The origin of diversity in Insects: speciation, adaptation and the Earth dynamics

International audienceThe diversity of Insects is often explained as a product of major radiations, trigerred by remarkable adaptations that allowed them to exploit different environments and to accompany the rise of flowering plants. A significant part of Insect diversity results however from allopatric speciation with niche conservatism that exposed species to different conditions and stimulated adaptive divergence. We demonstrated that for several groups of Insects (cockroaches, crickets and grasshoppers) in the island New Caledonia. Since Darwin and Wallace, islands are considered as laboratories of evolution, being closed systems of manageable size. New Caledonia is especially interesting in this respect, according to unique characteristics. Being the oldest oceanic island in the world and quite isolated from continents, biological evolution occurred there in situ during long periods. As a tropical and medium-sized island harbouring a very rich biodiversity, it also offered facilities to study many different evolutionary questions. New Caledonia (hereafter NC) has thus the best characteristics as a model system, allowing testing very diverse evolutionary assumptions with limited efforts and infrastructures. Unfortunately, these amazing geographical characteristics have also constrained the scientific study of NC until now, especially because of its isolation from large academic centers. Establishing NC as a modern oceanic model system resulted however from our work, later than the 90ies. Before, NC had the reputation of an amazingly old Gondwanan place and was intuitively considered as a continental fragment. If so, its usefulness as a model system to study evolution would have been limited since the biota of continental islands (e.g. Madagascar or New Zealand) are a complicated mix of organisms dating back to the separation with neighbouring continental territories or having colonized the island by dispersal. In most of these cases, it happened difficult to distinguish between both these different components and to examine evolutionary assumptions that require a reference dating point. The reasons why NC was traditionnally considered a continental territory were the age of its deep geological basement and the local occurrence of relict species. In agreement with this common assumption, the NC geological deep basement is ancient and predates gondwanan breakup. But this basement has been submited to important environmental disturbances because of the island location at the limit between two tectonic plates. Actually, the island has been submerged twice for a long time at Paleocene and Eocene epochs and only emerged around 37±3 Ma. This geological background was in need of independent testing with biological studies. We thus built multiple molecular phylogenetic trees of different groups of organisms, dated with probabilistic methods and external calibration points. A first review (Grandcolas et al., 2008) and a more recent meta-analysis (Nattier et al., 2017) of these studies showed that most groups colonized NC and diversified just after 37 My, confirming the geological scenario of recent terrestrial emergence. However a few local species belong to groups were dated much older than 37 My, representing true relicts, i.e. recent species that remained from ol

Biodiversity in France

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Comparison of the gut microbiota from soldier and worker castes of the termite Reticulitermes grassei

 The bacterial microbiota from the whole gut of soldier and worker castes of the termite Reticulitermes grassei was isolated and studied. In addition, the 16S rDNA bacterial genes from gut DNA were PCR-amplified using Bacteria-selective primers, and the 16S rDNA amplicons subsequently cloned into Escherichia coli. Sequences of the cloned inserts were then used to determine closest relatives by comparison with published sequences and with sequences from our previous work. The clones were found to be affiliated with the phyla Spirochaetes, Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Synergistetes, Verrucomicrobia, and candidate phyla Termite Group 1 (TG1) and Termite Group 2 (TG2). No significant differences were observed with respect to the relative bacterial abundances between soldier and worker phylotypes. The phylotypes obtained in this study were compared with reported sequences from other termites, especially those of phylotypes related to Spirochaetes, Wolbachia (an Alphaproteobacteria), Actinobacteria, and TG1. Many of the clone phylotypes detected in soldiers grouped with those of workers. Moreover, clones CRgS91 (soldiers) and CRgW68 (workers), both affiliated with 'Endomicrobia', were the same phylotype. Soldiers and workers also seemed to have similar relative protist abundances. Heterotrophic, poly-β-hydroxyalkanoate-accumulating bacteria were isolated from the gut of soldiers and shown to be affiliated with Actinobacteria and Gammaproteobacteria. We noted that Wolbachia was detected in soldiers but not in workers.Overall, the maintenance by soldiers and workers of comparable axial and radial redox gradients in the gut is consistent with the similarities in the prokaryotes and protists comprising their microbiota

Are successful colonizers necessarily invasive species? The case of the so-called invading parthenogenetic cockroach, Pycnoscelus surinamensis, in the Brazilian Atlantic forest

Les espèces colonisatrices sont potentiellement des espèces invasives. Même dans le cas où elles ne seraient pas encore devenues invasives à proprement parler, elles offrent l'occasion d'étudier des situations analogues aux étapes précédant ou amorçant l'invasion. Leur étude devrait permettre de mieux identifier les caractéristiques écologiques spécifiques qui conduisent à l'invasion biologique, en particulier par comparaison entre invasions réussies et invasions avortées. Ce type d'analyse doit nécessairement compléter la compilation habituelle des caractéristiques des espèces invasives. La « blatte parthénogénétique envahissante » (selon son appellation la plus commune), Pycnoscelus surinamensis, a été étudiée dans la région Atlantique du Brésil, afin de déterminer si elle est capable de se disperser des plantations colonisées aux fragments forestiers perturbés et adjacents. P surinamensis a été observée extrêmement rarement dans les fragments forestiers et sa présence n'a pas pu être reliée à son abondance dans les plantations adjacentes mais plutôt à l'activité humaine à l'intérieur du fragment. Cette blatte n'est donc pas une espèce invasive localement mais seulement une espèce colonisatrice efficace. Des observations futures devront déterminer si la cause de cette absence d'invasion peut être recherchée dans une faible capacité de dispersion.Successful colonizers are potentially invasive species. They offer the opportunity to study the first steps toward invasions, even if these colonizing species failed until now to become invasive. They should allow the critical characteristics which first permit species to become invasive to be better understood, especially when comparing failed and successful invasions. This kind of analysis complements the listing of ali characteristics of invasive species which are supposed to favor invasiveness. The so-called invasive parthenogenetic cockroach, Pycnoscelus surinamensis, has been studied in the Atlantic region of Brazil to assess if it is able to spread from colonized plantations to adjacent disturbed forest fragments. P. surinamensis is extremely rare in forest fragments and its presence cannot be related to its commonness in adj acent plantations but merely to man's activity inside the fragment. This cockroach is only a successful colonizer, not an invasive species. Pending on further observations, we hypothesize that its failure to in vade is probably related to a low ability for dispersal

Old lineage on an old island : Pixibinthus, a new cricket genus endemic to New Caledonia shed light on gryllid diversification in a hotspot of biodiversity

Few studies have focused on the early colonization of New Caledonia by insects, after the re-emergence of the main island, 37 Myr ago. Here we investigate the mode and tempo of evolution of a new endemic cricket genus, Pixibinthus, recently discovered in southern New Caledonia. First we formally describe this new monotypic genus found exclusively in the open shrubby vegetation on metalliferous soils, named 'maquis minier', unique to New Caledonia. We then reconstruct a dated molecular phylogeny based on five mitochondrial and four nuclear loci in order to establish relationships of Pixibinthus within Eneopterinae crickets. Pixibinthus is recovered as thesister clade of the endemic genus Agnotecous, mostly rainforest-dwellers. Dating results show that the island colonization by their common ancestor occurred around 34.7 Myr, shortly after New Caledonia re-emergence. Pixibinthus and Agnotecous are then one of the oldest insect lineages documented so far for New Caledonia. This discovery highlights for the first time two clear-cut ecological specializations between sister clades, as Agnotecous is mainly found in rainforests with 19 species, whereas Pixibinthus is found in open habitats with a single documented species. The preference of Pixibinthus for open habitats and of Agnotecous for forest habitats nicely fits an acoustic specialization, either explained by differences in body size or in acoustic properties of their respective habitats. We hypothesize that landscape dynamics, linked to major past climatic events and recent change in fire regimes are possible causes for both present-day low diversity and rarity in genus Pixibinthus. The unique evolutionary history of this old New Caledonian lineage stresses the importance to increase our knowledge on the faunal biodiversity of 'maquis minier', in order to better understand the origin and past dynamics of New Caledonian biota

Photography-based taxonomy is inadequate, unnecessary, and potentially harmful for biological sciences

The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009; Cianferoni & Bartolozzi 2016; Amorim et al. 2016). This question was again raised in a letter supported by 35 signatories published in the journal Nature (Pape et al. 2016) on 15 September 2016. On 25 September 2016, the following rebuttal (strictly limited to 300 words as per the editorial rules of Nature) was submitted to Nature, which on 18 October 2016 refused to publish it. As we think this problem is a very important one for zoological taxonomy, this text is published here exactly as submitted to Nature, followed by the list of the 493 taxonomists and collection-based researchers who signed it in the short time span from 20 September to 6 October 2016

Paradicta n. gen. et Neorhicnoda n. gen., deux nouveaux genres de Blaberinae (Dict., Blattaria, Blaberidae)

Summary. — We describe two new south american genera belonging to Blaberinae subfamily. Paradicta, n. gen. displays large species inhabiting trunk holes in forest understorey. Neorhicnoda, n. gen. is erected for Hyporhicnoda maronensis Hebard 1921 of which males were unknown until now and greatly differ from other Hyporhicnoda species.Résumé. — Deux nouveaux genres sud-américains de Blaberinae sont décrits. Paradicta, n. gen. présente de grandes espèces habitant les arbres creux en forêt tropicale. Neorhicnoda, n. gen. a été créé pour Hyporhicnoda maronensis Hebard 1921 dont le mâle était jusqu'à présent inconnu et qui diffère très nettement des autres espèces d'Hyporhicnoda.Grandcolas Philippe. Paradicta n. gen. et Neorhicnoda n. gen., deux nouveaux genres de Blaberinae (Dict., Blattaria, Blaberidae). In: Bulletin de la Société entomologique de France, volume 97 (1), mars 1992. pp. 7-15