Ectoparasites,Fitness, and Social Behaviour of Yellow-Bellied Marmots

Parasites can cause a loss of fitness for their hosts, potentially influencing social behaviour patterns of the host that promote or hinder parasite transmission. I studied yellow-bellied marmots (Marmota flaviventris) and their ectoparasites to determine if ectoparasites reduce the fitness of marmots and to test whether ectoparasite loads differ according to social behaviour. Three taxa of ectoparasites were identified, fleas (Oropsylla Stanfordi), lice (Linognathoides marmotae), and mites (family Dermanyssidae). High ectoparasite loads were related to slower growth, lower overwinter survival, and reduced reproduction, suggesting that ectoparasites are a fitness cost for marmots. Ectoparasite loads were not higher in colonial than in noncolonial marmots, nor in polygynous than in monogamous adult males. There was a trend, however, toward higher ectoparasite loads in marmots that were dispersing rather than philopatric. Further, ectoparasite loads differed among groups of marmots that nested or hibernated communally, indicating that spatial scale is important in understanding the relationships between parasites and social behaviour.     

Host inflammatory response governs fitness in an avian ectoparasite, the northern fowl mite (Ornithonyssus sylviarum)

Vertebrate immune responses to ectoparasites influence pathogen transmission and host fitness costs. Few studies have characterized natural immune responses to ectoparasites and resultant fitness effects on the ectoparasite. These are critical gaps in understanding vertebrate-ectoparasite interaction, disease ecology and host-parasite co-adaptation. This study focused on an ectoparasite of birds—the northern fowl mite (NFM) (Ornithonyssus sylviarum). Based on prior evidence that chickens develop resistance to NFM, these experiments tested two hypotheses: (i) skin inflammation blocks mite access to blood, impairing development, reproduction and survival; and (ii) host immunogenetic variation influences the inflammatory response and subsequent effects on the ectoparasite. On infested hosts, histology of skin inflammation revealed increased epidermal cell number and size, immigration of leukocytes and deposition of serous exudates on the skin surface. Survival of adult mites and their offspring decreased as the area of skin inflammation increased during an infestation. Inflammation increased the distance to blood vessels beyond the length of mite mouthparts (100-160 μm) and prevented protonymphs and adults from reaching a blood source. Consequently, protonymphs could not complete development, evidenced by a significant inverse relationship between inflammation and protonymph feeding success, as well as an increasing protonymph/adult ratio. Adult females were unable to feed and reproduce, indicated by an inverse relationship between inflammation and egg production, and decreasing female/juvenile ratio. These combined impacts of host inflammation reversed NFM population growth. Intensity of inflammation was influenced by the genotype of the major histocompatibility complex (MHC), supporting previous research that linked these immunological loci with NFM resistance. Overall, these data provide a model for a mechanism of avian resistance to an ectoparasitic arthropod and the fitness costs to the parasite of that host defense.     

Palatability of passerines to parasites: within-brood variation in nestling responses to experimental parasite removal and carotenoid supplementation

Asynchronous hatching of eggs in avian clutches produces a size hierarchy among nestlings that may lead to variation within broods in resistance to pathogens or parasites. In this study, we tested several predictions regarding variation in immunocompetence and distribution of parasites within avian broods by combining parasite removal and carotenoid supplementation treatments in nests of mountain bluebirds Sialia currucoides . Last-hatched nestlings were less likely to invest carotenoids in an induced cell-mediated immune response, suggesting they may be more susceptible to parasites; however, parasite removal disproportionately benefited middle-ranked nestlings. This supports the hypothesis that some avian ectoparasites balance host resistance against nutritional benefits by preferentially parasitizing nestlings of intermediate quality and immunocompetence. We found no evidence that males positioned last in the hatching sequence were differentially affected by ectoparasites, and, contrary to some previous studies in other passerines, last-hatched nestlings in asynchronously hatching broods were not less immunocompetent than their nest mates. In fact, junior nestlings exhibited weaker immune responses than their siblings in more synchronously hatching broods, and we suggest this may reflect environment-dependent maternal effects that warrant further investigation. Overall, our results highlight the importance of understanding the feeding and host selection behaviour of ectoparasites, as well as the fitness consequences thereof, since many predictions related to within-brood distribution of parasites require that parasites are able to discern the relative quality of available hosts.     

Heritability of resistance against ectoparasitism in the Drosophila-Macrocheles system

Ectoparasites are abundant in natural communities, can have pronounced deleterious fitness consequences to their host and are important vectors of transmissible parasitic disease. Yet very few studies have estimated the magnitude of heritable genetic variation underlying resistance against ectoparasitism, which significantly limits our ability to predict the evolution of this ecologically important character. The present paper reports results of artificial selection for increased resistance in Drosophila nigrospiracula against ectoparasitic, haematophagous mites, Macrocheles subbadius. In this system, which occurs naturally in the Sonoran Desert of North America, ectoparasitism significantly damages the expression of host fitness traits, including longevity, fecundity and male mating success. In the present study, resistance, which was modelled as a threshold trait, responded significantly to selection applied on either sex. Realized heritability, calculated as a mean across four replicates, was estimated to be 0.152 +/- 0.014 (SE). The heritability estimate from selection on males did not differ from that on females, but both estimates differed significantly from zero. This documented presence of additive genetic variation for resistance, coupled with knowledge of the fitness consequences of ectoparasitism, indicates that the host population possesses significant evolutionary potential. Selection was applied on the pre-attachment phase, thereby targeting behavioural forms of defence. This study therefore establishes parallels between insects and other animals in their ability to protect themselves and evolve behavioural defences against ectoparasites.     

Ectoparasitism as a possible cost of social life: a comparative analysis using Australian passerines (Passeriformes)

The hypothesis that cooperative breeding entails a cost in terms of transmission of ectoparasites was tested by a comparative analysis among sympatric Australian passerines. The general trend found using the allometry method and outgroup analysis indicates that contagious ectoparasites are not more common on cooperatively breeding than on non-cooperatively breeding hosts. Body weight, migratory patterns and relative abundance of hosts are factors far more important than cooperative breeding that affect the levels of ectoparasitism in the host genera studies. Ectoparasitism increases with host body weight and relative adundance, while sedentary host genera tended to show less hippoboscid fly diversity than migratory host genera. There is an interaction between breeding system and migratory pattern when relative density of contagious ectoparasites (i.e. mites, ticks and bird lice) is considered: the number of contagious ectoparasites per host is larger on cooperatively breeding host genera than on non-cooperatively breeding host genera among sedentary passerines, but the trend is reversed for migrant passerines.     

Weather dependent effects of nest ectoparasites on their bird hosts

This study reports the relationships between rainfall and ambient temperature with the abundances and prevalences of three species of ectoparasitic arthropods (viz, mites, blowfly larvae, fleas) in pied flycatcher Ficedula hypoleuca nests in three different breeding seasons In addition to its effects on the growth of nestling pied flycatchers, weather conditions were found to determine patterns of abundance and prevalence of ectoparasites Nest ectoparasites had detrimental effects on the fitness (nestling growth and survival until fledgling) of their hosts although the effects and the identity of harmful ectoparasites varied across the years Among the three species of nest ectoparasites, mites had the most consistent harmful effects on nestling growth Fleas were detrimental in the more cold and rainy year, while blowflies caused nestling mortality in the wanner year Different host-parasite interactions were present each year, most likely due to the effects of weather on the activity and timing of development of parasite populations     

A method for testing the host specificity of ectoparasites: give them the opportunity to choose

Host-choice experiments were carried out with rodent and bat ectoparasites on Ilha Grande, state of Rio de Janeiro, Brazil. We constructed experimental chambers that enclosed three different rodent or bat host species, and then introduced a selected set of ectoparasitic arthropods. When given the opportunity to choose among host species, the ectoparasites showed a strong tendency to select their primary hosts, and reject novel host species. These kinds of simple experiments can be valuable tools for assessing the ability of ectoparasites to locate and discern differences between host species, and make choices about which hosts to infest, and which hosts to avoid.     

Host preference and specialization in Gnathia sp., a common parasitic isopod of coral reef fishes

A gnathiid species (Crustacea: Isopoda; one of the most common ectoparasites of coral reef fishes) from the Great Barrier Reef, Australia, was allowed to choose among fishes from three different families to feed on (using two species of fishes per family). Gnathiids showed a strong preference for labrids, rarely feeding on pomacentrids or apogonids. In a separate experiment, gnathiid host preference did not vary among three labrid fish species. Gnathiids that fed on labrids had higher survival than those that fed on apogonids. Male gnathiids that fed on labrids also moulted to the adult stage more quickly. This suggests that host specialization and local adaptation might be occurring between these ectoparasites and their host fishes at the host fish family level.     

Host density and ectoparasite avoidance in the common lizard (Lacerta vivipara)

Increased transmission of parasites and diseases is generally considered as a major cost of social life. In this study we tested the hypothesis regarding ectoparasites as a cost of living in crowded habitats in the common lizard (Lacerta vivipara). We used two approaches to explore this question. First, we tested if ectoparasite load and prevalence are positively correlated with host density in the field. Second, we experimentally tested if lizards avoid parasitized conspecifics. Contrary to expectation, we found that (1) ectoparasite load is negatively correlated with lizard density; (2) prevalence does not significantly increase with density; (3) unparasitized lizards do not avoid parasitized conspecifics but are attracted by them whatever their parasite load. These findings suggest that ectoparasites cannot be considered as a cost of living at high density in the common lizard, in spite of the potential negative impact mites may have on lizard fitness. Received: 18 August 1996 / Accepted: 7 February 1997     

Host-ectoparasite associations; the role of host traits,season and habitat on parasitism interactions of the rodents of northeastern Iran

Rodents play a significant role as reservoirs of zoonotic diseases. Nevertheless, in general their ectoparasite assemblage and host-ectoparasite associations are poorly known. This study intended to provide new insights into the relationships between ectoparasites and rodents in northeastern Iran. Rodents were captured using live traps during the years 2016–2020, and their ectoparasites were collected. Parasitological indices such as infestation rate, prevalence and mean intensity of infestation were analyzed. A total of 284 rodents, belonging to 17 species, were trapped and found to be infested by 178 ectoparasites from five orders Siphonaptera, Phthiraptera, Ixodida, Mesostigmata and Trombidiformes. The overall infestation rate was 50.3%. The flea Nosopsyllus fasciatus and the louse Polyplax asiatica dominated among all fleas and lice, respectively. Haemaphysalis punctata and Haemolaelaps sp. were recorded as the most abundant tick and mite, respectively. Nosopsyllus fasciatus exhibited low and Polyplax asiatica moderate host specificity. Approximately 64.2% of ectoparasites shared more than one host, and others were singletons. Seasonal fluctuations were found in the occurrence of ectoparasite; fleas and lice were more abundant in spring and winter, respectively. Ticks demonstrated high abundance in spring and summer and mites were more common in autumn. The overall prevalence of ectoparasite on male rodents was greater than that on females (56.4% vs. 44.4%), while similar mean intensities were detected for both sexes. This study extends the knowledge on the distribution, seasonality and host choice of four main groups of ectoparasites in association with rodents. Further studies are needed to provide deep insight into how relationships and interactions between ectoparasite and rodents are formed, and how they can be applied in epidemiology.     

Types of parasitism of acarines and insects on terrestrial vertebrates

According to the recent taxonomic revisions, over 40000 species of insects and acarines are parasites or micropredatory blood-suckers of mammals and birds. The largest fraction of them are micropredators and temporary or permanent ectoparasites, the minority being endoparasitic. Some arthropods (blood-sucking dipterans) use the host primarily as a food resource, whereas for others (many astigmatic mites) the host constitutes the entire environment. A number of life forms, or types of parasitism, have arisen in the insects and acarines in the course of their adaptive evolution to parasitism on terrestrial vertebrates. The term “type of parasitism” designates a set of convergently arising morpho-physiological and ecological adaptations (adaptive complexes), demonstrated by different arthropod taxa. A classification of the types of parasitism in arthropods is proposed based on their temporal, spatial, and trophic associations with vertebrates. The following seven types of parasitism are distinguished: micropredatory blood-suckers, nest ectoparasites (nidicoles), temporary ectoparasites with prolonged feeding, permanent ectoparasites, intracutaneous endoparasites, cavity endoparasites, and tissue endoparasites.     

Density-dependent host selection in ectoparasites: An application of isodar theory to fleas parasitizing rodents

Parasites should make the same decisions that every animal makes regarding fitness reward. They can maximize reproductive success by selection of those habitats that guarantee the greatest fitness output. We consider the host population as a habitat of a parasite population. Consequently, hosts (=habitats) that differ quantitatively or qualitatively will support different numbers of parasites. The nature of habitat selection can be detected by isodars, lines along which habitat selection yields equivalent fitness reward. We applied this approach to study host selection of five fleas, each infesting two desert rodents. Xenopsylla conformis, Xenopsylla ramesis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis parasitize Gerbillus dasyurus and Meriones crassus. Synosternus cleopatrae pyramidis parasitizes Gerbillus andersoni allenbyi and Gerbillus pyramidum. Three fleas ( X. conformis, X. ramesis and S. c. pyramidis) were able to perceive quantitative (amount of the resource; e.g. organic matter in the nest for flea larvae) and/or qualitative (pattern of resource acquisition; e.g. host defensiveness) differences between hosts. Two other fleas did not perceive between-host differences. X. conformis was a density-dependent host selector that showed sharp selectivity at low density. X. ramesis and S. c. pyramidis were density-independent host selectors with a direct correspondence of density with habitat quality. N. i. theodori and S. t. medialis were non-selectors with no relationship at all between density and host quality. The results of the application of the isodar theory suggest that ectoparasites, like other animals, behave as if they are able to make choices and decisions that favour environments in which their reproductive benefit is maximized.     

Experimental evidence for costs due to chewing lice in the European bee-eater (Merops apiaster)

Animals frequently host organisms on their surface which can be beneficial, have no effect or a negative effect on their host. Ectoparasites, by definition, are those which incur costs to their host, but these costs may vary. Examples of avian ectoparasites are chewing lice which feed exclusively on dead feather or skin material; therefore, costs to their bird hosts are generally considered small. Theoretically, many possible proximate effects exist, like loss of tissue or food, infected bites, transmission of microparasitic diseases or reduced body insulation due to loss of feathers, which may ultimately also have fitness consequences. Here, we experimentally examined a possible negative impact of 2 feather-eating louse species (Meropoecus meropis and Brueelia apiastri) on male and female European bee-eaters (Merops apiaster) by removing or increasing louse loads and comparing their impact to a control group (lice removed and immediately returned) after 1 month. A negative effect of chewing lice was found on body mass and sedimentation rate and to a lesser extent on haematocrit levels. Males and females lost more weight when bearing heavy louse loads, and were more susceptible to infestations as indicated by the higher sedimentation rate. Our results further suggest differences in sex-specific susceptibility.     

Patterns of coexistence: ectoparasites on small mammals in northern Fennoscandia

The total aestival ectoparasitic burden of six small mammal species ( Sorex araneus, Clethrionomys glareolus, C. rutilus, C. rufocanus, Microtus agrestis , and M. oeconomus ) was investigated in terms of frequency distribution, frequency of occurrence, species diversity and joint occurrences. The mammals were collected in northern Fennoscandia during peak density years. The frequency distribution of the ectoparasites was best described as negative binomial on C. glareolus, M. agrestis , and M. oeconomus but not so on S. araneus, C. rutilus and C. rufocanus. The distribution did not fit the Poisson distribution in any species. The percentage of S. araneus that had ectoparasites was 49%, and of the microtidae species, 73-96% had ectoparasites. The median number of ectoparasites on the vole species was between 2 and 9 specimens of 1 or 2 species. There was a significant, positive correlation between the number of ectoparasitic species and the total number of individuals on all host species. Pairs of ectoparasitic species occurring together more or less often than expected by chance were found on all host species. However, the pairs rarely repeated themselves on the same host species under different environmental conditions, or on other host species under similar circumstances. Differences in total infestation between reproductive categories and sexes were observed in M. agrestis but not in S. araneus and C. glareolus.     

Effects of fleas on nest success of Arctic barnacle geese: experimentally testing the mechanism

Parasites have detrimental effects on their hosts’ fitness. Therefore, behavioural adaptations have evolved to avoid parasites or, when an individual is already in contact with a parasite, prevent or minimize infections. Such anti‐parasite behaviours can be very effective, but can also be costly for the host. Specifically, ectoparasites can elicit strong host anti‐parasite behaviours and interactions between fleas (Siphonaptera) and their hosts are one of the best studied. In altricial bird species, nest fleas can negatively affect both parent and offspring fitness components. However, knowledge on the effects of fleas on precocial bird species is scarce. Research on geese in the Canadian Arctic indicated that fleas have a negative impact on reproductive success. One possible hypothesis is that fleas may affect female incubation behaviour. Breeding females with many fleas in their nest may increase the frequency and/or duration of incubation breaks and could even totally desert their nest. The aim of our study was to 1) determine if a similar negative relationship existed between flea abundance and reproductive success in our study colony of Arctic breeding barnacle geese Branta leucopsis and 2) experimentally quantify if such effects could be explained by a negative effect of nest fleas on female behaviour. We compared host anti‐parasite and incubation behaviour between experimentally flea‐reduced and control nests using wildlife cameras and temperature loggers. We found that flea abundance was negatively associated with hatching success. We found little experimental support, however, for changes in behaviour of the breeding female as a possible mechanism to explain this effect.     

Ticks from a Morelet's crocodile in Belize.

Parasitism of crocodilians by ticks has rarely been reported, and to our knowledge only seven published accounts exist. On 3 July 1999, we collected four ticks from a subadult Morelet's crocodile (Crocodylus moreletii) captured in northern Belize. These were identified as Amblyomma dissimile (one female), and Amblyomma sp. (two nymphs, one larva). The crocodile was captured on land approximately 100 m from water, and all four ticks were attached to loose skin on the lateral surface of the tail. Crocodilians are most susceptible to terrestrial ectoparasites, including ticks, during overland movements. However, most such movements occur in response to drought, when tick questing activity is suppressed, which likely accounts for the small numbers of tick specimens recorded from crocodilians and the absence of any noticeable impact of parasitism on host fitness.     

A new parasitological index for the estimation of peculiarities of the relationships between parasite and its host, and biotope of the host

A new parasitological index (hostal-topical index) for the estimation of the degree of ectoparasite's relationship with its host and biotope of the host is proposed: [formula: see text], where [formula: see text]--hostal-topical index; n--amount of ectoparasites of the given species on the given host species in the biotope; N--amount of ectoparasites of all species from the given taxonomic group on the given host species in the biotope; n1--amount of hosts of the given species in the biotope; N1--amount of hosts of all species from the given taxonomic group in the biotope; n2--amount of ectoparasites of the given species in the biotope; N2--amount of ectoparasites of all species from the given taxonomic group in the biotope. Values [formula: see text] < 0.1 indicate that there is a distinct relationship with the biotope in spite of the host; values fallen into the range 0.1 < [formula: see text] < 0.5 indicate a moderate relationship with the biotope through the host; values [formula: see text] > 0.5 indicate a significant relationship with the host. By means of this index we have analyzed peculiarity of several parasitic species of fleas and gamasid mites to their hosts, biotopes, and biotope through the host. As it was found on the materials from different native zones and subzones of the Omsk Region (Western Siberia, Russia), values of the hostal-topical index for polyhostal parasitic species are lesser than those for oligohostal species. Values of this index can be different for the same species in the different native zones and subzones as well as in the different biotopes of the same native zone (subzone).     

Determinants of ectoparasite assemblage structure on rodent hosts from South American marshlands: the effect of host species,locality and season

The relative effects of host species identity, locality and season on ectoparasite assemblages (relative abundances and species richness) harboured by four cricetid rodent hosts (Akodon azarae, Oligoryzomys flavescens, Oxymycterus rufus and Scapteromys aquaticus) were assessed across six closely located sites in Buenos Aires province, Argentina. Relative abundances of ectoparasites (14 species including gamasid mites, an ixodid tick, a trombiculid mite, lice and fleas), as well as total ectoparasite abundance and species richness, were determined mainly by host species and to a lesser extent by locality (despite the small spatial scale of the study), whereas seasonal effect was weak, albeit significant. The abundances of some ectoparasites were determined solely by host, whereas those of other ectoparasites (sometimes belonging to the same higher taxon) were also affected by locality and/or season. In gamasids, there was a significant effect of locality for some species, but not for others. In fleas and lice, the effect of locality was similar in different species, suggesting that this effect is related to the characteristic life history strategy.     

High host specificity of obligate ectoparasites

Abstract.  1. Host specificity is the degree to which a parasite species occurs in association with a host species.
2. The degree to which obligate ectoparasites are host specific has been debated, but effects of sampling contamination were usually not addressed. Data from a controlled mammal–ectoparasite survey were used to assess host specificity of an obligate group of ectoparasites – streblid bat flies.
3. Host–parasite associations were categorised as primary or non-primary. Non-primary host associations were evaluated against primary associations via proportional comparison.
4. Results indicate that host specificity was high, exceeding previous reports. Natural host transfers were rare.
5. Non-primary host associations were almost completely explained by disturbance transfers during sampling of the host or by contamination upon sampling the parasite. These conclusions likely hold for other taxa of obligate parasites.     

Predator-prey interactions between ectoparasites

Vertebrates represent a resource frequently exploited by ectoparasites. But the ectoporosites themselves also represent a resource that can be exploited by specialized predators. Some o f these predators have been classified as ectoparasites, but in some cases the vertebrate blood in their crops comes from their blood-sucking prey. In fact, as Lance Durden explains, the assemblage o f arthropods that inhabit the vertebrate skin surface, or pelage, seems to show a complete spectrum of adaptations from predators to facultative and obligate blood-suckers, together with those feeding on other materials in this special habitat. The dynamics of their interactions are further complicated by responses of the host to the arthropods, and much further study is needed before the role o f predators in controlling ectoparasites can be clarified.