Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Life Cycle”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 19 recordsLinked to original sources
PubMed2004

A classification system for mosquito life cycles: life cycle types for mosquitoes of the northeastern United States.

A system for the classification of mosquito life cycle types is presented for mosquito species found in the northeastern United States. Primary subdivisions include Univoltine Aedine, Multivoltine Aedine, Multivoltine Culex/Anopheles, and Unique Life Cycle Types. A montotypic subdivision groups life cycle types restricted to single species. The classification system recognizes 11 shared life cycle types and three that are limited to single species. Criteria for assignments include: 1) where the eggs are laid, 2) typical larval habitat, 3) number of generations per year, and 4) stage of the life cycle that overwinters. The 14 types in the northeast have been named for common model species. A list of species for each life cycle type is provided to serve as a teaching aid for students of mosquito biology.

Animals↗
PubMed1994

Competitive exclusion and coexistence of species with complex life cycles.

Complex life cycles are life histories in which abrupt ontogenetic transformations and niche shifts occur at the transition between stages. The effects of this niche differentiation between stages on coexistence between species are investigated using a simple discrete model of two-stage populations. The model incorporates exploitation competition for limiting resources within stages, between stages, and between species. While species with simple life cycles can never coexist at equilibrium, stable coexistence is shown to be possible between species with complex life cycles provided that (1) one species is more efficient in resource utilization at low resource abundance in the larval stage while the other is more efficient at low resource abundance in the adult stage; and (2) each species is mainly limited by that stage which is less efficient at low resource abundance. Stable coexistence is somewhat easier between a species with a simple life cycle and one with a complex life cycle. It requires that (1) the species with the simple life cycle should not be decidedly more efficient than that with the complex life cycle in utilizing the resource on which it lives; and (2) the main resource limitation for the species with a complex life cycle should occur in that stage which escapes competition with the species with a simple life cycle. Lastly, a complex life cycle can offer a decisive competitive superiority over a simple life cycle in interspecific competition, which suggests that competition can be a driving force of the evolution of complex life cycles.

Animals↗
PubMed1950

Studies on the life cycle of spirochetes; the life cycle of the Nichols pathogenic Treponema pallidum in the rabbit testis as seen by phase contrast microscopy.

A series of observations with the phase contrast microscope on the occurrence of a complex life cycle in the pathogenic Treponema pallidum as it occurs in the syphilitic rabbit testis has been presented and it seems likely from these observations that there are two means of vegetative reproduction, consisting of (1) transverse division (the most important under usual conditions); and (2) the production of gemmae or buds which eventuate into unispirochetal cysts comparable to those described for saprophytic forms, within each of which single spirochetes develop and differentiate, and from which they subsequently emerge. In addition preliminary evidence is presented which suggests that a more complex process is involved in which multispirochetal cysts develop following aggregation of two or more organisms. Within each of these larger cysts numerous organisms develop and subsequently emerge as tangled ropes. Following emergence, they subsequently undergo transverse division and gemmae formation, and so reproduce vegetatively. Subsequent papers will elaborate upon these processes.

Animals↗
PubMed1989

Psychological issues affecting women throughout the life cycle.

Throughout life, some psychological issues facing women are shared with men, and some are unique to women. This article compares the traditional life cycle perspective with the complementary perspective of different lines of development that characterize women's lives. Traditionally, there was a concept, especially of the woman's life cycle, linking growth and reproduction to expected work, social status, and sources of self-esteem. Today, there is no single life cycle for women, but rather a number of predictable areas of growth and development. The article will explore the biologic-reproductive life cycle, the family-marital life cycle, and the educational-vocational life cycle, from before birth to old age. It will also review psychological problems most common at each stage, and it will discuss how societal changes in expectations of women may be changing women's growth and development today.

Aging↗
PubMed2002

Life cycle emission distributions within the economy: implications for life cycle impact assessment.

Refinements of methods for life cycle impact assessment (LCIA) are directed at removing unjustified simplifications and quantifying and reducing uncertainties in results. The amount of uncertainty reduction that is actually achieved through LCIA method refinement depends on the structure of the life cycle inventory model. We investigate the general structure of inventory models using an economic input/output (I/O) life cycle assessment model of the U.S. economy. In particular, we study the results of applying a streamlining algorithm to the I/O LCA model. The streamlining algorithm retains only those "branches" of the process tree that are jointly required to account for a specified fraction of the total impacts upstream of each point in the tree. We examine the implications of these "tree pruning" results for site-informed LCIA. Percentiles are presented for U.S. commodities and several important pollutants, for the share of total upstream emissions contributed by the set of processes in each supply tier, that is, each set of processes that directly supply inputs to another set of processes Capturing at least 90% of the total direct plus upstream emissions for criteria air pollutants and toxic releases for at least 75% of the commodities in the U.S. economy requires full modeling of direct emissions plus the first five supply tiers. The requirements for capturing a high percentage (e.g., >80%) of total emissions vary widely across products or commodities. To capture more than 60% of total emissions for more than half of all commodities requires models with more than 4,000 process instances. To well characterize the total impacts of products, life cycle impact assessment methods must characterize foreground process impacts in a site-informed way and mean impacts of far-removed processes in an unbiased way.

Air Pollutants↗
PubMed2005

Human papillomavirus type 16 E1circumflexE4 contributes to multiple facets of the papillomavirus life cycle.

The life cycle of human papillomaviruses (HPVs) is tightly linked to the differentiation program of the host's stratified epithelia that it infects. E1(circumflex)E4 is a viral protein that has been ascribed multiple biochemical properties of potential biological relevance to the viral life cycle. To identify the role(s) of the viral E1(circumflex)E4 protein in the HPV life cycle, we characterized the properties of HPV type 16 (HPV16) genomes harboring mutations in the E4 gene in NIKS cells, a spontaneously immortalized keratinocyte cell line that when grown in organotypic raft cultures supports the HPV life cycle. We learned that E1(circumflex)E4 contributes to the replication of the viral plasmid genome as a nuclear plasmid in basal cells, in which we also found E1(circumflex)E4 protein to be expressed at low levels. In the suprabasal compartment of organotypic raft cultures harboring E1(circumflex)E4 mutant HPV16 genomes there were alterations in the frequency of suprabasal cells supporting DNA synthesis, the levels of viral DNA amplification, and the degree to which the virus perturbs differentiation. Interestingly, the comparison of the phenotypes of various mutations in E4 indicated that the E1(circumflex)E4 protein-encoding requirements for these various processes differed. These data support the hypothesis that E1(circumflex)E4 is a multifunctional protein and that the different properties of E1(circumflex)E4 contribute to different processes in both the early and late stages of the virus life cycle.

Cell Line↗
PubMed2003

Two separate growth phases during the development of Leishmania in sand flies: implications for understanding the life cycle.

The life cycle of Leishmania alternates between two main morphological forms: intracellular amastigotes in the mammalian host and motile promastigotes in the sand fly vector. Several different forms of promastigote have been described in sandfly infections, the best known of these being metacyclic promastigotes, the mammal-infective stages. Here we provide evidence that for Leishmania (Leishmania) mexicana and Leishmania (Leishmania) infantum (syn. chagasi) there are two separate, consecutive growth cycles during development in Lutzomyia longipalpis sand flies involving four distinct life cycle stages. The first growth cycle is initiated by procyclic promastigotes, which divide in the bloodmeal in the abdominal midgut and subsequently give rise to non-dividing nectomonad promastigotes. Nectomonad forms are responsible for anterior migration of the infection and in turn transform into leptomonad promastigotes that initiate a second growth cycle in the anterior midgut. Subsequently, leptomonad promastigotes differentiate into non-dividing metacyclic promastigotes in preparation for transmission to a mammalian host. Differences in timing, prevalence and persistence of the four promastigote stages were observed between L. mexicana and L. infantum in vivo, which were reproduced in cultures initiated with lesion amastigotes, indicating that development is to some extent governed by a programmed series of events. A new scheme for the life cycle in the subgenus Leishmania (Leishmania) is proposed that incorporates these findings.

Animals↗
PubMedDate not supplied

On nitric oxide signaling, metamorphosis, and the evolution of biphasic life cycles.

Complex life cycles are ancient and widely distributed, particularly so in the marine environment. Generally, the marine biphasic life cycle consists of pre-reproductive stages that exist in the plankton for various periods of time before settling and transforming into a benthic reproductive stage. Pre-reproductive stages are frequently phenotypically distinct from the reproductive stage, and the life cycle transition (metamorphosis) linking the larval and juvenile stages varies in extent of change but is usually rapid. Selection of suitable adult sites apparently involves the capacity to retain the larval state after metamorphic competence is reached. Thus two perennial and related questions arise: How are environmentally dependent rapid transitions between two differentiated functional life history stages regulated (a physiological issue) and how does biphasy arise (a developmental issue)? Two species of solitary ascidian, a sea urchin and a gastropod, share a nitric oxide (NO)-dependent signaling pathway as a repressive regulator of metamorphosis. NO also regulates life history transitions among several simple eukaryotes. We review the unique properties of inhibitory NO signaling and propose that (a) NO is an ancient and widely used regulator of biphasic life histories, (b) the evolution of biphasy in the metazoa involved repression of juvenile development, (c) functional reasons why NO-based signaling is well suited as an inhibitory regulator of metamorphosis after competence is reached, and (d) signaling pathways that regulate metamorphosis of extant marine animals may have participated in the evolution of larvae.

Animals↗
PubMed2006

An approach to revealing blood fluke life cycles, taxonomy, and diversity: provision of key reference data including DNA sequence from single life cycle stages.

Revealing diversity among extant blood flukes, and the patterns of relationships among them, has been hindered by the difficulty of determining if specimens described from different life cycle stages, hosts, geographic localities, and times represent the same or different species. Persistent collection of all available life cycle stages and provision of exact collection localities, host identification, reference DNA sequences for the parasite, and voucher specimens eventually will provide the framework needed to piece together individual life cycles and facilitate reconciliation with classical taxonomic descriptions, including those based on single life cycle stages. It also provides a means to document unique or rare species that might only ever be recovered from a single life cycle stage. With an emphasis on the value of new information from field collections of any available life cycle stages, here we provide data for several blood fluke cercariae from freshwater snails from Kenya, Uganda, and Australia. Similar data are provided for adult worms of Macrobilharzia macrobilharzia and miracidia of Bivitellobilharzia nairi. Some schistosome and sanguinicolid cercariae that we recovered have peculiar morphological features, and our phylogenetic analyses (18S and 28S rDNA and mtDNA CO1) suggest that 2 of the new schistosome specimens likely represent previously unknown lineages. Our results also provide new insights into 2 of the 4 remaining schistosome genera yet to be extensively characterized with respect to their position in molecular phylogenies, Macrobilharzia and Bivitellobilharzia. The accessibility of each life cycle stage is likely to vary dramatically from one parasite species to the next, and our examples validate the potential usefulness of information gleaned from even one such stage, whatever it might be.

Animals↗
PubMed1977

The parasitic ecology of the rodent mite, Myobia musculi. IV. Life cycle.

The life cycle of Myobia musculi was determined by daily examination (under anesthesia) of experimentally infested mice. It was found that the larval period lasted 10 days followed by a 5-day nymphal period. Adult forms were seen on the 16th day. Adults produced fertile eggs within 24 hours of their appearance and eggs hatched in 7 days. Thus, the life cycle was completed in 23 days. Application of this information for a successful treatment regimen was discussed. Any treatment which does not kill embryonated eggs must be repeated subsequent to hatching of the eggs but prior to oviposition of fertile eggs by newly hatched females.

Animals↗
PubMed2002

Thermoregulation in a parasite's life cycle.

The life cycle of the malaria parasite Plasmodium falciparum goes through three developmental stages (schizogony, gametogony and sporogony), each of which presents different environmental constraints that must be met by an adaptive response in the parasite. Here we show that thermoregulation, in which the transcription of select RNAs is upregulated at cooler temperatures, is crucial to the developmental transition that occurs during the transmission of P. falciparum from human to mosquito. Our findings offer new insight into how the malaria parasite senses and reacts to its environment.

Adaptation, Physiological↗
PubMed1963

LIFE CYCLE ANALYSIS OF MAMMALIAN CELLS. I. A METHOD FOR LOCALIZING METABOLIC EVENTS WITHIN THE LIFE CYCLE, AND ITS APPLICATION TO THE ACTION OF COLCEMIDE AND SUBLETHAL DOSES OF X-IRRADIATION.

Equations are presented describing the accumulation of cells at any part of the life cycle as a result of addition of specific blocking agents. An experimental methodology using these relationships is described which makes possible analysis with relatively high resolution of the distribution of cells throughout the life cycle in normal cultures or those treated with various agents. The action of colcemide on S3 HeLa cells studied by this method revealed that colcemide has no effect on the G1, S, or G2 stages; it blocks cells quantitatively at the metaphase-anaphase region; but it accumulates mitotic figures only from the cells which have not yet entered mitosis at the time of its addition. The technique was also applied to study the efficiency of x-irradiation in delaying the entrance of G2 cells into mitosis. A definite lag was found at the lowest dose studied which was 9 rads. Only the cells confined to a central region of G2 at the time of irradiation are affected by this dose.

Animals↗
PubMed1993

Life cycle benefits.

Life cycle benefits are designed to meet the needs of employees throughout the stages of life. Many employers in both the public and private sectors are finding that this approach to benefits makes sense from a number of perspectives.

Absenteeism↗