Eine phylogeographische, oekologische und genomische Analyse der Arealausweitung der Wespenspinne Argiope bruennichi

Rapid, poleward range expansions are observed for an increasing number of species in the past decades. These distributional changes are commonly attributed to global environmental change. Recent research, however, indicates that genetic adaptation might also play an important role in explaining the success of range expansions. Considering the fast pace of many range expansions, such contemporary evolutionary processes are unlikely to rely on the emergence of new mutations. Instead, standing genetic variation acts as important resource to fuel adaptation. This variation can be present in a population´s gene pool or it is introduced by secondary contact and admixture of formerly isolated genetic lineages. In the past years, ample evidence has been compiled for an association of admixture, adaptation and range expansions for numerous plant and animal species. Here, I present an analysis of the recent range expansion of the European wasp spider Argiope bruennichi. Originally, this species inhabited the Mediterranean region and warm oceanic climates in France and South-Western Germany. From around 1930 onwards, the spider started expanding its range into increasingly continental climates and can now be found as far north as Finland. This thesis aims to disentangle environmental and genetic factors, involved in the species´ range expansion. In particular, I analyze the interconnection of genetic admixture and invasion success. I approach these questions using population genetic and phylogeographic methods, morphological analyses, ecological experiments and finally whole genome- and transcriptome sequencing. In chapter one, I conduct a detailed genetic and ecological analysis of the spider´s range expansion. I base this study on a dense sampling of more than 2.000 contemporary specimens. In addition, I include about 500 historical spiders from natural history collections. I present genetic and morphological data, as well as several ecological experiments on thermal tolerance and preference and a reciprocal transplant study. My results indicate that the spider´s range expansion is associated with admixture of formerly isolated genetic lineages from around 1930 onwards. The ecological experiments indicate that invasive spider populations have simultaneously adapted to colder temperatures by shifting their thermal preference and tolerance. Like many other spider species, Argiope bruennichi has a wide ranging Palearctic distribution. In chapter two, I conduct a phylogeographic survey over the species´ whole range, from the Macaronesian islands over Europe to East Asia. Next to Argiope bruennichi, I include a second widely distributed spider species, the nursery web spider Pisaura mirabilis. The study is based on mitochondrial and nuclear genetic markers. I highlight the importance of outer-European glacial refugia for the wasp spider. I then show the effects of secondary contact in shaping the postglacial genetic structure of the two species. The analysis identifies several instances of incongruent phylogenetic patterns for mitochondrial and nuclear DNA markers, possibly due to recurrent selection on mitochondria. DNA from natural history collections provides a valuable resource to trace historical genetic changes during range expansions. For that reason, I present an analysis of DNA sequencing and microsatellite genotyping success in historical spider specimens in chapter three. In addition, I exemplarily illustrate the utility of historical specimens to trace historical genetic changes in populations. In the above chapters, I have presented evidence for admixture leading to differential adaptation in spider populations. However, the functional basis of this adaptation remains unknown. For that reason I embark towards unraveling its genomic architecture in chapter four. Initially, I generate the first available draft genome sequence of a spider species. Based on this data, I analyze genome-wide differences of native and invasive wasp spider populations across an environmental gradient. Gene regulatory evolution is a possible mechanism to provide the means for rapid contemporary adaptation to environmental stress. For this reason, I conduct a genome-wide gene expression analysis of native and invasive wasp spiders, which have been exposed to temperature stress in chapter five. I discuss the gene expression divergence between Northern and Southern European spiders in relation to the possibility of recent contemporary adaptation.In den letzten Jahrzehnten weiten immer mehr Tier- und Pflanzenarten ihr Areal in Richtung der Pole aus. Für gewöhnlich werden diese Expansionen auf den globalen Wandel zurückgeführt. Neue Forschungsergebnisse deuten allerdings darauf hin, dass auch genetische Anpassungen einen bedeutenden Anteil am Erfolg derartiger Arealausweitungen haben. Die hohe Geschwindigkeit vieler Invasionen macht eine Beteiligung neu auftretender Mutationen an solchen, rezenten evolutionären Prozessen unwahrscheinlich. Stattdessen könnte existierende genetische Variation als eine wichtige Quelle für Anpassungen dienen. Die nötige Variation kann im Genpool einer Population bereits vorhanden sein oder durch sekundären Kontakt vormals isolierter Linien eingebracht werden. Einige Beispiele für eine Assoziation von genetischer Durchmischung, evolutionären Anpassungen und Arealausweitungen bei diversen Pflanzen- und Tierarten sind bereits bekannt. Die vorliegende Arbeit präsentiert eine Analyse der rezenten Arealausweitung der Europäischen Wespenspinne Argiope bruennichi. Ursprünglich war die Art vor allem im Mittelmeerraum und einigen warmen Regionen in Frankreich und Südwestdeutschland verbreitet. Um 1930 begann die Spinne ihr Areal in zunehmend kontinentale Klimaregionen auszuweiten und wird heute sogar in Finnland gefunden. In meiner Dissertation versuche ich sowohl Umwelteinflüsse als auch genetische Ursachen zu identifizieren, die an der Arealausweitung der Wespenspinne beteiligt sind. Im Besonderen untersuche ich die Verbindung von genetischer Durchmischung und dem Invasionserfolg. Zur Identifikation dieser Faktoren nutze ich populationsgenetische und phylogeographische Methoden, morphologische Analysen, ökologische Experimente und schließlich Gesamtgenom- und Transkriptomsequenzierungen. Im ersten Kapitel präsentiere ich eine detaillierte Untersuchung der Arealausweitung der Wespenspinne. Die Studie basiert auf einer flächendeckenden Besammlung von mehr als 2.000 rezenten Spinnen. Zusätzlich untersuche ich ca. 500 historische Proben aus naturhistorischen Museen. Neben genetischen und morphologischen Daten präsentiere ich ökologische Versuche über die Temperaturtoleranz und –präferenz sowie ein reziprokes Transplantationsexperiment. Meine Ergebnisse zeigen, dass die Arealausweitung der Spinne mit der Durchmischung genetischer Linien ungefähr seit den 1930er Jahren assoziiert ist. Die ökologischen Versuche deuten an, dass invasive Spinnenpopulationen sich über eine Verschiebung ihrer Temperaturtoleranz und -präferenz an kühlere Temperaturen angepasst haben. Argiope bruennichi ist eine weit verbreitete, paläarktische Art. In Kapitel zwei führe ich eine phylogeographische Untersuchung über das gesamte Areal der Art durch, von den Makaronesischen Inseln über Europa bis nach Ostasien. Neben Argiope bruennichi, untersuche ich eine zweite, weit verbreitete Spinnenart, die Raubspinne Pisaura mirabilis. Die Studie basiert auf mitochondrialen und nukleären Markern. Ich identifiziere mehrere, außereuropäische Glazialrefugien für Argiope bruennichi. Außerdem zeige ich die Bedeutung von sekundärem Kontakt um die postglaziale, genetische Struktur der beiden Arten zu erklären. Meine Analyse zeigt mehrere Fälle von inkongruenten phylogenetischen Mustern für mitochondriale und nukleäre Marker, möglicherweise aufgrund von wiederholter Selektion von Mitochondrien. DNA aus Naturhistorischen Sammlungen stellt eine wertvolle Ressource dar, um historische genetische Veränderungen während Arealausweitungen zu verfolgen. Aus diesem Grund präsentiere ich in Kapitel drei eine Analyse des Genotypisierungserfolges bei historischen Spinnenproben. Zusätzlich zeige ich anhand einiger Beispiele den Nutzen alter DNA, um historische, genetische Veränderungen in Populationen zu verfolgen. In den vorhergehenden Kapiteln habe ich gezeigt, dass genetische Durchmischung mit differentieller Anpassung von Spinnenpopulationen einhergeht. Allerdings bleibt die funktionelle Basis dieser Anpassungen unbekannt. Aus diesem Grund unternehme ich in Kapitel vier einen ersten Schritt, um die genetische Architektur dieser Adaptionen zu entschlüsseln. Zunächst generiere ich die bislang erste, verfügbare Rohfassung der Genomsequenz einer Spinnenart. Darauf basierend analysiere ich genomweite Sequenzunterschiede zwischen nativen und invasiven Wespenspinnenpopulationen über einen Umweltgradienten. Genregulatorische Evolution ist ein möglicher Mechanismus, um schnelle Anpassung an Umweltstress zu ermöglichen. Daher untersuche ich in Kapitel fünf genomweite Genexpressionsunterschiede nativer und invasiver Wespenspinnen, die Temperaturstress ausgesetzt waren. Ich diskutiere die Rolle von Genexpressionsdifferenzierung zwischen Nord- und Südeuropäischen Populationen im Zusammenhang mit der Möglichkeit rasanter Anpassung

DNA barcoding and community assembly—A simple solution to a complex problem

Identifying the current and past processes driving community assembly is critical in the effort to understand the Earth\u27s biodiversity and its response to future environmental change. But while studies on community assembly often emphasize the role of contemporary ecological drivers, it has been particularly challenging to account for the effects of past processes in shaping present-day communities. In this issue of Molecular Ecology, Hao et al. (2020) provide a holistic analysis of factors driving the assembly of diverse communities of Lepidoptera in two mountain ranges in northeastern China. The authors use an impressively large data set and exceptionally comprehensive analyses to test how processes of range expansion and gene flow, speciation and extinction, dispersal limitation, environmental filtering and competition have led to present-day diversity patterns. A key novelty of this work is the exhaustive use of DNA barcodes, relatively simple yet powerful molecular markers, to tackle complex biological questions. The authors elegantly show the utility of DNA barcoding data for research beyond simple taxonomic assignment. Their approach is remarkable as it manages to integrate population genetics, phylogenetic history, species diversity and ecology into a well-rounded picture of community assembly. With this work, Hao et al. demonstrate the great promise of DNA barcoding for exhaustive community analysis of even highly diverse and complex systems, raising the bar for future research

High-throughput sequencing for community analysis: the promise of DNA barcoding to uncover diversity, relatedness, abundances and interactions in spider communities

Large-scale studies on community ecology are highly desirable but often difficult to accomplish due to the considerable investment of time, labor and, money required to characterize richness, abundance, relatedness, and interactions. Nonetheless, such large-scale perspectives are necessary for understanding the composition, dynamics, and resilience of biological communities. Small invertebrates play a central role in ecosystems, occupying critical positions in the food web and performing a broad variety of ecological functions. However, it has been particularly difficult to adequately characterize communities of these animals because of their exceptionally high diversity and abundance. Spiders in particular fulfill key roles as both predator and prey in terrestrial food webs and are hence an important focus of ecological studies. In recent years, large-scale community analyses have benefitted tremendously from advances in DNA barcoding technology. High-throughput sequencing (HTS), particularly DNA metabarcoding, enables community-wide analyses of diversity and interactions at unprecedented scales and at a fraction of the cost that was previously possible. Here, we review the current state of the application of these technologies to the analysis of spider communities. We discuss amplicon-based DNA barcoding and metabarcoding for the analysis of community diversity and molecular gut content analysis for assessing predator-prey relationships. We also highlight applications of the third generation sequencing technology for long read and portable DNA barcoding. We then address the development of theoretical frameworks for community-level studies, and finally highlight critical gaps and future directions for DNA analysis of spider communities

Categorization of species as native or nonnative using DNA sequence signatures without a complete reference library.

New genetic diagnostic approaches have greatly aided efforts to document global biodiversity and improve biosecurity. This is especially true for organismal groups in which species diversity has been underestimated historically due to difficulties associated with sampling, the lack of clear morphological characteristics, and/or limited availability of taxonomic expertise. Among these methods, DNA sequence barcoding (also known as "DNA barcoding") and by extension, meta-barcoding for biological communities, has emerged as one of the most frequently utilized methods for DNA-based species identifications. Unfortunately, the use of DNA barcoding is limited by the availability of complete reference libraries (i.e., a collection of DNA sequences from morphologically identified species), and by the fact that the vast majority of species do not have sequences present in reference databases. Such conditions are critical especially in tropical locations that are simultaneously biodiversity rich and suffer from a lack of exploration and DNA characterization by trained taxonomic specialists. To facilitate efforts to document biodiversity in regions lacking complete reference libraries, we developed a novel statistical approach that categorizes unidentified species as being either likely native or likely nonnative based solely on measures of nucleotide diversity. We demonstrate the utility of this approach by categorizing a large sample of specimens of terrestrial insects and spiders (collected as part of the Moorea BioCode project) using a generalized linear mixed model (GLMM). Using a training data set of known endemic (n = 45) and known introduced species (n = 102), we then estimated the likely native/nonnative status for 4,663 specimens representing an estimated 1,288 species (412 identified species), including both those specimens that were either unidentified or whose endemic/introduced status was uncertain. Using this approach, we were able to increase the number of categorized specimens by a factor of 4.4 (from 794 to 3,497), and the number of categorized species by a factor of 4.8 from (147 to 707) at a rate much greater than chance (77.6% accuracy). The study identifies phylogenetic signatures of both native and nonnative species and suggests several practical applications for this approach including monitoring biodiversity and facilitating biosecurity

Rapid and cost-effective generation of single specimen multilocus barcoding data from whole arthropod communities by multiple levels of multiplexing

In light of the current biodiversity crisis, molecular barcoding has developed into an irreplaceable tool. Barcoding has been considerably simplified by developments in high throughput sequencing technology, but still can be prohibitively expensive and laborious when community samples of thousands of specimens need to be processed. Here, we outline an Illumina amplicon sequencing approach to generate multilocus data from large collections of arthropods. We reduce cost and effort up to 50-fold, by combining multiplex PCRs and DNA extractions from pools of presorted and morphotyped specimens and using two levels of sample indexing. We test our protocol by generating a comprehensive, community wide dataset of barcode sequences for several thousand Hawaiian arthropods from 14 orders, which were collected across the archipelago using various trapping methods. We explore patterns of diversity across the Archipelago and compare the utility of different arthropod trapping methods for biodiversity explorations on Hawaii, highlighting undergrowth beating as highly efficient method. Moreover, we show the effects of barcode marker, taxonomy and relative biomass of the targeted specimens and sequencing coverage on taxon recovery. Our protocol enables rapid and inexpensive explorations of diversity patterns and the generation of multilocus barcode reference libraries across whole ecosystems

Multiple paths toward repeated phenotypic evolution in the spiny-leg adaptive radiation (Tetragnatha; Hawai'i)

The repeated evolution of phenotypes provides clear evidence for the role of natural selection in driving evolutionary change. However, the evolutionary origin of repeated phenotypes can be difficult to disentangle as it can arise from a combination of factors such as gene flow, shared ancestral polymorphisms or mutation. Here, we investigate the presence of these evolutionary processes in the Hawaiian spiny-leg Tetragnatha adaptive radiation, which includes four microhabitat-specialists or ecomorphs, with different body pigmentation and size (Green, Large Brown, Maroon, and Small Brown). We investigated the evolutionary history of this radiation using 76 newly generated low-coverage, whole-genome resequenced samples, along with phylogenetic and population genomic tools. Considering the Green ecomorph as the ancestral state, our results suggest that the Green ecomorph likely re-evolved once, the Large Brown and Maroon ecomorphs evolved twice and the Small Brown evolved three times. We found that the evolution of the Maroon and Small Brown ecomorphs likely involved ancestral hybridization events, while the Green and Large Brown ecomorphs likely evolved through novel mutations, despite a high rate of incomplete lineage sorting in the dataset. Our findings demonstrate that the repeated evolution of ecomorphs in the Hawaiian spiny-leg Tetragnatha is influenced by multiple evolutionary processes.publishedVersio

Richness and resilience in the Pacific: DNA metabarcoding enables parallelized evaluation of biogeographic patterns

Islands make up a large proportion of Earth\u27s biodiversity, yet are also some of the most sensitive systems to environmental perturbation. Biogeographic theory predicts that geologic age, area, and isolation typically drive islands\u27 diversity patterns, and thus potentially impact non-native spread and community homogenization across island systems. One limitation in testing such predictions has been the difficulty of performing comprehensive inventories of island biotas and distinguishing native from introduced taxa. Here, we use DNA metabarcoding and statistical modelling as a high throughput method to survey community-wide arthropod richness, the proportion of native and non-native species, and the incursion of non-natives into primary habitats on three archipelagos in the Pacific – the Ryukyus, the Marianas and Hawaii – which vary in age, isolation and area. Diversity patterns largely match expectations based on island biogeography theory, with the oldest and most geographically connected archipelago, the Ryukyus, showing the highest taxonomic richness and lowest proportion of introduced species. Moreover, we find evidence that forest habitats are more resilient to incursions of non-natives in the Ryukyus than in the less taxonomically rich archipelagos. Surprisingly, we do not find evidence for biotic homogenization across these three archipelagos: the assemblage of non-native species on each island is highly distinct. Our study demonstrates the potential of DNA metabarcoding to facilitate rapid estimation of biogeographic patterns, the spread of non-native species, and the resilience of ecosystems

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