Maternal and direct effects of the intestinal nematode Heligmosomoides polygyrus on offspring growth and susceptibility to infection

Parasitism in viviparous vertebrates: an overview

The reproductive mode of viviparity has independently evolved in various animal taxa. It refers to the condition in which the embryos or young develop inside the female's body during gestation, providing advantages such as protection, nutrition, and improved survival chances. However, parasites and diseases can be an evolutionary force that limit the host's resources, leading to physiological, morphological, and behavioral changes that impose additional costs on both the pregnant female and her offspring. This review integrates the primary literature published between 1980 and 2021 on the parasitism of viviparous hosts. We describe aspects such as reproductive investment in females, offspring sex ratios, lactation investment in mammals, alterations in birth intervals, current reproductive investment, variations between environments, immune system activity in response to immunological challenges, and other factors that can influence the interaction between viviparous females and parasites. Maintaining pregnancy incurs costs in managing the mother's resources and regulating the immune system's responses to the offspring, while simultaneously maintaining an adequate defense against parasites and pathogens. Parasites can significantly influence this reproductive mode: parasitized females adjust their investment in survival and reproduction based on their life history, environmental factors, and the diversity of encountered parasites.

Experimental reduction of haemosporidian infection affects maternal reproductive investment, parental behaviour and offspring condition

When hosts have a long coevolutionary history with their parasites, fitness costs of chronic infection have often been assumed to be negligible. Yet, experimental manipulation of infections sometimes reveals effects of parasites on their hosts, particularly during reproduction. Whether these effects translate into fitness costs remains unclear. Here, we present the results of an experimental study conducted in a free-ranging population of red-winged blackbirds (Agelaius phoeniceus) naturally experiencing a high prevalence of haemosporidian infections, with more than 95% of breeding adults infected with parasites from one or more haemosporidian genus. To assess effects of infection during reproduction, we manipulated adult red-winged blackbird females' parasite burden by administering an anti-haemosporidian medication before onset of egg-laying. Experimental reduction of infection resulted in significant benefits to mothers and their offspring. Medicated females laid heavier clutches, invested more in incubation and provisioning behaviour, and produced more fledglings than control females. Nestlings of medicated females had higher haematocrit, higher blood glucose, and lower reactive oxygen metabolites than nestlings of control females. Overall, our results provide evidence that, even in a species with high prevalence of infection, parasites can lead to decreased maternal investment and offspring quality, substantially reducing fitness.

Within-litter covariance of allele-specific MHC heterozygosity, coccidian endoparasite load and growth is modulated by sibling differences in starting mass

Although littermates in altricial mammals usually experience highly similar environmental conditions during early life, considerable differences in growth and health can emerge among them. In a study on subadults of a European rabbit (Oryctolagus cuniculus) population with low MHC polymorphism, we tested whether litter-sibling differences in endoparasitic coccidia load and body mass at the end of the vegetation period were associated with within-litter differences in starting body mass (measured around 2 weeks prior to weaning) and in immune-genetic (MHC class II DRB) constitution. We hypothesized that siblings with a lighter starting mass might be more susceptible to endoparasite infections and thus, negative effects of a more unfavourable MHC constitution might be particularly pronounced in such individuals. Within-litter comparisons revealed that animals with a lighter starting mass reached a relatively lower body mass in autumn. Furthermore, there were indications for an allele-specific heterozygote advantage, as animals with heterozygous combinations of the allele Orcu-DRB*4 had relatively lower hepatic coccidia loads than their littermates with certain homozygous allele combinations. Consistent with our hypothesis, significantly higher hepatic coccidia loads and tendentially lower autumn body masses in homozygous compared to heterozygous individuals for the allele Orcu-DRB*4 were evident in initially lighter but not in heavier siblings, suggesting synergistic effects between an unfavourable MHC constitution and a light starting mass. Taken together, these effects might lead to notable differences in fitness among litter siblings, as a low body mass and a high endoparasite burden are key factors limiting young rabbits' survival during winter.

Behavioral, physiological and morphological correlates of parasite intensity in the wild Cururu toad (Rhinella icterica)

Large numbers of parasites are found in various organs of anuran amphibians, with parasite intensities thought to modulate the host's Darwinian fitness traits. Interaction between the anuran hosts and their multiple parasites should modulate the host's phenotypic characteristic, such as those associated with high energetic demand (such as calling effort and locomotor performance), energy balance (standard metabolic rate), and morphological plasticity (as indicated by organ masses). The present study investigated the impact of parasite intensities on the behavioral, physiological, and morphological traits of wild adult male Rhinella icterica (Anura: Bufonidae). We tested as to whether individuals with higher parasite intensities would present: 1) lower vocal calling effort in the field, as well as poorer locomotor performance and body-condition index; and 2) higher standard metabolic rates and internal organ masses. Measurements included: calling effort in the field; standard metabolic rate; locomotor performance; parasite intensity; internal organ masses (heart, liver, kidneys, intestines, stomach, lungs, hind limb muscle, and spleen); and the body-condition index. Results showed a negative association of parasite intensities with locomotor performance, and standard metabolic rate of R. icterica. A positive association between parasite intensities and relative organ masses (heart, intestines and kidneys) was also evident. Toads with higher pulmonary and intestinal parasites intensities also showed higher total parasite intensities.

Helminth Interaction with the Host Immune System: Short-Term Benefits and Costs in Relation to the Infectious Environment

Chronic infections imply that the parasite and the host immune system closely interact for a long time without a fatal outcome. Environmental changes encountered by hosts and parasites, such as coinfections, can deeply affect the stability of this apparent equilibrium. Our study aimed to determine the effect of the infectious environment on the costs and benefits of chronic infection with the gut nematode Heligmosomoides polygyrus in mice. Heligmosomoides polygyrus is known for its capacity to actively interfere with the host immune response by secreting molecules that can dampen immunity. We simulated bacterial coinfection of H. polygyrus-infected CBA-strain mice during the chronic phase of the infection by injecting them with Escherichia coli lipopolysaccharide. We found that infection by H. polygyrus induced only weak costs for the host (in terms of reproductive investment) and was characterized by the upregulation of both Th1 (interferon-γ) and anti-inflammatory (transforming growth factor-β) cytokines, which is favorable to parasite persistence. However, when co-occurring with the simulated bacterial infection, H. polygyrus infection was associated with a pronounced shift toward a pro-inflammatory status, which was deleterious to both the parasite and the host. Our study highlights the dynamic equilibrium reached during chronic infection, where a rapid environmental change, such as a concomitant bacterial infection, can deeply affect the outcome of the host-parasite interaction.

Speeding up Growth: Selection for Mass-Independent Maximal Metabolic Rate Alters Growth Rates

Investigations into relationships between life-history traits, such as growth rate and energy metabolism, typically focus on basal metabolic rate (BMR). In contrast, investigators rarely examine maximal metabolic rate (MMR) as a relevant metric of energy metabolism, even though it indicates the maximal capacity to metabolize energy aerobically, and hence it might also be important in trade-offs. We studied the relationship between energy metabolism and growth in mice (Mus musculus domesticus Linnaeus) selected for high mass-independent metabolic rates. Selection for high mass-independent MMR increased maximal growth rate, increased body mass at 20 weeks of age, and generally altered growth patterns in both male and female mice. In contrast, there was little evidence that the correlated response in mass-adjusted BMR altered growth patterns. The relationship between mass-adjusted MMR and growth rate indicates that MMR is an important mediator of life histories. Studies investigating associations between energy metabolism and life histories should consider MMR because it is potentially as important in understanding life history as BMR.

Assessing the energetic costs and trade-offs of a PHA-induced inflammation in the subterranean rodent Ctenomys talarum: immune response in growing tuco-tucos

A traditional approach used to assess whether immune defense is costly is to explore the existence of trade-offs between immunity and other functions; however, quantitative studies of the energetic costs associated with the activation of the immune system are scarce. We assessed the magnitude of a PHA-triggered immune response and the associated energetic costs in 60-day old Ctenomys talarum. We expected that the magnitude of the macroscopic inflammatory response to PHA is lower in young tuco-tucos compared with that of adults, given the allocation of substantial energy to growth, and that the magnitude of the inflammation is lower in male pups compared to females, due to the higher investment in growth of the larger sex. Concomitantly, we expected that the pups challenged with PHA show an increase in oxygen consumption compared to control animals and that a positive association exists between magnitude of the PHA-induced inflammation and oxygen consumption. Contrary to what was expected, young tuco-tucos mounted a higher inflammatory response compared with adults and there were no differences in the magnitude of this response between sexes. The inflammatory response induced by a PHA injection did not represent a significant energetic cost for young tuco-tucos. There were no differences in oxygen consumption between PHA-injected and control animals, and tuco-tucos that mounted a higher inflammatory response to PHA did not show higher oxygen consumption. Energy expenditure, however, is not the only physiological cost involved in trade-offs between immune response and various functions of the organism, and other currencies are discussed.

Ectoparasite performance when feeding on reproducing mammalian females: an unexpected decrease when on pregnant hosts

Reproduction is an energy-demanding activity in mammalian females, with increased energy requirements during pregnancy and, especially, during lactation. To better understand the interactions between parasitism and host reproduction, we investigated feeding and reproductive performance of fleas (Xenopsylla ramesis) parasitizing non-reproducing, pregnant or lactating gerbilline rodents (Meriones crassus). Based on energetic considerations, we predicted that feeding and reproductive performance of fleas would be lowest on non-breeding females, moderate on pregnant females and highest on lactating females. We estimated feeding performance of the fleas via absolute and mass-specific bloodmeal size and reproductive performance via egg production and latency to peak oviposition. Host reproductive status had no effect on either absolute or mass-specific bloodmeal size or the day of peak oviposition, but significantly affected the daily number of eggs produced by a female flea. Surprisingly, and contrary to our predictions, egg production of fleas fed on pregnant rodents was significantly lower than that of fleas on non-reproducing and lactating rodents, while no difference in egg production between fleas feeding on non-reproducing and lactating hosts was found. Our results suggest that differences in parasite reproduction when feeding on hosts of different reproductive status are not associated with the different energy requirements of the hosts at non-breeding, pregnancy and lactation but rather with variation in hormonal and/or immune status during these periods.

Parental experience of a risky environment leads to improved offspring growth rate

Parasites (or diseases) are major selective force for the evolution of life history traits and parasite-host evolution. Mothers can show a variety of responses to parasites during pregnancy with different consequences for them or their offspring. However, whether information in the maternal environment before pregnancy can cause a change in the phenotype of the offspring is unknown. To avoid the confounding effect of pathogens and to reduce the risk of direct effect of mother's immune activation, we injected female laboratory mice with lipopolysaccharides (LPS) before mating. In order to provide a constant information on the potential infectious risk of the environment, females were mated with males that were also exposed to LPS before mating. Offspring from immune-challenged parents were larger and grew at a faster rate than offspring from control parents (injected with PBS). Additionally, offspring from immune-challenged parents that suffered the most from inflammation grew at a faster rate than offspring from low suffering parents. Producing heavier offspring that will reach sexual maturity earlier is likely to have fitness benefit for parents and offspring through improved reproductive success.

Maternal protein deficiency during a gastrointestinal nematode infection alters developmental profile of lymphocyte populations and selected cytokines in neonatal mice

Neonatal immune development begins in pregnancy and continues into lactation and may be affected by maternal diet. We investigated the possibility that maternal protein deficiency (PD) during a chronic gastrointestinal (GI) nematode infection could impair neonatal immune development. Beginning on d 14 of pregnancy, mice were fed protein-sufficient (PS; 24%) or protein-deficient (PD; 6%) isoenergetic diets and were infected weekly with either 0 (sham) or 100 Heligmosomoides bakeri larvae. Pups were killed on d 2, 7, 14, and d 21 and dams on d 20 of lactation. Lymphoid organs were weighed. Cytokine concentration in maternal and pup serum and in milk from pup stomachs and lymphoid cell populations in pup spleen and thymus were determined using luminex and flow cytometry, respectively. GI nematode infection increased Th2 cytokines (IL-4, IL-5, IL-13), IL-2, IL-10, and eotaxin in serum of dams whereas PD reduced IL-4 and IL-13. The lower IL-13 in PD dams was associated with increased fecal egg output and worm burdens. Maternal PD increased vascular endothelial growth factor in pup milk and eotaxin in pup serum. Maternal infection increased eotaxin in pup serum. Evidence of impaired neonatal immune development included reduced lymphoid organ mass in pups associated with both maternal infection and PD and increased percentage of T cells and T:B cell ratio in the spleen associated with maternal PD. Findings suggest that increases in specific proinflammatory cytokines as a result of the combination of infection and dietary PD in dams can impair splenic immune development in offspring.

Infection before pregnancy affects immunity and response to social challenge in the next generation

Natural selection should favour parents that are able to adjust their offspring's life-history strategy and resource allocation in response to changing environmental and social conditions. Pathogens impose particularly strong and variable selective pressure on host life histories, and parental genes will benefit if offspring are appropriately primed to meet the immunological challenges ahead. Here, we investigated transgenerational immune priming by examining reproductive resource allocation by female mice in response to direct infection with Babesia microti prior to pregnancy. Female mice previously infected with B. microti gained more weight over pregnancy, and spent more time nursing their offspring. These offspring generated an accelerated response to B. microti as adults, clearing the infection sooner and losing less weight as a result of infection. They also showed an altered hormonal response to novel social environments, decreasing instead of increasing testosterone production upon social housing. These results suggest that a dominance-resistance trade-off can be mediated by cues from the previous generation. We suggest that strategic maternal investment in response to an infection leads to increased disease resistance in the following generation. Offspring from previously infected mothers downregulate investment in acquisition of social dominance, which in natural systems would reduce access to mating opportunities. In doing so, however, they avoid the reduced disease resistance associated with increased testosterone and dominance. The benefits of accelerated clearance of infection and reduced weight loss during infection may outweigh costs associated with reduced social dominance in an environment where the risk of disease is high.

Maternal transfer of antibodies in vertebrates: trans-generational effects on offspring immunity

Maternal effects by which females provide their offspring with non-genetic factors such as hormones, nutrients and antibodies can have an important impact on offspring fitness. In vertebrates, maternal antibodies (matAb) are transferred from the mother, via the placenta, egg yolk or milk during lactation to offspring until they are 2 weeks (birds), 4-10 weeks (rodents) and 9 months (humans) old, respectively. matAb transfer can have direct effects on offspring growth rate in birds and rodents, probably by passively protecting the newborn from common pathogens before their endogenous immune system has matured. Indirect long-term effects of matAb transfer on the offspring's own immunity can be synergistic, if matAb act as antigen templates of the accumulated immunological experience of the mother and educate the newborn's immune system. However, it may also be suppressive if matAb reduce antigen presentation to the newborn resulting in antigen-specific blocking of offspring endogenous immunity. Our aim is to review the mechanisms and direct effects of matAb transfer in vertebrates with an emphasis on birds, outline a framework for research on the long-term effects of matAb on the endogenous immune system of the mature offspring and encourage ecological and evolutionary studies of matAb transfer in non-domesticated animals.

Parasites prevent summer breeding in white-footed mice, Peromyscus leucopus

Food and parasites can independently play a role in destabilizing population fluctuations of animals, and yet, more than 50 years ago, David Lack proposed that these two factors should act in concert. We examined the role of these factors on the vital rates of free-living white-footed mice (Peromyscus leucopus) over the summer and autumn months. We used a replicated factorial experiment in which deer exclosures doubled acorn availability and anthelmintic application reduced gastrointestinal helminths. Specifically, we wanted to know if either factor or an interaction between the two accounted for the midsummer breeding hiatus observed in this species. We found no influence of habitat quality on mouse breeding, vital rates, or demography; however, anthelmintic treatment resulted in mice continuing to reproduce during the hiatus at the same rate as previously, and they also exhibited increased body condition, growth rate, and survival. These results provide evidence that gastrointestinal helminths reduce P. leucopus reproductive output in central Pennsylvania, and these effects on reproduction could play a role in the unstable dynamics of small mammals.

Maternal antibodies reduce costs of an immune response during development

Young vertebrates are dependent primarily on innate immunity and maternally derived antibodies for immune defense. This reliance on innate immunity and the associated inflammatory response often leads to reduced growth rates after antigenic challenge. However, if offspring have maternal antibodies that recognize an antigen, these antibodies should block stimulation of the inflammatory response and reduce growth suppression. To determine whether maternal and/or offspring antigen exposure affect antibody transmission and offspring growth, female Japanese quail (Coturnix japonica) and their newly hatched chicks were immunized. Mothers were immunized with lipopolysaccharide (LPS), killed avian reovirus vaccine (AR), or were given a control, phosphate-buffered saline, injection. Within each family, one-third of offspring were immunized with LPS, one-third were immunized with AR, and one-third were given the control treatment. Maternal immunization significantly affected the specific types of antibodies that were transmitted. In general, immunization depressed offspring growth. However, offspring immunized with the same antigen as their mother exhibited elevated growth in comparison to siblings immunized with a different antigen. This suggests that the growth suppressive effects of antigen exposure during development can be partially ameliorated by the presence of maternal antibodies, but in the absence of specific maternal antibodies, offspring are dependent on more costly innate immune defenses. Together, the results suggest that the local disease environment of mothers prior to reproduction significantly affects maternal antibody transmission and these maternal antibodies may allow offspring to partially maintain growth during infection in addition to providing passive humoral immune defense.

Leptin levels and body composition of mice selectively bred for high voluntary locomotor activity

Selective breeding produced four replicate lines of high-runner (HR) mice that run on wheels for approximately 2.7 times more revolutions per day than four unselected control lines. Previous studies found that HR mice of both sexes have lower body fat (isotope dilution at 15 wk of age) and that males (females not studied) have smaller retroperitoneal fat pads (17 wk). HR mice also exhibit elevated plasma corticosterone and insulin-stimulated glucose uptake by some hindlimb muscles but apparently do not differ in circulating insulin or glucose levels (males at 18 wk). Given their lower body fat and higher activity levels, we hypothesized that HR mice would have lower circulating leptin levels than controls. Female mice were given wheel access for 6 d at 7 wk of age, as part of the routine wheel testing for the selective breeding protocol, and then were killed after one additional week without wheels to reduce possible acute effects of activity on leptin. As hypothesized, serum leptin levels were significantly lower in HR mice. ANCOVA indicated that leptin was strongly positively correlated with both total body fat (measured by ether extraction) and body mass change from weaning, but HR mice still had significantly lower adjusted leptin levels (ANCOVA). Within HR lines but not within control lines, individual variation in leptin levels was negatively correlated with amount or speed of wheel running measured a week before being killed. Growth from weaning to euthanasia and body dry mass were lower in HR mice than in controls, but absolute dry masses of the ventricles, liver, gut, and uterus plus ovaries did not significantly differ, nor did percentage of the total dry mass as fat. HR mice offer a novel model for studying the causes and consequences of physiologically relevant variations in serum leptin.

Linking demography and host dispersal to Trichuris arvicolae distribution in a cyclic vole species

Spatial structure in the distribution of pathogen infection can influence both epidemiology and host-parasite coevolutionary processes. It may result from the spatial heterogeneity of intrinsic and extrinsic factors, or from the local population dynamics of hosts and parasites. In this study, we investigated the effects of landscape, host dispersal and demography (population abundance and phase of the fluctuation) on the distribution of a gastro-intestinal nematode Trichuris arvicolae in the fossorial water vole Arvicola terrestris sherman. This rodent exhibits outbreaks occurring regularly in Franche-Comté (France). Thirteen out-of-phase populations were studied in autumn 2003. They exhibited highly different T. arvicolae prevalences. The heterogeneity in prevalences was not explained by population structure, landscape or vole abundance, but by the phase of the vole population fluctuations. Populations at the end of the high density phase showed null prevalence whereas populations in increase or outbreak phases exhibited higher prevalences. Population genetic analyses based on microsatellites revealed significant differentiation between vole populations, and higher dispersal rates of young voles compared with old ones. These younger individuals were also infected more frequently than older voles. This suggested a role of host dispersal in the distribution of T. arvicolae. However, there was a strong discrepancy between the spatial patterns of prevalence and of host genetics or demographic phase. Genetic differentiation and differences in demographic phase exhibited significant spatial autocorrelations whereas prevalence did not. We concluded that the distribution of T. arvicolae is influenced by vole dispersal, although this effect might be overwhelmed by local adaptation processes or environmental conditions.

Transgenerational priming of immunity: maternal exposure to a bacterial antigen enhances offspring humoral immunity

Young vertebrates have limited capacity to synthesize antibodies and are dependent on the protection of maternally transmitted antibodies for humoral disease resistance early in life. However, mothers may enhance fitness by priming their offspring's immune systems to elevate disease resistance. Transgenerational induced defences have been documented in plants and invertebrates, but maternal priming of offspring immunity in vertebrates has been essentially neglected. To test the ability of mothers to stimulate the immune systems of offspring, we manipulated maternal and offspring antigen exposure in a wild population of birds, pied flycatchers (Ficedula hypoleuca). We show that immunization of the mother before egg laying apparently stimulates a transgenerational defence against pathogens by elevating endogenous offspring antibody production. If the disease environments encountered by mothers and offspring are similar, this transgenerational immune priming may allow young to better cope with the local pathogen fauna.

The use of Trichuris suis and other helminth therapies to treat Crohn’s disease

Infections with gastrointestinal (GI) nematodes are prevalent worldwide, despite the fact that anti-helminthic medications are regarded as safe, efficient, and widely available globally. In this review, we highlight the potential therapeutic benefits that may be realized through the clinical use of Trichuris suis and other helminths for Crohn's disease (CD). Long-lived helminthic parasites are remarkable in their ability to down-regulate host immunity, protecting themselves from elimination, and also minimize severe pathological host changes. This review summarizes what is known about the underlying mechanisms that may account for the observed patterns in humans treated with helminths for CD. The Th2 arm of the immune system is emphasized as a component of primary importance in the association between the host immune system and GI nematode infections. Although GI nematode infections in humans cause significant morbidity and mortality, the existence and nature of protective mechanisms these helminths may confer remain largely unclear.

Opisthorchis viverrini: influence of maternal infection in hamsters on offspring infected with homologous parasite and their IgG antibody response

We investigated the influence in hamsters of a maternal Opisthorchis viverrini infection on their offspring infected with homologous parasites and the kinetics of the O. viverrini-specific IgG antibody responses. No significant difference (P > 0.05) was found in the specific IgG antibody response and the number of O. viverrini eggs per gram feces (EPG) between infected offspring from infected mothers and infected offspring from uninfected mothers. A significant difference (P < 0.05) of EPG per worm was found between infected offspring from infected mothers and infected offspring from uninfected mothers only when the offspring were infected with O. viverrini after weaning at 5 weeks of age. The worm loads in infected offspring from infected mothers were significantly less than that in infected offspring from uninfected mothers. This study demonstrated that maternal infection effects worm fecundity and the worm load in an infected offspring.

Effects of three simultaneous demands on glucose transport, resting metabolism and morphology of laboratory mice

In nature, animals must successfully respond to many simultaneous demands from their environment in order to survive and reproduce. We examined physiological and morphological responses of mice given three demands: intestinal parasite infection with Heligmosomoides polygyrus followed by caloric restriction (70% of ad libitum food intake versus ad libitum for 10 days) and/or cold exposure (5 degrees C vs. 23 degrees C for 10 days). We found significant interactions between these demands as well as independent effects. Small intestine structure and function changed with demands in both independent and interactive ways. Body mass decreased during caloric restriction and this decrease was greater for cold-exposed than warm-exposed mice. In ad libitum fed mice, body mass did not change with either cold exposure or parasite infection but body composition (fat versus lean mass of whole body or organs) changed with both demands. Generally, organ masses decreased with caloric restriction (even after accounting for body mass effects) and increased with cold exposure and parasite infection whereas fat mass decreased with both caloric restriction and parasite infection. Mass adjusted resting metabolic rate (RMR) increased with cold exposure, decreased with caloric restriction but, unlike previous studies with laboratory mice, did not change with parasite infection. Our results demonstrate that the ability of mice to respond to a demand is influenced by other concurrent demands and that mice show phenotypic plasticity of morphological and physiological features ranging from the tissue level to the level of the whole organism when given three simultaneous demands.

Immune response to fleas in a wild desert rodent: effect of parasite species, parasite burden, sex of host and host parasitological experience

We studied immune responses of the jird Meriones crassus to different flea species belonging to the same family. We used jirds maintained in an outdoor enclosure (enclosure; N=18) and parasitized by fleas Xenopsylla conformis mycerini and Xenopsylla ramesis, and also jirds born in the laboratory to previously parasitized mothers(laboratory animals; N=23). We asked (i) whether cross-immunity to different fleas occurs, (ii) whether there is a sex difference in immune responses to flea parasitism and (iii) whether the severity of the immune responses depends on parasite load. In the enclosure animals, immune response to antigen from the unfamiliar flea Synosternus cleopatrae pyramidisdid not differ from those to antigens from the familiar fleas. In contrast,laboratory rodents demonstrated no difference in the immune response between S. c. pyramidis antigen and either the phytohemagglutinin treatment or controls, although their responses to antigens of fleas familiar to their mothers (X. c. mycerini and X. ramesis) were significantly higher than those to antigen of S. c. pyramidis and phytohemagglutinin. The results clearly demonstrated that (i) cross-reactivity in rodent responses to different flea species occurred for enclosure but not for laboratory jirds and (ii) immune-naïve animals whose mothers were parasitized by fleas had some degree of immunity against fleas. The only sex difference in immunological parameters was the higher level of circulating immune complexes in females than in males. Only phagocytic activity was affected by flea burden, decreasing with an increase in flea numbers.

Aerobic Performance of Wild‐Derived House Mice Does Not Change with Cold Exposure or Intestinal Parasite Infection

Aerobic performance is affected by numerous endogenous and exogenous factors. We investigated the effects of ambient temperature and parasite infection on resting metabolism and maximal exercise-induced oxygen consumption in wild-derived house mice (Mus musculus). We also collected preliminary data for effects of lactation on these measures of aerobic performance. Mice were experimentally infected with a naturally occurring intestinal nematode (Heligmosomoides polygyrus) and then exposed to cold temperatures for 10 d or allowed to mate and reproduce. Wild-derived house mice did not change their resting metabolism with H. polygyrus infection or cold exposure, which is in stark contrast to similar studies with laboratory mice. Preliminary data also showed no effect of lactation on aerobic performance. Similarly, maximal exercise-induced oxygen consumption and hematocrit and hemoglobin were unaffected by all experimental treatments. We conclude that resting metabolism, maximal oxygen consumption, and hematology of wild-derived house mice are unaffected by exogenous (temperature) and endogenous (H. polygyrus) demands and, therefore, wild-derived mice respond to these demands without incurring potential costs associated with changes in aerobic performance.

Are mice calorically restricted in nature?

An important question about traditional caloric restriction (CR) experiments on laboratory mice is how food intake in the laboratory compares with that of wild mice in nature. Such knowledge would allow us to distinguish between two opposing views of the anti-aging effect of CR--whether CR represents, in laboratory animals, a return to a more normal level of food intake, compared with excess food consumption typical of laboratory conditions or whether CR represents restriction below that of animals living in nature, i.e. the conditions under which house mice evolved. To address this issue, we compared energy use of three mouse genotypes: (1) laboratory-selected mouse strains (= laboratory mice), (2) house mice that were four generations or fewer removed from the wild (= wild-derived mice) and (3) mice living in nature (= wild mice). We found, after correcting for body mass, that ad libitum fed laboratory mice eat no more than wild mice. In fact, under demanding natural conditions, wild mice eat even more than ad libitum fed laboratory mice. Laboratory mice do, however, eat more than wild-derived mice housed in similar captive conditions. Therefore, laboratory mice have been selected during the course of domestication for increased food intake compared with captive wild mice, but they are not particularly gluttonous compared with wild mice in nature. We conclude that CR experiments do in fact restrict energy consumption beyond that typically experienced by mice in nature. Therefore, the retarded aging observed with CR is not due to eliminating the detrimental effects of overeating.