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Blood-feeding leeches of the genus Placobdella have acquired intracellular alphaproteobacterial endosymbionts of the genus Reichenowia that potentially aid in the production of B vitamins, thereby ameliorating the lack of these essential nutrients in the diet of the hosts. For Placobdella associates, little is still known about the diversity, genetic makeup, and the mode of transmission of bacteria between leeches. We aimed to (i) place the bacterial symbionts in a phylogenetic context, (ii) compare patterns of cladogenesis between the bacteria and hosts to search for evidence of co-speciation, and (iii) explore the mode of bacterial transmission between leech parent and offspring. DNA sequencing of the bacterial 16S rDNA and 23S rDNA loci suggests that, whereas Reichenowia forms a monophyletic group within the alphaproteobacterial family Rhizobiaceae, no evidence for co-speciation between hosts and bacteria can be traced. Attempts at DNA amplification for ovarial tissues were negative for a range of species, but two 16S rDNA sequences retrieved from the testisacs of P. rugosa showed very high similarity with Reichenowia. Although we cannot rule out that this may be a contamination, or a different, potentially free-living species of bacteria, our results may indicate that Reichenowia is transferred from leech parent to offspring via the testisacs. [ABSTRACT FROM AUTHOR]

In reconstructing the common evolutionary history of hosts and parasites, the current method of choice is the phylogenetic tree reconciliation. In this model, we are given a host tree H, a parasite tree P, and a function σ mapping the leaves of P to the leaves of H and the goal is to find, under some biologically motivated constraints, a reconciliation, that is a function from the vertices of P to the vertices of H that respects σ and allows the identification of biological events such as co-speciation, duplication and host switch. The maximum co-divergence problem consists in finding the maximum number of co-speciations in a reconciliation. This problem is NP-hard for arbitrary phylogenetic trees and no approximation algorithm is known. In this paper we consider the influence of tree topology on the maximum co-divergence problem. In particular we focus on a particular tree structure, namely caterpillar, and show that—in this case—the heuristics that are mostly used in the literature provide solutions that can be arbitrarily far from the optimal value. Then, we prove that finding the max co-divergence is equivalent to compute the maximum length of a subsequence with certain properties of a given permutation. This equivalence leads to two consequences: (1) it shows that we can compute efficiently in polynomial time the optimal time-feasible reconciliation and (2) it can be used to understand how much the tree topology influences the value of the maximum number of co-speciations. [ABSTRACT FROM AUTHOR]

Fungi belonging to the Entorrhizales (Entorrhizomycota) comprise biotrophic pathogens associated with roots of the Cyperaceae and Juncaceae plant species. They are nearly globally distributed but rarely studied due to a hidden lifestyle without causing visible effects on host plants. Therefore, the evolutionary origin and phylogenetic relationships of the group are still poorly understood and it is not known whether species diversification was the result of co-evolution with their hosts or the result of host jumps. To infer hypotheses about the evolutionary history of the Entorrhizales, divergence times were estimated and plant-fungal tanglegrams calculated. Relaxed molecular clock analyses suggest that the Entorrhizomycota originated around the Neoproterozoic-Palaeozoic and diverged during the Late Cretaceous-Paleogene into the extant orders Entorrhizales and Talbotiomycetales. The split of the major lineages within the Entorrhizales took place in the Eocene, somewhat later than the divergence of the host families Cyperaceae and Juncaceae. Topology- and distance-based co-phylogenetic analyses of the fungi and their hosts revealed a large number of co-speciation and lineage sorting events in early fungal speciation, which resulted in a phylogenetic split corresponding to species infecting Cyperaceae or Juncaceae. Given that this split is congruent with spore differences, Entorrhiza s. str. is emended for species infecting hosts in the Cyperaceae, and a new genus Juncorrhiza is described for species restricted to hosts in the Juncaceae. Additionally, three new species are described: Entorrhiza fuirenae, Juncorrhiza maritima and J. oxycarpi. [ABSTRACT FROM AUTHOR]