Genotypic similarities among the parthenogenetic Darevskia rock lizards with different hybrid origins.

BACKGROUND: The majority of parthenogenetic vertebrates derive from hybridization between sexually reproducing species, but the exact number of hybridization events ancestral to currently extant clonal lineages is difficult to determine. Usually, we do not know whether the parental species are able to contribute their genes to the parthenogenetic vertebrate lineages after the initial hybridization. In this paper, we address the hypothesis, whether some genotypes of seven phenotypically distinct parthenogenetic rock lizards (genus Darevskia) could have resulted from back-crosses of parthenogens with their presumed parental species. We also tried to identify, as precise as possible, the ancestral populations of all seven parthenogens. RESULTS: We analysed partial mtDNA sequences and microsatellite genotypes of all seven parthenogens and their presumed ansectral species, sampled across the entire geographic range of parthenogenesis in this group. Our results confirm the previous designation of the parental species, but further specify the maternal populations that are likely ancestral to different parthenogenetic lineages. Contrary to the expectation of independent hybrid origins of the unisexual taxa, we found that genotypes at multiple loci were shared frequently between different parthenogenetic species. The highest proportions of shared genotypes were detected between (i) D. sapphirina and D. bendimahiensis and (ii) D. dahli and D. armeniaca, and less often between other parthenogens. In case (ii), genotypes at the remaining loci were notably distinct. CONCLUSIONS: We suggest that both observations (i-ii) can be explained by two parthenogenetic forms tracing their origin to a single initial hybridization event. In case (ii), however, occasional gene exchange between the unisexual and the parental bisexual species could have taken place after the onset of parthenogenetic reproduction. Indeed, backcrossed polyploid hybrids are relatively frequent in Darevskia, although no direct evidence of recent gene flow has been previously documented. Our results further suggest that parthenogens are losing heterozygosity as a result of allelic conversion, hence their fitness is expected to decline over time as genetic diversity declines. Backcrosses with the parental species could be a rescue mechanism which might prevent this decline, and therefore increase the persistance of unisexual forms.

Phylogeny of caucasian rock lizards (Darevskia) and other true lizards based on mitogenome analysis: Optimisation of the algorithms and gene selection.

We generated a phylogeny for Caucasian rock lizards (Darevskia), and included six other families of true lizards (Lacertini), based on complete mitochondrial genome analysis. Next-generation sequencing (NGS) of genomic DNA was used to obtain 16 new mitogenomes of Darevskia. These, along with 35 sequences downloaded from GenBank: genera Darevskia, Zootoca, Podarcis, Phoenicolacerta, Takydromus, Lacerta, and Eremias-were used in the analysis. All four analytical methods (Bayesian Inference, BI; Maximum Likelihood, ML; Maximum Parsimony, MP; and Neighbor-Joining, NJ) showed almost congruent intra-generic topologies for Darevskia and other lizard genera. However, ML and NJ methods on one side, and BI and MP methods on the other harvested conflicting phylogenies. The ML/NJ topology supports earlier published separation of Darevskia into three mitochondrial clades (Murphy, Fu, Macculloch, Darevsky, and Kupinova, 2000), but BI and MP topologies support that the basal branching occurred between D. parvula from the western Lesser Caucasus and the rest of Darevskia. All topologies altered the phylogenetic position of some individual species, including D. daghestanica, D. derjugini, and D. chlorogaster. Reanalysis after excluding four saturated genes from the data set, and excluding genus Eremias gives fully convergent topologies. The most basal branching for true lizards was between Far Eastern Takydromus and the Western Eurasian genera (BI). Comparing phylogenetic performance of individual genes relative to whole mitogenome data, concatenated 16S RNA (the least saturated gene in our analyses) and Cytochrome b genes generate a robust phylogeny that is fully congruent with that based on the complete mitogenome.

Identification of Two Pathogenic Aeromonas Species Isolated from Juvenile Burbot during Production-Related Epizootics.

In response to population declines of North American Burbot Lota lota maculosa (hereafter, Burbot), conservation aquaculture methods have been developed for this species. In general, Burbot are relatively resistant to many salmonid pathogens; however, cultured juvenile Burbot have experienced periodic epizootic disease outbreaks during production. A series of trials was conducted to determine the virulence of select bacteria isolated from juvenile Burbot after outbreaks that occurred in 2012 and 2013 at the University of Idaho's Aquaculture Research Institute. Initial clinical diagnostics and sampling resulted in the isolation of numerous putative bacterial pathogens. To determine which bacteria were the most likely causative agents contributing to these epizootics, juvenile Burbot received intraperitoneal (IP) injections of select bacteria in log-phase growth. Mortality associated with specific isolates was recorded, and more comprehensive challenges followed this initial screening. These challenges used side-by-side IP and immersion methods to expose Burbot to potential pathogens. The challenges resulted in significantly higher mortalities in fish after IP injection with two Aeromonas sp. isolates compared to controls, but no significant difference in mortality for immersion-challenged groups was observed. Results demonstrate that two Aeromonas sp. isolates cultured from the epizootics are virulent to Burbot.

Endophytes influence protection and growth of an invasive plant.

We investigated the symbiotic activities of fungal endophytes isolated from spotted knapweed, Centaurea stoebe. Previously, an analysis of community similarity had demonstrated differences in the endophyte communities of C. stoebe in its native and invaded ranges. Here, we found that specific endophytes can exert positive effects on their host, whereas others exert negative effects. Endophytes produced metabolites that inhibited germination of a competitor of C. stoebe. Endophytes also repelled a specialist insect herbivore, perhaps by producing biologically active volatiles. Yet other endophytes acted as cryptic pathogens of C. stoebe, suppressing its germination, reducing its growth, increasing the abundance of a generalist insect herbivore, and delaying or suppressing its flowering. Since, as reported here, endophytes are not functionally interchangeable, previously reported community differences could be contributing to the invasiveness of C. stoebe.

Hidden diversity of endophytic fungi in an invasive plant.

Fungal endophytes are important in plant ecology and common in plants. We attempted to test cointroduction and host-jumping hypotheses on a community basis by comparing endophytes isolated from invasive spotted knapweed (Centaurea stoebe, Asteraceae) in its native and invaded ranges. Of 92 combined, sequence-based haplotypes representing eight classes of Fungi, 78 occurred in only one of the two ranges. In the native range of C. stoebe, one haplotype of Alternaria alternata was clearly dominant, whereas in the invaded range, no haplotype was dominant. Many haplotypes were closely related to one another and novel. For example, six putative, new species of Botrytis were discovered as endophytes of C. stoebe, which has never been reported to have Botrytis spp.. Apparent differences between the two communities of endophytes were significant according to an analysis of similarity, but phylogenetic community structure did not differ significantly between the ranges. Both host-jumping and cointroduction of fungal endophytes likely took place during the spotted knapweed invasion.

Induced paternal effects mimic cytoplasmic incompatibility in Drosophila.

Wolbachia is an intracellular microbe found in a wide diversity of arthropod and filarial nematode hosts. In arthropods these common bacteria are reproductive parasites that manipulate central elements of their host's reproduction to increase their own maternal transmission in one of several ways. Cytoplasmic incompatibility (CI) is one such manipulation where sperm are somehow modified in infected males and this modification must be rescued by the presence of the same bacterial strain in the egg for normal development to proceed. The molecular mechanisms involved in the expression of CI are unknown. Here we show that Wolbachia infection results in increased mRNA and protein expression of the Drosophila simulans nonmuscle myosin II gene zipper. Induced overexpression of zipper in Wolbachia-free transgenic D. melanogaster males results in paternal-effect lethality that mimics the fertilization defects associated with CI. Likewise, overexpression of the tumor suppressor gene, lethal giant larvae [l(2)gl], results in egg lethality and a CI phenotype. Stoichiometric levels of zipper and l(2)gl are required for proper segregation of cellular determinants during neuroblast stem cell division. Taken together these results form the basis of a working hypothesis whereby Wolbachia induces paternal effects in sperm by manipulating the expression of key regulators of cytoskeletal activity during spermatogenesis.

Widespread prevalence of wolbachia in laboratory stocks and the implications for Drosophila research.

Wolbachia is an intracellular microbe harbored by a wide variety of arthropods (including Drosophila) and filarial nematodes. Employing several different strategies including male killing, induced parthenogenesis, cytoplasmic incompatibility, and feminization, and acting by as-yet-unknown mechanisms, Wolbachia alters host reproduction to increase its representation within a population. Wolbachia is closely associated with gametic incompatibility but also interacts with Drosophila in other, little understood ways. We report here significant and widespread infection of Wolbachia within laboratory stocks and its real and potential impact on Drosophila research. We describe the results of a survey indicating that approximately 30% of stocks currently housed at the Bloomington Drosophila Stock Center are infected with Wolbachia. Cells of both reproductive tissues and numerous somatic organs harbor Wolbachia and display considerable variation in infection levels within and between both tissue types. These results are discussed from the perspective of Wolbachia's potential confounding effects on both host fitness and phenotypic analyses. In addition to this cautionary message, the infection status of stock centers may provide further opportunities to study the genetic basis of host/symbiosis.

Host specialization of the mycoparasite Eudarluca caricis and its evolutionary relationship to Ampelomyces.

Eudarluca caricis is assumed to be a nonspecific mycoparasite of rust fungi. The evidence for its mycoparasitism has rested on constant association with uredinia. In this study, stable isotopes provided additional evidence of mycoparasitism, as E. caricis was enriched with 15N relative to its associated rust fungus, as were parasites and mycoparasites generally with respect to their hosts. Host specificity was directly tested in inoculations in the greenhouse. Isolates of E. caricis from Puccinia on two Eurasian grasses (i.e. Holcus lanatus and Phalaris arundinacaea) did not infect Melampsora on Populus that, in contrast, was successfully infected by a poplar isolate of E. caricis. An isolate from M. medusae on P. deltoides infected a significantly greater percentage of uredinia of M. medusae on P. deltoides than uredinia of M. occidentalis on P. trichocarpa. The host specificity of the three isolates was reflected in their divergence in a phylogenetic analysis based on ITS sequences. Interestingly, the analysis revealed that mycoparasites of rust and powdery mildew fungi have evolved from a common ancestor.

Microgemma vivaresi n. sp. (Microsporidia, Tetramicridae), infecting liver and skeletal muscle of sea scorpions, Taurulus bubalis (Euphrasen 1786) (Osteichthyes, Cottidae), an inshore, littoral fish.

The ultrastructure of a new microsporidian species Microgemma vivaresi n. sp. causing liver cell xenoma formation in sea scorpions, Taurulus bubalis, is described. Stages of merogony, sporogony, and sporogenesis are mixed in the central cytoplasm of developing xenomas. All stages have unpaired nuclei. Uninucleate and multinucleate meronts lie within vacuoles formed from host endoplasmic reticulum and divide by binary or multiple fission. Sporonts, no longer in vacuoles, deposit plaques of surface coat on the plasma membrane that cause the surface to pucker. Division occurs at the puckered stage into sporoblast mother cells, on which plaques join up to complete the surface coat. A final binary fission gives rise to sporoblasts. A dense globule, thought to be involved in polar tube synthesis, is gradually dispersed during spore maturation. Spores are broadly ovoid, have a large posterior vacuole, and measure 3.6 microm x 2.1 microm (fresh). The polar tube has a short wide anterior section that constricts abruptly, then runs posteriad to coil about eight times around the posterior vacuole with granular contents. The polaroplast has up to 40 membranes arranged in pairs mostly attached to the wide region of the polar tube and directed posteriorly around a cytoplasm of a coarsely granular appearance. The species is placed alongside the type species Microgemma hepaticusRalphs and Matthews 1986 within the family Tetramicridae, which is transferred from the class Dihaplophasea to the class Haplophasea, as there is no evidence for the occurrence of a diplokaryotic phase.