Host Body Size Research Articles

Helminth parasite richness among vertebrates

The numbers of intestinal helminth species (parasite richnesS) recorded from each of 488 vertebrate host species are compared using data compiled from the published literature. Associations between parasite richness, sampling effort, host size and host habitat (aquatic versus terrestrial) are assessed using a method designed to control for phylogenetic association. Parasite richness increases with the number of surveys on which each estimate of parasite richness is based (sampling effort). When the effects of sampling effort are controlled for, there remains a strong positive relationship between parasite richness and host body size. There is no tendency for aquatic hosts to harbour more parasite species than terrestrial hosts independently of differences in sampling effort and body size. The results are interpreted in the context of hosts representing habitats for parasite colonization, resource allocation between parasite species, and the age of the major mammalian radiations.

The evolution of body size in the Monogenea: the role of host size and latitude

Monogeneans form a diverse group of parasitic platyhelminths that show substantial interspecific variation in body size, though this variation remains largely unexplained. The relationships between monogenean body size and both host body size and latitude were examined in comparative analyses using data from 613 monogenean species. First, phylogenetically independent contrasts among 39 monogenean families revealed no relationship between host size and parasite size. However, large parasite size was consistently associated with high latitude, suggesting that larger body size in monogeneans may result more from external factors such as temperature than from host-related factors. The potential effects of other variables (site of attachment on the host, host taxonomy, and type of aquatic habitat) could not be assessed in the analysis. Second, analyses among genera within families failed to show any consistent relationships between monogenean body size and either host size or latitude. The results of this study suggest that latitude had an evolutionary influence on monogenean body size, though this may be only visible in comparisons among higher taxonomic levels, and that monogenean body size has not simply adjusted to host body size following host-switching events.

Patterns in the evenness of gastrointestinal helminth communities

Within a parasite community, the relative abundance of each parasite species, or species evenness, is a key component of the structure of that community. However, little is known about which, if any, ecological factors determine the evenness of the parasite community in a given host. Here, the associations between selected ecological variables and the evenness of gastrointestinal helminth communities were evaluated across species of vertebrate hosts. Using host species as statistically independent observations, evenness correlated negatively with parasite abundance in fish hosts, and positively with community richness in bird hosts. After controlling for host-phylogenetic effects, the correlation between evenness and parasite abundance in fish hosts was still present. In addition, a link between parasite community evenness and host body size became apparent among fish hosts, and evenness correlated positively with richness in mammal hosts. These trends lack solid explanations, and point to new directions in the study of parasite community ecology.

Allometry and simple epidemic models for microparasites.

Simple mathematical models for microparasites offer a useful way to examine the population dynamics of different viral and bacterial pathogens. One constraint in applying these models in free-living host populations is the paucity of data with which to estimate transmission rates. Here we recast a standard epidemiological model by setting the birth and death rates of the host population and its density as simple allometric functions of host body weight. We then use standard threshold theorems for the model in order to estimate the minimum rate of transmission for the parasite to establish itself in a mammalian host population. Transmission rates that produce different comparable values of the parasites' basic reproductive number, RO, are themselves allometric functions of host body size. We have extended the model to show that hosts having different body sizes suffer epidemic outbreaks whose frequency scales with body size. The expected epidemic periods for pathogens in different mammalian populations correspond to cycles observed in free-living populations.

Body size evolution of oxyurid (Nematoda) parasites: the role of hosts.

Studying the diversification of body size in a taxon of parasites allows comparison of patterns of variation observed in the parasites with patterns found in free-living organisms. The distributions of body size of oxyurid nematodes (obligate parasites of vertebrates and invertebrates) are lognormally right-skewed, except for male oxyurids in invertebrates which show left-skewed distributions. In these parasitic forms, speciose genera do not have the smallest body sizes. Parasite body size is positively correlated with host body size, the largest hosts possessing the largest parasites. This trend is shown to occur within one monophyletic group of oxyurids, those of Old World primates. Comparative methods are used to take account of the effects of phylogeny. The use of multiple linear regression on distance matrices allows measurements of the contribution of phylogeny to the evolution of body size of parasites. Evolution of body size in female pinworms of Old World primates appears to be dependent only on the body size of their hosts. The tendency of parasite body size to increase with host body size is discussed in the light of the evolution of life-history traits.

Phylogeny, Ecology, and the Richness of Parasite Communities in Vertebrates

The makeup of parasite communities is the result, among other factors, of interactions between the evolutionary history and ecological characteristics of hosts. This study evaluates the relative importance of some ecological factors (host body size, diet, habitat, latitude, and the mean number of parasite individuals per host) as determinants or correlates of parasite community richness in vertebrates, before and after controlling for potential effects of host phylogenetic relationships. Data were obtained from the literature on 596 parasite communities belonging to one of four distinct types: gastrointestinal parasite communities of fish, birds, or mammals, and ectoparasite communities of fish. There were positive correlations between the number of hosts sampled and mean species richness of the parasite community of each genus. In analyses treating host genera as independent statistical observations and using estimates of parasite species richness corrected for host sample size, positive correlations were observed between richness and host body size in gastrointestinal communities of all three groups of vertebrates. The mean number of parasite individuals per host also was correlated positively with species richness. In fish, richness increased with increases in the proportion of animal food in the host diet. Aquatic birds had richer parasite communities than their terrestrial counterparts, whereas marine fish had richer gastrointestinal parasite communities than freshwater fish. The richness of ectoparasite communities on fish showed no association with any of the ecological variables investigated. Using host genera as independent points in the analyses may lead to biased results since some host lineages are descended from recent common ancestors, and are therefore not truly independent. The comparative analysis was repeated using phylogenetically independent contrasts derived from the phylogeny of hosts. Once the effects of host phylogeny were removed, somewhat different results were obtained: host body size showed no relationship with parasite species richness in birds, and there was no evidence that habitat transitions resulted in significant changes in parasite species richness in any of the types of communities studied. Of the ecological factors studied, the comparative analyses suggest that only host body size can be an important determinant of parasite community richness in certain host groups. This study illustrates clearly the need to control for phylogeny in investigations of host—parasite interactions.

Patchiness in the abundance of metacercariae parasitizingPoecilia gillii (Poeciliidae) isolated in pools of an intermittent tropical stream

Prevalence and intensity of a clinostomatid in the fishPoecilia gilliii were measured in six dry season pools of a small intermittent Costa Rican stream, and the prevalence of two diplostomulid parasites (‚diplostomulum’ and ‚neascus’) were monitored in 14 residual pools of a second intermittent stream of the same drainage. There were significant among-pool differences in the prevalence of the three parasites. There was no evidence to suggest that clinostomatid or ‚diplostomulum’ prevalence was influenced by the position of pools within the downstream gradient; however, ‚neascus’ prevalence tended to decrease with distance downstream. Host length accounted for some of the variation in parasite prevalence among pools for both diplostomulids. Prevalence and intensity of a clinostomid in the body cavity varied with host gender and body size. There was a positive relationship between body size and clinostomatid parasitization in female hosts. Most males examined were less than 50 mm (total length). For fish less than 50 mm, males were more parasitized than females. Prevalence of the two diplostomulids was not related to the relative net periphyton production or the dissolved oxygen concentration of the pools. However, a positive correlation between the density ofP. gillii and ‚diplostomulum’ prevalence was found across the fourteen pools, and ‘neascus’ prevalence was positively related to pool area.

A nested parasite species subset pattern in tropical fish: host as major determinant of parasite infracommunity structure.

The number of monogenean gill parasite species associated with fish hosts of different sizes is evaluated for 35 host individuals of the West African cyprinid Labeo coubie. The length of host individuals explains 86% of the total variation in monogenean species richness among individuals. Larger hosts harbour more species than smaller ones. The existence of a hierarchical association of parasite species in individuals of L. coubie is demonstrated. Monogenean infracommunities on larger fish hosts consist of all species found on smaller hosts plus those restricted to the larger size categories, suggesting some degree of compositional persistence among host individuals. The findings provide strong support for an interpretation of the relationship between monogenean parasite species richness and host body size in terms of a nested species subset pattern, thus providing a new record of repetitive structure and predictability for parasite infracommunities of hosts.

Sexual and Temporal Differences in Phorid Parasitism of Photinus marginellus Fireflies (Coleoptera: Lampyridae)

Photinus marginellus LeConte fireflies maintain discrete breeding aggregations in which males fly and flash in search of conspecific females, while females respond from perches in vegetation. Sexual differences and temporal patterns in parasitism by the phorid Apocephalus antennatus Malloch, a specialist parasitoid of lampyrid beetles, were investigated by determining parasitism rates during the flight season within a P. marginellus deme. Female P. marginellus were attacked by parasitoids at slightly higher rates (35% of all females) than were males (25%), and females hosted significantly more parasitoid larvae per individual than did males. A distinct temporal pattern in parasitism rate was observed; for both male and female hosts, the probability of an individual being killed by A. antennatus increased markedly from early- to mid-season. Within each sex, there were no differences in host body size between parasitized and nonparasitized beetles, and no relationship was found between host body size and the number of phorid larvae that emerged. Intersexual differences and temporal patterns of parasitism observed in this study suggest that A. antennatus may affect P. marginellus life histories and reproductive ecology.

Host selection and distribution of Hypermastus placentae (Eulimidae), and ectoparasitic gastropod on the sand dollar Arachnoides placenta (Echinoidea)

The intertidal sand dollar Arachnoides placenta is parasitized by the eulimid Hypermastus placentae at Pallarenda Beach, Townsville, Queensland. A. placenta is the only echinoderm species in the region with which H. placentae associates. Sand dollars are distributed in an aggregated pattern within the littoral zone at Pallarenda Beach, and the distribution of parasites within the adult sand dollar population conforms closely to Poisson expectations. A. placenta adults in all size classes are equally susceptible to parasitization by H. placentae, whereas juveniles are not parasitized; host selection may be determined by a requirement for host gonadal tissue in the diet of the parasite. Infestation rate and number of parasites per host decrease as host density increases. Parasite body size is not related to host body size.

The parasites of Anolis lizards in the northern Lesser Antilles : I. Patterns of distribution and abundance.

The helminth communities from ten species of lizard on seven islands in the Caribbean were sampled by collecting one hundred specimens of each species. Nine genera of parasites were identified; these included six nematodes, two digeneans and an acanthocephalan. No relationship was discernible between parasite density or abundance and island area or altitude, although dry islands tend to have fewer species of parasites. Anolis lizards of the bimaculatus and wattsi series share similar parasites with four out of nine species common to both series. The parasite community of lizards on these islands is depauperate with respect to similar surveys on the larger islands of the Greater Antilles.On three of the islands lizards were sub-sampled by collecting from moist woodland and more xeric habitats. These data suggest that differences between habitats are as significant as differences between islands in determining parasite burdens. Worm burdens of the commonest parasite species, T. cubensis, increased monotonically with host body size and no evidence was found to suggest that these parasites affect either host survival or fecundity. The sex-ratio of this species correlated with mean abundance of the parasite, with females the dominant sex on islands or in habitats where the parasite was common. This pattern may reflect haplodiploid sexual determination in this species.

Can host body size explain the parasite species richness in tropical freshwater fishes?

The variability of monogenean gill ectoparasite species richness in 19 West African cyprinid species was analyzed using the following seven predictor variables: host size, number of drainage basins, number of sympatric cyprinid species, host diversity, association with mainland forest, host ecology, and monogenean biological labelling. The size of the host species accounted for 77% of the variation in the number of parasite species per host, and host ecology an additional 8%. Together the effects of host size and host ecology accounted for 85% of the variation in monogenean species richness. This study shows that the deciding factors for explaining monogenean species richness in West African cyprinid fishes are host species size and host ecology. These results were compared with main factors responsible for parasite species richness in fish communities. Other possible explanations of monogenean community structure in west African cyprinids are discussed.

Comparative study of the antennal sensilla of five species of root maggots: Delia radicum L., D. floralis F., D. antiqua Mg., D. platura MG. (Diptera : Anthomyiidae) and Psila rosae F. (Diptera : Psilidae)

A comparative study of the antennal sensilla of Delia radicum L., D. floralis F., D. antiqua Mg., D. platura Mg. (Diptera : Anthomyiidae) and Psila rosae F. Diptera Psilidae) is undertaken. For both sexes of each species, the type, distribution, and density of sensilla are determined. All 5 species have trichoid (olfactory) and grooved (olfactory) sensilla. Basiconica I (blunt) sensilla (olfactory) are found on each of the species examined, except D. platura. Basiconica II (tapered) (olfactory) and clavate (olfactory) sensilla are found only on Delia species. Also, only Delia species have single-chambered, dorsal pits, and these contain basiconic II pit sensilla (olfactory). Common to all 5 species is a multi-chambered ventral pit (olfactory). In the ventral pit, all 5 species have grooved pit sensilla (olfactory). In addition to this type of sensillum the Delia species have smooth-walled conical pit sensilla (hygro-/thermosensitive) and P. rosae has granular pit sensilla (hygro-/thermosensitive). Smooth-walled tapered pit sensilla (hygro-/thermosensitive) are found in D. radicum. Similarities and differences in the density of surface sensilla between dorsal and ventral funicular surfaces, male and female flies, and oligophagous (D. antiqua, D. radicum, D. floralis and P. rosae) and polyphagous (D. platura) species are compared. Several differences in sensillum density between the dorsal and ventral funicular surfaces are observed, but these do not fit into a consistent trend. Except for D. radicum, there are differences in sensillum density between male and female flies. For the oligophagous species, females have a greater sensillum density, whilst for the polyphagous D. platura males have a greater sensillum density. Comparisons between species show the greatest differences between the Delia species and P. rosae, and within the 4 Delia species, differences in sensillum density do not correlate with host range or body size.

Condition and fecundity of the damselfly, Enallagma ebrium (Hagen): the importance of ectoparasites.

The extent, magnitude, and cause of natural covariation between degree of parasitism and other variables known or suspected of influencing host fitness (such as host age or body size) has been understudied. We demonstrate that degree of parasitism by larval water mites (Arrenurus spp.) was associated with reduced condition of males and with lowered fecundity of young females of the damselfly, Enallagma ebrium (Hagen) (Odonata: Coenagrionidae). We also demonstrate that degree of parasitism can covary with both age and size of host damselflies. We explain the putative causes of such natural covariation, and we suggest that degree of parasitism, host age, and host size can all interact to determine damselfly fitness. We expect that natural covariation between the host's phenotype and degree of parasitism will be frequently observed. Studies of such natural covariation will help researchers to assess better the importance of several variables on host reproductive success and to understand better the dynamics of host-parasite interactions.

Intravernal Changes in the Level of Parasitization of the Southern Green Stink Bug (Hemiptera: Pentatomidae), by the Feather-Legged Fly (Diptera: Tachinidae): Host Sex, Mating Status, and Body Size as Correlated Factors

In 1989, the number of eggs of the parasitoid, Trichopoda pennipes (F.), on the cuticle of southern green stink bugs, Nezara viridula (L.), increased throughout the spring for the cohort emerging from overwintering diapause. Initially, the size of N. viridula males was positively correlated with the number of parasitoid eggs and probability of mating. By late spring, mating status was not influenced by size and the relationship between size and number of parasitoid eggs was much reduced. This may reflect a loss of viability for larger, more parasitized males resulting in a concomitant reduction in attractiveness to potential mates and parasitoids. The proportion of males in the cohort dropped significantly and coincidentally with increased levels of parasitization. Throughout the spring, females were parasitized much less than males. The risk of parasitization for females derived primarily from their association with males during courtship and/or copulation.

Parasites and Host Geographic Range as Illustrated by Waterfowl

Several papers have suggested that host species with larger geographic ranges tend to harbour a greater number of parasite species than those with smaller ranges. However, few of these investigations have dealt quantitatively with problems related to host sampling and/or phylogeny. This paper describes a positive relationship between the number of helminth parasite species per host and host species geographic range in Holarctic waterfowl. The analysis controls for the effects of differential sampling of host species and for the effects of taxonomic association. Neither host body size, population size, population density, nor social tendency correlate significantly with the number of parasite species per host corrected for number of hosts examined, and therefore association with these variables is unlikely to confound the relationship between parasites and host geo-

Short Interval Time Measurement by a Parasitoid Wasp

The number of eggs laid by the parasitoid wasp Trichogramma varies with host volume. The duration of the wasp's initial transit across the host surface during host examination is used to determine the number of eggs laid. A 2.5-second reduction in initial transit resulted in a 30% reduction in eggs oviposited, demonstrating that these wasps measure short time intervals. This measure is used for progeny allocation independent of host body size.

PEST CHIGGER, EUTROMBICULA ALFREDDUGESI INFESTATION OF SMALL MAMMALS IN PIEDMONT HABITATS OF GEORGIA1 (ACARINA: TROMBICULIDAE)

More than 2600 Eutrombicula alfreddugesi larvae were taken from 40 of 596 individual small mammals of 20 species over a 23 month period. Mammals were infested during June, July, and August only, with maximum rate of infestation in June and severity of infestation in July. Male and female Sigmodon hispidus had equal rates and severities of infestation during the chigger season. Infrapopulations of E. alfreddugesi are positively associated with host body size. Amount of time spent in arboreal activity by mammal species played no role in determining pest chigger infestation.

Relations between water mites of the genusHydrachna and the corixidsSigara striata andCymatia coleoptrata

The larvae of the water mitesHydrachna conjecta andH. cruenta are parasitic on corixids.H. conjecta larvae are attached to the underside of the hemelytra of the host and those ofH. cruenta to the legs. The growth ofH. cruenta larvae is less than that of the more shelteredH. conjecta larvae. The infection influences the egg production of the host: infectedSigara striata females have fewer eggs in the ovarioles than uninfected ones. The number of eggs in the ovarioles of the host is related to the size of the parasite. It may be assumed that the presence ofH. conjecta larvae causes a lower fecundity in the host than those ofH. cruenta. InCymatia coleoptrata, a much smaller host thanS. striata, the fecundity is even more impaired by both parasite species. For in the ovarioles of infectedC. coleoptrata females no developed eggs were found at all. So, it is clear that it is anyhow the relation between body size of host and parasite that matters.

Some Factors Influencing Incidence And Degree Of Ectoparasitism Of Small Mammals From Taiwan1

During January-February, 1962, small mammals of 2 orders and 9 genera were collected from 5 habitats at 2 different montane localities in Taiwan. Records of ectoparasites removed from these hosts were analyzed. Distribution of ticks was related to cover-type; incidence of infestation to host head and body length. Fleas were found most commonly at high, cold localities. Incidence of fleas, but not degree of infestation, was directly related to host body size. Lice were recovered from four genera, most common Apodemus and Rattus. Sex did not affect frequency or degree of infestation significantly. Degree of infestation was directly related to host body size.