Sex determination mechanisms play a central role in life-history characteristics, affecting mating systems, sex ratios, inbreeding tolerance, etc. Downstream components of sex determination pathways ...are highly conserved, but upstream components evolve rapidly. Evolutionary dynamics of sex determination remain poorly understood, particularly because mechanisms appear so diverse. Here we investigate the origins and evolution of complementary sex determination (CSD) in ants and bees. The honey bee has a well-characterized CSD locus, containing tandemly arranged homologs of the transformer gene complementary sex determiner (csd) and feminizer (fem). Such tandem paralogs appear frequently in aculeate hymenopteran genomes. However, only comparative genomic, but not functional, data support a broader role for csd/fem in sex determination, and whether species other than the honey bee use this pathway remains controversial. Here we used a backcross to test whether csd/fem acts as a CSD locus in an ant (Vollenhovia emeryi). After sequencing and assembling the genome, we computed a linkage map, and conducted a quantitative trait locus (QTL) analysis of diploid male production using 68 diploid males and 171 workers. We found two QTLs on separate linkage groups (CsdQTL1 and CsdQTL2) that jointly explained 98.0% of the phenotypic variance. CsdQTL1 included two tandem transformer homologs. These data support the prediction that the same CSD mechanism has indeed been conserved for over 100 million years. CsdQTL2 had no similarity to CsdQTL1 and included a 236-kb region with no obvious CSD gene candidates, making it impossible to conclusively characterize it using our data. The sequence of this locus was conserved in at least one other ant genome that diverged >75 million years ago. By applying QTL analysis to ants for the first time, we support the hypothesis that elements of hymenopteran CSD are ancient, but also show that more remains to be learned about the diversity of CSD mechanisms.
In the major eusocial species of Hymenoptera, the regulatory mechanisms controlling queen/worker differentiation and exclusive reproduction by queens have been studied extensively. These studies have ...shown that insulin/insulin‐like growth factors and juvenile hormones (JHs) act as key endocrine factors. However, although considerable knowledge has accumulated in this area, large disparities in the regulatory mechanisms governing caste differentiation have been observed in different hymenopteran taxa to date. We focused on the queenless ant Pristomyrmex punctatus (Hymenoptera: Formicidae), which exhibits the simplest type of sociality and in which reproductive tasks (egg production) are distributed among morphologically and genetically identical workers. To elucidate the molecular mechanisms underlying reproduction in P. punctatus, we analyzed the correlations between the gene expression profiles of a reproductive marker gene, vitellogenin (PripuVTG1), and candidate regulatory genes comprising the major components of the JH and insulin/insulin‐like growth factor signaling pathways that are involved in the regulation of reproduction upstream of JH signaling. Expression of insulin‐like peptide 1 (PripuILP1) and JH signaling‐related genes was negatively correlated with PripuVTG1 expression. On the contrary, insulin‐like peptide 2 (PripuILP2a) was positively correlated with PripuVTG1. These findings suggest that an equilibrium perhaps controlled by switches in JH signaling exists between these two ILP paralogs, and that these interactions are important for regulating reproduction. Our findings are expected to be useful for understanding how various modes of sociality have evolved in insects.
The ant Pristomyrmex punctatus has no specific queens. We found that equilibrium between two ILP paralogs followed by switches in JH signaling is important for the regulation of reproduction in this species.
Reseacrh Highlights
The ant Pristomyrmex punctatus has no specific queens. We found that equilibrium between two ILP paralogs followed by switches in JH signaling is important for the regulation of reproduction in this species.
The genetic and molecular components of the sex-determination cascade have been extensively studied in the honeybee, Apis mellifera, a hymenopteran model organism. However, little is known about the ...sex-determination mechanisms found in other non-model hymenopteran taxa, such as ants. Because of the complex nature of the life cycles that have evolved in hymenopteran species, it is difficult to maintain and conduct experimental crosses between these organisms in the laboratory. Here, we describe the methods for conducting inbreeding crosses and for evaluating the success of those crosses in ant Vollenhovia emeryi. Inducing inbreeding in the laboratory using V. emeryi, is relatively simple because of the unique biology of the species. Specifically, this species produces androgenetic males, and female reproductives exhibit wing polymorphism, which simplifies identification of the phenotypes in genetic crosses. In addition, evaluating the success of inbreeding is straightforward as males can be produced continuously by inbreeding crosses, while normal males only appear during a well-defined reproductive season in the field. Our protocol allow for using V. emeryi as a model to investigate the genetic and molecular basis of the sex determination system in ant species.
summary Average marginal bone resorption of about 1 mm after the first year of functional loading, which is followed by an annual loss of approximately 0·1 mm, has been reported in stable implants. ...However, finite element analyses on bone stress around implants have been limited to analysing the bone stress in the absence of any bone resorption. Thus, a three‐dimensional finite element analysis was performed to compare the bone stresses in a non‐resorption model with those in four models with bone resorption of two depths (1·3 and 2·6 mm) and types (horizontal resorption and angular defects). Axial and bucco‐lingual forces were separately applied to the center of the superstructure and the maximum equivalent stress was calculated. The main tendencies of bone stress (highest stress concentration around implant neck, higher stresses under bucco‐lingual than axial load, as well as in the cortical than cancellous bone) were the same in the non‐resorption and resorption models. Bone stress distributions were similar in the non‐resorption and horizontal resorption models, but differed from those in the angular defect models. Moreover, the changes of the bone stress values with resorption depth differed for the two resorption types. Thus, in FEA, accurate simulation of the marginal bone shape in the implant neck region is advisable.
Since dental casting requires replication of complex shapes with great accuracy, this study examined how well some commercial titanium alloys and experimental titanium–copper alloys filled a mold ...cavity. The metals examined were three types of commercial dental titanium commercially pure titanium (hereinafter noted as CP-Ti), Ti–6Al–4V (T64) and Ti–6Al–7Nb (T67), and experimental titanium–copper alloys 3%, 5% and 10% Cu (mass %). The volume percentage filling the cavity was evaluated in castings prepared in a very thin perforated sheet pattern and cast in a centrifugal casting machine. The flow behavior of the molten metal was also examined using a so-called “tracer element technique.” The amounts of CP-Ti and all the Ti–Cu alloys filling the cavity were similar; less T64 and T67 filled the cavity. However, the Ti–Cu alloys failed to reach the end of the cavities due to a lower fluidity compared to the other metals. A mold prepared with specially designed perforated sheets was effective at differentiating the flow behavior of the metals tested. The present technique also revealed that the more viscous Ti–Cu alloys with a wide freezing range failed to sequentially flow to the end of the cavity.
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