Observations of Breinlia booliati in a new host, Rattus rattus jalorensis, from Kuantan, state of Pahang, Malaysia

Breinlia booliati Singh and Ho, 1973 is described from the Malaysian wood rat, Rattus rattus jalorensis Bonhote. The parasites presented here were originally discovered in 1955 in Kuantan, Malaysia, but were not classified until now. On the basis of morphological observations of anatomical structures and comparisons with other species of Breinlia, it was determined that the parasites were B. booliati. The parasites discussed here show slight deviation from B. booliati, but they do not warrant a new species classification. There is some variation in anatomical measurements, the number of male caudal papillae, and the morphology of the microfilariae. Breinlia booliati from a new host is described in this article, with a brief discussion on Rattus species that are hosts of B. booliati and vectors that transmit the parasite. The occurrence of B. booliati in R. r. jalorensis represents the first report of the parasite in this host.     

Does investment into ��expensive�� tissue compromise anti-parasitic defence? Testes size, brain size and parasite diversity in rodent hosts

Species richness of parasite assemblages varies among host species. Earlier studies that searched for host-related determinants of parasite diversity mainly considered host traits that affect the probability of host encounter with parasites, whereas host traits related to defensibility against parasites have rarely been investigated. From the latter perspective, evolutionary investment in ??expensive?? tissue or organs (like testes or brain) may trade off against energetically costly anti-parasitic defences. If so, richer parasite assemblages are expected in hosts with larger testes and brains. We studied the relationships between testes and brain size and diversity of parasites (fleas, gamasid mites and helminths) in 55 rodent species using a comparative approach and application of two methods, namely the method of independent contrasts and generalized least-squares (GLS) analysis. Both phylogenetically correct methods produced similar results for flea and helminth species richness. Testes size positively correlated with flea and helminth species richness but not gamasid mite species richness. No correlation between brain size and species richness of any parasite group was found by the method of independent contrasts. However, GLS analysis indicated negative correlation between brain size and mite species richness. Our results cast doubt on the validity of the expensive tissue hypothesis, but suggest instead that larger testes are associated with higher parasite diversity via their effect on mobility and/or testosterone-mediated immunosuppression.     

Bat fly species richness in Neotropical bats: correlations with host ecology and host brain

Patterns of ectoparasite species richness in mammals have been investigated in various terrestrial mammalian taxa such as primates, ungulates and carnivores. Several ecological or life traits of hosts are expected to explain much of the variability in species richness of parasites. In the present comparative analysis we investigate some determinants of parasite richness in bats, a large and understudied group of flying mammals, and their obligate blood-sucking ectoparasite, streblid bat flies (Diptera). We investigate the effects of host body size, geographical range, group size and roosting ecology on the species richness of bat flies in tropical areas of Venezuela and Peru, where both host and parasite diversities are high. We use the data from a major sampling effort on 138 bat species from nine families. We also investigate potential correlation between bat fly species richness and brain size (corrected for body size) in these tropical bats. We expect a relationship if there is a potential energetic trade-off between costly large brains and parasite-mediated impacts. We show that body size and roosting in cavities are positively correlated with bat fly species richness. No effects of bat range size and group size were observed. Our results also suggest an association between body mass-independent brain size and bat fly species richness. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Host population density and body mass as determinants of species richness in parasite communities: comparative analyses of directly transmitted nematodes of mammals

Epidemiological theory predicts positive correlations between host population density or body mass and species richness among parasite communities. Here I test these predictions by a comparative study of communities of directly transmitted mammalian parasites, gastrointestinal strongylid nematodes. I use data from 45 species of mammals, representing examination of 17 200 individual hosts. The variable studied was the average number of gastrointestinal strongylid nematode species per host population, and three different methods were used to obtain estimates of parasite species richness that are unbiased by number of host individuals examined. Analyses were done using the phylogenetically independent contrast method. Host population density and parasite species richness were strongly positively correlated when the effects of host body weight had been controlled for. Controlling for other variables did not change this, and the relationship was found regardless of method used to correct for uneven sampling effort among host species. A positive relationship between parasite species richness and host body weight was also found, but the effect of host densities had to be controlled for to see this. These relationships between host traits and species richness of directly transmitted parasites are stronger than patterns found using data on indirectly transmitted mammalian parasites, and suggests that links between host traits and parasite species richness are stronger than previously suggested. The results are consistent with parasite species richness being positively linked to pathogen transmission rates and reductions in transmission rates possibly increasing extinction probabilities in parasite populations. The results also suggest that parasites may exert a cost of increases in rate of population energy usage, and thus show that pathogens may be important in generating independence between body mass and rate of population energy usage among host species.     

Host longevity and parasite species richness in mammals

Hosts and parasites co-evolve, with each lineage exerting selective pressures on the other. Thus, parasites may influence host life-history characteristics, such as longevity, and simultaneously host life-history may influence parasite diversity. If parasite burden causes increased mortality, we expect a negative association between host longevity and parasite species richness. Alternatively, if long-lived species represent a more stable environment for parasite establishment, host longevity and parasite species richness may show a positive association. We tested these two opposing predictions in carnivores, primates and terrestrial ungulates using phylogenetic comparative methods and controlling for the potentially confounding effects of sampling effort and body mass. We also tested whether increased host longevity is associated with increased immunity, using white blood cell counts as a proxy for immune investment. Our analyses revealed weak relationships between parasite species richness and longevity. We found a significant negative relationship between longevity and parasite species richness for ungulates, but no significant associations in carnivores or primates. We also found no evidence for a relationship between immune investment and host longevity in any of our three groups. Our results suggest that greater parasite burden is linked to higher host mortality in ungulates. Thus, shorter-lived ungulates may be more vulnerable to disease outbreaks, which has implications for ungulate conservation, and may be applicable to other short-lived mammals.     

Ectoparasites on small mammals in Iceland: Origin and population characteristics of a species-poor insular community

The Icelandic small mammal fauna is depauperated as is the associated ectoparasite fauna. Three small mammal species occur, viz. Apodemus sylvaticus L., Mus musculus L., and Rattus norvegicus Berk. ( R. rattus is probably not a regular member). The mice supposedly came to the island by settlers from the 10th century and onwards.
Apodemus and Mus from five localities altogether had seven ectoparasite species, five mites and two fleas. All species occurred on Apodemus whereas Mus was infested by four. Compared with the numbers of ectoparasite species recorded in similar studies in the Nordic countries, there are conspicuously few species in Iceland. Further, Apodemus had an overall higher infestation frequency than Mus (90% and 30%, respectively) and a higher total density of ectoparasites (3.3–20.3 and 0.5 inds/host, respectively). The density figures were high compared with those for mainland Apodemus . Especially the mite Laelaps agilis C. L. Koch and the flea Ctenophthalmus agyrtes (Heller) were common on Icelandic Apodemus . Reduced competition among parasites and/or low predator pressure on small mammals may explain the density figures obtained.
The ectoparasite species compositions on small mammals in Scandinavia and Iceland have many features in common that renders it probable that Apodemus originate from Scandinavia.     

Host traits and parasite species richness in even and odd-toed hoofed mammals, Artiodactyla and Perissodactyla

Host social, ecological and life history traits are predicted to influence both parasite establishment within host species and the distribution of parasites among host species. Yet only a few studies have investigated the role multiple host traits play in determining patterns of infection across diverse parasite groups. To explore the association between host traits and parasite species richness (PSR), we assembled a comprehensive database encompassing 601 parasites (including viruses, bacteria, protozoa, helminths and arthropods) reported to infect 96 species from two well-studied and diverse host clades: even- and odd-toed hoofed mammals (Artiodactyla and Perissodactyla). Comparative analyses were used to examine associations between three sets of host variables (life history and body mass, social and mating behavior, and ecological traits) and PSR for all parasites combined and for distinct parasite sub-groups. Results from a combination of phylogenetic and non-phylogenetic tests showed that PSR increased with host body size across all parasites groups. Counter to expectations, measures of parasite diversity decreased with host longevity and social group size, and associations between group size and PSR further depended on the underlying mating system of the host species. Our results suggest that body mass, longevity, and social organization influence the diversity and types of parasites reported to infect wild populations of hoofed mammals, and that multiple host and parasite traits can combine in unexpected ways to shape observed patterns.     

Helminth species diversity of mammals: parasite species richness is a host species attribute

Studies investigating parasite diversity have shown substantial geographical variation in parasite species richness. Most of these studies have, however, adopted a local scale approach, which may have masked more general patterns. Recent studies have shown that ectoparasite species richness in mammals seems highly repeatable among populations of the same mammal host species at a regional scale. In light of these new studies we have reinvestigated the case of parasitic helminths by using a large data set of parasites from mammal populations in 3 continents. We collected homogeneous data and demonstrated that helminth species richness is highly repeatable in mammals at a regional scale. Our results highlight the strong influence of host identity in parasite species richness and call for future research linking helminth species found in a given host to its ecology, immune defences and potential energetic trade-offs.     

Parasite species richness in carnivores: effects of host body mass, latitude, geographical range and population density

Aim  Comparative studies have revealed strong links between ecological factors and the number of parasite species harboured by different hosts, but studies of different taxonomic host groups have produced inconsistent results. As a step towards understanding the general patterns of parasite species richness, we present results from a new comprehensive data base of over 7000 host–parasite combinations representing 146 species of carnivores (Mammalia: Carnivora) and 980 species of parasites.
Methods  We used both phylogenetic and non-phylogenetic comparative methods while controlling for unequal sampling effort within a multivariate framework to ascertain the main determinants of parasite species richness in carnivores.
Results  We found that body mass, population density, geographical range size and distance from the equator are correlated with overall parasite species richness in fissiped carnivores. When parasites are classified by transmission mode, body mass and home range area are the main determinants of the richness of parasites spread by close contact between hosts, and population density, geographical range size and distance from the equator account for the diversity of parasites that are not dependent on close contact. For generalist parasites, population density, geographical range size and latitude are the primary predictors of parasite species richness. We found no significant ecological correlates for the richness of specialist or vector-borne parasites.
Main conclusions  Although we found that parasite species richness increases instead of decreases with distance from the equator, other comparative patterns in carnivores support previous findings in primates, suggesting that similar ecological factors operate in both these independent evolutionary lineages.     

Density, body mass and parasite species richness of terrestrial mammals

We investigated the relationships between helminth species richness and body mass and density of terrestrial mammals. Cross-species analysis and the phylogenetically independent contrast method produced different results. A non-phylogenetic approach (cross-species comparisons) led to the conclusion that parasite richness is linked to host body size. However, an analysis using phylogenetically independent contrasts showed no relationship between host body size and parasite richness. Conversely, a non-phylogenetic approach generated a negative relationship between parasite richness and host density, whereas the independent contrast method showed the opposite trend – that is, parasite richness is positively correlated with host density. From an evolutionary perspective, our results suggest that opportunities for parasite colonization depend more closely on how many hosts are available in a given area than on how large the hosts are. From an epidemiological point of view, our results confirm theoretical models which assume that host density is linked to the opportunity of a parasite to invade a population of hosts. Our findings also suggest that parasitism may be a cost associated with host density. Finally, we provide some support for the non-linear allometry between density and mammal body mass (Silva and Downing, 1995), and explain why host density and host body mass do not relate equally to parasite species richness.     

Introduced species: domestic mammals are more significant transmitters of parasites to native mammals than are feral mammals

The study of parasitism related to biological invasion has focused on attributes and impacts of parasites as invaders and the impact of introduced hosts on endemic parasitism. Thus, there is currently no study of the attributes of hosts which influence the invasiveness of parasites. We aimed to determine whether the degree of domestication of introduced mammalian species – feral introduced mammals, livestock or pets, hereafter ‘D’ – is important in the spillover of introduced parasites. The literature on introduced parasites of mammals in Chile was reviewed. We designed an index for estimating the relevance of the introduced host species to parasite spillover and determined whether the D of introduced mammals predicted this index. A total of 223 introduced parasite species were found. Our results indicate that domestic mammals have a higher number of introduced parasites and spillover parasites, and the index indicates that these mammals, particularly pets, are more relevant introducers than introduced feral mammals. Further analyses indicated that the higher impact is due to higher parasite richness, a longer time since introduction and wider dispersal, as well as how these mammals are maintained. The greater relevance of domestic mammals is important given that they are basically the same species distributed worldwide and can become the main transmitters of parasites to native mammals elsewhere. This finding also underlines the feasibility of management in order to reduce the transmission of parasites to native fauna through anti-parasitic treatment of domestic mammals, animal-ownership education and the prevention of importing new parasite species.     

Host diversity drives parasite diversity: meta‐analytical insights into patterns and causal mechanisms

Statistical correlations of biodiversity patterns across multiple trophic levels have received considerable attention in various types of interacting assemblages, forging a universal understanding of patterns and processes in free‐living communities. Host–parasite interactions present an ideal model system for studying congruence of species richness among taxa as obligate parasites are strongly dependent upon the availability of their hosts for survival and reproduction while also having a tight coevolutionary relationship with their hosts. The present meta‐analysis examined 38 case studies on the relationship between species richness of hosts and parasites, and is the first attempt to provide insights into the patterns and causal mechanisms of parasite biodiversity at the community level using meta‐regression models. We tested the distinct role of resource (i.e. host) availability and evolutionary co‐variation on the association between biodiversity of hosts and parasites, while spatial scale of studies was expected to influence the extent of this association. Our results demonstrate that species richness of parasites is tightly correlated with that of their hosts with a strong average effect size (r= 0.55) through both host availability and evolutionary co‐variation. However, we found no effect of the spatial scale of studies, nor of any of the other predictor variables considered, on the correlation. Our findings highlight the tight ecological and evolutionary association between host and parasite species richness and reinforce the fact that host–parasite interactions provide an ideal system to explore congruence of biodiversity patterns across multiple trophic levels.     

Infracommunity structure of parasites of Hemigymnus melapterus (Pisces: Labridae) from Lizard Island, Australia: the importance of habitat and parasite body size

This study describes the community of all metazoan parasites from 14 individuals of thicklip wrasse, Hemigymnus melapterus, from Lizard Island, Australia. All fish were parasitized, and 4,649 parasite individuals were found. Twenty-six parasite species were identified although only 6 species were abundant and prevalent: gnathiid isopods, the copepod Hatschekia hemigymni, the digenean Callohelmis pichelinae, and 3 morphotypes of tetraphyllidean cestode larvae. We analyzed whether the body size and microhabitat of the parasites and size of the host affected understanding of the structure of the parasite community. We related the abundance, biovolume, and density of parasites with the host body size and analyzed the abundances and volumetric densities of some parasite species within microhabitats. Although the 2 most abundant species comprised 75% of all parasite individuals, 4 species, each in similar proportion, comprised 85% of the total biovolume. Although larger host individuals had higher richness, abundance, and biovolume of parasites than smaller individuals, overall parasite volumetric density actually decreased with the host body size. Moreover, parasites exhibited abundances and densities significantly different among microhabitats; some parasite species depended on the area available, whereas others selected a specific microhabitat. Parasite and habitat size exhibited interesting relationships that should be considered more frequently. Considerations of these parameters improve understanding of parasite community structure and how the parasites use their habitats.     

Evolutionary associations between host traits and parasite load: insights from Lake Tanganyika cichlids

Parasite diversity and abundance (parasite load) vary greatly among host species. However, the influence of host traits on variation in parasitism remains poorly understood. Comparative studies of parasite load have largely examined measures of parasite species richness and are predominantly based on records obtained from published data. Consequently, little is known about the relationships between host traits and other aspects of parasite load, such as parasite abundance, prevalence and aggregation. Meanwhile, understanding of parasite species richness may be clouded by limitations associated with data collation from multiple independent sources. We conducted a field study of Lake Tanganyika cichlid fishes and their helminth parasites. Using a Bayesian phylogenetic comparative framework, we tested evolutionary associations between five key host traits (body size, gut length, diet breadth, habitat complexity and number of sympatric hosts) predicted to influence parasitism, together with multiple measures of parasite load. We find that the number of host species that a particular host may encounter due to its habitat preferences emerges as a factor of general importance for parasite diversity, abundance and prevalence, but not parasite aggregation. In contrast, body size and gut size are positively related to aspects of parasite load within, but not between species. The influence of host phylogeny varies considerably among measures of parasite load, with the greatest influence exerted on parasite diversity. These results reveal that both host morphology and biotic interactions are key determinants of host–parasite associations and that consideration of multiple aspects of parasite load is required to fully understand patterns in parasitism.     

Comparing the richness of metazoan ectoparasite communities of marine fishes: controlling for host phylogeny

Parasite communities are the product of acquisitions and losses of parasite species during the evolutionary history of their host. When comparing the parasite communities of different host species to assess the role of ecological variables as determinants of parasite species richness, a correction must be made for the possible phylogenetic inheritance of parasites from ancestral hosts independent of host ecology. We performed a comparative analysis of the metazoan ectoparasite communities on the heads and gills of 111 species of marine fish. The influences of host body size, host schooling behaviour and water temperature were tested after controlling for both sampling and phylogenetic effects. Overall, water temperature correlated positively with both parasite species richness and abundance, whereas fish size only correlated with parasite abundance. The correlation across all fish species between water temperature and parasite species richness was dependent on an outlier point. The results, however, generally held when fish from different biogeographical areas (Pacific and Atlantic) were analysed separately. In all analyses, parasite species richness always correlated strongly with parasite abundance. There was no evidence that schooling fish taxa harboured richer or more abundant ectoparasite communities than their non-schooling sister taxa, possibly because of the small number of contrasts available for that test. Overall, whereas both water temperature and host size affect the number of parasite individuals that can be harboured by a fish, only temperature appears important as a determinant of ectoparasite community richness. Received: 30 May 1996 / Accepted: 23 October 1996     

Latitudinal gradients of parasite species richness in primates

Infectious disease risk is thought to increase in the tropics, but little is known about latitudinal gradients of parasite diversity. We used a comparative data set encompassing 330 parasite species reported from 119 primate hosts to examine latitudinal gradients in the diversity of micro and macroparasites per primate host species. Analyses conducted with and without controlling for host phylogeny showed that parasite species richness increased closer to the equator for protozoan parasites, but not for viruses or helminths. Relative to other major parasite groups, protozoa reported from wild primates were transmitted disproportionately by arthropod vectors. Within the protozoa, our results revealed that vector‐borne parasites showed a highly significant latitudinal gradient in species richness. This higher diversity of vector‐borne protozoa near the tropics could be influenced by a greater abundance or diversity of biting arthropods in the tropics, or by climatic effects on vector behaviour and parasite development. Many vector‐borne diseases, such as leishmaniasis, trypanosomiasis, and malaria pose risks to both humans and wildlife, and nearly one‐third of the protozoan parasites from free‐living primates in our data set have been reported to infect humans. Because the geographical distribution and prevalence of many vector‐borne parasites are expected to increase because of global warming, these results are important for predicting future parasite‐mediated threats to biodiversity and human health.     

Population biology of Schistosoma mansoni in the black rat: host regulation and basic transmission rate.

A simple mathematical model was built to investigate the population biology of Schistosoma mansoni in its natural definitive host, the black rat (Rattus rattus). Prevalence and parasite abundance over 13 years from field studies and data from laboratory experiments were used to set up the model. Sensitivity analysis showed that the abundance of parasites is strongly influenced by variation in the values of infection parameters. The model shows that the parasite is able to control populations of definitive hosts. We discuss the factors that may explain the long-term persistence of S. mansoni among its natural definitive host, R. rattus and its intermediate host, the snail Biomphalaria glabrata in Guadeloupe (French West Indies). The impact of the parasite does not appear to explain the apparent persistence of the host-parasite association over a 13 year period. Our results seem to support the influence of environmental factors, which may act on the infection process by reducing, or increasing, the rate of encounters between hosts and free-living stages of the parasite.     

Life history strategy influences parasite responses to habitat fragmentation

Anthropogenic habitat use is a major threat to biodiversity and is known to increase the abundance of generalist host species such as rodents, which are regarded as potential disease carriers. Parasites have an intimate relationship with their host and the surrounding environment and it is expected that habitat fragmentation will affect parasite infestation levels. We investigated the effect of habitat fragmentation on the ecto- and endoparasitic burdens of a broad niche small mammal, Rhabdomys pumilio, in the Western Cape Province, South Africa. Our aim was to look at the effects of fragmentation on different parasite species with diverse life history characteristics and to determine whether general patterns can be found. Sampling took place within pristine lowland (Fynbos/Renosterveld) areas and at fragmented sites surrounded and isolated by agricultural activities. All arthropod ectoparasites and available gastrointestinal endoparasites were identified. We used conditional autoregressive models to investigate the effects of habitat fragmentation on parasite species richness and abundance of all recovered parasites. Host density and body size were larger in the fragments. Combined ecto- as well as combined endoparasite taxa showed higher parasite species richness in fragmented sites. Parasite abundance was generally higher in the case of R. pumilio individuals in fragmented habitats but it appears that parasites that are more permanently associated with the host’s body and those that are host-specific show the opposite trend. Parasite life history is an important factor that needs to be considered when predicting the effects of habitat fragmentation on parasite and pathogen transmission.     

Life history, ecology and parasite community structure in Soviet birds

The paper describes an investigation of parasite richness in relation to host life history and ecology using data from an extensive survey of helminth parasites (cestodes, trematodes and nematodes) in Soviet birds. Correlates of parasite richness (number of parasite species per host species) were sought among 13 life-history variables, 13 ecological variables and one non-biological variable (number of host individuals examined) across a sample of 158 species of host. A statistical method to control for the effects of phylogenetic association was adopted throughout. Parasite richness correlates positively with the number of hosts examined (sample size) in all three parasite groups. Positive correlations (after controlling for the effects of sample size) were also found between host body weight and parasite richness for trematodes and nematodes, but not for cestodes.
A number of ecological variables were associated with parasite richness. However, when the effects of sample size and body weight were controlled for, only a single significant correlation (an association between trematode richness and aquatic habitat) remained. Similarly, a number of significant correlates of parasite richness were found among the life-history variables examined. Though several of these were robust to the confounding effects of sample size, all could be explained by the co-variation between life-history traits and body weight among the host species under investigation.