Host specificity shapes population structure of pinworm parasites in Caribbean reptiles

Insights into the phylogenetic position and phylogeography of the monospecific skink-parasite genus

Neoentomelas asatoi Hasegawa, 1989 is a parasitic nematode that infests only the scincid lizard Ateuchosaurus pellopleurus (Hallowell, 1861) that inhabits the forest floor in the Northern and Central Ryukyu Archipelago, Japan. As a member of Rhabdiasidae, the reproductive mode of N. asatoi is characterised by the alternation of the protandrous hermaphroditic mode and gonochoristic mode throughout the life cycle. The intrafamily phylogenetic position and intraspecific diversity of this nematode species were inferred by molecular phylogenetic analyses. The results revealed the phylogenetic distinctiveness of Neoentomelas Hasegawa, 1989 in Rhabdiasidae that supports the unique generic status of Neoentomelas within the family. The intraspecific phylogenetic analyses of N. asatoi revealed a minor concordant phylogenetic pattern with the host and mosaic geographic arrangement of the major clades that was discordant with the host. The analyses and distribution pattern of subclades suggested that this geographic arrangement can be explained by at least three dispersal events and subsequent switching to indigenous host populations. Colonisation events might be promoted by the high establishment rate of new populations stemming from the parthenogenesis-like reproduction mode of N. asatoi. This study demonstrated that reproductive modes can affect the intraspecific genetic diversity of parasites.

Eimeria sciurorum (Apicomplexa, Coccidia) From the Calabrian Black Squirrel (Sciurus meridionalis): An Example of Lower Host Specificity of Eimerians

Host specificity plays one of the key roles in parasitism. It affects the evolution and diversification of both host and parasite, as well as it influences their geographical distribution, and epidemiological significance. For most of parasites, however, host specificity is unknown or misrepresented because it is difficult to be determined accurately. Here we provide the information about the lower host specificity of Eimeria sciurorum infecting squirrels, and its new host record for the Calabrian black squirrel Sciurus meridionalis, a southern Italian endemic species.

The population genetics of parasitic nematodes of wild animals

Parasitic nematodes are highly diverse and common, infecting virtually all animal species, and the importance of their roles in natural ecosystems is increasingly becoming apparent. How genes flow within and among populations of these parasites - their population genetics - has profound implications for the epidemiology of host infection and disease, and for the response of parasite populations to selection pressures. The population genetics of nematode parasites of wild animals may have consequences for host conservation, or influence the risk of zoonotic disease. Host movement has long been recognised as an important determinant of parasitic nematode population genetic structure, and recent research has also highlighted the importance of nematode life histories, environmental conditions, and other aspects of host ecology. Commonly, factors influencing parasitic nematode population genetics have been studied in isolation, such that an integrated view of the drivers of population genetic structure of parasitic nematodes is still lacking. Here, we seek to provide a comprehensive, broad, and integrative picture of these factors in parasitic nematodes of wild animals that will be a useful resource for investigators studying non-model parasitic nematodes in natural ecosystems. Increasingly, new methods of analysing the population genetics of nematodes are becoming available, and we consider the opportunities that these afford in resolving hitherto inaccessible questions of the population genetics of these important animals.

Host specificity driving genetic structure and diversity in ectoparasite populations: Coevolutionary patterns in Apodemus mice and their lice

A degree of host specificity, manifested by the processes of host-parasite cospeciations and host switches, is assumed to be a major determinant of parasites' evolution. To understand these patterns and formulate appropriate ecological hypotheses, we need better insight into the coevolutionary processes at the intraspecific level, including the maintenance of genetic diversity and population structure of parasites and their hosts. Here, we address these questions by analyzing large-scale molecular data on the louse Polyplax serrata and its hosts, mice of the genus Apodemus, across a broad range of European localities. Using mitochondrial DNA sequences and microsatellite data, we demonstrate the general genetic correspondence of the Apodemus/Polyplax system to the scenario of the postglacial recolonization of Europe, but we also show several striking discrepancies. Among the most interesting are the evolution of different degrees of host specificity in closely related louse lineages in sympatry, or decoupled population structures of the host and parasites in central Europe. We also find strong support for the prediction that parasites with narrower host specificity possess a lower level of genetic diversity and a deeper pattern of interpopulation structure as a result of limited dispersal and smaller effective population size.

The importance of integrative approaches in nematode taxonomy: the validity of Parapharyngodon and Thelandros as distinct genera

Despite the advances of molecular tools, new nematode species are still described mainly based on morphological characters. Parapharyngodon and Thelandros are two genera of oxyurids with unclear related taxonomic histories. Here we use morphological characters (linear measurements and categorical variables) and genetic information (18S rRNA, 28S rRNA and COI partial gene sequences) to confirm the relationships between representatives of these two genera and to determine whether they can be discriminated morphologically. Genetic results confirm the existence of two main clades, mostly congruent with Parapharyngodon and Thelandros genera but with several discordances. Thelandros is polyphyletic, with two of the species analysed (T. filiformis and T. tinerfensis) being part of the Thelandros clade, but with a third one (T. galloti) falling within the Parapharyngodon clade. Regarding the Parapharyngodon clade, P. cubensis, P. scleratus and Parapharyngodon sp. from Mexico form congruent lineages, while most P. echinatus samples cluster in another group, with one exception. Interestingly, P. micipsae samples are scattered across the Parapharyngodon clade, suggesting that they were misidentified or rather represent alternative morphotypes of other species. Morphological analysis identified the length of the tail, number of caudal papillae, position of the nerve ring, presence of caudal alae and length of the lateral alae as reliable characters to distinguish between Parapharyngodon and Thelandros genetic clades. Our study highlights the current taxonomic inconsistency in these groups, mainly derived from the exclusive use of morphological data. As such, we advocate for the routine implementation of molecular data in nematode taxonomic studies.

Integrative approach on Pharyngodonidae (Nematoda: Oxyuroidea) parasitic in reptiles: Relationship among its genera, importance of their diagnostic features, and new data on Parapharyngodon bainae

The first integrative approach using sequences of two genes (18S and 28S rRNA) plus morphological and life history traits, was explored in Pharyngodonidae nematodes parasitic in reptiles. Additionally, first genetic characterization of Parapharyngodon bainae and new data on its morphology are given. This approach evaluated the phylogenetic relationships among genera within Pharyngodonidae, as well as the importance of their diagnostic morphological features. Specimens of P. bainae were collected from faecal pellets of the lizard Tropidurus torquatus in the State of Minas Gerais, Brazil. Nematodes were fixed for scanning electron microscopy and molecular procedures. Morphological observations revealed the accurate structures of cephalic end, of cloacal region in males, of vulva and eggs. Phylogenetic reconstructions were based upon four datasets: aligned sequences of the 18S, of the 28S, of both concatenated genes and of combined morphological and molecular datasets. Bayesian inference and maximum likelihood were performed to infer the phylogenies of molecular datasets and maximum parsimony to infer that of all-combined data. Pharyngodonid parasites of reptiles seem to configure two general monophyletic lineages, as previously assertions. Results also showed the monophyly of Spauligodon, Skrjabinodon and Parapharyngodon, as well as the clear separation between the latter and Thelandros. Combination of datasets improved nodal supports. Analysis of the all-combined datasets revealed the importance of vulval position and egg morphology as phylogenetic informative traits. However, characters of male caudal morphology appear as are highly homoplastic, and seem to be product of convergent evolution or multiple losses of ancestral traits. The closely-related Thelandros and Parapharyngodon are kept valid and their diagnosis should be based upon the position of the operculum in eggs (terminal or subterminal, respectively). Some inconsistencies in the scarce molecular and morphological databases were noted. Thus, new genetic data is required for further conclusions and current database must be evaluated with attention.

Mysteries of host switching: Diversification and host specificity in rodent-coccidia associations

Recent studies show that host switching is much more frequent than originally believed and constitutes an important driver in evolution of host-parasite associations. However, its frequency and ecological mechanisms at the population level have been rarely investigated. We address this issue by analyzing phylogeny and population genetics of an extensive sample, from a broad geographic area, for commonly occurring parasites of the genus Eimeria within the abundant rodent genera Apodemus, Microtus and Myodes, using two molecular markers. At the most basal level, we demonstrate polyphyletic arrangement, i.e. multiple origin, of the rodent-specific clusters within the Eimeria phylogeny, and strong genetic/phylogenetic structure within these lineages determined at least partially by specificities to different host groups. However, a novel and the most important observation is a repeated occurrence of host switches among closely related genetic lineages which may become rapidly fixed. Within the studied model, this phenomenon applies particularly to the switches between the eimerians from Apodemus flavicollis/Apodemus sylvaticus and Apodemus agrarius groups. We show that genetic differentiation and isolation between A. flavicollis/A. sylvaticus and A. agrarius faunas is a secondary recent event and does not reflect host-parasite coevolutionary history. Rather, it provides an example of rapid ecology-based differentiation in the parasite population.

Allopatric speciation of Meteterakis (Heterakoidea: Heterakidae), a highly dispersible parasitic nematode, in the East Asian islands

To clarify how the species diversity of highly dispersible parasites has developed, molecular phylogenetic analyses of Meteterakis spp., multi-host endoparasitic nematodes of reptiles and amphibians from the East Asian islands, were conducted. The results demonstrated the existence of two major clades, the J- and A-groups, with exclusive geographic ranges that are discordant with the host faunal province. However, diversification within the J-group was concordant with the host biogeography and suggested co-divergence of this group with vicariance of the host fauna. In contrast, the phylogenetic pattern within the A-group was discordant with host biogeography and implied diversification by repeated colonization. In addition, the mosaic distribution pattern of a J-group and an A-group species in the Japanese Archipelago, along with comparison of population genetic parameters and the genetic distance from their closest relatives, suggested the initial occurrence of a J-group lineage followed by exclusion in the western part of this region caused by invasion of an A-group lineage. Thus, the present study suggested that the species diversity of highly dispersible parasites including Meteterakis is formed not only by co-divergence with host faunal vicariance but also by peripatric speciation and exclusive interactions between species.

Broad infectivity of Leidynema appendiculatum (Nematoda: Oxyurida: Thelastomatidae) parasite of the smokybrown cockroach Periplaneta fuliginosa (Blattodea: Blattidae)

Host specificity of parasites is important for the understanding of evolutionary strategies of parasitism that would be a basis of predictions of the disease expansion when parasitized hosts invade new environments. The nematode order Oxyurida is an interesting parasite group for studying the evolution of parasitism as it includes parasites of both invertebrates and vertebrates. In our survey, we found that the smokybrown cockroach Periplaneta fuliginosa was primarily infected with only one nematode species Leidynema appendiculatum. In two cases, L. appendiculatum was isolated from two additional cockroach species Pycnoscelus surinamensis, sold in Japan as a reptile food, and Blatta lateralis, captured in the field and cultured in the laboratory. Inoculation of L. appendiculatum into three additional cockroach species P. japonica, Blattella nipponica, and P. surinamensis also resulted in parasitism. Infection prevalence was high, and timing of postembryonic development from hatched nematode larva to mature adult in these hosts was identical with that in P. fuliginosa. While ecological interactions strongly determine the host range, such broad infectivity is still possible in this parasitic nematode.

Along for the ride or missing it altogether: exploring the host specificity and diversity of haemogregarines in the Canary Islands

Background

Host-parasite relationships are expected to be strongly shaped by host specificity, a crucial factor in parasite adaptability and diversification. Because whole host communities have to be considered to assess host specificity, oceanic islands are ideal study systems given their simplified biotic assemblages. Previous studies on insular parasites suggest host range broadening during colonization. Here, we investigate the association between one parasite group (haemogregarines) and multiple sympatric hosts (of three lizard genera: Gallotia, Chalcides and Tarentola) in the Canary Islands. Given haemogregarine characteristics and insular conditions, we hypothesized low host specificity and/or occurrence of host-switching events.

Methods

A total of 825 samples were collected from the three host taxa inhabiting the seven main islands of the Canarian Archipelago, including locations where the different lizards occurred in sympatry. Blood slides were screened to assess prevalence and parasitaemia, while parasite genetic diversity and phylogenetic relationships were inferred from 18S rRNA gene sequences.

Results

Infection levels and diversity of haplotypes varied geographically and across host groups. Infections were found in all species of Gallotia across the seven islands, in Tarentola from Tenerife, La Gomera and La Palma, and in Chalcides from Tenerife, La Gomera and El Hierro. Gallotia lizards presented the highest parasite prevalence, parasitaemia and diversity (seven haplotypes), while the other two host groups (Chalcides and Tarentola) harbored one haplotype each, with low prevalence and parasitaemia levels, and very restricted geographical ranges. Host-sharing of the same haemogregarine haplotype was only detected twice, but these rare instances likely represent occasional cross-infections.

Conclusions

Our results suggest that: (i) Canarian haemogregarine haplotypes are highly host-specific, which might have restricted parasite host expansion; (ii) haemogregarines most probably reached the Canary Islands in three colonization events with each host genus; and (iii) the high number of parasite haplotypes infecting Gallotia hosts and their restricted geographical distribution suggest co-diversification. These findings contrast with our expectations derived from results on other insular parasites, highlighting how host specificity depends on parasite characteristics and evolutionary history.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2760-5) contains supplementary material, which is available to authorized users.

Lack of genetic structure in pinworm populations from New World primates in forest fragments

Microevolutionary processes in parasites are driven by factors related to parasite biology, host abundance and dispersal, and environmental conditions. Here, we test the prediction that isolation of host populations results in reduced genetic diversity and high differentiation among parasite populations. We conducted a population genetic analysis of two pinworms, Trypanoxyuris minutus and Trypanoxyuris atelis, commonly found parasitizing howler and spider monkeys in tropical rainforests across south-eastern Mexico, whose populations are currently isolated due to anthropogenic habitat loss and fragmentation. Mitochondrial DNA was employed to assess parasite genetic patterns, as well as to analyse their demography and population history. Both pinworm species showed high haplotype diversity but, unexpectedly, lower nucleotide diversity than that reported for other parasites. No genetic differentiation or population structure was detected in either pinworm species despite habitat loss, fragmentation and host isolation. Several scenarios are discussed that could help to explain the genetic panmixia found in both pinworm species, including higher than expected primate inter-fragment dispersal movements, and passive dispersal facilitating gene flow between parasite populations. The results suggest that large population sizes of parasites could be helping them to cope with the isolation and fragmentation of populations, delaying the effects of genetic drift. The present study highlights the complexity of the drivers that intervene in the evolutionary processes of parasites. Detailed genetic studies are needed, both in host and parasite populations, to assess the effects that habitat perturbation and environmental changes could have on the evolutionary dynamics of pinworms and primates.

The diversity and evolution of nematodes (Pharyngodonidae) infecting New Zealand lizards

Host-parasite co-evolutionary studies can shed light on diversity and the processes that shape it. Molecular methods have proven to be an indispensable tool in this task, often uncovering unseen diversity. This study used two nuclear markers (18S rRNA and 28S rRNA) and one mitochondrial (cytochrome oxidase subunit I) marker to investigate the diversity of nematodes of the family Pharyngodonidae parasitizing New Zealand (NZ) lizards (lygosomine skinks and diplodactylid geckos) and to explore their co-evolutionary history. A Bayesian approach was used to infer phylogenetic relationships of the parasitic nematodes. Analyses revealed that nematodes parasitizing skinks, currently classified as Skrjabinodon, are more closely related to Spauligodon than to Skrjabinodon infecting NZ geckos. Genetic analyses also uncovered previously undetected diversity within NZ gecko nematodes and provided evidence for several provisionally cryptic species. We also examined the level of host-parasite phylogenetic congruence using a global-fit approach. Significant congruence was detected between gecko-Skrjabinodon phylogenies, but our results indicated that strict co-speciation is not the main co-evolutionary process shaping the associations between NZ skinks and geckos and their parasitic nematodes. However, further sampling is required to fully resolve co-phylogenetic patterns of diversification in this host-parasite system.

Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 2. Separating the relative effects of gene flow and genetic drift

Studying wild pathogen populations in natural ecosystems offers the opportunity to better understand the evolutionary dynamics of biotic diseases in crops and to enhance pest control strategies. We used simulations and genetic markers to investigate the spatial and temporal population genetic structure of wild populations of the beet cyst nematode Heterodera schachtii on a wild host plant species, the sea beet (Beta vulgaris spp. maritima), the wild ancestor of cultivated beets. Our analysis of the variation of eight microsatellite loci across four study sites showed that (i) wild H. schachtii populations displayed fine-scaled genetic structure with no evidence of substantial levels of gene flow beyond the scale of the host plant, and comparisons with simulations indicated that (ii) genetic drift substantially affected the residual signals of isolation-by-distance processes, leading to departures from migration-drift equilibrium. In contrast to what can be suspected for (crop) field populations, this showed that wild cyst nematodes have very low dispersal capabilities and are strongly disconnected from each other. Our results provide some key elements for designing pest control strategies, such as decreasing passive dispersal events to limit the spread of virulence among field nematode populations.

Helminth parasites of the Mediterranean gecko, Hemidactylus turcicus (Sauria: Gekkonidae), from Texas, United States with a summary of helminths of this host

One hundred-thirty six Mediterranean geckos, Hemidactylus turcicus, were collected between December 1986 and March 2016 in Hardin (n = 7), Harris (n = 57), and Tom Green (n = 72) counties, Texas, USA., and examined for helminth parasites. Fifty-two H. turcicus (38%) were infected with at least one helminth species. Found were a trematode, Mesocoelium meggitti, three cestodes, Mesocestoides sp. (tetrathyridia), Oochoristica ameivae and Oochoristica scelopori, and four nematodes, Cosmocercoides variabilis, Oswaldocruzia pipiens, Parapharyngodon cubensis, and larvae of Physaloptera sp. Oochoristica ameivae, O. scelopori, P. cubensis, Physaloptera sp., and Os. pipiens represent new host records for H. turcicus and M. meggitti is reported from Texas for the first time. A summary of the helminth parasites of both native and non-native H. turcicus is presented.

Biogeography of Parasitic Nematode Communities in the Galápagos Giant Tortoise: Implications for Conservation Management

The Galápagos giant tortoise is an icon of the unique, endemic biodiversity of Galápagos, but little is known of its parasitic fauna. We assessed the diversity of parasitic nematode communities and their spatial distributions within four wild tortoise populations comprising three species across three Galápagos islands, and consider their implication for Galápagos tortoise conservation programmes. Coprological examinations revealed nematode eggs to be common, with more than 80% of tortoises infected within each wild population. Faecal samples from tortoises within captive breeding centres on Santa Cruz, Isabela and San Cristobal islands also were examined. Five different nematode egg types were identified: oxyuroid, ascarid, trichurid and two types of strongyle. Sequencing of the 18S small-subunit ribosomal RNA gene from adult nematodes passed with faeces identified novel sequences indicative of rhabditid and ascaridid species. In the wild, the composition of nematode communities varied according to tortoise species, which co-varied with island, but nematode diversity and abundance were reduced or altered in captive-reared animals. Evolutionary and ecological factors are likely responsible for the variation in nematode distributions in the wild. This possible species/island-parasite co-evolution has not been considered previously for Galápagos tortoises. We recommend that conservation efforts, such as the current Galápagos tortoise captive breeding/rearing and release programme, be managed with respect to parasite biogeography and host-parasite co-evolutionary processes in addition to the biogeography of the host.

Patterns of genetic variation and life history traits of Zeuxapta seriolae infesting Seriola lalandi across the coastal and oceanic areas in the southeastern Pacific Ocean: potential implications for aquaculture

BACKGROUND

The monogenean, Zeuxapta seriolae, is a host-specific parasite that has an extensive geographical distribution on its host, Seriola lalandi, and is considered highly pathogenic in farmed fish. In recent years, developing cultures of S. lalandi in different coastal localities in Southeastern Pacific Ocean (SEP) have been affected by moderate and heavy infections of this parasite, attributed to contagion from wild to farmed fish. Here, we evaluated the pattern of genetic variations and biological traits of Z. seriolae in a spatial and temporal scale across its geographical distribution in SEP to determine its genetic status and biological traits, which could affect its transmission dynamics from wild to farmed fish.

METHODS

Wild fish and their parasites were sampled from fisheries in the northern Chilean coast (NCC: 24°S-30°S) and Eastern islands (JFA: ca 33°S; 80°W) between 2012 and 2014. Fragments of 816 bp of the cytochrome c oxidase subunit I (COI) gene was sequenced for 112 individuals from NCC and 63 from JFA and compared using AMOVA. Prevalence and intensity of Z. seriolae were calculated for each area. The parasite body size, fecundity and size at sexual maturity were estimated for 177 parasites from NCC and 128 from JFA, and significant differences were evaluated using GLM.

RESULTS

Geographical genetic structuring was detected for Z. seriolae across SEP, with a population in NCC and the other in JFA, both with the same high haplotype diversity. Neutrality tests and mismatch analyses indicated that both Z. seriolae populations are stable. Parasite biological traits such as fecundity, body size, and size at sexual maturity, and population parameters varied significantly between geographical areas.

CONCLUSION

Two genetic groups of Z. seriolae were detected in wild fish across SEP. Because of the seasonal migration of wild host and temporal contact with farming, quantifying the genetic diversity and level of gene flow or isolation between parasite populations is useful for fish health management in farming. The smallest size of sexual maturity in parasites from NCC is predictive of shorter life cycles, and their high genetic diversity suggests high evolutionary potential and high transmission of this parasite to farmed hosts.

Contrasting definitive hosts as determinants of the genetic structure in a parasite with complex life cycle along the south-eastern Pacific

The spatial genetic structure (and gene flow) of parasites with complex life cycles, such as digeneans, has been attributed mainly to the dispersion ability of the most mobile host, which most often corresponds to the definitive host (DH). In this study, we compared the genetic structure and diversity of adult Neolebouria georgenascimentoi in two fish species (DHs) that are extensively distributed along the south-eastern Pacific (SEP). The analysis was based on the cytochrome oxidase subunit I gene sequences of parasites collected between 23°S and 45°S. In total, 202 sequences of N. georgenascimentoi in Pinguipes chilensis isolated from nine sites and 136 sequences of Prolatilus jugularis from five sites were analysed. Our results showed that N. georgenascimentoi is a species complex that includes three different parasite species; however, in this study, only lineage 1 and 2 found in P. chilensis and P. jugularis, respectively, were studied because they are widely distributed along the coastline. Lineage 1 parasites had two common haplotypes with wide distribution and unique haplotypes in northern sites. Lineage 2 had only one common haplotype with wide distribution and a large number of unique haplotypes with greater genetic diversity. Both lineages have experienced recent population expansion. Only lineage 1 exhibited a genetic structure that was mainly associated with a biogeographical break at approximately 30°S along the SEP. Our finding suggests that host access to different prey (=intermediate hosts) could affect the genetic structure of the parasite complex discovered here. Consequently, difference between these patterns suggests that factors other than DH dispersal are involved in the genetic structure of autogenic parasites.