Host-parasite Cospeciation Research Articles

Historical dispersal and host-switching formed the evolutionary history of a globally distributed multi-host parasite – The Ligula intestinalis species complex

Studies on parasite biogeography and host spectrum provide insights into the processes driving parasite diversification. Global geographical distribution and a multi-host spectrum make the tapeworm Ligula intestinalis a promising model for studying both the vicariant and ecological modes of speciation in parasites. To understand the relative importance of host association and biogeography in the evolutionary history of this tapeworm, we analysed mtDNA and reduced-represented genomic SNP data for a total of 139 specimens collected from 18 fish-host genera across a distribution range representing 21 countries. Our results strongly supported the existence of at least 10 evolutionary lineages and estimated the deepest divergence at approximately 4.99–5.05 Mya, which is much younger than the diversification of the fish host genera and orders. Historical biogeography analyses revealed that the ancestor of the parasite diversified following multiple vicariance events and was widespread throughout the Palearctic, Afrotropical, and Nearctic between the late Miocene and early Pliocene. Cyprinoids were inferred as the ancestral hosts for the parasite. Later, from the late Pliocene to Pleistocene, new lineages emerged following a series of biogeographic dispersal and host-switching events. Although only a few of the current Ligula lineages show narrow host-specificity (to a single host genus), almost no host genera, even those that live in sympatry, overlapped between different Ligula lineages. Our analyses uncovered the impact of historical distribution shifts on host switching and the evolution of host specificity without parallel host-parasite co-speciation. Historical biogeography reconstructions also found that the parasite colonized several areas (Afrotropical and Australasian) much earlier than was suggested by only recent faunistic data.

Monogeneans and chubs: Ancient host-parasite system under the looking glass

Host-parasite coevolution is one of the fundamentals of evolutionary biology. Due to the intertwined evolutionary history of two interacting species and reciprocal coadaptation processes of hosts and parasites, we can expect that studying parasites will shed more light onto the evolutionary processes of their hosts. Monogenea (ectoparasitic Platyhelminthes) and their cyprinoid fish hosts represent one of the best models for studying host-parasite evolutionary relationships using a cophylogenetic approach. These parasites have developed remarkably high host specificity, where each host species often serves as a potential host for its own host-specific monogenean species. Here, the cophylogenetic relationships in the Dactylogyrus-Squalius system was investigated, as Squalius is one of several cyprinoid genera with puzzling phylogeography and inhabits all four major peri-Mediterranean peninsulas. Of 29 endemic Squalius species examined for the presence of Dactylogyrus parasites, a total of 13 Dactylogyrus species were collected from the gills of 20 Squalius species across a wide range of distribution. Phylogenetic reconstruction revealed a polyphyletic origin for Dactylogyrus species parasitizing congeneric Squalius, with four major clades being recognized. On the basis of the delimitation of host specificity, strict specialists parasitizing single host species, geographic specialists parasitizing congeners in a limited geographical region, and true generalists parasitizing congeners in various geographical regions were recognized in Dactylogyrus species parasitizing Squalius. The phylogenetic reconstruction of Squalius hosts revealed two major clades, the first encompassing only peri-Mediterranean species and the second including species from other Euro-Asian regions. Distance-based cophylogenetic methods did not reveal a statistically significant global cophylogenetic structure in the studied system; however, several host-parasite links among Iberian endemic species contributed significantly to the overall structure. The widest host range and associated genetic variability were recorded for D. folkmanovae, parasitizing nine Squalius species, and D. vistulae, parasitizing 13 Squalius species. Two different dispersion mechanisms and morphological adaptations to Squalius hosts were clearly reflected in the contrasting cophylogenetic patterns for these two species with different levels of host specificity. While host-parasite cospeciation plays an important role in diversification within D. folkmanovae, diversification within D. vistulae is driven mainly by host switching.

A novel Ceratomyxa species (Myxozoa: Cnidaria) infecting an Amazonian catfish.

Parasites are important organisms for the health of ecosystems. While the Amazon Basin is home to a great diversity of ichthyofauna, our knowledge of myxozoan diversity in the biome remains relatively limited. The present study describes a new myxozoan species, Ceratomyxa mandii n. sp., parasitizing the gallbladder of the Amazonian catfish Pimelodina flavipinnis (Pimelodidae) from the Solimões River, in the region of Manaus, Brazil. Light and electron microscopy, small subunit ribosomal DNA (SSU rDNA) sequencing and phylogenetic analysis were performed. The new species exhibited worm-like plasmodia with undulatory motility. The SSU rDNA based phylogenetic analysis revealed it to be a sister taxon of C. gracillima, which also parasitizes an Amazonian pimelodid fish, possibly reflecting a host-parasite co-speciation process. This study contributes to our understanding of this little sampled group of organisms.

The Piroplasmida Babesia, Cytauxzoon, and Theileria in farm and companion animals: species compilation, molecular phylogeny, and evolutionary insights.

The order Piroplasmida, including the genera Babesia, Cytauxzoon, and Theileria is often referred to as piroplasmids and comprises of dixenous hemoprotozoans transmitted by ticks to a mammalian or avian host. Although piroplasmid infections are usually asymptomatic in wild animals, in domestic animals, they cause serious or life-threatening consequences resulting in fatalities. Piroplasmids are particularly notorious for the enormous economic loss they cause worldwide in livestock production, the restrictions they pose on horse trade, and the negative health impact they have on dogs and cats. Furthermore, an increasing number of reported human babesiosis cases are of growing concern. Considerable international research and epidemiological studies are done to identify existing parasite species, reveal their phylogenetic relationships, and develop improved or new drugs and vaccines to mitigate their impact. In this review, we present a compilation of all piroplasmid species, isolates, and species complexes that infect domestic mammals and which have been well defined by molecular phylogenetic markers. Altogether, 57 taxonomic piroplasmid entities were compiled, comprising of 43 piroplasmid species, 12 well-defined isolates awaiting formal species description, and two species complexes that possibly mask additional species. The extrapolation of the finding of at least 57 piroplasmid species in only six domestic mammalian groups (cattle, sheep, goat, horse, dog, and cat) allows us to predict that a substantially higher number of piroplasmid parasites than vertebrate host species exist. Accordingly, the infection of a vertebrate host species by multiple piroplasmid species from the same and/or different phylogenetic lineages is commonly observed. Molecular phylogeny using 18S rRNA genes of piroplasmids infecting domestic mammals results in the formation of six clades, which emerge due to an anthropocentric research scope, but not due to a possibly assumed biological priority position. Scrutinizing the topology of inferred trees reveals stunning insights into some evolutionary patterns exhibited by this intriguing group of parasites. Contrary to expectations, diversification of parasite species appears to be dominated by host-parasite cospeciation (Fahrenholz's rule), and, except for piroplasmids that segregate into Clade VI, host switching is rarely observed. When only domestic mammalian hosts are taken into account, Babesia sensu lato (s.l.) parasites of Clades I and II infect only dogs and cats, respectively, Cytauxzoon spp. placed into Clade III only infect cats, Theileria placed into Clade IV exclusively infect horses, wheras Theileria sensu stricto (s.s.) of Clade V infects only cattle and small ruminants. In contrast, Babesia s.s. parasites of Clade VI infect all farm and companion animal species. We outline how the unique ability of transovarial transmission of Babesia s.s. piroplasmids of Clade VI facilitates species diversification by host switching to other host vertebrate species. Finally, a deterioration of sequence fidelity in databases is observed which will likely lead to an increased risk of artifactual research in this area. Possible measures to reverse and/or avoid this threat are discussed.

Do host habitat use and cospeciation matter in the evolution of Oswaldocruzia (Nematoda, Molineidae) from neotropical amphibians?

The genus Oswaldocruzia Travassos, 1917 includes approximately 90 species that are parasitic on amphibians and reptiles around the world, of which 43 occur in the neotropical region. However, molecular data supporting the taxonomic status of most species of the genus are scarce, and their phylogenetic relationships remain unknown. Using specimens of four molineid taxa (Oswaldocruzia belenensis Santos, Giese, Maldonado Jr. and Lanfredi, 2008; Oswaldocruzia chabaudi Ben Slimane & Durette-Desset, 1996, Oswaldocruzia chambrieri Ben Slimane & Durette-Desset, 1996 and Kentropyxia hylae Feitosa, Furtado, Santos and Melo, 2015) from amphibian hosts collected in different regions of Pará, Brazil, we conducted morphological studies, molecular analyses and phylogenies (maximum likelihood and Bayesian inference) using the cytochrome c oxidase subunity I (Cox1) gene. The newly generated sequences were compared with those of ten publicly available Cox1 sequences of Oswaldocruzia from Mexico. Our findings demonstrated significant differences between the sequences of amazonian specimens and sequences from specimens collected in Mexico, and we suggest that host-parasite cospeciation or habitat use might be related to molineid evolution in amphibian hosts. Additionally, this work presents new hosts and new geographical records for species of Oswaldocruzia from the neotropics.

Generalist Eimeria species in rodents: Multilocus analyses indicate inadequate resolution of established markers.

Intracellular parasites of the genus Eimeria are described as tissue/host‐specific. Phylogenetic classification of rodent Eimeria suggested that some species have a broader host range than previously assumed. We explore whether Eimeria spp. infecting house mice are misclassified by the most widely used molecular markers due to a lack of resolution, or whether, instead, these parasite species are indeed infecting multiple host species.With the commonly used markers (18S/COI), we recovered monophyletic clades of E. falciformis and E. vermiformis from Mus that included E. apionodes identified in other rodent host species (Apodemus spp., Myodes glareolus, and Microtus arvalis). A lack of internal resolution in these clades could suggest the existence of a species complex with a wide host range infecting murid and cricetid rodents. We question, however, the power of COI and 18S markers to provide adequate resolution for assessing host specificity. In addition to the rarely used marker ORF470 from the apicoplast genome, we present multilocus genotyping as an alternative approach. Phylogenetic analysis of 35 nuclear markers differentiated E. falciformis from house mice from isolates from Apodemus hosts. Isolates of E. vermiformis from Mus are still found in clusters interspersed with non‐Mus isolates, even with this high‐resolution data.In conclusion, we show that species‐level resolution should not be assumed for COI and 18S markers in coccidia. Host–parasite cospeciation at shallow phylogenetic nodes, as well as contemporary coccidian host ranges more generally, is still open questions that need to be addressed using novel genetic markers with higher resolution.

Shift or stick? Untangling the signatures of biased host switching, and host-parasite co-speciation

A recommendation of: Jan Engelstaedter & Nicole Fortuna The dynamics of preferential host switching: host phylogeny as a key predictor of parasite prevalence and distribution https://doi.org/10.1101/209254

Phoretic dispersal influences parasite population genetic structure.

Dispersal is a fundamental component of the life history of most species. Dispersal influences fitness, population dynamics, gene flow, genetic drift and population genetic structure. Even small differences in dispersal can alter ecological interactions and trigger an evolutionary cascade. Linking such ecological processes with evolutionary patterns is difficult, but can be carried out in the proper comparative context. Here, we investigate how differences in phoretic dispersal influence the population genetic structure of two different parasites of the same host species. We focus on two species of host-specific feather lice (Phthiraptera: Ischnocera) that co-occur on feral rock pigeons (Columba livia). Although these lice are ecologically very similar, "wing lice" (Columbicola columbae) disperse phoretically by "hitchhiking" on pigeon flies (Diptera: Hippoboscidae), while "body lice" (Campanulotes compar) do not. Differences in the phoretic dispersal of these species are thought to underlie observed differences in host specificity, as well as the degree of host-parasite cospeciation. These ecological and macroevolutionary patterns suggest that body lice should exhibit more genetic differentiation than wing lice. We tested this prediction among lice on individual birds and among lice on birds from three pigeon flocks. We found higher levels of genetic differentiation in body lice compared to wing lice at two spatial scales. Our results indicate that differences in phoretic dispersal can explain microevolutionary differences in population genetic structure and are consistent with macroevolutionary differences in the degree of host-parasite cospeciation.

Molecular evidence for host–parasite co-speciation between lizards and Schellackia parasites

Current and past parasite transmission may depend on the overlap of host distributions, potentially affecting parasite specificity and co-evolutionary processes. Nonetheless, parasite diversification may take place in sympatry when parasites are transmitted by vectors with low mobility. Here, we test the co-speciation hypothesis between lizard final hosts of the Family Lacertidae, and blood parasites of the genus Schellackia, which are potentially transmitted by haematophagous mites. The effects of current distributional overlap of host species on parasite specificity are also investigated. We sampled 27 localities on the Iberian Peninsula and three in northern Africa, and collected blood samples from 981 individual lizards of seven genera and 18 species. The overall prevalence of infection by parasites of the genus Schellackia was ∼35%. We detected 16 Schellackia haplotypes of the 18S rRNA gene, revealing that the genus Schellackia is more diverse than previously thought. Phylogenetic analyses showed that Schellackia haplotypes grouped into two main monophyletic clades, the first including those detected in host species endemic to the Mediterranean region and the second those detected in host genera Acanthodactylus, Zootoca and Takydromus. All but one of the Schellackia haplotypes exhibited a high degree of host specificity at the generic level and 78.5% of them exclusively infected single host species. Some host species within the genera Podarcis (six species) and Iberolacerta (two species) were infected by three non-specific haplotypes of Schellackia, suggesting that host switching might have positively influenced past diversification of the genus. However, the results supported the idea that current host switching is rare because there existed a significant positive correlation between the number of exclusive parasite haplotypes and the number of host species with current sympatric distribution. This result, together with significant support for host–parasite molecular co-speciation, suggests that parasites of the genus Schellackia co-evolved with their lizard hosts.

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.

A statistical method for analysing cospeciation in tritrophic ecology using electrical circuit theory.

We introduce a new method to test efficiently for cospeciation in tritrophic systems. Our method utilises an analogy with electrical circuit theory to reduce higher order systems into bitrophic data sets that retain the information of the original system. We use a sophisticated permutation scheme that weights interactions between two trophic layers based on their connection to the third layer in the system. Our method has several advantages compared to the method of Mramba et al. [Mramba, L. K., S. Barber, K. Hommola, L. A. Dyer, J. S. Wilson, M. L. Forister and W. R. Gilks (2013): "Permutation tests for analyzing cospeciation in multiple phylogenies: applications in tri-trophic ecology," Stat. Appl. Genet. Mol. Biol., 12, 679-701.]. We do not require triangular interactions to connect the three phylogenetic trees and an easily interpreted p-value is obtained in one step. Another advantage of our method is the scope for generalisation to higher order systems and phylogenetic networks. The performance of our method is compared to the methods of Hommola et al. [Hommola, K., J. E. Smith, Y. Qiu and W. R. Gilks (2009): "A permutation test of host-parasite cospeciation," Mol. Biol. Evol., 26, 1457-1468.] and Mramba et al. [Mramba, L. K., S. Barber, K. Hommola, L. A. Dyer, J. S. Wilson, M. L. Forister and W. R. Gilks (2013): "Permutation tests for analyzing cospeciation in multiple phylogenies: applications in tri-trophic ecology," Stat. Appl. Genet. Mol. Biol., 12, 679-701.] at the bitrophic and tritrophic level, respectively. This was achieved by evaluating type I error and statistical power. The results show that our method produces unbiased p-values and has comparable power overall at both trophic levels. Our method was successfully applied to a dataset of leaf-mining moths, parasitoid wasps and host plants [Lopez-Vaamonde, C., H. Godfray, S. West, C. Hansson and J. Cook (2005): "The evolution of host use and unusual reproductive strategies in achrysocharoides parasitoid wasps," J. Evol. Biol., 18, 1029-1041.], at both the bitrophic and tritrophic levels.

Host responses to cycles of climate change shape parasite diversity across North America's Intermountain West

Host-parasite cospeciation, in which parasite divergence occurs in response to host divergence, is commonly proposed as a driver of parasite diversification, yet few empirical examples of strict cospeciation exist. Host-parasite co-evolutionary histories commonly reflect complex mosaics of cospeciation, dispersal, lineage extinction and other phenomena. The episodic host-switching model of parasite diversification accounts for complexity by suggesting that diversification and faunal assembly is a consequence of fluctuation between environmental disruption and environmental stability. The phylogeographic predictions of the strict cospeciation and episodic host-switching models were tested using the North American pika/parasite assemblage, with a primary focus on the American pika, Ochotona princeps (Richardson, 1828), and a suite of its endoparasitic cestodes and nematodes. This approach integrating phylogeographic and demographic methods with inferences drawn from species distribution modelling revealed that the parasite community of pikas has been shaped by climate-driven range fluctuation of hosts and bouts of geographic and host colonization by parasites associated with transitions between glacial and interglacial phases.

Introduction of Steven A. Nadler, Recipient of the Henry Baldwin Ward Medal for 2013

Introduction of Steven A. Nadler, Recipient of the Henry Baldwin Ward Medal for 2013

Polynomial-Time Algorithms for Building a Consensus MUL-Tree

A multi-labeled phylogenetic tree, or MUL-tree, is a generalization of a phylogenetic tree that allows each leaf label to be used many times. MUL-trees have applications in biogeography, the study of host-parasite cospeciation, gene evolution studies, and computer science. Here, we consider the problem of inferring a consensus MUL-tree that summarizes a given set of conflicting MUL-trees, and present the first polynomial-time algorithms for solving it. In particular, we give a straightforward, fast algorithm for building a strict consensus MUL-tree for any input set of MUL-trees with identical leaf label multisets, as well as a polynomial-time algorithm for building a majority rule consensus MUL-tree for the special case where every leaf label occurs at most twice. We also show that, although it is NP-hard to find a majority rule consensus MUL-tree in general, the variant that we call the singular majority rule consensus MUL-tree can be constructed efficiently whenever it exists.

Phylogenetic host specificity and understanding parasite sharing in primates

Understanding how parasites are transmitted to new species is of great importance for human health, agriculture and conservation. However, it is still unclear why some parasites are shared by many species, while others have only one host. Using a new measure of 'phylogenetic host specificity', we find that most primate parasites with more than one host are phylogenetic generalists, infecting less closely related primates than expected. Evolutionary models suggest that phylogenetic host generalism is driven by a mixture of host-parasite cospeciation and lower rates of parasite extinction. We also show that phylogenetic relatedness is important in most analyses, but fails to fully explain patterns of parasite sharing among primates. Host ecology and geographical distribution emerged as key additional factors that influence contacts among hosts to facilitate sharing. Greater understanding of these factors is therefore crucial to improve our ability to predict future infectious disease risks.

Monogeneans of West African cichlid fish: evolution and cophylogenetic interactions.

The goals of this paper were to investigate phylogenetic and evolutionary patterns of cichlid fish from West Africa and their Cichlidogyrus and Scutogyrus monogenean parasites, to uncover the presence of host-parasite cospeciation and to assess the level of morphological adaptation in parasites. This required the following steps, each one representing specific objectives of this paper: (1) to build phylogenetic trees for Cichlidogyrus and Scutogyrus species based on ribosomal DNA sequences, (2) to investigate phylogenetic relationships within West African cichlid fish based on the analysis of mitochondrial cytochrome b DNA sequences, (3) to investigate host-parasite cophylogenetic history to gain clues on parasite speciation process, and (4) to investigate the link between the morphology of the attachment apparatus and parasite phylogeny. Phylogenetic analyses supported the monophyletic origin of the Cichlidogyrus/Scutogyrus group, and suggested that Cichlidogyrus is polyphyletic and that Scutogyrus is monophyletic. The phylogeny of Cichlidae supported the separation of mouthbrooders and substrate-brooders and is consistent with the hypothesis that the mouthbrooding behavior of Oreochromis and Sarotherodon evolved from substrate-brooding behavior. The mapping of morphological characters of the haptor onto the parasite phylogenetic tree suggests that the attachment organ has evolved from a very simple form to a more complex one. The cophylogenetic analyses indicated a significant fit between trees using distance-based tests, but no significant cospeciation signal using tree-based tests, suggesting the presence of parasite duplications and host switches on related host species. This shed some light on the diversification process of Cichlidogyrus species parasitizing West African cichlids.

Ultrastructural characterization and comparative phylogenetic analysis of new microsporidia from Siberian mosquitoes: Evidence for coevolution and host switching

A survey of mosquito larvae infected with microsporidia was conducted from 2005 to 2008 in the Tomsk, Kemerovo and Novosibirsk regions of western Siberia, Russia. Twenty-one morphologically and genetically unique species of microsporidia were isolated from nine species of Anopheles, Aedes, Culex and Ochlerotatus mosquitoes including: (1) 14 proposed new species of Amblyospora (A. bakcharia, A. baritia, A. bogashovia, A. chulymia, A. hristinia, A. jurginia, A. kazankia, A. mavlukevia, A. mocrushinia, A. modestium, A. salairia, A. severinia, A. shegaria, and A. timirasia); (2) a newly proposed genus and species, Novothelohaniaovalae and; (3) six species of Amblyospora (A. flavescens, A. kolarovi, A. rugosa), Parathelohania (P. divulgata and P. tomski) and Trichoctosporea (T. pygopellita) from which gene sequences had not been previously obtained. Detailed ultrastructure of meiospores revealed unique cytological features associated with the length, arrangement and ratio of broad to narrow coils of the polar filament, comparative thickness of the exospore and endospore, and overall size of each species reaffirming their value in distinguishing taxonomic relationships. SSU rDNA sequences obtained from each species of microsporidia were unique when compared with GenBank entries. Phylogenetic trees constructed by Maximum Parsimony, Maximum Likelihood and Neighbor Joining analyses yielded similar topologies with a high degree of congruence between parasite and host at the generic level. Species that parasitize Aedes/Ochlerotatus and Culex mosquitoes segregate into distinct monophyletic groupings mirroring their host phylogeny, while species from Anopheles mosquitoes group as a sister clade basal to the entire group of mosquito-parasitic microsporidia as their Anopheles hosts cluster as a sister clade to the entire group of culicine mosquitoes. This provides strong evidence for host-parasite coevolution by descent at the generic level and limited host lineage switching between unrelated taxa. Among parasites of Aedes/Ochlerotatus and Anopheles mosquitoes, we found several instances where a single mosquito species serves as a host for two or more related species of microsporidia, an observation consistent with host switching and independent parasite speciation. Among the microsporidian parasites of Culex mosquitoes, we found only one parasite per host indicating a higher degree of host specificity and less host switching among parasites of this genus. Findings suggest a degree of host-parasite co-speciation with host switching occurring occasionally when the “normal” host is unavailable in the aquatic ecosystem. Frequency of host switching seems to be occurring in proportion to host relatedness and does not cross generic boundaries in this system.

A Permutation Test of Host-Parasite Cospeciation

We introduce a statistical method that explores host-parasite coevolution by testing the null hypothesis that hosts and their associated parasites evolved independently. This test is simple and intuitive and involves only suitable randomization of the observed data. It is not even necessary to construct host and parasite phylogenetic trees, as the test can be performed directly on distance matrices. Statistical power of the test was evaluated using simulated data consistent with the alternative hypothesis of cospeciation. Results were compared with the method of Mantel (1967) and the ParaFit method of Legendre et al. (2002). We observed that our method has greater power overall and thus a higher ability to detect cospeciation in closely related host-parasite systems. Our test was also successful when applied to the pocket gopher and chewing lice system.

Treemap Versus BPA (Again): A Response to Dowling

AbstractTreeMap is a computer program for analysing host-parasite cospeciation. We respond to Dowling’s (Cladistics, 18: 416-435) recent comparison of TreeMap and Brooks Parsimony Analysis (BPA) by showing that Dowling’s comparison suffers from several mistakes and flaws. We discuss the problems with both BPA and TreeMap, and show that BPA incorrectly counts the true number coevolutionary events more often than TreeMap 1. We also discuss the two main limitations of TreeMap 1 correctly identified by Dowling, namely its inability to handle widespread parasites, and its coarse optimality criterion (the number of cospeciation events). We suggest a simple fix for widespread parasites. The newly released TreeMap 2 uses a more sensitive optimality criterion than TreeMap 1, addressing Dowling’s second concern.

Molecular phylogeny supports a Northern Hemisphere origin of Golovinomyces ( Ascomycota: Erysiphales)

Golovinomyces is a strictly herb-parasitic genus in the Erysiphaceae. Host–parasite co-speciation was reported recently between the genus Golovinomyces and Asteraceae from molecular phylogenetic analyses. The Asteraceae originated in South America and latterly expanded their geographic distribution into the Northern Hemisphere. If the co-speciation between Golovinomyces and Asteraceae originated in South America, the geographic origin of Golovinomyces could be assumed to be South America. To address this question, Golovinomyces species from hosts of the tribe Mutisieae, an asteraceous tribe endemic to South America, were collected and the ITS and 28S rDNA regions sequenced. Results indicate that Oidium mutisiae and Golovinomyces leuceriae isolated from the Mutisieae do not belong at the base of the Golovinomyces tree. Instead, they are situated separately within two different clades of Golovinomyces isolates from the Northern Hemisphere. Therefore, the tribe Mutisieae is not the most early host of Golovinomyces. Present results suggest that Golovinomyces originated in the Northern Hemisphere, and not in South America. The new species Oidium reginae for the previous O. mutisiae on Mutisia decurrens is proposed.