SEARCH · PubMed Health

Results for “Parthenogenesis”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources

PubMed1999

An uncoupling of male and sexual egg production leads to reduced inbreeding in the cyclical parthenogen Daphnia

Cyclical parthenogenesis involves an alternation of parthenogenetic and sexual reproduction. In cyclical parthenogens with a short generation time, seasonal succession of clones switching to sexual reproduction at different periods of the growing season entails the risk of severe inbreeding with associated fitness costs. We show, however, that differences in genotype frequencies between males and sexual females result in a substantial reduction in the probability of selfing in natural Daphnia populations. This suggests that responses to male- and sexual egg-inducing stimuli may be uncoupled at the level of individual clones as a mechanism to avoid severe inbreeding.

Journal Article↗

PubMed2000

Wolbachia infection frequencies in insects: evidence of a global equilibrium?

Wolbachia are a group of cytoplasmically inherited bacteria that cause reproduction alterations in arthropods, including parthenogenesis, reproductive incompatibility, feminization of genetic males and male killing. Previous general surveys of insects in Panama and Britain found Wolbachia to be common, occurring in 16-22% of species. Here, using similar polymerase chain reaction methods, we report that 19.3% of a sample of temperate North American insects are infected with Wolbachia, a frequency strikingly similar to frequencies found in two other studies in widely separated locales. The results may indicate a widespread equilibrium of Wolbachia infection frequencies in insects whose maintenance remains to be explained. Alternatively, Wolbachia may be increasing in global insect communities. Within each of the three geographic regions surveyed, Hymenoptera are more frequently infected with A group Wolbachia and Lepidoptera more frequently infected with B group Wolbachia.

Animals↗

PubMed2003

Evolution as a critical component of plankton dynamics.

Microevolution is typically ignored as a factor directly affecting ongoing population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for more than 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific but reproducible plankton dynamics which are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.

Animals↗

PubMed2006

The emerging diversity of Rickettsia.

The best-known members of the bacterial genus Rickettsia are associates of blood-feeding arthropods that are pathogenic when transmitted to vertebrates. These species include the agents of acute human disease such as typhus and Rocky Mountain spotted fever. However, many other Rickettsia have been uncovered in recent surveys of bacteria associated with arthropods and other invertebrates; the hosts of these bacteria have no relationship with vertebrates. It is therefore perhaps more appropriate to consider Rickettsia as symbionts that are transmitted vertically in invertebrates, and secondarily as pathogens of vertebrates. In this review, we highlight the emerging diversity of Rickettsia species that are not associated with vertebrate pathogenicity. Phylogenetic analysis suggests multiple transitions between symbionts that are transmitted strictly vertically and those that exhibit mixed (horizontal and vertical) transmission. Rickettsia may thus be an excellent model system in which to study the evolution of transmission pathways. We also focus on the emergence of Rickettsia as a diverse reproductive manipulator of arthropods, similar to the closely related Wolbachia, including strains associated with male-killing, parthenogenesis, and effects on fertility. We emphasize some outstanding questions and potential research directions, and suggest ways in which the study of non-pathogenic Rickettsia can advance our understanding of their disease-causing relatives.

Animals↗

PubMed1994

Selection by parasites for clonal diversity and mixed mating.

On theoretical grounds, coevolutionary interactions with parasites can select for cross-fertilization, even when there is a twofold advantage gained by reproducing through uniparental means. The suspected advantage of cross-fertilization stems from the production of genetically rare offspring, which are expected to be more likely to escape infection by coevolving enemies. In the present study, we consider the effects that parasites have on parthenogenetic mutants in obligately sexual, dioecious populations. Computer simulations show that repeated mutation to parthenogenesis can lead to the accumulation of clones with different resistance genotypes, and that a moderately diverse set of clones could competitively exclude the ancestral sexual subpopulation. The simulations also show that, when there are reasonable rates of deleterious mutation, Muller's ratchet combined with coevolutionary interactions with parasites can lead to the evolutionary stability of cross-fertilization. In addition, we consider the effects that parasites can have on the evolution of uniparental reproduction in cosexual populations. Strategy models show that parasites and inbreeding depression could interact to select for evolutionarily stable reproductive strategies that involve mixtures of selfed and outcrossed progeny.

Animals↗

PubMed2005

SERK and APOSTART. Candidate genes for apomixis in Poa pratensis.

Seed production generally requires the mating of opposite sex gametes. Apomixis, an asexual mode of reproduction, avoids both meiotic reduction and egg fertilization. The essential feature of apomixis is that an embryo is formed autonomously by parthenogenesis from an unreduced egg of an embryo sac generated through apomeiosis. If apomixis were well understood and harnessed, it could be exploited to indefinitely propagate superior hybrids or specific genotypes bearing complex gene sets. A more profound knowledge of the mechanisms that regulate reproductive events would contribute fundamentally to understanding the genetic control of the apomictic pathway. In Poa pratensis, we isolated and characterized two genes, PpSERK (SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE) and APOSTART. These full-length genes were recovered by rapid amplification of cDNA ends and their temporal and spatial expression patterns were assessed by reverse transcription-polymerase chain reaction and in situ hybridization, respectively. The expression of PpSERK and APOSTART differed in apomictic and sexual genotypes. Their putative role in cell-signaling transduction cascades and trafficking events required during sporogenesis, gametogenesis, and embryogenesis in plants is reported and discussed. We propose that, in nucellar cells of apomictic genotypes, PpSERK is the switch that channels embryo sac development and that it may also redirect signaling gene products to compartments other than their typical ones. The involvement of APOSTART in meiosis and programmed cell death is also discussed.

Amino Acid Sequence↗

PubMed2003

Phylogenetic evidence for hybrid origins of asexual lineages in an aphid species.

Understanding the mode of origin of asexuality is central to ongoing debates concerning the evolution and maintenance of sexual reproduction in eukaryotes. This is because it has profound consequences for patterns of genetic diversity and ecological adaptability of asexual lineages, hence on the outcome of competition with sexual relatives both in short and longer terms. Among the possible routes to asexuality, hybridization is a very common mechanism in animals and plants. Aphids present frequent transitions from their ancestral reproductive mode (cyclical parthenogenesis) to permanent asexuality, but the mode of origin of asexual lineages is generally not known because it has never been thoroughly investigated with appropriate molecular tools. Rhopalosiphum padi is an aphid species with coexisting sexual (cyclically parthenogenetic) and asexual (obligately parthenogenetic) lineages that are genetically distinct. Previous studies have shown that asexual lineages of R. padi are heterozygous at most nuclear loci, suggesting either that they have undergone long-term asexuality (under which heterozygosity tends to increase) or that they have hybrid origins. To discriminate between these alternatives, we conducted an extensive molecular survey combining the sequence analysis of alleles of two nuclear DNA markers and mitochondrial DNA haplotypes in sexual and asexual lineages of R. padi. Both nuclear and cytoplasmic markers clearly showed that many asexual lineages have hybrid origins, the first such demonstration in aphids. Our results also indicated that asexuals result from multiple events of hybridization between R. padi and an unknown sibling species, and are of recent origin (contradicting previous estimates that asexual R. padi lineages were of moderate longevity). This study constitutes another example that putatively ancient asexual lineages are actually of much more recent origin than previously thought. It also presents a robust approach for testing whether hybrid origin of asexuality is also a common phenomenon in aphids.

Animals↗

PubMed2004

Intratetrad mating and the evolution of linkage relationships.

Mating among the immediate products of meiosis (intratetrad mating) is a common feature of many organisms with parthenogenesis or with mating-type determination in the haploid phase. Using a three-locus deterministic model we show that intratetrad mating, unlike other systems of mating, allows sheltering of deleterious recessive alleles even if there is only partial linkage between a mating locus and a load locus. Moreover, modifiers that reduce recombination between the load and mating-type locus will spread to fixation, even when there is no linkage disequilibrium between these loci in the population as a whole. This seeming contradiction to classical expectation is because partial linkage generates linkage disequilibrium among segregating loci within a tetrad, which then acts as the "mating unit."

Alleles↗

PubMed2004

Intra-individual coexistence of a Wolbachia strain required for host oogenesis with two strains inducing cytoplasmic incompatibility in the wasp Asobara tabida.

Cytoplasmically inherited symbiotic Wolbachia bacteria are known to induce a diversity of phenotypes on their numerous arthropod hosts including cytoplasmic incompatibility, male-killing, thelytokous parthenogenesis, and feminization. In the wasp Asobara tabida (Braconidae), in which all individuals harbor three genotypic Wolbachia strains (wAtab1, wAtab2 and wAtab3), the presence of Wolbachia is required for insect oogenesis. To elucidate the phenotype of each Wolbachia strain on host reproduction, especially on oogenesis, we established lines of A. tabida harboring different combinations of these three bacterial strains. We found that wAtab3 is essential for wasp oogenesis, whereas the two other strains, wAtabl and wAtab2, seem incapable to act on this function. Furthermore, interline crosses showed that strains wAtab1 and wAtab2 induce partial (about 78%) cytoplasmic incompatibility of the female mortality type. These results support the idea that bacterial genotype is a major factor determining the phenotype induced by Wolbachia on A. tabida hosts. We discuss the implications of these findings for current hypotheses regarding the evolutionary mechanisms by which females of A. tabida have become dependent on Wolbachia for oogenesis.

Animals↗

PubMed2004

Parasites and sexual reproduction in psychid moths.

Persistence of sexual reproduction among coexisting asexual competitors has been a major paradox in evolutionary biology. The number of empirical studies is still very limited, as few systems with coexisting sexual and strictly asexual lineages have been found. We studied the ecological mechanisms behind the simultaneous coexistence of a sexually and an asexually reproducing closely related species of psychid moth in Central Finland between 1999 and 2001. The two species compete for the same resources and are often infected by the same hymenopteran parasitoids. They are extremely morphologically and behaviorally similar and can be separated only by their reproductive strategy (sexual vs. asexual) or by genetic markers. We compared the life-history traits of these species in two locations where they coexist to test predictions of the cost-of-sex hypothesis. We did not find any difference in female size, number of larvae, or offspring survival between the sexuals and asexuals, indicating that sexuals are subject to cost of sex. We also used genetic markers to check and exclude the possibility of Wolbachia bacteria infection inducing parthenogenesis. None of the samples was infected by Wolbachia and, thus, it is unlikely that these bacteria could affect our results. We sampled 38 locations to study the prevalence of parasitoids and the moths' reproductive strategy. We found a strong positive correlation between prevalence of sexual reproduction and prevalence of parasitoids. In locations where parasitoids are rare asexuals exist in high densities, whereas in locations with a high parasitoid load the sexual species was dominant. Spatial distribution alone does not explain the results. We suggest that the parasite hypothesis for sex may offer an explanation for the persistence of sexual moths in this system.

Analysis of Variance↗

PubMed1995

Ovarian teratomas in mice lacking the protooncogene c-mos.

Parthenogenesis has been suggested to be tightly coupled with development of ovarian teratomas. Indeed, ovarian tumors developed in c-mos-deficient female mice, which are characterized by the parthenogenetic activation of oocytes. The tumors appeared at a frequency of 30% between 4 and 8 months of age, and did not develop in younger or older mice. Most of the tumors were benign and consisted of multi-focal cysts most notably with mature ectodermal components, but also with mesodermal and endodermal components. One among 17 tumors observed consisted of extra-embryonic tissues alone, and two bore malignant components with metastasis to peritoneal organs. The results strongly suggest the involvement of c-mos mutations in human germ cell tumors.

Age Factors↗

PubMed1988

Production of a hybrid between the bedbugs Cimex hemipterus and Cimex lectularius.

Of 479 eggs laid by female Cimex lectularius Linnaeus and C.hemipterus (Fabricius) mated by males of the other species, one was fertile and gave rise to a first stage nymph. The egg showed sculpturing typical of C.hemipterus, the female parent, and the nymph conformed to the narrow pronotum and abdomen of this species, being significantly different from C.lectularius in the width of the abdomen. Because the orientation and lengths of the bristles on the sides of the abdomen were distinctly different from C.hemipterus and closely resembled C.lectularius, the single nymph obtained from the cross C.hemipterus x lectularius was interpreted as being a hybrid rather than a product of parthenogenesis.

Animals↗

PubMed2004

Molecular evidence for the hybrid origin of species in the soft coral genus Alcyonium (Cnidaria: Anthozoa: Octocorallia).

Several recent studies have suggested that hybridization may play a previously unrecognized and important role in the evolution of corals. Our observations of polymorphic and recombinant sequences in the multicopy ribosomal internal transcribed spacer (ITS) region suggested the possible hybrid origin of two European soft coral species, Alcyonium hibernicum and Bellonella bocagei. To examine this possibility further we cloned and sequenced ITS-1 from multiple individuals and populations of these two species as well as two sympatric congeners, A. coralloides and A. sp. M2. Phylogenetic analyses separated the observed sequence variants into two distinct clades. All A. coralloides sequences belonged to clade A, while A. sp. M2 had only clade B sequences. A majority of A. hibernicum individuals, however, contained both clade A and B sequences that were identical to the predominant sequence variants found in A. coralloides and A. sp. M2, respectively. This pattern of additivity suggests that A. hibernicum originated from a hybrid cross between A. coralloides and A. sp. M2, a hypothesis that is supported by its unusual mode of reproduction (meiotic parthenogenesis). The predominant sequence variant found in B. bocagei was a unique, derived clade B sequence; in addition, however, most individuals of this species also had copies of a sequence identified as a recombinant between clade A and clade B sequence types. The presence of this recombinant sequence in the B. bocagei genome suggests that this species may also be the product of past hybridization events within the clade. Reticulate evolution may explain the failure of several previous studies to resolve the phylogeny of these four species.

Animals↗

PubMed2004

Distribution of the bacterial symbiont Cardinium in arthropods.

Abstract 'Candidatus Cardinium', a recently described bacterium from the Bacteroidetes group, is involved in diverse reproduction alterations of its arthropod hosts, including cytoplasmic incompatibility, parthenogenesis and feminization. To estimate the incidence rate of Cardinium and explore the limits of its host range, 99 insect and mite species were screened, using primers designed to amplify a portion of Cardinium 16S ribosomal DNA (rDNA). These arthropods were also screened for the presence of the better-known reproductive manipulator, Wolbachia. Six per cent of the species screened tested positive for Cardinium, compared with 24% positive for Wolbachia. Of the 85 insects screened, Cardinium was found in four parasitic wasp species and one armoured scale insect. Of the 14 mite species examined, one predatory mite was found to carry the symbiont. A phylogenetic analysis of all known Cardinium 16S rDNA sequences shows that distantly related arthropods can harbour closely related symbionts, a pattern typical of horizontal transmission. However, closely related Cardinium were found to cluster among closely related hosts, suggesting host specialization and horizontal transmission among closely related hosts. Finally, the primers used revealed the presence of a second lineage of Bacteroidetes symbionts, not related to Cardinium, in two insect species. This second symbiont lineage is closely allied with other arthropod symbionts, such as Blattabacterium, the primary symbionts of cockroaches, and male-killing symbionts of ladybird beetles. The combined data suggest the presence of a diverse assemblage of arthropod-associated Bacteroidetes bacteria that are likely to strongly influence their hosts' biology.

Animals↗

PubMed2005

Hierarchical analysis of population genetic structure in the monogynous ant Cataglyphis cursor using microsatellite and mitochondrial DNA markers.

Despite having winged queens, female dispersal in the monogynous ant Cataglyphis cursor is likely to be restricted because colonies reproduce by fission. We investigated the pattern of population genetic structure of this species using eight microsatellite markers and a mitochondrial DNA (mtDNA) sequence, in order to examine the extent of female and nuclear gene flow in two types of habitat. Sampling was carried out at a large spatial scale (16 sites from 2.5 to 120 km apart) as well as at a fine spatial scale (two 4.5-km transects, one in each habitat type). The strong spatial clustering of mtDNA observed at the fine spatial scale strongly supported a restricted effective female dispersal. In agreement, patterns of the mtDNA haplotypes observed at large and fine spatial scales suggested that new sites are colonized by nearby sites. Isolation by distance and significant nuclear genetic structure have been detected at all the spatial scales investigated. The level of local genetic differentiation for mitochondrial marker was 15 times higher than for the nuclear markers, suggesting differences in dispersal pattern between the two sexes. However, male gene flow was not sufficient to prevent significant nuclear genetic differentiation even at short distances (500 m). Isolation-by-distance patterns differed between the two habitat types, with a linear decrease of genetic similarities with distance observed only in the more continuous of the two habitats. Finally, despite these low dispersal capacities and the potential use of parthenogenesis to produce new queens, no signs of reduction of nuclear genetic diversity was detected in C. cursor populations.

Animals↗

PubMed1994

Taxonomic position of the rickettsiae: current knowledge.

The term rickettsiae initially encompassed all intracellular bacteria. Early rickettsial taxonomy was based on a comparison of a few phenotypic characteristics and recently, molecular studies brought new bases for rickettsial taxonomy. All rickettsial species studied so far belong to the alpha and gamma groups of the Proteobacteria. Ehrlichiae complex groups Cowdria ruminantium, Anaplasma marginale and Wolbachia pipientis and the related parthenogenesis and cytoplasmic incompatibility bacteria, whereas Rochalimaea species group with Bartonella bacilliformis. Rickettsia tsutsugamushi may form an independent lineage, whereas molecular data allow to regroup serologically defined typhus and spotted fever group rickettsiae. The true scale of Rickettsia and Coxiella genera remain to be determined.

Alphaproteobacteria↗

PubMed2002

Characterization of Wolbachia host cell range via the in vitro establishment of infections.

Maternally transmitted bacteria of the genus Wolbachia are obligate, intracellular symbionts that are frequently found in insects and cause a diverse array of reproductive manipulations, including cytoplasmic incompatibility, male killing, parthenogenesis, and feminization. Despite the existence of a broad range of scientific interest, many aspects of Wolbachia research have been limited to laboratories with insect-rearing facilities. The inability to culture these bacteria outside of the invertebrate host has also led to the existing bias of Wolbachia research toward infections that occur in host insects that are easily reared. Here, we demonstrate that Wolbachia infections can be simply established, stably maintained, and cryogenically stored in vitro using standard tissue culture techniques. We have examined Wolbachia host range by introducing different Wolbachia types into a single tissue culture. The results show that an Aedes albopictus (Diptera: Culicidae) cell line can support five different Wolbachia infection types derived from Drosophila simulans (Diptera: Drosophilidae), Culex pipiens (Culicidae), and Cadra cautella (Lepidoptera: Phycitidae). These bacterial types include infection types that have been assigned to two of the major Wolbachia clades. As an additional examination of Wolbachia host cell range, we demonstrated that a Wolbachia strain from D. simulans could be established in host insect cell lines derived from A. albopictus, Spodoptera frugiperda (Lepidoptera: Noctuidae), and Drosophila melanogaster. These results will facilitate the development of a Wolbachia stock center, permitting novel approaches for the study of Wolbachia infections and encouraging Wolbachia research in additional laboratories.

Aedes↗

PubMed1998

Cloning and characterization of a gene encoding the major surface protein of the bacterial endosymbiont Wolbachia pipientis.

The maternally inherited intracellular symbiont Wolbachia pipientis is well known for inducing a variety of reproductive abnormalities in the diverse arthropod hosts it infects. It has been implicated in causing cytoplasmic incompatibility, parthenogenesis, and the feminization of genetic males in different hosts. The molecular mechanisms by which this fastidious intracellular bacterium causes these reproductive and developmental abnormalities have not yet been determined. In this paper, we report on (i) the purification of one of the most abundantly expressed Wolbachia proteins from infected Drosophila eggs and (ii) the subsequent cloning and characterization of the gene (wsp) that encodes it. The functionality of the wsp promoter region was also successfully tested in Escherichia coli. Comparison of sequences of this gene from different strains of Wolbachia revealed a high level of variability. This sequence variation correlated with the ability of certain Wolbachia strains to induce or rescue the cytoplasmic incompatibility phenotype in infected insects. As such, this gene will be a very useful tool for Wolbachia strain typing and phylogenetic analysis, as well as understanding the molecular basis of the interaction of Wolbachia with its host.

Amino Acid Sequence↗