Metamorphosis offsets the link between larval stress, adult asymmetry and individual quality

Decoupling carry-over effects from environment in fish nursery grounds

Life-history trait expression not only depends on the current environmental constraints, but also on the past ones that shaped traits expressed earlier in life. Such an effect, named carry-over, can occur in fish nursery grounds when juvenile performances after settlement are influenced by their larval traits in combination with conditions experienced in nurseries. To date, the impacts of environmental and human stressors on post-settlement traits have been assessed, but independently from larval traits, so that the contributions of environmental versus carry-over constraints remain unquantified. Here, we used a reconstructive approach based on otolith microstructure to investigate how carry-over and environment affect life-history traits of the European seabass, Dicentrarchus labrax. In the northeast Atlantic Ocean, seabass juveniles were collected in six French estuarine nursery areas with contrasted environmental conditions (water temperature, salinity, food availability, and anthropogenic impacts), and five of their life-history traits across ontogenetic stages were measured (pelagic growth, larval duration, size at settlement, post-settlement growth and body condition). Piecewise structural equation model emphasized the strong co-variation of larval traits in response to food availability and temperature in the pelagic environment, stressing that fast growing larvae are characterized by shorter pelagic larval duration, but larger size at recruitment. However, the magnitude of carry-over effects greatly varied between traits, revealing that larval trait impacts on post-settlement traits remained minor as compared to the nursery environment. In estuarine nurseries, our findings suggest that resource allocation results from a trade-off between somatic growth and energy storage. Fish juveniles exposed to anthropogenic stress or risk of food limitation tended to predominantly invest in storage, whereas individuals in favourable conditions allocated their resources in somatic growth. These findings highlight the importance of heterogeneity in pelagic and nursery environments in understanding trait variations and population dynamic of estuarine dependent fish.

Complex delayed and transgenerational effects driven by the interaction of heat and insecticide in the maternal generation of the wheat aphid, Sitobion avenae

BACKGROUND

Experience of an earlier environment plays an important role in the induction of delayed and even intergenerational phenotypes of an organism. Evidence suggests that rapid adaptation to an environmental stressor can change the performance of organisms, and even enable them to deal with other stressors. The goal of this study was to determine the effects of adult imidacloprid exposure on life-history traits within and between generations of the cereal aphid, Sitobion avenae, under three developmental conditions: constant temperature, 22°C; a low-intensity thermal condition, 22 + 34°C for 2 h per day; and a high-intensity thermal condition, 22 + 38°C for 2 h per day.

RESULTS

Early thermal experience not only changed the tolerance of S. avenae to the insecticide, imidacloprid, but also caused adults to incur fitness costs: the higher the heat intensity, the higher the costs. Negative transgenerational impacts of combined heat and insecticide stressors were limited to the developmental stage, whereas positive stimulation of heat intensity was observed during the adult stage. Overall, nymphal thermal experience exacerbated the detrimental effects of adult insecticidal exposure on the intrinsic rate of population increase in the maternal generation, but stimulated a net reproductive rate in the succeeding offspring generation.

CONCLUSION

These findings underpin the importance of considering the experience of the early developmental environment, but also enhance our understanding of the transgenerational effects of combined thermal and insecticide stressors on the population fate of S. avenae. They also help to assess the efficacy of chemical control in a warming world. © 2021 Society of Chemical Industry.

Intraspecific Morphological Variation in the Dragonfly Erythrodiplax Media (Odonata: Libellulidae) Among South American Grassland Physiognomies

We assessed the intraspecific morphological variation in Erythrodiplax media Borror 1942 (Odonata, Libellulidae) among grassland physiognomies ("Coastal," "Highland," and "Steppic") in the South Brazilian Campos. We measured six morphological traits (total body length, thorax height, length, and width of the fore- and hindwings) from 90 specimens (60 males and 45 females). We tested the effect of the grassland type on the set of traits using one-way MANOVA and principal component analysis (PCA) (separately for each sex). Grassland physiognomy affected the morphology of males and females. In both sexes, the PCA mostly opposed the specimens of the Coastal from the Highland and Steppic grasslands. The first PCA axis separated specimens according to body lengths, thorax heights, and wing width, while the second PCA axis opposed specimens according to wing length and thorax height from specimens with broader wings and longer body lengths. Males from the Coastal had longer body lengths and shorter thorax heights than Highland and Steppic grasslands, while males from the Steppic had longer fore- and hindwings than specimens from the Coastal and Highland grasslands. Females from the Coastal had significantly shorter forewings than specimens from the Steppic grasslands and shorter hindwings than Highland grasslands. Our results are likely explained by the differences in climate and habitat complexity among grassland types and indicate that the processes driving odonate performance vary among grassland biotopes. This study potentially indicates that dragonflies are sensitive to changes in the vegetation structure in South American subtropical grasslands.

The Fluctuating Asymmetry of the Butterfly Wing Pattern Does Not Change along an Industrial Pollution Gradient

The rapid and selective responses to changes in habitat structure and climate have made butterflies valuable environmental indicators. In this study, we asked whether the decline in butterfly populations near the copper-nickel smelter in Monchegorsk in northwestern Russia is accompanied by phenotypic stress responses to toxic pollutants, expressed as a decrease in body size and an increase in fluctuating asymmetry. We measured the concentrations of nickel and copper, forewing length, and fluctuating asymmetry in two elements of wing patterns in Boloria euphrosyne, Plebejus idas, and Agriades optilete collected 1–65 km from Monchegorsk. Body metal concentrations increased toward the smelter, confirming the local origin of the collected butterflies. The wings of butterflies from the most polluted sites were 5–8% shorter than those in unpolluted localities, suggesting adverse effects of pollution on butterfly fitness due to larval feeding on contaminated plants. However, fluctuating asymmetry averaged across two hindwing spots did not change systematically with pollution, thereby questioning the use of fluctuating asymmetry as an indicator of habitat quality in butterfly conservation projects.

Indirect Effects of Iron Oxide on Stream Benthic Communities: Capturing Ecological Complexity with Controlled Mesocosm Experiments

Ferric iron (Fe(III)) oxyhydroxides commonly precipitate at neutral pH and in highly oxygenated conditions in waterways receiving acid mine drainage, degrading stream benthic communities by smothering of habitat, primary producers, and aquatic invertebrates. Stream mesocosms were used to expose naturally colonized benthic communities to a gradient of ferric Fe (0-15 mg/L) for 14 days to estimate the effects of Fe precipitates on primary production, larval and emerging adult aquatic insects, and the macroinvertebrate community structure. Community composition was significantly altered at concentrations near or below the US Environmental Protection Agency chronic Fe criterion (1.0 mg/L). Iron exposure significantly decreased larval and emerging adult abundances of Baetidae (mayfly) and Chironomidae (Diptera); however, while Simuliidae (Diptera) larvae were not reduced by the Fe treatments, abundance of emerged adults significantly decreased. Iron substantially decreased the colonization biomass of green algae and diatoms, with estimated EC₂₀ values well below the Fe criterion. In contrast, cyanobacteria were stimulated with increasing Fe concentration. By integrating environmentally realistic exposure conditions to native benthic communities that have complex structural and functional responses, the ability to predict the effects of Fe in the field is improved. Traditional toxicity testing methodologies were not developed to evaluate indirect effects of contaminants, and modernized approaches such as community mesocosm experiments better characterize and predict responses in aquatic ecosystems outside the laboratory. Therefore, the development of water quality standards would benefit by including mesocosm testing results.

Carryover effects of larval environment on individual variation in a facultatively diadromous fish

Intraspecific trait variation may result from "carryover effects" of variability of environments experienced at an earlier life stage. This phenomenon is particularly relevant in partially migrating populations composed of individuals with divergent early life histories. While many studies have addressed the causes of partial migration, few have investigated the consequences for between-individual variability later in life.We studied carryover effects of larval environment in a facultatively diadromous New Zealand fish, Gobiomorphus cotidianus, along an estuarine salinity gradient. We investigated the implications of varying environmental conditions during this critical stage of ontogeny for adult phenotype.We inferred past environmental history of wild-caught adult fish using otolith microchemistry (Sr/Ca) as a proxy for salinity. We tested for main and interactive effects of larval and adult environment on a suite of traits, including growth rates, behavior (exploration and activity), parasite load, and diet (stable isotopes and gut contents).We found a Sr/Ca consistent with a continuum from freshwater to brackish environments, and with different trajectories from juvenile to adult habitat. Fish with Sr/Ca indicating upstream migration were more vulnerable to trematode infection, suggesting a mismatch to freshwater habitat. Diet analysis suggested an interactive effect of larval and adult environments on trophic position and diet preference, while behavioral traits were unrelated to environment at any life stage. Growth rates did not seem to be affected by past environment.Overall, we show that early life environment can have multiple effects on adult performance and ecology, with the potential for lifetime fitness trade-offs associated with life history. Our study highlights that even relatively minor variation in rearing conditions may be enough to generate individual variation in natural populations.

Stream Mesocosm Experiments Show Significant Differences in Sensitivity of Larval and Emerging Adults to Metals

Evaluations of aquatic insect responses to contaminants typically use larval life stages to characterize taxa sensitivity, but the effects of contaminants to emerging terrestrial adults have received less attention. We present the results of two stream mesocosm experiments that exposed aquatic insects to mixtures of Cu and Zn. We compared responses of larvae and emerging adults in a single-species experiment with the mayfly Rhithrogena robusta and a benthic community experiment. Results showed that R. robusta larvae and emerging adults were highly tolerant of metals. In the benthic community experiment, larval and emerging adult life stages of the mayfly Baetidae were highly sensitive to metals exposure, with significant alterations in adult sex ratios. In contrast, the emergence of Chironomidae (midge) was unaffected, but larval abundance strongly decreased. Timing of adult emergence was significantly different among treatments and varied among taxa, with emergence stimulation in Chironomidae and delays in emergence in R. robusta and Simuliidae (black fly). Our results demonstrate that metal tolerance in aquatic insects is life stage dependent and that taxa sensitivity is influenced by a combination of physiology and phylogeny. Regulatory frameworks would benefit by including test results that account for effects of contaminants on metamorphosis and adult insect emergence for the development of aquatic life standards.

Incidence of deformities and variation in shape of mentum and wing of Chironomus columbiensis (Diptera, Chironomidae) as tools to assess aquatic contamination

Constantly, aquatic ecosystems are under pressure by complex mixtures of contaminants whose effects are not always easy to evaluate. Due to this, organisms are sought in which early warning signs may be detected upon the presence of potentially toxic xenobiotic substances. Thereby, the study evaluated the incidence of deformities and other morphometric variations in the mentum and wing of Chironomus columbiensis exposed to water from some of the Colombian Andes affected by mining, agriculture, and cattle raising. Populations of C. columbiensis were subjected throughout their life cycle (24 days) for two generations (F₁ and F₂). Five treatments were carried out in controlled laboratory conditions (water from the site without impact, site of mining mercury, mining mercury + cyanide, cattle raising, and agriculture) and the respective control (reconstituted water). Thereafter, the percentage of deformities in the mentum was calculated, and for the morphometric analysis 29 landmarks were digitized for the mentum and 12 for the wing. As a result, four types of deformities were registered in the C. columbiensis mentum, like absence of teeth, increased number of teeth, fusion and space between teeth, none of them detected in the individuals from the control. Additionally, the highest incidence of deformity in F₁ occurred in the treatment of mining mercury, while for F₂ this took place in the treatments of mining mercury + cyanide, cattle raising and agriculture. Differences were also found with respect to the morphometric variations of the mentum and wing of C. columbiensis among the control and the treatments with water from the creeks intervened. The treatments of mining mercury + cyanide and agriculture had the highest morphological variation in the mentum and wing of C. columbiensis. The results suggest that the anthropogenic impacts evaluated generate alterations in the oral apparatus of the larval state of C. columbiensis and in the adult state provoke alterations in the wing shape (increased width and reduced basal area). These deformities may be related to multiple stress factors, among them the xenobiotics metabolized by the organisms under conditions of environmental contamination.

In vivo isotopic fractionation of zinc and biodynamic modeling yield insights into detoxification mechanisms in the mayfly Neocloeon triangulifer

Diversity and biomass of aquatic insects decline in metal-rich aquatic environments, but the mechanisms by which insects from such environments cope with potentially toxic metal concentrations to survive through adulthood are less well understood. In this study, we measured Zn concentrations and isotopes in laboratory-reared diatoms and mayflies (Neocloeon triangulifer) from larval through adult stages. The larvae were fed Zn-enriched diatoms, and bio-concentrated Zn by a factor of 2.5-5 relative to the diatoms but maintained the same Zn-isotopic ratio. These results reflect the importance of dietary uptake and the greater rate of uptake relative to excretion or growth. Upon metamorphosis to subimago, Zn concentrations declined by >70%, but isotopically heavy Zn remained in the subimago bodies. We surmised that the loss of isotopically light Zn during metamorphosis was due to the loss of detoxified Zn and retention of metabolically useful Zn. Through the transition from subimago to imago, Zn concentrations and isotope ratios were virtually unchanged. Because the decrease in Zn body concentration and increase in heavier Zn are seen in the subimagos relative to the larvae, the compartmentalization of Zn must be occurring within the larvae. A biodynamic model was constructed, allowing for isotopic fractionation and partitioning of Zn between metabolically essential and detoxified Zn reservoirs within larvae. The model provides a consistent set of rate and fractionation constants that successfully describe the experimental observations. Specifically, metabolically essential Zn is isotopically heavier and is tightly held once assimilated, and excess, isotopically light Zn is sequestered, detoxified, and ultimately lost during the metamorphosis of larvae to subimagos. To our knowledge, this is the first documentation of in vivo isotopic fractionation in insects, offering an improved understanding of the mechanisms and rates by which the N. triangulifer larvae regulate excess Zn in their bodies.

Blue light-induced immunosuppression in Bactrocera dorsalis adults, as a carryover effect of larval exposure

Detrimental effects of ultraviolet (UV) light on living organisms are well understood, little is known about the effects of blue light irradiation. Although a recent study revealed that blue light caused more harmful effects on insects than UV light and blue light irradiation killed insect pests of various orders including Diptera, the effects of blue light on physiology of insects are still largely unknown. Here we studied the effects of blue light irradiation on cuticular melanin in larval and the immune response in adult stage of Bactrocera dorsalis. We also evaluated the effects of blue light exposure in larval stage on various age and mass at metamorphosis and the mediatory role of cuticular melanin in carryover effects of larval stressors across metamorphosis. We found that larvae exposed to blue light decreased melanin contents in their exoskeleton with smaller mass and delayed metamorphosis than insects reared without blue light exposure. Across metamorphosis, lower melanotic encapsulation response and higher susceptibility to Beauveria bassiana was detected in adults that had been exposed to blue light at their larval stage, thereby constituting the first evidence that blue light impaired adult immune function in B. dorsalis as a carryover effect of larval exposure.

Strong Delayed Interactive Effects of Metal Exposure and Warming: Latitude-Dependent Synergisms Persist Across Metamorphosis

As contaminants are often more toxic at higher temperatures, predicting their impact under global warming remains a key challenge for ecological risk assessment. Ignoring delayed effects, synergistic interactions between contaminants and warming, and differences in sensitivity across species' ranges could lead to an important underestimation of the risks. We addressed all three mechanisms by studying effects of larval exposure to zinc and warming before, during, and after metamorphosis in Ischnura elegans damselflies from high- and low-latitude populations. By integrating these mechanisms into a single study, we could identify two novel patterns. First, during exposure zinc did not affect survival, whereas it induced mild to moderate postexposure mortality in the larval stage and at metamorphosis, and very strongly reduced adult lifespan. This severe delayed effect across metamorphosis was especially remarkable in high-latitude animals, as they appeared almost insensitive to zinc during the larval stage. Second, the well-known synergism between metals and warming was manifested not only during the larval stage but also after metamorphosis, yet notably only in low-latitude damselflies. These results highlight that a more complete life-cycle approach that incorporates the possibility of delayed interactions between contaminants and warming in a geographical context is crucial for a more realistic risk assessment in a warming world.

Metamorphosis Affects Metal Concentrations and Isotopic Signatures in a Mayfly (Baetis tricaudatus): Implications for the Aquatic-Terrestrial Transfer of Metals

Insect metamorphosis often results in substantial chemical changes that can alter contaminant concentrations and fractionate isotopes. We exposed larval mayflies (Baetis tricaudatus) and their food (periphyton) to an aqueous zinc gradient (3-340 μg Zn/l) and measured zinc concentrations at different stages of metamorphosis: larval, subimago, and imago. We also measured changes in stable isotopes (δ¹⁵N and δ¹³C) in unexposed mayflies. Larval zinc concentrations were positively related to aqueous zinc, increasing 9-fold across the exposure gradient. Adult zinc concentrations were also positively related to aqueous zinc, but were 7-fold lower than larvae. This relationship varied according to adult substage and sex. Tissue concentrations in female imagoes were not related to exposure concentrations, but the converse was true for all other stage-by-sex combinations. Metamorphosis also increased δ¹⁵N by ∼0.8‰, but not δ¹³C. Thus, the main effects of metamorphosis on insect chemistry were large declines in zinc concentrations coupled with increased δ¹⁵N signatures. For zinc, this change was largely consistent across the aqueous exposure gradient. However, differences among sexes and stages suggest that caution is warranted when using nitrogen isotopes or metal concentrations measured in one insect stage (e.g., larvae) to assess risk to wildlife that feed on subsequent life stages (e.g., adults).

Larval nutritional stress affects vector life history traits and human malaria transmission

Exposure to stress during an insect’s larval development can have carry-over effects on adult life history traits and susceptibility to pathogens. We investigated the effects of larval nutritional stress for the first time using field mosquito vectors and malaria parasites. In contrast to previous studies, we show that larval nutritional stress may affect human to mosquito transmission antagonistically: nutritionally deprived larvae showed lower parasite prevalence for only one gametocyte carrier; they also had lower fecundity. However, they had greater survival rates that were even higher when infected. When combining these opposing effects into epidemiological models, we show that larval nutritional stress induced a decrease in malaria transmission at low mosquito densities and an increase in transmission at high mosquito densities, whereas transmission by mosquitoes from well-fed larvae was stable. Our work underscores the importance of including environmental stressors towards understanding host–parasite dynamics to improve disease transmission models and control.

Delayed effects of chlorpyrifos across metamorphosis on dispersal-related traits in a poleward moving damselfly

How exposure to contaminants may interfere with the widespread poleward range expansions under global warming is largely unknown. Pesticide exposure may negatively affect traits shaping the speed of range expansion, including traits related to population growth rate and dispersal-related traits. Moreover, rapid evolution of growth rates during poleward range expansions may come at a cost of a reduced investment in detoxification and repair thereby increasing the vulnerability to contaminants at expanding range fronts. We tested effects of a sublethal concentration of the widespread pesticide chlorpyrifos on traits related to range expansion in replicated edge and core populations of the poleward moving damselfly Coenagrion scitulum reared at low and high food levels in a common garden experiment. Food limitation in the larval stage had strong negative effects both in the larval stage and across metamorphosis in the adult stage. Exposure to chlorpyrifos during the larval stage did not affect larval traits but caused delayed effects across metamorphosis by increasing the incidence of wing malformations during metamorphosis and by reducing a key component of the adult immune response. There was some support for an evolutionary trade-off scenario as the faster growing edge larvae suffered a higher mortality during metamorphosis. Instead, there was no clear support for the faster growing edge larvae being more vulnerable to chlorpyrifos. Our data indicate that sublethal delayed effects of pesticide exposure, partly in association with the rapid evolution of faster growth rates, may slow down range expansions.

Larval food quantity affects the capacity of adult mosquitoes to transmit human malaria

Adult traits of holometabolous insects are shaped by conditions experienced during larval development, which might impact interactions between adult insect hosts and parasites. However, the ecology of larval insects that vector disease remains poorly understood. Here, we used Anopheles stephensi mosquitoes and the human malaria parasite Plasmodium falciparum, to investigate whether larval conditions affect the capacity of adult mosquitoes to transmit malaria. We reared larvae in two groups; one group received a standard laboratory rearing diet, whereas the other received a reduced diet. Emerging adult females were then provided an infectious blood meal. We assessed mosquito longevity, parasite development rate and prevalence of infectious mosquitoes over time. Reduced larval food led to increased adult mortality and caused a delay in parasite development and a slowing in the rate at which parasites invaded the mosquito salivary glands, extending the time it took for mosquitoes to become infectious. Together, these effects increased transmission potential of mosquitoes in the high food regime by 260-330%. Such effects have not, to our knowledge, been shown previously for human malaria and highlight the importance of improving knowledge of larval ecology to better understand vector-borne disease transmission dynamics.

Contrasting effects of fish predation on benthic versus emerging prey: a meta-analysis

Predator-prey interactions are often studied entirely within the ecosystem of the predator. However, many prey transition between ecosystems during development, expanding the effects of predators across ecosystems. Prey are often vulnerable to predation during this transition, facing a predator gauntlet as they leave their source ecosystem. As a result of predation during this transition, predators may have stronger effects on prey fluxes to the neighboring ecosystem than on prey densities in the predator's own ecosystem. I used meta-analysis of predator (fish) and prey (invertebrate) interactions in freshwater ecosystems to test the hypothesis that fish have stronger effects on prey flux to the terrestrial ecosystem, by reducing insect emergence biomass, than on prey densities in the aquatic ecosystem, by reducing benthic insect/invertebrate biomass. Fish reduced insect emergence by 39 % on average, more than twice as strong as their reductions of benthic prey (16 % reduction; averages are variance-weighted). In fact, fish effects on benthic prey were not significantly different from zero, but were significant for emergence. These results indicate that predator effects can not only cascade from one ecosystem to another but also that effects can be stronger outside than within the ecosystem of the predator. Failure to account for this may underestimate the effects of predators on prey.

Combined effects of larval exposure to a heat wave and chlorpyrifos in northern and southern populations of the damselfly Ischnura elegans

Heat waves are generally associated with an increased energy consumption and could thus increase the vulnerability to subsequent pesticide exposure. We investigated the combined effect of a heat wave and subsequent exposure to the pesticide chlorpyrifos in Ischnura elegans damselfly larvae. To assess local thermal adaptation to heat waves, we applied these combined stressors on replicated low- and high-latitude populations in Europe. Unexpectedly, we observed positive sublethal effects of the heat wave: fat content and phenoloxidase activity increased. Chlorpyrifos had strong negative effects on survival, growth rate, and fat content, while phenoloxidase activity increased; these effects between latitudes were found similar. We found little indication of a higher ability to withstand a heat wave in southern larvae. We did detect a synergistic negative effect on AChE activity. This result highlights the importance of considering delayed effects of extreme temperature events when assessing the impact of pesticides under climate change.

Metamorphosis enhances the effects of metal exposure on the mayfly, Centroptilum triangulifer

The response of larval aquatic insects to stressors such as metals is used to assess the ecological condition of streams worldwide. However, nearly all larval insects metamorphose from aquatic larvae to winged adults, and recent surveys indicate that adults may be a more sensitive indicator of stream metal toxicity than larvae. One hypothesis to explain this pattern is that insects exposed to elevated metal in their larval stages have a reduced ability to successfully complete metamorphosis. To test this hypothesis we exposed late-instar larvae of the mayfly, Centroptilum triangulifer, to an aqueous Zn gradient (32-476 μg/L) in the laboratory. After 6 days of exposure, when metamorphosis began, larval survival was unaffected by zinc. However, Zn reduced wingpad development at concentrations above 139 μg/L. In contrast, emergence of subimagos and imagos tended to decline with any increase in Zn. At Zn concentrations below 105 μg/L (hardness-adjusted aquatic life criterion), survival between the wingpad and subimago stages declined 5-fold across the Zn gradient. These results support the hypothesis that metamorphosis may be a survival bottleneck, particularly in contaminated streams. Thus, death during metamorphosis may be a key mechanism explaining how stream metal contamination can impact terrestrial communities by reducing aquatic insect emergence.

Exposure to sediments from polluted rivers has limited phenotypic effects on larvae and adults of Chironomus riparius

Laboratory studies have sometimes failed to detect a relationship between toxic stress and morphological defects in invertebrates. Several hypotheses have been proposed to account for this lack of effect. (1) It was suggested that only a combination of stressful conditions - rather than a single one - would affect the phenotype. (2) Phenotypic defects should be detected on adult individuals, rather than on juveniles. (3) Phenotypic abnormalities might mostly affect the progeny of the exposed individuals, some contaminants exhibiting trans-generational effects. In the present study, we test those three hypotheses. We first examined the effects of a multiple exposure by using laboratory Chironomus riparius larvae cultured on two sediments sampled in contaminated rivers and those containing a mixture of mineral and organic compounds. On the larvae, we investigated mentum phenotypes: the frequency of phenodeviants, the shape fluctuating asymmetry and the mean shape. To test whether adult's morphology was more sensitive than the larval's, we also measured asymmetry and mean shape of the adult wings. Finally, to test for a trans-generational phenotypic effect, we measured mentum shape variations in the offspring derived from the measured adults. Overall, our results point out a very limited phenotypic response to contaminated sediments, suggesting that a multiple exposure is not necessarily sufficient to generate phenotypic defects. Adult traits were no more affected than larval traits, discarding the hypothesis that adult phenotypes would be more sensitive biomarkers. Finally, no effect was detected on the offspring generation, suggesting that no trans-generational effect occurs. This general lack of effect suggests that the use of phenotypic defects in C. riparius as an indicator of sediment contamination should be considered cautiously.

Fitness Effects of Chlorpyrifos in the Damselfly Enallagma cyathigerum Strongly Depend upon Temperature and Food Level and Can Bridge Metamorphosis

Interactions between pollutants and suboptimal environmental conditions can have severe consequences for the toxicity of pollutants, yet are still poorly understood. To identify patterns across environmental conditions and across fitness-related variables we exposed Enallagma cyathigerum damselfly larvae to the pesticide chlorpyrifos at two food levels or at two temperatures and quantified four fitness-related variables (larval survival, development time, mass at emergence and adult cold resistance). Food level and temperature did not affect survival in the absence of the pesticide, yet the pesticide reduced survival only at the high temperature. Animals reacted to the pesticide by accelerating their development but only at the high food level and at the low temperature; at the low food level, however, pesticide exposure resulted in a slower development. Chlorpyrifos exposure resulted in smaller adults except in animals reared at the high food level. Animals reared at the low food level and at the low temperature had a higher cold resistance which was not affected by the pesticide. In summary our study highlight that combined effects of exposure to chlorpyrifos and the two environmental conditions (i) were mostly interactive and sometimes even reversed in comparison with the effect of the environmental condition in isolation, (ii) strongly differed depending on the fitness-related variable under study, (iii) were not always predictable based on the effect of the environmental condition in isolation, and (iv) bridged metamorphosis depending on which environmental condition was combined with the pesticide thereby potentially carrying over from aquatic to terrestrial ecosystems. These findings are relevant when extrapolating results of laboratory tests done under ideal environmental conditions to natural communities.

Patterns of fluctuating asymmetry and shape variation in Chironomus riparius (Diptera, Chironomidae) exposed to nonylphenol or lead

Deformities and fluctuating asymmetry in chironomid larvae have been proposed as sensitive indicators of biological stress and are commonly used to assess the ecological impact of human activities. In particular, they have been associated in Chironomus riparius, the most commonly used species, with heavy metal and pesticide river pollution. In this study, the effect of lead and 4-nonylphenol on mouthpart morphological variation of Chironomus riparius larvae was investigated by traditional and geometric morphometrics. For this purpose, first to fourth instar larvae were exposed to sediment spiked with lead (from 3.0 to 456.9 mg/kg dry weight) or 4-NP (from 0.1 to 198.8 mg/kg dry weight). Mentum phenotypic response to pollutants was assessed by four parameters: (1) the frequency of deformities, (2) fluctuating asymmetry of mentum length, (3) fluctuating asymmetry of mentum shape and (4) the mentum mean shape changes. Despite the bioaccumulation of pollutants in the chironomid’s body, no significant differences between control and stressed groups were found for mouthpart deformities and fluctuating asymmetry of mentum length. Slight effects on mentum shape fluctuating asymmetry were observed for two stressed groups. Significant mean shape changes, consisting of tooth size increase and tooth closing, were detected for lead and 4-NP exposure respectively. Those variations, however, were negligible in comparison to mentum shape changes due to genetic effects. These results suggest that the use of mentum variation as an indicator of toxic stress in Chironomus riparius should be considered cautiously.

Evolutionary ecology of Odonata: a complex life cycle perspective

Most insects have a complex life cycle with ecologically different larval and adult stages. We present an ontogenetic perspective to analyze and summarize the complex life cycle of Odonata within an evolutionary ecology framework. Morphological, physiological, and behavioral pathways that generate carry-over effects across the aquatic egg and larval stages and the terrestrial adult stage are identified. We also highlight several mechanisms that can decouple life stages including compensatory mechanisms at the larval and adult stages, stressful and stochastic events during metamorphosis, and stressful environmental conditions at the adult stage that may overrule effects of environmental conditions in the preceding stage. We consider the implications of these findings for the evolution, selection, and fitness of odonates; underline the role of the identified numerical and carry-over effects in shaping population and metapopulation dynamics and the community structure across habitat boundaries; and discuss implications for applied conservation issues.

Stage-specific effects of population density on the development and fertility of the western tarnished plant bug, Lygus hesperus

The western tarnished plant bug Lygus hesperus Knight (Heteroptera: Miridae), a major pest of cotton and other key economic crops, was tested for its sensitivity to population density during nymph and adult stages. Nymphs reared to adulthood under increasing densities in laboratory conditions exhibited incremental delays in maturation, heightened mortality rates, and reductions in body mass and various size parameters. In contrast, gonadal activity in both males and females rose with initial density increases. Supplemental nutrients provided to the nymphs failed to offset the negative effects of high density, suggesting that contact frequency, rather than resource partitioning, may be the primary stress. Unlike nymphs, newly enclosed adults exposed to increasing population densities did not suffer negative physiological effects; body mass, mortality rates and patterns of ovipositional activity were unchanged. Collectively, these results indicate that population density can dramatically influence Lygus development, but the specific effects are stage-dependent.

Replenishment success linked to fluctuating asymmetry in larval fish

Fluctuating asymmetry (FA), defined as random deviations from perfect symmetry, has become a popular tool with which to examine the effects of stress during the development of bilaterally symmetrical organisms. Recent studies have suggested that FA in otoliths may serve as an indicator of stress in fish larvae. We examined the relationship between otolith asymmetry and temporal patterns in the occurrence of late-stage larvae to a tropical reef (i.e. replenishment) for the Caribbean lizardfish, Saurida suspicio (family Synodontidae). Late-stage larvae were collected in light traps over a period of 18 consecutive lunar months in the San Blas Archipelago, Panama. Asymmetry within otolith pairs was calculated from 24 variables: area, perimeter, longest and shortest axis of the otolith and 20 shape descriptors (Fourier harmonics). Otolith asymmetry was correlated strongly with fluctuations in lunar light trap catches. Two measured variables, otolith area and one of the 20 shape descriptors, accounted for 60% of the variability in lunar replenishment of S. suspicio. Individuals from small replenishment pulses exhibited higher levels of asymmetry compared to larvae from large pulses. When dry and wet seasons were analysed separately, otolith asymmetry explained a surprising 70 and 97% of the variation, respectively. Although the generality of these results remain to be tested among other populations and species, otolith asymmetry may be an important indicator, and potentially a predictor, of larval quality and replenishment success.