Identification of Drosophila-based endpoints for the assessment and understanding of xenobiotic-mediated male reproductive adversities

Adult exposure of atrazine alone or in combination with carbohydrate diet hastens the onset/progression of type 2 diabetes in Drosophila

AIM

The combined impact of traditional and non-traditional risk factors of type 2 diabetes (T2D) on the development and progression of insulin resistance and associated complications is poorly understood. Therefore, we assessed the effect of moderately rich sugar diet coupled with environmental chemical exposure on the development and progression of T2D using Drosophila as a model organism.

MAIN METHODS

We reared newly eclosed Drosophila males on a diet containing atrazine (20 μg/ml; non-traditional risk factor) and/or moderately high sucrose (0.5 M/1 M; to mimic binge eating, Traditional risk factor) for 20-30 days. Subsequently, we assessed diabetic parameters, oxidative stress parameters and also the abundance of advanced glycation end products (AGEs) along with their receptor (RAGE) in these flies. For diabetic cardiomyopathy, we examined the pericardin (tissue fibrosis marker) level in Drosophila heart.

KEY FINDINGS

Flies reared on 20 μg/ml atrazine alone showed T2D hallmarks at 30 days. In contrast, flies reared on 0.5 M sucrose+ 20 μg/ml atrazine showed insulin resistance characterized by hyperglycemia and increased Drosophila insulin-like peptides along with reduced insulin signaling at 20 days, similar to those reared on high sucrose diet. In addition, both groups had high levels of oxidative stress and showed starvation response (converting triglycerides into fatty acids). Alarmingly, flies fed with sucrose+atrazine for 20 and 30 days had elevated pericardin in heart tissues, indicating early onset of diabetic complications such as cardiomyopathy.

SIGNIFICANCE

Lifestyle-chemical exposure synergistically impairs glucose metabolism, affects organisms' redox state and leads to the early onset of T2D and associated complications like cardiomyopathy.

Altered sperm fate in the reproductive tract milieu due to oxidative stress leads to sub-fertility in type 1 diabetes females: A Drosophila-based study

AIMS

Female sub-fertility, a prominent complication due to Type 1 diabetes (T1D), is generally attributed to disturbances in menstrual cycles and/or ovarian defects/disorders. T1D women, however, are high in oxidative stress, although the impact of the same on their reproduction and associated events remains unknown. Therefore, we assessed the repercussions of elevated oxidative stress on the sperm fate (storage/utilization) in the reproductive tract milieu of T1D females and their fertility using the Drosophila T1D model (Df[dilp1-5]), which lacks insulin-like peptides and displays reduced female fertility.

MAIN METHODS

We mated Df[dilp1-5] females to normal males and thereafter examined sperm storage and/or utilization in conjunction with oxidative stress parameters in mated Df[dilp1-5] females at different time points. Also, the impact of antioxidant (Amla or Vitamin C) supplementation on the above oxidative stress parameters in Df[dilp1-5] females and the consequences on their sperm and fertility levels were examined.

KEY FINDINGS

Df[dilp1-5] females showed elevated oxidative stress parameters and a few of their reproductive tract proteins are oxidatively modified. Also, these females stored significantly fewer sperm and also did not utilize sperm as efficiently as their controls. Surprisingly, amelioration of the oxidative stress in Df[dilp1-5] females' milieu through antioxidant (Amla or vitamin C) supplementation enhanced sperm storage and improved fertility.

SIGNIFICANCE

Hyperglycemia coupled with elevated oxidative stress within the female reproductive tract environment affects the sperm fate, thereby reducing female fertility in T1D. In addition, these findings suggest that antioxidant supplementation may substantially aid in the mitigation of sub-fertility in T1D females.

Female factors modulate Sex Peptide's association with sperm in Drosophila melanogaster

BACKGROUND

Male-derived seminal fluid proteins (SFPs) that enter female fruitflies during mating induce a myriad of physiological and behavioral changes, optimizing fertility of the mating pair. Some post-mating changes in female Drosophila melanogaster persist for ~10-14 days. Their long-term persistence is because the seminal protein that induces these particular changes, the Sex Peptide (SP), is retained long term in females by binding to sperm, with gradual release of its active domain from sperm. Several other "long-term response SFPs" (LTR-SFPs) "prime" the binding of SP to sperm. Whether female factors play a role in this process is unknown, though it is important to study both sexes for a comprehensive physiological understanding of SFP/sperm interactions and for consideration in models of sexual conflict.

RESULTS

We report here that sperm in male ejaculates bind SP more weakly than sperm that have entered females. Moreover, we show that the amount of SP, and other SFPs, bound to sperm increases with time and transit of individual seminal proteins within the female reproductive tract (FRT). Thus, female contributions are needed for maximal and appropriate binding of SP, and other SFPs, to sperm. Towards understanding the source of female molecular contributions, we ablated spermathecal secretory cells (SSCs) and/or parovaria (female accessory glands), which contribute secretory proteins to the FRT. We found no dramatic change in the initial levels of SP bound to sperm stored in mated females with ablated or defective SSCs and/or parovaria, indicating that female molecules that facilitate the binding of SP to sperm are not uniquely derived from SSCs and parovaria. However, we observed higher levels of SP (and sperm) retention long term in females whose SSCs and parovaria had been ablated, indicating secretions from these female tissues are necessary for the gradual release of Sex Peptide's active region from stored sperm.

CONCLUSION

This study reveals that the SP-sperm binding pathway is not entirely male-derived and that female contributions are needed to regulate the levels of SP associated with sperm stored in their storage sites.

Toxicity Assessment of Curculigo orchioides Leaf Extract Using Drosophila melanogaster: A Preliminary Study

Curculigo orchioides is used in Indian and Chinese traditional medicinal systems for various health benefits. However, its toxicological effects are mostly unknown. This study assesses the potential toxicity of aqueous leaf (A.L.) extract of C. orchioides using Drosophila melanogaster as an experimental model. Preliminary phytochemical tests were followed by the Fourier transform infrared (FTIR) tests to identify the functional group in the A.L. extract of C. orchioides. Drosophila larvae/adults were exposed to varying concentrations of C. orchioides A.L. extract through diet, and developmental, lifespan, reproduction, and locomotory behaviour assays were carried out to assess the C. orchioides toxicity at organismal levels. The cellular toxicity of A.L. extract was examined by analysing the expression of heat shock protein (hsps), reactive oxygen species (ROS) levels, and cell death. The FTIR analysis showed the presence of functional groups indicating the presence of secondary metabolites like saponins, phenolics, and alkaloids. Exposure to A.L. extract during development resulted in reduced emergence and wing malformations in the emerged fly. Furthermore, a significant reduction in reproductive performance and the organism's lifespan was observed when adult flies were exposed to A.L. extract. This study indicates the adverse effect of C. orchioides A.L. extract on Drosophila and raises concerns about the practice of indiscriminate therapeutic use of plant extracts.

Drosophila ecdysone receptor activity-based ex vivo assay to assess the endocrine disruption potential of environmental chemicals

Insect pollinators, critical for both agricultural output and the ecosystem, are declining at an alarming levels partly due to human-made chemicals. Majority of environmental chemicals hamper the endocrine function and studies on the same in insects remain neglected. Here, we report a Drosophila-based ex vivo assay system that employs a reproductive tissue from transgenic males carrying a reporter gene (lacZ) downstream of ecdysone receptor response element (EcRE) and permits the evaluation of chemical-mediated activity modulation of all three isoforms of ecdysone receptor, which are critical for male fertility. We show agonistic [plasticizers, cypermethrin, atrazine, methyl parathion, imidacloprid, cadmium chloride, mercuric chloride or 3-(4-methylbenzylidene) camphor] or antagonistic (apigenin, tributyltin chloride) effects or lack of effect thereof (rutin hydrate, dichlorvos, lead acetate, parabens) for seven different classes of environmental chemicals on ecdysone receptor activity reflecting the specificity and sensitivity of the developed ex vivo assay. Exposure to a few of these chemicals in vivo hampers the fertility of Drosophila males, thus linking the observed endocrine disruption to a quantifiable reproductive phenotype. The developed ex vivo assay offers a quick Drosophila-based screening tool for throughput monitoring of environmental chemicals for their ability to hamper the endocrine function of insect pollinators and other invertebrates.

Systematic toxicity assessment of CdTe quantum dots in Drosophila melanogaster

The risk assessment of cadmium (Cd)-based quantum dots (QDs) used for biomedical nanotechnology applications has stern toxicity concerns. Despite cytotoxicity studies of cadmium telluride (CdTe) QDs, the systematic in vivo study focusing on its organismal effects are more relevant to public health. Therefore, the present study aims to investigate the effect of chemically synthesized 3-mercapto propionic acid-functionalized CdTe QDs on organisms' survival, development, reproduction, and behaviour using Drosophila melanogaster as a model. The sub-cellular impact on the larval gut was also evaluated. First/third instar larvae or the adult Drosophila were exposed orally to green fluorescence emitting CdTe QDs (0.2-100 μM), and organisms' longevity, emergence, reproductive performance, locomotion, and reactive oxygen species (ROS), and cell death were assessed. Uptake of semiconductor CdTe QDs was observed as green fluorescence in the gut. A significant decline in percentage survivability up to 80% was evident at high CdTe QDs concentrations (25 and 100 μM). The developmental toxicity was marked by delayed and reduced fly emergence after CdTe exposure. The teratogenic effect was evident with significant wing deformities at 25 and 100 μM concentrations. However, at the reproductive level, adult flies' fecundity, fertility, and hatchability were highly affected even at low concentrations (1 μM). Surprisingly, the climbing ability of Drosophila was unaffected at any of the used CdTe QDs concentrations. In addition to organismal toxicity, the ROS level and cell death were elevated in gut cells, confirming the sub-cellular toxicity of CdTe QDs. Furthermore, we observed a significant rescue in CdTe QDs-associated developmental, reproductive, and survival adversities when organisms were co-exposed with N-acetyl-cysteine (NAC, an antioxidant) and CdTe QDs. Overall, our findings indicate that the environmental release of aqueously dispersible CdTe QDs raises a long-lasting health concern on the development, reproduction, and survivability of an organism.

Exposure to phthalates: germline dysfunction and aneuploidy

Epidemiological studies continue to reveal the enduring impact of exposures to environmental chemicals on human physiology, including our reproductive health. Phthalates, a well characterized class of endocrine disrupting chemicals and commonly utilized plasticizers, are among one of the many toxicants ubiquitously present in our environment. Phthalate exposure has been linked to increases in the rate of human aneuploidy, a phenomenon that is detected in 0.3% of livebirths resulting in genetic disorders including trisomy 21, approximately 4% of stillbirths, and over 35% of miscarriages. Here we review recent epidemiological and experimental studies that have examined the role that phthalates play in germline dysfunction, including increases in apoptosis, oxidative stress, DNA damage, and impaired genomic integrity, resulting in aneuploidy. We will further discuss subject variability, as it relates to diet and polymorphisms, and the sexual dimorphic effects of phthalate exposure, as it relates to sex-specific targets. Lastly, we discuss some of the conserved effects of phthalate exposure across humans, mammalian models and nonmammalian model organisms, highlighting the importance of using model organisms to our advantage for chemical risk assessment and unveiling potential mechanisms that underlie phthalate-induced reproductive health issues across species.

The Implementation of the Three Rs in Regulatory Toxicity and Biosafety Assessment: The Indian Perspective

Animal models have long served as a basis for scientific experimentation, biomedical research, drug development and testing, disease modelling and toxicity studies, as they are widely thought to provide meaningful, human-relevant predictions. However, many of these systems are resource intensive and time-consuming, have low predictive value and are associated with great social and ethical dilemmas. Often drugs appear to be effective and safe in these classical animal models, but later prove to be ineffective and/or unsafe in clinical trials. These issues have paved the way for a paradigm shift from the use of in vivo approaches, toward the 'science of alternatives'. This has fuelled several research and regulatory initiatives, including the ban on the testing of cosmetics on animals. The new paradigm has been shifted toward increasing the relevance of the models for human predictivity and translational efficacy, and this has resulted in the recent development of many new methodologies, from 3-D bio-organoids to bioengineered 'human-on-a-chip' models. These improvements have the potential to significantly advance medical research globally. This paper offers a stance on the existing strategies and practices that utilise alternatives to animals, and outlines progress on the incorporation of these models into basic and applied research and education, specifically in India. It also seeks to provide a strategic roadmap to streamline the future directions for the country's policy changes and investments. This strategic roadmap could be a useful resource to guide research institutions, industries, regulatory agencies, contract research organisations and other stakeholders in transitioning toward modern approaches to safety and risk assessment that could replace or reduce the use of animals without compromising the safety of humans or the environment.

Drosophila seminal sex peptide associates with rival as well as own sperm, providing SP function in polyandrous females

When females mate with more than one male, the males’ paternity share is affected by biases in sperm use. These competitive interactions occur while female and male molecules and cells work interdependently to optimize fertility, including modifying the female’s physiology through interactions with male seminal fluid proteins (SFPs). Some modifications persist, indirectly benefiting later males. Indeed, rival males tailor their ejaculates accordingly. Here, we show that SFPs from one male can directly benefit a rival’s sperm. We report that Sex Peptide (SP) that a female Drosophila receives from a male can bind sperm that she had stored from a previous male, and rescue the sperm utilization and fertility defects of an SP-deficient first-male. Other seminal proteins received in the first mating ‘primed’ the sperm (or the female) for this binding. Thus, SP from one male can directly benefit another, making SP a key molecule in inter-ejaculate interaction.

When fruit flies and other animals reproduce, a compatible male and a female mate, allowing sperm from the male to swim to and fuse with the female’s egg cells. The males also produce proteins known as seminal proteins that travel with the sperm. These proteins increase the likelihood of sperm meeting an egg and induce changes in the female that increase the number, or quality, of offspring produced.

Some seminal proteins help a male to compete against its rivals by decreasing their chances to fertilize eggs. However, since many of the changes seminal proteins induce in females are long-lasting, it is possible that a subsequent male may actually benefit indirectly from the effects of a prior male’s seminal proteins. It remains unclear whether the seminal proteins of one male are also able to directly interact with and help the sperm of another male.

Male fruit flies make a seminal protein known as sex peptide. Normally, a sex peptide binds to the sperm it accompanies into the female, increasing the female’s fertility and preventing her from mating again with a different male. To test whether the sex peptide from one male can bind to and help a rival male’s sperm, Misra and Wolfner mated female fruit flies with different combinations of males that did, or did not, produce the sex peptide.

The experiments found that female flies that only mated with mutant males lacking the sex peptide produced fewer offspring than if they had mated with a ‘normal’ male. However, in females that mated with a mutant male followed by another male who provided the sex peptide, the second male’s sex peptide was able to bind to the mutant male’s sperm (as well as to his own). This in turn allowed the mutant male’s sperm to be efficiently used to sire offspring, at levels comparable to a normal male providing the sex peptide.

These findings demonstrate that the ways individual male fruit flies interact during reproduction are more complex than just simple rivalry. Since humans and other animals also produce seminal proteins comparable to those of fruit flies, this work may aid future advances in human fertility treatments and strategies to control the fertility of livestock and pests, including mosquitoes that transmit diseases.

Candle soot derived carbon nanoparticles: An assessment of cellular and progressive toxicity using Drosophila melanogaster model

The biomedical demand of the nanomaterials is continuously increasing due to their wide range of applications in the field. However, before the implementation of these nanomaterials, toxicity assessment is essential for its safe usage. In the present study, the toxicity of carbon nanoparticles (CNPs) was investigated which was derived from candle soot and compared with commercially available multi-walled carbon nanotubes (CNTs) by using Drosophila melanogaster as a model system. First instar Drosophila larvae were exposed to CNPs as well as CNTs, and the toxic effects of these nanomaterials were compared. The result shows that both nanomaterials enhance the level of reactive oxygen species and oxidative stress in the Drosophila, which leads to the upregulation of heat shock proteins that may cause cytotoxicity in exposed Drosophila larvae. In contrast, exposure to CNPs and CNTs did not affect the developmental period of the larvae. Morphology of the internal organs, brain, gut and Malpighian tubules was also not altered in the exposed larvae. Similarly, no change observed in the cytoskeleton (F-actin) of these organs. Reproductive performance was slightly reduced in the case of CNPs compare to control. However, CNTs exposure did not show any significant effect on the reproductive performance of the flies that emerged from exposed larvae in comparison to control. Hence the study concludes that exposure to CNPs and CNTs cause a moderate level of cytotoxicity in Drosophila. The study also indicates that the inexpensive CNPs may use as an alternative to expensive CNTs for biomedical and biological applications.

Xenobiotic mediated diabetogenesis: Developmental exposure to dichlorvos or atrazine leads to type 1 or type 2 diabetes in Drosophila

The increased incidence of diabetes to the magnitude of a global epidemic is attributed to non-traditional risk factors, including exposure to environmental chemicals. However, the contribution of xenobiotic exposure during the development of an organism to the etiology of diabetes is not fully addressed. Developing stages are more susceptible to chemical insult, but knowledge on the consequence of the same to the onset of diabetes is residual. In this context, by using Drosophila melanogaster having conserved Insulin/Insulin growth factor-like signaling (IIS) as well as glucose homeostasis as a model, we evaluated the potential of developmental exposure to dichlorvos (DDVP, an organophosphorus pesticide) or atrazine (herbicide) to cause diabetes in exposed organisms. Flies exposed to DDVP during their development display insulin deficiency or type 1 diabetes (T1D) while those exposed to atrazine show insulin resistance or type 2 diabetes (T2D), suggesting that exposure to these xenobiotics during organismal development can result in diabetes and that different mechanisms underlie pesticide mediated diabetes. We show that oxidative stress-mediated c-Jun N-terminal kinase (JNK) signaling activation underlies insulin resistance in flies exposed to atrazine during their development while DDVP-mediated T1D involves activation of caspase-mediated cell death pathway. Mitigation of oxidative stress through over-expression of SOD2 in atrazine (20μg/ml) exposed flies, revealed significantly decreased oxidative stress levels and reduced phosphorylation of JNK. Moreover, glucose and Akt phosphorylation levels in SOD2 over-expression flies exposed to atrazine were comparable to those in controls, suggesting restoration in insulin sensitivity. Therefore, exposure to xenobiotics during development is a common risk factor for the development of type 1 or type 2 diabetes. Accordingly, the present study cautions against the use of such diabetogenic pesticides. Also, mitigation of oxidative stress or anti-oxidant supplementation could be a potential therapy for xenobiotic mediated type 2 diabetes.

Atrazine or bisphenol A mediated negative modulation of mismatch repair gene, mlh1 leads to defective oogenesis and reduced female fertility in Drosophila melanogaster

The study reports the effects of an herbicide (atrazine) and a plasticizer (Bisphenol A, BPA) on the transcriptional modulation of a mismatch repair gene (mlh1) and its adverse consequences on female fertility using Drosophila as a model. Through a chemical screen, we show that exposure to atrazine or BPA significantly downregulates mlh1 and the exposed flies had reduced fertility with smaller ovaries having reduced number of mature oocytes and abnormal distribution of ovarian follicles with increased apoptosis in them. These females had increased double-strand breaks as well as reduced synaptonemal complex formation in their ovaries suggesting altered meiotic crossing over. The eggs of these females were defective in their maternal transcripts as well as proteins and consequently, after fertilization, these eggs exhibited abnormal embryonic development. Interestingly, these phenotypes parallel that of mlh1 mutants. Further, exposure of females having reduced Mlh1 levels (mlh1^e00130/CyO) to atrazine or BPA caused severe defective phenotypes at a higher proportion than normal flies. Our findings reveal the critical role of mlh1 in atrazine and BPA mediated female reproductive toxicity, and opens up a possibility of toxicants affecting female fertility by modulating the MMR genes.

Nosema ceranae, Fipronil and their combination compromise honey bee reproduction via changes in male physiology

The honey bee is threatened by biological agents and pesticides that can act in combination to induce synergistic effects on its physiology and lifespan. The synergistic effects of a parasite/pesticide combination have been demonstrated on workers and queens, but no studies have been performed on drones despite their essential contribution to colony sustainability by providing semen diversity and quality. The effects of the Nosema ceranae/fipronil combination on the life traits and physiology of mature drones were examined following exposure under semi-field conditions. The results showed that the microsporidia alone induced moderate and localized effects in the midgut, whereas fipronil alone induced moderate and generalized effects. The parasite/insecticide combination drastically affected both physiology and survival, exhibiting an important and significant generalized action that could jeopardize mating success. In terms of fertility, semen was strongly impacted regardless of stressor, suggesting that drone reproductive functions are very sensitive to stress factors. These findings suggest that drone health and fertility impairment might contribute to poorly mated queens, leading to the storage of poor quality semen and poor spermathecae diversity. Thus, the queens failures observed in recent years might result from the continuous exposure of drones to multiple environmental stressors.

Functional male accessory glands and fertility in Drosophila require novel ecdysone receptor

In many insects, the accessory gland, a secretory tissue of the male reproductive system, is essential for male fertility. Male accessory gland is the major source of proteinaceous secretions, collectively called as seminal proteins (or accessory gland proteins), which upon transfer, manipulate the physiology and behavior of mated females. Insect hormones such as ecdysteroids and juvenoids play a key role in accessory gland development and protein synthesis but little is known about underlying molecular players and their mechanism of action. Therefore, in the present study, we examined the roles of hormone-dependent transcription factors (Nuclear Receptors), in accessory gland development, function and male fertility of a genetically tractable insect model, Drosophila melanogaster. First, we carried out an RNAi screen involving 19 hormone receptors, individually and specifically, in a male reproductive tissue (accessory gland) for their requirement in Drosophila male fertility. Subsequently, by using independent RNAi/ dominant negative forms, we show that Ecdysone Receptor (EcR) is essential for male fertility due to its requirement in the normal development of accessory glands in Drosophila: EcR depleted glands fail to make seminal proteins and have dying cells. Further, our data point to a novel ecdysone receptor that does not include Ultraspiracle but is probably comprised of EcR isoforms in Drosophila male accessory glands. Our data suggest that this novel ecdysone receptor might act downstream of homeodomain transcription factor paired (prd) in the male accessory gland. Overall, the study suggests novel ecdysone receptor as an important player in the hormonal regulation of seminal protein production and insect male fertility.

Insects are the major contributors to biodiversity and have economic, agricultural and health importance. This unparalleled abundance of insects, in part, can be attributed to their high reproductive potential. In many insects, proteins derived from the accessory gland, the secretory tissue of male reproductive system, are critical for fertility. The production of these accessory gland proteins is regulated by insect hormones but the underlying mechanisms/molecular players remain poorly understood. Elucidation of the same has potential applications in designing pest control management strategies and to understand the effect of environmental chemicals on reproduction. In view of this, we analyzed the role, if any, of various insect hormone receptors in development and function of the male accessory gland in a genetically tractable insect model, Drosophila melanogaster. Here, we report the involvement of Ecdysone receptor (EcR with novel composition) in Drosophila male fertility. We show that the depletion of this receptor causes cell death in male accessory glands, which fail to produce seminal fluid proteins leading to sterility/sub-fertility of Drosophila males. These findings will find potential applications in designing insect pest control strategies.

Estrogen related receptor is required for the testicular development and for the normal sperm axoneme/mitochondrial derivatives in Drosophila males

Estrogen related receptors (ERRs), categorized as orphan nuclear receptors, are critical for energy homeostasis and somatic development. However, significance of ERRs in the development of reproductive organs/organelles/cells remain poorly understood, albeit their homology to estrogen receptors. In this context, here, we show that knockdown of ERR in the testes leads to improperly developed testes with mis-regulation of genes (aly, mia, bruce, bam, bgcn, fzo and eya) involved in spermatogenesis, resulting in reduced male fertility. The observed testicular deformity is consistent with the down-regulation of SOX-E group of gene (SOX100B) in Drosophila. We also show dispersion/disintegration of fusomes (microtubule based structures associated with endoplasmic reticulum derived vesicle, interconnecting spermatocytes) in ERR knockdown testes. A few ERR knockdown testes go through spermatogenesis but have significantly fewer sperm. Moreover, flagella of these sperm are defective with abnormal axoneme and severely reduced mitochondrial derivatives, suggesting a possible role for ERR in mitochondrial biogenesis, analogous to mammalian ERRα. Interestingly, similar knockdown of remaining seventeen nuclear receptors did not yield a detectable reproductive or developmental defect in Drosophila. These findings add newer dimensions to the functions envisaged for ERR and provide the foundation for deciphering the relevance of orphan nuclear receptors in ciliopathies and testicular dysgenesis.

Drone exposure to the systemic insecticide Fipronil indirectly impairs queen reproductive potential

A species that requires sexual reproduction but cannot reproduce is doomed to extinction. The important increasing loss of species emphasizes the ecological significance of elucidating the effects of environmental stressors, such as pesticides, on reproduction. Despite its special reproductive behavior, the honey bee was selected as a relevant and integrative environmental model because of its constant and diverse exposure to many stressors due to foraging activity. The widely used insecticide Fipronil, the use of which is controversial because of its adverse effects on honey bees, was chosen to expose captive drones in hives via syrup contaminated at 0.1 μg/L and gathered by foragers. Such environmental exposure led to decreased spermatozoa concentration and sperm viability coupled with an increased sperm metabolic rate, resulting in drone fertility impairment. Subsequently, unexposed queens inseminated with such sperm exhibited fewer spermatozoa with lower viability in their spermatheca, leaving no doubt about the detrimental consequences for the reproductive potential of queens, which are key for colony sustainability. These findings suggest that pesticides could contribute to declining honey bee populations through fertility impairment, as exemplified by Fipronil. More broadly, reproductive disorders should be taken into consideration when investigating the decline of other species.

Exposure to endosulfan influences sperm competition in Drosophila melanogaster

Dwindling male fertility due to xenobiotics is of global concern. Accordingly, male reproductive toxicity assessment of xenobiotics through semen quality analysis in exposed males, and examining progeny production of their mates is critical. These assays, in part, are biased towards monogamy. Females soliciting multiple male partners (polyandry) is the norm in many species. Polyandry incites sperm competition and allows females to bias sperm use. However, consequences of xenobiotic exposure to the sperm in the light of sperm competition remain to be understood. Therefore, we exposed Drosophila melanogaster males to endosulfan, and evaluated their progeny production as well as the ability of their sperm to counter rival control sperm in the storage organs of females sequentially mated to control/exposed males. Endosulfan (2 μg/ml) had no significant effect on progeny production and on the expression of certain genes associated with reproduction. However, exposed males performed worse in sperm competition, both as 1(st) and 2(nd) male competitors. These findings indicate that simple non-competitive measures of reproductive ability may fail to demonstrate the harmful effects of low-level exposure to xenobiotics on reproduction and advocate consideration of sperm competition, as a parameter, in the reproductive toxicity assessment of xenobiotics to mimic situations prevailing in the nature.