Population genomics of sexual and asexual lineages in fissiparous ribbon worms (Lineus,Nemertea): hybridization,polyploidy and the Meselson effect

Comparative population genetics in asexual vs. sexual species offers the opportunity to investigate the impact of asexuality on genome evolution. Here, we analyse coding sequence polymorphism and divergence patterns in the fascinating Lineus ribbon worms, a group of marine, carnivorous nemerteans with unusual regeneration abilities, and in which asexual reproduction by fissiparity is documented. The population genomics of the fissiparous L. pseudolacteus is characterized by an extremely high level of heterozygosity and unexpectedly elevated π_N/π_S ratio, in apparent agreement with theoretical expectations under clonal evolution. Analysis of among‐species allele sharing and read‐count distribution, however, reveals that L. pseudolacteus is a triploid hybrid between Atlantic populations of L. sanguineus and L. lacteus. We model and quantify the relative impact of hybridity, polyploidy and asexuality on molecular variation patterns in L. pseudolacteus and conclude that (i) the peculiarities of L. pseudolacteus population genomics result in the first place from hybridization and (ii) the accumulation of new mutations through the Meselson effect is more than compensated by processes of heterozygosity erosion, such as gene conversion or gene copy loss. This study illustrates the complexity of the evolutionary processes associated with asexuality and identifies L. pseudolacteus as a promising model to study the first steps of polyploid genome evolution in an asexual context.     

Molecular Phylogeny of Some European Heteronemertean (Nemertea) Species and the Monophyletic Status ofRiseriellus, Lineus,andMicrura

The 16S rRNA mitochondrial gene was used to reconstruct the relationships among 10 heteronemertean species (subclass Heteronemertea, phylum Nemertea);Lineus ruberandL. viridisare represented by more than one specimen to assess intraspecific variation in these enigmatic species, and the analysis includes in total 14 terminal taxa incorporating one palaeonemertean species (Tubulanus annulatus) for outgroup rooting. The aligned sequences were subjected to maximum parsimony, maximum-likelihood, and neighbor-joining analyses to estimate the phylogenetic relationship of the species. The results were concordant from all analyses and indicate that neitherLineusnorMicruraare monophyletic taxa, and that there is no support from a phylogenetic point of view to establish the monotypic genusRiseriellus.     

Numerical analysis of phenotypic properties,genomic fingerprinting,and multilocus sequence analysis of Bradyrhizobium strains isolated from root nodules of Lembotropis nigricans of the tribe Genisteae

Purpose

The aim of this study was to estimate the level of genomic and phenotypic diversity as well as the genus and species position of bacterial strains isolated from root nodules of Lembotropis nigricans (family Fabaceae).

Methods

The genomic diversity of studied L. nigricans nodule symbionts was examined by using BOX-PCR and AFLP (amplified fragment length polymorphism) fingerprinting techniques. To assign bacteria to the genus, numerical analysis of phenotypic features and comparative analysis of 16S rDNA sequences were performed. The comparative analysis of combined atpD, dnaK, gyrB, and rpoB gene sequences (multilocus sequence analysis, MLSA) was used to determine the most closely related species to the studied bacteria.

Results

Both BOX-PCR and AFLP techniques revealed a high level of genomic heterogeneity of L. nigricans nodulators. Among 33 studied bacteria, 32 genotypes were delineated by the AFLP method and 27 genotypes were identified by the BOX-PCR fingerprinting. The numerical analysis of 86 phenotypic characteristics of L. nigricans nodule isolates and reference rhizobia showed that studied bacteria belong to the genus Bradyrhizobium. Affiliation of L. nigricans nodule isolates to the genus Bradyrhizobium was supported by comparative analysis of 16S rDNA sequences and the concatenation of atpD, dnaK, gyrB, and rpoB gene sequences. MLSA indicated also that L. nigricans microsymbionts are members of Bradyrhizobium japonicum.

Conclusion

L. nigricans root nodule symbionts are members of Bradyrhizobium japonicum and exhibit high phenotypic and genomic diversity important for their survival in soil.

     

Histocompatibility in Nemertines: Fates of Multiparental Lineus Constructed by Grafting of Pieces from Many Donors

The difficulties that usually prevent successful constructionof animals by piecing together body parts from different adultsare overcome by using nemertines of the genus Lineus. I haveconstructed viable composite orthotopic (anatomically complementary)or heterotopic Lineus by grafting. In species capable of reproducingvegetatively, composite worms were obtained from adults of thesame clone. In species unable to reproduce asexually, and instudies to follow chimera components by genetic markers, compositeworms were produced from pieces of genetically different donors.The fates of syngeneic (intraclonal), allogeneic (intraspecific),and xenogeneic (interspecific) chimeras were in accordance withthe basic principle of tissue transplantation in Lineus, i.e.,isografts and allografts succeed but xenografts fail. In L.ruber, the greater the number of donors, the more fragile wereintraspecific chimeras, although this fragility has not preventedsuccessful long-term experiments (multiparental worms live severalyears). Also generally the less orthopic the construction atgrafting, the less the vitality of the chimeras. By transferring pieces, various manipulations of anatomicalpatterns of body segments were tested. In multi-donor orthotopicallyconstructed L. ruber, putative allogeneic immunorecognitionwas investigated. Multi-donor heterotopically constructed Lineusprovided evidence for mechanisms of regulation as well as forthe persistence of mosaic status in developmental processes.Skin pigmentation and sex characteristics were useful markersboth to probe chimerism and to study humoral and cell interactionsbetween chimeric parts derived from donors of two sexes. Adults of the marine ribbon worm Lineus offer a convenient experimentalsystem for better understanding mechanisms of communicationbetween differentiated cells.     

卫矛属一新变种——腥臭卫矛

报道了卫矛属(Euonymus)一新变种——腥臭卫矛(Euonymus sanguineus var.paedidus L.M.Wang)。该新变种与原变种石枣子(Euonymus sanguineus Loes.var.sanguineus)相似,但其独特的强烈腥臭花不仅明显可与石枣子区别,而且也有别于卫矛属中所有其他种类。另外,该变种叶柄极短,一般短于5mm,可以与原变种区别。对腥臭卫矛的分布与生境做了简略讨论。     

大兴安岭舟形藻科(硅藻门)中国新记录植物

在大兴安岭沼泽硅藻生物多样性的研究过程中,对采自大兴安岭的600余号标本进行了详细的观察,共观察到舟形藻科中国新记录植物10个分类单位,隶属于4个属,其中类缝藻属1种:粗脉肋缝藻;长篦藻属3种:大长篦藻、细尖长篦藻、双型长篦藻;舟形藻属1种:乌普萨拉舟形藻;辐节藻属5种:两头辐节藻、河生辐节藻、细长辐节藻、豆形辐节藻、地中海辐节藻。本文对这些种类的分类学特征及生态分布特点进行了详细的描述。     

Morphological characterization of the testicular cells and seminiferous epithelium cycle in six species of Neotropical bats

We know little about the process of spermatogenesis in bats, a great and diverse clade of mammals that presents different reproductive strategies. In the present study, spermatogenesis in six species of Neotropical bats was investigated by light microscopy. On the basis of chromatin condensation, nuclear morphology, relative position to the basal membrane and formation of the flagellum, three types of spermatogonia were recognized: dark type A (A_d), pale type A (A_p), and type B; the development of spermatids was divided into seven steps. With the exception of Myotis nigricans, the seminiferous epithelium cycle of the other five species studied was similar to those of other mammals, showing gradual stages by the tubular morphology method. Asynchrony was observed in the seminiferous epithelium cycle of M. nigricans, shown by overlapping stages and undefined cycles. The frequencies found in the three phases of the cycle were variable with the greatest frequency occurring in the postmeiotic phase (>50%) and the least in the meiotic phase (<10%). The similarities observed in the five species of Phyllostomidae appeared to be related to their phylogenetic relationship and shorter divergence times, whereas the differences in M. nigricans appeared to be related to its greater phylogenetic distance because the Vespertilionidae family diverged earlier. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Comparative phylogeography and species boundaries in Echinolittorina snails in the central Indo-West Pacific

Aim This study aimed to test monophyly and geographical boundaries in five marine intertidal snail species from the central Indo‐West Pacific. We tested the prediction that phylogenetic breaks between the Indian and Pacific Ocean basins should be more pronounced in continental than oceanic settings, and sought common geographical patterns of interspecific boundaries and intraspecific phylogenetic breaks in the region. Location The tropical seas of the Indo‐West Pacific. Methods We sequenced over 1200 bp of the mitochondrial cytochrome oxidase subunit I gene (COI) from 18–92 individuals sampled from throughout the ranges of each of five species of Echinolittorina (Littorinidae): three members of the Echinolittorina trochoides species complex; Echinolittorina reticulata; and Echinolittorina vidua, together with sister species, in order to test species boundaries. In addition, 630 bp of the nuclear 28S rRNA gene were sequenced from E. reticulata and its sister Echinolittorina millegrana. Phylogenetic structure was assessed using neighbour‐joining and parsimony analyses. Results COI data confirmed species boundaries and geographical distributions for all species except the pair E. reticulata and E. millegrana, which were nevertheless reciprocally monophyletic for 28S rRNA. The species from ecologically ‘continental’ habitats (E. trochoides A and E. vidua, but not E. trochoides B) mostly showed strong interoceanic breaks (with age estimates 0.58–4.4 Ma), while the ecologically ‘oceanic’E. trochoides D and E. reticulata did not. The sister species E. trochoides A and B occupy the shores of the continental shelves of Southeast Asia and Australasia respectively; between them lies the oceanic ‘eastern Indonesian corridor’ occupied by E. trochoides D and E. reticulata. The widespread continental species E. vidua showed a complex pattern of deep division into six haplotype clades with apparently parapatric distributions. Main conclusions Our results show that ecological differences (in this case continental vs. oceanic habitat) influence both intraspecific phylogenetic structure and interspecific boundaries in these snails of intertidal rocky shores. Two of the three species restricted to continental shelves show phylogenetic breaks between the Indian and Pacific Oceans, consistent with vicariant separation during Plio‐Pleistocene low sea levels. The two oceanic species do not show breaks, suggesting that they maintained interoceanic connections through the eastern Indonesian corridor. The geographical location of the interspecific boundary between continental E. trochoides A and oceanic E. trochoides D mirrors intraspecific breaks reported in other species. The sister relationship of E. trochoides A and B in Asia and Australasia, respectively, is an example of a ‘marine Wallace's line’ distribution, and we suggest that it is the result of separation of two continental species by a barrier of unsuitable oceanic habitat.     

Taxonomic implications for diaptomid copepods based on contrasting patterns of mitochondrial DNA sequence divergences in four morphospecies

Morphological identification methods do not provide reliable and meaningful species identifications for taxa where morphological differences among distinct species are either absent or overlooked (i.e., cryptic species). For example, due to the minute nature of the morphological characters used to delineate diaptomid copepod species and the apparent potential for copepod speciation to occur with little or no morphological change (i.e., morphological stasis), morphological identifications of diaptomid species may not adequately capture their true species diversity. Here, we present results from a geographic survey of mtDNA sequences from populations across the geographic ranges of four North American diaptomid species—Leptodiaptomus minutus, Skistodiaptomus pallidus, Skistodiaptomus reighardi, and Onychodiaptomus sanguineus. Shallow mitochondrial DNA sequence divergences (maximum of 1.1%) among haplotypes of L. minutus from across its geographic range suggest that current morphological identification techniques reliably identify this species. In contrast, we found large mitochondrial DNA sequence divergences (14–22%) among populations within the currently recognized morphospecies of S. pallidus, S. reighardi, and O. sanguineus. However, pairwise sequence divergences within four distinct S. pallidus clades and within populations of S. reighardi and O. sanguineus were similarly low (maximum of 1.5%) as found within L. minutus as a whole. Thus, the S. pallidus, S. reighardi, and O. sanguineus morphospecies may be considered best as cryptic species complexes. Our study therefore indicates that morphological identifications, while sufficient for some species, likely underestimate the true species diversity of diaptomid copepods. As such, we stress the need for extensive taxonomic revision that integrates genetic, morphological, reproductive, and ecological analyses of this diverse and important group of freshwater zooplankton. Furthermore, we believe an extensive taxonomic revision will shed important insight into major questions regarding the roles of geography, phylogeny, and habitat on the frequency of cryptic species on earth. Handling editor: S. I. Dodson     

Allozyme divergence and evolution in the genusLens

The genusLens includes 5 taxonomic species:L. culinaris is cultivated andL. orientalis, L. odemensis, L. ervoides, andL. nigricans are wild. All the species are annual and almost exlusively selfers. The wild lentils are distributed over a large geographical area and form small disjunct populations which are composed of a small number of plants. 67Lens populations were assayed electrophoretically for 9 enzyme systems; 15 enzymic genes with 37 alleles were identified. The genetic distances (D) measured between the pairs of populations indicated a significantly greater similarity between populations belonging to the same taxonomic species. Assuming the populations represent a random sample of the variability in each of the species the genetic distances (D) between the 5 taxa were calculated. The shortest genetic distance was found betweenL. orientalis andL. culinaris. Another significant feature of the data is the apparent isolation ofL. nigricans from the other 4 species. The genetic distances between theLens species are compared to the patterns of crossability barriers between them.     

Isoenzyme differences between three closely related species of Lineus (Heteronemertea)

Starch-gel electrophoresis was employed to compare six enzymes in three closely related species of nemertean worms, Lineus ruber (Müller, 1774), Lineus sanguineus (Rathke, 1799), and Linens viridis (Müller, 1774). Differences in mobility recorded for most of the enzyme loci examined support the hypothesis that these nemerteans are distinct taxa.     

Repeated losses of TTAGG telomere repeats in evolution of beetles (Coleoptera)

We studied the occurrence of (TTAGG) _n telomere repeats in 12 species of beetles, representing main lineages of the Coleoptera phylogenetic tree, by Southern hybridization and fluorescence in situ hybridization (FISH). In contrast to other insect orders, beetles were heterogeneous with respect to the occurrence of TTAGG repeats. In addition, the presence or absence of (TTAGG) _n motif was irrespective of phylogenetic relationships. In the suborder Polyphaga, six species displayed positive hybridization signals. These were Silpha obscura, Agrilus viridis, Ampedus sanguineus, Stegobium paniceum, Oryzaephilus surinamensis, and Leptinotarsa decemlineata. Whereas negative signals were obtained in three polyphagan species, Geotrupes stercorarius, Thanasimus formicarius, and Sitophilus granarius. In the suborder Adephaga, the TTAGG sequence was present in one species, Graphoderus cinereus, and absent in two species, Orectochilus villosus and Pterostichus oblongopunctatus. We concluded that the telomerase-dependent (TTAGG) _n motif had been repeatedly lost in different phylogenetic branches of Coleoptera and probably replaced with another mechanism of telomere elongation. This had to happen at least 5–6 times. The results suggest a predisposition or a backup mechanism of telomere maintenance in the genome of beetles that enabled them to make frequent evolutionary changes in the telomere composition.     

Chloroplast DNA variation and evolution in the genus Lens Mill

 Chloroplast DNA (cpDNA) restriction site diversity was assessed by 21 enzyme/probe combinations in 30 accessions of six Lens species, including the recently recognized L. lamottei and L. tomentosus. A total of 118 fragments were scored and 26 restriction site mutations were identified. The cpDNA restriction pattern supports circumscribing L. lamottei and L. tomentosus as independent species. The value of the data for reconstructing phylogeny in the genus is discussed. The cpDNA of all 13 accessions of the lentil’s wild progenitor, L. culinaris subsp. orientalis, differed from that of the single lentil cultivars used in this study. This diversity indicates that other populations of this subspecies from Turkey and Syria examined by Mayer and Soltis (1994) are potentially the founder members of lentil. Examination of L. lamottei×L. nigricans hybrids between accessions having different restriction patterns showed paternal plastid inheritance in L. nigricans. Received: 2 July 1996 / Accepted: 19 July 1996     

Assessing extinction-risk of endangered plants using species distribution models: a case study of habitat depletion caused by the spread of greenhouses

The species distribution models (SDMs) are useful tools for investigating rare and endangered species as well as the environmental variables affecting them. In this paper, we propose the application of SDMs to assess the extinction-risk of plant species in relation to the spread of greenhouses in a Mediterranean landscape, where habitat depletion is one of the main causes of biodiversity loss. For this purpose, presence records of the model species (Linaria nigricans, a endemic and threatened species) and the greenhouses, a dataset of environmental variables, and different only presence-based modelling algorithms (Bioclim, Domain, GARP, MaxEnt and ENFA) were used to build SDMs for L. nigricans as well as for greenhouses. To evaluate the models a modified approach of the area-under-curve ROC was applied. Combining the most accurate models, we generated an extinction-risk model of L. nigricans populations, which enabled us to assess the sustainability of the most threatened populations. Our results show that is possible to model greenhouses spreading as a “biological invasion”. The procedure explained and used in this work is quite novel, and offers an objective spatial criterion intended for the management of natural resources and for the conservation of the biodiversity in areas threatened by habitat depletion processes as particular as greenhouses expansion.     

23 Phylogenetic position of Alaria Fistulosa (laminariales,phaeophyceae) based on nuclear its and plastid coding genes

Alaria is a common kelp genus generally found in the lower intertidal and shallow subtidal regions of rocky shores in the cold waters of the northern Hemisphere. About 16 species are currently recognized worldwide and, of these, A. fistulosa is distinguished by having hollow midrib and large blades with 10–30 m in length and 30–90 cm in width. It is the only canopy‐producing kelp in the northwest Pacific, where it is restricted to the waters of north Hokkaido, Kamchatka, Aleutian Islands, and Alaska. In order to know the phylogenetic position of A. fistulosa, sequences of nr DNA ITS and plastid rbcL including spacer and psaA regions were determined in A. fistulosa and compared with homologous positions of newly sequenced putative relatives and with published sequences of other kelp species. Combined data of ITS and Rubisco spacer show that A. fistulosa was more related to the clade of Lessoniopsis and Pterygophora than to the clade of other species of Alaria, which is supported by the rbcL and psaA sequence data. The topologies from nuclear and plastid DNA sequences lead to phylogenetic independence of A. fistulosa, which is clearly different from the genus Alaria.     

Die Erregungsübertragung bei Lineus sanguineus Rathke (Nemertini)

Zusammenfassung Mit histochemischer Methodik läßt sich in den Geweben von Lineus sanguineus (Nemertini) Acetylcholinesterase (ACHE; Spezifitätskontrolle: Eserin- und iso-OMPA-Test) nachweisen. Das Enzym kommt im zentralen und peripheren Nervensystem (Ganglienzellen, Neuropilem, Nervenfasern) vor. Daneben sind die Epithelien der Frontalorgane und Kopfspalten, die Cerebralorgane, die Muskulatur und die Blutzellen ACHE-reaktiv. Die Enzymverteilung läßt auf einen cholinergen Transmittermechanismus schließen.Die Befunde werden in Zusammenhang mit Befunden am aminergen Nervensystem von Lineus (Reutter, 1969) besprochen. Möglicherweise werden doppelt innervierte Sinnesorgane (z.B. Frontalorgane) cholinerg erregt und aminerg kontrolliert, analog zum Parasympathicus-Sympathicus-System der Wirbeltiere. Die ACHE-Aktivität im Bereich der Muskulatur, die frei von aminergen Fasern ist, läßt darauf schließen, daß sie cholinerg erregt wird.

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Impulse transmission in Lineus sanguineus Rathke (Nemertini)II. The cholinergic nervous system

Summary With histochemical methods acetylcholinesterase (ACHE; the specifity of which was tested with eserine and iso-OMPA) was demonstrated within several tissues of Lineus sanguineus (Nemertini). The enzyme is mainly located in the central and in the peripheral nervous system (neurons, neuropileme, and nerve fibers). The epithelia of the frontal organs and of the lateral head folds, the cerebral organs, the musculature and the blood cells are ACHE-reactive, too. The distribution of the enzyme may indicate cholinergic neurotransmission.The results are discussed in view to the adrenergic nervous system of Lineus (Reutter, 1969). Possibly double innervated organs (i.e. the frontal organs) are stimulated cholinergically and are controlled aminergically. This will be in analogy to the parasympathetic-sympathetic system of vertebrates. The activity of ACHE within the musculature, where no aminergic nerve fibers are found, indicates its cholinergic stimulation.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Clarification of the Rhipicephalus sanguineus group (Acari,Ixodoidea, Ixodidae). II. R. sanguineus (Latreille, 1806) and related species

In this, our second study on the biosystematics of the Rhipicephalus sanguineus group, we consider an additional five species found in the Afrotropical region, namely R. sanguineus, R. camicasi, R. guilhoni, R. moucheti and R. bergeoni.Cross-breeding experiments have shown that R. sanguineus (Latreille, 1806) sensu stricto is genetically distinct from R. camicasi Morel, Mouchet & Rodhain, 1976. Further cross-breeding trials confirmed that R. camicasi also occurs in Saudi Arabia: a field strain from this country was more productive than a laboratory-reared strain from Egypt. R. sanguineus, which parasitises mainly dogs, probably occurs throughout the Afrotropical region. R. camicasi parasitises both large and small domestic ruminants and is restricted to the arid and semi-arid lowlands of northeastern Africa and the Arabian peninsula. The larva, nymph, male and female of these two last named species are described with the aid of scanning electron micrographs (SEMs).The two western African species, R. guilhoni Morel & Vassiliades, 1963 and R. moucheti Morel, 1964, are accepted as valid members of the R. sanguineus group, but we have little material available for critical study. The male and female of R. guilhoni are briefly redescribed with the aid of SEMs. R. bergeoni Morel & Balis, 1976 occurs predominantly on cattle in the wetter highlands and subhighlands of Ethiopia and Sudan. The male and female are briefly described. Current morphological and ecological data suggest that the inclusion of this species in the R. sanguineus group is questionable.     

Comparative sperm ultrastructure in Nemertea

Although the monophyly of Nemertea is strongly supported by unique morphological characters and results of molecular phylogenetic studies, their ingroup relationships are largely unresolved. To contribute solving this problem we studied sperm ultrastructure of 12 nemertean species that belong to different subtaxa representing the commonly recognized major monophyletic groups. The study yielded a set of 26 characters with an unexpected variation among species of the same genus (Tubulanus and Procephalothrix species), whereas other species varied in metric values or only one character state (Ramphogordius). In some species, the sperm nucleus has grooves (Zygonemertes virescens, Amphiporus imparispinosus) that may be twisted and give a spiral shape to the sperm head (Paranemertes peregrina, Emplectonema gracile). To make the characters from sperm ultrastructure accessible for further phylogenetic analyses, they were coded in a character matrix. Published data for eight species turned out to be sufficiently detailed to be included. Comparative evaluation of available information on the sperm ultrastructure suggests that subtaxa of Heteronemertea and Hoplonemertea are supported as monophyletic by sperm morphology. However, the data do not provide information on the existing contradictions regarding the internal relationships of “Palaeonemertea.” Nevertheless, our study provides evidence that sperm ultrastructure yields numerous potentially informative characters that will be included in upcoming phylogenetic analyses. J. Morphol. 2010. © 2010 Wiley‐Liss, Inc.