Is the feeding and reproductive performance of the flea, Xenopsylla ramesis, affected by the gender of its rodent host, Meriones crassus?

Within-host and external environments differentially shape β-diversity across parasite life stages

Uncovering drivers of community assembly is a key aspect of learning how biological communities function. Drivers of community similarity can be especially useful in this task as they affect assemblage-level changes that lead to differences in species diversity between habitats. Concepts of β-diversity originally developed for use in free-living communities have been widely applied to parasite communities to gain insight into how infection risk changes with local conditions by comparing parasite communities across abiotic and biotic gradients. Factors shaping β-diversity in communities of immature parasites, such as larvae, are largely unknown. This is a key knowledge gap as larvae are frequently the infective life-stage and understanding variation in these larval communities is thus key for disease prevention. Our goal was to uncover links between β-diversity of parasite communities at different life stages; therefore, we used gastrointestinal nematodes infecting African buffalo in Kruger National Park, South Africa, to investigate within-host and extra-host drivers of adult and larval parasite community similarity. We employed a cross-sectional approach using PERMANOVA that examined each worm community at a single time point to assess independent drivers of β-diversity in larvae and adults as well as a longitudinal approach with path analysis where adult and larval communities from the same host were compared to better link drivers of β-diversity between these two life stages. Using the cross-sectional approach, we generally found that intrinsic, within-host traits had significant effects on β-diversity of adult nematode communities, while extrinsic, extra-host variables had significant effects on β-diversity of larval nematode communities. However, the longitudinal approach provided evidence that intrinsic, within-host factors affected the larval community indirectly via the adult community. Our results provide key data for the comparison of community-level processes where adult and immature stages inhabit vastly different habitats (i.e. within-host vs. abiotic environment). In the context of parasitism, this helps elucidate host infection risk via larval stages and the drivers that shape persistence of adult parasite assemblages, both of which are useful for predicting and preventing infectious disease.

Fitness consequences of host colonization in two generalist fleas: Context-dependency and the effect of spatial co-occurrence

We studied the fitness consequences of colonizing a novel host by experimental lines of fleas (Synosternus cleopatrae and Xenopsylla ramesis) maintained for 18-22 generations on the principal or novel (sympatric or allopatric) hosts via number, developmental success and size of the offspring of the fleas exploiting these hosts. We asked whether (a) fitness on non-principal hosts increases after prolonged maintenance; (b) the colonization success depends on the spatial co-occurrence of a flea and a host and (c) colonization of a novel host is accompanied by a decreased ability to exploit an original host. The ability of fleas to colonize novel hosts differed between species, with S. cleopatrae, but not X. ramesis, increasing its offspring production on novel hosts. Spatial co-occurrence did not affect colonization success. Maintenance on an alternative host was not accompanied by decreased adaptation to the original host. When fleas returned to the original host, their reproductive output was higher than that of their ancestors. We conclude that the success of colonizing a novel host is (a) context-dependent and varies between flea and host species and (b) not accompanied by the loss of ability to exploit an ancestral host but may lead to an increase in this ability.

Adaptation to a novel host and performance trade-off in host-generalist and host-specific insect ectoparasites

We investigated the performance trade-offs of fleas (Siphonaptera) while adapting to a novel host using two host generalists (Xenopsylla conformis and Xenopsylla ramesis) and one host specialist (Parapulex chephrenis) maintained on their principal hosts (Meriones crassus for Xenopsylla and Acomys cahirinus for P. chephrenis). We asked whether, over generations, (i) a host generalist may become a specialist by evolving the ability to exploit a novel host and losing the ability to exploit an original host and (ii) a host specialist can become a generalist by evolving the ability to exploit a novel host without losing the ability to exploit an original host. We established an experimental line of each species on a novel host (Acomys russatus for Xenopsylla and M. crassus for P. chephrenis) and maintained this line on this host during 23 generations. We compared reproductive performance of progenitors of each line and their descendants when they exploited either original or novel host in terms of egg number and size, hatching success, offspring production, and offspring size. We found changes in performance over generations in female offspring size only. Xenopsylla conformis demonstrated a tendency to become a host specialist (increased performance on the novel host with a concomitant decreased performance on the original host), whereas P. chephrenis demonstrated a tendency to become a host generalist (increased performance on the novel host without a concomitant decreased performance on the original host). We conclude that the probability of generalist to specialist transition, and vice versa, is context-dependent and varies between species.

Effects of ectoparasite infestation during pregnancy on physiological stress and reproductive output in a rodent-flea system

Biotic and abiotic stressors impose various fitness costs on individuals across a variety of taxa. In vertebrates, these stressors typically trigger complex neuroendocrine responses that stimulate glucocorticoid (GC) secretion from the adrenal cortex. Short-term elevation of GCs can be adaptive as it shifts energy toward physiological processes that cope with acute stressors; however, chronic increases in GC levels could have detrimental effects on fitness. Parasitism can be considered an important biotic stressor in nature and a possible cause of reproductive failure that could substantially affect an individual's fitness. Thus, we aimed to test the effects of parasitism and maternal stress, as measured by GCs, during pregnancy and the relationship between these variables and measures of reproductive output using a rodent-flea system. Female Egyptian spiny mice (Acomys cahirinus) were randomly assigned to flea (Parapulex chephrenis) infested or uninfested treatments before and during pregnancy. The offspring of these females were flea-free. Feces were collected at five time points during the experiment to determine maternal fecal glucocorticoid metabolite (FGCM) concentrations. Overall, infested females had lower FGCM levels during gestation but higher FGCM levels post-parturition and larger mass changes than uninfested females. Additionally, models related to pup quality and quantity often included some measure of maternal investment or body condition moderating relationships between infestation and stress. This suggests that flea parasitism or high GC levels alone might not significantly impact host reproduction but rather females can experience different effects depending on their level of investment, which could be limited by body condition and/or the number of pups present in a litter.

The relationship between fleas and small mammals in households of the Western Yunnan Province, China

The Yunnan province has one of the most serious outbreaks of the plague epidemic in China. Small mammals and fleas are risk factors for the occurrence of plague in commensal plague foci. Understanding the relationship between fleas and small mammals will help control fleas and prevent the onset of the plague. Four hundred and twenty-one small mammals, belonging to 9 species, were captured. Of these, 170 small mammals (40.4%) were found infested with fleas. A total of 992 parasitic fleas (including 5 species) were collected. The number of Leptopsylla segnis and Xenopsylla cheopis accounted for 91.03% (903/992). The final multiple hurdle negative binomial regression model showed that when compared with Rattus tanezumi, the probability of flea infestation with Mus musculus as well as other host species decreased by 58% and 99%, respectively, while the number of flea infestations of the other host species increased by 4.71 folds. The probability of flea prevalence in adult hosts increased by 74%, while the number of fleas decreased by 76%. The number of flea infestations in small male mammals increased by 62%. The number of fleas in small mammals weighing more than 59 g has been multiplied by about 4. R. tanezumi is the predominant species in households in the west Yunnan province, while L.segnis and X. cheopis were dominant parasitic fleas. There is a strong relationship between the abundance of fleas and the characteristics of small mammals (e.g. Species, age, sex, and body weight).

Flea infestation, social contact, and stress in a gregarious rodent species: minimizing the potential parasitic costs of group-living

Both parasitism and social contact are common sources of stress that many gregarious species encounter in nature. Upon encountering such stressors, individuals secrete glucocorticoids and although short-term elevation of glucocorticoids is adaptive, long-term increases are correlated with higher mortality and deleterious reproductive effects. Here, we used an experimental host-parasite system, social rodents Acomys cahirinus and their characteristic fleas Parapulex chephrenis, in a fully-crossed design to test the effects of social contact and parasitism on stress during pregnancy. By analysing faecal glucocorticoid metabolites, we found that social hierarchy did not have a significant effect on glucocorticoid concentration. Rather, solitary females had significantly higher glucocorticoid levels than females housed in pairs. We found a significant interaction between the stressors of parasitism and social contact with solitary, uninfested females having the highest faecal glucocorticoid metabolite levels suggesting that both social contact and infestation mitigate allostatic load in pregnant rodents. Therefore, the increased risk of infestation that accompanies group-living could be outweighed by positive aspects of social contact within A. cahirinus colonies in nature.

Effects of maternal and grandmaternal flea infestation on offspring quality and quantity in a desert rodent: evidence for parasite-mediated transgenerational phenotypic plasticity

Parasites can cause a broad range of sublethal fitness effects across a wide variety of host taxa. However, a host's efforts to compensate for possible parasite-induced fitness effects are less well-known. Parental effects may beneficially alter the offspring phenotype if parental environments sufficiently predict the offspring environment. Parasitism is a common stressor across generations; therefore, parental infestation could reliably predict the likelihood of infestation for offspring. However, little is known about relationships between parasitism and transgenerational phenotypic plasticity. Thus, we investigated how maternal and grandmaternal infestation with fleas (Xenopsylla ramesis) affected offspring quality and quantity in a desert rodent (Meriones crassus). We used a fully-crossed design with control and infested treatments to examine litter size, pup body mass at birth, and pup mass gain before weaning for combinations of maternal and grandmaternal infestation status. No effect of treatment on litter size or pup body mass at birth was found. However, maternal and grandmaternal infestation status significantly affected pre-weaning body mass gain, a proxy for the rate of maturation, in male pups. Pups gained significantly more weight before weaning if maternal and grandmaternal infestation statuses matched, regardless of the treatment. Thus, pups whose mothers and grandmothers experienced similar risks of parasitism, either both non-parasitized or both infested, would reach sexual maturity more quickly than those pups whose mothers' infestation status did not match that of their grandmothers. These results support the contention that parents can receive external cues such as the risk of parasitism, that prompt them to alter offspring provisioning. Therefore, parasites could be a mediator of environmentally-induced maternal effects and could affect host reproductive fitness across multiple generations.

Can we predict the success of a parasite to colonise an invasive host?

To understand whether a parasite can exploit a novel invasive host species, we measured reproductive performance (number of eggs per female per day, egg size, development rate and size of new imagoes) of fleas from the Negev desert in Israel (two host generalists, Synosternus cleopatrae and Xenopsylla ramesis, and a host specialist, Parapulex chephrenis) when they exploited either a local murid host (Gerbillus andersoni, Meriones crassus and Acomys cahirinus) or two alien hosts (North American heteromyids, Chaetodipus penicillatus and Dipodomys merriami). We asked whether (1) reproductive performance of a flea differs between an alien and a characteristic hosts and (2) this difference is greater in a host specialist than in host generalists. The three fleas performed poorly on alien hosts as compared to local hosts, but the pattern of performance differed both among fleas and within fleas between alien hosts. The response to alien hosts did not depend on the degree of host specificity of a flea. We conclude that successful parasite colonisation of an invasive host is determined by some physiological, immunological and/or behavioural compatibility between a host and a parasite. This compatibility is unique for each host-parasite association, so that the success of a parasite to colonise an invasive host is unpredictable.

Flea fitness is reduced by high fractional concentrations of CO₂ that simulate levels found in their hosts' burrows

Nidicolous ectoparasites such as fleas and gamasid mites that feed on small and medium-sized mammals spend much of their time in their hosts' burrows, which provide an environment for living, and often feeding, to their pre-imaginal and/or adult stages. Thus, these ectoparasites should be adapted to environmental conditions in burrows, including high fractional concentrations of CO2 (F(CO2)). We examined how a high F(CO2) (0.04) affected survival and reproductive success of a hematophagous ectoparasite of burrowing rodents using fleas Xenopsylla ramesis and Sundevall's jirds Meriones crassus. In the first experiment, fleas fed on hosts housed in high-CO2 (F(CO2) =0.04) or atmospheric-CO2 (F(CO2) ≈0.0004) air, and were allowed to breed. In a second experiment, fleas were maintained in high CO2 or CO2-free air with no hosts to determine how CO2 levels affect survival and activity levels. We found that at high F(CO2) fleas laid fewer eggs, reducing reproductive success. In addition, at high F(CO2), activity levels and survival of fleas were reduced. Our results indicate that fleas do not perform well in the F(CO2) used in this experiment. Previous research indicated that the type and intensity of the effects of CO2 concentration on the fitness of an insect depend on the F(CO2) used, so we advise caution when generalizing inferences drawn to insects exposed to other F(CO2). If, however, F(CO2) found in natural mammal burrows brings about reduced fitness in fleas in general, then burrowing hosts may benefit from reduced parasite infestation if burrow air F(CO2) is high.

Preliminary Survey of Ectoparasites and Associated Pathogens from Norway Rats in New York City

The Norway rat (Rattus norvegicus) is a reservoir of many zoonotic pathogens and lives in close proximity to humans in urban environments. Human infection with rodent-borne disease occurs either directly through contact with a rat or its excreta, or indirectly via arthropod vectors such as fleas and ticks. Here, we report on the diversity and abundance of ectoparasitic arthropod species and associated pathogenic bacteria from 133 Norway rats trapped over a 10-mo period in Manhattan, New York, NY. Norway rats were host to the tropical rat mite [Ornithonyssus bacoti (Hirst)], the spiny rat mite (Laelaps echidnina Berlese), Laelaps nuttalli Hirst, the spined rat louse [Polyplax spinulosa (Burmeister)], and the Oriental rat flea [(Xenopsylla cheopis) (Rothschild)], with an average of 1.7 species per individual. A flea index of 4.1 X. cheopis was determined, whereas previous studies in New York City reported 0.22 fleas per rat. Multiple species of pathogenic Bartonella were identified from Oriental rat fleas that were related to Bartonella tribocorum, Bartonella rochalimae, and Bartonella elizabethae. However, no evidence of Yersinia pestis or Rickettsia spp. infection was detected in fleas. The identification of multiple medically important ectoparasite species in New York City underscores the need for future efforts to fully characterize the diversity and distribution of ectoparasites on Norway rats, and assess the risk to humans of vector-borne disease transmission.

Sex differences in flea infections among rodent hosts: is there a male bias?

Recognizing patterns of parasite distribution among wildlife hosts is of major importance due to growing risk of transmission of zoonotic diseases to humans. Thus, sex-dependent parasite distribution in higher vertebrates is extensively studied, and males are often found more parasitized than females. Male-biased parasitism may be the result of weaker immunocompetence of male hosts owing to the immunosuppressive effect of androgens. Moreover, larger hosts (males) may demonstrate higher parasite infestation levels than smaller individuals (females), as they constitute a better nutritional resource for parasites and provide them with a greater variety of niches. In the present work, we investigated sex-dependent patterns of flea distribution among three common rodent species (Apodemus agrarius, Apodemus flavicollis, and Myodes glareolus). We hypothesized that males have a higher flea infestation than females. We confirm male-biased parasitism in A. agrarius and M. glareolus, but not in A. flavicollis. Additionally, flea infestation increased with body mass in A. agrarius, but not in A. flavicollis and M. glareolus. The detected differences in parasite distribution among sexes are probably the result of immunosuppressive effects of androgens and spatial behavior of males.

Variable effects of host characteristics on species richness of flea infracommunities in rodents from three continents

We studied the effect of host gender and body mass on species richness of flea infracommunities in nine rodent host species from three biomes (temperate zone of central Europe, desert of the Middle East and the tropics of East Africa). Using season- and species-specific generalized linear mixed models and controlling for year-to-year variation, spatial clustering of rodent sampling and over-dispersion of the data, we found inconsistent associations between host characteristics and flea species richness. We found strong support for male-biased flea parasitism, especially during the reproductive period (higher species richness in male hosts than in females) in all considered European rodents (Apodemus agrarius, Myodes glareolus and Microtus arvalis) and in one rodent species from the Middle East (Dipodillus dasyurus). In contrast, two of three African rodent species (Lophuromys kilonzoi and Praomys delectorum) demonstrated a trend of female-biased flea species richness. Positive associations between body mass and the number of flea species were detected mainly in males (five of nine species: A. agrarius, M. glareolus, M. arvalis, D. dasyurus and Mastomys natalensis) and not in females (except for M. natalensis). The results of this study support earlier reports that gender-biased, in general, and male-biased, in particular, infestation by ectoparasites is not a universal rule. This suggests that mechanisms of parasite acquisition by an individual host are species-specific and have evolved independently in different rodent host-flea systems.

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.

Host reproductive status and reproductive performance of a parasite: offspring quality and trade-offs in a flea parasitic on a rodent

We investigated offspring quality in fleas (Xenopsylla ramesis) feeding on non-reproducing, pregnant or lactating rodents (Meriones crassus) and asked whether (a) quality of flea offspring differs dependent on host reproductive status; (b) fleas trade off offspring quantity for quality; and (c) quality variables are inter-correlated. Emergence success was highest when parents exploited pregnant hosts, while development time was longest when parents exploited lactating hosts. Male offspring from fleas fed on non-reproductive and pregnant hosts were larger than those from lactating hosts whereas female offspring from fleas fed on pregnant hosts were larger than those from both lactating and non-reproductive hosts. Male offspring survived under starvation the longest when their parents exploited lactating hosts and the shortest when their parents exploited pregnant hosts. Female offspring of parents that exploited lactating hosts survived under starvation longer than those that exploited non-reproductive and pregnant hosts. Emergence success and development time decreased as mean number of eggs laid by mothers increased. Fleas that were larger and took longer to develop lived significantly longer under starvation. These results indicate the presence of a trade-off between offspring quantity and quality in fleas exploiting female Sundevall's jird in varying reproductive condition but this trade-off depended on the quality trait considered.

Energy expenditure for egg production in arthropod ectoparasites: the effect of host species

We studied the energy cost of egg production in two flea species (Parapulex chephrenis and Xenopsylla ramesis) feeding on principal (Acomys cahirinus and Meriones crassus, respectively) and auxiliary (M. crassus and A. cahirinus, respectively) rodent hosts. We predicted that fleas feeding on principal as compared with auxiliary hosts will (a) expend less energy for egg production; (b) produce larger eggs and (c) live longer after oviposition. Both fleas produced more eggs and spent less energy per egg when exploiting principal hosts. Parapulex chephrenis produced larger eggs after exploiting auxiliary hosts, while the opposite was true for X. ramesis. After oviposition, P. chephrenis fed on the auxiliary hosts survived for a shorter time than those fed on the principal hosts, while in X. ramesis the survival time did not differ among hosts. Our results suggested that one of the proximate causes for lower reproductive performance and subsequent lower abundance of fleas on auxiliary hosts is the higher energy cost of egg production. However, in some species, lower offspring number may be compensated to some extent by their size, although this compensation may also compromise their future reproduction via decreased survival. In addition, the reproductive strategy of exploitation of low profitable (i.e. auxiliary) hosts may differ between flea species.

Sex-biased parasitism is not universal: evidence from rodent-flea associations from three biomes

The distribution of parasites among individual hosts is characterised by high variability that is believed to be a result of variations in host traits. To find general patterns of host traits affecting parasite abundance, we studied flea infestation of nine rodent species from three different biomes (temperate zone of central Europe, desert of Middle East and tropics of East Africa). We tested for independent and interactive effects of host sex and body mass on the number of fleas harboured by an individual host while accounting for spatial clustering of host and parasite sampling and temporal variation. We found no consistent patterns of the effect of host sex and body mass on flea abundance either among species within a biome or among biomes. We found evidence for sex-biased flea infestation in just five host species (Apodemus agrarius, Myodes glareolus, Microtus arvalis, Gerbillus andersoni, Mastomys natalensis). In six rodent species, we found an effect of body mass on flea abundance (all species mentioned above and Meriones crassus). This effect was positive in five species and negative in one species (Microtus arvalis). In M. glareolus, G. andersoni, M. natalensis, and M. arvalis, the relationship between body mass and flea abundance was mediated by host sex. This was manifested in steeper change in flea abundance with increasing body mass in male than female individuals (M. glareolus, G. andersoni, M. natalensis), whereas the opposite pattern was found in M. arvalis. Our findings suggest that sex and body mass are common determinants of parasite infestation in mammalian hosts, but neither of them follows universal rules. This implies that the effect of host individual characteristics on mechanisms responsible for flea acquisition may be manifested differently in different host species.

Effects of Bartonella spp. on flea feeding and reproductive performance

Numerous pathogens are transmitted from one host to another by hematophagous insect vectors. The interactions between a vector-borne organism and its vector vary in many ways, most of which are yet to be explored and identified. These interactions may play a role in the dynamics of the infection cycle. One way to evaluate these interactions is by studying the effects of the tested organism on the vector. In this study, we tested the effects of infection with Bartonella species on fitness-related variables of fleas by using Bartonella sp. strain OE 1-1, Xenopsylla ramesis fleas, and Meriones crassus jirds as a model system. Feeding parameters, including blood meal size and metabolic rate during digestion, as well as reproductive parameters, including fecundity, fertility, and life span, were compared between fleas experimentally infected with Bartonella and uninfected fleas. In addition, the developmental time, sex ratio, and body size of F1 offspring fleas were compared between the two groups. Most tested parameters did not differ between infected and uninfected fleas. However, F1 males produced by Bartonella-positive females were significantly smaller than F1 males produced by Bartonella-negative female fleas. The findings in this study suggest that bartonellae are well adapted to their flea vectors, and by minimally affecting their fitness they have evolved to better spread themselves in the natural environment.

Reproductive consequences of host age in a desert flea

We tested for the effect of age of a rodent host (Meriones crassus) on reproductive performance of fleas in terms of number and quality of offspring and predicted that fleas would perform better on juvenile and old than on subadult and adult hosts. The number of flea offspring was evaluated via egg and new imago production, while their quality was estimated via duration of development, resistance to starvation and body size. Although fleas produced more eggs when they exploited adults than when they exploited juvenile, subadult and old hosts, significantly more new imago emerged from fleas fed on juvenile and old hosts than on subadult and adult hosts. Fleas performed better when they fed on juvenile and/or old hosts than on subadult and adult hosts in 2 of 3 measures of offspring quality (duration of development and body size). Nevertheless, when offspring quality was estimated via resistance to starvation of a new imago, fleas demonstrated good performance in young (juvenile and subadult) hosts, while they performed poorly in old hosts. Thus, general reproductive performance of fleas was better when they exploited young and old hosts than when they exploited median age cohorts. However, the effect of host age on flea reproductive performance was manifested somewhat differently between (a) male and female hosts and (b) male and female flea offspring.

Remnant fragments within an agricultural matrix enhance conditions for a rodent host and its fleas

Habitat fragmentation can adversely impact biodiversity, although where remnant fragments of natural vegetation provide favourable conditions the negative effects of fragmentation may be mitigated. Host-parasite systems in fragmented areas have only recently been examined, with parasites generally showing higher prevalence and richness in fragments, mediated by changes in host density. However, the effect of fragmentation on parasite body size and fecundity remains poorly investigated. Thus, here we compared the body size and condition of a generalist rodent host, Rhabdomys pumilio and the body size of 2 common flea species between pristine natural areas and remnant fragments within agriculture areas. Host body length, weight and body condition values were significantly larger in fragments than in pristine natural vegetation. Listropsylla agrippinae fleas showed the same pattern, being significantly larger in fragments, while Chiastopsylla rossi fleas did not differ in size between fragments and natural areas. The differential response of the 2 flea species may reflect the strength of association between the host and parasite, with the former spending a greater proportion of its lifespan on the host. Therefore, in this study agriculture fragments provide better conditions for both an opportunistic rodent and a closely associated flea species.

Digesting blood of an auxiliary host in fleas: effect of phylogenetic distance from a principal host

Fleas are haematophagous ectoparasites that exhibit varying degrees of host specificity. Flea abundance is highest on principal hosts and lower on auxiliary hosts but may vary greatly among auxiliary hosts. We investigated the feeding and energy expenditure for digestion in two flea species Parapulex chephrenis and Xenopsylla ramesis on a principal host (Acomys cahirinus and Meriones crassus, respectively) and eight auxiliary host species. We predicted that fleas would perform better - that is (i) a higher proportion of fleas would take a blood meal, (ii) fleas would take larger blood meals and (iii) fleas would spend less energy on digestion - if they fed on (i) a principal host compared with an auxiliary host and (ii) an auxiliary host phylogenetically close to a principal host compared with an auxiliary host phylogenetically distant from a principal host. Energy costs of digestion were estimated using CO(2) emission and represented energy cost during the first stage of blood digestion. Contrary to our predictions, fleas did not always perform better on a principal than on an auxiliary host or on auxiliary hosts phylogenetically closer to the principal host than on auxiliary hosts phylogenetically distant from a principal host. Variation in flea feeding performance may result from the interplay of several factors including co-occurrence between hosts and susceptibility of a host to flea attacks, the species-specific level of immunocompetence of a host and the level of host specificity of a flea. This study describes the first investigation into the metabolic expenditure of parasitism and its relationship to phylogenetic relationships amongst hosts.

Gerbils

The gerbil is usually nonaggressive and is one of the easiest rodents to maintain and handle. Its disposition, curious nature, relative freedom from naturally occurring infectious diseases, and adaptability to its environment have contributed to its popularity as a laboratory animal. Gerbils are found in deserts and semiarid geographical regions of the world. The Mongolian gerbils that are available today originated from 20 pairs of captured animals that were maintained in 1935 in a closed, random-bred colony at the Kitasato Institute in Japan. Gerbils have several unique anatomical and physiological features. Mature gerbils are smaller than rats, but larger than mice. Mongolian gerbils are attracted to saliva and use salivary cues to discriminate between siblings and nonsiblings, and females use oral cues in the selection of sociosexual partners. Gerbils have been used as experimental models in a number of areas of biomedical research. Gerbils are excellent subjects for laboratory animal research as they are susceptible to bacterial, viral, and parasitic pathogens that affect humans and other species. Gerbils may have spontaneous seizures secondary to stress such as handling, cage change, abrupt noises, or changes in the environment. Cystic ovaries are seen commonly in female gerbils over 1 year of age. Gerbils have unique characteristics, which make them appropriate for a number of animal models. Classically, gerbils have been used in research involving stroke, parasitology, infectious diseases, epilepsy, brain development and behavior, and hearing.

Feeding performance of fleas on different host species: is phylogenetic distance between hosts important?

We asked if and how feeding performance of fleas on an auxiliary host is affected by the phylogenetic distance between this host and the principal host of a flea. We investigated the feeding of 2 flea species, Parapulex chephrenis and Xenopsylla ramesis, on a principal (Acomys cahirinus and Meriones crassus, respectively) and 8 auxiliary host species. We predicted that fleas would perform better (higher proportion of fleas would feed and take larger bloodmeals) on (a) a principal rather than an auxiliary host and (b) auxiliary hosts phylogenetically closer to a principal host. Although feeding performance of fleas differed among different hosts, we found that: (1) fleas did not always perform better on a principal host than on an auxiliary host; and (2) flea performance on an auxiliary host was not negatively correlated with phylogenetic distance of this host from the principal host. In some cases, fleas fed better on hosts that were phylogenetically distant from their principal host. We concluded that variation in flea feeding performance among host species results from interplay between (a) inherent species-specific host defence abilities, (b) inherent species-specific flea abilities to withstand host defences and (c) evolutionary tightness of association between a particular host species and a particular flea species.

The effect of host age on feeding performance of fleas

We asked whether the age of a rodent host affects the feeding performance of fleas. We predicted that fleas would perform better on young and old than on adult rodents. To test this prediction, we determined bloodmeal size, rate of digestion and time of survival after a single bloodmeal inXenopsylla ramesisfeeding onMeriones crassusof different ages. Fleas took less blood from subadult and adult than from juvenile and old animals. Fleas digested blood of old hosts at the highest rate and blood of juvenile hosts most slowly. After a bloodmeal, fleas survived the longest if fed on a juvenile host. The effect of host gender on bloodmeal size and survival after a bloodmeal was manifested only in (a) subadult and adult hosts and (b) subadult hosts, respectively. Host gender affected the rate of digestion differently among digestion stages and host age cohorts. We explain the observed patterns in flea performance in terms of changes in the host's immune defences and nutritional quality of blood during the host's individual life. Our observations suggested that a host of a particular age could not be unequivocally predicted to be more or less beneficial for a parasite than a younger or an older host.

Influence of host profitability and microenvironmental conditions on parasite specialization on a main and an alternative hosts

Parasite success depends on both host profitability and the microenvironment provided by the host, which together define host-parasite compatibility and can differ between hosts. We experimentally disentangled the effects of host profitability and microenvironmental conditions provided by nest material on the reproduction of a nest-based ectoparasite when exploiting its main and an alternative avian host species. Parasite reproductive performance was similar on both hosts when breeding in nests of their own species, suggesting no difference in host-parasite compatibility between hosts. The apparent parasite specialization could therefore result from differences in host-parasite encounter processes. However, when hosts were successful, the main host produced more young in infested nests, whereas the alternative host produced less; furthermore, host reproductive performance was higher in nests of the main host species, suggesting that this nest material alleviates parasitism cost. Therefore, our results suggest different evolutionary responses to parasites of the main and alternative hosts, with either higher tolerance or higher resistance, modulated by nest material.

Host gender and offspring quality in a flea parasitic on a rodent

The quality of offspring produced by parent fleas (Xenopsylla ramesis) fed on either male or female rodent hosts (Meriones crassus) was studied. The emergence success, duration of development, resistance to starvation upon emergence and body size of the flea offspring were measured. It was predicted that offspring of fleas produced by parents that fed on male hosts (i) will survive better as pre-imago, (ii) will develop faster, (iii) will live longer under starvation after emergence and (iv) will be larger than offspring of fleas fed on female hosts. The emergence success of pre-imaginal fleas was relatively high, ranging from 46.9% to 100.0% and averaging 78.4±3.0%, and was not affected by host gender. The duration of development of pre-imaginal fleas depended on the gender of the host of parents and differed between male and female offspring, with female fleas developing faster. Furthermore, male fleas developed faster if their parents fed on female rather than on male hosts, whereas no difference in the duration of development between host genders was found in female fleas. The time to death under starvation did not depend on the gender of either the flea or the host. A newly emerged flea, on average, lived 31.9±1.0 days without access to food. The relationship between host gender and body size of male flea offspring was the only effect that supported the predictions. An increase in body size in male fleas could increase their mating success and, ultimately, their fitness.

Variation within and among host species in engorgement of larval trombiculid mites

We recovered larval trombiculid mites (i.e. chiggers), vectors of scrub typhus, from small mammal hosts in Taiwan, and compared the relative degree of engorgement (RDE) of the dominant chigger (Leptotrombidium imphalum) from different hosts. Naturally occurring chiggers recovered from Rattus losea and Bandicota indica were 1·4x and 1·3x as engorged as those from Apodemus agrarius. Within each host species, RDE was negatively related to chigger loads, but was mostly unrelated to gender or to body or reproductive condition of hosts. We documented significant variation in chigger engorgement both within and among host species; to the extent that RDE is a proxy for fitness, this contradicts predictions of the Ideal Free Distribution (IFD) that the per capita fitness of vectors should be similar among hosts. Failure to meet predictions of the IFD may reflect the limited mobility of chiggers, which consequently must be less selective in the hosts on which they feed. Further disease control efforts should consider vector feeding success in addition to vector abundance and may be able to capitalize on the unsuitability of certain hosts in supporting disease vectors.

The effect of larval density on pre-imaginal development in two species of desert fleas

We studied the effect of density of larvae on pre-imaginal development in 2 flea species (Xenopsylla conformis and Xenopsylla ramesis) parasitic on 2 desert rodent species (Dipodillus dasyurus, adult body mass 20 g and Meriones crassus, 80 g). We predicted a decrease in duration of development with an increase in density of larvae. In general, in both flea species, duration of larva-to-pupa development decreased with an increasing larval density. In addition, this stage of development was longer in male fleas and in fleas from parents fed on D. dasyurus. The effect of larval density on larval development was manifested mainly when parent fleas fed on D. dasyurus. Duration of pupation decreased with increasing larval density only in offspring of fleas fed on G. dasyurus. In both fleas, pupation was longer in males. The effect of parent host on duration of pupation was found in X. ramesis only (longer if the host was M. crassus). Resistance of newly emerged fleas to starvation depended mainly on parent host species. Young X. conformis survived longer if their parents fed on D. dasyurus, whereas young X. ramesis survived longer if their parents fed on M. crassus. It was also found that (a) an individual flea that spent more time as a larva also spent more time as a pupa and (b) longer larval development resulted in a shorter time that a newly emerged flea was able to survive when starved.