Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host

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Host specificity shapes population structure of pinworm parasites in Caribbean reptiles

Host specificity is one of the potential factors affecting parasite diversification because gene flow may be facilitated or constrained by the number of host species that a parasite can exploit. We test this hypothesis using a costructure approach, comparing two sympatric pinworm parasites that differ in host specificity – Parapharyngodon cubensis and Spauligodon anolis – on the Puerto Rican Bank and St. Croix in the Caribbean. Spauligodon anolis specializes on Anolis lizards, whereas P. cubensis parasitizes Anolis lizards as well as many other species of lizards and snakes. We collected lizards from across the Puerto Rican Bank and St. Croix, sampled them for S. anolis and P. cubensis and generated nuclear and mitochondrial sequence data from the parasites. We used these data to show that P. cubensis is comprised of multiple cryptic species that exhibit limited population structure relative to S. anolis, which is consistent with our prediction based on their host specificity. We also provide evidence that the distribution of P. cubensis species is maintained by competitive exclusion, and in contrast to previous theoretical work, the parasites with the greatest number of host species also reach the highest prevalence rates. Overall, our results are consistent with the hypothesis that host specificity shapes parasite diversification, and suggest that even moderate differences in host specificity may contribute to substantial differences in diversification.     

Reproduction of parasitic mites Varroa destructor in original and new honeybee hosts

The ectoparasitic mite, Varroa destructor, shifted host from the eastern honeybee, Apis cerana, to the western honeybee, Apis mellifera. Whereas the original host survives infestations by this parasite, they are lethal to colonies of its new host. Here, we investigated a population of A. cerana naturally infested by the V. destructor Korea haplotype that gave rise to the globally invasive mite lineage. Our aim was to better characterize traits that allow for the survival of the original host to infestations by this particular mite haplotype. A known major trait of resistance is the lack of mite reproduction on worker brood in A. cerana. We show that this trait is neither due to a lack of host attractiveness nor of reproduction initiation by the parasite. However, successful mite reproduction was prevented by abnormal host development. Adult A. cerana workers recognized this state and removed hosts and parasites, which greatly affected the fitness of the parasite. These results confirm and complete previous observations of brood susceptibility to infestation in other honeybee host populations, provide new insights into the coevolution between hosts and parasites in this system, and may contribute to mitigating the large‐scale colony losses of A. mellifera due to V. destructor.     

Checklist of parasites for Ponto-Caspian gobies (Actinopterygii: Gobiidae) in their native and non-native ranges

This study provides a comprehensive checklist of parasites reported for native and non-native populations of seven Ponto-Caspian goby species, i.e. Babka gymnotrachelus, Neogobius fluviatilis, N. melanostomus, Ponticola gorlap, P. kessleri, Proterorhinus semilunaris and P. semipellucidus, all of which have recently expanded their natural range, either by transoceanic translocation or along the three main European intracontinental invasion corridors. In some cases, invasion success is facilitated by loss of natural enemies, such as predators and parasites; thus, knowledge of a species natural parasite fauna is essential for assessments of enemy release in the host's non-native range. The study is based on published literature and personal unpublished data related to parasites of Ponto-Caspian gobiids. A total of 249 parasite taxa have been reported during 1931—2019, with higher numbers reported from native (214) than non-native (151) ranges. This checklist indicates apparent reduction in native parasites in non-native ranges in all goby species, although parasite colonisation in non-native ranges differs between fish species and invasion corridors. Interestingly, the cumulative number of species reported is still gradually increasing in both ranges. Acquisition of high number of local parasite species also indicates competence of Ponto-Caspian gobies to a wide range of generalist parasites.     

Contrasting the seasonal and elevational prevalence of generalist avian haemosporidia in co‐occurring host species

Understanding the ecology and evolution of parasites is contingent on identifying the selection pressures they face across their infection landscape. Such a task is made challenging by the fact that these pressures will likely vary across time and space, as a result of seasonal and geographical differences in host susceptibility or transmission opportunities. Avian haemosporidian blood parasites are capable of infecting multiple co‐occurring hosts within their ranges, yet whether their distribution across time and space varies similarly in their different host species remains unclear. Here, we applied a new PCR method to detect avian haemosporidia (genera Haemoproteus, Leucocytozoon, and Plasmodium) and to determine parasite prevalence in two closely related and co‐occurring host species, blue tits (Cyanistes caeruleus, N = 529) and great tits (Parus major, N = 443). Our samples were collected between autumn and spring, along an elevational gradient in the French Pyrenees and over a three‐year period. Most parasites were found to infect both host species, and while these generalist parasites displayed similar elevational patterns of prevalence in the two host species, this was not always the case for seasonal prevalence patterns. For example, Leucocytozoon group A parasites showed inverse seasonal prevalence when comparing between the two host species, being highest in winter and spring in blue tits but higher in autumn in great tits. While Plasmodium relictum prevalence was overall lower in spring relative to winter or autumn in both species, spring prevalence was also lower in blue tits than in great tits. Together, these results reveal how generalist parasites can exhibit host‐specific epidemiology, which is likely to complicate predictions of host–parasite co‐evolution.     

Some like it cold: the glossiphoniid parasites of the Sicilian endemic pond turtle Emys trinacris (Testudines,Emydidae), an example of ‘parasite inertia’?

The freshwater turtles of the genus Emys and some leech species of the family Glossiphoniidae are the only Palaearctic representatives of primarily Nearctic taxa, which jointly colonized Eurasia and the Maghreb during the Miocene. The strict trophic relationships occurring between the glossiphoniid parasite leech Placobdella costata and its host, the emydid Emys orbicularis, make them a prime example of host–parasite cophylogenetic evolution. In the light of the discovery of the Sicilian cryptic endemic species Emys trinacris, which is the sister species to the widespread Palaearctic E. orbicularis, the possible cophylogenetic divergence of the turtle hosts and their leech parasites was investigated. In spite of the deep divergence scored between the two pond turtle species and of their allopatric distribution, their leech parasites proved to be conspecific and indistinguishable based on the implemented molecular marker. This unexpected decoupling might likely be ascribed to the different dispersal abilities of the two taxa and/or to the recent, human‐mediated introduction of the leech parasites in Sicily. If this last scenario is confirmed, the long‐term effects of the introduced leech parasite on the endemic Sicilian pond turtle Emys trinacris should be carefully monitored. In the frame of this study, representatives of the widely spread predatory leech Helobdella stagnalis were observed on E. trinacris. Molecular analyses of their stomach content allowed to rule out the possibility of the existence of a trophic relationships between these two taxa, in contrast to what was previously suspected, and suggest that H. stagnalis specimens were rather attached to the turtles for non‐nutritional reasons.     

A link between host dispersal and parasite diversity in two sympatric cichlids of Lake Tanganyika

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Host range and community structure of avian nest parasites in the genus Philornis (Diptera: Muscidae) on the island of Trinidad

Parasite host range can be influenced by physiological, behavioral, and ecological factors. Combining data sets on host–parasite associations with phylogenetic information of the hosts and the parasites involved can generate evolutionary hypotheses about the selective forces shaping host range. Here, we analyzed associations between the nest‐parasitic flies in the genus Philornis and their host birds on Trinidad. Four of ten Philornis species were only reared from one species of bird. Of the parasite species with more than one host bird species, P. falsificus was the least specific and P. deceptivus the most specific attacking only Passeriformes. Philornis flies in Trinidad thus include both specialists and generalists, with varying degrees of specificity within the generalists. We used three quantities to more formally compare the host range of Philornis flies: the number of bird species attacked by each species of Philornis, a phylogenetically informed host specificity index (Poulin and Mouillot's S_TD), and a branch length‐based S_TD. We then assessed the phylogenetic signal of these measures of host range for 29 bird species. None of these measures showed significant phylogenetic signal, suggesting that clades of Philornis did not differ significantly in their ability to exploit hosts. We also calculated two quantities of parasite species load for the birds – the parasite species richness, and a variant of the S_TD index based on nodes rather than on taxonomic levels – and assessed the signal of these measures on the bird phylogeny. We did not find significant phylogenetic signal for the parasite species load or the node‐based S_TD index. Finally, we calculated the parasite associations for all bird pairs using the Jaccard index and regressed these similarity values against the number of nodes in the phylogeny separating bird pairs. This analysis showed that Philornis on Trinidad tend to feed on closely related bird species more often than expected by chance.     

Pythons,parasites, and pests: anthropogenic impacts on Sarcocystis (Sarcocystidae) transmission in a multi‐host system

Parasites are essential components of ecosystems and can be instrumental in maintaining host diversity and populations; however, their role in trophic interactions has often been overlooked. Three apicomplexan parasite species of Sarcocystis (S. singaporensis, S. zamani, and S. villivillosi) use the reticulated python as their definitive hosts and several species within the Rattus genus as intermediate hosts, and they form a system useful for studying interactions between host–parasite and predator–prey relationships, as well as anthropogenic impacts on parasite transmission. Based on predictions from a 1998 survey, which detected an inverse relationship between urban development and Sarcocystis infection in Rattus, we tested the hypothesis that Sarcocystis transmission in Singapore will decrease over time due to anthropogenic activities. Despite a large proportion of the reticulated python diet consisting of Rattus species at all sizes of pythons, Sarcocystis infection rates decreased from 1998 to 2010. Pythons found in industrial areas had lower Sarcocystis infection rates, particularly in the western industrial area of Singapore Island. Average python size also decreased, with implications that we predict may disrupt host–parasite relationships. Anthropogenic activities such as habitat modification, fragmentation, and systematic removal and translocation of pythons have negative impacts on Sarcocystis transmission in Singapore, which in turn may augment pest rat populations. Trends observed may ultimately have negative impacts on human health and biodiversity in the region.     

Has the introduction of brown trout altered disease patterns in native New Zealand fish?

1. It is well recognised that non-indigenous species (NIS) can affect native communities via the 'spillover' of introduced parasites. However, two other potentially important processes, the 'spillback' of native parasites from a competent NIS host, where the latter acts as a reservoir leading to amplified infection in native hosts, and the 'dilution' of parasitism by a NIS host acting as a sink for native parasites, have either not been tested or largely overlooked.
2. We surveyed the helminth parasite fauna of native New Zealand fish in Otago streams that varied in the abundance of introduced brown trout Salmo trutta , to look for evidence of spillback and/or dilution. Spillover is not an issue in this system, with trout introduced as parasite-free eggs.
3. Seven native parasite species were present across 12 sites; significant inverse relationships with an index of trout abundance (i.e. dilution) were documented for three species infecting the native upland bully Gobiomorphus breviceps , and one species infecting the native roundhead galaxias Galaxias anomalus .
4. An inverse relationship between bully energy status and infection intensity of one parasite species suggests that parasite dilution could have positive effects on bully populations. Our failure to detect similar relationships for the other parasites does not preclude the possibility that dilution is beneficial to native fish, since parasites may have subtle or unmeasured impacts.
5. The parasite dilution patterns reported are compelling in that they occurred across several native host and parasite species; as such they have important implications for invasion ecology, providing an interesting contrast to the largely negative impacts reported for NIS. Mechanisms potentially responsible for the patterns observed are discussed.     

Host species,and not environment,predicts variation in blood parasite prevalence,distribution, and diversity along a humidity gradient in northern South America

Environmental factors strongly influence the ecology and evolution of vector‐borne infectious diseases. However, our understanding of the influence of climatic variation on host–parasite interactions in tropical systems is rudimentary. We studied five species of birds and their haemosporidian parasites (Plasmodium and Haemoproteus) at 16 sampling sites to understand how environmental heterogeneity influences patterns of parasite prevalence, distribution, and diversity across a marked gradient in water availability in northern South America. We used molecular methods to screen for parasite infections and to identify parasite lineages. To characterize spatial heterogeneity in water availability, we used weather‐station and remotely sensed climate data. We estimated parasite prevalence while accounting for spatial autocorrelation, and used a model selection approach to determine the effect of variables related to water availability and host species on prevalence. The prevalence, distribution, and lineage diversity of haemosporidian parasites varied among localities and host species, but we found no support for the hypothesis that the prevalence and diversity of parasites increase with increasing water availability. Host species and host × climate interactions had stronger effects on infection prevalence, and parasite lineages were strongly associated with particular host species. Because climatic variables had little effect on the overall prevalence and lineage diversity of haemosporidian parasites across study sites, our results suggest that independent host–parasite dynamics may influence patterns in parasitism in environmentally heterogeneous landscapes.     

Drivers of community turnover differ between avian hemoparasite genera along a North American latitudinal gradient

The latitudinal diversity gradient (LDG) is an established macroecological pattern, but is poorly studied in microbial organisms, particularly parasites. In this study, we tested whether latitude, elevation, and host species predicted patterns of prevalence, alpha diversity, and community turnover of hemosporidian parasites. We expected parasite diversity to decrease with latitude, alongside the diversity of their hosts and vectors. Similarly, we expected infection prevalence to decrease with latitude as vector abundances decrease. Lastly, we expected parasite community turnover to increase with latitudinal distance and to be higher between rather than within host species. We tested these hypotheses by screening blood and tissue samples of three closely related avian species in a clade of North American songbirds (Turdidae: Catharus, n = 466) across 17.5° of latitude. We used a nested PCR approach to identify parasites in hemosporidian genera that are transmitted by different dipteran vectors. Then, we implemented linear‐mixed effects and generalized dissimilarity models to evaluate the effects of latitude, elevation, and host species on parasite metrics. We found high diversity of hemosporidian parasites in Catharus thrushes (n = 44 lineages) but no evidence of latitudinal gradients in alpha diversity or prevalence. Parasites in the genus Leucocytozoon were most prevalent and lineage rich in this study system; however, there was limited turnover with latitude and host species. Contrastingly, Plasmodium parasites were less prevalent and diverse than Leucocytozoon parasites, yet communities turned over at a higher rate with latitude and host species. Leucocytozoon communities were skewed by the dominance of one or two highly prevalent lineages with broad latitudinal distributions. The few studies that evaluate the hemosporidian LDG do not find consistent patterns of prevalence and diversity, which makes it challenging to predict how they will respond to global climate change.     

Molecular phylogenetics supports a clade of red algal parasites retaining native plastids: taxonomy and terminology revised

Parasitism is a life strategy that has repeatedly evolved within the Florideophyceae. Historically, the terms adelphoparasite and alloparasite have been used to distinguish parasites based on the relative phylogenetic relationship of host and parasite. However, analyses using molecular phylogenetics indicate that nearly all red algal parasites infect within their taxonomic family, and a range of relationships exist between host and parasite. To date, all investigated adelphoparasites have lost their plastid, and instead, incorporate a host‐derived plastid when packaging spores. In contrast, a highly reduced plastid lacking photosynthesis genes was sequenced from the alloparasite Choreocolax polysiphoniae. Here we present the complete Harveyella mirabilis plastid genome, which has also lost genes involved in photosynthesis, and a partial plastid genome from Leachiella pacifica. The H. mirabilis plastid shares more synteny with free‐living red algal plastids than that of C. polysiphoniae. Phylogenetic analysis demonstrates that C. polysiphoniae, H. mirabilis, and L. pacifica form a robustly supported clade of parasites, which retain their own plastid genomes, within the Rhodomelaceae. We therefore transfer all three genera from the exclusively parasitic family, Choreocolacaceae, to the Rhodomelaceae. Additionally, we recommend applying the terms archaeplastic parasites (formerly alloparasites), and neoplastic parasites (formerly adelphoparasites) to distinguish red algal parasites using a biological framework rather than taxonomic affiliation with their hosts.     

Can invasive Burmese pythons inhabit temperate regions of the southeastern United States?

Understanding potential for range expansion is critical when evaluating the risk posed by invasive species. Burmese pythons (Python molurus bivittatus) are established in southern Florida and pose a significant threat to native ecosystems. Recent studies indicate that climate suitable for the species P. molurus exists throughout much of the southern United States. We examined survivorship, thermal biology, and behavior of Burmese pythons from South Florida in a semi-natural enclosure in South Carolina, where winters are appreciably cooler than in Florida, but within the predicted region of suitable climate. All pythons acclimated to the enclosure, but most died after failing to seek appropriate refugia during sub-freezing weather. The remaining snakes used refugia but died during an unusually cold period in January 2010. Although all snakes died during the study, most survived extended periods at temperatures below those typical of southern Florida and none exhibited obvious signs of disease. Our study represents a first step in evaluating the results of climate matching models and we address factors that may affect range expansion in this invasive species.     

Infection with a trematode parasite differentially alters competitive interactions and antipredator behaviour in native and invasive crayfish

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Spatial population genetic structure of a bacterial parasite in close coevolution with its host

Knowledge of a species’ population genetic structure can provide insight into fundamental ecological and evolutionary processes including gene flow, genetic drift and adaptive evolution. Such inference is of particular importance for parasites, as an understanding of their population structure can illuminate epidemiological and coevolutionary dynamics. Here, we describe the population genetic structure of the bacterium Pasteuria ramosa, a parasite that infects planktonic crustaceans of the genus Daphnia. This system has become a model for investigations of host–parasite interactions and represents an example of coevolution via negative frequency‐dependent selection (aka “Red Queen” dynamics). To sample P. ramosa, we experimentally infected a panel of Daphnia hosts with natural spore banks from the sediments of 25 ponds throughout much of the species range in Europe and western Asia. Using 12 polymorphic variable number tandem repeat loci (VNTR loci), we identified substantial genetic diversity, both within and among localities, that was structured geographically among ponds. Genetic diversity was also structured among host genotypes within ponds, although this pattern varied by locality, with P. ramosa at some localities partitioned into distinct host‐specific lineages, and other localities where recombination had shuffled genetic variation among different infection phenotypes. Across the sample range, there was a pattern of isolation by distance, and principal components analysis coupled with Procrustes rotation identified congruence between patterns of genetic variation and geography. Our findings support the hypothesis that Pasteuria is an endemic parasite coevolving closely with its host. These results provide important context for previous studies of this model system and inform hypotheses for future research.     

Metazoan parasites of African annual killifish (Nothobranchiidae): abundance,diversity, and their environmental correlates

Estimates of biodiversity and its global patterns are affected by parasite richness and specificity. Despite this, parasite communities are largely neglected in biodiversity estimates, especially in the tropics. We studied the parasites of annual killifish of the genus Nothobranchius that inhabit annually desiccating pools across the African savannah and survive the dry period as developmentally arrested embryos. Their discontinuous, non‐overlapping generations make them a unique organism in which to study natural parasite fauna. We investigated the relationship between global (climate and altitude) and local (pool size, vegetation, host density and diversity, and diversity of potential intermediate hosts) environmental factors and the community structure of killifish parasites. We examined metazoan parasites from 21 populations of four host species (Nothobranchius orthonotus, N. furzeri, N. kadleci, and N. pienaari) across a gradient of aridity in Mozambique. Seventeen parasite taxa were recorded, with trematode larval stages (metacercariae) being the most abundant taxa. The parasites recorded were both allogenic (life cycle includes non‐aquatic host; predominantly trematodes) and autogenic (cycling only in aquatic hosts; nematodes). The parasite abundance was highest in climatic regions with intermediate aridity, while parasite diversity was associated with local environmental characteristics and positively correlated with fish species diversity and the amount of aquatic vegetation. Our results suggest that parasite communities of sympatric Nothobranchius species are similar and dominated by the larval stages of generalist parasites. Therefore, Nothobranchius serve as important intermediate or paratenic hosts of parasites, with piscivorous birds and predatory fish being their most likely definitive hosts.     

Climate,host phylogeny and the connectivity of host communities govern regional parasite assembly

Aim

Identifying barriers that govern parasite community assembly and parasite invasion risk is critical to understand how shifting host ranges impact disease emergence. We studied regional variation in the phylogenetic compositions of bird species and their blood parasites (Plasmodium and Haemoproteus spp.) to identify barriers that shape parasite community assembly.

Location

Australasia and Oceania.

Methods

We used a data set of parasite infections from >10,000 host individuals sampled across 29 bioregions. Hierarchical models and matrix regressions were used to assess the relative influences of interspecies (host community connectivity and local phylogenetic distinctiveness), climate and geographic barriers on parasite local distinctiveness and composition.

Results

Parasites were more locally distinct (co‐occurred with distantly related parasites) when infecting locally distinct hosts, but less distinct (co‐occurred with closely related parasites) in areas with increased host diversity and community connectivity (a proxy for parasite dispersal potential). Turnover and the phylogenetic symmetry of parasite communities were jointly driven by host turnover, climate similarity and geographic distance.

Main conclusions

Interspecies barriers linked to host phylogeny and dispersal shape parasite assembly, perhaps by limiting parasite establishment or local diversification. Infecting hosts that co‐occur with few related species decreases a parasite's likelihood of encountering related competitors, perhaps increasing invasion potential but decreasing diversification opportunity. While climate partially constrains parasite distributions, future host range expansions that spread distinct parasites and diminish barriers to host shifting will likely be key drivers of parasite invasions.     

Old pythons stay fit; effects of haematozoan infections on life history traits of a large tropical predator

We document the impact of blood parasite infections caused by Hepatozoon sp. on water python (Liasis fuscus) life history traits such as growth rates, condition, reproductive output and survival. Individual snakes maintained similar among-year parasite loads. Hepatozoon infections affected python growth rate, i.e. snakes suffering from high infection levels exhibited significantly slower growth compared to individuals with low parasite loads. Our results suggest that the parasites also affected the pythons nutritional status (condition), as snakes with low condition scores suffered from higher parasite infection levels than snakes with high scores. Furthermore, our data suggest that parasitaemia may affect female reproductive output, as reproductive female pythons harboured lower parasite loads compared to non-reproductive adult females. High levels of parasite infections also affected juvenile python survival, as recaptured snakes harboured significantly lower parasite loads compared to non-recaptured yearling pythons. In our study area, water python have very few natural predators and, hence, experience low mortality rates and commonly reach an age of >15 years. In contrast to results obtained in other studies, parasite loads in larger/older pythons were lower compared to younger snakes, suggesting that only snakes harbouring lower levels of parasitaemia were able to survive to old age. We suggest that a possible cause for the opposing results regarding parasite prevalence and host age may be due to different levels of extrinsic mortality rates and longevity. Long-lived organisms, such as water pythons, may invest relatively more into crucial self-maintenance functions such as parasite defence, compared to short-lived organisms.