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Results for “Reproduction, Asexual”

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At least 55 records · Page 3Linked to original sources

PubMed2007

Botryllus schlosseri: a model ascidian for the study of asexual reproduction.

Botryllus schlosseri, a cosmopolitan colonial ascidian reared in the laboratory for more than 50 years, reproduces both sexually and asexually and is used as a model organism for studying a variety of biological problems. Colonies are formed of numerous, genetically identical individuals (zooids) and undergo cyclical generation changes in which the adult zooids die and are replaced by their maturing buds. Because the progression of the colonial life cycle is intimately correlated with blastogenesis, a shared staging method of bud development is required to compare data coming from different laboratories. With the present review, we aim (1) to introduce B. schlosseri as a valuable chordate model to study various biological problems and, especially, sexual and asexual development; (2) to offer a detailed description of bud development up to adulthood and the attainment of sexual maturity; (3) to re-examine Sabbadin's (1955) staging method and re-propose it as a simple tool for in vivo recognition of the main morphogenetic events and recurrent changes in the blastogenetic cycle, as it refers to the developmental stages of buds and adults.

Animals↗

PubMedDate not supplied

[Asexual reproduction of planarians: metric studies].

A relationship was studied between fission and restoration of body and its individual parts under different experimental conditions in planarians of the Dugesia tigrina asexual race. The body and its fragments were studied morphomterically. After fission, the growth of planarians demonstrated topographic differences. The separated tail fragments and postpharyngeal area, in which the zone of fission is formed, were growing at the highest rate. More active growth was also noted over the long body axis. Fission and growth were more active in isolated planarians, as compared to those kept in groups.

Animals↗

PubMedDate not supplied

[Effect of weak and superweak magnetic fields on intensity and asexual reproduction of the planarian Dugesia tigrina].

It was shown that the exposure to combined weak and extraweak magnetic fields (permanent component 42 microT; variable component of an amplitude of 100 nT, frequency 1-60 Hz) increases the intensity of asexual propagation of planarians Dugesia tigrina. The effect of combined magnetic fields is most pronounced at frequencies of 1, 3.7, and 32 Hz. The presence of concomitant technogeneous fields (50 Hz, 30 nT) does not markedly influence the effects of weak magnetic fields with a small variable component. Upon realization of effects of weak magnetic fields, their both components are of great importance; the absence of one (permanent) component changes the sing of the effect to the opposite. The transfer of the effect to planarians through water pretreated with magnetic fields probably indicates that aqueous medium is involved in the realization of biological effects of weak magnetic fields.

Animals↗

PubMed2001

The importance of sexual and asexual reproduction in the recent evolution of Allium vineale.

In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. In the whole sample, 77 nuclear multilocus genotypes and four chloroplast haplotypes (chlorotypes) were found. Populations exhibited a high degree of subdivision for nuclear and cytoplasmic markers as estimated from hierarchical F-statistics; at the same time, identical chlorotypes could be found in populations separated by large distances. Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring. Nevertheless, within each chlorotype, the distribution of markers from pairs of nuclear loci was incompatible with a purely clonal structure, suggesting that many multilocus genotypes have originated by sexual recombination rather than by mutation within asexual lineages. It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe.

Allium↗

PubMed2004

Light-regulated asexual reproduction in Paecilomyces fumosoroseus.

The entomopathogenic fungus Paecilomyces fumosoroseus has been successfully used in the control of several insect pests. Asexually produced spores (conidia) are the means for dispersal and transmission of the entomopathogen; upon contact with the insect cuticle they germinate and penetrate the host. In model fungal systems it has been found that phototropism, resetting of the circadian rhythm, the induction of carotenogenesis and the development of reproductive structures are controlled by blue light. The effect of light quality on conidial yield of P. fumosoroseus was investigated. Incubation in total darkness resulted in continued vegetative growth and lack of reproductive structures. In contrast, growth of the fungus in continuous illumination or under a night-day regime resulted in prolific formation of conidiophores bearing abundant mature conidia. Conidiation was photoinduced in competent mycelia by a single pulse of blue light and colonies were competent only after they had grown at least 72 h under total darkness. The fluence-response curves generated with blue light indicated that the minimal fluence required for the photomorphogenetic response was 180 micro mol m(-2) and the half-maximal response was at 400 micro mol m(-2). A fluence of 540 micro mol m(-2) was enough to saturate the system, inducing the maximum production of 2.12x10(8) conidia per colony. Higher light intensities markedly decreased conidiation, suggesting the occurrence of a process of adaptation. The authors propose the existence of a dual light-perception system with at least two photoreceptors in P. fumosoroseus, one promoting and one inhibiting conidiation.

Animals↗

PubMed2004

Population genetic structure of Titanotrichum oldhamii (Gesneriaceae), a subtropical bulbiliferous plant with mixed sexual and asexual reproduction.

BACKGROUND AND AIMS: Titanotrichum oldhamii is a monotypic genus distributed in Taiwan, adjacent regions of China and the Ryukyu Isands of Japan. Its conservation status is vulnerable as most populations are small and widely scattered. Titanotrichum has a mixed system of reproduction with vegetative bulbils and seeds. The aim of this study was to understand the population genetic structure of Titanotrichum in relation to its specific reproductive behaviour and to determine possible implications for conservation strategies. METHODS: After an extensive inventory of most wild populations of Titanotrichum in East Asia, samples from 25 populations within its major distribution were carried out utilizing RAPD and inter-SSR molecular fingerprinting analysis. KEY RESULTS: The findings support the conclusion that many populations reproduce predominantly asexually but that some genetic variation still exists within populations. However, significant amounts of variation exist between populations, perhaps reflecting population differentiation by drift. This partitioning of genetic diversity indicates that the level of inter-population gene exchange is extremely low. These findings are consistent with field observations of very limited seed production. The Chinese populations are similar to those of Northern Taiwan, while the Ryukyu populations fall within the range of variation of the north-central Taiwan populations. The Taiwanese populations are relatively variable and differentiation between north, east and south Taiwan is evident. CONCLUSIONS: The distribution of Titanotrichum seems to be consistent with a former land connection between China, Taiwan and the Ryukyu Islands at a glacial maximum during the Quaternary, followed by progressive fragmentation of the populations. North-central Taiwan is the centre of genetic diversity, possibly due to the proximity of the former land bridge between the regions, together with the variety of suitable habitats in north Taiwan. The significance of these findings for conservation is discussed.

Base Sequence↗

PubMed2004

Regeneration and asexual reproduction share common molecular changes: upregulation of a neural glycoepitope during morphallaxis in Lumbriculus.

Neural morphallaxis is a regenerative process characterized by wide-spread anatomical and physiological changes in an adult nervous system. During segmental regeneration of the annelid worm, Lumbriculus variegatus, neural morphallaxis involved a reorganization of sensory, interneuronal, and motor systems as posterior fragments gained a more anterior body position. A monoclonal antibody, Lan 3-2, which labels a neural glyco-domain in the leech, was reactive in Lumbriculus. In the worm, this antibody labeled neural structures, particularly axonal tracts and giant fiber pathways of the central nervous system. A 60kDa protein, possessing a lumbriculid mannose-rich glycoepitope, was upregulated during neural morphallaxis, peaking in its expression at 3 weeks post-amputation. Peak upregulation of the Lan 3-2 epitope, or the protein possessing it, corresponded to the time of major neurobehavioral plasticity during regeneration. Analyses of asexually reproducing animals also revealed induction of the Lan 3-2 epitope. In this developmental context, Lan 3-2 epitope upregulation was also confined to segments expressing both changes in positional identity and neurobehavioral plasticity, but these molecular and behavioral changes occurred prior to body fragmentation. These results suggest that the lumbriculid Lan 3-2 glycoepitope and proteins that bear them have been co-opted for neural morphallactic programs, induced both in anticipation of reproductive fragmentation and in compensation for injury-induced fragmentation.

Animals↗

PubMed1999

Risky business: sexual and asexual reproduction in variable environments.

Patterns of reproductive uncertainty can have an important influence on population dynamics. There is a crucial distinction between what we describe here as aggregate uncertainty (in which reproductive output in each generation is correlated among the individuals in a population) and idiosyncratic risk (in which reproductive output is independent across individuals). All else being equal, populations experiencing idiosyncratic risk enjoy a higher asymptotic growth rate than do those experiencing aggregate uncertainty. Therefore individuals in populations of the former type will have a competitive advantage over individuals in populations of the latter type. Applying this distinction to models of randomly fluctuating environments, we point out that genetic variation among offspring can serve to reduce aggregate uncertainty, transforming it into a more idiosyncratic form of risk. We show that this transformation underlies the dynamics observed in several previous models of the role of outcrossing in the evolution of sex.

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PubMed1974