RESUMEN

The microbiome is increasingly recognized for its complex relationship with host fitness. Bumblebees are host to a characteristic gut microbiome community that is derived and reinforced through social contact between individuals. The bumblebee microbiome is species-poor, and primarily composed from a small number of core taxa that are associated with the greater tribe of corbiculate bees. Experimental findings support a role for the core bumblebee microbiome in resistance to severe infections by a common trypanosomal parasite, Crithidia bombi. However, most studies have been small in scale, often considering just one or two bumblebee species, or making use of commercially-reared bees. To better understand the microbiome diversity of wild populations, we have deeply sampled field populations of ten sympatric species found throughout central and down east Maine in a three-year microbiome field survey. We have used 16S amplicon sequencing to produce microbiome community profiles, and qPCR to screen samples for infections by Crithidia bombi. The breadth of our dataset has enabled us to test for seasonal and interspecific trends in the microbiome community. Controlling for these external sources of variation, we have identified microbial factors associated with infection and parasite load that support the role of the core microbiome in resistance to severe infection.

RESUMEN

Sexual dimorphism is common in animals. The most complete model of sex determination comes from Drosophila melanogaster, where the relative dosage of autosomes and X chromosomes leads indirectly to sex-specific transcripts of doublesex (dsx). Female Dsx interacts with a mediator complex protein encoded by intersex (ix) to activate female development. In males, the transcription factor encoded by fruitless (fru) promotes male-specific behaviour. The genetics of sex determination have been examined in a small number of other insects, yet several questions remain about the plesiomorphic state. Is dsx required for female and male development? Is fru conserved in male behaviour or morphology? Are other components such as ix functionally conserved? To address these questions, we report expression and functional tests of dsx, ix and fru in the hemipteran Oncopeltus fasciatus, characterizing three sexual dimorphisms. dsx prevents ix phenotypes in all sexes and dimorphic traits in the milkweed bug. ix and fru are expressed across the body, in females and males. fru and ix also affect the genitalia of both sexes, but have effects limited to different dimorphic structures in different sexes. These results reveal roles for ix and fru distinct from other insects, and demonstrate distinct development mechanisms in different sexually dimorphic structures.

Asunto(s)

RESUMEN

The development of dimorphic adult sexes is a critical process for most animals, one that is subject to intense selection. Work in vertebrate and insect model species has revealed that sex determination mechanisms vary widely among animal groups. However, this variation is not uniform, with a limited number of conserved factors. Therefore, sex determination offers an excellent context to consider themes and variations in gene network evolution. Here we review the literature describing sex determination in diverse insects. We have screened public genomic sequence databases for orthologs and duplicates of 25 genes involved in insect sex determination, identifying patterns of presence and absence. These genes and a 3.5 reference set of 43 others were used to infer phylogenies and compared to accepted organismal relationships to examine patterns of congruence and divergence. The function of candidate genes for roles in sex determination (virilizer, female-lethal-2-d, transformer-2) and sex chromosome dosage compensation (male specific lethal-1, msl-2, msl-3) were tested using RNA interference in the milkweed bug, Oncopeltus fasciatus. None of these candidate genes exhibited conserved roles in these processes. Amidst this variation we wish to highlight the following themes for the evolution of sex determination: (1) Unique features within taxa influence network evolution. (2) Their position in the network influences a component's evolution. Our analyses also suggest an inverse association of protein sequence conservation with functional conservation.

Asunto(s)

RESUMEN

Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes-formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon-were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of ß-lactam- and ß-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal double and triple bonds. Furthermore, 2-(1-azacyclobutylidene)carbene was found to be nearly isoenergetic with its ring-expanded isomer, and 1-oxacyclopent-2-yne was notably higher in energy than its precursor carbene. In all other cases, the cycloalkynes were lower in energy than the corresponding carbenes. The transition states for ring-expansion were always lower for the 1,2-carbon shifts than for 1,2-nitrogen or oxygen shifts, but higher than for the 1,2-sulfur shifts. These predictions should be verifiable using carbenes bearing appropriate isotopic labels. Computed vibrational spectra for the carbenes, and their ring-expanded isomers, are presented and could be of value to matrix isolation experiments.

Asunto(s)