Phenotypic plasticity in host choice behavior in black bean aphid, Aphis fabae (Homoptera: Aphididae)

The study of phenotypic plasticity in host choice behavior is crucial to predict evolutionary patterns of insect–plant interactions. The presence of sufficient variation in plasticity may facilitate host race formation and sympatric speciation. In this study, 13 Aphis fabae Scopoli genotypes reared both on broad bean and nasturtium exhibited statistically significant genotypic variability in host selection behavior. Some genotypes displayed increase in preference and acceptance in a novel host plant through generations. There are also strong conditioning effects of nasturtium as nasturtium reared genotypes are more willing to choose nasturtium over broad bean while broad bean reared genotypes do not show differences in choosing between the two host plants. There are also positive relationships between fitness and host choice behavior particularly for nasturtium. Results of the study supported the hypothesis that phenotypic plasticity in host choice behavior may be one of the major determinants of the evolutionary trajectory of a parasitic species, such as aphids.     

Differences in escape behavior between pea aphid biotypes reflect their host plants’ palatability to mammalian herbivores

Phytophagous insects have evolved traits that help them avoid predation risks, traits that may be affected by characteristics of the host plant. Since most phytophagous insects have narrow host ranges, we expect differences in risk avoidance between plant-specialized populations of several closely related insect lineages. To test this hypothesis, we used the pea aphid (Acyrthosiphon pisum), which forms a complex of about 15 biotypes, each adapted to one or a few species of legume plants (Fabaceae). We examined the differences in defensive behaviors of 38 clones from 13 distinct plant-specialized biotypes of pea aphids. We exposed mature aphids to simulated breath of a mammalian herbivore, a cue that causes part of the aphids in a colony to immediately drop off the plant to avoid incidental ingestion during mammal feeding. Dropping tendency varied substantially between biotypes (15–93% average rates). Dropping rates of a certain biotype of aphid reflected their host’s palatability to mammalian herbivores, with ∼80–90% rates in fodder and pasture plants and ∼15–40% dropping in inedible plants. The dropping tendency showed no correlation with walking ability (tarsal & body length), nor with the tendency to escape in response to the alarm pheromone released by conspecifics in response to arthropod enemies. The specialization on a specific host plant brings with it particular selective pressures, and it seems that the palatability of the plants to mammals promotes behavioral divergence between biotypes, reinforcing diversification through ecological divergence.     

Evolutionary history of aphid-plant associations and their role in aphid diversification

Aphids are intimately linked with their host plants that constitute their only food resource and habitat, and thus impose considerable selective pressure on their evolution. It is therefore commonly assumed that host plants have greatly influenced the diversification of aphids. Here, we review what is known about the role of host plant association on aphid speciation by examining both macroevolutionary and population-level studies. Phylogenetic studies conducted at different taxonomic levels show that, as in many phytophagous insect groups, the radiation of angiosperms has probably favoured the major Tertiary diversification of aphids. These studies also highlight many aphid lineages constrained to sets of related host plants, suggesting strong evolutionary commitment in aphids’ host plant choice, but they fail to document cospeciation events between aphid and host lineages. Instead, phylogenies of several aphid genera reveal that divergence events are often accompanied by host shifts, and suggest, without constituting a formal demonstration, that aphid speciation could be a consequence of adaptation to new hosts. Experimental and field studies below the species level support reproductive isolation between host races as partly due to divergent selection by their host plants. Selected traits are mainly feeding performances and life cycle adaptations to plant phenology. Combined with behavioural preference for favourable host species, these divergent adaptations can induce pre- and post-zygotic barriers between host-specialized aphid populations. However, the hypothesis of host-driven speciation is seldom tested formally and must be weighed against overlooked explanations involving geographic isolation and non-ecological reproductive barriers in the process of speciation.     

Evolutionary relationships between Fusarium oxysporum f. sp. lycopersici and F. oxysporum f. sp. radicis-lycopersici isolates inferred from mating type, elongation factor-1α and exopolygalacturonase sequences

Fusarium oxysporum is a ubiquitous species complex of soilborne plant pathogens that comprises many different formae speciales, each characterized by a high degree of host specificity. In this study, the evolutionary relationships between different isolates of the F. oxysporum species complex have been examined, with a special emphasis on the formae speciales lycopersici and radicis-lycopersici, sharing tomato as host while causing different symptoms. Phylogenetic analyses of partial sequences of a housekeeping gene, the elongation factor-1α (EF-1α) gene, and a gene encoding a pathogenicity trait, the exopolygalacturonase (pgx4) gene, were conducted on a worldwide collection of F. oxysporum strains representing the most frequently observed vegetative compatibility groups of these formae speciales. Based on the reconstructed phylogenies, multiple evolutionary lineages were found for both formae speciales. However, different tree topologies and statistical parameters were obtained for the cladograms as several strains switched from one cluster to another depending on the locus that was used to infer the phylogeny. In addition, mating type analysis showed a mixed distribution of the MAT1-1 and MAT1-2 alleles in the F. oxysporum species complex, irrespective of the geographic origin of the tested isolates. This observation, as well as the topological conflicts that were detected between EF-1α and pgx4, are discussed in relation to the evolutionary history of the F. oxysporum species complex.     

Restoration of an endangered plant,Hygrophila pogonocalyx,leads to an adaptive host shift of the chocolate pansy (Junonia iphita iphita)

Anthropogenic introduction of a plant species may cause novel encounters between the plant and local herbivores, and initiate evolutionary changes in host plant usage by herbivores. Until recently the endemic aquatic plant Hygrophila pogonocalyx was endangered and had a restricted distribution in Taiwan. Massive restoration efforts since 1997 have led to an expansion of the plant's distribution and a novel encounter between it and an Asian butterfly, the chocolate pansy, Junonia iphita (Nymphalidae). This butterfly appears to have colonized H. pogonocalyx, switching from its original host, Strobilanthes penstemonoides var. formosana. In the present study, we aimed to investigate whether the utilization of H. pogonocalyx as a host plant has initiated a differentiation between butterflies using the novel and the original hosts. To this purpose we collected butterflies from patches of the two host plants which grow sympatrically. We tested oviposition preference for the two hosts and larval performance on them. Female adults exhibited distinct oviposition preference toward the host plant their mothers preferred. Offspring showed greater survivorship and pupal weight when fed on the host plant their mothers preferred. Male adults displayed territorial behaviors on the host plant that their mothers had preferred. Finally, the survival rate of offspring produced from cross-mating between individuals with different host plant preference was lower than that of non-hybrids. Taken together, we suggest that genetic differentiation has occurred between individuals preferring H. pogonocalyx versus S. penstemonoides as host plants via host shifting. This process was likely induced by the mass restoration of the formerly rare and endangered plant species.     

Ancient host shifts followed by host conservatism in a group of ant parasitoids

While ant colonies serve as host to a diverse array of myrmecophiles, few parasitoids are able to exploit this vast resource. A notable exception is the wasp family Eucharitidae, which is the only family of insects known to exclusively parasitize ants. Worldwide, approximately 700 Eucharitidae species attack five subfamilies across the ant phylogeny. Our goal is to uncover the pattern of eucharitid diversification, including timing of key evolutionary events, biogeographic patterns and potential cophylogeny with ant hosts. We present the most comprehensive molecular phylogeny of Eucharitidae to date, including 44 of the 53 genera and fossil-calibrated estimates of divergence dates. Eucharitidae arose approximately 50 Ma after their hosts, during the time when the major ant lineages were already established and diversifying. We incorporate host association data to test for congruence between eucharitid and ant phylogenies and find that their evolutionary histories are more similar than expected at random. After a series of initial host shifts, clades within Eucharitidae maintained their host affinity. Even after multiple dispersal events to the New World and extensive speciation within biogeographic regions, eucharitids remain parasitic on the same ant subfamilies as their Old World relatives, suggesting host conservatism despite access to a diverse novel ant fauna.     

Multifaceted determinants of host specificity in an aphid parasitoid

The host specificity of insect parasitoids and herbivores is thought to be shaped by a suite of traits that mediate host acceptance and host suitability. We conducted laboratory experiments to identify mechanisms shaping the host specificity of the aphid parasitoid Binodoxys communis. Twenty species of aphids were exposed to B. communis females in microcosms, and detailed observations and rearing studies of 15 of these species were done to determine whether patterns of host use resulted from variation in factors such as host acceptance or variation in host suitability. Six species of aphids exposed to B. communis showed no signs of parasitism. Four of these species were not recognized as hosts and two effectively defended themselves from attack by B. communis. Other aphid species into which parasitoids laid eggs had low suitability as hosts. Parasitoid mortality occurred in the egg or early larval stages for some of these hosts but for others it occurred in late larval stages. Two hypotheses explaining low suitability were investigated in separate experiments: the presence of endosymbiotic bacteria conferring resistance to parasitoids, and aphids feeding on toxic plants. An association between resistance and endosymbiont infection was found in one species (Aphis craccivora), and evidence for the toxic plant hypothesis was found for the milkweed aphids Aphis asclepiadis and Aphis nerii. This research highlights the multifaceted nature of factors determining host specificity in parasitoids.     

Comparative genomic analysis of Ralstonia solanacearum reveals candidate genes for host specificity

Background

Ralstonia solanacearum is a vascular soil-borne plant pathogen with an unusually broad host range. This economically destructive and globally distributed bacterium has thousands of distinct lineages within a heterogeneous and taxonomically disputed species complex. Some lineages include highly host-adapted strains (ecotypes), such as the banana Moko disease-causing strains, the cold-tolerant potato brown rot strains (also known as R3bv2) and the recently emerged Not Pathogenic to Banana (NPB) strains.

Results

These distinct ecotypes offer a robust model to study host adaptation and the emergence of ecotypes because the polyphyletic Moko strains include lineages that are phylogenetically close to the monophyletic brown rot and NPB strains. Draft genomes of eight new strains belonging to these three model ecotypes were produced to complement the eleven publicly available R. solanacearum genomes. Using a suite of bioinformatics methods, we searched for genetic and evolutionary features that distinguish ecotypes and propose specific hypotheses concerning mechanisms of host adaptation in the R. solanacearum species complex. Genome-wide, few differences were identified, but gene loss events, non-synonymous polymorphisms, and horizontal gene transfer were identified among type III effectors and were associated with host range differences.

Conclusions

This extensive comparative genomics analysis uncovered relatively few divergent features among closely related strains with contrasting biological characteristics; however, several virulence factors were associated with the emergence of Moko, NPB and brown rot and could explain host adaptation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1474-8) contains supplementary material, which is available to authorized users.     

PHYLOGENY AND THE EVOLUTION OF HOST PLANT ASSOCIATIONS IN THE LEAF BEETLE GENUS OPHRAELLA (COLEOPTERA,CHRYSOMELIDAE)

Species of Ophraella, a North American genus of leaf beetles (Chrysomelidae), feed variously on eight genera in four tribes of Asteraceae. A phylogenetic analysis, based on morphological features and allozymes, was undertaken to deduce the history of host affiliation within the genus. The two data sets are combined to arrive at a provisional phylogeny of the species, onto which host associations are parsimoniously mapped. Among and within the 12 species studied, at least two shifts are postulated to have occurred among congeneric plant species, five between genera in the same tribe, and four between different tribes of Asteraceae. The phylogeny of Ophraella appears not to be congruent with that of its hosts. This and other evidence indicates that many host shifts in Ophraella postdate the divergence of the host plants, a conclusion that may apply commonly to phytophagous insects. A phenetic analysis of the plants' secondary compounds provides modest support for the hypothesis that host shifts are facilitated by commonalities in plant chemistry. A possible trend in host shifts is evident, from chemically simpler to chemically more forbidding plants. The chemical barriers to host shifts in Ophraella appear to require adaptation in both behavior and in physiological attributes. There is no evidence that the host associations of these insects or the divergence in secondary chemistry of their hosts can be attributed to coevolution.     

Molecular insight into systematics,host associations,life cycles and geographic distribution of the nematode family Rhabdiasidae

Rhabdiasidae Railliet, 1915 is a globally distributed group of up to 100 known species of nematodes parasitic in amphibians and reptiles. This work presents the results of a molecular phylogenetic analysis of 36 species of Rhabdiasidae from reptiles and amphibians from six continents. New DNA sequences encompassing partial 18S rDNA, ITS1, 5.8S rDNA, ITS2 and partial 28S rDNA regions of nuclear ribosomal DNA were obtained from 27 species and pre-existing sequences for nine species were incorporated. The broad taxonomic, host and geographical coverage of the specimens allowed us to address long-standing questions in rhabdiasid systematics, evolution, geographic distribution, and patterns of host association. Our analysis demonstrated that rhabdiasids parasitic in snakes are an independent genus sister to the rest of the Rhabdiasidae, a status supported by life cycle data. Based on the combined evidence of molecular phylogeny, morphology and life cycle characteristics, a new genus Serpentirhabdias gen. nov. with the type species Serpentirhabdias elaphe (Sharpilo, 1976) comb. nov. is established. The phylogeny supports the monophyly of Entomelas Travassos, 1930, Pneumonema Johnston, 1916 and the largest genus of the family, Rhabdias Stiles and Hassall, 1905. DNA sequence comparisons demonstrate the presence of more than one species in the previously monotypic Pneumonema from Australian scincid lizards. The distribution of some morphological characters in the genus Rhabdias shows little consistency within the phylogenetic tree topology, in particular the apical structures widely used in rhabdiasid systematics. Our data suggest that some of the characters, while valuable for species differentiation, are not appropriate for differentiation among higher taxa and are of limited phylogenetic utility. Rhabdias is the only genus with a cosmopolitan distribution, but some of the lineages within Rhabdias are distributed on a single continent or a group of adjacent zoogeographical regions. Serpentirhabdias, Entomelas and Pneumonema show rather strict specificity to their host groups. The evolution of the Rhabdiasidae clearly included multiple host switching events among different orders and families of amphibians as well as switching between amphibians and squamatan reptiles. Only a few smaller lineages of Rhabdias demonstrate relatively strict associations with a certain group of hosts.     

Host phylogeny is the primary determinant of ectomycorrhizal fungal community composition in the permafrost ecosystem of eastern Siberia at a regional scale

Ectomycorrhizal (EM) fungal communities have been studied worldwide; however, those in the very cold and dry continental climate zone of northern Eurasia remain understudied. We investigated EM fungal community structure on plant roots and its determinants in eastern Siberia. We identified 291 EM fungal taxa belonging to 37 fungal genera from nine sites spanning 2100 km. In a variation partitioning analysis, host plant phylogeny was the primary factor that explained variation in fungal community composition, followed by spatial distance, soil, and climate. Host specificity and preference were attributed to differences in EM fungal community composition among host plants. The EM fungal community on Larix cajanderi, the dominant canopy tree in the region, was characterized by a high proportion of Suillus and Rhizopogon species. This implies that these specialist fungal symbionts have a close ecological relationship with pioneer Larix trees to adapt to the harsh continental climate of Siberia.     

Phylogenetic analyses of DNA and allozyme data suggest that Gonioctena leaf beetles (Coleoptera; Chrysomelidae) experienced convergent evolution in their history of host-plant family shifts

A phylogenetic analysis of the genus Gonioctena (Coleoptera, Chrysomelidae) based on allozyme data (17 loci) and mitochondrial DNA sequence data (three gene fragments, 1,391 sites) was performed to study the evolutionary history of host-plant shifts among these leaf beetles. This chrysomelid genus is characteristically associated with a high number of different plant families. The diverse molecular data gathered in this study are to a large extent congruent, and the analyses provide a well-supported phylogenetic hypothesis to address questions about the evolution of host-plant shifts in the genus Gonioctena. The most-parsimonious reconstruction of the ancestral host-plant associations, based on the estimated phylogeny, suggests that the Fabaceae was the ancestral host-plant family of the genus. Although most of the host-plant shifts (between different host species) in Gonioctena have occurred within the same plant family or within the same plant genus, at least eight shifts have occurred between hosts belonging to distantly related and chemically dissimilar plant families. In these cases, host shifts may have been simply directed toward plant species available in the environment. Yet, given that two Gonioctena lineages have independently colonized the same three new plant families (Salicaceae, Betulaceae, Rosaceae), including four of the same new genera (Salix, Alnus, Prunus, Sorbus), some constraints are likely to have limited the different possibilities of interfamilial host-plant shifts.     

Oviposition in Yponomeuta cagnagellus: the importance of contact cues for host plant acceptance

Small ermine moths (Yponomeutidae: Lepidoptera) are specialist herbivores. Species within the genus Yponomeuta are each specialized on a limited number of plant species, mainly within genera belonging to the Celastraceae. European Yponomeuta species have developed new specialized host affiliations, mainly on rosaceous hosts. Since these host shifts are reputed to be of consequence for speciation, the role of the ovipositing female is of particular interest. Study of the pre-oviposition behaviour of gravid Y. cagnagellus (Hb.) moths on host (Euonymus europaeus), non-host (Crateagus monogyna) and artificial oviposition substrates, provided information on the nature of the cues used for host plant acceptance and the insect’s perception of these cues. Host selection by adult females occurs with contact chemoreceptors probably located on the antennae or tarsi. MeOH-soluble, non-volatile phytochemical compounds washed from the host plant’s surface and applied on an artificial twig are sufficient to stimulate a complete sequence of behavioural elements leading to oviposition. Volatiles do not have a large effect on the pre-oviposition behaviour.     

Avian malaria on Madagascar: prevalence,biodiversity and specialization of haemosporidian parasites

Previous studies about geographic patterns of species diversity of avian malaria parasites and others in the Order Haemosporida did not include the avian biodiversity hotspot Madagascar. Since there are few data available on avian malaria parasites on Madagascar, we conducted the first known large-scale molecular-based study to investigate their biodiversity. Samples (1067) from 55 bird species were examined by a PCR method amplifying nearly the whole haemosporidian cytochrome b gene (1063?bp). The parasite lineages found were further characterized phylogenetically and the degree of specialization was determined with a newly introduced host diversity index (Hd). Our results demonstrate that Madagascar indeed represents a biodiversity hotspot for avian malaria parasites as we detected 71 genetically distinct parasite lineages of the genera Plasmodium and Haemoproteus. Furthermore, by using a phylogenetic approach and including the sequence divergence we suspect that the detected haemosporidian lineages represent at least 29 groups i.e. proposed species. The here presented Hd values for each parasite regarding host species, genus and family strongly support previous works demonstrating the elastic host ranges of some avian parsites of the Order Haemosporida. Representatives of the avian parasite genera Plasmodium and Leucocytozoon tend to more often be generalists than those of the genus Haemoproteus. However, as demonstrated in various examples, there is a large overlap and single parasite lineages frequently deviate from this rule.     

Molecular phylogenetics of heliothine moths (Lepidoptera: Noctuidae: Heliothinae), with comments on the evolution of host range and pest status

Abstract The Heliothinae are a cosmopolitan subfamily of about 365 species that include some of the world’s most injurious crop pests. This study re‐assesses evolutionary relationships within heliothines, providing an improved phylogeny and classification to support ongoing intensive research on heliothine genomics, systematics, and biology. Our phylogeny estimate is based on two nuclear gene regions, namely elongation factor‐1α (EF‐1α; 1240 bp) and dopa decarboxylase (DDC; 687 bp), and on the barcoding region of mitochondrial cytochrome oxidase I (COI; 708 bp), providing a total of 2635 bp. These were sequenced for 71 heliothines, representing all major genera and nearly all recognized subgenera and species groups, and for 16 outgroups representing all major lineages of trifine Noctuidae. Analysis of the combined data by maximum likelihood, unweighted parsimony and Bayesian methods gave nearly identical topologies, and the individual gene trees showed only one case of potentially strong conflict. Relationships among genera and subgenera are resolved with strong bootstrap support. The earliest‐diverging lineages (c. 200 species in total) consist almost entirely of host specialists, reflecting the inferred ancestral heliothine host range under parsimony. The remaining species form a clade – the Heliothis group – that includes most of the polyphages (30% of heliothines) and all of the major pests. Many other species in the Heliothis group, however, are host specialists. Our results extend previous efforts to subdivide this large clade, and show the most notorious pest groups, the corn earworm complex (Helicoverpa) and the tobacco budworm (Heliothis virescens) group, to be closely related, joining with a small oligophagous genus in what we term the major‐pest lineage. Thus, genomic/experimental results from one model pest may extrapolate well to other pest species. The frequency of evolutionary expansion and contraction in host range appears to increase dramatically at the base of the Heliothis group, in contrast to the case for earlier‐diverging lineages. We ascribe this difference provisionally to differential evolutionary constraints arising from contrasting life‐history syndromes. Host‐specific behaviour and crypsis, coupled with low fecundity and vagility, may discourage host‐range expansion in earlier‐diverging lineages. By contrast, in the Heliothis group, the absence of host‐specific traits, coupled with high vagility and fecundity, may more readily permit expansion or contraction of the host range in response to varying ecological pressures such as host species abundance or differential competition and predation.     

Linking patterns and processes of species diversification in the cone flies Strobilomyia (Diptera: Anthomyiidae)

Phytophagous insects provide useful models for the study of ecological speciation. Much attention has been paid to host shifts, whereas situations where closely related lineages of insects use the same plant during different time periods have been relatively neglected in previous studies of insect diversification. Flies of the genus Strobilomyia are major pests of conifers in Eurasia and North America. They are specialized feeders in cones and seeds of Abies (fir), Larix (larch) ,and Picea (spruce). This close association is accompanied by a large number of sympatric Strobilomyia species coexisting within each tree genus. We constructed a molecular phylogeny with a 1320 base-pair fragment of mitochondrial DNA that demonstrated contrasting patterns of speciation in larch cone flies, as opposed to spruce and fir cone flies; this despite their comparable geographic distributions and similar resource quality of the host. Species diversity is the highest on larch, and speciation is primarily driven by within-host phenological shifts, followed by allopatric speciation during geographical expansion. By contrast, fewer species exploit spruce and fir, and within-host phenological shifts did not occur. This study illustrates within-host adaptive radiation through phenological shifts, a neglected mode of sympatric speciation.     

Into and out of the tropics: global diversification patterns in a hyperdiverse clade of ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi, symbiotic mutualists of many dominant tree and shrub species, exhibit a biogeographic pattern counter to the established latitudinal diversity gradient of most macroflora and fauna. However, an evolutionary basis for this pattern has not been explicitly tested in a diverse lineage. In this study, we reconstructed a mega‐phylogeny of a cosmopolitan and hyperdiverse genus of ECM fungi, Russula, sampling from annotated collections and utilizing publically available sequences deposited in GenBank. Metadata from molecular operational taxonomic unit cluster sets were examined to infer the distribution and plant association of the genus. This allowed us to test for differences in patterns of diversification between tropical and extratropical taxa, as well as how their associations with different plant lineages may be a driver of diversification. Results show that Russula is most species‐rich at temperate latitudes and ancestral state reconstruction shows that the genus initially diversified in temperate areas. Migration into and out of the tropics characterizes the early evolution of the genus, and these transitions have been frequent since this time. We propose the ‘generalized diversification rate’ hypothesis to explain the reversed latitudinal diversity gradient pattern in Russula as we detect a higher net diversification rate in extratropical lineages. Patterns of diversification with plant associates support host switching and host expansion as driving diversification, with a higher diversification rate in lineages associated with Pinaceae and frequent transitions to association with angiosperms.     

Host Plant Specialization in the Sugarcane Aphid Melanaphis sacchari

Most aphids are highly specialized on one or two related plant species and generalist species often include sympatric populations adapted to different host plants. Our aim was to test the hypothesis of the existence of host specialized lineages of the aphid Melanaphis sacchari in Reunion Island. To this end, we investigated the genetic diversity of the aphid and its association with host plants by analyzing the effect of wild sorghum Sorghum bicolor subsp. verticilliflorum or sugarcane as host plants on the genetic structuring of populations and by performing laboratory host transfer experiments to detect trade-offs in host use. Genotyping of 31 samples with 10 microsatellite loci enabled identification of 13 multilocus genotypes (MLG). Three of these, Ms11, Ms16 and Ms15, were the most frequent ones. The genetic structure of the populations was linked to the host plants. Ms11 and Ms16 were significantly more frequently observed on sugarcane, while Ms15 was almost exclusively collected in colonies on wild sorghum. Laboratory transfer experiments demonstrated the existence of fitness trade-offs. An Ms11 isofemale lineage performed better on sugarcane than on sorghum, whereas an Ms15 lineage developed very poorly on sugarcane, and two Ms16 lineages showed no significant difference in performances between both hosts. Both field and laboratory results support the existence of host plant specialization in M. sacchari in Reunion Island, despite low genetic differentiation. This study illustrates the ability of asexual aphid lineages to rapidly undergo adaptive changes including shifting from one host plant to another.     

Host specificity of avian haemosporidian parasites is unrelated among sister lineages but shows phylogenetic signal across larger clades

Parasites can vary in the number of host species they infect, a trait known as “host specificity”. Here we quantify phylogenetic signal—the tendency for closely related species to resemble each other more than distantly related species—in host specificity of avian haemosporidian parasites (genera Plasmodium, Haemoproteus and Leucocytozoon) using data from MalAvi, the global avian haemosporidian database. We used the genetic data (479 base pairs of cytochrome b) that define parasite lineages to produce genus level phylogenies. Combining host specificity data with those phylogenies revealed significant levels of phylogenetic signal while controlling for sampling effects; phylogenetic signal was higher when the phylogenetic diversity of hosts was taken into account. We then tested for correlations in the host specificity of pairs of sister lineages. Correlations were generally close to zero for all three parasite genera. These results suggest that while the host specificity of parasite sister lineages differ, larger clades may be relatively specialised or generalised.     

Re-analysis of the 18S rRNA gene phylogeny of the ciliate class Colpodea

We critically re-analyzed the 18S rRNA gene phylogeny of the ciliate class Colpodea where four main lineages have been recognized: (1) Bursariomorphida including bryometopids, (2) Platyophryida including sorogenids, (3) Cyrtolophosidida, and (4) Colpodida including bryophryids and grossglockneriids. The Platyophryida branched off first and the Cyrtolophosidida and Colpodida were classified as sister groups. On basis of multiple statistical tests, we unraveled three problematic issues in colpodean phylogenies: the positions of the Bursariomorphida and Platyophryida are unstable and depend on alignment masking; a sister relationship of the Platyophryida and Cyrtolophosidida cannot be excluded by any statistical tree topology test; and clustering of bryophryids and grossglockneriids outside the Colpodida are also statistically valid possibilities. Natural classification of the highly diverse order Colpodida remains puzzling, possibly due to the lack of a phylogenetic signal and morphostasis of the oral ciliature in several Colpoda-like lineages. According to the “Ur-Colpoda” hypothesis, Colpoda represents the stem lineage from which both Colpoda-like and morphologically more derived taxa might have branched off. This evolutionary concept preserves not only information on morphology, ecology, and evolutionary processes of colpodid ciliates, but also aids practicability because the connection to the traditional literature is optimally maintained.