Leafflower plant/leafflower moth brood pollination mutualisms are widespread in the Paleotropics. Leafflower moths pollinate leafflower plants, but their larvae consume a subset of the hosts' seeds. These interactions are highly phylogenetically constrained: six clades of leafflower plants are each associated with a unique clade of leafflower moths (Epicephala). Here, we report a previously unrecognized basal seventh pollinating Epicephala lineageassociated with the highly derived leafflower clade Glochidionin Asia. Epicephala lanceolaria is a pollinator and seed predator of Glochidion lanceolarium. Phylogenetic inference indicates that the ancestor of E. lanceolaria most likely shifted onto the ancestor of G. lanceolarium and displaced the ancestral allospecific Epicephala pollinator in at least some host populations. The unusual and apparently coadapted aspects of the G. lanceolarium/E. lanceolaria reproductive cycles suggest that plant-pollinator coevolution may have played a role in this displacement and provide insights into the dynamics of host shifts and trait coevolution in this specialized mutualism.

Sonoran Desert Drosophila mettleri breeds in soil soaked by the necrotic cacti juices from saguaro (Carnegiea gigantea) and cardon (Pachycereus pringlei). An isolated population on Santa Catalina Island, 300 kilometers NW of the Sonoran Desert limit, was discovered breeding in several Opuntia cacti species. Host shifts are associated with the speciation process in phytophagous insects. I tested for evidence of premating isolation, postmating isolation, and ecological differences among allopatric populations of Drosophila mettleri using a variety of approaches. No sexual isolation was detected. However, Drosophila mettleri from Santa Catalina Island shows significant behavioral and physiological differences compared with Sonoran Desert populations. Furthermore, Drosophila mettleri from Santa Catalina Island was significantly genetically differentiated from all other populations in the study. Finally, I observed sufficiently significant F1 male sterility in crosses involving the Santa Catalina Island population to consider it indicative of early postzygotic isolation.

Insects are host to a diverse range of vertically transmitted micro-organisms, but while their bacterial symbionts are well-studied, little is known about their vertically transmitted viruses. The sigma virus (DMelSV) is currently the only natural hostspecific pathogen to be described in Drosophila melanogaster. In this thesis I have examined; the diversity and evolution of sigma viruses in Drosophila, their transmission and population dynamics, and their ability to host shift. I have described six new rhabdoviruses in five Drosophila species — D. affinis, D. obscura, D. tristis, D. immigrans and D. ananassae — and one in a member of the Muscidae, Muscina stabulans (Chapters two and four). These viruses have been tentatively named as DAffSV, DObsSV, DTriSV, DImmSV, DAnaSV and MStaSV respectively. I sequenced the complete genomes of DObsSV and DMelSV, the L gene from DAffSV and partial L gene sequences from the other viruses. Using this new sequence data I created a phylogeny of the rhabdoviruses (Chapter two). The sigma viruses form a distinct clade which is closely related to the Dimarhabdovirus supergroup, and the high levels of divergence between these viruses suggest that they may deserve to be recognised as a new genus. Furthermore, this analysis produced the most robustly supported phylogeny of the Rhabdoviridae to date, allowing me to reconstruct the major transitions that have occurred during the evolution of the family. This data suggests that the bias towards research into plants and vertebrates means that much of the diversity of rhabdoviruses has been missed, and rhabdoviruses may be common pathogens of insects. In Chapter three I examined whether the new sigma viruses in Drosophila affinis and Drosophila obscura are both vertically transmitted. As is the case for DMelSV, both males and females can transmit these viruses to their offspring. Males transmit lower viral titres through sperm than females transmit through eggs, and a lower proportion of their offspring become infected. I then examined natural populations of D. obscura in the UK; 39% of flies were infected and the viral population shows clear evidence of a recent expansion, with extremely low genetic diversity and a large excess of rare polymorphisms. Using sequence data I estimate that the virus has swept across the UK within the last ~11 years, during which time the viral population size doubled approximately every 9 months. Using simulations based on lab estimates of transmission rates, I show that the biparental mode of transmission allows the virus to invade and rapidly spread through populations, at rates consistent with those measured in the field. Therefore, as predicted by the simulations, the virus has undergone an extremely rapid and recent increase in population size. In Chapter four I investigated for the first time whether vertically transmitted viruses undergo host shifts or cospeciate with their hosts. Using a phylogenetic approach I show that sigma viruses have switched between hosts during their evolutionary history. These results suggest that sigma virus infections may be short-lived in a given host lineage, so that their long-term persistence relies on rare horizontal transmission events between hosts. In Chapter five I examined the ability of three Drosophila sigma viruses to persist and replicate in 51 hosts sampled across the Drosophilidae phylogeny. I used a phylogenetic mixed model to account for the non-independence of host taxa due to common ancestry, which additionally allows integration over the uncertainty in the host phylogeny. In two out of the three viruses there was a negative correlation between viral titre and genetic distance from the natural host. Additionally the host phylogeny explains an extremely high proportion of the variation (after considering genetic distance from the natural host) in the ability of these viruses to replicate in novel hosts (>0.8 for all viruses). There were strong phylogenetic correlations between all the viruses (>0.65 for all pairs), suggesting a given species’ level of resistance to one virus is strongly correlated with its resistance to other viruses. This suggests the host phylogeny, and genetic distance from the natural host, may be important in determining viruses ability to host switch. This work has aimed to address fundamental questions relating to host-parasite coevolution and pathogen emergence. The data presented suggests that sigma viruses are likely to be widespread vertically transmitted insect viruses, which have dynamic interactions with their hosts. These viruses appear to have switched between hosts during their evolutionary history and it is likely the host phylogeny is a determinant of such host shifts.

Emerald ash borer (EAB), Agrilus planipennis (Coleoptera: Buprestidae), is an aggressive invader from Asia that has killed millions of trees in North America. Recently EAB has been documented developing in a novel host, white fringetree, Chionanthus virginicus. I evaluated larval performance in two common ash species and white fringetree by infesting excised bolts with emerald ash borer eggs. In addition I evaluated several plant characteristics to determine which most influence larval development. I also conducted choice and no choice assays using the classical biological control agent, Tetrastichus planipennisi (Hymenoptera: Eulophidae), to assess its ability to locate larval EAB in the different host plants. I found significantly lower survival rates of EAB larvae in white fringetree compared to white ash, F. americana. Larval phloem consumption and larval growth were lower in fringetree than in both ash tested. In choice and no choice assays T. planipennisi failed to parasitize larvae in fringetree. Failure of T. planipennisi to parasitize larvae within fringetree has implications for the efficacy of this classical biological control agent. Coupled with the use of white fringetree as a reservoir host, the enemy free space provided to EAB through use of this alternate host may have repercussions for EAB invasion dynamics.

Our world is changing rapidly and factors like urbanisation, changed agricultural practices and climate change are causing losses in butterfly diversity. It is therefore of importance to understand the source of their diversity. Given the remarkable diversity of herbivorous insects compared to their non-herbivorous sister groups, changes in host use have been implicated as a promoter of speciation. This thesis looks at geographical aspects of host range evolution and the plasticity of host use. We show that butterflies in the subfamily Nymphalinae that feed on a wide range of host plants have larger geographic ranges than species with narrower host ranges. Although tropical butterflies appear to be more specialised than temperate species, this effect is lost when controlling for the differences in geographic range. Geographic variation in host plant use within Polygonia faunus, related to morphologically distinct subspecies, did not show any genetic differentiation. This suggests that the observed variation in host plant use is a plastic response to environmental differences. Reconstructing host use for the Polygonia-Nymphalis and Vanessa group shows that plasticity is also important for understanding host use at the level of butterfly genera. Using unequal transition costs and including larval feeding ability revealed that frequent colonisations of the same plant genus can often be explained by non-independent processes, such as multiple partial losses of host use, recolonisation of ancestral hosts, and parallel colonisations following a preadaptation for host use. These processes are further reflected in the conservative use of host plant orders within the butterfly family Nymphalidae. Few taxa feed on more than one host plant order, and these expansions occur at the very tips of the tree, which we argue is evidence of the transient nature of generalist host use. These insights improve our understanding of how host range evolution may promote diversification. / At the time of the doctoral defence,the following papers were unpublished and had a status as follows: Paper 3: Submitted; Papers 4 and 5: Manuscripts

The remarkable diversity of plant-feeding insects could be explained by the dynamics of their plant associations, where host plant shifts and specialization onto a small fraction of available plants may promote diversification. Neotropical Adelpha butterflies contain a large number of species, and previous work indicated the colonization of a novel host plant family (Rubiaceae) fueled its rapid diversification. However, accumulating host records indicate wide taxonomic host breadth at family level and below. Here, we categorize Adelpha diet breadth based on known host plant relationships across the Neotropics and from Costa Rica, Ecuador and Brazil. We also use a diet breadth index that identifies plants used in similar ways by Adelpha, pointing to potential plant traits that could facilitate or prevent plant-insect interactions. We find that diet breadth in Adelpha is not likely to change at different geographic scales, and that regional resource specialization was uncommon. Additionally, the diversification fueled by the switch to Rubiacae, appears to have led to some lowland-clade Adelpha species specializing on a restricted subset of host genera and species within Rubiaceae, as well as in Urticaceae. In contrast, the A. serpa-group shows generalization, with each species tending to feed on its own set of several unrelated plant families. Taken together, these results indicate that Rubiaceae and additional plant families appear as important ecological factors that have promoted adaptations in Adelpha and host plant family-level switches have not always had the same effect on diversification, corroborating the importance of Rubiaceae for this butterfly genus. Further research involving detailed phylogenies is needed to investigate associations between changes in diet breadth and speciation events, and test hypotheses of diet evolution.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第25144号 / 理博第5051号 / 新制||理||1720(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)准教授 高山 浩司, 教授 田村 実, 教授 石田 厚 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Host shifts -- where a pathogen jumps from one host species to another -- have been described as one of the main factors leading to emerging infectious diseases (EID). The harm that a pathogen causes to a host (virulence) varies following a host shift. Differences in susceptibilities among host species means that pathogens may be more likely to switch between certain groups of hosts. Factors that determine the variation in host susceptibility are still unknown, but one possible predictor is the host evolutionary history. Here, we examine how phylogenetically related hosts vary in susceptibility when dealing with infections of two viruses differing in pathogenicity. We infected 39 species of Drosophilidae with Drosophila A virus (DAV), a virus initially described as avirulent, and we measured host mortality (virulence) and virus replication (viral load). Then, we compared our results to previously collected data from the virulent Drosophila C virus (DCV) and we analysed the data of both viruses together. We found large variation in DAV virulence and viral load, with benign infections in some cases and high mortality in others. There was phylogenetic correlation in viral load, with species presenting similar viral load clustering together in the phylogeny. However, we did not find correlation for virulence, indicating that DAV virulence was not predictable based on viral load. Also, we did not find correlation between DAV and DCV results, indicating that variation in host susceptibility is not predictable by other pathogens infections. It is possible that hosts and parasites ecology or genetic traits may be also influencing susceptibility variation. These results suggest that although some traits are predicted by phylogeny, to determine the factors driving host susceptibility variation to different pathogens following host shifts is a very complex task / Trocas de hospedeiro -- quando um patógeno passa de uma espécie de hospedeiro para outra -- são descritas como um dos principais fatores causadores de doenças infecciosas emergentes (DIE). O dano que um patógeno causa a seu hospedeiro (virulência) varia quando trocas de hospedeiro ocorrem. Diferenças em susceptibilidade entre espécies de hospedeiros indicam que patógenos são mais propensos a realizar trocas entre determinados grupos de hospedeiros. Os fatores que determinam a variação na susceptibilidade do hospedeiro ainda são desconhecidos, porém um possível preditor é a história evolutiva do hospedeiro. Nesse estudo, nós examinamos como hospedeiros filogeneticamente relacionados variam em susceptibilidade ao lidar com duas infecções de vírus que variam em patogenicidade. Infectamos 39 espécies de Drosophilidae com o vírus A de Drosophila (DAV), inicialmente descrito como não virulento, e medimos mortalidade do hospedeiro (virulência) e replicação viral (carga). Em seguida, nós comparamos nossos resultados com informações do vírus C de Drosophila (DCV), um virulento, e analisamos os dados dos dois vírus conjuntamente. Encontramos uma grande variação nos dados de virulência e carga viral para DAV, com infecções benignas em alguns casos e alta mortalidade em outros. Encontramos correlação para carga viral, com espécies com cargas virais semelhantes aparecendo filogeneticamente próximas. Contudo, não há correlação filogenética para virulência, indicando que a virulência de DAV não pode ser predita com base na carga viral. Além disso, nós não encontramos correlação entre os resultados de DAV e DCV, indicando que a variação na susceptibilidade não pode ser predita por infecções de outros patógenos. É possível que fatores ecológicos e genéticos do hospedeiro e do parasita estejam influenciando a variação em susceptibilidade. Esses resultados sugerem que, apesar de alguns traços possam ser preditos pela filogenia, determinar os fatores causadores da variação na susceptibilidade a diferentes patógenos após trocas de hospedeiros é um trabalho extremamente complexo

Les herbivores polyphages sont des généralistes capables d’exploiter une large gamme de plantes hôtes. Au cours des travaux de cette thèse en évolution expérimentale, nous étudions l’évolution de traits d’histoire de vie de différentes populations d’une espèce de ravageur de culture, l’acarien Tetranychus urticae, suite à la colonisation d’un même nouvel hôte, la tomate. Au cours des deux premiers chapitres, des mesures de traits d’histoire de vie ont été collectées depuis le stade œuf jusqu’à la mort des individus permettant de décrire finement le cycle de vie de cet acarien en réponse à l’exploitation de la tomate. Dans le chapitre 1, j’ai montré que la survie au stade juvénile était étroitement liée à des effets maternels. Notamment, les mères s’étant préalablement développées sur la plante de tomate conféraient à leurs descendants une meilleure survie juvénile sur cet hôte. Cependant, ces juvéniles quittaient davantage la plante une fois adulte et avaient une fécondité (pour les femelles) réduite. De plus, l’histoire évolutive des populations affectait la proportion de femelles produites par les mères améliorant potentiellement la démographie des populations. Dans le second chapitre, j’ai montré que plusieurs traits d’histoire de vie (survie juvénile, survie adulte mâle et fécondité) avaient évolué dans les populations exposées à la tomate depuis plusieurs générations à comparer des populations témoins ayant évolué sur haricot. Néanmoins, l’étude du succès reproducteur total des femelles intégrant l’effet de plusieurs traits de vie montre paradoxalement un signal clair d’adaptation au nouvel hôte seulement pour des populations ayant évolué sur cet hôte pendant environ 38 générations et non pour des populations ayant évolué sur cette plante hôte pendant environ 78 générations. L’étude de la diversité génétique, sur la base de marqueurs microsatellites, suggère que ces dernières populations ont souffert de goulots d’étranglement, ce qui pourrait avoir compromis leur adaptation. Pour finir, dans le chapitre 3, je teste si les populations nouvellement adaptées à la tomate sont plus tolérantes aux défenses de la plante, induites par l’attaque d’herbivores, ou bien si ces populations induisent différents niveaux de défense chez les plantes attaquées, affectant la performance des acariens qui les colonisent ultérieurement. Pour cela, des acariens ont été mis en ponte sur des plantes de tomates non pré-infestées, pré-infestées par des acariens adaptés à la tomate ou pré-infestées par des acariens non adaptés à cet hôte. Les populations adaptées à la tomate ont une fécondité plus forte sur cette plante, quel que soit le traitement de la plante, tandis que toutes les populations d’acariens voient leur mortalité augmenter sur les plantes pré-infestées par des acariens adaptés à la tomate. Mes résultats semblent indiquer que l’évolution sur tomate se manifeste par une plus grande capacité à tolérer les défenses de cette plante et une plus grande induction de ces défenses.Ainsi, mon étude décrit un continuum de réponses évolutives chez un polyphage allant de l’absence de détection d’adaptation, conduisant à l’extinction des populations, à la présence de réponses plastiques adaptatives, jusqu’au processus d’adaptation à la plante hôte via possiblement l’acquisition de la capacité à tolérer les défenses de la plante hôte. Ces travaux soulignent l’importance d’intégrer l’effet des variations contrastées de différents traits d’histoire de vie dans une mesure de valeur sélective afin de décrire l’adaptation à une nouvelle plante hôte. Des investigations futures en ce sens permettraient d’enrichir la littérature sur la persistance des herbivores suite à la colonisation de nouvelles plantes hôtes mais aussi d’affiner nos compétences en terme de contrôle d’espèces de ravageurs. / Polyphagous herbivores are generalists able to exploit a large range of host-plants. In this thesis, using experimental evolution, I study the evolution of life history traits in different populations of a crop pest, the spider mite Tetranychus urticae, after colonization of a new host, the tomato plant. In the first two chapters, measures of life history traits were collected from the egg stage to the death of individuals allowing the precise description of the life cycle of mites in response to the exploitation of tomato plants. As described chapter 1, I found that juvenile survival on the new host was influenced by maternal effects. In particular, mothers having developed on tomato had offspring surviving better on this host as juvenile. However, these juveniles left more often the plant as adults and had a reduced fecundity (for females). Moreover, the evolutionary history of populations affected the proportion of females produced by mothers, potentially enhancing demography of populations having previously evolved on this host. In chapter 2, I show that several life history traits (juvenile survival, male adult lifespan and fecundity) had evolved in all populations exposed to tomato for several generations relative to control populations evolving on bean. Nevertheless, the study of female lifetime reproductive success integrating the effect of several successive traits only showed, paradoxically, an adaptive signal for populations having evolved on this host for approximately 38 generations and not for populations having evolved on tomato for approximately 78 generations. The study of genetic diversity with microsatellite markers suggests that these latter populations may have suffered from bottlenecks, which could have compromised their adaptation. Finally, as shown chapter 3, I test whether populations newly adapted to tomato are more tolerant to the host-plant defenses, induced by herbivore attacks, and/or whether these populations differentially trigger the defences of damaged plants, affecting the performance of mites that subsequently colonize this host. For that purpose, I recorded the fecundity and mortality of female adult mites put on clean tomato plants, or on tomato plant pre-infested by tomato-adapted mites or by mites not adapted to this host. Populations adapted to tomato had a higher fecundity on this host irrespective of the plant treatment, while mortality increased for all populations on plants pre-infested with tomato-adapted mites. My results thus suggest that evolution on tomato leads to an increased capacity to tolerate host-plant defences and also to a higher induction of such defences. My studies describe a continuum of evolutionary responses in a polyphagous species from failure of adaptation, leading to the eventual extinction of populations, to the presence of adaptive plastic responses and finally to host-plant adaptation via the possible acquisition of higher tolerance to host-plant defenses. My work also underlines the relevance of integrating the effects of different life history traits with contrasted variations within a same fitness measure to describe host-plant adaptation. Further investigations in this direction should enrich our understanding of mechanisms of herbivore persistence on a new host-plant but also allow developing better crop pest management strategies.

O interesse de compreender comportamento de insetos envolvidos em processos de invasão biológica, sobretudo em relação a seus hospedeiros tem aumentado em razão da relevância do assunto para introdução de pragas exóticas em novas áreas. Dentre as espécies de drosofilídeos, Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae), de origem asiática, tornou-se praga em diversos países por atacar pequenos frutos de tegumento fino, já que dispõe de ovipositor adaptado para essa ação. Por ser inseto polífago, vários estudos têm investigado preferência, atratividade, e atributos que levam a destacar os potenciais hospedeiros da espécie. A despeito de estudos já desenvolvidos, ainda não havia sido verificado se a viabilidade ecológica dessa espécie poderia ser influenciada em condições de troca de frutos hospedeiros. Assim, no presente estudo foram avaliadas variáveis biológicas como fecundidade e período de oviposição, associados ao tempo de sobrevivência quando submetidos à troca de frutos hospedeiros, em particular de framboesa para o morango, bem como os fisiológicos, como a concentração de nutrientes em indivíduos de D. suzukii. Analisou-se também a microbiota associada aos indivíduos utilizados no experimento de troca de frutos, através de metagenômica. Os resultados encontrados indicam que a fecundidade foi significativamente maior na framboesa do que no morango, e entre as gerações que estavam no morango. O período de oviposição foi maior para os insetos que continuaram na framboesa, e a proporção de prole viável foi maior no morango. Além disso, foi visto que a quantidade de ovos está associada ao tempo de sobrevivência no fruto. Os resultados sobre a metagenômica mostraram que apesar de não haver diferença significativa em relação à comunidade de simbiontes nos diferentes tratamentos, ambas as populações e as gerações tiveram alta diversidade e equitabilidade. As populações do sul e sudeste diferem quanto a presença de Wolbachia, indicando que o simbionte está presente apenas nos indivíduos do sudeste. / Understanding the behaviour of insects in a biological invasion context, mainly in relation to their hosts, has become very important, because of the multitude of effects in the community that arise from the introduction of exotic pests in new areas. Within the species of drosofilids, Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae), became a pest in several countries, attacking small fruits and berries. As it is considered polyphagous, many studies have investigated the preference, attractiveness, and attributes of potential hosts. Thus far, no study has verified if the ecological viability was driven by fruit-host shift. In the present study, we analyse fecundity and oviposition period jointly with survival times of D. suzukii when submitted to fruit shift, in particular from raspberry to strawberry. We also study the effects on physiological attributes, such as the concentration of nutrients in individuals of D. suzukii. It was also analyzed the microbiota associated to these individuals that were used in the host shift experiment, through metagenomics. Our results showed that fecundity was significantly higher in raspberry than in strawberry. The oviposition period was higher for insects that continued in the raspberry, and the proportion of viable offspring was higher in the strawberry. Furthermore, we found that the number of eggs is related to the survival time in the fruit. No significant difference was observed in the macronutrient concentration, indicating that changes in host do not affect this physiological aspect. The metagenomic data showed that although there is no significant difference in relation to the symbiont community in the different treatments, both populations and generations had high diversity and equitability. The Southeast population has Wolbachia symbiont, differing from the south population.