Cycle Synchrony Research Articles

Do nomadic avian predators synchronize population fluctuations of small mammals? a field experiment.

Three-to-five-year population oscillations of northern small rodents are usually synchronous over hundreds of square kilometers. This regional synchrony could be due to similarity in climatic factors, or due to nomadic predators reducing the patches of high prey density close to the average density of a larger area. We estimated avian predator and small rodent densities in 4-5 predator reduction and 4-5 control areas (c. 3 km2 each) during 1989-1992 in western Finland. We studied whether nomadic avian predators concentrate at high prey density areas, and whether this decreases spatial variation in prey density. The yearly mean number of avian predator breeding territories was 0.2-1.0 in reduction areas and 3.0-8.2 in control areas. Hunting birds of prey concentrated in high prey density areas after their breeding season (August), but not necessarily during the breeding season (April to June), when they were constrained to hunt in vicinity of the nest. The experimental reduction of breeding avian predators increased variation in prey density among areas but not within areas. The difference in variation between raptor reduction and control areas was largest in the late breeding season of birds of prey, and decreased rapidly after the breeding season. These results appeared to support the hypothesis that the geographic synchrony of population cycles in small mammals may be driven by nomadic predators concentrating in high prey density areas. Predation and climatic factors apparently are complementary, rather than exclusive, factors in contributing to the synchrony.

POPULATION CYCLES IN NORTHERN SMALL MAMMALS

I. The regular multiannual oscillations of small mammals at northern latitudes have been a subject of intensive study from the beginning of this century. The existence of a subjective bias in the research due to different schools of study together with a long series of failures and seemingly contradictory results in experiments testing a multitude of hypotheses have brought confusion to the field of study. Much of this confusion has resulted from a failure to recognize sharply the problem studied, which in turn has masked the progress made during the years. Northern mammal cycles are not a single problem but a composition of many related problems. Every problem may have a single-factor explanation, but even with a single-factor explanation, one factor is not necessarily an answer to all of the related problems. 2. At present, we can state that the cyclicity is caused by a predator-prey interaction. Both the 8-11-year and the 3-5-year cycles may be special cases of a more general cycle, most likely caused by a herbivore-resident specialist predator interaction, where the period of the cycles is determined by size-related constraints affecting the increase rate of the populations. The factors determining the amplitude of the cycles probably vary regionally and/or temporally. The operation of generalist and nomadic predators is largely responsible for the regional and geographic synchrony in cycles, although climatic factors may also contribute to the geographic synchrony. The northern distribution of animal communities; both these factors affect the density of generalist predators, which act as a stabilizing factor in the system. The age-related survival pattern seems to be mainly caused by predation, and the cyclically fluctuating reproductive output and mean body mass may be caused by changes in prey behaviour in response to fluctuating predation risk. Thus, we can already give a plausible explanation for most problems related to northern mammal cycles. 3. In all problems discussed, predation seems to be involved, and in most problems, it seems to be the factor which explains the observed patterns. Thus, as a generalization, it can be said that predation seems to be the key factor in the explanation of the northern multiannual cycles of small mammals. 4. There seems to be a linkage between diversity and cyclicity, probably because the diversity of the community (the number of prey species available) may determine the diet choice of a predator, which in turn determines whether the predators have a stabilizing or a destabilizing impact on prey populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Variability and partial synchrony of the cell cycle in the germinal zone of the early embryonic cerebral cortex

Cell cycle parameters were estimated using the cumulative 3H-thymidine S-phase labeling and percentage of labeled mitoses methods in the embryonic day 14 and 15 germinal zone of the rat cerebral cortex. The shortest cell cycle time was seen in the dorsal neocortex and the longest in the lateral neocortex and fimbria (the latter also had a low growth fraction). No differences were observed in cell cycle times between the cells in the ventricular and subventricular zone in the same neocortical region. The results suggest gradients of lengthening cell cycle times extending ventrolaterally and ventromedially from the dorsomedial neocortex. Although a majority of proliferating cells in individual cortical regions seem to belong to one population in terms of cell kinetics, several pieces of evidence suggest some heterogeneity: the asymmetric shapes of the percentages of labeled mitoses curves, the small population of noncycling neuroepithelial cells in the neocortex and mesocortex, and small population of cells that become pyknotic. Groups of DNA-synthesizing nuclei that were ectopically located in the inner half of the ventricular zone also indicate the existence of different subpopulations of neuroepithelial cells. In addition, after a pulse injection of 3H-thymidine the germinal zone is characterized by alternating clusters of heavily and lightly labeled cell nuclei that may reflect the simultaneous passage of a cluster of cells through the same portion of S-phase. We suggest that partial cell cycle synchrony within groups of ventricular cells may explain the presence of these iterative cell kinetic patterns in the developing cortex.

Ionizing radiation damage to cells: effects of cell cycle redistribution.

If a population of cycling cells is exposed to a fixed dose of ionizing radiation delivered over time T, it is sometimes observed that increasing T increases the amount of cell killing. This is essentially because at first the radiation preferentially kills cells in a sensitive portion of the cycle and the surviving, more resistant cells then have time to reach more sensitive stages. We refer to this effect as population resensitization, caused by redistribution within the cell cycle. We investigate the effect theoretically by employing the McKendrick-von Foerster equation for age-structured proliferating cell populations, generalized by introducing a radiation damage term. Within our formalism, we show that population resensitization occurs whenever: (a) prior to irradiation the cell population has the stable age-distribution approached asymptotically by an unirradiated population, and (b) T is sufficiently small. Examples and other cases are outlined. The methods of Volterra integral equations, renewal theory, and positive semigroup theory are applied. The effect of varying T is evaluated by considering the ultimate amplitude of the stable age-distribution population at times much greater than both the irradiation duration and the average cell-cycle time. The main biological limitations of the formalism are the following: considering only radiation damage which is not subject to enzymatic repair or quadratic misrepair, using an overly naive method of ensuring loss of cell cycle synchrony, neglecting nonlinear effects such as density inhibition of growth, and neglecting radiatively induced perturbations of the cell cycle. Possible methods for removing these limitations are briefly discussed.

Linear Aggregations of Stomata and Epidermal Cells in Tradescantia Leaves: Evidence for Their Group Patterning as a Function of the Cell Cycle

We tested Charlton's hypothesis (1990) that stomata are present and patterned in linear cell aggregations using the monocot Tradescantia. We examined the following features of the leaf epidermis in support of this theory: linear groups (strings) of stomatal complexes and of epidermal cells were sought in immature and mature regions of entire leaves; the lengths (in cell number) and incidences (numerical occurrence) of both string types were determined; the uniformity and progression of stomatal differentiation within strings were studied; physical characteristics of differentiating strings within cell files were measured. Undifferentiated epidermal cells from the leaf base were stained with DAPI to reveal precursors of stomatal strings immediately proximal to the stomatal initial region. The results indicated that the Tradescantia epidermis in the leaf blade consists of linear groups of stomata and epidermal cells, which did not change in cell number nor incidence during development. The incidence of stomata by length was nonrandom. Although incidence decreased with string length, the decline was not linear nor exponential. Stomatal strings show cell cycle synchrony in DAPI staining of stomatal precursors and synchrony of stomatal differentiation within a string. The irregularity in the length of the stomatal development region, and each differentiation stage in it, by cell file was consistent with the variation in string length and unity in string development. The evidence supports Charlton's hypothesis that cells are patterned based on their position in the cell cycle and that linear groups of stomata reflect cell lineages, which maintain a degree of cell cycle synchrony.

Cycle synchrony and probability of conception in female hamadryas baboonsPapio hamadryas

We investigated the factors affecting conception in a captive population ofPapio hamadryas. We collected data on reproductive states from 16 females over 12 years. Probability of conception was related to the outcome of the immediately preceding pregnancy and the fate of the preceding offspring. After abortions or when an infant survived more than 6 months, a female needed more cycles to conceive than when an infant died within the first 6 months post partum. The degree of estrus synchrony within, but not between, one-male units influenced the probability of conception. Females experiencing conceptive estrus showed less synchrony than those experiencing nonconceptive estrus. The number of females simultaneously in estrus within a one-male unit was negatively correlated with the probability of conception. Within our captive population, group size and male and female age had no influence on the probability of conception. The results indicate that sperm may be a limited resource in the one-male reproductive units of hamadryas baboons. Female-female competition for conception may exist and should influence the demography of one-male units.

Cycle synchrony and probability of conception in female hamadryas baboons Papio hamadryas

Cycle synchrony and probability of conception in female hamadryas baboons Papio hamadryas

Changes of G1 cyclins, cdk2, and cyclin A during the differentiation of HL60 cells induced by TPA.

Differentiation induction by 12-o-tetradecanoyl 13-acetate (TPA) results in the growth arrest of HL60 cells in the G1 phase. However, little is known about the changes of cell cycle-regulating genes during this differentiation process. We investigated the changes of mRNA for various cyclins (A, C, D1, D2, D3 and E) and cdk2. Synchronized HL60 cells began to proliferate immediately after release from cell cycle block and cell cycle synchrony was obvious until the second S phase. TPA-treated cells accumulated in G1 phase within 24 h and most of the cells were arrested in this phase at 36 h. The expression of cyclins and cdk2 was studied by Northern blot hybridization of the reverse-transcription polymerase chain reaction (RT-PCR). TPA treatment altered the expression of all genes studied. The expression of cdk2 and cyclin A mRNA was markedly down-regulated. Cyclin E mRNA expression was also prominently down-regulated from 12 h to 36 h, at which time a second increase of its expression was observed in control cells. In contrast, the expression of cyclin D1 mRNA was induced by TPA, while its expression in control cells was undetectable by Northern blot hybridization throughout the cell cycle. Cyclin C expression was faint and fluctuated irrelevant of cell cycle, but its expression in both control and TPA-treated cells was higher than at baseline. Cyclin D2 expression remained stable in control cells and TPA treatment resulted in slight down-regulation at 12 h, but no difference was observed after 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Microinjection of suc1 transcripts delays the cell cycle clock in Patella vulgata embryos.

The suc1 protein is a cell cycle regulator whose precise function remains to be elucidated. The suc1 cDNA of the mollusk Patella vulgata was cloned and sequenced. It encodes a 9 kD protein showing a strong similarity with its human counterparts and to a lesser extend with its yeast counterparts. The expression of suc1 in maturing oocytes was shown to be tightly cell cycle-regulated. The abundance of the suc1 transcripts is high in prophase- and metaphase-arrested oocytes but drops dramatically upon exit from M-phase, after fertilization. The microinjection of suc1 synthetic messengers into embryonic blastomeres delayed the cell cycle clock, thus disrupting the perfect cell cycle synchrony exhibited by the blastomeres of early Patella embryos. Interestingly, this suc1 delaying effect was significantly reversed when cyclin B messengers were co-injected with suc1 messengers. These results show that Patella embryos offer a quite valuable model to study cell cycle regulation. Moreover, they support the existence of a negative control exerted by suc1 on the cell cycle traverse in a higher eukaryote.

The retinoblastoma protein associates with the protein phosphatase type 1 catalytic subunit.

The retinoblastoma protein (p110RB) interacts with many cellular proteins in complexes potentially important for its growth-suppressing function. We have developed and used an improved version of the yeast two-hybrid system to isolate human cDNAs encoding proteins able to bind p110RB. One clone encodes a novel type 1 protein phosphatase catalytic subunit (PP-1 alpha 2), which differs from the originally defined PP-1 alpha by an amino-terminal 11-amino-acid insert. In vitro-binding assays demonstrated that PP-1 alpha isoforms preferentially bind the hypophosphorylated form of p110RB. Moreover, similar p110RB sequences are required for binding PP-1 alpha 2 and SV40 large T antigen. Cell cycle synchrony experiments revealed that this association occurs from mitosis to early G1. The implications of these findings on the regulation of both proteins are discussed.

Effects of fractionated radiation therapy on human brain tumor multicellular spheroids

We investigated the cytotoxic effects of fractionated radiation therapy on multicellular spheroids of human malignant glioma cell lines U-87 MG, U-251 MG, and U-373 MG. Graded doses of x-rays were administered in 1, 3, 8, 15, and30 fractions over 15 days. The isoeffect dose for a 1 log cell kill ranged from 4-4.5 Gy for a single fraction to 7–8 Gy for an 8-fraction protocol; no additional dose-sparing was achieved with more fractions. Therefore, the effects of individual doses (1.56 Gy) of the 8-fraction protocol were studied in U-251 MG spheroids. A cell survival assay showed that the first dose of radiation killed 30–50% of the cells; subsequent doses usually killed fewer cells. The cell kill after all 8 doses was about 1.0 log. No consistent relationship between the intracellular glutathione level and fraction number was observed. The 24-hour labeling index of the spheroids did not decrease until after the second fraction. Thus, the higher cell kill of the first dose does not seem to be related to cell cycle synchrony. Multinuclear and mononuclear giant cells were limited almost entirely to the periphery of the spheroids and increased with the number of radiation fractions. We conclude that multicellular spheroids can be used to study the biological effects of fractionated radiation therapy on human brain tumor cells. Although this model cannot be used to evaluate the effect of radiation on normal tissue, it may be useful in developing more effective radiation therapy protocols for human brain tumors.

Chapter 17 Cytoplasmic Extracts from the Eggs of Sea Urchins and Clams for the Study of Microtubule-Associated Motility and Bundling

Publisher Summary This chapter describes clarified cytoplasmic extracts made from the eggs of sea urchins or clams that are used to study microtubule-associated translocation and bundling in the presence of soluble cytoplasmic proteins. In the extracts, microtubules made from endogenous tubulin both translocate across coverslips and bundle to each other. In addition, the microtubules serve as a substrate for the bidirectional movement of organelles. Sea urchin oocytes and eggs are a rich source of the cytoskeletal components necessary for the rapid cell divisions following fertilization. Three of the materials stockpiled for postfertilization events include tubulin, microtubule-associated proteins, and microtubule motor proteins. Sea urchin egg fertilization should be carried out in ATA seawater to allow for removal of the fertilization membrane. The oocytes of the surf clam Spisula solidissima can be collected in quantities suitable for biochemical studies and are excellent cytological specimens. The mature Spisula oocyte has an intact germinal vesicle with a tetraploid complement of partially condensed chromosomes. The proximity in time between fertilization and the first meiotic division allows the harvesting of cells in high cell cycle synchrony.

Cell cycle synchrony in the developing chicken lens epithelium

Synchronous oscillations of DNA synthesis and histone 2B mRNA expression occur during normal development of 13-to 16-day-old embryonic chicken lens epithelium. At least four cycles were observed with peak values of DNA synthesis and histone 2B mRNA 5 to 10 times greater than baseline values. Fourier analysis of DNA synthesis identified a statistically significant oscillatory period of 18 hr, the approximate length of the cell cycle at this age. Minor components of 7–9 and 12 hr were also identified in the data sets. Lenses labeled with 3H-thymidine and analyzed by autoradiography at 13.8 days of embryogenesis revealed more than twice the number of labeled nuclei at this time than in lenses labeled 9 hr later; histone 2B mRNA followed this same pattern. These findings demonstrate that a significant population of cells is synchronized with respect to the cell cycle in the developing lens epithelium in ovo. The temporal pattern of mitosis may be the basis of the fiber cell architecture and consequent lens transparency.

A demonstration of asynchronous local cycles in an acarine predator-prey system

Population fluctuations in a continuous predator-prey system consisting of the spider mite,Tetranychus urticae Koch and its predator,Typhlodromus occidentalis Nesbitt, were assessed for almost 2 years (ca. 50 prey generations), on six mini-orchards of young apple trees in a climatically controlled glasshouse. During the first half of the experiment the plants were either ‘connected’ to each other with dowel rods or ‘unconnected’ and separate. In the second half, the plants were all ‘connected’. Population densities of both prey and predator on the unconnected mini-orchards were always higher than on the connected ones. Within the mini-orchards (=local scale), prey and predator populations go through a pattern of large amplitude cycles which continued throughout the experimental period. At the regional scale (mean over all mini-orchards) two types of fluctuations were observed. Large amplitude fluctuations associated with synchrony of the local cycles and small amplitude fluctuations associated with periods when local population cycles are proceeding out of phase. Transition from synchronous to asynchronous cycles took place very fast (within a few weeks), suggesting a mechanism generating asynchrony and possibly also partial refuges, which in turn trigger stabilising mechanisms at a regional scale. Causes of the synchrony are unclear. They may relate to the application of a pesticide (pirimicarb) used to control aphids, but there may just as well be an indirect form of causation, e.g. whereby the factors that promote aphid outbreaks also promote spider-mite population growth and temporary escape from control by the predators. Despite the synchronising factors the predator-prey system persisted, without external inputs, at a fairly small spatial scale, the size of a small glasshouse. Assessing the spatial scale and heterogeneity whereby decoupling of local cycles is sufficient for the cycles to proceed out of phase, remains an important area of experimental research. The experiment reported here provides some first clues and may form a standard for forthcoming experiments to assess the mechanisms promoting asynchrony, persistence and possibly also stability.

The effect of pheromones from cows in oestrus on the duration of the post-partum anoestrous period in beef cows

The term pheromone is used to describe a substance that is produced by an animal and creates a response in other Individuals of the same species.Reproduction in females can be affected by pheromones from other females in a number of mammals. This can invoke a degree of synchrony of oestrous cycles in for example the hamster (Handelmann et al, 1980) and the human (McClintock, 1971). Izard and Vandenberg (1983) demonstrated that in heifers which had their oestrous cycles synchronised using exogenous prostaglandin the degree of synchrony was enhanced when they were exposed to cervical mucus from cows in oestrus. They suggested that cervical mucus from cows in oestrus contains a pheromone which can enhance the degree of synchrony of oestrus in heifers.

Discrete Generations in Host--Parasitoid Models with Contrasting Life Cycles

(1) Previous theoretical studies have shown that parasitoids are capable of producing cycles in their host populations with periods of about one host generation. These studies have modelled host--parasitoid interactions where parasitoid development proceeds independently from that of its host. (2) We present experimental results of a particular host--parasitoid association, Cadra cautella--Venturia canescens, and show that the development of the parasitoid is synchronized with that of its host. (3) The empirical evidence is used to formulate an age-structured model of an idealized host--parasitoid system where the onset of parasitoid development is dependent on the state of the host. The properties of the model are described and contrasted with a model that assumes there is no developmental synchrony in host and parasitoid life cycles. (4) Our results are similar to the findings of previous studies, showing that the differences in the behaviour of population models with and without life cycle synchrony are quantitative rather than qualitative. We show that when developmental synchrony occurs, ratios of parasitoid/host development durations must be interpreted with care, when predicting whether single generation cycles are to be expected in a particular host-parasitoid system.

Asynchrony within estrous synchrony among ringtailed lemurs (Primates: Lemuridae)

Data from wild and semifree-ranging groups of ringtailed lemurs ( Lemur catta) were combined to evaluate the hypothesis that female ringtailed lemurs exhibit asynchrony of estrus within seasonal synchrony of estrous cycles. Photoperiodic and probably social entrainments lead all females within social groups of ringtailed lemurs to experience estrus annually within periods of 7 to 20 days. Among an average of five adult females in each of 11 group-years, however, only 2 separate instances of dyadic estrous overlap were observed. Computer simulations of estrus occurring independently among group-living females revealed that this was unlikely to have occurred by chance. Recent research on social enhancement and suppression of ovarian cycles in mammals suggests that a single pheromone-based signal-response system could mediate both ringtailed lemurs' remarkable annual estrous synchrony and the subsidiary asnchrony reported here. Asynchrony of estrus probably functions to maximize each female's ability to exercise mate choice by circumventing temporal conflict among females. Asynchrony of estrus and female mate choice cause current models to explain male membership in primate groups to fail for ringtailed lemurs. Such results highlight the need for detailed information on behavioral and physiological reproductive tactics before generally applicable models of reproductive strategies can be developed.

Global Climate Change: Policy Implications for Fisheries

Several government agencies are evaluating policy options for addressing global climate change. These include planning for anticipated effects and developing mitigation options where feasible if climate does change as predicted. For fisheries resources, policy questions address effects on international, national, and regional scales. Climate change variables expected to affect inland and offshore fisheries include temperature rise, changes in the hydrologic cycle, alterations in nutrient fluxes, and reduction and relocation of spawning and nursery habitat. These variables will affect resources at all levels of biological organization, including the genetic, organism, population, and ecosystem levels. In this context, changes in primary productivity, species composition in the food-web, migration, invasions, synchrony in biological cycles, shifts in utilization of niches, and problems of larvae entrainment in estuaries have been identified. Maintaining ecosystem robustness (i.e., high biodiversity) is another component of the problem. Action requires establishing priorities for information needs, determining appropriate temporal and spatial scales at which to model effects, and accounting for interactive changes in physical and biological cycles. A policy response can be derived when these results are integrated with social needs and human population constraints.

The Relationship between Radiosensitivity and Cell Kinetic Effects after Low- and High-Dose-Rate Irradiation in Five Human Tumors in Nude Mice

Radiation-induced synchronization of cells in the radiosensitive G2 phase can, theoretically, be applied to individual tailoring of fractionation schemes, possibly rendering radiotherapy more effective. For that purpose, cell cycle perturbations were studied in five xenografts by flow cytometry. A dose-dependent increase of cells in G2 phase was noticed in all five tumor cell lines after high-dose-rate irradiation, and in four tumor cell lines after low-dose-rate irradiation. The timing of maximum accumulation was not related to dose, but coincided with the cell cycle time of the respective tumors. Furthermore, the increase in the number of cells in G2 phase correlated with the radiosensitivity of the tumors as assessed by measurements of regrowth delays. The observed synchronization provides a basis for further investigations on the relevance of radiation-induced cell cycle synchrony to the effectiveness of fractionated radiotherapy.

Geographical Synchrony in Microtine Population Cycles: A Theoretical Evaluation of the Role of Nomadic Avian Predators

A simple mathematical model is developed and analyzed to evaluate the hypothesis that regional synchrony in microtine population cycles is caused by nomadic avian predators. We show that predation by nomadic predators, capable of rapidly tracking the local prey densities, may indeed have a synchronizing effect. However, in contrast to the original hypothesis, our model requires no additional mechanism than predation (e.g. behavioural response of prey to predation) to produce synchronous prey cycles. In addition to the synchronizing effect, heavy predation pressure by nomadic predators is expected to shorten the period and dampen the amplitude of the prey cycles. Non-migrating predators having impact on their prey year round have a stronger synchronizing effect than migrating predators absent during the winter. We predict that geographic regions with few non-migrating predators are less likely to have synchronized microtine populations than regions with many such predators and that highly synchronized microtine populations have cycles with smaller amplitudes and shorter periods than microtine populations in geographic regions where local populations are not synchronized.