Michelle Soares

Genomic signatures of evolutionary transitions from solitary to group living

For bees, many roads lead to social harmony Eusociality, where workers sacrifice their reproductive rights to support the colony, has evolved repeatedly and represents the most evolved form of social evolution in insects. Kapheim et al. looked across the genomes of 10 bee species with varying degrees of sociality to determine the underlying genomic contributions. No one genomic path led to eusociality, but similarities across genomes were seen in features such as increases in gene regulation and methylation. It also seems that selection pressures relaxed after the emergence of complex sociality. Science, this issue p. 1139 Social evolution in bees has followed diverse genomic paths but shares genomic patterns. The evolution of eusociality is one of the major transitions in evolution, but the underlying genomic changes are unknown. We compared the genomes of 10 bee species that vary in social complexity, representing multiple independent transitions in social evolution, and report three major findings. First, many important genes show evidence of neutral evolution as a consequence of relaxed selection with increasing social complexity. Second, there is no single road map to eusociality; independent evolutionary transitions in sociality have independent genetic underpinnings. Third, though clearly independent in detail, these transitions do have similar general features, including an increase in constrained protein evolution accompanied by increases in the potential for gene regulation and decreases in diversity and abundance of transposable elements. Eusociality may arise through different mechanisms each time, but would likely always involve an increase in the complexity of gene networks.

Genes involved in thoracic exoskeleton formation during the pupal-to-adult molt in a social insect model, Apis mellifera

BackgroundThe insect exoskeleton provides shape, waterproofing, and locomotion via attached somatic muscles. The exoskeleton is renewed during molting, a process regulated by ecdysteroid hormones. The holometabolous pupa transforms into an adult during the imaginal molt, when the epidermis synthe3sizes the definitive exoskeleton that then differentiates progressively. An important issue in insect development concerns how the exoskeletal regions are constructed to provide their morphological, physiological and mechanical functions. We used whole-genome oligonucleotide microarrays to screen for genes involved in exoskeletal formation in the honeybee thoracic dorsum. Our analysis included three sampling times during the pupal-to-adult molt, i.e., before, during and after the ecdysteroid-induced apolysis that triggers synthesis of the adult exoskeleton.ResultsGene ontology annotation based on orthologous relationships with Drosophila melanogaster genes placed the honeybee differentially expressed genes (DEGs) into distinct categories of Biological Process and Molecular Function, depending on developmental time, revealing the functional elements required for adult exoskeleton formation. Of the 1,253 unique DEGs, 547 were upregulated in the thoracic dorsum after apolysis, suggesting induction by the ecdysteroid pulse. The upregulated gene set included 20 of the 47 cuticular protein (CP) genes that were previously identified in the honeybee genome, and three novel putative CP genes that do not belong to a known CP family. In situ hybridization showed that two of the novel genes were abundantly expressed in the epidermis during adult exoskeleton formation, strongly implicating them as genuine CP genes. Conserved sequence motifs identified the CP genes as members of the CPR, Tweedle, Apidermin, CPF, CPLCP1 and Analogous-to-Peritrophins families. Furthermore, 28 of the 36 muscle-related DEGs were upregulated during the de novo formation of striated fibers attached to the exoskeleton. A search for cis-regulatory motifs in the 5′-untranslated region of the DEGs revealed potential binding sites for known transcription factors. Construction of a regulatory network showed that various upregulated CP- and muscle-related genes (15 and 21 genes, respectively) share common elements, suggesting co-regulation during thoracic exoskeleton formation.ConclusionsThese findings help reveal molecular aspects of rigid thoracic exoskeleton formation during the ecdysteroid-coordinated pupal-to-adult molt in the honeybee.

Expression profile of a Laccase2 encoding gene during the metamorphic molt in Apis mellifera (Hymenoptera,Apidae)

Expression profile of a Laccase2 encoding gene during the metamorphic molt in Apis mellifera (Hymenoptera, Apidae). Metamorphosis in holometabolous insects occurs through two subsequent molting cycles: pupation (metamorphic molt) and adult differentiation (imaginal molt). The imaginal molt in Apis mellifera L. was recently investigated in both histological and physiological-molecular approaches. Although the metamorphic molt in this model bee is extremely important to development, it is not well-known yet. In the current study we used this stage as an ontogenetic scenario to investigate the transcriptional profile of the gene Amlac2, which encodes a laccase with an essential role in cuticle differentiation. Amlac2 expression in epidermis was contrasted with the hemolymph titer of ecdysteroid hormones and with the most evident morphological events occurring during cuticle renewal. RT-PCR semiquantitative analyses using integument samples revealed increased levels of Amlac2 transcripts right after apolysis and during the subsequent pharate period, and declining levels near pupal ecdysis. Compared with the expression of a cuticle protein gene, AmelCPR14, these results highlighted the importance of the ecdysteroid-induced apolysis as an ontogenetic marker of gene reactivation in epidermis for cuticle renewal. The obtained results strengthen the comprehension of metamorphosis in Apis mellifera. In addition, we reviewed the literature about the development of A. mellifera, and emphasize the importance of revising the terminology used to describe honey bee molting cycles.

Exploring integument transcriptomes, cuticle ultrastructure, and cuticular hydrocarbons profiles in eusocial and solitary bee species displaying heterochronic adult cuticle maturation

Differences in the timing of exoskeleton melanization and sclerotization are evident when comparing eusocial and solitary bees. This cuticular maturation heterochrony may be associated with life style, considering that eusocial bees remain protected inside the nest for many days after emergence, while the solitary bees immediately start outside activities. To address this issue, we characterized gene expression using large-scale RNA sequencing (RNA-seq), and quantified cuticular hydrocarbon (CHC) through gas chromatography-mass spectrometry in comparative studies of the integument (cuticle plus its underlying epidermis) of two eusocial and a solitary bee species. In addition, we used transmission electron microscopy (TEM) for studying the developing cuticle of these and other three bee species also differing in life style. We found 13,200, 55,209 and 30,161 transcript types in the integument of the eusocial Apis mellifera and Frieseomelitta varia, and the solitary Centris analis, respectively. In general, structural cuticle proteins and chitin-related genes were upregulated in pharate-adults and newly-emerged bees whereas transcripts for odorant binding proteins, cytochrome P450 and antioxidant proteins were overrepresented in foragers. Consistent with our hypothesis, a distance correlation analysis based on the differentially expressed genes suggested delayed cuticle maturation in A. mellifera in comparison to the solitary bee. However, this was not confirmed in the comparison with F. varia. The expression profiles of 27 of 119 genes displaying functional attributes related to cuticle formation/differentiation were positively correlated between A. mellifera and F. varia, and negatively or non-correlated with C. analis, suggesting roles in cuticular maturation heterochrony. However, we also found transcript profiles positively correlated between each one of the eusocial species and C. analis. Gene co-expression networks greatly differed between the bee species, but we identified common gene interactions exclusively between the eusocial species. Except for F. varia, the TEM analysis is consistent with cuticle development timing adapted to the social or solitary life style. In support to our hypothesis, the absolute quantities of n-alkanes and unsaturated CHCs were significantly higher in foragers than in the earlier developmental phases of the eusocial bees, but did not discriminate newly-emerged from foragers in C. analis. By highlighting differences in integument gene expression, cuticle ultrastructure, and CHC profiles between eusocial and solitary bees, our data provided insights into the process of heterochronic cuticle maturation associated to the way of life. Author Summary From our previous observation that bees with distinct habits of life, eusocial and solitary, exhibit different degrees of cuticle melanization and sclerotization at the emergence, we decided to analyze the genetic signatures and ultrastructure of the integument, as well as the CHC profiles that could be involved in cuticle maturation. The expression patterns of certain genes involved in the melanization/sclerotization pathway, chitin metabolism, cuticle structure, and also regulators of cuticle renewal and tanning, in addition to other genes, might be grounded the slow process of cuticle maturation in the eusocial bees in comparison to the solitary ones. The electron micrographs revealed differences in the timing of cuticle deposition for the eusocial and solitary species. Among the identified CHCs, the proportions and quantities of n-alkanes in the developing cuticle are consistent with the faster cuticular maturation in the solitary bee, thus supporting our hypothesis.

07-P011 Differential expression of cuticle protein genes during metamorphosis of the honeybee, Apis mellifera

embryo and differentiated adult tissues, with particular focus on a cancer associated variant that excludes the 4th exon (DE4), but retains replication function. Using RT-PCR, qPCR and immunohistochemistry, we find that, although Ciz1 is present in most cells throughout development, high levels are restricted to adult testes, with temporal regulation within the developing germ cell lineage. Over 40% of adult testicular transcripts are alternatively spliced, with some variants unique to this tissue. The regulated induction and alternative splicing of Ciz1 coincides with activation of the spermatogenic cycle. The protein is dynamically regulated in germ cells at discreet stages of the differentiation process, characterised most notably by loss of Ciz1 from post-replicative cells and subsequent re-activation at greatly enhanced levels later in the differentiation process. Our data suggests that following initial replicative phases in spermatogonia and pre-leptotene spermatocytes ‘old’ Ciz1 is released or degraded. ‘New’ Ciz1 is then produced in copious amounts, indicating that Ciz1 has a novel post-replicative role in the mammalian germ cell differentiation process.

07-P001 Differential hind leg development in Apis mellifera castes

07-P001 Differential hind leg development in Apis mellifera castes Ana Durvalina Bomtorin, Livia Moda, Marcela A.F.B. Laure, Alexandre S. Cristino, Michelle P.M. Soares, Rodrigo A. Faccioli, Marcia M.G. Bitondi, Angel Roberto Barchuk, Zila L.P. Simoes Departamento de Genetica-FMRP/USP, Ribeirao Preto, Sao Paulo, Brazil Departamento de Fsica e Informtica – IFSC/USP, Sao Carlos, Sao Paulo, Brazil Departamento de Biologia – FFCLRP/USP, Ribeirao Preto, Sao Paulo, Brazil Departamento de Engenharia Eltrica – EESC/USP, Sao Carlos, Sao Paulo, Brazil Departamento de Ciencias Biomedicas, Unifal, Alfenas, Minas Gerais, Brazil