Biology subjects

Prasad, N. G.

Publications and source records attributed to Prasad, N. G..

At least 19 recordsLinked to original sources

bioRxiv2026

Non-Additive Transcriptional Regulation Underpins Additive Survival Trait In Populations Of Drosophila Selected For Increased Post Infection Survival

Understanding how immunity evolves requires integrating organismal resistance with the underlying genetic and regulatory mechanisms. Using Drosophila melanogaster populations experimentally selected for increased survival post infection with Enterococcus faecalis, we dissected the quantitative genetic basis of post-infection survival and the transcriptional architecture associated with it. F1 hybrid analyses revealed an additive genetic basis for survivorship in both sexes, consistent with a polygenic response to selection. In contrast, gene expression showed extensive sex-specific regulation and hybrid misexpression. Males strongly upregulated antimicrobial peptides yet suffered greater mortality, suggesting a costly or inefficient immune strategy. Females relied on distinct effector pathways and exhibited superior survivorship. Notably, transcriptional induction of the melanization precursor PPO1 did not correspond to increased phenoloxidase enzyme activity, revealing a post-transcriptional constraint on immune deployment. Together, these results show that while the genetic basis of survivorship is additive, the evolved immune phenotype is shaped by sex-specific regulatory divergence, hybrid incompatibilities, and functional bottlenecks. This emphasizes the need to integrate quantitative genetic, transcriptomic, and functional assays to understand the evolution of immune defense.

evolutionary biology↗

bioRxiv2025

Dose- and outcome-dependent effects of bacterial infection on female fecundity in Drosophila melanogaster

The virulence of a pathogenic infection challenge can manifest in the form of increased host mortality rates and/or reduced host fecundity. Reduced fecundity in infected hosts can result from resource-allocation trade-offs: increased investment in immune defences depletes the common pool of resources, which are also required for reproduction. Alternatively, reduced fecundity may result from damage to host organs, especially reproductive organs, caused by the infection. We infected Drosophila melanogaster females with the bacterial pathogen Enterococcus faecalis at different infection doses and found that increasing the infection dose led to greater suppression of fecundity, without a corresponding increase in mortality rates. We further found that the reduction in host fecundity is contingent on the infection outcome (whether the host lives or dies after being infected), particularly in flies infected with a high dose of bacteria. Interestingly, survivors of the infection challenge had exhibited comparable fecundity irrespective of the dose used to infect them, whereas amongst females that died after infection, a higher infection dose led to a lower fecundity. We therefore propose that our results indicate that fecundity suppression in E. faecalis-infected females is likely caused by host organ damage rather than by diversion of limited resources towards immune function.

evolutionary biology↗

bioRxiv2025

Socio-sexual environment influences fecundity, but not response to bacterial infection, in Drosophila melanogaster females

It is common for a host exposed to a pathogenic infection challenge to exhibit suppression of fecundity. This suppression can be driven by either a resource allocation-based trade-off between fecundity and immune function, or by infection-induced damage to host soma (particularly the reproductive organs). Alternatively, hosts can increase their fecundity to compensate for the curtailed lifespan resulting from lethal infection. Various factors, both extrinsic and intrinsic to the host, determine the actual effect of any infection challenge on host fecundity. While the hosts physiological and abiotic environmental factors have been thoroughly explored in this context, the role of the hosts biotic environment - especially its social and sexual environment - is rarely addressed. We investigated whether the socio-sexual environment (SSE) of D. melanogaster females influenced the effect of bacterial infection on their fecundity. We altered the socio-sexual environment of the females by housing them with different numbers of same-sex and opposite-sex companions. Our results indicate that while such alterations of the SSE changed the baseline reproductive effort of the females, they had no role in determining female susceptibility to infections or how infection affected female fecundity.

evolutionary biology↗

bioRxiv2024

Timing of starvation determines its effects on susceptibility to infection in Drosophila melanogaster females independent of host evolutionary history

An organisms susceptibility to pathogens is contingent on various environmental factors, including the availability of nutrition. Starvation can alter host susceptibility to infections, either directly via depletion of resources essential for proper functioning of the immune system, or indirectly via the various physiological changes it induces within the host body. We tested if the susceptibility of Drosophila melanogaster populations to Enterococcus faecalis infection is affected by (a) whether the hosts are starved before or after the infection, and (b) the evolutionary history of the host. Hosts from laboratory fly populations that have been experimentally evolved to be more resistant to E. faecalis, and their corresponding control populations, were subjected to infection with or without being starved prior to and after being infected. We found that the effect of starvation on susceptibility to E. faecalis changed with the timing of starvation: starvation after infection improved survival of infected hosts, irrespective of how they were treated before infection, while starving only prior to infection (and not after) compromised post-infection survival. The changes in infection susceptibility were uniform in both the evolved and the control populations, suggesting that the effects of starvation are not dependent on pre-existing resistance to the infecting pathogen.

evolutionary biology↗

bioRxiv2024

Experimental evolution for improved post-infection survival selects for increased disease resistance in Drosophila melanogaster

Disease resistance (defined as the host capacity to limit systemic infection intensity) and disease tolerance (defined as the host capacity to limit infection-induced damage) are two complementary defense strategies that help the hosts maximize their survival and fitness when infected with pathogens and parasites. In addition to the underlying physiological mechanisms, existing theory postulates that these two strategies differ in terms of the conditions under which each strategy evolves in host populations, their evolutionary dynamics, and the ecological and epidemiological consequences of their evolution. Here we explored if one or both of these strategies evolve when host populations are subjected to selection for increased post-infection survival. We experimentally evolved Drosophila melanogaster populations, selecting for the flies that survived an infection with the entomopathogen Enterococcus faecalis, and found that the host populations evolved increased disease resistance in response. This was despite the physiological costs associated with increased resistance. We did not find evidence of any change in disease tolerance in the host populations. We have therefore demonstrated that in an experimental evolution set-up, where insect hosts must survive an infection with a pathogenic bacterium, the hosts evolve improved disease resistance but not disease tolerance.

evolutionary biology↗

bioRxiv2024

Parental effects of pathogenic bacterial infections in Drosophila melanogaster: trans-generational immune priming without apparent costs

Parental experience with pathogens and parasites can shape offspring susceptibility to infections, a phenomenon commonly referred to as trans-generational immune priming (TgIP) in insects. TgIP can influence the evolution of both host immune traits and pathogen virulence. The host ecology and its environmental pathogen load can in turn shape the evolution of TgIP. Therefore, the functional limits of TgIP and the conditions under which it is observed need to be explored in a variety of species. Majority of empirical studies addressing this phenomenon focus on non-pathogenic infections of parents, implemented via either the use of pathogen substitutes (viz., liposaccharide molecules), or the use of sub-lethal infection doses, by using inactivated pathogens to infect the parents. We tested if exposing parents to pathogenic bacterial infections affects offspring susceptibility to homologous (same pathogen as the one used to infect the parents) and heterologous (different pathogen than the one used to infect the parents) infection challenges in Drosophila melanogaster. We found that parental infection increases offspring survival following a homologous challenge. Similar effects were seen in the case of heterologous challenges too, with the breadth of cross-reactivity being dependent on the pathogen used to infect the parents. Parental infection also improves offspring capacity to restrict systemic pathogen proliferation following a homologous challenge, suggesting increased disease resistance. Parental infection has no effect on offspring reproduction, either in presence or absence of infection, suggesting an absence of associated costs and limited benefit of trans-generational immune priming. Overall, we have demonstrated that parental infection helps offspring better counter infection challenges in D. melanogaster without incurring any measurable costs.

evolutionary biology↗

bioRxiv2023

Nature and location of modifier alleles determine the resolution of intralocus sexual conflict

When selection favours different levels of expression for a shared trait in males and females, the population is said to be in Intralocus Sexual Conflict (IaSC). In a landmark study, Connallon and Clark (2010) showed that modifiers (alleles at a different locus that alter the expression of the trait under IaSC in a sex-specific manner), effectively resolve IaSC. Their model assumed that modifier alleles are "perfect"; i.e., they fully rescue the harmful effects of the deleterious allele while leaving the positive effects of the beneficial allele unaffected. In the present study, we relaxed this assumption to include more realistic "imperfect" modifier alleles. Imperfect modifiers are those that reduce the expressions of both detrimental allele and beneficial allele to different extents in a given sex. We also ask whether autosomes or X chromosomes are more conducive to resolution of IaSC. Our results suggest that the resolution of IaSC may not always be guaranteed when the modifier allele is "imperfect." Interestingly, IaSC gets resolved more easily on autosomes only when modifier alleles are "perfect" or near "perfect" in concordance with the assumption made by Connallon and Clark (2010). However, in general, X chromosomes are more conducive to the resolution of IaSC.

evolutionary biology↗

bioRxiv2022

Selection for increased post-infection survival ameliorates mating induced immune suppression in Drosophila melanogaster females

Sexual activity (mating) negatively affects immune function in various insect species, in both sexes. In the experiments reported in this manuscript, we tested if hosts adapted to regular pathogen challenges are less susceptible to mating induced immune suppression, using experimentally evolved Drosophila melanogaster populations selected for increased post-infection survival when infected with a Gram-positive bacterium, Enterococcus faecalis. Mating increased susceptibility of females to bacterial pathogens, but in a pathogen specific manner. Mating-induced increase in susceptibility was also affected by host evolutionary history, with females from selected populations exhibiting similar post-infection survival irrespective of mating status, while females from control populations became more susceptible to bacterial infections after mating. Post-infection survival of males, irrespective of their evolutionary history, was not affected by their mating status. We therefore conclude that hosts evolved to better survive bacterial infections are also better at resisting mating-induced increase in susceptibility to infections in Drosophila melanogaster.

evolutionary biology↗

bioRxiv2022

Correlated responses to experimental evolution of increased post-infection survival in Drosophila melanogaster: Life-history trade-offs and reaction to novel stressors

Evolution of increased immune defence is often limited by costs: correlated changes in other traits (viz. life-history traits) that otherwise reduce the fitness of the host organisms. Experimental evolution studies are useful for understanding the evolution of immune function, and correlated changes in other traits. We experimentally evolved replicate Drosophila melanogaster populations to better survive infection challenge with an entomopathogenic bacteria, Enterococcus faecalis. Within 35 generations of forward selection, selected populations showed marked increase in post-infection survival compared to ancestrally paired controls. We next measured various life-history traits of these populations. Our results show that the selected populations do not differ from control populations for larval development time and body weight at eclosion. No difference is also observed in case of fecundity and longevity (following the acute phase of infection), either when the flies are subjected to infection or when the flies were uninfected; although infected flies from all populations die much earlier compared to uninfected flies. Selected flies and control flies are also equally good at surviving abiotic stressors (starvation and desiccation), although infected flies from all populations are more susceptible to stress than uninfected flies. Therefore, we conclude that (a) D. melanogaster populations can rapidly evolve to be more immune to infection with E. faecalis; (b) evolution of increased defence against E. faecalis entails no life-history cost for the hosts; and (c) evolving defence against a biotic threat (pathogen) does not make flies more resistant to abiotic stressors.

evolutionary biology↗

bioRxiv2022

Pathogen dependence and inter-individual variability of post-infection reproductive fitness in Drosophila melanogaster

In the experiments reported in this manuscript, we explore the effect of bacterial infections on the reproductive output of Drosophila melanogaster females. Canonical view of host-pathogen interactions supposes two possible outcomes. Because of immune defence being an energy/resource intensive function, an infected female reallocates resources away from reproductive processes and towards immune defence, therefore compromising its reproductive output. Alternatively, faced with impending mortality, an infected female increases its reproductive output to compensate for lost opportunities of future reproduction. We tested if pathogen identity, infection outcome (survival vs. death), and/or time of death determines the reproductive output of females infected with three bacterial pathogens. Our results show that pathogen identity is a reliable predictor of population level response of infected females but does not reliably predict the behaviour of individual females. Additionally, females succumbing to infection exhibit greater variability in reproductive output, compared to both survivors and controls, but this variability is not explained by either the time of death or the identity of the infecting pathogen. Furthermore, survivors of infection have reproductive output similar to control females.

evolutionary biology↗

bioRxiv2022

Discordant effects of resource limitation on host survival and systemic pathogen growth in Drosophila-bacteria infection models: resistance vs. tolerance

In the experiments presented here, we explore the effect of resource limitation, in form of starvation (which leads to decrease in accessible resources and depletion of reserves) and sexual activity (which leads to reallocation of resources from somatic defence towards reproduction), on immune function of female Drosophila melanogaster flies. We infected females with five bacterial pathogens and measured their post-infection survival when subjected to either starvation or sexual activity (mating). Additionally, we measured within host pathogen levels in case of three of these pathogens. Based on previous literature, we predicted that both modes of resource limitation will increase post-infection mortality, but only sexual activity will lead to increase of pathogen load (because of compromised immune function), while starvation will either not affect or reduce pathogen loads (because of reduced availability of resources for the pathogen to proliferate within the host). Our results indicate that both starvation and sexual activity can lead to increased within-host pathogen levels, in addition to increased post-infection mortality, but in a pathogen-specific manner.

ecology↗

bioRxiv2022

Cold stress upregulates the expression of heat shock proteins and Frost genes, but evolution of cold stress resistance is apparently not mediated through either heat shock proteins or Frost genes in the cold stress selected population

The ability to thermal adaptation can alter insects reproductive traits and physiologic response. A number of studies in Drosophila documented the higher expression levels of heat shock proteins (Hsps) and Frost (Fst) genes during the recovery phase of cold shock treatment and suggested that higher expression levels of these genes and lipids can protect from cold stress. However, these genes expression and cold adaptation have not been well studied. Therefore, understanding the molecular and biochemical basis of cold adaptation, we examined the levels of lipid and expression patterns of Hsp22, Hsp23, Hsp40, Hsp68, Hsp70, Hsp 83, and Fst genes under the cold stress or benign condition in the populations of Drosophila melanogaster selected for increased resistance to cold shock. We observed the significant up-regulation of Hsp22, Hsp23, Hsp40, Hsp68, and Fst genes in the FSB and FCB populations during the recovery phase post cold shock compared to the no shock condition. However, there was not a significant change in the transcript levels of these genes between FSB and FCB under both the cold stress or no shock condition. Additionally, we noticed higher total lipid levels in the females from cold shock treatment than those from no shock treatment. This finding suggests that cold selected populations have different mechanisms to sustain cold stress.

evolutionary biology↗

bioRxiv2022

Effect of larval diet on adult immune function is contingent upon selection history and host sex in Drosophila melanogaster

Mounting an immune response requires a considerable energy investment by the host. This makes expression of immune phenotypes susceptible to changes in availability of resources. There is ample evidence in scientific literature to suggest that hosts become more vulnerable to infection by pathogens and parasites when access to nutrition is limited. Using populations of Drosophila melanogaster experimentally evolved to better survive bacterial infections, we explore if host selection history influences host response to resource deprivation in terms of immune function. We find that when reared on a suboptimal diet (both in larval and adult stages), adult flies from evolved populations are still more immune to infections compared to flies from control populations. Furthermore, we observe a sex-dependent effect of interaction between selection history and diet on immune function. We thus conclude that immune function of hosts adapted to pathogen challenge is less affected by resource limitation compared to non-adapted hosts.

evolutionary biology↗

bioRxiv2022

Increasing adult density compromises anti-bacterial defense in Drosophila melanogaster

The density-dependent prophylaxis hypothesis predicts that risk of pathogen transmission increases with increase in population density, and in response to this, organisms mount a prophylactic immune response when exposed to high density. This prophylactic response is expected to help organisms improve their chances of survival when exposed to pathogens. Alternatively, organisms living at high densities can exhibit compromised defense against pathogens due to lack of resources and density associated physiological stress; the density stress hypothesis. We housed adult Drosophila melanogaster flies at different densities and measured the effect this has on their post-infection survival and resistance to starvation. We find that flies housed at higher densities show greater mortality after being infected with bacterial pathogens, while also exhibiting increased resistance to starvation. Our results are more in line with the density-stress hypothesis that postulates a compromised immune system when hosts are subjected to high densities.

evolutionary biology↗

bioRxiv2021

Recurrent evolution of cross-resistance in response to selection for improved post-infection survival in Drosophila melanogaster

The host susceptibility to one pathogen can decrease, increase, or remain unaffected by virtue of the host evolving resistance towards a second pathogen. Negative correlations between a host susceptibility to different pathogens is an often-cited explanation for maintenance of genetic variation in immune function determining traits in a host population. In this study, we investigated the change in susceptibility of Drosophila melanogaster flies to various novel bacterial pathogens after being experimentally selected for increased resistance to one particular bacterial pathogen. We independently selected flies to become more resistant towards Enterococcus faecalis and Pseudomonas entomophila, and baring a few exceptions the evolved populations exhibited cross-resistance against the range of pathogens tested in the study. Neither the identity of the native pathogen nor the host sex was major determining factors in predicting the pattern of cross-resistance exhibited by the selected populations. We therefore report that a generalized cross-resistance to novel pathogens can repeatedly evolve in response to selection for resistance against a single pathogen.

evolutionary biology↗

bioRxiv2021

Investigating the interaction between inter-locus and intra-locus sexual conflict using hemiclonal analysis in Drosophila melanogaster

Divergence in the evolutionary interests of males and females leads to sexual conflict. Traditionally, sexual conflict has been classified into two types: inter-locus sexual conflict (IeSC) and intra-locus sexual conflict (IaSC). IeSC is modeled as a conflict over outcomes of intersexual reproductive interactions mediated by loci that are sex-limited in their effects. IaSC is thought to be a product of selection acting in opposite directions in males and females on traits with a common underlying genetic basis. While in their canonical formalisms IaSC and IeSC are mutually exclusive, there is growing support for the idea that the two may interact. Empirical evidence for such interactions, however, is limited. Here, we investigated the interaction between IeSC and IaSC in Drosophila melanogaster. Using hemiclonal analysis, we sampled 39 hemigenomes from a laboratory-adapted population of D. melanogaster. We measured the contribution of each hemigenome to adult male and female fitness at three different intensities of IeSC, obtained by varying the operational sex-ratio. Subsequently, we estimated the intensity of IaSC at each sex-ratio by calculating the intersexual genetic correlation for fitness and the proportion of sexually antagonistic fitness-variation. Our results indicate a statistically non-significant trend suggesting that increasing the strength of IeSC ameliorates IaSC in the population.

evolutionary biology↗

bioRxiv2020

Evolutionary genetics of Drosophila melanogaster immunity: role of the X chromosome and sex-specific dominance

Intralocus Sexual Conflict (IaSC) ensues when males and females of the same species experience divergent selection on shared traits. A large number of traits have been implicated in IaSC and there is growing evidence for sexual antagonism associated with immunity. X chromosomes are thought to be hotspots of sexually antagonistic genetic variation and have been shown to harbour substantial immunity-related genetic variation. Here, using interpopulation crosses and cytogenetic cloning, we investigated the role of the X chromosome in improved immune response of laboratory populations of the fruit-fly Drosophila melanogaster selected against systemic infection by Pseudomonas entomophila. We could not detect any contribution of the X chromosome in the evolved immune response of our selected populations. However, we found strong evidence of sex-specific dominance related to immunity in our populations. Our results indicate that alleles that confer a superior immune response to the selected populations are, on average, partially dominant in females but partially recessive in males. We argue that sex-specific dominance over immunity evolved as a by-product of sexually antagonistic selection in the wild ancestors of our populations. We also highlight sex-specific dominance as a potential mechanism of sex differences in immunity, with population-level sex differences primarily driven by sex differences in heterozygotes.

evolutionary biology↗

bioRxiv2020

Evolutions of reproductive traits have no life-history associated cost in Drosophila melanogaster selected for cold resistance

In insect species like Drosophila melanogaster, the ability to evolve greater resistance or evolution of certain traits under specific environmental conditions leads to energy trade-offs with other important life-history traits. A number of studies from multiple fields have documented the life-history associated cost. However, no known studies have assessed the life-history associated cost with evolved reproductive traits and increase egg viability in cold shock selected population. To explore this, we used replicate populations of D. melanogaster that have evolved reproductive traits and egg viability in response to increased resistance to non lethal cold shock. To assess life-history cost; we measured longevity, life time fecundity, Larvae to adults development time, and larvae to adults survival. We found that there were no significant differences in longevity, life time fecundity, larvae to adults survival, and male body weight between the selected and control populations. However, selected populations have significantly longer pre adults developmental time compared to their control population. Females from the selected populations were bigger in size compared to the control populations. These findings suggest that there is no life-history cost associated with the evolution of greater resistance in the aspect of faster recovery of egg viability and reproductive traits post cold-shock. It quite possible the cost of the evolution of reproductive traits and egg viability in response to cold shock resistant is paid in terms of reduced resistance to other stresses

evolutionary biology↗