Is sex-biased ectoparasitism related to sexual size dimorphism in small mammals of Central Europe?

Abiotic and biotic determinants of tick burdens in the eastern rock sengi (Elephantulus myurus)

Ticks are important vectors of pathogens of medical and veterinary importance worldwide. In spite of their economic importance, our current knowledge about the factors affecting tick prevalence and abundance in tropical and subtropical regions is rather limited. Both abiotic (e.g. temperature) as well as biotic variables (e.g. host sex) have been identified as key determinants of distributions. Eastern rock sengis or elephant shrews (Elephantulus myurus, Macroscelidea: Cacroscelididae, Thomas & Schwann) are widely distributed throughout Africa and can harbour a large number of tick species and substantial tick burdens. In the present study, we evaluated the contribution of climate and host factors on tick burdens of sengis. Throughout the year sengis carried high abundances of immature stages of a single tick species, Rhipicephalus sp. near warburtoni. There was no evidence that host parameters affected tick burdens. However, larval abundance decreased with increasing ambient temperatures and both larvae and nymphs were negatively affected by rainfall 2 months before the sampling month. In addition, nymphal burdens decreased with increasing minimum temperatures. Our results suggest that climate factors are the largest constraint for the immature stages of R. sp. near warburtoni and that eastern rock sengis could play a crucial role in the dynamics of tick-borne diseases as a result of the large tick burdens they can sustain.

Measuring animal welfare within a reintroduction: an assessment of different indices of stress in water voles Arvicola amphibius

Reintroductions are an increasingly common conservation restoration tool; however, little attention has hitherto been given to different methods for monitoring the stress encountered by reintroduced individuals. We compared ten potential measures of stress within four different categories (neuroendocrine, cell function, body condition and immune system function) as proxies for animal welfare in water voles being reintroduced to the Upper Thames region, Oxfordshire, UK. Captive-bred voles were assessed pre-release, and each month post-release for up to five months. Wild-born voles were captured in the field and assessed from two months post-release. Plasma corticosteroid, hydration and body condition of captive-bred voles differed between their pre-release measures and both their first (“short-term”) recapture, and their final recapture (“long-term” release), however only body condition and immunocompetence measured using the Nitroblue Tetrazolium (NBT) test were significantly different post-release between the first and last recaptures. Captive-bred animals had lower fat reserves, higher weight/length ratios and better immunocompetence (NBT) than did wild-born voles. Captive-bred males had higher ectoparasite burdens compared to wild-born males and, as reintroduction site quality decreased, became less hydrated. These observations indicate that some methods can identify changes in the stress response in individuals, highlighting areas of risk in a reintroduction programme. In addition, a single measure may not provide a full picture of the stress experienced; instead, a combination of measures of different physiological systems may give a more complete indication of stress during the reintroduction process. We highlight the need to monitor stress in reintroductions using measures from different physiological systems to inform on possible animal welfare improvements and thus the overall success rate of reintroductions.

Ectoparasite Community Structure of Two Bats (Myotis lucifugus and M. septentrionalis) from the Maritimes of Canada

Prevalence of bat ectoparasites on sympatric Myotis lucifugus and M. septentrionalis was quantitatively characterized in Nova Scotia and New Brunswick by making systematic collections at swarming sites. Six species of ectoparasite were recorded, including Myodopsylla insignis, Spinturnix americanus, Cimex adjunctus, Macronyssu scrosbyi, Androlaelap scasalis, and an unknown species of the genus Acanthophthirius. Male M. lucifugus and M. septentrionalis had similar prevalence of any ectoparasite (22% and 23%, resp.). Female M. lucifugus and M. septentrionalis had 2-3 times higher prevalence than did conspecific males (68% and 44%, resp.). Prevalence of infection of both genders of young of the year was not different from one another and the highest prevalence of any ectoparasite (M. lucifugus 64%, M. septentrionalis 72%) among all bat groups. Ectoparasite prevalence and intensity varied positively with roost group size and negatively with grooming efficacy and energy budgets, suggesting that these variables may be important in ectoparasite community structure.

From parasite encounter to infection: multiple-scale drivers of parasite richness in a wild social primate population

Host parasite diversity plays a fundamental role in ecological and evolutionary processes, yet the factors that drive it are still poorly understood. A variety of processes, operating across a range of spatial scales, are likely to influence both the probability of parasite encounter and subsequent infection. Here, we explored eight possible determinants of parasite richness, comprising rainfall and temperature at the population level, ranging behavior and home range productivity at the group level, and age, sex, body condition, and social rank at the individual level. We used a unique dataset describing gastrointestinal parasites in a terrestrial subtropical vertebrate (chacma baboons, Papio ursinus), comprising 662 fecal samples from 86 individuals representing all age-sex classes across two groups over two dry seasons in a desert population. Three mixed models were used to identify the most important factor at each of the three spatial scales (population, group, individual); these were then standardized and combined in a single, global, mixed model. Individual age had the strongest influence on parasite richness, in a convex relationship. Parasite richness was also higher in females and animals in poor condition, albeit at a lower order of magnitude than age. Finally, with a further halving of effect size, parasite richness was positively correlated to day range and temperature. These findings indicate that a range of factors influence host parasite richness through both encounter and infection probabilities but that individual-level processes may be more important than those at the group or population level.

An attempt to use ectoparasites as tags for habitat occupancy by small mammalian hosts in central Europe: effects of host gender, parasite taxon and season

OBJECTIVE

We used data on fleas and gamasid mites parasitic on 8 species of small mammals to test whether (a) species composition of ectoparasite infracommunities may be used to predict host habitat occupancy and (b) the accuracy of this prediction differs between ectoparasite taxa, host genders and seasons.

METHODS

We used a Random Forests algorithm that is based on the methodology of classification trees.

RESULTS

The accuracy of prediction of habitat occupancy was relatively low and varied substantially among host species. The combined rate of the correct prediction of host habitat occupancy from data on ectoparasites was significantly higher than 50%, albeit being relatively low. The accuracy of prediction (a) did not differ between male and female hosts when it was based on species composition of fleas in summer or of mites in summer and winter, (b) was significantly higher in male hosts than in female hosts when the winter data on fleas were used and (c) was significantly higher for flea than mite assemblages. The effect of season was found in mites but not in fleas with the accuracy of prediction being significantly higher in summer than in winter assemblages.

CONCLUSIONS

Ectoparasites appeared to be not especially useful as biological markers for distinguishing host populations in different habitats in temperate zones.

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.

Spatial variation in gender-biased parasitism: host-related, parasite-related and environment-related effects

The gender-biased pattern of parasite infestation has been shown to be a complicated phenomenon that cannot be explained by a single mechanism but rather involves several different mechanisms. We asked what are the factors that affect the manifestation and extent of gender-biased parasitism and studied the relationship between parasite-related (mean abundance, mean species richness and total species richness of all parasites), host-related (rodent density and proportion of reproductive males and females both separately and together) and environment-related (mean daily maximal and minimal temperatures, rainfall and relative humidity) factors and the magnitude of gender-biased infestation of a South African rodent Rhabdomys pumilio by ixodid ticks, gamasid mites, lice and fleas. We found that spatial variation in gender differences in parasite infestation was affected by parasite-, host- and environment-related factors, although the set of factors affecting gender differences in infestation differed among higher taxa of ectoparasites. Gender differences in infestation by fleas and lice were affected mainly by parasite-related factors, whereas gender differences in infestation by ticks and, in part, by mites were affected mainly by host-related and environmental factors. In addition, spatial variation in most measures of gender difference in mite infestation remained unexplained.

Parasite-specific variation and the extent of male-biased parasitism; an example with a South African rodent and ectoparasitic arthropods

We asked whether the occurrence and the extent of host gender-biased parasitism vary among higher parasite taxa, among individual species within these taxa and within parasite species among localities. To answer this question, we studied prevalence, abundance, species richness and the level of aggregation of ectoparasites (ticks, mites, lice and fleas) collected from male and female striped mice (Rhabdomys pumilio) in 9 localities of the Western Cape Province of South Africa. We used meta-analyses to compare parasitological variables between male and female hosts across localities for individual parasite species and higher taxa as well as across parasite species within a higher taxon. Whenever gender-biased parasitism was found, it indicated higher infestation of male than female hosts (except 1 low abundant mite species). We found that the occurrence and extent of gender-biased infestation varied mainly within a parasite species among localities and among parasite species within a higher taxon but not among parasite taxa. Our results suggest that the extent of a gender-biased pattern of parasite infestation of the same host may not only involve host-related mechanisms but also depends on biological features of a particular parasite species.

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

Male-biased parasitism is commonly found in higher vertebrates and is most likely to be a result of higher mobility and lower immunocompetence of male hosts than female hosts. The latter would result in higher fitness of parasites exploiting males rather than females. To test this hypothesis, we investigated foraging and reproductive performance of fleas (Xenopsylla ramesis) parasitizing male and female Meriones crassus, a gerbilline rodent. We allowed fleas to feed on groom-restricted rodents and predicted that: (1) the size of a blood meal would be greater from a male than a female host and (2) female fleas will produce more eggs when exploiting a male than a female host. There was no effect of host gender on the mass-specific amount of blood consumed by a flea across eight days of feeding. However, on the first day fleas on a male rodent consumed significantly more blood than fleas on a female rodent. Thereafter, the amount of blood consumed from a male host tended to decrease whereas that from a female host tended to increase. A higher proportion of fleas satiated earlier than 60 min when they fed on male rather than on female hosts but this proportion decreased from the first to the last feeding event. Fleas produced significantly more eggs when they fed on male rather than on female hosts for days one to five of oviposition. We concluded that gender difference in immune defence is the mechanism behind male-biased parasitism.

Patterns of parasitism and body size in red squirrels (Tamiasciurus hudsonicus)

Parasites use their hosts for nutrition, shelter, and even dispersal; the latter can result in sex-biased parasite distribution. Host sex-biased parasitism has been well documented in vertebrates, including mammals, and males are often more parasitized than females. Male-biased parasitism is often attributed to sexual size dimorphism, with larger animals being more parasitized. Here, we used a natural population of red squirrels ( Tamiasciurus hudsonicus (Erxleben, 1777)), a species without sexual size dimorphism, to test for sex-biased parasitism in ectoparasites and intestinal helminth parasites. We also tested for size-dependent parasitism to determine the importance of body size on parasitism. We predicted that males would be more parasitized and that larger individuals would be more parasitized. As well, we predicted a male-biased flea distribution on male squirrels. Parasitism fluctuated over the course of 4 months, with flea infection peaking in August and helminth infection peaking in June. We found evidence of male-biased parasitism in helminth and ectoparasite infections. Flea infection was weakly correlated with body size in females but not in males, while no correlation was found between body size and helminth infection. Lastly, fleas had a female-biased population; however, male fleas were more likely to be found on male squirrels, and this could be to maximize dispersal to avoid inbreeding.

Intraspecific patterns of ectoparasite abundances on Paraguayan bats: effects of host sex and body size

Although levels of parasitism can vary greatly among individual bats of the same species, little is known about the characteristics of hosts that affect such variation. Bats were captured via mist nets from June 1995 to July 1997 from 28 localities throughout Paraguay. Over 17 500 ectoparasites were collected from 2909 bats; however, analyses of ectoparasite abundance were restricted to more abundant taxa of host and ectoparasite. We quantified the abundances of 29 taxa of ectoparasite on 19 species of bat host, as well as total abundance of ectoparasites regardless of taxonomic affiliation for 22 species of bat from Paraguay. The effects of host sex and host body size on these estimates of ectoparasite abundance were evaluated separately for each species of host. Ectoparasites did not respond consistently to host body size: ectoparasite abundance increased with host body size in 12 instances and decreased with host body size in 11 instances. Regardless of the existence or direction of effects of host body size on ectoparasite abundance, female hosts generally harboured more ectoparasites than did male hosts. Differences in host quality associated with the sex of bats, especially those related to behaviour, may be a more important determinant of ectoparasite abundance than are differences in size. Opportunities for host transfer are critical for species persistence of ectoparasites; consequently, ectoparasite populations on host individuals that form social groups or colonies should be larger, less prone to stochastic extinction, and have greater opportunity for speciation.

Host sex and ectoparasites choice: preference for, and higher survival on female hosts

1. Sex differences in levels of parasite infection are a common rule in a wide range of mammals, with males usually more susceptible than females. Sex-specific exposure to parasites, e.g. mediated through distinct modes of social aggregation between and within genders, as well as negative relationships between androgen levels and immune defences are thought to play a major role in this pattern. 2. Reproductive female bats live in close association within clusters at maternity roosts, whereas nonbreeding females and males generally occupy solitary roosts. Bats represent therefore an ideal model to study the consequences of sex-specific social and spatial aggregation on parasites' infection strategies. 3. We first compared prevalence and parasite intensities in a host-parasite system comprising closely related species of ectoparasitic mites (Spinturnix spp.) and their hosts, five European bat species. We then compared the level of parasitism between juvenile males and females in mixed colonies of greater and lesser mouse-eared bats Myotis myotis and M. blythii. Prevalence was higher in adult females than in adult males stemming from colonial aggregations in all five studied species. Parasite intensity was significantly higher in females in three of the five species studied. No difference in prevalence and mite numbers was found between male and female juveniles in colonial roosts. 4. To assess whether observed sex-biased parasitism results from differences in host exposure only, or, alternatively, from an active, selected choice made by the parasite, we performed lab experiments on short-term preferences and long-term survival of parasites on male and female Myotis daubentoni. When confronted with adult males and females, parasites preferentially selected female hosts, whereas no choice differences were observed between adult females and subadult males. Finally, we found significantly higher parasite survival on adult females compared with adult males. 5. Our study shows that social and spatial aggregation favours sex-biased parasitism that could be a mere consequence of an active and adaptive parasite choice for the more profitable host.

Sex-biased parasitism, seasonality and sexual size dimorphism in desert rodents

We investigated seasonality of gender differences in the patterns of flea infestation in nine rodent species to test if sex-biased parasitism in terms of mean abundance, species richness, prevalence and the level of aggregation (a) varies among hosts and between seasons, and (b) is linked to sexual size dimorphism. Sexual size differences were significant in both summer and winter in Acomys cahirinus, Gerbillus pyramidum and Meriones crassus, and in winter only in Acomys russatus, Gerbillus dasyurus, Gerbillus nanus and Sekeetamys calurus. Sexual size dimorphism was male biased except for A. russatus in which it was female biased. Manifestation of sexual differences in flea infestation was different among hosts between seasons. A significant effect of sex on mean flea abundance was found in six hosts, on mean flea species richness in five hosts and on prevalence in two hosts. Male-biased parasitism was found in summer in one host only and in winter in five hosts. Female-biased parasitism occurred in winter in A. russatus. Gender differences in the slopes of the regressions of log-transformed variances against log-transformed mean abundances occurred in three hosts. No relationship was found between sexual size dimorphism and any parasitological parameter in any season using both conventional regressions and the method of independent contrasts. Our results suggest that sex-biased parasitism is a complicated phenomenon that involves several different mechanisms.