Multi-host parasite species in cophylogenetic studies

Cophylogeny Reconstruction Allowing for Multiple Associations Through Approximate Bayesian Computation

Phylogenetic tree reconciliation is extensively employed for the examination of coevolution between host and symbiont species. An important concern is the requirement for dependable cost values when selecting event-based parsimonious reconciliation. Although certain approaches deduce event probabilities unique to each pair of host and symbiont trees, which can subsequently be converted into cost values, a significant limitation lies in their inability to model the invasion of diverse host species by the same symbiont species (termed as a spread event), which is believed to occur in symbiotic relationships. Invasions lead to the observation of multiple associations between symbionts and their hosts (indicating that a symbiont is no longer exclusive to a single host), which are incompatible with the existing methods of coevolution. Here, we present a method called AmoCoala (an enhanced version of the tool Coala) that provides a more realistic estimation of cophylogeny event probabilities for a given pair of host and symbiont trees, even in the presence of spread events. We expand the classical 4-event coevolutionary model to include 2 additional outcomes, vertical and horizontal spreads, that lead to multiple associations. In the initial step, we estimate the probabilities of spread events using heuristic frequencies. Subsequently, in the second step, we employ an approximate Bayesian computation approach to infer the probabilities of the remaining 4 classical events (cospeciation, duplication, host switch, and loss) based on these values. By incorporating spread events, our reconciliation model enables a more accurate consideration of multiple associations. This improvement enhances the precision of estimated cost sets, paving the way to a more reliable reconciliation of host and symbiont trees. To validate our method, we conducted experiments on synthetic datasets and demonstrated its efficacy using real-world examples. Our results showcase that AmoCoala produces biologically plausible reconciliation scenarios, further emphasizing its effectiveness.

Horizontal transmission maintains host specificity and codiversification of symbionts in a brood parasitic host

In host-symbiont systems, interspecific transmissions create opportunities for host switches, potentially leading to cophylogenetic incongruence. In contrast, conspecific transmissions often result in high host specificity and congruent cophylogenies. In most bird-feather mite systems, conspecific transmission is considered dominant, while interspecific transmission is supposedly rare. However, while mites typically maintain high host specificity, incongruent cophylogenies are common. To explain this conundrum, we quantify the magnitude of conspecific vs. interspecific transmission in the brood parasitic shiny cowbird (Molothrus bonariensis). M. bonariensis lacks parental care, allowing the assessment of the role of horizontal transmission alone in maintaining host specificity. We found that despite frequent interspecific interactions via foster parental care, mite species dispersing via conspecific horizontal contacts are three times more likely to colonize M. bonariensis than mites transmitted vertically via foster parents. The results highlight the previously underappreciated rate of transmission via horizontal contacts in maintaining host specificity on a microevolutionary scale. On a macroevolutionary scale, however, host switches were estimated to have occurred as frequently as codivergences. This suggests that macroevolutionary patterns resulting from rare events cannot be easily generalized from short-term evolutionary trends.

Genomic evidence for contrasting patterns of host-associated genetic differentiation across shared host-plant species in leaf- and bud-galling sawflies

Resource specialization and ecological speciation arising through host-associated genetic differentiation (HAD) are frequently invoked as an explanation for the high diversity of plant-feeding insects and other organisms with a parasitic lifestyle. While genetic studies have demonstrated numerous examples of HAD in insect herbivores, the rarity of comparative studies means that we still lack an understanding of how deterministic HAD is, and whether patterns of host shifts can be predicted over evolutionary timescales. We applied genome-wide single nucleotide polymorphism and mitochondrial DNA sequence data obtained through genome resequencing to define species limits and to compare host-plant use in population samples of leaf- and bud-galling sawflies (Hymenoptera: Tenthredinidae: Nematinae) collected from seven shared willow (Salicaceae: Salix) host species. To infer the repeatability of long-term cophylogenetic patterns, we also contrasted the phylogenies of the two galler groups with each other as well as with the phylogeny of their Salix hosts estimated based on RADseq data. We found clear evidence for host specialization and HAD in both of the focal galler groups, but also that leaf gallers are more specialized to single host species compared with most bud gallers. In contrast to bud gallers, leaf gallers also exhibited statistically significant cophylogenetic signal with their Salix hosts. The observed discordant patterns of resource specialization and host shifts in two related galler groups that have radiated in parallel across a shared resource base indicate a lack of evolutionary repeatability in the focal system, and suggest that short- and long-term host use and ecological diversification in plant-feeding insects are dominated by stochasticity and/or lineage-specific effects.

Persistence of single species of symbionts across multiple closely-related host species

Some symbiont species are highly host-specific, inhabiting only one or a very few host species, and typically have limited dispersal abilities. When they do occur on multiple host species, populations of such symbionts are expected to become genetically structured across these different host species, and this may eventually lead to new symbiont species over evolutionary timescales. However, a low number of dispersal events of symbionts between host species across time might be enough to prevent population structure and species divergence. Overall, processes of evolutionary divergence and the species status of most putative multi-host symbiont systems are yet to be investigated. Here, we used DNA metabarcoding data of 6,023 feather mites (a total of 2,225 OTU representative sequences) from 147 infracommunities (i.e., the assemblage consisting of all mites of different species collected from the same bird host individual) to investigate patterns of population genetic structure and species status of three different putative multi-host feather mite species Proctophyllodes macedo Vitzthum, 1922, Proctophyllodes motacillae Gaud, 1953, and Trouessartia jedliczkai (Zimmerman, 1894), each of which inhabits a variable number of different closely related wagtail host species (genus Motacilla). We show that mite populations from different host species represent a single species. This pattern was found in all the mite species, suggesting that each of these species is a multi-host species in which dispersal of mites among host species prevents species divergence. Also, we found evidence of limited evolutionary divergence manifested by a low but significant level of population genetic structure among symbiont populations inhabiting different host species. Our study agrees with previous studies showing a higher than expected colonization opportunities in host-specific symbionts. Indeed, our results support that these dispersal events would allow the persistence of multi-host species even in symbionts with limited dispersal capabilities, though additional factors such as the geographical structure of some bird populations may also play a role.

Fish hosts, glochidia features and life cycle of the endemic freshwater pearl mussel Margaritifera dahurica from the Amur Basin

Margaritiferidae is a small freshwater bivalve family with 16 species. In spite of a small number of taxa and long-term history of research, several gaps in our knowledge on the freshwater pearl mussels still exist. Here we present the discovery of host fishes for Margaritifera dahurica, i.e. Lower Amur grayling, sharp-snouted lenok, and blunt-snouted lenok. The host fishes were studied in rivers of the Ussuri Basin. The identification of glochidia and fish hosts was confirmed by DNA analysis. The life cycle of M. dahurica and its glochidia are described for the first time. The SEM study of glochidia revealed that the rounded, unhooked Margaritifera dahurica larvae are similar to those of the other Margaritiferidae. Margaritifera dahurica is a tachytictic breeder, the larvae of which attach to fish gills during the Late August – September and finish the metamorphosis in June. Ancestral host reconstruction and a review of the salmonid - pearl mussel coevolution suggest that the ancestral host of the Margaritiferidae was a non-salmonid fish, while that of the genus Margaritifera most likely was an early salmonid species or their stem lineage. The overfishing of lenoks and graylings appears to be the most significant threat for this rare mussel species.

The joint evolution of the Myxozoa and their alternate hosts: A cnidarian recipe for success and vast biodiversity

The relationships between parasites and their hosts are intimate, dynamic and complex; the evolution of one is inevitably linked to the other. Despite multiple origins of parasitism in the Cnidaria, only parasites belonging to the Myxozoa are characterized by a complex life cycle, alternating between fish and invertebrate hosts, as well as by high species diversity. This inspired us to examine the history of adaptive radiations in myxozoans and their hosts by determining the degree of congruence between their phylogenies and by timing the emergence of myxozoan lineages in relation to their hosts. Recent genomic analyses suggested a common origin of Polypodium hydriforme, a cnidarian parasite of acipenseriform fishes, and the Myxozoa, and proposed fish as original hosts for both sister lineages. We demonstrate that the Myxozoa emerged long before fish populated Earth and that phylogenetic congruence with their invertebrate hosts is evident down to the most basal branches of the tree, indicating bryozoans and annelids as original hosts and challenging previous evolutionary hypotheses. We provide evidence that, following invertebrate invasion, fish hosts were acquired multiple times, leading to parallel cospeciation patterns in all major phylogenetic lineages. We identify the acquisition of vertebrate hosts that facilitate alternative transmission and dispersion strategies as reason for the distinct success of the Myxozoa, and identify massive host specification-linked parasite diversification events. The results of this study transform our understanding of the origins and evolution of parasitism in the most basal metazoan parasites known.

Role of ecology and phylogeny in determining tapeworm assemblages in skates (Rajiformes)

An understanding of the mechanisms that determine host and parasite relationships is a central aim in parasitology. Association of a parasite species with a host species may be influenced primarily by phylogenetic constraints that cause parasite species to co-speciate with their host species, or predominantly by ecological parameters that influence all other co-evolutionary scenarios. This study aimed to investigate the role of co-speciation as well as other co-evolutionary scenarios in influencing the assemblages of tapeworm parasites (marine cestodes) in skate hosts (Rajiformes) using a modification of the PACo (Procrustean Approach to Cophylogeny) method. The study found that phylogeny and host ecology are both significant predictors of skate-tapeworm relationships, implying that co-speciation as well as other co-evolutionary scenarios are shaping these associations. The study also investigated the key ecological parameters influencing host-switching and found that host diet, distribution depth, average body size and geographical location have a combined effect. Given the importance of parasites in ensuring healthy and stable marine ecosystems, the findings of this study have implications for conservation management worldwide.

Topological congruence between phylogenies of Anacanthorus spp. (Monogenea: Dactylogyridae) and their Characiformes (Actinopterygii) hosts: A case of host-parasite cospeciation

Cophylogenetic studies aim at testing specific hypotheses to understand the nature of coevolving associations between sets of organisms, such as host and parasites. Monogeneans and their hosts provide and interesting platform for these studies due to their high host specificity. In this context, the objective of the present study was to establish whether the relationship between Anacanthorus spp. with their hosts from the upper Paraná River and its tributaries can be explained by means of cospeciation processes. Nine fish species and 14 monogenean species, most of them host specific, were studied. Partial DNA sequences of the genes RAG1, 16S and COI of the fish hosts and of the genes ITS2, COI and 5.8S of the parasite species were used for phylogenetic reconstruction. Maximum likelihood phylogenetic trees of the host and parasite species were built and used for analyses of topological congruence with PACo and ParaFit. The program Jane was used to estimate the nature of cospeciation events. The comparison of the two phylogenies revealed high topological congruence between them. Both PACo and ParaFit supported the hypothesis of global cospeciation. Results from Jane pointed to duplications as the most frequent coevolutionary event, followed by cospeciation, whereas duplications followed by host-switching were the least common event in Anacanthorus spp. studied. Host-sharing (spreading) was also identified but only between congeneric host species.

Fungal-algal association patterns in lichen symbiosis linked to macroclimate

Both macroclimate and evolutionary events may influence symbiont association and diversity patterns. Here we assess how climatic factors and evolutionary events shape fungal-algal association patterns in the widely distributed lichen-forming fungal genus Protoparmelia. Multilocus phylogenies of fungal and algal partners were generated using 174 specimens. Coalescent-based species delimitation analysis suggested that 23 fungal hosts are associating with 20 algal species. Principal component analysis (PCA) was performed to infer how fungal-algal association patterns varied with climate. Fungi associated with one to three algal partners whereas algae accepted one to five fungal partners. Both fungi and algae were more specific, associating with fewer partners, in the warmer climates. Interaction with more than one partner was more frequent in cooler climates for both the partners. Cophylogenetic analyses suggest congruent fungal-algal phylogenies. Host switch was a more common event in warm climates, whereas failure of the photobiont to diverge with its fungal host was more frequent in cooler climates. We conclude that both environmental factors and evolutionary events drive fungal and algal evolution in Protoparmelia. The processes leading to phylogenetic congruence of fungi and algae are different in different macrohabitats in our study system. Hence, closely related species inhabiting diverse habitats may follow different evolutionary pathways.

Evolutionary relationships between digeneans of the family Brachycladiidae Odhner, 1905 and their marine mammal hosts: A cophylogenetic study

Cophylogenetic studies examine the congruence between host and parasite phylogenies. There are few studies that quantify the relative contribution of coevolutionary events, i.e. duplication, loss, failure-to-diverge, host-switching and spreading in trophically-transmitted parasites at the marine realm. We addressed this issue in the Brachycladiidae, a cosmopolitan digenean family specific to marine mammals. We used, for the first time, distance-based and event-based methods to explicitly test the coevolutionary events that have shaped the current brachycladiid-marine mammal associations. Parasite phylogeny was constructed using mtDNA ND3 sequences of nine brachycladiid species, and host phylogeny using cytochrome b sequences of 104 mammalian species. A total of 50 host-parasite links were identified. Distance-based methods supported the hypothesis of a global non-random association of host and parasite phylogenies. Significant individual links (i.e., 24 out of 50) were those related to Campula oblonga, Nasitrema delphini, N. globicephalae and Brachycladium atlanticum and their associated taxa from the Delphinoidea. Regarding event-based methods, we explored 54 schemes using different combinations of costs for each potential coevolutionary event. Three coevolutionary scenarios were identified across all schemes and in all cases the number of loss events (87-156) was the most numerous, followed by failure-to-diverge (40), duplication (3-6), host-switching (0-3) and cospeciation (0-2). We developed a framework to interpret the evolution of this host-parasite system and confirmed that failure-to-diverge and colonization with or without subsequent diversification could have been decisive in the establishment of the associations between brachycladiids and marine mammals.

Host generalists and specialists emerging side by side: an analysis of evolutionary patterns in the cosmopolitan chewing louse genus Menacanthus

Parasites with wide host spectra provide opportunities to study the ecological parameters of speciation, as well as the process of the evolution of host specificity. The speciose and cosmopolitan louse genus Menacanthus comprises both multi-host and specialised species, allowing exploration of the ecological and historical factors affecting the evolution of parasites using a comparative approach. We used phylogenetic analysis to reconstruct evolutionary relationships in 14 species of Menacanthus based on the sequences of one mitochondrial and one nuclear gene. The results allowed us to validate species identification based on morphology, as well as to explore host distribution by assumed generalist and specialist species. Our analyses confirmed a narrow host use for several species, however in some cases, the supposed host specialists had a wider host spectrum than anticipated. In one case a host generalist (Menacanthus eurysternus) was clustered terminally on a clade almost exclusively containing host specialists. Such a clade topology indicates that the process of host specialisation may not be irreversible in parasite evolution. Finally, we compared patterns of population genetic structure, geographic distribution and host spectra between two selected species, M. eurysternus and Menacanthus camelinus, using haplotype networks. Menacanthus camelinus showed limited geographical distribution in combination with monoxenous host use, whereas M. eurysternus showed a global distribution and lack of host specificity. It is suggested that frequent host switching maintains gene flow between M. eurysternus populations on unrelated hosts in local populations. However, gene flow between geographically distant localities was restricted, suggesting that geography rather than host-specificity is the main factor defining the global genetic diversity of M. eurysternus.

Host switching promotes diversity in host-specialized mycoparasitic fungi: uncoupled evolution in the Biatoropsis-usnea system

Fungal mycoparasitism-fungi parasitizing other fungi-is a common lifestyle in some basal lineages of the basidiomycetes, particularly within the Tremellales. Relatively nonaggressive mycoparasitic fungi of this group are in general highly host specific, suggesting cospeciation as a plausible speciation mode in these associations. Species delimitation in the Tremellales is often challenging because morphological characters are scant. Host specificity is therefore a great aid to discriminate between species but appropriate species delimitation methods that account for actual diversity are needed to identify both specialist and generalist taxa and avoid inflating or underestimating diversity. We use the Biatoropsis-Usnea system to study factors inducing parasite diversification. We employ morphological, ecological, and molecular data-methods including genealogical concordance phylogenetic species recognition (GCPSR) and the general mixed Yule-coalescent (GMYC) model-to assess the diversity of fungi currently assigned to Biatoropsis usnearum. The degree of cospeciation in this association is assessed with two cophylogeny analysis tools (ParaFit and Jane 4.0). Biatoropsis constitutes a species complex formed by at least seven different independent lineages and host switching is a prominent force driving speciation, particularly in host specialists. Combining ITS and nLSU is recommended as barcode system in tremellalean fungi.

Cophylogenetic relationships between Anicetus parasitoids (Hymenoptera: Encyrtidae) and their scale insect hosts (Hemiptera: Coccidae)

BACKGROUND

Numerous studies have investigated cospeciation between parasites and their hosts, but there have been few studies concerning parasitoids and insect hosts. The high diversity and host specialization observed in Anicetus species suggest that speciation and adaptive radiation might take place with species diversification in scale insect hosts. Here we examined the evolutionary history of the association between Anicetus species and their scale insect hosts via distance-based and tree-based methods.

RESULTS

A total of 94 Anicetus individuals (nine parasitoid species) and 113 scale insect individuals (seven host species) from 14 provinces in China were collected in the present study. DNA sequence data from a mitochondrial gene (COI) and a nuclear ribosomal gene (28S D2 region) were used to reconstruct the phylogenies of Anicetus species and their hosts. The distance-based analysis showed a significant fit between Anicetus species and their hosts, but tree-based analyses suggested that this significant signal could be observed only when the cost of host-switching was high, indicating the presence of parasite sorting on related host species.

CONCLUSIONS

This study, based on extensive rearing of parasitoids and species identification, provides strong evidence for a prevalence of sorting events and high host specificity in the genus Anicetus, offering insights into the diversification process of Anicetus species parasitizing scale insects.

Spatial variation in the phylogenetic structure of flea assemblages across geographic ranges of small mammalian hosts in the Palearctic

We investigated spatial variation in the phylogenetic structure (measured as a degree of phylogenetic clustering) of flea assemblages across the geographic ranges of 11 Palearctic species of small mammalian hosts and asked whether the phylogenetic structure of the flea assemblage of a host in a locality is affected by (i) distance of this locality from the centre of the host's geographic range, (ii) geographic position of the locality (distance to the equator) and (iii) phylogenetic structure of the entire flea assemblage of the locality. Our results demonstrated that the key factor underlying spatial variation of the phylogenetic structure of the flea assemblage of a host was the distance from the centre of the host's geographic range. However, the pattern of this spatial variation differed between host species and might be explained by their species-specific immunogenetic and/or distributional patterns. Local flea assemblages may also, to some extent, be shaped by environmental filtering coupled with historical events. In addition, the phylogenetic structure of a local within-host flea assemblage may mirror the phylogenetic structure of the entire across-host flea assemblage in that locality and, thus, be affected by the availability of certain phylogenetic lineages.

PACo: a novel procrustes application to cophylogenetic analysis

We present Procrustean Approach to Cophylogeny (PACo), a novel statistical tool to test for congruence between phylogenetic trees, or between phylogenetic distance matrices of associated taxa. Unlike previous tests, PACo evaluates the dependence of one phylogeny upon the other. This makes it especially appropriate to test the classical coevolutionary model that assumes that parasites that spend part of their life in or on their hosts track the phylogeny of their hosts. The new method does not require fully resolved phylogenies and allows for multiple host-parasite associations. PACo produces a Procrustes superimposition plot enabling a graphical assessment of the fit of the parasite phylogeny onto the host phylogeny and a goodness-of-fit statistic, whose significance is established by randomization of the host-parasite association data. The contribution of each individual host-parasite association to the global fit is measured by means of jackknife estimation of their respective squared residuals and confidence intervals associated to each host-parasite link. We carried out different simulations to evaluate the performance of PACo in terms of Type I and Type II errors with respect to two similar published tests. In most instances, PACo performed at least as well as the other tests and showed higher overall statistical power. In addition, the jackknife estimation of squared residuals enabled more elaborate validations about the nature of individual links than the ParaFitLink1 test of the program ParaFit. In order to demonstrate how it can be used in real biological situations, we applied PACo to two published studies using a script written in the public-domain statistical software R.

A simple model explains the dynamics of preferential host switching among mammal RNA viruses

A growing number of studies support a tendency toward preferential host switching, by parasites and pathogens, over relatively short phylogenetic distances. This suggests that a host switch is more probable if a potential host is closely related to the original host than if it is a more distant relative. However, despite its importance for the health of humans, livestock, and wildlife, the detailed dynamics of preferential host switching have, so far, been little studied. We present an empirical test of two theoretical models of preferential host switching, using observed phylogenetic distributions of host species for RNA viruses of three mammal orders (primates, carnivores, and ungulates). The analysis focuses on multihost RNA virus species, because their presence on multiple hosts and their estimated ages of origin indicate recent host switching. Approximate Bayesian computation was used to compare observed phylogenetic distances between hosts with those simulated under the theoretical models. The results support a decreasing sigmoidal model of preferential host switching, with a strong effect from increasing phylogenetic distance, on all three studied host phylogenies. This suggests that the dynamics of host switching are fundamentally similar for RNA viruses of different mammal orders and, potentially, a wider range of coevolutionary systems.

Migratory behavior of birds affects their coevolutionary relationship with blood parasites

Host traits, such as migratory behavior, could facilitate the dispersal of disease-causing parasites, potentially leading to the transfer of infections both across geographic areas and between host species. There is, however, little quantitative information on whether variation in such host attributes does indeed affect the evolutionary outcome of host-parasite associations. Here, we employ Leucocytozoon blood parasites of birds, a group of parasites closely related to avian malaria, to study host-parasite coevolution in relation to host behavior using a phylogenetic comparative approach. We reconstruct the molecular phylogenies of both the hosts and parasites and use cophylogenetic tools to assess whether each host-parasite association contributes significantly to the overall congruence between the two phylogenies. We find evidence for a significant fit between host and parasite phylogenies in this system, but show that this is due only to associations between nonmigrant parasites and their hosts. We also show that migrant bird species harbor a greater genetic diversity of parasites compared with nonmigrant species. Taken together, these results suggest that the migratory habits of birds could influence their coevolutionary relationship with their parasites, and that consideration of host traits is important in predicting the outcome of coevolutionary interactions.

A phylogenetic assessment of the colonisation patterns in Spauligodon atlanticus Astasio-Arbiza et al., 1987 (Nematoda: Oxyurida: Pharyngodonidae), a parasite of lizards of the genus Gallotia Boulenger: no simple answers

Parasite taxonomy traditionally relies on morphometric and life-cycle characteristics which may not reflect complex phylogenetic relationships. However, genetic analyses can reveal cryptic species within morphologically described parasite taxa. We analysed the phylogenetic variation within the nematode Spauligodon atlanticus Astasio-Arbiza, Zapatero-Ramos, Ojeda-Rosas & Solera-Puertas, 1987, a parasite of the Canarian lizard genus Gallotia Boulenger, inferring the origin of their current association. We also attempted to determine its relationship with other Spauligodon spp. Three different markers, mitochondrial COI plus nuclear 18S and 28S ribosomal RNA, were used to estimate the evolutionary relationships between these nematodes. S. atlanticus was found to be paraphyletic, suggesting that Gallotia spp. were colonised by two independent lineages of Spauligodon. Additional analyses of other Spauligodon spp. are required for a more complete interpretation of the evolution of this genus from the Canarian archipelago and its closest taxa. Our results emphasise the importance of extensive sampling and phylogenetic studies at the intrageneric level, and highlight the limitations of a morphologically based taxonomy in these parasites.

Comparative phylogenetic histories of two louse genera found on Catharus thrushes and other birds

The louse genera Brueelia (Ischnocera) and Myrsidea (Amblycera) are broadly codistributed on songbirds (Passeriformes), but differ in a variety of life history characteristics. We used mitochondrial and nuclear DNA sequences to assess levels of genetic divergence and reconstruct phylogenies of these 2 genera, focusing especially on Catharus thrushes in North America. We then qualitatively compared the phylogenies and levels of divergence within these 2 genera of codistributed parasites. Neither Brueelia nor Myrsidea appears to cospeciate with Catharus thrushes or passerine birds in general. The Myrsidea phylogeny exhibits significant levels of biogeographic structure, whereas the Brueelia phylogeny does not. Myrsidea and Brueelia also differ in their levels of intra-generic genetic divergence, with Myrsidea showing higher levels of genetic divergence and host specificity than Brueelia. Our genetic data support traditional morphology-based taxonomy in several instances in which the same species of Brueelia has been reported on multiple host taxa, e.g., all migrant Catharus spp. carry B. antiqua, with little haplotype divergence. Myrsidea found on each Catharus sp. are in general genetically distinct, except for M. incerta, which parasitizes both Catharus ustulatus and Catharus minimus. The strong biogeographic signal in the Myrsidea phylogeny and higher relative levels of host specificity of Myrsidea spp. suggest that infrequent host-switching, followed by speciation, is shaping the evolutionary history of this group. In contrast, the relatively lower host specificity of Brueelia spp. suggests that host-switching, combined with more frequent ongoing dispersal, has been more important in the evolutionary history of Brueelia.

Host specialization differentiates cryptic species of feather-feeding lice

Parasite species with differentiated host-specific populations provide a natural opportunity to explore factors involved in parasite diversification. Columbicola macrourae is a species of ectoparasitic feather louse currently recognized from 15 species of New World pigeons and doves. Mitochondrial sequences reveal five divergent haplotype clusters within C. macrourae, suggesting cryptic species. Each cluster is relatively host specific, with only one or a few hosts. We conducted a reciprocal transfer experiment with two of these lineages to test whether host use has an adaptive component. Our results demonstrate that the fitness of each lineage is considerably higher on its native host than on the novel host suggesting that one or more selective agents favor host specialization by the different lineages. In addition, we were able to morphologically separate individual lice from the two experimental lineages using discriminant function analysis. Furthermore, differences in the size of these louse lineages match differences in the size of their respective hosts, paralleling the strong correlation between parasite and host body size across the genus Columbicola. Together, these results suggest that selection in this cryptic species complex reflects selection across the whole genus, and that this selection, in part, contributes to the maintenance of host specialization.

Molecular markers reveal strong geographic, but not host associated, genetic differentiation in Aphidius transcaspicus, a parasitoid of the aphid genus Hyalopterus

Host plant associated genetic differentiation is a common phenomenon in phytophagous insects, but the degree to which such associations sequentially drive diversification at higher trophic levels is not as well understood. A recent study examining neutral molecular markers in Hyalopterus aphids revealed that genetic structure in this genus is strongly determined by primary host plant use (Prunus spp.). In this paper, we take a similar approach to determine whether this host plant specificity has affected genetic structure in the parasitoid Aphidius transcaspicus, an important natural enemy of Hyalopterus spp. in the Mediterranean. Mitochondrial DNA (428 bp) and seven microsatellite loci were examined in parasitoids collected from aphid populations on almond, apricot, peach and plum trees from Spain and Greece. In contrast to the previous findings for Hyalopterus from the same regions, here we find no evidence for host associated diversification in A. transcaspicus at the species level or below, though geographic structure between regional populations is exceptionally high. These findings have several implications for our understanding of the ecology and evolution of A. transcaspicus as well as for its use as a biological control agent for Hyalopterus, suggesting that a consideration of host plant specificity may be less critical than factors such as climatic suitability or geographic origins of invasive populations.

Host specificity and genealogy of the louse Polyplax serrata on field mice, Apodemus species: a case of parasite duplication or colonisation?

The genealogy, population structure and population dynamics of the sucking louse Polyplax serrata were analysed across four host species of the genus Apodemus. An analysis of 126 sequences of cytochrome c oxidase subunit I using phylogenetic approaches and haplotype networking revealed a clear structure of European samples, forming three distinct and genetically distant clades with different host specificities. Although a clear connection was detected between the host and parasite genealogies/phylogenies, a uniform pattern of co-speciation was not found. For example, a dramatic shift in the degree of host specificity was demonstrated for two related louse lineages living in sympatry and sharing one of their host species. While one of the louse lineages frequently parasitised two different host taxa (Apodemus sylvaticus and Apodemus flavicollis), the other louse lineage was strictly specific to A. flavicollis. The estimate of divergence time between the two louse lineages indicates that they may have arisen due to parasite duplication on A. flavicollis.

Comparative phylogeography of Trypanosoma rangeli and Rhodnius (Hemiptera: Reduviidae) supports a long coexistence of parasite lineages and their sympatric vectors

To make reliable interpretations about evolutionary relationships between Trypanosoma rangeli lineages and their insect vectors (triatomine bugs of the genus Rhodnius) and, thus, about the determinant factors of lineage segregation within T. rangeli, we compared phylogenies of parasite isolates and vector species. Sixty-one T. rangeli isolates from invertebrate and vertebrate hosts were initially evaluated in terms of polymorphism of the spliced-leader gene (SL). Further analysis based on SL and SSUrRNA sequences from 33 selected isolates, representative of the overall phylogenetic diversity and geographical range of T. rangeli, supported four phylogenetic lineages within this species. By comparing the phylogeny of Rhodnius species with that inferred for T. rangeli isolates and through analysis of the geographical range of the isolates, we showed that there is a very significant overlap in the distribution of Rhodnius species and T. rangeli lineages. Congruence between phylogeographical analysis of both T. rangeli lineages and complexes of Rhodnius species are consistent with the hypothesis of a long coexistence of parasites and their vectors, with lineage divergence associated with sympatric species of Rhodnius apparently without association with particular vertebrate hosts. Separation of T. rangeli isolates from vectors of distinct complexes living in sympatry favours the absence of gene flow between the lineages and suggests evolution of T. rangeli lineages in independent transmission cycles, probably associated to specific Rhodnius spp. ecotopes. A polymerase chain reaction assay based on SL intergenic sequences was developed for simultaneous identification and lineage genotyping of T. rangeli in epidemiological surveys.

Cophylogenetic relationships between penguins and their chewing lice

It is generally thought that the evolution of obligate parasites should be linked intimately to the evolution of their hosts and that speciation by the hosts should cause speciation of their parasites. The penguins and their chewing lice present a rare opportunity to examine codivergence between a complete host order and its parasitic lice. We estimated a phylogeny for all 15 species of lice parasitising all 17 species of penguins from the third domain of the mitochondrial 12S ribosomal rRNA gene, a portion of the mitochondrial cytochrome oxidase subunit 1 gene and 55 morphological characters. We found no evidence of extensive cospeciation between penguins and their chewing lice using TreeMap 2.02beta. Despite the paucity of cospeciation, there is support for significant congruence between the louse and penguin phylogenies due to possible failure to speciate events (parasites not speciating in response to their hosts speciating).

Traversing the tangle: algorithms and applications for cophylogenetic studies

Cophylogenetic analysis supposes that two or more phylogenetic trees for linked groups have been constructed, and explores the relationships the trees have with each other. These types of analyses are most commonly used to assess relationships between hosts and their parasites, however the methodology can also be applied to diverse types of problems such as an examination of the phylogenies of genes with respect to those of organisms or those of geographic areas and the organisms that reside there. The working hypothesis is that the trees are correct, though sometimes attempts are made to take into account their uncertainty. Cophylogeny is computationally hard: that is, there are no known fast methods to compute relationships among such trees for any but the simplest of models. A review of methodology that has been developed to examine cophylogenetic relationships is presented and a brief discussion of some medically relevant examples is given.