Gender based disruptive selection maintains body size polymorphism in Drosophila melanogaster

Genetic Variation in Sexual Size Dimorphism Is Associated with Variation in Sex-Specific Plasticity in Drosophila

AbstractThe difference in body size between females and males, or sexual size dimorphism (SSD), is ubiquitous, yet we have a poor understanding of the developmental genetic mechanisms that generate it and how these mechanisms may vary within and among species. Such an understanding of the genetic architecture of SSD is important if we are to evaluate alternative models of SSD evolution, but the genetic architecture is difficult to describe because SSD is a characteristic of populations, not individuals. Here, we overcome this challenge by using isogenic lineages of Drosophila to measure SSD for 196 genotypes. We demonstrate extensive genetic variation for SSD, primarily driven by higher levels of genetic variation for body size among females than among males. While we observe a general increase in SSD with sex-averaged body size (pooling for sex) among lineages, most of the variation in SSD is independent of sex-averaged body size and shows a strong genetic correlation with sex-specific plasticity, such that increased female-biased SSD is associated with increased body size plasticity in females. Our data are consistent with the condition dependence hypothesis of sexual dimorphism and suggest that SSD in Drosophila is a consequence of selection on the developmental genetic mechanisms that regulate the plasticity of body size.

Heightened immune surveillance in Drosophila melanogaster populations selected for faster development and extended longevity

Maximization of life-history traits is under constraints due to both, limitations of resource acquisition and the restricted pathways of resource allocation. Drosophila melanogaster has served as an excellent model organism to not only unravel various trade-offs among life history traits but also numerous aspects of host immune response. Drosophila larvae are semi-aquatic that live, feed and excrete inside the food source-often over-ripe fruits and vegetables that are rich in both commensal and pathogenic microbiota that can impact the larval survival. In this study, we have used six populations of D. melanogaster, three of which are selected for faster pre-adult development and extended adult longevity, and their three ancestral controls, to explore the impact of selection on the basal immune activity in the larval stage. The larvae from selected populations had nearly significantly upregulated plasmatocyte density, significantly higher percent phagocytosis, phagocytic index and higher transcript levels of Tep3, eater and NimC1. Selected populations also had significantly upregulated crystal cell number along with higher transcript of PPO2. Out of seven tested AMPs level, Drosomycin was significantly upregulated in selected populations while Drosocin was significantly higher in control populations. ROS levels were comparable in the selected and control populations. Our results strongly suggest that enhanced basal immune activity during larval stage manages the faster development and could be responsible for comparable larval survival of selected and control populations.

Gender Identification and Classification of Drosophila melanogaster Flies Using Machine Learning Techniques

Drosophila melanogaster is an important genetic model organism used extensively in medical and biological studies. About 61% of known human genes have a recognizable match with the genetic code of Drosophila flies, and 50% of fly protein sequences have mammalian analogues. Recently, several investigations have been conducted in Drosophila to study the functions of specific genes exist in the central nervous system, heart, liver, and kidney. The outcomes of the research in Drosophila are also used as a unique tool to study human-related diseases. This article presents a novel automated system to classify the gender of Drosophila flies obtained through microscopic images (ventral view). The proposed system takes an image as input and converts it into grayscale illustration to extract the texture features from the image. Then, machine learning (ML) classifiers such as support vector machines (SVM), Naive Bayes (NB), and K-nearest neighbour (KNN) are used to classify the Drosophila as male or female. The proposed model is evaluated using the real microscopic image dataset, and the results show that the accuracy of the KNN is 90%, which is higher than the accuracy of the SVM classifier.

Management of altered metabolic activity in Drosophila model of Huntington's disease by curcumin

Huntington's disease (HD) is a devastating polyglutamine disorder characterized by extensive neurodegeneration and metabolic abnormalities at systemic, cellular and intracellular levels. Metabolic alterations in HD manifest as abnormal body weight, dysregulated biomolecule levels, impaired adipocyte functions, and defective energy state which exacerbate disease progression and pose acute threat to the health of challenged individuals in form of insulin resistance, cardiovascular disease, and energy crisis. To colossally mitigate disease symptoms, we tested the efficacy of curcumin in Drosophila model of HD. Curcumin is the bioactive component of turmeric (Curcuma longa Linn), well-known for its ability to modulate metabolic activities. We found that curcumin effectively managed abnormal body weight, dysregulated lipid content, and carbohydrate level in HD flies. In addition, curcumin administration lowered elevated reactive-oxygen-species levels in adult adipose tissue of diseased flies, and improved survival and locomotor function in HD flies at advanced disease stage. Altogether, these findings clearly suggest that curcumin efficiently attenuates metabolic derangements in HD flies and can prove beneficial in alleviating the complexities associated with HD.

Fitness consequences of biochemical adaptation in Drosophila melanogaster populations under simultaneous selection for faster pre-adult development and extended lifespan

In holometabolous insects like Drosophila melanogaster, critical size is an important time point during larval life, for irreversible commitment to metamorphosis. Here, we studied the impact of restricted growth duration in terms of selection for faster pre-adult development in Drosophila melanogaster populations which resulted in the evolution of reduced critical size on adult life history traits. Selection for faster pre-adult development resulted in biochemical adaptation in larval physiology with no compromise in major biomolecules at critical size time point. The flies from the selected populations seem to not only commit to metamorphosis on the attainment of critical size but also seem to channelize resources to reproduction as indicated by similar life-time fecundity of CS and NS flies from selected populations, while the Control CS flies significantly lower life-time fecundity compared to Control NS flies. The flies from selected populations seem to achieve longevity comparable to control flies despite being significantly smaller in size-thus resource constrained due to faster pre-adult development.

Wing patterning in faster developing Drosophila is associated with high ecdysone titer and wingless expression

'Developmental robustness' is the ability of biological systems to maintain a stable phenotype despite genetic, environmental or physiological perturbations. In holometabolous insects, accurate patterning and development is guaranteed by alignment of final gene expression patterns in tissues at specific developmental stage such as molting and pupariation, irrespective of individual rate of development. In the present study, we used faster developing Drosophila melanogaster populations that show reduction of ~22% in egg to adult development time. Flies from the faster developing population exhibit phenotype constancy, although significantly small in size. The reduction in development time in faster developing flies is possibly due to coordination between higher ecdysteroid release and higher expression of developmental genes. The two together might be ensuring appropriate pattern formation and early exit at each development stage in the populations selected for faster pre-adult development compared to their ancestral controls. We report that apart from plasticity in the rate of pattern progression, alteration in the level of gene expression may be responsible for pattern integrity even under reduced development time.

Evolution of reduced minimum critical size as a response to selection for rapid pre-adult development in Drosophila melanogaster

Adult body size in holometabolus insects is directly proportional to the time spent during the larval period. The larval duration can be divided into two parts: (i) pre-critical duration-time required to attain a critical size/critical weight that would result in successful completion of development and metamorphosis even under non-availability of nutrition beyond the time of attainment of critical size, and (ii) post-critical duration-the time duration from the attainment of critical size till pupation. It is of interest to decipher the relative contribution of the two larval growth phases (from the hatching of the egg to the attainment of critical size, and from the attainment of critical size to pupation) to the final adult size. Many studies using Drosophila melanogaster have shown that selecting populations for faster development results in the emergence of small adults. Some of these studies have indirectly reported the evolution of smaller critical size. Using two kinds of D. melanogaster populations, one of which is selected for faster/accelerated pre-adult development and the other their ancestral control, we demonstrate that the final adult size is determined by the time spent as larvae post the attainment of critical size despite having increased growth rate during the second larval instar. Our populations under selection for faster pre-adult development are exhibiting adaptive bailout due to intrinsic food limitation as against extrinsic food limitation in the yellow dung fly.

Sedentary behavior and altered metabolic activity by AgNPs ingestion in Drosophila melanogaster

Among several nanoparticles, silver nanoparticles (AgNPs) are extensively used in a wide variety of consumer products due to its unique antimicrobial property. However, dosage effect of AgNPs on behavior and metabolic activity in an in vivo condition is not well studied. Therefore, to elucidate the impact of AgNPs on behavior and metabolism, systematic and detailed dosages study of AgNPs was performed by rearing Drosophila melanogaster on food without and with AgNPs. We found that dietary intake of AgNPs at early larval stage leads to behavioral abnormalities such as poor crawling and climbing ability of larvae and adults respectively. Interestingly, intake of higher dosage of AgNPs at larval stage significantly altered metabolic activity that includes lipid, carbohydrate and protein levels in adult flies. Further, detailed analysis revealed that AgNPs causes remarkable reduction in the number of lipid droplets (LDs) which are lipid storage organelles in Drosophila. We also observed an increased production of reactive oxygen species (ROS) in AgNPs ingested larval tissues. These results strongly imply that higher dosage of AgNPs ingestion from early larval stage of Drosophila is inimical and thereby draws concern towards the usage of AgNPs in consumer goods.

Altered lipid metabolism in Drosophila model of Huntington's disease

Huntington’s disease (HD) is late-onset, progressive neurodegenerative disorder caused by expansion of polyglutamine (polyQ) repeat within Huntingtin (Htt) protein. In HD patients, energy-related manifestations such as modulation of weight during entire course of disease with energy deficit at terminal stage have been reported, however, underlying reason remains elusive till date. Lipids, carbohydrate and protein constitute a predominant fraction of body’s energy reservoir and perturbation in their homeostasis may influence weight. To discern role of these energy molecules in weight alteration, we quantified them in an in vivo transgenic Drosophila model of HD. We document that diseased flies exhibit change in weight due to an altered lipid metabolism, as evident from considerably high lipid levels at the time of disease onset followed by a pathologic decline at end-stage. An alteration in intracellular lipid droplet size suggested altered cellular lipid turnover. Furthermore, diseased flies displayed substantial changes in carbohydrate and protein content. Interestingly, alteration in weight and lipid levels are independent of the feeding pattern in diseased condition and exhibit weak correlation with insulin-like peptide or adipokinetic hormone producing cells. We propose that therapeutic intervention aimed at restoring lipid levels and associated metabolic pathways may improve longevity and quality of patient’s life.

Sex-Specific Allometry of Morphometric and Reproductive Traits in Oriental Fruit Flies (Diptera: Tephritidae)

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a highly invasive and polyphagous pest of many horticultural crops in the world, and is currently present in Asia, Africa, and Oceania. To provide essential knowledge for quality control in mass-rearing programs for sterile insect technique against the pest, we investigated how adult body weight and hind-tibial length were correlated in each sex and how body size of each sex affected lifetime reproductive fitness . We show that body weight and hind-tibial length were significantly positively correlated in both sexes, indicating that either trait can be used as an index of body size. However, the weight-tibial length relationships were sex specific, with females gaining disproportionally more weight than males with the increase of hind-tibial length. Body size was not significantly correlated with longevity of either sex, but males lived significantly longer than females. Larger females laid significantly more eggs regardless of body size of the male partner, suggesting that male size has no effect on fecundity. However, body size of both sexes had a significant effect on fertility. We conclude that selection on body size-reproductive fitness relations operates in different directions for the two sexes of B. dorsalis , with larger females and average males having highest reproductive fitness.

Curcumin enhances parental reproductive lifespan and progeny viability in Drosophila melanogaster

Organismal lifespan is a complex trait that is governed by both its genetic makeup as well as the environmental conditions. The improved socioeconomic condition of humans has led to many lifestyle changes that in turn have altered the demography that includes postponement of procreation. Late age progeny is shown to suffer from many congenital diseases. Hence, there is a need to identify and evaluate natural molecules that could enhance reproductive health span. We have used the well-established model organism, Drosophila melanogaster, and ascertained the consequence of diet supplementation with curcumin. Flies reared on curcumin-supplemented diet had significantly higher lifespan. The progeny of flies reared on curcumin had a higher viability. The activity of a key mitochondrial enzyme-aconitase was significantly higher in flies reared on curcumin-supplemented diet. The results suggest that curcumin can not only correct a key step in the citric acid cycle and help in the release of additional energy but also permanently correct developmental and morphogenetic processes.