Search

After the loss of a trait, theory predicts that the molecular machinery underlying its phenotypic expression should decay. Yet, empirical evidence is contrasting. Here, we test the hypotheses that (i) the molecular ground plan of a lost trait could persist due to pleiotropic effects on other traits and (ii) that gene co-expression network architecture could constrain individual gene expression. Our testing ground has been the Bacillus stick insect species complex, which contains close relatives that are either bisexual or parthenogenetic. After the identification of genes expressed in male reproductive tissues in a bisexual species, we investigated their gene co-expression network structure in two parthenogenetic species. We found that gene co-expression within the male gonads was partially preserved in parthenogens. Furthermore, parthenogens did not show relaxed selection on genes upregulated in male gonads in the bisexual species. As these genes were mostly expressed in female gonads, this preservation could be driven by pleiotropic interactions and an ongoing role in female reproduction. Connectivity within the network also played a key role, with highly connected—and more pleiotropic—genes within male gonad also having a gonad-biased expression in parthenogens. Our findings provide novel insight into the mechanisms which could underlie the production of rare males in parthenogenetic lineages; more generally, they provide an example of the cryptic persistence of a lost trait molecular architecture, driven by gene pleiotropy on other traits and within their co-expression network. [ABSTRACT FROM AUTHOR]

Termites (Insecta, Blattodea, Termitoidae) are a widespread and diverse group of eusocial insects known for their ability to digest wood matter. Herein, we report the draft genome of the subterranean termite Reticulitermes lucifugus, an economically important species and among the most studied taxa with respect to eusocial organization and mating system. The final assembly (~813 Mb) covered up to 88% of the estimated genome size and, in agreement with the Asexual Queen Succession Mating System, it was found completely homozygous. We predicted 16,349 highly supported gene models and 42% of repetitive DNA content. Transposable elements of R. lucifugus show similar evolutionary dynamics compared to that of other termites, with two main peaks of activity localized at 25% and 8% of Kimura divergence driven by DNA, LINE and SINE elements. Gene family turnover analyses identified multiple instances of gene duplication associated with R. lucifugus diversification, with significant lineage‐specific gene family expansions related to development, perception and nutrient metabolism pathways. Finally, we analysed P450 and odourant receptor gene repertoires in detail, highlighting the large diversity and dynamical evolutionary history of these proteins in the R. lucifugus genome. This newly assembled genome will provide a valuable resource for further understanding the molecular basis of termites biology as well as for pest control. [ABSTRACT FROM AUTHOR]

The Phasmida genus Candovia comprises nine traditionally recognized species, all endemic to Australia. In this study, Candovia diversity is explored through molecular species-delimitation analyses using the COI Fol gene fragment and phylogenetic inferences leveraging seven additional mitochondrial and nuclear loci. Molecular results were integrated with morphological observations, leading us to confirm the already described species and to the delineation of several new taxa and of the new genus Paracandovia. New Candovia species from various parts of Queensland and New South Wales are described and illustrated (C. alata sp. nov. , C. byfieldensis sp. nov. , C. dalgleishae sp. nov. , C. eungellensis sp. nov. , C. karasi sp. nov. , C. koensi sp. nov. and C. wollumbinensis sp. nov.). New combinations are proposed and species removed from synonymy with the erection of the new genus Paracandovia (P. cercata stat. rev. , comb. nov. , P. longipes stat. rev. , comb. nov. , P. pallida comb. nov. , P. peridromes comb. nov. , P. tenera stat. rev. comb. nov.). Phylogenetic analyses suggest that the egg capitulum may have independently evolved multiple times throughout the evolutionary history of these insects. Furthermore, two newly described species represent the first taxa with fully developed wings in this previously considered apterous clade. [ABSTRACT FROM AUTHOR]

The repetitive DNA content of the stick insect species Bacillus rossius (facultative parthenogenetic), Bacillus grandii (gonochoric), and Bacillus atticus (obligate parthenogenetic) was analyzed through the survey of random genomic libraries roughly corresponding to 0.006% of the genome. By repeat masking, 19 families of transposable elements were identified (two LTR and six non-LTR retrotransposons; 11 DNA transposons). Moreover, a de novo analysis revealed, among the three libraries, the first MITE family observed in polyneopteran genomes. On the whole, transposable element abundance represented 23.3% of the genome in B. rossius, 22.9% in B. atticus, and 18% in B. grandii. Tandem repeat content in the three libraries is much lower: 1.32%, 0.64%, and 1.86% in B. rossius, B. grandii, and B. atticus, respectively. Microsatellites are the most abundant in all species. Minisatellites were only found in B. rossius and B. atticus, and five monomers belonging to the Bag320 satellite family were detected in B. atticus. Assuming the survey provides adequate representation of the relative genome, the obligate parthenogenetic species (B. atticus), compared with the other two species analyzed, does not show a lower transposable element content, as expected from some theoretical and empirical studies. Key words: genomic sequence survey, miniature inverted repeats (MITEs), stick insects, tandem repeats, transposable elements. Les auteurs ont analyse le contenu en ADN repete chez les phasmes Bacillus rossius (a parthenogenese facultative), Bacillus grandii (gonochorique) et Bacillus atticus (a parthenogenese obligatoire) en explorant aleatoirement des banques genomiques correspondant a environ 0,006% du genome. En masquant les sequences repetees, 19 familles d'elements transposables ont ete identifiees (deux familles de retrotransposons a LTR et six familles sans LTR; 11 familles de transposons a ADN). De plus, une analyse de novo a permis de decouvrir, au sein des trois banques, la premiere famille d'elements MITE au sein des polyneopteres. Globalement, l'abondance des elements transposables representait 23,3% du genome chez le B. rossius, 22,9% chez le B. atticus et 18% chez le B. grandii. Les sequences repetees en tandem etaient beaucoup moins abondantes au sein des trois banques : 1,32%, 0,64% et 1,86% respectivement chez le B. rossius, le B. grandii et le B. atticus. Les microsatellites etaient les plus abondants chez les trois especes. Des minisatellites n'ont ete observes que chez le B. rossius et le B. atticus, tandis que cinq monomeres de la famille de satellites Bag320 ont ete detectes de maniere unique chez le B. atticus. En supposant que cet echantillonnage du genome soit suffisamment representatif de chaque genome, il s'avere que le genome de l'espece a parthenogenese obligatoire (B. atticus) ne presente pas un contenu en elements transposables inferieur a celui des deux autres especes, tel que le predisaient certaines etudes theoriques et empiriques. [Traduit par la Redaction] Mots-cles: releve de sequences genomiques, sequences repetees inversees miniatures (MITE), phasmes, repetitions en tandem, elements transposables., Introduction A significant fraction of eukaryotic genomes harbours DNA sequences repeated either in tandem (head-to-tail arranged) or interspersed (Richard et al. 2008). Tandem repeats are made by monomeric units, whose [...]

Abstract: Nuclear ribosomal DNA constitutes a multigene family, with tandemly arranged units linked by an intergenic spacer (IGS), which contains initiation/termination transcription signals and usually tandemly arranged subrepeats. The structure [...]