Attack of the dark clones the genetics of reproductive and color traits of South African honey bees (Apis mellifera spp.)

The traits of two subspecies of western honey bees, Apis mellifera scutellata and A.m. capensis, endemic to the Republic of South Africa (RSA), are of biological and commercial relevance. Nevertheless, the genetic basis of important phenotypes found in these subspecies remains poorly understood. We performed a genome wide association study on three traits of biological relevance in 234 A.m. capensis, 73 A.m. scutellata and 158 hybrid individuals. Thirteen markers were significantly associated to at least one trait (P ≤ 4.28 × 10−6): one for ovariole number, four for scutellar plate and eight for tergite color. We discovered two possible causative variants associated to the respective phenotypes: a deletion in GB46429 or Ebony (NC_007070.3:g.14101325G>del) (R69Efs*85) and a nonsense on GB54634 (NC_007076.3:g.4492792A>G;p.Tyr128*) causing a premature stop, substantially shortening the predicted protein. The mutant genotypes are significantly associated to phenotypes in A.m. capensis. Loss-of-function of Ebony can cause accumulation of circulating dopamine, and increased dopamine levels correlate to ovary development in queenless workers and pheromone production. Allelic association (P = 1.824 x 10−5) of NC_007076.3:g.4492792A>G;p.Tyr128* to ovariole number warrants further investigation into function and expression of the GB54634 gene. Our results highlight genetic components of relevant production/conservation behavioral phenotypes in honey bees.

Reproductive Potential Impacts Body Maintenance Parameters and Global DNA Methylation in Honeybee Workers (Apis mellifera L.)

The widely accepted hypothesis in life history evolution about the trade-off between fecundity and longevity is not confirmed by long-living and highly fecund queens in eusocial insects. The fact that the queens and facultatively sterile workers usually arise from genetically identical eggs but differ in DNA methylation makes them a good model for studies on senescence, eusocial evolution, and epigenetics. Therefore, honeybees seem to be especially useful here because of long living rebel-workers (RW) with high reproductive potential recently described. Longevity, ovariole number, nosema tolerance, and global DNA methylation have been assayed in normal workers (NW) versus RW in hives and cages. RW always lived longer than NW and unexpectedly extended longevity of NW when they were together, similarly as the presence of a queen did. RW lived longer despite the fact that they had higher Nosema spore load; surprisingly they became infected more easily but tolerated the infection better. Global DNA methylation increased with age, being lower in RW than in NW. Therefore, RW are queen-like considering global DNA methylation and the link between fecundity, longevity, and body maintenance. Presented features of RW expands possibilities of the use of honeybees as a model for studies on senescence, nosemosis, eusocial evolution, and epigenetics.

Distinct gene expression dynamics in germ line and somatic tissue during ovariole morphogenesis in Drosophila melanogaster

The survival and evolution of a species is a function of the number of offspring it can produce. In insects the number of eggs that an ovary can produce is a major determinant of reproductive capacity. Insect ovaries are made up of tubular egg-producing subunits called ovarioles, whose number largely determines the number of eggs that can be potentially laid. Ovariole number is directly determined by the number of cellular structures called terminal filaments, which are stacks of cells that assemble in the larval ovary. Elucidating the developmental and regulatory mechanisms of terminal filament formation is thus key to understanding the regulation of insect reproduction through ovariole number regulation. We systematically measured mRNA expression of all cells in the larval ovary at the beginning, middle and end of terminal filament formation. We also separated somatic and germ line cells during these stages and assessed their tissue-specific gene expression during larval ovary development. We found that the number of differentially expressed somatic genes is highest during late stages of terminal filament formation and includes many signaling pathways that govern ovary development. We also show that germ line tissue, in contrast, shows greater differential expression during early stages of terminal filament formation, and highly expressed germ line genes at these stages largely control cell division and DNA repair. We provide a tissue-specific and temporal transcriptomic dataset of gene expression in the developing larval ovary as a resource to study insect reproduction.

Distinct gene expression dynamics in germ line and somatic tissue during ovariole morphogenesis in Drosophila melanogaster

The survival and evolution of a species is a function of the number of offspring it can produce. In insects the number of eggs that an ovary can produce is a major determinant of reproductive capacity. Insect ovaries are made up of tubular egg-producing subunits called ovarioles, whose number largely determines the number of eggs that can be potentially laid. Ovariole number is directly determined by the number of cellular structures called terminal filaments, which are stacks of cells that assemble in the larval ovary. Elucidating the developmental and regulatory mechanisms of terminal filament formation is thus key to understanding the regulation of insect reproduction through ovariole number regulation. We systematically measured mRNA expression of all cells in the larval ovary at the beginning, middle and end of terminal filament formation. We also separated somatic and germ line cells during these stages and assessed their tissue-specific gene expression during larval ovary development. We found that the number of differentially expressed somatic genes is highest during late stages of terminal filament formation and includes many signaling pathways that govern ovary development. We also show that germ line tissue, in contrast, shows greater differential expression during early stages of terminal filament formation, and highly expressed germ line genes at these stages largely control cell division and DNA repair. We provide a tissue-specific and temporal transcriptomic dataset of gene expression in the developing larval ovary as a resource to study insect reproduction.

Topology-driven protein-protein interaction network analysis detects genetic sub-networks regulating reproductive capacity

Understanding the genetic regulation of organ structure is a fundamental problem in developmental biology. Here, we use egg-producing structures of insect ovaries, called ovarioles, to deduce systems-level gene regulatory relationships from quantitative functional genetic analysis. We previously showed that Hippo signalling, a conserved regulator of animal organ size, regulates ovariole number in Drosophila melanogaster. To comprehensively determine how Hippo signalling interacts with other pathways in this regulation, we screened all known signalling pathway genes, and identified Hpo-dependent and Hpo-independent signalling requirements. Network analysis of known protein-protein interactions among screen results identified independent gene regulatory sub-networks regulating one or both of ovariole number and egg laying. These sub-networks predict involvement of previously uncharacterised genes with higher accuracy than the original candidate screen. This shows that network analysis combining functional genetic and large-scale interaction data can predict function of novel genes regulating development.

Repeated loss of variation in insect ovary morphology highlights the role of developmental constraint in life-history evolution

The number of offspring an organism can produce is a key component of its evolutionary fitness and lifehistory. Here we perform a test of the hypothesized trade off between the number and size of offspring using thousands of descriptions of the number of egg-producing compartments in the insect ovary (ovarioles), a common proxy for potential offspring number in insects. In contrast to prior claims, we find that ovariole number is not generally negatively correlated with the size of insect eggs, and we highlight several factors that may have contributed to this size-number trade off being strongly asserted in previous studies. We reconstruct the evolutionary history of the nurse cell arrangement within the ovariole, and show that the diversification of ovariole number and egg size have both been largely independent of nurse cell presence or position within the ovariole. Instead we show that ovariole number evolution has been shaped by a series of transitions between variable and invariant states, with multiple independent lineages evolving to have almost no variation in ovariole number. We highlight the implications of these invariant lineages on our understanding of the specification of ovariole number during development, as well as the importance of considering developmental processes in theories of life-history evolution.

Morphometry of the reproductive system of the predator Podisus nigrispinus (Dallas, 1851) (Hemiptera, Pentatomidae) when submitted to different temperatures

ABSTRACT: In order to manipulate the mass rearing of natural enemies, temperature variations can be used. The effects are widely studied for their survival and developmental duration; however, there is little information about their reproductive system in the literature. Therefore, the purpose of this study was to evaluate the effects of different temperatures on the reproductive system of the predator Podisus nigrispinus (Dallas, 1851) (Hemiptera: Pentatomidae). The predator was kept at temperature conditions of 17, 21, 25, and 29 °C until reaching 15 days of age, the adult stage. The insects were then killed, measured for both weight and size, dissected, and then evaluated for the following parameters: length of the most developed ovariole; number of ovarioles per ovary; number of oocytes per the more developed ovarioles; number of oocytes per P. nigrispinus female; and the total area of the testicles was measured in the male insects. Results showed that as the temperature increased, the parameters were positively affected. These temperature variations can be used to manipulate the mass rearing of P. nigrispinus under controlled conditions.

Topology-driven protein-protein interaction network analysis detects genetic sub-networks regulating reproductive capacity

Understanding the genetic regulation of organ structure is a fundamental problem in developmental biology. Here, we use egg-producing structures of insect ovaries, called ovarioles, to deduce systems-level gene regulatory relationships from quantitative functional genetic analysis. We previously showed that Hippo signalling, a conserved regulator of animal organ size, regulates ovariole number in Drosophila melanogaster. To comprehensively determine how Hippo signalling interacts with other pathways in this regulation, we screened all known signalling pathway genes, and identified Hpo-dependent and Hpo-independent signalling requirements. Network analysis of known protein-protein interactions among screen results identified independent gene regulatory sub-networks regulating one or both of ovariole number and egg laying. These sub-networks predict involvement of previously uncharacterised genes with higher accuracy than the original candidate screen. This shows that network analysis combining functional genetic and large-scale interaction data can predict function of novel genes regulating development.

Ancestral and offspring nutrition interact to affect life-history traits in Drosophila melanogaster

Ancestral environmental conditions can impact descendant phenotypes through a variety of epigenetic mechanisms. Previous studies on transgenerational effects in Drosophila melanogaster suggest that parental nutrition may affect the body size, developmental duration and egg size of the next generation. However, it is unknown whether these effects on phenotype remain stable across generations, or if specific generations have general responses to ancestral diet. In the current study, we examined the effect on multiple life-history phenotypes of changing diet quality across three generations. Our analysis revealed unforeseen patterns in how phenotypes respond to dietary restriction. Our generalized linear model showed that when considering only two generations, offspring phenotypes were primarily affected by their own diet, and to a lesser extent by the diet of their parents or the interaction between the two generations. Surprisingly, however, when considering three generations, offspring phenotypes were primarily impacted by their grandparents' diet and their own diet. Interactions among different generations’ diets affected development time, egg volume and pupal mass more than ovariole number or wing length. Furthermore, pairwise comparisons of diet groups from the same generation revealed commonalities in strong responses to rich versus poor diet: ovariole number, pupal mass and wing length responded more strongly to poor diet than to rich diet, while development time responded strongly to both rich and poor diets. To improve investigations into the mechanisms and consequences of transgenerational, epigenetic inheritance, future studies should closely examine how phenotypes change across a higher number of generations, and consider responses to broader variability in diet treatments.