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Adaptation of a polyphagous herbivore to a novel host plant extensively shapes the transcriptome of herbivore and host
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Generalist arthropod herbivores rapidly adapt to a broad range of host plants. However, the extent of transcriptional reprogramming in the herbivore and its hosts associated with adaptation remains poorly understood. Using the spider mite Tetranychus urticae and tomato as models with available genomic resources, we investigated the reciprocal genomewide transcriptional changes in both spider mite and tomato as a consequence of mite's adaptation to tomato. We transferred a genetically diverse mite population from bean to tomato where triplicated populations were allowed to propagate for 30 generations. Evolving populations greatly increased their reproductive performance on tomato relative to their progenitors when reared under identical conditions, indicative of genetic adaptation. Analysis of transcriptional changes associated with mite adaptation to tomato revealed two main components. First, adaptation resulted in a set of mite genes that were constitutively downregulated, independently of the host. These genes were mostly of an unknown function. Second, adapted mites mounted an altered transcriptional response that had greater amplitude of changes when re-exposed to tomato, relative to nonadapted mites. This gene set was enriched in genes encoding detoxifying enzymes and xenobiotic transporters. Besides the direct effects on mite gene expression, adaptation also indirectly affected the tomato transcriptional responses, which were attenuated upon feeding of adapted mites, relative to the induced responses by nonadapted mite feeding. Thus, constitutive downregulation and increased transcriptional plasticity of genes in a herbivore may play a central role in adaptation to host plants, leading to both a higher detoxification potential and reduced production of plant defence compounds.
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Selection for costly traits result in a vacant mating niche and in the evolution of a genetic male dimorphism
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The expected strong directional selection for traits that increase a male’s mating ability conflicts with the frequent observation that within species, males may show extreme variation in sexual traits. These male reproductive polymorphisms are usually attributed to direct male–male competition. It is currently unclear, however, how directional selection for sexually selected traits may convert into disruptive selection, and if female preference for elaborate traits may be an alternative mechanism driving the evolution of male polymorphism. Here, we explore this mechanism using the polyandric dwarf spider Oedothorax gibbosus as a model. We first show that males characterized by conspicuous cephalic structures serving as a nuptial feeding device (“gibbosus males”) significantly outperform other males in siring offspring of previously fertilized females. However, significant costs in terms of development time of gibbosus males open a mating niche for an alternative male type lacking expensive secondary sexual traits. These “tuberosus males” obtain virtually all fertilizations early in the breeding season. Individual-based simulations demonstrate a hitherto unknown general principle, by which males selected for high investment to attract females suffer constrained mating opportunities. This creates a vacant mating
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Evolutionary history of a dispersal-associated locus across sympatric and allopatric divergent populations of a wing-polymorphic beetle across Atlantic Europe
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Studying the evolutionary history of trait divergence, in particular those related to dispersal capacity, is of major interest for the process of local adaptation and metapopulation dynamics. Here, we reconstruct the evolution of different alleles at the nuclear-encoded mitochondrial NADP+-dependent isocitrate dehydrogenase (mtIdh) locus of the ground beetle Pogonus chalceus that are differentially and repeatedly selected in short- and long-winged populations in response to different hydrological regimes at both allopatric and sympatric scales along the Atlantic European coasts. We sequenced 2788 bp of the mtIdh locus spanning a ~7-kb genome region and compared its variation with that of two supposedly neutral genes. mtIdh sequences show (i) monophyletic clustering of the short-winged associated mtIDH-DE haplotypes within the long-winged associated mtIDH-AB haplotypes, (ii) a more than tenfold lower haplotype diversity associated with the mtIDH-DE alleles compared to the mtIDH-AB alleles and (iii) a high number of fixed nucleotide differences between both mtIDH haplotype clusters. Coalescent simulations suggest that this observed sequence variation in the mtIdh locus is most consistent with a singular origin in a partially isolated subpopulation, followed by a relatively recent spread of the mtIDHDE allele in short-winged populations along the Atlantic coast. These results demonstrate that even traits associated with decreased dispersal capacity can rapidly spread and that reuse of adaptive alleles plays an important
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Endosymbiont dominated bacterial communities in a dwarf spider
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The microbial community of spiders is little known, with previous studies focussing primarily on the medical importance of spiders as vectors of pathogenic bacteria and on the screening of known cytoplasmic endosymbiont bacteria. These screening studies have been performed by means of specific primers that only amplify a selective set of endosymbionts, hampering the detection of unreported species in spiders. In order to have a more complete overview of the bacterial species that can be present in spiders, we applied a combination of a cloning assay, DGGE profiling and high-throughput sequencing on multiple individuals of the dwarf spider Oedothorax gibbosus. This revealed a co-infection of at least three known (Wolbachia, Rickettsia and Cardinium) and the detection of a previously unreported endosymbiont bacterium (Rhabdochlamydia) in spiders. 16S rRNA gene sequences of Rhabdochlamydia matched closely with those of Candidatus R. porcellionis, which is currently only reported as a pathogen from a woodlouse and with Candidatus R. crassificans reported from a cockroach. Remarkably, this bacterium appears to present in very high proportions in one of the two populations only, with all investigated females being infected. We also recovered Acinetobacter in high abundance in one individual. In total, more than 99% of approximately 4.5M high-throughput sequencing reads were restricted to these five bacterial species. In contrast to previously reported screening studies of terrestrial arthropods, our results suggest that the bacterial communities in this spider species are dominated by, or even restricted to endosymbiont bacteria. Given the high prevalence of endosymbiont species in spiders, this bacterial community pattern could be widespread in the Araneae order.
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Craniodental and postcranial morphology of Indohyaenodon raoi from the Early Eocene of India, and its implications for ecology, phylogeny, and biogeography of hyaenodontid mammals
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New remains of the early Eocene hyaenodontid Indohyaenodon raoi are described from the Vastan Lignite Mine in Gujarat, western India, including the first known rostrum, upper dentition, and postcrania, substantially expanding our knowledge of the species and providing insights into its functional morphology and relationships. Craniodental morphology suggests that I. raoi had a broad diet, including non-vertebrate material as well as flesh of a diversity of prey species. Postcranial morphology is broadly similar to that of other early hyaenodontids and suggests a scansorial locomotor repertoire. Dental morphology indicates that I. raoi is closely related to other South Asian hyaenodontids, with shared features including strong cingula, narrow premolars, and a reduced P4 protocone. We present the most comprehensive phylogenetic analysis of Hyaenodontidae to date, which corroborates this relationship but finds South Asian hyaenodontids to be the stem of a group that includes most African hyaenodontids. This and other higher-level relationships within Hyaenodontidae are, however, weakly supported, and substantially different alternative hypotheses of relationships are not significantly less parsimonious, reflecting strong character conflict. Factors contributing to this conflict include the isolation of hyaenodontid faunas on different continents during much of the Eocene, canalization and simplification of carnivorous dentitions, and a lack of non-dental material for critical hyaenodontid groups. The new phylogeny is consistent with either an African or an Asian origin for the group.
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Red Iron-Pigmented Tooth Enamel in a Multituberculate Mammal from the Late Cretaceous Transylvanian “Haţeg Island”
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Mammals that inhabit islands are characterized by peculiar morphologies in comparison to their mainland relatives. Here we report the discovery of a partial skull associated with the lower jaws of a Late Cretaceous (~70 Ma) multituberculate mammal from the Carpathian “Haţeg Island” of Transylvania, Romania. The mammal belongs to the Kogaionidae, one of the rare families that survived the Cretaceous—Paleogene mass extinction in Europe. The excellent preservation of this specimen allows for the first time description of the complete dentition of a kogaionid and demonstration that the enigmatic Barbatodon transylvanicus presents a mosaic of primitive and derived characters, and that it is phylogenetically basal among the Cimolodonta. Another peculiarity is the presence of red pigmentation in its tooth enamel. The red coloration is present on the anterior side of the incisors and on the cusps of most of the teeth. Energy-dispersive X-ray spectrometry (EDS) analysis reveals that the pigmented enamel contains iron, as in living placentals. Such a red pigmentation is known in living soricine shrews and many families of rodents, where it is thought to increase the resistance of the enamel to the abrasion that occurs during “grinding” mastication. The extended pattern of red pigment distribution in Barbatodon is more similar to that in eulipotyplan insectivores than to that in rodents and suggests a very hard diet and, importantly, demonstrates that its grasping incisors were not ever-growing. As inferred for other endemic Transylvanian vertebrates such as dwarf herbivorous dinosaurs and unusual theropod dinosaurs, insularity was probably the main factor of survival of such a primitive mammalian lineage relative to other mainland contemporaries of the Northern hemisphere.
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Flora and fauna from a new Famennian (Upper Devonian) locality at Becco, eastern Belgium
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The Becco locality (Liège province), belongs to the Theux tectonic window and represents a proximal, probably fluvial, environment corresponding to a channel infill. We present here a preliminary report of the fossil assemblage discovered at the locality. The Becco site has yielded a diverse flora of early seed plants including Moresnetia zalesskyi, Dorinnotheca streeli and Condrusia sp. This assemblage, characteristic of the Belgian Famennian, highlights the diversity of early spermatophytes in the country. Becco has also delivered a rich vertebrate fauna with antiarch, groenlandaspid and phyllolepid placoderms, diplacanthiform acanthodians, as well as actinopterygians and various sarcopterygians. The fossiliferous assemblage of Becco resembles those of several Devonian tetrapod- bearing localities, including that of Strud in Belgium, and could therefore provide a favorable palaeoecological setting in the search for early tetrapods.
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Chapter 19: Ammonites on the brink of extinction: diversity, abundance, and ecology of the Order Ammonoidea at the Cretaceous-Paleogene (K/Pg) boundary
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Characterization of the placoderm (Gnathostomata) assemblage from the tetrapod-bearing locality of Strud (Belgium, Upper Famennian)
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The placoderm fauna of the late Famennian tetrapod-bearing locality of Strud, Belgium, is studied on the basis of historical and newly collected material. It includes the previously described antiarch Grossilepis rikiki, the groenlandaspidid Turrisaspis strudensis sp. nov. and the actinolepidoideid Phyllolepis undulata. P. undulata is thoroughly described and joins the list of the valid Phyllolepis species confidently diagnosed. A morphometrical analysis performed on the centronuchal and anterior ventrolateral plates of the Phyllolepis material demonstrates that there is only one species of Phyllolepis in Belgium (thus, Phyllolepis konincki becomes a junior synonym of P. undulata), that P. rossimontina (Pennsylvania) is a synonym of P. undulata and that the unity of the genus Phyllolepis is strongly supported, although the characterization of several species within this genus is blurred. The strong resemblance between the faunal compositions in Strud and Red Hill (Pennsylvania, USA) suggests important faunal exchanges between these regions of the Euramerica landmass.
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First early Eocene tapiroid from India and its implication for the paleobiogeographic origin of perissodactyls
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The presence of cambaytheres, the sister group of perissodactyls, in western India near or before the time of collision with Asia suggests that Perissodactyla may have originated on the Indian Plate during its final drift towards Asia. Herein we reinforce this hypothesis by reporting two teeth of the first early Eocene tapiromorph Perissodactyla from the Cambay Shale Formation of Vastan Lignite Mine (c. 54.5 Ma), Gujarat, western India, which we allocate to a new genus and species, Vastanolophus holbrooki. It presents plesiomorphic characters typical of the paraphyletic “Isectolophidae,” such as small size and weak lophodonty. However, the weaker hypoconulid and low paralophid, higher cusps, lower cristid obliqua, and the lingual opening of the talonid are found in Helaletidae, the most primitive tapiroid family. V. holbrooki, gen. et sp. nov., may be the oldest and the most primitive tapiroid, suggesting that at least tapiroid perissodactyls originated on India.
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