Larval Competition Research Articles

Asymmetric evolution of egg laying behavior following reciprocal host shifts by a seed-feeding beetle

Colonization of new environments can lead to rapid changes in fitness-related traits. For herbivorous insects, switching to a new host plant can be comparable to invading a new habitat. Behavioral, physiological, and life-history traits commonly vary among insect populations associated with different plants, but how host shifts cause trait divergence is often unclear. We investigated whether experimental host shifts would modify a key insect trait, egg-laying behavior, in a seed beetle. Beetle populations associated long-term with either a small-seeded host (mung bean) or a large-seeded host (cowpea) were switched to each other’s host. After 36–55 generations, we assayed three aspects of oviposition behavior known to differ between the mung bean- and cowpea-adapted populations. Responses to the host shifts were asymmetrical. Females from lines transferred from mung bean to cowpea produced less uniform distributions of eggs among seeds, were more likely to add an egg to an occupied seed, and were more likely to “dump” eggs when seeds were absent. These lines thus converged toward the cowpea-adapted population. In contrast, the reciprocal host shift had no effect; oviposition behavior was unchanged in lines transferred from cowpea to mung bean. We suggest that these results reflect an asymmetry in the fitness consequences of each host shift, which in turn depended on differences in larval competitiveness in the original populations. Interactions among multiple fitness components are likely to make evolutionary responses less predictable in novel environments.

Infections of Wolbachia may destabilize mosquito population dynamics

Recent efforts in controlling mosquito-borne diseases focus on biocontrol strategies that incapacitate pathogens inside mosquitoes by altering the mosquito's microbiome. A case in point is the introduction of Wolbachia into natural mosquito populations in order to eliminate Dengue virus. However, whether this strategy can successfully control vector-borne diseases is debated; particularly, how artificial infection affects population dynamics of hosts remains unclear. Here, we show that natural Wolbachia infections are associated with unstable mosquito population dynamics by contrasting Wolbachia-infected versus uninfected cage populations of the Asian tiger mosquito (Aedes albopictus). By analyzing weekly data of adult mosquito abundances, we found that the variability of the infected populations is significantly higher than that of the uninfected. The elevated population variability is explained by increased instability in dynamics, as quantified by system nonlinearity (i.e., state-dependence). In addition, predictability of infected populations is substantially lower. A mathematical model analysis suggests that Wolbachia may alter mosquito population dynamics by modifying larval competition of hosts. These results encourage examination for effects of artificial Wolbachia establishment on mosquito populations, because an enhancement of population variability with reduced predictability could pose challenges in management. Our findings have implications for application of microbiome alterations in biocontrol programs.

Life-shortening Wolbachia infection reduces population growth of Aedes aegypti

Wolbachia bacteria are being introduced into natural populations of vector mosquitoes, with the goal of reducing the transmission of human diseases such as Zika and dengue fever. The successful establishment of Wolbachia infection is largely dependent on the effects of Wolbachia infection to host fitness, but the effects of Wolbachia infection on the individual life-history traits of immature mosquitoes can vary. Here, the effects of life-shortening Wolbachia (wMelPop) on population growth of infected individuals were evaluated by measuring larval survival, developmental time and adult size of Aedes aegypti in intra- (infected or uninfected only) and inter-group (mixed with infected and uninfected) larval competition assays. At low larval density conditions, the population growth of wMelPop infected and uninfected individuals was similar. At high larval densities, wMelPop infected individuals had a significantly reduced population growth rate relative to uninfected individuals, regardless of competition type. We discuss the results in relation to the invasion of the wMelPop Wolbachia infection into naturally uninfected populations.

Weak Larval Competition Between Two Invasive Mosquitoes Aedes koreicus and Aedes albopictus (Diptera: Culicidae).

Aedes (Hulecoeteomyia) koreicus (Edwards) and Aedes (Stegomyia) albopictus (Skuse) are two invasive mosquito species well established in northeastern Italy, and these two species may co-occur in artificial larval habitats such as tires, buckets, drums, and catch basins. Because Ae. albopictus has been shown experimentally to be a superior competitor to several mosquito species, we investigated larval competition between Ae. koreicus and Ae. albopictus using two diet levels (low level and high level) and 10 Ae. albopictus: Ae. koreicus density combination levels (30:0, 60:0, 15:15, 30:30, 10:20, 20:10, 20:40, 40:20, 0:60, and 0:30). A multivariate analysis (MANOVA) demonstrated a significant effect of the density combination on Ae. koreicus survivorship, female development time, and female wing length considered simultaneously in low-level diet and high-level diet treatments. Pairwise comparisons across low-level diet treatments showed a significant reduction of Ae. koreicus survivorship in 20:10 combination treatments (i.e. 20 Ae. albopictus and 10 Ae. koreicus larvae) compared to 10:20, 20:40, and 30:30 combination treatments, while no difference was detected for Ae. albopictus between density combination treatments. Furthermore, Ae. albopictus developed faster than Ae. koreicus regardless of diet and density combination treatments. Our results show weak larval competition between Ae. koreicus and Ae. albopictus with a slight advantage of the latter species. On the other hand, the presence of Ae. albopictus seems to favor the emergence of larger Ae. koreicus females. We suggest that factors such as habitats preferences or seasonal distributions may be determinant for the invasion success of Ae. koreicus.

Discrimination of infested cotton squares by females of Anthonomus grandis

The avoidance of infested squares of Gossypium hirsutum as oviposition substrate by females of Anthonomus grandis was studied following two approaches. First, the preference for oviposition in infested versus non-infested squares was studied in laboratory. Second, the distribution of ovipositions by A. grandis in nature was analyzed in cotton plots from Argentina. In addition, the consequences of multiple ovipositions were assessed in terms of emergence rate, adult weight and sex ratio. In the laboratory, the number of ovipositions was significantly higher in non-infested than in infested squares. Likewise, females were found to reject infested squares more frequently than non-infested squares. In the field, oviposition pattern fitted a uniform distribution for squares collected from the ground, while the distribution in squares sampled from the plant fitted random and uniform distributions. This suggests that oviposition decisions could be dynamic and change with the infestation conditions. Multiple ovipositions resulted in the elimination of competing larvae between L1 and L2 instars. The weight of the individual that develops to the adult stage was negatively affected by the level of larval competition, and the sex ratio deviated toward females. Our results suggest that females of A. grandis tend to avoid already infested squares. This behavior would allow reducing the levels of intraspecific competition, which we also found can seriously affect the development of their progeny. A deeper knowledge of the oviposition behavior of A. grandis could contribute to developing control methods against this important cotton pest.

Possible coexistence of native and exotic parasitoids and their impact on control of Halyomorpha halys

Introduction of exotic natural enemies for biological control of invasive pests may disrupt existing ecological interactions, which may influence the outcome of biological control introductions. The interactions between Asian egg parasitoids, proposed as classical biological control agents of the highly polyphagous invasive pest Halyomorpha halys (Stal), and parasitoids native to the introduced area are largely unknown. Therefore, adult and larval interspecific competition between the exotic Trissolcus japonicus (Ashmead) and the European Anastatus bifasciatus (Geoffroy) was assessed (1) by observing aggressive interactions between adults of the two species following parasitization and (2) by providing each parasitoid species with previously parasitized H. halys egg masses at various time intervals. The results suggest that T. japonicus and A. bifasciatus engage in counterbalance competition, with the former being a superior extrinsic competitor (egg guarding and aggressiveness) and the latter being a superior intrinsic competitor (successful development from multiparasitized eggs of all ages). We suggest that the presence of T. japonicus is unlikely to have a negative impact on A. bifasciatus, and that those two species can coexist and potentially act synergistically in the biological control of H. halys.

Pathogen's level and parasitism rate in Ips typographus at high population densities: importance of time

AbstractWe compared the levels of pathogen infection in parental beetles, parasitism of the offspring, abundance of predators and breeding performance success of univoltine populations of Ips typographus in plots characterized by short‐term (2–3 years) outbreaks vs. those with long‐term (>10 years) outbreaks on two localities at ca. 1100 m altitude in the Šumava Mts. The numbers of I. typographus were high in all plots, whether the plots were characterized by long‐term outbreaks or short‐term outbreaks. The numbers of maternal galleries in the sample areas ranged from 300 to 400 per m2. The density of parental beetle galleries, abundance of surviving specimens of I. typographus, and length of maternal galleries did not differ between plots. The short‐term outbreaks had only fewer ectoparasitoids of I. typographus and a lower percentage of parasitism and infection level of Mattesia schwenkei than the long‐term outbreaks even though the maternal gallery densities and beetle production were the same. The most mortality appeared to be caused by intraspecific larval competition, and the identical reproductive success in plots with short‐term and long‐term outbreaks indicates that the negative feedback resulting from parasitoids and entomopathogens does not substantially reduce beetle numbers. Although entomopathogenic fungi as Beauveria bassiana occur naturally in the galleries of spruce bark beetles, there was no evidence of its presence in the studied population. The low levels of predation and/or parasitism in both kinds of plots indicate that natural enemies did not play a significant role in reducing outbreak numbers of I. typographus.

Population dynamics of Telenomus fariai (Hymenoptera: Scelionidae), a parasite of Chagas' disease vectors. V. Parasite size and vital space.

Some ecological aspects of the developmental process of the endophagous egg parasite Telenomus fariai when reared in Triatoma phyllosoma pallidiPennis eggs, have been investigated. It was shown that mortality among pupae and last instar larvae does not account for the constancy in parasite progeny emergence per host egg, suggesting that if there is any population regulation mechanism based on larval competition, it would be operating among the youngest instars. Simple and multiple linear correlations between parasite size and host egg volume, and progeny production per host egg show that both factors are relevant in determing parasite size, but the effect of progeny production per host egg is on the average three times as important as host egg volume. Vital space (mm3 of host egg volume available per parasite) shows an extremely high correlation (0.970) with parasite size. The elasticity function of vital space on parasite size shows that with increasing values of the former, there is always a higher percentile increase of the latter.

Testing for intraspecific and interspecific larval competition between two anurans: Hyla savignyi and Bufotes viridis

Intraspecific and interspecific competition can be important factors affecting anuran tadpoles in temporary pools. We focus on two co-occurring anuran species that are of conservation concern in Israel and may negatively interact: Bufotes viridis (Laurenti, 1768) and Hyla savignyi (Audouin, 1829). We conducted a replacement design mesocosm experiment to examine intraspecific and interspecific competition between tadpoles of these two species. Plastic tubs were assigned to five replacement design treatments: 0 Hyla + 20 Bufotes; 0 Hyla + 40 Bufotes; 20 Hyla + 20 Bufotes; 20 Hyla + 0 Bufotes; and 40 Hyla + 0 Bufotes, and a control with no tadpoles which was used to test for effects of the tadpoles on invertebrate community structure. While H. savignyi was significantly affected by intraspecific density, with smaller body mass and longer time to metamorphosis at the high-density treatment, B. viridis showed no intraspecific or interspecific density-dependent effects. However, B. viridis time to metamorphosis was negatively correlated with water temperature, while its survivorship was positively correlated with water temperature. The tadpoles affected neither abundance nor taxon richness of invertebrates. Our results suggest that stronger intraspecific competition than interspecific competition may contribute to the common co-occurrence of these two anurans in the same pools.

Aedes aegypti Control Through Modernized, Integrated Vector Management.

Introduction: In the context of the ongoing, unprecedented Zika virus outbreak in the Americas, the World Health Organization has expressed its support for developing and up-scaling three novel approaches to controlling the Aedes aegypti mosquito: the Sterile Insect Technique (SIT), the Release of Insects carrying Dominant Lethal genes (RIDL) and the release of Wolbachia-infected mosquitoes. Whereas the former two approaches are temporary insect population suppression strategies, Wolbachia infection is a self-sustaining, invasive strategy that uses inherited endosymbiotic bacteria to render natural mosquito populations arbovirus resistant.Methods: A mathematical model is parameterised with new, Brazilian field data informing the mating competitiveness of mass-reared, released insects; and simulations compare and contrast projections of vector control achieved with the alternative approaches.Results: Important disadvantages of Wolbachia and SIT are identified: both strategies result in mosquitoes ovipositing non-viable eggs and, by alleviating intense larval competition, can cause an overall increase in survival to the adult stage. However, it is demonstrated that strategically combining the suppression methods with Wolbachia can generate a sustained control while mitigating the risks of inadvertent exacerbation of the wild mosquito population.Discussion: This initial analysis demonstrates potential for good synergy when combining novel mosquito approaches in a modernized, integrated vector control programme.

Females trade off the uncertainty of breeding resource suitability with male quality during mate choice in an anuran

In many species, females may be particularly selective about the expected direct benefits of choosing a potential mate or the male's genetic contribution to their offspring. Growing evidence suggests that female choosiness can also be influenced, for instance, by local abiotic factors, the social environment or the presence of heterospecifics. In amphibians that breed in highly temporary ponds with limited trophic resources (such as the yellow-bellied toad, Bombina variegata), competition during larval development may have a strong impact on the fitness of offspring. Accordingly, one might expect females to apply hierarchical decision making, balancing intraspecific competition risks during larval growth against the relative indirect benefits associated with the quality of the male. To investigate this issue, we conducted experiments in seminatural enclosures to test whether the preference of yellow-bellied toad females for good call attractiveness (determined by fundamental frequency) is affected by the risk of larval competition within the pond occupied by the callers. Overall, our results showed that females have a preference for low-frequency calls when prior information does not enable them to assess the relative quality of ponds. However, when prior information enables females to unambiguously determine relative pond quality, females appear to apply hierarchical decision making in which the quality of a pond prevails over call cues related to the quality of the male.

Aggressive Behavior in Olive Fruit Fly Females: Oviposition Site Guarding against Parasitic Wasps

Among Tephritidae flies, the females display agonistic behavior to maintain single oviposition sites and reduce larval competition for food. In the olive fruit fly, Bactrocera oleae, female-female aggressive interactions are characterized by reciprocal wing waving, chasing, head butting and boxing with forelegs. Little is known on tephritid aggressive behaviors directed towards natural enemies, with special reference to parasitoids attacking their young instars. In this study, we quantified the aggressive behavior of B. oleae females guarding their oviposition site against the braconid parasitoid Psyttalia concolor. The fly aggressive behavior displayed against the parasitoids was compared that directed towards paper dummies mimicking P. concolor adults. When a P. concolor female came close (<20 mm) to a B. oleae female guarding the oviposition site, the 91.67% of the flies displayed wing-waving, the 63.34% chased the parasitoid, the 45% showed head-butting, while boxing was observed only in the 26.67% of the aggressions. When paper dummies were tested, only the 66.67% of the flies displayed wing-waving, the 8.33% performed chasing, followed by head butting (5.00%) and boxing (3.33%). B. oleae displayed longer aggression bouts towards live wasps over dummies. Overall, this is the first evidence pointing out that tephritid aggressive acts, besides their role in intraspecific interactions, were also highly effective to displace parasitic wasps from the fly oviposition site. Further research on potential consequences on fitness traits arising from the above-discussed behaviors, as well as on parasitoid learning-mediated responses to tephritid aggressions, is urgently required.

Larval competition risk shapes male–male competition and mating behavior in an anuran

Mate preference was long assumed to be static and open-ended. However, a growing body of evidence actually suggests that the predominant factor in mate choice fluctuates due to the context dependence of the factors involved in sexual selection. In particular, fluctuation in the local environment, the density of individuals, and the presence of heterospecifics can all alter the strength, form, or direction of sexual selection by shaping the fitness costs and benefits of the traits that mediate male–female interactions. Amphibians constitute useful biological models to examine context dependence in sexual selection as the availability of suitable breeding resources may significantly impact the cost–benefit trade-off between mating strategies. Using an experimental approach, we examined how the risk of larval competition in breeding ponds affects pond occupancy, male–male spacing behavior, and spawning decisions in an anuran, the yellow-bellied toad (Bombina variegata). Then, we examined how female mate choice is affected by male body condition and how the risk of larval competition might influence females when choosing a mate. Our results indicate that male pond preference is strongly affected by the presence of conspecific tadpoles. Males preferentially selected ponds free of tadpoles, and spawning mainly occurred in these same ponds. This preference influenced male spacing behavior by enhancing the proximity of competing males when the availability of good-quality sites was experimentally manipulated, which had further significant consequences on females’ choice of mate. The article also discusses the evolutionary causes and consequences of such context-dependent mate choice in amphibians and beyond.

Biotic Resistance to an Alien Amphibian: Larval Competition between Japanese Frogs and Invasive Cane Toads.

Understanding negative effects of native species on introduced taxa may suggest novel ways to control the invasive species by enhancing such effects. Previous studies have reported that the larvae of invasive cane toads (Rhinella marina) are suppressed by competition with the larvae of native anurans in Australia, but not in North America. We conducted laboratory trials to measure the effect of exposure to the larvae of Japanese frogs (Microhyla ornata, Fejervarya sakishimensis, Rhacophorus owstoni) on rates of survival, growth and development of cane toad tadpoles in Ishigaki Island, in southern Japan. Survival rates were not affected by native species, but competition with Dicroglossids and Rhacophorids (but not Microhylids) strongly reduced rates of growth and development in the tadpoles of cane toads. Dicroglossid tadpoles also reduced the body condition to toad tadpoles in addition to effects on SVL and mass. Encouraging populations of native frogs in toad-invaded areas of Japan thus may help to reduce the numbers of invasive cane toads.

Assessment of Aedes albopictus (Skuse) (Diptera: Culicidae) clutch size in wild and laboratory populations.

Aedes albopictus (Skuse) is an invasive mosquito species found across the southern U.S. with range expansion into many northern states. Intra- and interspecific larval competition have been evaluated for Ae. albopictus with respect to subsequent adult size, immature and adult survivability, and its capacity to vector pathogens as an adult. However, limited data are available on egg production as related to larval rearing conditions. Because Ae. albopictus is a container-inhabiting mosquito that oviposits in resource-limited habitats, it is found under variable density-dependent conditions. Therefore, we examined the impact of specific rearing conditions on Ae. albopictus clutch size and adult body size; comparing the egg production values and wing lengths from known developmental densities to those from field-collected populations. Field populations varied significantly among collection sites in mean clutch size (23 to 46). These clutch sizes were comparable to the mean clutch sizes of females reared at the larval densities of nine (20 eggs) and three (53 eggs) larvae per 3 ml of water in the laboratory. Field populations experienced density-dependent effects impacting adult mosquito size. Mosquitoes from the four sample sites had mean wing lengths of 1.99, 2.47, 2.51, and 2.54 mm, which were less than the mean wing length of mosquitoes reared at larval densities of three larvae per 3 ml of water (2.57 mm).

The influence of larval competition on Brazilian Wolbachia-infected Aedes aegypti mosquitoes.

BackgroundWith field releases starting in Brazil, particular interest must be given to understanding how the endosymbiotic bacterium Wolbachia pipientis affects Aedes aegypti mosquitoes with a Brazilian genetic background. Currently, there is limited information on how the bacterium affects phenotypic traits such as larval development rate, metabolic reserves and morphometric parameters in Ae. aegypti. Here, we analyze for the first time, the effect of Wolbachia on these key phenotypes and consider how this might impact the potential of the bacterium as a disease control agent in Brazil.MethodsWe examined the influence of the wMel strain of Wolbachia in laboratory Ae. aegypti with a Brazilian genetic background, reared under different larval densities. Pupae formation was counted daily to assess differences in development rates. Levels of metabolic reserves and morphometric parameters were assessed in adults resulting from each larval condition.ResultswMel infection led to more rapid larval development at higher densities for both males and females, with no effect under less crowded conditions in females. Infection also led to reduced body size at both high and low density, but not at intermediate density, although the scale of this difference was maintained regardless of larval density, in comparison to uninfected individuals. Wing shape also varied significantly between infected and uninfected mosquitoes due to larval density. Glycogen levels in uninfected mosquitoes decreased under higher larval density, but were consistently high with Wolbachia infection, regardless of larval density.ConclusionsWe demonstrate that the wMel Wolbachia strain can positively influence some important host fitness traits, and that this interaction is directly linked to the conditions in which the host is reared. Combined with previously published data, these results suggest that this Wolbachia strain could be successfully used as part of the Eliminate Dengue Program in Brazil.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1559-5) contains supplementary material, which is available to authorized users.

Host specialisation and competition asymmetry in coleopteran parasitoids.

When specialists and generalists compete for a limited resource, specialists are more constrained because they are less likely to find an alternative resource. In parasitoids with overlapping host ranges, asymmetric competition should therefore exist where specialists are more likely to win the host in a contest. Competition between parasitoids has been studied mostly in hymenopterans. In hymenopteran parasitoid wasps, females must reach the host to lay their eggs and can thus strongly influence the outcome of competition between future offspring by killing eggs or larvae of competitors. We studied competition between the free-ranging larvae of two sympatric coleopteran parasitoid rove beetles (one specialist, Aleochara bilineata and a generalist, Aleochara bipustulata) with overlapping host ranges competing in agricultural fields for pupae of the cabbage root fly. In these species, females lay their eggs in the soil, then first instars find the host where they will develop as solitary parasitoids and deal with potential competitors. Because adult longevity and fecundity favour the generalist, we postulated that first instars of the specialist would be superior larval competitors. Accordingly, we studied the outcome of encounters between first instars of the two species provided with a single host. Irrespective of its release prior to or simultaneously with its generalist competitor, the larva of the specialist most often won. Moreover, specialist larvae still won half of the encounters when generalist larvae were given a 24-h advantage. This might explain the coexistence of the two species in the field.

Impact of inter‐ and intra‐specific competition among larvae on larval, adult, and life‐table traits of Aedes aegypti and Aedes albopictus females

Few studies have taken a comprehensive approach of measuring the impact of inter- and intra-specific larval competition on adult mosquito traits. In this study, the impact of competition Aedes aegypti and A. albopictus was quantified over the entire life of a cohort.Competitive treatments affected hatch-to-adult survivorship and development time to adulthood of females for both species, but affected median wing length of females only for A. albopictus. Competitive treatments had no significant effect on the median adult female longevity nor were there any effects on other individual traits related to bloodfeeding and reproductive success.Analysis of life table traits revealed no effect of competitive treatment on net reproductive rate (R0) but there were significant effects on cohort generation time (Tc) and cohort rate of increase (r) for both species.Inter-specific and intra-specific competition among Aedes larvae may produce individual and population-level effects that are manifest in adults; however, benign conditions may enable resulting adults to compensate for some impacts of competition, particularly those affecting blood feeding success, fecundity, and net reproductive rate, R0. The effect of competition, therefore, affects primarily larva - to - adult survivorship and larval development time, which in turn impact the cohort generation time, Tc and ultimately cohort rate of increase, r.The lack of effects of larval rearing environment on adult longevity suggests that effects on vectorial capacity due to longevity may be limited if adults have easy access to sugar and blood meals.

The Effects of Larval Habitat Quality on Aedes albopictus Skip Oviposition.

Aedes albopictus is an invasive mosquito species that transmits human-disease-causing pathogens. It is a container-inhabiting species that oviposits in resource-limited habitats. To mitigate larval competition, Ae. albopictus females may choose to distribute eggs from a single gonotrophic cycle among multiple containers through skip oviposition. With the use of individual females released in indoor and outdoor caged trials, we evaluated the oviposition choices made by gravid Ae. albopictus offered larval habitats with different qualities. Our results demonstrate that Ae. albopictus performs skip oviposition and that the degree of egg distribution is related to the quality of the larval habitat. In a 4-choice arena, individual Ae. albopictus oviposited in fewer containers when presented with ovisites of high-quality larval habitat (uncrowded conditions) compared with oviposition in low-quality (crowded conditions) larval habitats. Additionally, the females selectively oviposited in high-quality habitats when offered both low- and high-quality habitats, but distributed eggs more evenly among multiple high-quality habitats. Our results have important implications for mosquito management plans that include the use of lethal ovitraps, as well as the role of this behavior in distribution of disease-causing pathogens.

Reduction in the cumulative effect of stress-induced inbreeding depression due to intragenerational purging in Drosophila melanogaster.

Environmental stress generally exacerbates the harmful effects of inbreeding and it has been proposed that this could be exploited in purging deleterious alleles from threatened inbred populations. However, understanding what factors contribute to variability in the strength of inbreeding depression (ID) observed across adverse environmental conditions remains a challenge. Here, we examined how the nature and timing of stress affects ID and the potential for purging using inbred and outbred Drosophila melanogaster larvae exposed to biotic (larval competition, bacteria infection) and abiotic (ethanol, heat) stressors compared with unstressed controls. ID was measured during (larval survival) and after (male mating success) stress exposure. The level of stress imposed by each stressor was approximately equal, averaging a 42% reduction in outbred larval survival relative to controls. All stressors induced on average the same ID, causing a threefold increase in lethal equivalents for larval survival relative to controls. However, stress-induced ID in larval success was followed by a 30% reduction in ID in mating success of surviving males. We propose that this fitness recovery is due to 'intragenerational purging' whereby fitness correlations facilitate stress-induced purging that increases the average fitness of survivors in later life history stages. For biotic stressors, post-stress reductions in ID are consistent with intragenerational purging, whereas for abiotic stressors, there appeared to be an interaction between purging and stress-induced physiological damage. For all stressors, there was no net effect of stress on lifetime ID compared with unstressed controls, undermining the prediction that stress enhances the effectiveness of population-level purging across generations.