Gender differences in phenoloxidase activity of Panorpa vulgaris hemocytes

Effect of infection with Aeromonas hydrophila on antioxidant capacity, inflammation response, and apoptosis proteins in Chinese mitten crab (Eriocheir sinensis)

Aeromonas hydrophila (A. hydrophila) as a serious bacterial disease endangering aquaculture and the Chinese mitten crabs (Eriocheir sinensis) industry. The present study was conducted to investigate the effects of A. hydrophila on the antioxidant, inflammation, immunity and apoptosis of the E. sinensis. The E. sinensis (female: 150 crabs and male: 150 crabs; 67.11 ± 0.76 g) were randomly divided into the control group (Foot injection with 200 μl PBS) and infection group (Foot injection with 200 μl A. hydrophila of 10⁶ cfu/mL). The hepatopancreas and serum was collected to detect the related indicators after injection 24 h. The results showed that A. hydrophila significantly reduced the malondialdehyde (MDA) level and gamma-glutamyl-cysteine synthetase (γ-GCS) activity in the hepatopancreas of male and female crabs (P < 0.05). A.hydrophila also significantly decreased the total-superoxide dismutase (T-SOD) activity while the levels of total antioxidant capacity (T-AOC) and total glutathione (T-GSH) were significantly increased in the hepatopancreas and serum of male crabs (P < 0.05). At the transcriptional level, the expression of catalase (CAT) and glutathione peroxidases (GPx), Glutathione S-transferase (GST) in the hepatopancreas of male and female crabs was significantly reduced compared to the control group (P < 0.05). However, A. hydrophila could not significantly change the Kelch-like ECH-associated protein 1 (Keap1) gene expression level in both of male and female carbs. A. hydrophila injection for 24 h, the lysozyme (LZM) and phenoloxidase (PO) activity was significantly increased in the hepatopancreas and serum of the male and female crabs (P < 0.05). Simultaneous increase of immune-related enzyme activity (acid phosphatase and alkaline phosphatase) was found in the serum of male and female crabs (P < 0.05). However, the acid phosphatase (ACP) and alkaline phosphatase (ALP) activity was significantly decreased in the hepatopancreas of male and female crabs (P < 0.05). Meanwhile, the LZM mRNA level was significantly decreased in the hepatopancreas of E. sinensis (P < 0.05). Furthermore, A. hydrophila significantly inhibited the mRNA expression of immune regulated factors (Interleukin enhancer binding factor 2: ILF2, interleukin-16: IL-16, Toll-like receptor: TLR) in the male and female crabs. The levels of inflammatory cytokines (interleukin-1β: IL-1β, interleukin-6: IL-6, interleukin-8: IL-8, interleukin-10: IL-10) were significantly increased in the hepatopancreas of male and female crabs. Moreover, A.hydrophila increased the mRNA expression of apoptosis - related genes in male crabs (p38 mitogen-activated protein kinase: p38, adamalysin 17: ADAM17, Cysteine-aspartic acid protease 3: Caspase 3, and Bcl-2-associated X: BAX), but reduced the expression of p38, ADAM17, Caspase 3 and BAX genes in female crabs. In conclusion, A. hydrophila could induce oxidative stress and the response of inflammation and immunity, and also trigger the mRNA expression changes of apoptosis related-genes in E. sinensis. This study provides a theoretical basis for the study of E. sinensis diseases.

Immunosenescence along with direct physiological allocation trade-offs between life history and immunity in the red palm weevil Rhynchophorus ferrugineus

Recent works have generally indicated that insects exhibit two immune response strategies: external and internal immune defense. However, the immune-related trade-offs and physiological regulatory mechanisms in red palm weevil, a major invasive pest, remain unclear. Based on postinfection survivorship experiments, we initially measured baseline constitutive external immunity (antibacterial activity of external secretions) and internal immunity (phenoloxidase and antibacterial activity of hemolymph) in uninfected individuals. Then, we challenged the individual immune system and examined subsequent investment in immune function. Our data showed that multiple factors (instar, age, sex, mating status, immune treatment) interacted to affect immune components and infection outcomes, but the magnitude and nature of the impact varied in each case. Although immune senescence is a common phenomenon in which immune function decreases with age, different components of the immune system changed differentially. Notably, mating activity may impose an immunity-related cost, with some evidence of sexual dimorphism and age-associated differences. Finally, parameters related to life-history traits usually decreased temporarily because of increased immunity, suggesting that the ultimate consequences of immune function fitness may be physiologically traded off with other fitness aspects, including growth, development, mating, reproduction, and longevity. These results reveal the complex factors that impact immunity as well as the physiological regulation of individual immunity, which may determine the evolution and outcome of immune senescence and trade-offs.

Morphological Characterisation of Haemocytes in the Mealworm Beetle Tenebrio molitor (Coleoptera, Tenebrionidae)

The immunocompetence of the mealworm beetle Tenebrio molitor has been well investigated at molecular and physiological levels, but information on morphological and functional characteristics of its immune cells (haemocytes) is still scarce and fragmentary. This study provides an updated overview of the morphology of circulating immune cells from mealworm beetle adults, using light and transmission electron microscopy. Based on their affinities for May-Grünwald Giemsa stain, haemocytes were defined as either eosinophilic, basophilic or neutral. Ultrastructural descriptions allowed to detect four main cell types in the haemolymph: prohaemocytes, plasmatocytes, granular cells and oenocytoids. The morphological plasticity of haemocytes and the evidence of mitotic circulating cells, intermediate cell stages, as well as autophagic activities suggest haemocyte proliferation, turnover and transdifferentiation as constantly active processes in the haemolymph. Cytochemical tests revealed differences in the distribution of carbohydrates among cell types underling the great plasticity of the immune response and the direct involvement of circulating immune cells in the resource allocation. In addition, our results provide a detailed morphological description of vesicle trafficking, macro- and microautophagy, apoptotic and necrotic processes, confirming the suitability of T. molitor haemocytes as a model for studying evolutionarily conserved cellular mechanisms.

Plants impact cellular immunity of caterpillars to an entomovirus

BACKGROUND

Tri-trophic interactions among plants, insect herbivores and entomopathogens are one of the hot topics in ecology. Although plants have been shown to impact the interactions between herbivores and entomopathogens, it is still unclear how plants affect the cellular immunity of herbivores to entomopathogens.

RESULTS

The number of hemocytes and the proportion of two main cell types (granular hemocytes and plasmatocytes), plasmatocyte-spreading rate, apoptosis rate, two Spodoptera exigua caspase (SeCasp-1, SeCasp-5) activities and gene expressions were all higher and the activities and gene expression of S. exigua inhibitor of apoptosis protein (SeIAP) were lower in nucleopolyhedrovirus (NPV)-infected caterpillars fed Ipomoea aquatica than those fed other plants or artificial diet. Scanning electron microscopy images were consistent with molecular patterns of immune responses.

CONCLUSION

This study suggests that host plants affect the immune responses of herbivores to entomopathogens by manipulating the composition, morphology and apoptosis of herbivore hemocytes, which sheds light on the mechanisms that allow host plants to influence multi-trophic interactions. © 2021 Society of Chemical Industry.

Why leveraging sex differences in immune trade-offs may illuminate the evolution of senescence

The immune system affects senescence (declines in probabilities of survival or reproduction with age), by shaping late age vulnerability to chronic inflammatory diseases and infections. It is also a dynamic interactive system that must balance competing demands across the life course. Thus, immune system function remains an important frontier in understanding the evolution of senescence.Here, we review our expanding mechanistic understanding of immune function over the life course, in the context of theoretical predictions from life-history evolution. We are especially interested in stage- and sex-dependent costs and benefits of investment in the immune system, given differential life-history priorities of the life stages and sexes.We introduce the costs likely to govern immune allocation across the life course. We then discuss theoretical expectations for differences between the sexes and their likely consequences in terms of how the immune system is both modulated by and may modulate senescence, building on information from life-history theory, experimental immunology and demography.We argue that sex differences in immune function provide a potentially powerful probe of selection pressures on the immune system across the life course. In particular, differences in 'competing' and 'caring' between the sexes have evolved across the tree of life, providing repeated instances of divergent selection pressures on immune function occurring within the same overall bauplan.We conclude by detailing an agenda for future research, including development of theoretical predictions of the differences between the sexes under an array of existing models for sex differences in immunity, and empirical tests of such predictions across the tree of life. A free http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13458/suppinfo can be found within the Supporting Information of this article.

Metabolic and immunological responses of male and female new Zealand Greenshell™ mussels (Perna canaliculus) infected with Vibrio sp

Massive mortalities due to pathogens are routinely reported in bivalve cultivation that have significant economic consequences for the global aquaculture industry. However, host-pathogen interactions and infection mechanisms that mediate these interactions are poorly understood. In addition, gender-specific immunological responses have been reported for some species, but the reasons for such differences have not been elucidated. In this study, we used a GC/MS-based metabolomics platform and flow cytometry approach to characterize metabolic and immunological responses in haemolymph of male and female mussels (Perna canaliculus) experimentally infected with Vibrio sp. Sex-based differences in immunological responses were identified, with male mussels displaying higher mortality, oxidative stress and apoptosis after pathogen exposure. However, central metabolic processes appeared to be similar between sexes at 24 h post injection with Vibrio sp. DO1. Significant alterations in relative levels of 37 metabolites were detected between infected and uninfected mussels. These metabolites are involved in major perturbations on the host's innate immune system. In addition, there were alterations of seven metabolites in profiles of mussels sampled on the second day and mussels that survived six days after exposure. These metabolites include itaconic acid, isoleucine, phenylalanine, creatinine, malonic acid, glutaric acid and hydroxyproline. Among these, itaconic acid has the potential to be an important biomarker for Vibrio sp. DO1 infection. These findings provide new insights on the mechanistic relationship between a bivalve host and a pathogenic bacterium and highlight the need to consider host sex as a biological variable in future immunological studies.

Effect of nutritional stress and sex on melanotic encapsulation rate in the sexually size dimorphic Cook Strait giant weta (Deinacrida rugosa)

Nutritional condition and sex are known to influence efficacy and investment in immune function. A poor diet is costly to immune function because it limits the resources (e.g., protein) available to effector systems (e.g., melanotic encapsulation), whereas males and females are expected to differ in how they allocate resources to fitness-related traits. Males are expected to invest less in immunity, and more in mating, than females, but this pattern could be reversed if fitness is more condition-dependent in males than in females. I tested the effects of nutritional condition and sex on melanotic encapsulation rate in the Cook Strait giant weta (Deinacrida rugosa Buller, 1871), an orthopteran insect exhibiting strong female-biased sexual size dimorphism that is, at least in part, the result of strong sexual selection for small male size. I found that male D. rugosa have a stronger encapsulation response than females, while nutritional condition has only a small positive effect on this particular effector system in both sexes. Whether the observed sex difference in encapsulation ability is due to a physiological constraint in females or whether males allocate more resources to this effector system because their fitness is more condition-dependent than female’s remains to be determined.

Parental care improves immunity in the seahorse (Hippocampus erectus)

In the present study, the sexual dimorphism in immune response in the seahorse Hippocampus erectus in which males compete for mates and invest heavily in parental care was assessed. Variability in immunocompetence in virginal seahorses with differing levels of sexual maturity (i.e., immaturity, early maturity and maturity) and with different mating statuses (i.e., virginal, experienced mating failure and experienced mating success) were analyzed by evaluating immune parameters in the plasma. Additionally, ultrastructural characteristics of the inner epithelium of the brood pouch were compared between males that had experienced mating failure and those that had succeeded. Generally, immunity in sexually mature virgin males was greater than in females, and mating competition significantly reduced males' immunity. However, parental care gave males stronger immune and metabolic abilities and resulted in their immunity significantly rebounding after a successful mating. The present study quantitatively clarifies, for the first time, how parental care and mating competition jointly affect immunity. Moreover, previous findings that females display more efficient immune defenses than males in conventional species (i.e., males are as competitor and females as care giver) and that males' immunity is higher than females' in the pipefish (i.e., females are as competitor and males as care giver) in combination with the present results indicate that parental care is a key factor for sexual dimorphism in immunity. The care-giving sex has strong immunity regardless of the sex in charge of mating competition or not.

Phenoloxidase activity in the infraorder Isoptera: unraveling life-history correlates of immune investment

Within the area of ecological immunology, the quantification of phenoloxidase (PO) activity has been used as a proxy for estimating immune investment. Because termites have unique life-history traits and significant inter-specific differences exist regarding their nesting and foraging habits, comparative studies on PO activity can shed light on the general principles influencing immune investment against the backdrop of sociality, reproductive potential, and gender. We quantified PO activity across four termite species ranging from the phylogenetically basal to the most derived, each with their particular nesting/foraging strategies. Our data indicate that PO activity varies across species, with soil-dwelling termites exhibiting significantly higher PO levels than the above-ground wood nester species which in turn have higher PO levels than arboreal species. Moreover, our comparative approach suggests that pathogenic risks can override reproductive potential as a more important driver of immune investment. No gender-based differences in PO activities were recorded. Although termite PO activity levels vary in accordance with a priori predictions made from life-history theory, our data indicate that nesting and foraging strategies (and their resulting pathogenic pressures) can supersede reproductive potential and other life-history traits in influencing investment in PO. Termites, within the eusocial insects, provide a unique perspective for inferring how different ecological pressures may have influenced immune function in general and their levels of PO activity, in particular.

No Effect of Host Species on Phenoloxidase Activity in a Mycophagous Beetle

Ecological immunology is an interdisciplinary field that helps elucidate interactions between the environment and immune response. The host species individuals experience have profound effects on immune response in many species of insects. However, this conclusion comes from studies of herbivorous insects even though species of mycophagous insects also inhabit many different host species. The goal of this study was to determine if fungal host species as well as individual, sex, body size, and host patch predict one aspect of immune function, phenoloxidase activity (PO). We sampled a metapopulation of Bolitotherus cornutus, a mycophagous beetle in southwestern Virginia. B. cornutus live on three species of fungus that differ in nutritional quality, social environment, and density. A filter paper phenoloxidase assay was used to quantify phenoloxidase activity. Overall, PO activity was significantly repeatable among individuals (0.57) in adult B. cornutus. While there was significant variance among individuals in PO activity, there were surprisingly no significant differences in PO activity among subpopulations, beetles living on different host species, or between the sexes; there was also no effect of body size. Our results suggest that other factors such as age, genotype, disease prevalence, or natal environment may be generating variance among individuals in PO activity.

Comparative Transcriptome Analysis Reveals Sex-Biased Gene Expression in Juvenile Chinese Mitten Crab Eriocheir sinensis

Sex-biased genes are considered to account for most of phenotypic differences between males and females. In order to explore the sex-biased gene expression in crab, we performed the whole-body transcriptome analysis in male and female juveniles of the Chinese mitten crab Eriocheir sinensis using next-generation sequencing technology. Of the 23,349 annotated unigenes, 148 were identified as sex-related genes. A total of 29 candidate genes involved in primary sex determination pathways were detected, indicating the sex determination cascade of the mitten crab might be more complex than previously supposed. Differential expression analysis showed 448 differentially expressed genes (DEGs) between the two transcriptomes. Most of DEGs were involved in processes such as metabolism and immunity, and not associated with obvious sexual function. The pathway predominantly enriched for DEGs were related to lysosome, which might reflect the differences in metabolism between males and females. Of the immune DGEs, 18 up-regulated genes in females were humoral immune factors, and eight up-regulated genes in males were pattern recognition receptors, suggesting sex differences of immune defense might exist in the mitten crab. In addition, two reproduction-related genes, vitellogenin and insulin-like androgenic gland factor, were identified to express in both sexes but with significantly higher level in males. Our research provides the first whole-body RNA sequencing of sex-specific transcriptomes for juvenile E. sinensis and will facilitate further studies on molecular mechanisms of crab sexual dimorphism.

DNA damage in haemocytes and midgut gland cells of Steatoda grossa (Theridiidae) spiders exposed to food contaminated with cadmium

The aim of this study was to assess the genotoxic effects of Cd on haemocytes and midgut gland cells of web-building spiders, Steatoda grossa (Theridiidae), exposed to the metal under laboratory conditions. Analyzes were conducted on adult females and males, fed for four weeks with cadmium-contaminated Drosophila hydei flies, grown on a medium suplemented with 0.25 mM CdCl2. The comet assay, providing a quantitative measure of DNA strand breaks, was used to evaluate the DNA damage caused by the metal. Cadmium content was measured in whole spider bodies by the AAS method. Metal body burden was significantly lower in females (0.25 µgg(-1) dry weight) than in males (3.03 µgg(-1) dry weight), suggesting that females may have more effective mechanisms controlling the uptake of metal, via the digestive tract, or its elimination from the body. Irrespectively of sex, spiders fed prey contaminated with cadmium showed significantly higher values of comet parameters: tail DNA (TDNA), tail length (TL) and olive tail moment (OTM), in comparison with the control. In midgut gland cells, the level of DNA damage was higher for males than females, while in haemocytes the genotoxic effect of cadmium was greater in females. The obtained results indicate that in spiders cadmium displays strong genotoxic effects and may cause DNA damage even at low concentrations, however the severity of damage seems to be sex- and internal organ-dependent. The comet assay can be considered a sensitive tool for measuring the deleterious effect of cadmium on DNA integrity in spiders.

Patterns of phenoloxidase activity in insecticide resistant and susceptible mosquitoes differ between laboratory-selected and wild-caught individuals

Background

Insecticide resistance has the potential to alter vector immune competence and consequently affect the transmission of diseases.

Methods

Using both laboratory isogenic strains and field-caught Culex pipiens mosquitoes, we investigated the effects of insecticide resistance on an important component of the mosquito immune system: the phenoloxidase (PO) activity. As infection risk varies dramatically with the age and sex of mosquitoes, allocation to PO immunity was quantified across different stages of the mosquito life cycle.

Results

Our results were consistent in showing that larvae have a higher PO activity than adults, females have a higher PO activity than males, and PO activity declines with adult age. We obtained, however, a marked discrepancy between laboratory and field-collected mosquitoes on the effect of insecticide resistance on PO activity. In the laboratory selected strains we found evidence of strong interactions between insecticide resistance and the age and sex of mosquitoes. In particular, 7 and 14 day old esterase-resistant adult females and acetylcholine-esterase resistant males had significantly higher PO activities than their susceptible counterparts. No such effects were, however, apparent in field-caught mosquitoes.

Conclusions

Combined, the field and laboratory-based approaches employed in this study provide a powerful test of the effect of insecticide resistance on PO-mediated immunity. The use of laboratory-selected insecticide-resistant strains is still the most widely used method to investigate the pleiotropic effects of insecticide resistance. Our results suggest that the outcome of these laboratory-selected mosquitoes must be interpreted with caution and, whenever possible, compared with mosquitoes captured from the field.

Antioxidative responses in females and males of the spider Xerolycosa nemoralis (Lycosidae) exposed to natural and anthropogenic stressors

The aim of this study was to assess the intensity of enzymatic antioxidative parameters [i.e., superoxide dismutase (SOD), catalase (CAT), and the glutathione peroxidases each selene dependent, GPOX or selene independent, including GSTPx, glutathione S-transferase, and GST] and non-enzymatic antioxidative parameters [i.e., glutathione total (GSH-t), the heat shock proteins of Hsp70, and metallothioneins (Mt)] in the midgut glands of female and male wolf spiders Xerolycosa nemoralis (Lycosidae) exposed to natural stressors (i.e., heat shock and starvation) and anthropogenic stressors (i.e., the organophosphorous pesticide dimethoate) under laboratory conditions. The spiders were collected from two differentially polluted sites both localized in southern Poland: Olkusz, which is heavily polluted with metals, and Pilica, the reference site. In response to the stressing factors, increases in Hsp70 levels, in the concentrations of total glutathione and in the activity levels of glutathione-dependent enzymes (GPOX, GSTPx, and GST) were found in the midgut glands of males. In the females, high levels of activity of CAT and SOD were revealed, as well as an increased percentage of Mt-positive cells. Preexposed females, in comparison to the individuals from the reference site, responded with increased SOD activity, irrespective of the stressing factor. In contrast, the changes in the antioxidative parameters in the midgut glands of male X. nemoralis seem to reflect a short-term reaction to the applied stressors and do not confirm the effects of long-term selection in a polluted environment.

Gender differences in the immune system activities of sea urchin Paracentrotus lividus

In the immune system of vertebrates, gender-specific differences in individual immune competence are well known. In general, females possess more powerful immune response than males. In invertebrates, the situation is much less clear. For this purpose we have chosen to study the immune response of the two sexes of the echinoderm Paracentrotus lividus in pre- and post-spawning phases. The coelomic fluid from the echinoderms contains several coelomocyte types and molecules involved in innate immune defenses. In this article we report that the degree of immune responses in the P. lividus differs according to sex in both pre- and post-spawning phases. We found in all tests that females were more active than males. The results indicate that females possess a significant higher number of immunocytes consisting of phagocytes and uncolored spherulocytes. Since the immunological activity is mainly based on immunocytes, it was not surprising that females possessed the highest values of cytotoxicity and hemolysis activity and showed a greater ability to uptake neutral red and phagocyte yeasts cells, while the average number of ingested particles per active phagocyte was not significantly different. Furthermore, agglutinating activity was more evident in the coelomocyte lysate and coelomic fluid of females than in those of males. Finally we found that the acidic extract of female gonads possessed greater antimicrobial activity than that of male gonads. These results make it very likely that gender differences in the immune response are not restricted to vertebrates; rather, they are a general evolutionary phenomenon.

Variations of immune parameters in terrestrial isopods: a matter of gender, aging and Wolbachia

Ecological factors modulate animal immunocompetence and potentially shape the evolution of their immune systems. Not only environmental parameters impact on immunocompetence: Aging is one major cause of variability of immunocompetence between individuals, and sex-specific levels of immunocompetence have also been frequently described. Moreover, a growing core of data put in light that vertically transmitted symbionts can dramatically modulate the immunocompetence of their hosts. In this study, we addressed the influence of gender, age and the feminising endosymbiont Wolbachia (wVulC) on variations in haemocyte density, total PO activity and bacterial load in the haemolymph of the terrestrial isopod Armadillidium vulgare. This host-symbiont system is of particular interest to address this question since: (1) wVulC was previously shown as immunosuppressive in middle-aged females and (2) wVulC influences sex determination. We show that age, gender and Wolbachia modulate together immune parameters in A. vulgare. However, wVulC, which interacts with aging, appears to be the prominent factor interfering with both PO activity and haemocyte density. This interference with immune parameters is not the only aspect of wVulC virulence on its host, as reproduction and survival are also altered.

Correlation of hemocyte counts with different developmental parameters during the last larval instar of the tobacco hornworm, Manduca sexta

We determined the changes in hemocyte titer and in the abundance of hemocyte types of the tobacco hornworm Manduca sexta during the fourth and fifth larval stadium and the beginning of the pupal stadium. As we analyzed the samples of individual insects at daily intervals, we were able to correlate phenotypical features, body weight, as well as total protein content and lysozyme activity in the hemolymph with the observations on hemocytes. In the course of the fifth larval stadium, the hemocyte titer decreased slightly and declined further after pupation. Using calculated values for total hemocyte numbers, females had about five times and males three times more hemocytes in the circulating population at the beginning of the wandering stage (in the middle of the fifth larval stadium) than immediately after the last larval--larval molt (from the fourth to the fifth larval stadium). This sexual difference was mainly due to an increase in the number of plasmatocytes, which was more prominent in females than in males. Granular cells were dominant in early fifth larval stadium while plasmatocytes were the most abundant cells in pupae. Oenocytoids and spherule cells disappeared during the wandering stage. Lysozyme activity in the hemolymph rose to a maximum during the wandering stage, with females having lysozyme values twice as high as those for males. These changes in lysozyme activity, however, did not correlate with the increase of total hemolymph protein titer which occurred already at the beginning of the wandering stage. We postulate that changes in hemocyte titers are under direct hormonal control, which has to be proven in future experiments.

Male-biased sex-ratio distortion caused by Octosporea bayeri, a vertically and horizontally-transmitted parasite of Daphnia magna

Female-biased sex-ratio distortion is often observed in hosts infected with vertically-transmitted microsporidian parasites. This bias is assumed to benefit the spread of the parasite, because male offspring usually do not transmit the parasite further. The present study reports on sex-ratio distortion in a host-parasite system with both horizontal and vertical parasite transmission: the microsporidium Octosporea bayeri and its host, the planktonic cladoceran Daphnia magna. In laboratory and field experiments, we found an overall higher proportion of male offspring in infected than in uninfected hosts. In young males, there was no parasite effect on sperm production, but, later in life, infected males produced significantly less sperm than uninfected controls. This shows that infected males are fertile. As males are unlikely to transmit the parasite vertically, an increase in male production could be advantageous to the host during phases of sexual reproduction, because infected mothers may obtain uninfected grandchildren through their sons. Life-table experiments showed that, overall, sons harboured more parasite spores than their sisters, although they reached a smaller body size and died earlier. Male production may thus be beneficial for the parasite when horizontal transmission has a large pay-off as males may contribute more effectively to parasite spread than females.

The correlation between immunocompetence and an ornament trait changes over lifetime in Panorpa vulgaris scorpionflies

The immunocompetence-handicap hypothesis posits that costly male ornament traits might function to signal superior heritable immunocompetence to females. Quite a number of studies have aimed at testing this hypothesis. Yet the empirical data obtained so far are ambiguous. Many studies analysed the phenotypic correlation between handicap expression and immunocompetence at the same time point. However, since immunocompetence may change drastically over an individual's lifetime, such a singular measurement may not represent genetic differences among males and the benefits of choosing handicapped males for females might thus be weak. Here, I tested the correlation of a potential immunocompetence-handicap, the production of salivary secretions as nuptial gifts in a scorpionfly (Panorpa vulgaris), with immunocompetence at two different time points. I found a positive correlation with the handicap, but only if immunocompetence was measured shortly after expression of the handicap, i.e. briefly after mating in 2 weeks old scorpionflies. By contrast, there was no correlation with immunocompetence of the same flies at a younger age, i.e. shortly after adult emergence and a weak, insignificant trend for increased immunocompetence in offspring. These results are in agreement with positive phenotypic correlations between immunocompetence and handicap expression reported from other species, but advise caution when generalizing such one-time correlations.

Does gender really matter in contaminant exposure? A case study using invertebrate models

Exposure to contaminants in the environment is indiscriminate and multiple species/populations of all sexes are potentially at risk. In this paper we examine the current information available on gender specific differences in invertebrates following exposure to environmental contaminants. Because of their close association with the environment and diversity of habitats, invertebrates are uniquely at risk for adverse responses to pollutants. Since 97% of all animal species are invertebrates, it would be impossible to cover each of the phyla in this review. Instead, this paper discusses major invertebrate species including insects (Periplaneta americana, Panorpa vulgaris, Lycosa hilaris, Haematobia irritans irritans (L.), and Drosophilia melanogaster), nematodes (Caenorhabditis elegans), crustaceans (Streptocephalus dichotomus, Amphiascus tenuiremis, Microarthridion littorale, Tisbe bulbisetosa, Acartia tonsa, and Palaemonetes pugio), mollusks (Pinctada fucata martensii, Ilyanassa obsoleta, Nucella lapillus, Hinia reticulata, Thais clavigera, and Mercenaria mercenaria), corals (Euphyllia ancora and Montipara capitata), and echinoderms (Asterias rubens) that have been used in studies examining the differences between males and females. Our discussion focuses on gender differences that occur in both toxicokinetic mechanisms (uptake and elimination, metabolism and physiology) and other toxicological endpoints (survival and behavior as well as morphology and development). It will become evident that the endocrine systems of invertebrates have many traits and/or pathways that are comparable to those observed in higher organisms. Yet the sensitivity of some elements of the invertebrate endocrine system, e.g., disruption of neuropeptide hormone signaling following TBT exposure, highlights the uniqueness of their systems and their potential for disruption.

Age-dependent induction of immunity and subsequent survival costs in males and females of a temperate damselfly

BACKGROUND

To understand variation in resistance to parasites within host populations, researchers have examined conditions under which immunity is induced and/or is costly. Both host sex and age have been found to influence immune expression and subsequently are likely factors influencing the costs of resistance. The purpose of this study was to examine immune expression and associated survival costs for two age groups (newly emerged and sexually mature individuals) of the damselfly, Enallagma boreale Selys. Survival was assessed for experimentally challenged and control damselflies, housed initially at 22 degrees C and then subjected to low temperatures (15 degrees C) associated with reduced foraging activity and food deprivation. Experimental conditions emulated natural local variation in bouts of good weather followed by inclement weather (successions of days with hourly mean temperatures around 15 degrees C and/or rainy weather).

RESULTS

At least one of three immune traits was induced to higher levels for both newly emerged and mature E. boreale challenged by Lippopolysaccharide (LPS) relative to saline-injected controls, when housed at 22 degrees C. The immune traits assayed included haemocyte concentration, Phenoloxidase activity and antibacterial activity and their induction varied among ages and between males and females. For matures, those injected with LPS had lowered survivorship compared to saline-injected controls that were housed initially at 22 degrees C and subsequently at 15 degrees C. Newly emerged LPS-injected damselflies did not show reduced survivorship relative to newly-emerged controls, despite showing immune induction.

CONCLUSION

Reduced longevity following induction of immunity was observed for reproductively mature damselflies, but not for newly emerged damselflies. Costs of resistance depend only partly on the immune trait induced and more on the age (but not sex) of the host. In four years, we often observed bouts of inclement weather following good days and these bouts occurred primarily during the emergence periods, but also during the flight periods, of E. boreale. The duration of these bouts appear sufficient to compromise survival of mature damselflies that responded immunologically to LPS challenge. We further suggest the environmental conditions likely experienced by different ages of damselflies, following resistance expression, has influenced optimal immune investment by individuals in different age classes and the likelihood of detecting costs of resistance.

Sex and immunity in the yellow dung fly Scathophaga stercoraria

The immune system is of increasing interest to evolutionary biologists. Immunity may trade-off against other fitness components, with recent work suggesting reproduction in particular impinges on immune defence. There may also be sex differences in the immune system. Additionally, while life history traits typically have low heritability, little is known about additive genetic variance of immunity. An insect's major defence against multicellular pathogens is to encapsulate the invader. Phenoloxidase (PO) is a key enzyme in the cascade resulting in the melanized capsule, and is often used to estimate resistance to an immune insult. We examined the effects of copulation, egg laying, sex and age on PO in Scathophaga stercoraria. We also measured the heritability of PO activity. The sexes differed in haemolymph PO activity and PO was significantly affected by age, but not by copulation or egg laying. There was significant heritable variation for haemolymph PO.

IMMUNE SUPPRESSION AND THE COST OF REPRODUCTION IN THE GROUND CRICKET, ALLONEMOBIUS SOCIUS

One of the most common life history trade-offs in animals is the reduction in survivorship with increasing reproductive effort. Despite the prevalence of this pattern, its underlying physiological mechanisms are not well understood. Here we test the hypothesis that immune suppression mediates this phenotypic trade-off by manipulating reproductive effort and measuring immune function and mortality rates in the striped ground cricket, Allonemobius socius. Because A. socius males provide females with a hemolymph-based nuptial gift during copulation, and many structural components of immunity reside in the hemolymph, we also predicted that sexual selection may differentially affect how disease resistance evolves in males and females. We found that an increased mating effort resulted in a reduced immune ability, coupled with an increased rate in age-specific mortality for both sexes. Thus, immune suppression appears to be a link between reproductive effort and cost in this system. In addition, males and females appeared to differentially invest in several aspects of immunity prior to mating, with males exhibiting a higher concentration of circulating hemocytes and a superior bacterial defense capability. This pattern may be the result of previously established positive selection on gift size due to its affect on female fecundity. In short, female choice for larger gifts may lead to a sexually dimorphic immune ability.

Variation in phenoloxidase activity and its relation to parasite resistance within and between populations of Daphnia magna

Estimates of phenoloxidase (PO) activity have been suggested as a useful indicator of immunocompetence in arthropods, with the idea that high PO activity would indicate high immunocompetence against parasites and pathogens. Here, we test for variation in PO activity among clones of the planktonic crustacean Daphnia magna and its covariation with susceptibility to infections from four different microparasite species (one bacterium and three microsporidia). Strong clonal variation in PO activity was found within and among populations of D. magna, with 45.6% of the total variation being explained by the clone effect. Quantitative measures of parasite success in infection correlated negatively with PO activity when tested across four host populations. However, these correlations disappeared when the data were corrected for population effects. We conclude that PO activity is not a useful measure of resistance to parasites or of immunocompetence within populations of D. magna. We further tested whether D. magna females that are wounded to induce PO activity are more resistant to infections with the bacterium Pasteuria ramosa than non-wounded controls. We found neither a difference in susceptibility nor a difference in disease progression between the induced group and the control group. These results do not question the function of the PO system in arthropod immune response, but rather suggest that immunocompetence cannot be assessed by considering PO activity alone. Immune response is likely to be a multifactorial trait with various host and parasite characteristics playing important roles in its expression.

Evaluation of an innate immune reaction to parasites in earthworms

Encapsulation is an essential process of the invertebrate immune system and includes the prophenoloxidase (proPO) cascade. We present an assay for evaluating this immune response, now newly adapted to earthworms. Coelomic fluid is withdrawn and coelomocytes are stained with l-Dopa. We studied assay repeatability and the correlation between number of PO-active cells and infection level of the parasitic protozoan Monocystis sp. in the earthworm Lumbricus terrestris. Our study showed high assay repeatability although the expected negative relationship between PO-active coelomocytes and parasite load was not observed; yet a suggestion toward a positive relationship was detected. This finding is contrary to previous assumptions that presume coelomocyte concentrations to be the independent variable determining parasite load.

Sex differences in immunity in two species of field crickets

Immune defense often differs between the sexes, with males often having a weaker response, at least among many vertebrates. We examined encapsulation ability, a cell-mediated immune response, in laboratory and field populations of two species of field crickets, Teleogryllus oceanicus (Le Guillou, 1841) and Teleogryllus commodus (Walker, 1869), which have different life histories. In the seasonally breeding T. commodus, males show a stronger encapsulation response than females in both the laboratory and the field, although the difference is more marked under field conditions. The aseasonal T. oceanicus showed no sex difference in encapsulation in either field or laboratory samples fed ad libitum, but when food was experimentally reduced, the same pattern of stronger male response emerged. It is possible that this pattern may result from selection on females to increase investment in reproduction when time and energy for breeding are limited, as is more likely for seasonal breeders or animals under food restriction.

Sex differences in melanotic encapsulation responses (immunocompetence) in the damselfly Lestes forcipatus Rambur

A few studies have shown that male and female invertebrates differ in immunity and that these differences appear related to differences in sexual dimorphism and gender differences in life histories. Melanotic encapsulation of foreign objects in insects is one form of immunity. The damselfly Lestes forcipatus Rambur is moderately sexually dimorphic, and much is known about patterns of mass gain in congeners relating to differences in life history between males and females. In this study, females were more immunoresponsive than males under controlled temperatures, following emergence, and at a time when parasitic mites were challenging these hosts. However, males and females that overlapped in mass at emergence did not differ in their immune responses. Males in better condition at emergence were more immunoresponsive than lighter males, but this relation was not found in females. Sex differences in immune expression may have implications for how females versus males are able to deal with challenges from parasites, under varying environmental conditions.

Bateman's principle and immunity

The immunocompetence handicap hypothesis (ICHH) of Folstad and Karter has inspired a large number of studies that have tried to understand the causal basis of parasite-mediated sexual selection. Even though this hypothesis is based on the double function of testosterone, a hormone restricted to vertebrates, studies of invertebrates have tended to provide central support for specific predictions of the ICHH. I propose an alternative hypothesis that explains many of the findings without relying on testosterone or other biochemical feedback loops. This alternative is based on Bateman's principle, that males gain fitness by increasing their mating success whilst females increase fitness through longevity because their reproductive effort is much higher. Consequently, I predict that females should invest more in immunity than males. The extent of this dimorphism is determined by the mating system and the genetic correlation between males and females in immune traits. In support of my arguments, I mainly use studies on insects that share innate immunity with vertebrates and have the advantage that they are easier to study.

Effects of age and gender on immune function of dragonflies (Odonata, Lestidae) from a wild population

Immunity is a crucial determinant of fitness. Despite this, very few studies have addressed the expression of immune function in insect populations in the wild. I present data on two immune parameters, hemocyte load and expression of phenoloxidase, in adult damselflies (Lestes viridis) from a wild population. In a comparison of newly emerged with sexually mature adults, it was found that the latter had higher hemocyte loads but lower phenoloxidase expression. Mature females showed significantly higher phenoloxidase expression than mature males. The sexual differences might be explained by gender differences in life history.