Women do not synchronize their menstrual cycles

It is widely believed that women who live together or who are close friends synchronize their menstrual cycles. We reexamined this phenomenon in two ways. First, we collected data on menstrual cycles from 186 Chinese women living in dorms for over a year. We found that women living in groups did not synchronize their cycles. Second, we reviewed the first study reporting menstrual synchrony. We found that group synchrony in that study was at the level of chance. We then show that cycle variability produces convergences and subsequent divergences of cycle onsets and may explain perceptions of synchrony. This study was supported by the Sichuan Youth Foundation of Science and Technology (Chuan Ke Ji [2001] 2) and NIH Grant No. 5R01MH065555-02. We thank Shuhuan Yang, Xia Xu, Jun Qu, Jing Zhu, Meijia Yu, & Chang Zhou for all their work in collecting the data. Without them, this study could never have been done. Zheng-Wei Yang is director and professor of the Morphometric Research Laboratory, North Sichuan Medical College, China. His main research interests are in spermatogenesis, morphometry, and stereology. Jeff Schank is associate professor of psychology at the University of California, Davis. His main research interests are in computational and biorobotic modeling of group behavior and the development of sensorimotor behavior in animals.     

Delayed density-dependent season length alone can lead to rodent population cycles

Studies of cyclic microtine populations (voles and lemmings) have suggested a relationship between the previous year's population density and the subsequent timing of the onset of reproduction by overwintered breeding females. No studies have explored the importance of this relationship in the generation of population cycles. Here we mathematically examine the implications of variation in reproductive season length caused by delayed density-dependent changes in its start date. We demonstrate that when reproductive season length is a function of past population densities, it is possible to get realistic population cycles without invoking any changes in birth rates or survival. When parameterized for field voles (Microtus agrestis) in Kielder Forest (northern England), our most realistic model predicts population cycles of similar periodicity to the Kielder populations. Our study highlights the potential importance of density-dependent reproductive timing in microtine population cycles and calls for investigations into the mechanism(s) underlying this phenomenon.     

Seasonal aspects of the life cycles of pseudoscorpions (Arachnida, Pseudoscorpiones)

Analysis of available information on the seasonal features of life cycles in pseudoscorpions (Arachnida, Pseudoscorpiones) shows that in the temperate climate of Europe with distinct seasonality, the development of these peculiar arachnids can be either eurychronous (= homodynamic), with a poorly pronounced seasonal arrangement, or stenochronous (= heterodynamic), with a distinct seasonal arrangement. This is similar to some other arachnids, particularly spiders and harvestmen. Eurychronous pseudoscorpions are characterized by the approximately year-round development (quite often with winter activity in the whole or part of the population), an overlapping of consecutive generations, the presence of alternative development with or without the dormant state (at all the postembryonic life cycle stages), lack of brood chamber production by females, and the start of free-living life at the protonymphal stage. Stenochronous pseudoscorpions, on the contrary, possess clearly arranged (usually univoltine) development with overwintering deutonymphs and tritonymphs (more rarely adults), a clear separation of adjacent generations, the production of brood chambers where the regressive protonymphs develop until their molt into deutonymphs, and the start of free-living life at the deutonymphal stage. These two types of life cycles are exemplified by two pseudoscorpions from South England, namely Neobisium muscorum with eurychronous development, and Chthonius orthodactylus with stenochronous, univoltine development (Goddard, 1976). There is no correlation between the taxonomic position and the seasonal characters of life cycles in representatives of Neobisiidae, Chthoniidae, and Chernetidae. There is, instead, a close connection between the eco-physiological state of these arachnids and the type of their gas exchange (continuous, diffusive and non-cyclic in the active state, as opposed to discontinuous, with cyclic emission of CO₂ and uptake of O₂ in the dormant state). The latter information may be useful for distinguishing different kinds of dormancy (diapause and quiescence) in these arachnids.     

You mate, I mate: macaque females synchronize sex not cycles

Extended female sexuality in species living in multimale-multifemale groups appears to enhance benefits from multiple males. Mating with many males, however, requires a low female monopolizability, which is affected by the spatiotemporal distribution of receptive females. Ovarian cycle synchrony potentially promotes overlapping receptivity if fertile and receptive periods are tightly linked. In primates, however, mating is often decoupled from hormonal control, hence reducing the need for synchronizing ovarian events. Here, we test the alternative hypothesis that females behaviorally coordinate their receptivity while simultaneously investigating ovarian cycle synchrony in wild, seasonal Assamese macaques (Macaca assamensis), a promiscuous species with extremely extended female sexuality. Using fecal hormone analysis to assess ovarian activity we show that fertile phases are randomly distributed, and that dyadic spatial proximity does not affect their distribution. We present evidence for mating synchrony, i.e., the occurrence of the females' receptivity was significantly associated with the proportion of other females mating on a given day. Our results suggest social facilitation of mating synchrony, which explains (i) the high number of simultaneously receptive females, and (ii) the low male mating skew in this species. Active mating synchronization may serve to enhance the benefits of extended female sexuality, and may proximately explain its patterning and maintenance.     

Three people can synchronize as coupled oscillators during sports activities

We experimentally investigated the synchronized patterns of three people during sports activities and found that the activity corresponded to spatiotemporal patterns in rings of coupled biological oscillators derived from symmetric Hopf bifurcation theory, which is based on group theory. This theory can provide catalogs of possible generic spatiotemporal patterns irrespective of their internal models. Instead, they are simply based on the geometrical symmetries of the systems. We predicted the synchronization patterns of rings of three coupled oscillators as trajectories on the phase plane. The interactions among three people during a 3 vs. 1 ball possession task were plotted on the phase plane. We then demonstrated that two patterns conformed to two of the three patterns predicted by the theory. One of these patterns was a rotation pattern (R) in which phase differences between adjacent oscillators were almost 2π/3. The other was a partial anti-phase pattern (PA) in which the two oscillators were anti-phase and the third oscillator frequency was dead. These results suggested that symmetric Hopf bifurcation theory could be used to understand synchronization phenomena among three people who communicate via perceptual information, not just physically connected systems such as slime molds, chemical reactions, and animal gaits. In addition, the skill level in human synchronization may play the role of the bifurcation parameter.     

Synrhabdosome life cycles

Synrhabdosomes are monospecific colonies of colonies of graptolites. Their mode of formation is unknown. We draw attention to a type of colony formation found in two genera of colonial rotifers and suggest that these represent plausible models for the life cycle of graptolite synrhabdosomes.     

A temperature-compensated model for circadian rhythms that can be entrained by temperature cycles

From the viewpoint that reaction rates will change with temperature, we present a general method to build circadian clock models that generate circadian oscillations with almost constant period under different constant ambient temperature, and propose an algorithm estimating the parameter condition for compensated period against the change of temperature based on the PER single-feedback loop model of Goldbeter [1995. A model for circadian oscillations in the Drosophila period protein (PER). Proc. R. Soc. London Ser. B 261, 319-324] for Drosophila. We show that the model with derived parameters can realize the temperature compensation over a wide range of temperature, and simultaneously can realize the entrainment to temperature cycles.     

Population cycles can maintain foraging polymorphism

The maintenance of genetic variability in morphological traits that affect fitness is poorly understood. We present a simple Mendelian model of genetic traits affecting foraging efficiency in grazing ungulates, based on a trade-off between rates of energy extraction at low versus high levels of plant abundance. The model suggests that variation in foraging efficiency could be maintained via lottery competition arising as a direct consequence of dynamically unstable interactions between consumers and their food resources. Lottery competition is a plausible mechanism for explaining wide variability in foraging efficiency, such as that documented in unstable Soay sheep populations on the St Kilda archipelago.     

Long life cycles in insects

Long life cycles covering more than one year are known for all orders of insects. There are different mechanisms of prolongation of the life cycle: (1) slow larval development; (2) prolongation of the adult stage with several reproduction periods; (3) prolongation of diapause; (4) combination of these mechanisms in one life cycle. Lasting suboptimal conditions (such as low temperature, low quality of food or instability of food resources, natural enemies, etc.) tend to prolong life cycles of all individuals in a population. In this case, the larvae feed and develop for longer than a year, and the active periods are interrupted by dormancy periods. The nature of this dormancy is unknown: in some cases it appears to be simple quiescence, in others it has been experimentally shown to be a true diapause. Induction and termination of these repeated dormancy states are controlled by different environmental cues, the day-length being the principal one as in the case of the annual diapause. The long life cycles resulting from prolonged adult lifespan were experimentally studied mainly in beetles and true bugs. The possibility of repeated diapause and several periods of reproductive activity is related to the fact that the adults remain sensitive to day length, which is the main environmental cue controlling their alternative physiological states (reproduction vs. diapause). Habitats with unpredictable environmental changes stimulate some individuals in a population to extend their life cycles by prolonged diapause. The properties of this diapause are poorly understood, but results of studies of a few species suggest that this physiological state differs from the true annual diapause in deeper suppression of metabolism. Induction and intensity of prolonged diapause in some species appear to be genetically controlled, so that the duration of prolonged diapause varies among individuals in a group, even that of sibles reared under identical conditions. Thus, long life cycles are realized due to the ability of insects to interrupt activity repeatedly and enter dormancy. This provides high resistance to various environmental factors. Regardless of the nature of this dormancy (quiescence, annual or prolonged diapause, or other forms) and the life cycle duration, the adults always appear synchronously after dormancy in the nature. The only feasible explanation of this is the presence of a special synchronizing mechanism, most likely both exo- and endogenous, since the adults appear not only synchronously but also in the period best suited for reproduction. As a whole, the long life cycles resulting from various structural modifications of the annual life cycle, are typical of the species living under stable suboptimal conditions when the pressure of individual environmental factors is close to the tolerance limits of the species, even though it represents its norm of existence. Such life cycles are also typical of the insects living in unstable environments with unpredictable variability of conditions, those developing in cones and galls, feeding on flowers, seeds, or fruits with limited periods of availability, those associated with the plant species with irregular patterns of blossoming and fruiting, and those consuming low-quality food or depending on unpredictable food sources (e.g., predators or parasites). Long cycles are more common in: (1) insect species at high latitudes and mountain landscapes where the vegetation season is short and unstable; (2) species living in deserts or arid areas where precipitation is unstable and often insufficient for survival of food plants; (3) inhabitants of cold and temporary water bodies that are not filled with water every year. At the same time, long life cycles sometimes occur in insects from other climatic zones as well. It is also important to note that while there is a large body of literature dealing with the long life cycles in insects, it mostly focuses on external aspects of the phenomenon. Experimental studies are needed to understand this phenomenon, first of all the nature of dormancy and mechanisms of synchronization of adult emergence.     

Seasonal cycles of zooplankton from San Francisco Bay

The two estuarine systems composing San Francisco Bay have distinct zooplankton communities and seasonal population dynamics. In the South Bay, a shallow lagoon-type estuary, the copepods Acartia spp. and Oithona davisae dominate. As in estuaries along the northeast coast of the U.S., there is a seasonal succession involving the replacement of a cold-season Acartia species (A. clausi s.l.) by a warm-season species (A. californiensis), presumably resulting from the differential production and hatching of dormant eggs. Oithona davisae is most abundant during the fall. Copepods of northern San Francisco Bay, a partially-mixed estuary of the Sacramento-San Joaquin Rivers, organize into discrete populations according to salinity distribution: Sinocalanus doerrii (a recently introduced species) at the riverine boundary, Eurytemora affinis in the oligohaline mixing zone, Acartia spp. in polyhaline waters (18–30\%), and neritic species (e.g., Paracalanus parvus) at the seaward boundary. Sinocalanus doerrii and E. affinis are present year-round. Acartia clausi s.l. is present almost year-round in the northern reach, and A. californiensis occurs only briefly there in summer-fall. The difference in succession of Acartia species between the two regions of San Francisco Bay may reflect differences in the seasonal temperature cycle (the South Bay warms earlier), and the perennial transport of A. clausi s.l. into the northern reach from the seaward boundary by nontidal advection.Large numbers (>10⁶ m^–3) of net microzooplankton (>64 µm), in cluding the rotifer Synchaeta sp. and three species of tintinnid ciliates, occur in the South Bay and in the seaward northern reach where salinity exceeds about 5–10 Maximum densities of these microzooplankton are associated with high concentrations of chlorophyll. Meroplankton (of gastropods, bivalves, barnacles, and polychaetes) constitute a large fraction of zooplankton biomass in the South Bay during winter-spring and in the northern reach during summer-fall.Seasonal cycles of zooplankton abundance appear to be constant among years (1978–1981) and are similar in the deep (>10 m) channels and lateral shoals (<3 m). The seasonal zooplankton community dynamics are discussed in relation to: (1) river discharge which alters salinity distribution and residence time of plankton; (2) temperature which induces production and hatching of dormant copepod eggs; (3) coastal hydrography which brings neritic copepods of different zoogeographic affinities into the bay; and (4) seasonal cycles of phytoplankton.     

Glutathione-dependent enzymes alone can produce paraquat resistance

HL60 cells exposed to increasing paraquat concentrations were screened for clones without increased superoxide dismutase activities in an effort to examine cytotoxic events occurring after superoxide production. The resulting resistance to paraquat was not associated with alterations in paraquat uptake, catalase, or NADPH-P450 reductase activity, but to alterations in glutathione-dependent enzyme activities. While increases in glutathione-dependent enzymes upon exposure to paraquat have been reported, the increases were considered a secondary response to increases in superoxide dismutase activities. Our results demonstrate that glutathione-dependent enzymes alone provide protection against paraquat toxicity, and their increase upon exposure to paraquat can be independent of the response of superoxide dismutases. This supports a previous finding that cells resistant to Adriamycin, based on elevated glutathione peroxidase and transferase activities are also cross-resistant to paraquat. Unlike this previous report, the increase in glutathione peroxidase was not a persistent genetic event, as activities returned to normal upon removal of paraquat. An isolated increase in glutathione peroxidase without accompanying increases in superoxide dismutases was a rare event, as nearly all clones examined after exposure to paraquat had increased superoxide dismutase.     

Alternative life cycles controlled by temperature and photoperiod in the oligophagous bug, Dybowskyia reticulata

Abstract. Effects of temperature and photoperiod on the induction and re-induction of adult diapause were examined in Dybowskyia reticulata (Dallas) (Heteroptera: Pentatomidae). Adults collected from the field after overwintering in early summer continued oviposition under long-day conditions of LD 16:8 h at 20 or 25°C, while they re-entered diapause under short-day conditions of LD 12:12 h at 25, 27.5 or 30°C. By contrast, adults reared in the laboratory from eggs at 20 or 25°C entered diapause under both long-day and short-day conditions, whereas those reared at 27.5 and 30°C entered diapause only under short-day conditions. Under quasi-natural conditions in 1993, when summer temperature was low, most adults of the first generation entered diapause in late July. However, in the warmer summer of 1996, oviposition was recorded in many females that ecdysed into adults from July to early August. Even though the seeds of the host plants occur in a restricted period from early summer to early autumn, in warmer years D. reticulata may produce a second generation. The response to temperature with a threshold between 25 and 27.5°C in D. reticulata brings about a switch between the univoltine and bivoltine life cycles.     

Dynamics of core body temperature cycles in long-term measurements under real life conditions in women

Studies under real life conditions become more and more relevant in chronobiological and chronomedical research. The present study aims to analyze one of the most prominent biological rhythms: the core body temperature (CBT) rhythm in the real world outside the laboratory. CBT was recorded continuously in 37 healthy women (age between 21 and 44 years, median 29 years) with a newly developed intravaginal temperature sensor for up to 102 days. Sleep logs were available from 23 participants. To quantify the daily dynamics of each individual CBT-curve, novel measurement parameters are introduced which permit the quantification of the phase and shape of the CBT rhythms as well as their relation to the sleep–wake cycle. In addition to the classical phase markers (i.e. nadir and peak), the daily curves were segmented into quartiles by introducing the t25/t50/t75-values which can be used as phase and shape markers. At variance to previous studies, a conspicuous day-to-day variation was shown not only for the time point of the peak, but also for the time point of the nadir. However, the t-values, particularly the t75-value were relatively closely locked to external time and thus represent more reliable phase markers than the nadir. The (variable) time point of the nadir determined the period length, phase and shape of the subsequent CBT cycle. If a nadir occurred close to the wake-up time, the following cycle was considerably shorter than 24 hours, while a nadir distant from the wake-up time was followed by a longer cycle. Thus, the period lengths of the daily CBT cycles of each individual were characterized by an “expand/contract” rhythm. The analyses of the novel phase markers (t25/t50/t75) of the CBT curves allowed to identify “early” and “late” participants who may differ in their phase-response curves with regard to the entraining effect of light. In addition, the novel phase markers mirrored the different social entrainment conditions on weekends and workdays.     

Integrating function across marine life cycles

Complex life cycles involve a set of discrete stages that candiffer dramatically in form and function. Transitions betweendifferent stages vary in nature and magnitude; likewise, thedegree of autonomy among stages enabled by these transitionscan vary as well. Because the selective value of traits is likelyto shift over ontogeny, the degree of autonomy among stagesis important for understanding how processes at one life-historystage alter the conditions for performance and selection atothers. We pose 3 questions that help to define a research focuson processes that integrate function across life cycles. First,to what extent do particular transitions between life-historystages allow those stages to function as autonomous units? Weidentify the roles that stages play in the life history, typesof transitions between stages, and 3 forces (structural, genetic/epigenetic,and experiential) that can contribute to integration among stages.Second, what are the potential implications of integration acrosslife cycles for assumptions and predictions of life-historytheory? We provide 3 examples where theory has traditionallyfocused on processes acting within stages in isolation fromothers. Third, what are the long-term consequences of carryoverof experience from one life cycle stage to the next? We distinguish3 scenarios: persistence (effects of prior experience persistthrough subsequent stages), amplification (effects persist andare magnified at subsequent stages), and compensation (effectsare compensated for and diminish at subsequent stages). We usethese scenarios to differentiate between effects of a carryoverof state and carryover into subsequent processes. The symposiumintroduced by our discussion is meant to highlight how discretestages can be functionally coupled, such that life cycle evolutionbecomes a more highly integrated response to selection thancan be deduced from the study of individual stages.     

How larvae and life cycles evolve

Marine larvae have factored heavily in pursuits to understand the origin and evolution of animal life cycles. Recent comparisons of gene expression and chromatin state in different species of sea urchin and annelid show how evolutionary changes in embryonic gene regulation can lead to markedly different larval forms.     

Mathematical description of holometabolous life cycles

The deterministic continuous equations are developed for the population levels of the various life stages of holometabolous species. Special attention is paid to the larval stage in which the variable of weight, in addition to the traditional variables of age and time, is included; growth rate and the genetic variability of the growth rate are allowed for. A pair of equations is derived that permits computation of the larval population level without regard to the levels of the other life stages. Finite difference equations are developed, simple analytical forms for vital rates are adopted, and a numerical example is given.     

Morphoprocess and life cycles of organisms

In developing the ideas of V.N. Beklemishev about an organism as a form, existing in a process of determined transformation and matter/energy exchange, we consider different aspects of the term "morphoprocess" and introduce corresponding additional terms. Momentary morphoprocess characterizes an organism in the given moment of time. This term reflects a constancy of the form ("momentary form"), where the existence of an organism can be imagined as a sequence of "momentary forms". "First derivative" of this momentary characteristic is particular morphoprocess--an organism from its origin to fission/division or death. Compound particular morphoprocess is a determined and reiterating sequence of different particular morphoprocesses. And, at last, general morphoprocess--a "second derivative" of momentary morphoprocess--is rhythmical reiteration of a particular morphoprocess on the long-term scale, an ancestors/descendants lineage. To describe consecutive changes in this material system, the terms ontogenesis and life cycle are used. Ontogenesis characterizes a sequence of the morpho-functional changes of an individual organism during its life, whereas life cycle reflects a sequence of changes during one complete segment of the general morphoprocess represented by a single or several particular morphoprocesses. We also discuss morphoprocess uniformity along with the phase nature of morphoprocesses, both particular and compound particular ones.