diploid and triploid cytotypes. We determined the ploidy levels of plants from 23 populations from Austria, Bosnia and Herzegovina, Finland, Italy, Norway, Romania, Slovakia, Switzerland and Ukraine. Data showed a non-overlapping pattern of cytotype distribution: sexually reproducing diploids (2n=2x=18) occur solely in the Eastern and Southern Carpathians, while apomictic triploids (2n=3x=27) cover the rest of the range. Such clear-cut allopatry is rather rare in vascular plants with geographical parthenogenesis. Comparison of absolute genome size indicates genome downsizing (by on average 3.7%) of haploid DNA amount in triploids relative to diploids. Genome size further correlated with longitude and latitude in the Alps, with decreasing absolute DNA content from west to east, and from south to north. While previously published data indicated complete male sterility of triploid plants, we found that plants from the Alps and Bosnia and Herzegovina commonly produced some pollen, whereas populations from the Western Carpathians and Scandinavia seemed to be almost completely pollen sterile. Scenarios about the evolution of geographical parthenogenesis in H. alpinum are discusse

Introgression of apomixis into sexual species is inhibited by mentor effects and ploidy barriers in the Ranunculus auricomus complex

Background and Aims Apomictic plants maintain functional pollen, and via pollination the genetic factors controlling apomixis can be potentially transferred to congeneric sexual populations. In contrast, the sexual individuals do not fertilize apomictic plants which produce seeds without fertilization of the egg cells. This unidirectional introgressive hybridization is expected finally to replace sexuality by apomixis and is thought to be a causal factor for the wide geographical distribution of apomictic complexes. Nevertheless, this process may be inhibited by induced selfing (mentor effects) of otherwise self-incompatible sexual individuals. Here whether mentor effects or actual cross-fertilization takes place between diploid sexual and polyploid apomictic cytotypes in the Ranunculus auricomus complex was tested via experimental crosses. ¿ Methods Diploid sexual mother plants were pollinated with tetra- and hexaploid apomictic pollen donators by hand, and the amount of well-developed seed compared with aborted seed was evaluated. The reproductive pathways were assessed in the well-developed seed via flow cytometric seed screen (FCSS). ¿ Key Results The majority of seed was aborted; the well-developed seeds have resulted from both mentor effects and cross-fertilization at very low frequencies (1.3 and 1.6% of achenes, respectively). Pollination by 4x apomictic pollen plants results more frequently in cross-fertilization, whereas pollen from 6x plants more frequently induced mentor effects. ¿Conclusions It is concluded that introgression of apomixis into sexual populations is limited by ploidy barriers in the R. auricomus complex, and to a minor extent by mentor effects. In mixed populations, sexuality cannot be replaced by apomixis because the higher fertility of sexual populations still compensates the low frequencies of potential introgression of apomixi