Browsing by Author "Gerth, Michael"

The complete mitochondrial genomes of three polycladids, the acotylean Hoploplana elisabelloi and the cotyleans Enchiridium sp. and Prosthiostomum siphunculus have been assembled with high coverage from Illumina sequencing data. The mt genomes contain 36 genes including 12 of the 13 protein-coding genes characteristic for metazoan mitochondrial genomes, two ribosomal RNA genes, and 22 transfer RNA genes. Gene annotation, gene order, genetic code, start and stop codons and codon bias have been identified. In comparison with the well investigated parasitic Neodermata, our analysis reveals a great diversity of gene orders within Polycladida and Platyhelminthes in general. By analyzing representative genomes of the main groups of Platyhelminthes we explored the phylogenetic relationships of this group. The phylogenetic analyses strongly supported the monophyly of Polycladida, and based on a small taxon sampling suggest the monophyly of Acotylea and Cotylea.

The genus Wolbachia (Alphaproteobacteria) comprises the most abundant inherited intracellular bacteria1. Despite their relevance as manipulators of human pathogen transmission2 and arthropod reproduction3, many aspects of their evolutionary history are not well understood4. In arthropods, Wolbachia infections are typically transient on evolutionary timescales5,6 and co-divergence between hosts and Wolbachia is supposedly rare. Consequently, much of our knowledge of Wolbachia genome evolution derives from very recently diverged strains, and a timescale for Wolbachia is lacking. Here, we investigated the genomes of four Wolbachia strains that have persisted within and co-diverged with their host lineage for ∼2 million years. Although the genomes showed very little evolutionary change on a nucleotide level, we found evidence for a recent lateral transfer of a complete biotin synthesis operon that has the potential to transform Wolbachia-host relationships7. Furthermore, this evolutionary snapshot enabled us to calibrate the divergence times of the supergroup A and B Wolbachia lineages using genome-wide data sets and relaxed molecular clock models. We estimated the origin of Wolbachia supergroups A and B to be ∼200 million years ago (Ma), which is considerably older than previously appreciated. This age coincides with the diversification of many insect lineages8 that represent most of Wolbachia's host spectrum.

Annelida is a highly diverse animal group with over 21,000 described species. As part of Lophotrochozoa, the vast majority of annelids are currently classified into two groups: Errantia and Sedentaria, together forming Pleistoannelida. Besides these taxa, Sipuncula, Amphinomidae, Chaetopteridae, Oweniidae and Magelonidae can be found branching at the base of the tree. Comparisons of mitochondrial genomes have been used to investigate phylogenetic relationship within animal taxa. Complete annelid mitochondrial genomes are available for some Sedentaria and Errantia and in most cases exhibit a highly conserved gene order. Only two complete genomes have been published from the basal branching lineages and these are restricted to Sipuncula. We describe the first complete mitochondrial genome sequences for all other basal branching annelid families: Owenia fusiformis (Oweniidae), Magelona mirabilis (Magelonidae), Eurythoe complanata (Amphinomidae), Chaetopterus variopedatus and Phyllochaetopterus sp. (Chaetopteridae). The mitochondrial gene order of all these taxa is substantially different from the pattern found in Pleistoannelida. Additionally, we report the first mitochondrial genomes in Annelida that encode genes on both strands. Our findings demonstrate that the supposedly highly conserved mitochondrial gene order suggested for Annelida is restricted to Pleistoannelida, representing the ground pattern of this group. All investigated basal branching annelid taxa show a completely different arrangement of genes than observed in Pleistoannelida. The gene order of protein coding and ribosomal genes in Magelona mirabilis differs only in two transposition events from a putative lophotrochozoan ground pattern and might be the closest to an ancestral annelid pattern. The mitochondrial genomes of Myzostomida show the conserved pattern of Pleistoannelida, thereby supporting their inclusion in this taxon.

Bacterial endosymbionts play key roles in arthropod biology, ranging from beneficial mutualists to parasitic sex ratio manipulators. The number of described endosymbiotic bacterial taxa has accumulated continuously in recent years. While the understanding of arthropod-microbe interactions has advanced significantly, especially in model organisms, relatively little is known about symbiont distribution and effects in non-model organisms. As a first step to alleviate this gap in understanding, we performed an endosymbiont survey in bees (Anthophila), an ecologically and economically important group of hymenopterans. To this end, we sampled 170 bee species and screened by PCR for the presence of Wolbachia, Rickettsia, Arsenophonus and Cardinium. Detected strains were then further diagnosed by additional markers. Additionally, we tested if certain ecological traits, bee phylogeny or geographic origin of bees explain endosymbiont distribution. Our results indicate that supergroup A Wolbachia are very common in bees and that their distribution can be significantly correlated to both host ecology and phylogeny, although a distinction of these factors is not possible. Furthermore, bees from the same region (Old World or New World) are more likely to harbour identical Wolbachia strains than expected by chance. Other endosymbionts (Rickettsia, Arsenophonus) were less common, and specific to particular host taxa, suggesting that host phylogeny is a major predictor for endosymbiont distribution in bees.

Endosymbionts are widely distributed in insects and can strongly affect their host ecology. The common green lacewing (Chrysoperla carnea) is a neuropteran insect which is widely used in biological pest control. However, their endosymbionts and their interactions with their hosts have not been very well studied. Therefore, we screened for endosymbionts in natural and laboratory populations of Ch. carnea using diagnostic PCR amplicons. We found the endosymbiont Rickettsia to be very common in all screened natural and laboratory populations, while a hitherto uncharacterized Sodalis strain was found only in laboratory populations. By establishing lacewing lines with no, single or co-infections of Sodalis and Rickettsia, we found a high vertical transmission rate for both endosymbionts (>89%). However, we were only able to estimate these numbers for co-infected lacewings. Sodalis negatively affected the reproductive success in single and co-infected Ch. carnea, while Rickettsia showed no effect. We hypothesize that the fitness costs accrued by Sodalis infections might be more tolerable in the laboratory than in natural populations, as the latter are also prone to fluctuating environmental conditions and natural enemies. The economic and ecological importance of lacewings in biological pest control warrants a more profound understanding of its biology, which might be influenced by symbionts.

Abstract Word-based or ‘alignment-free’ methods for phylogeny inference have become popular in recent years. These methods are much faster than traditional, alignment-based approaches, but they are generally less accurate. Most alignment-free methods calculate ‘pairwise’ distances between nucleic-acid or protein sequences; these distance values can then be used as input for tree-reconstruction programs such as neighbor-joining. In this paper, we propose the first word-based phylogeny approach that is based on ‘multiple’ sequence comparison and ‘maximum likelihood’. Our algorithm first samples small, gap-free alignments involving four taxa each. For each of these alignments, it then calculates a quartet tree and, finally, the program ‘Quartet MaxCut’ is used to infer a super tree for the full set of input taxa from the calculated quartet trees. Experimental results show that trees produced with our approach are of high quality.

Of all obligate intracellular bacteria, Wolbachia is probably the most common. In general, Wolbachia are either widespread, opportunistic reproductive parasites of arthropods or essential mutualists in a single group of filarial nematodes, including many species of medical significance. To date, a robust phylogenetic backbone of Wolbachia is lacking and consequently, many Wolbachia-related phenomena cannot be discussed in a broader evolutionary context. Here we present the first comprehensive phylogenomic analysis of Wolbachia supergroup relationships based on new whole-genome-shotgun data. Our results suggest that Wolbachia has switched between its two major host groups at least twice. The ability of some arthropod-infecting Wolbachia to universally infect and to adapt to a broad range of hosts quickly is restricted to a single monophyletic lineage (containing supergroups A and B). Thus, the currently observable pandemic has likely a single evolutionary origin and is unique within the radiation of Wolbachia strains.

The endosymbiotic bacterium Wolbachia enhances its spread via vertical transmission by generating reproductive effects in its hosts, most notably cytoplasmic incompatibility (CI). Additionally, frequent interspecific horizontal transfer is evident from a lack of phylogenetic congruence between Wolbachia and its hosts. The mechanisms of this lateral transfer are largely unclear. To identify potential pathways of Wolbachia movements, we performed multilocus sequence typing of Wolbachia strains from bees (Anthophila). Using a host phylogeny and ecological data, we tested various models of horizontal endosymbiont transmission. In general, Wolbachia strains seem to be randomly distributed among bee hosts. Kleptoparasite-host associations among bees as well as other ecological links could not be supported as sole basis for the spread of Wolbachia. However, cophylogenetic analyses and divergence time estimations suggest that Wolbachia may persist within a host lineage over considerable timescales and that strictly vertical transmission and subsequent random loss of infections across lineages may have had a greater impact on Wolbachia strain distribution than previously estimated. Although general conclusions about Wolbachia movements among arthropod hosts cannot be made, we present a framework by which precise assumptions about shared evolutionary histories of Wolbachia and a host taxon can be modelled and tested.

Wolbachia (Alphaproteobacteria) is an inherited endosymbiont of arthropods and filarial nematodes and was reported to be widespread across insect taxa. While Wolbachia's effects on host biology are not understood from most of these hosts, known Wolbachia-induced phenotypes cover a spectrum from obligate beneficial mutualism to reproductive manipulations and pathogenicity. Interestingly, data on Wolbachia within the most species-rich order of arthropods, the Coleoptera (beetles), are scarce. Therefore, we screened 128 species from seven beetle families (Buprestidae, Hydraenidae, Dytiscidae, Hydrophilidae, Gyrinidae, Haliplidae, and Noteridae) for the presence of Wolbachia. Our data show that, contrary to previous estimations, Wolbachia frequencies in beetles (31% overall) are comparable to the ones in other insects. In addition, we used Wolbachia MLST data and host phylogeny to explore the evolutionary history of Wolbachia strains from Hydraenidae, an aquatic lineage of beetles. Our data suggest that Wolbachia from Hydraenidae might be largely host genus specific and that Wolbachia strain phylogeny is not independent to that of its hosts. As this contrasts with most terrestrial Wolbachia-arthropod systems, one potential conclusion is that aquatic lifestyle of hosts may result in Wolbachia distribution patterns distinct from those of terrestrial hosts. Our data thus provide both insights into Wolbachia distribution among beetles in general and a first glimpse of Wolbachia distribution patterns among aquatic host lineages.