Biology subjects

Verma, T.

Publications and source records attributed to Verma, T..

12 recordsLinked to original sources

bioRxiv2025

Morphological variations in external genitalia do not explain the interspecific reproductive isolation in Nasonia species complex (Hymenoptera: Pteromalidae)

External genitalia play a crucial role in the successful copulation of conspecific partners in insects. Due to their structural specificity, external genitalia have often been used for distinguishing closely related species in different insects. However, in the young Pteromalid species complex Nasonia, these structures have not received much attention. Nasonia is a genus of parasitoid wasps, that lays eggs and completes its life cycle in dipteran pupae. All behavioral studies (including this study) conducted on this genus indicate that varied prezygotic isolation operates among these recently diverged ([~]1 million years) species. Whether such prezygotic isolation is caused by the incompatibility in their reproductive organs is not known. Here, we studied the internal male reproductive system of the four species and show that all four species have a similar organisation and thus ruling it out as a potential barrier. Furthermore, to investigate the role of male external genitalia as a prezygotic barrier, we also examined the ultrastructural details, including aedeagal length, aedeagal aperture length, and digital spines. We show that all these parameters and sperm length show variations across the four species. However, these variations do not correlate with the female acceptance of the heterospecific males. Therefore, we conclude that there must be other olfactory or behavioral isolating mechanisms and spatial or temporal factors that maintain the reproductive isolation of these four species.

zoology↗

bioRxiv2025

Nasonia vitripennis males exhibit greater effort and competency in detecting hosts with conspecific females than other Nasonia males.

Nasonia is a species complex of four parasitoid wasps. N. vitripennis is cosmopolitan, while the other three species are micro-sympatric with it. This distribution can select for distinct species-specific mate recognition capabilities. However, whether Nasonia males can identify hosts with conspecific females against hosts with heterospecific females is not known. Therefore, we tested this hypothesis in a cafeteria-based choice assay and show that N. vitripennis males can distinguish hosts with conspecific wasps against those parasitised by N. giraulti and N. oneida, exhibiting longer search time and distance traversed with faster search speed. We also found that N. longicornis males can distinguish hosts with conspecific wasps, but only against the hosts parasitised by N. oneida. We further investigated the pairwise differences in the cuticular hydrocarbon (CHC) profiles of the parasitised hosts and adult female wasps. The results reveal that the males show this ability only when the compounds responsible for differences in adult female CHC profiles were also the key differentiators of the host CHC profiles. The comparative mate searching behaviour of males of all reported species within a genus has rarely been studied. Therefore, this study makes a significant contribution to our understanding of interspecific variation of conspecific-mate searching behaviour.

zoology↗

bioRxiv2025

Insights into the protective mechanisms of N-acetyl cysteine against D-Galactosamine induced acute liver injury in rabbits

Pre-clinical studies in test animals like rodents, rabbits and pigs are extremely important in establishing the efficacy of therapeutic interventions ranging from formulations to medical devices. Diseases like acute liver failure (ALF) are although rare, but most often culminate into a situation where the patient needs an emergency liver transplant. Currently, not many medications are available to manage such patients. Out of the very few available options, N-acetyl cysteine (NAC) is the clinicians drug-of-choice. Administration of NAC has shown improvements in patients survival in the hospitals. Yet the mechanism and its systematic investigation in pre-clinical models like rabbits remains undone. In this report, we establish a drug-induced, controlled-ALF in rabbits using D-galactosamine (D-Gal). We also test the efficacy of NAC in this model system. We support the in-vivo findings with detailed in-vitro assays where we attempt to understand the mechanisms of the prophylactic usage of NAC against D-Gal induced ALF.

pathology↗

bioRxiv2024

Reconciling the importance of minerals for propagation of antibiotic resistance genes in the environment

The role of mineral surfaces in environmental processes, particularly their influence on DNA preservation, biofilm formation, and genetic transfer, has garnered attention due to its implications for the spread of antibiotic resistance genes (ARg). Despite the recognized significance of mineral-mediated DNA transfer, this mechanism remains poorly understood. Here we investigate the intricate interplay between soil minerals, bacteria, and DNA, to better understand the mechanisms driving ARg propagation in natural environments. We here study the uptake of mineral adsorbed DNA into the natural competent bacteria b. subtilis and further explore the influence of minerals on the viability and subsequent biofilm formation of both b. subtilis and A. baylyi. We further adsorbed DNA to mineral surfaces and allowed biofilm formation while monitoring the propagation of the ARg through out the biofilms. All the results are set in context of mineral surface properties such as surface charge, charge densities and surface area. Our results showed that the surface properties of the mineral surfaces are highly influencing the transformation efficiencies, viability and biofilm formation where in particular a high number of positive charged surface sites enhance biofilm formation and viability and inhibit transformation. The influence of the mineral surfaces diminishes as the biofilm develops and propagation of mineral adsorbed ARg are seen widely across the mineral surfaces. Our results have implication for mitigations strategies and reconcile mineral surfaces as hot spots for the propagation of antibiotic resistance-which indeed can be driven by transformation in the absence of bacteria carrying the traits. In principle all it takes is one successful transfer event from a mineral adsorbed ARg.

microbiology↗

bioRxiv2023

Functional loss of rffG and rfbB, encoding dTDP-glucose 4,6-dehydratase, changes colony morphology, cell shape, motility and virulence in Salmonella Typhimurium

Lipopolysaccharide (LPS) O-antigen and enterobacterial common antigen (ECA) play crucial roles in maintaining the structural integrity of the outer membrane in Gram-negative bacteria. Previous studies conducted with either LPS or ECA mutants have highlighted the importance of these cell surface polysaccharides in the physiology of Salmonella enterica serovar Typhimurium (S. Typhimurium). However, the functional consequences resulting from the abrogation of both O-antigen and ECA synthesis in S. Typhimurium are not well studied. In the present study, we generated single and double gene-deleted mutants of rffG and rfbB, which are paralogs, encoding dTDP-glucose 4,6-dehydratase that catalyze steps in the synthesis of both O-antigen and ECA. The functional loss of both rffG and rfbB ({Delta}rffG{Delta}rfbB), but not in single gene-deleted strains, results in a round cell morphology, smaller colony formation and altered LPS profile. In addition, the {Delta}rffG{Delta}rfbB strain displays defects in outer membrane permeability, causing hypersensitivity to bile and cell wall targeting antibiotics, e.g., meropenem and polymyxin B. Transcriptomic analysis identified flagellar and SPI-1 pathway to be highly down-regulated in the {Delta}rffG{Delta}rfbB strain which leads to impaired swimming and swarming motility and lower adhesion and invasion of HeLa cells. Importantly, the {Delta}rffG{Delta}rfbB strain is less proficient in colonizing Peyers patches, spleen and liver, is unable to induce pro-inflammatory cytokines and is attenuated in both the oral and intra-peritoneal models of S. Typhimurium infection in mice. Overall, this study highlights the importance of rffG and rfbB in maintaining cell wall integrity, colony and cellular morphology, motility and virulence in S. Typhimurium.

microbiology↗

bioRxiv2023

Fundamentals of biofilm formation in soil: From functionalized self-assembled monolayers to rewilding

Surface energy and surface charges play crucial roles in bacterial adhesion and biofilm formation, however the mechanisms underlying the bacteria-surface interaction, particularly on the formation of soil biofilms, remain unclear. In spite of considering the spatiotemporal dynamics of biofilm formation on different soil surfaces, we compared the impact of four different substrates on bacterial attachment and biofilm formation. The substrates were constituted of gold layer covered by NH2+, CH3, COO- and OH-terminated self-assembled monolayers (SAMS). Two soil habitat bacteria with different Gram barriers, Bacillus subtilis and Acinetobacter baylyi, were grown with incubation times of 6-72 h on each type of surfaces. Bacterial attachment and biofilm formation was assessed using metabolic activity of the cells adhered to the surfaces. The spatial distribution of adhere bacteria was visualized by scanning electron microscopy and confocal laser scanning microscopy. We also investigated whether the surface impacts the biofilm matrix composition. A general view of our results suggests a major influence of the surface chemistry on bacterial potential to form biofilms. The hydrophobic or positively charged substrates attract bacteria while a lack of attachment and biofilm formation on hydrophilic and negatively charged surfaces. This work points out the potential of surface treatments in the environment where it is intended to either repel or attract bacteria.

microbiology↗

bioRxiv2023

Sedimentary DNA can influence evolution:Establishing mineral facilitated horizontal gene transfer as a route to bacterial fitness

Horizontal gene transfer is one of the most important drivers of bacterial evolution. Transformation by uptake of extracellular DNA is traditionally not considered to be an effective mode of gene acquisition, simply because extracellular DNA is degraded in a matter of days when it is suspended in e.g. seawater. Mineral surfaces are, however, known to preserve DNA in the environment, and sedimentary ancient DNA studies have solidified that there are considerable amounts of fragmented DNA stored in sediments world-wide. Recently the age span of stored DNA was increased to at least 2 Ma. Here, we highlight that fragmented ancient DNA can be fueling the evolution of contemporary bacteria and advocate to consider this route for genetic variation in evolutionary history. We show that Acinetobacter baylyi can incorporate 60 bp DNA fragments adsorbed to a wide range of common sedimentary minerals and that the transformation frequencies scale with the mineral surface properties. Further, our results point to interfacial geochemical and sedimentologic processes as facilitators of evolutionary innovation where DNA-molecules are specific to the environment and the processes providing new DNA molecules may also provide the need to evolve. In contrast to heritable stochastic mutations as proposed by Darwin, the access by which bacteria acquire new genomic material at times with increased stress and also needs, would indicate a non-random mechanism that may propel evolution in a non-stochastic manner.

evolutionary biology↗

bioRxiv2022

Evolution of mate harm resistance in females from Drosophila melanogaster populations selection for faster development and early reproduction

Interlocus sexual conflict is predicted to result in sexually antagonistic coevolution between male competitive traits, which are also female-detrimental, and mate harm resistance (MHR) in females. Little is known about connection life-history evolution and sexually antagonistic coevolution. Here, we investigated the evolution of MHR in a set of experimentally evolved populations, where mate-harming ability has been shown to have evolved in males as a correlated response to the selection for faster development and early reproduction. We measured mortality and fecundity of females of these populations and those of their matched controls, under different male exposure conditions. We observed that the evolved females were more susceptible to mate harm - suffering from significantly higher mortality under continuous exposure to control males within the twenty-day assay period. Though these evolved females are known to have shorter lifespan, such higher mortality was not observed under virgin and single-mating conditions. We used fecundity data to show that this higher mortality in evolved females is unlikely due to cost of egg production. Further analysis indicated that this decreased MHR is unlikely to be due purely to the smaller size of these females. Instead, it is more likely to be an indirect experimentally evolved response attributable to the changed breeding ecology, and/or male trait evolution. Our results underline the implications of changes in life history traits, including lifespan, to the evolution of MHR in females.

evolutionary biology↗

bioRxiv2022

Spatial structure does not reduce population level interlocus sexual conflict but imposes additional sex-specific costs

Spatial structure is a common feature of all naturally occurring populations. Theoretically, spatial structuring of a habitat could modulate the intensity of Interlocus sexual conflict (ISC) in a population, possibly by modulating intersexual encounter rate. We tested this theory using laboratory populations of Drosophila melanogaster by measuring male induced fitness decline in females in three-patch habitat systems under two alternative habitat types - structured-interconnected and unstructured. Our results on reproductive and survival costs in females suggested significant costs due to (a) male presence (i.e., ISC) and (b) living on structured habitat. However, there was only a weak evidence supporting the theory of modulation of ISC by habitat structuring only. Through a follow up experiment, we further showed that the effect of habitat on ISC is also robust to the alteration of female conditions. Therefore, it appears that spatial structuring per se is unlikely to modulate ISC, but can impose additional survival costs. We further showed such survival cost could be sex-specific possibly reflecting female biased spontaneous dispersal.

evolutionary biology↗

bioRxiv2022

Cytoplasmic membrane thinning observed by interfacial dyes is likely a common effect of bactericidal antibiotics

The lipid membrane is a fundamental part of life. However, the effects of different stresses on membranal integrity and physiology are less understood. Using novel 4-aminophthalimide-based membrane-specific dyes (4AP-Cn: n is carbon chain-length), aided with confocal microscopy, fluorescence spectroscopy, molecular dynamics simulations, and flow cytometry, we have studied stress-mediated changes in E. coli membranes. By exploiting the depth-dependent positioning and subsequent environmental sensitivity of the dyes, we have proposed a measure of antibiotic-induced membrane damage: the fluorescence Peak Maxima Difference (PMD) between 4AP-C9 and 4AP-C13. The ROS-influenced PMD quantifies cytoplasmic membrane thickness and measures sensitivity against most bactericidal antibiotics, depending upon the extent of lipid peroxidation. Importantly, we have verified this observation using antibiotic-sensitive and resistant clinical isolates of E. coli and ESKAPE pathogens like K. pneumoniae and Enterobacter spp. This study underscores the role of antibiotic-induced membrane changes; a critical issue given the increasing global antimicrobial resistance.

microbiology↗

bioRxiv2021

Evolution of reduced mate-harming tendency of males in Drosophila melanogaster populations selected for faster life history

Detrimental effect of males on female, often termed mate harm, is a hallmark of sexual conflict. Allowed to evolve unchecked, mate harming traits are predicted to bring down average fitness of a population, unless mitigated by the evolution of resistance in females. In addition, life history may also modulate sexual conflict, but the mechanism is not clearly understood. Here we investigated the evolution of mate harm in a set of experimentally evolved laboratory populations of Drosophila melanogaster wherein a faster aging has evolved in response to >1000 generations of selection for faster development and early reproduction. We quantified mortality and fecundity of Oregon R females held with evolved (ACO) and ancestral males (CO) to show that the evolved males are significantly less detrimental to their mates. We compared our results from the ACO males with that from a phenocopied version of the ancestral regime (CCO) to show that only part of the observed difference in mate harm can be attributed to the evolved difference in body size. We further show that the reduction in mate harming ability evolved despite an increase in courtship activity, especially early in life. We discuss the causative role of an evolved reproductive schedule and altered breeding ecology. Significance statementSexually antagonistic male effects can significantly bring down female fitness. Along with female counter evolution of resistance traits, life history has been conjectured to impose constrains on the evolution of such harming ability in males. Here, we report the evolution of mate harming ability in males of a set of five replicate Drosophila melanogaster populations that evolved smaller size and faster aging as a result of >1000 generations of experimental evolution for faster development and early reproduction. We show that in spite of ample scope of sexual selection, the faster aging males have evolved reduced mate harming ability despite being more active in courting their mates. To the best of our knowledge, this is one of the first clear evidences demonstrating the causal relationship between evolution of life history and reduction in sexual antagonism in a population.

evolutionary biology↗

bioRxiv2018

Transgenerational effect of adult density through paternal effect in Drosophila melanogaster

O_LINotwithstanding recent evidences, paternal environment is thought to be a potential but unlikely source of fitness variation that can affect trait evolution. Here we studied intergenerational effects of males exposure to varying adult density in Drosophila melanogaster laboratory populations.\nC_LIO_LIWe held sires at normal (N), medium (M) and high (H) adult densities for two days before allowing them to mate with virgin females. This treatment did not introduce selection through differential mortality. Further, we randomly paired males and females and allowed a single round of mating between the sires and the dams. We then collected eggs from the dams and measured the egg size. Finally, we investigated the effect of the paternal treatment on juvenile and adult (male) fitness components.\nC_LIO_LIWe found a significant treatment effect on juvenile competitive ability where the progeny sired by the H-males had higher competitive ability. Since we did not find the treatment to affect egg size, this effect is unlikely to be mediated through variation in female provisioning.\nC_LIO_LIMale fitness components were also found to have a significant treatment effect: M-sons had lower dry weight at eclosion, higher mating latency and lower competitive mating success.\nC_LIO_LIWhile being the first study to show both adaptive and non-adaptive effect of the paternal density in Drosophila, our results highlight the importance of considering paternal environment as important source of fitness variation.\nC_LI

evolutionary biology↗