Menstrual synchrony

Several studies have now documented menstrual synchrony in human females. There is a broad consensus that the phenomenon mainly occurs in women who spend a significant amount of time together, such as close friends and coworkers, and that social contact rather than a similar environment plays an important role in mediating the effect. However, the mechanisms involved and the adaptive function of menstrual synchrony are not understood. There is some evidence that olfactory cues between females might underlie the effect. More research is needed before the precise mechanisms that regulate menstrual synchrony are elucidated. Cynthia Graham received her MSc in clinical psychology from Glasgow University and her PhD from McGill University. Her previous research has involved menstrual synchrony and the effects of oral contraceptives on premenstrual changes. Currently she is working on a World Health Organization project assessing the effects of steroidal contraceptives on well-being and sexuality.     

Population synchrony within and among Lepidoptera species in relation to weather, phylogeny, and larval phenology

Abstract.  1. The population dynamics of native herbivore species in central Appalachian deciduous forests were studied by analysing patterns of synchrony among intra- and interspecific populations and weather.
2. Spatial synchrony of 10 Lepidoptera species and three weather variables (minimum temperature, maximum temperature, precipitation) from 12 sites was measured using cross-correlation functions relating levels of synchrony to the distance separating each set of populations. Based on both the pattern of synchrony and the region-wide cross-correlation coefficients, Lepidoptera species appear to be synchronised, at least in part, by local weather conditions.
3. Interspecific cross-correlations were calculated for all sympatric species pairs and trends in interspecific synchrony were related to phylogenetic relatedness, life-history timing, and weather. Interspecific synchrony was highest among species whose larvae were present during the same time of the season, but there was no relationship between interspecific synchrony and phylogenetic affinity.
4. Spatial synchrony of weather variables was significantly related to both species of some interspecific pairs, indicating weather as a potential mechanism involved in synchronising populations of different species.     

Problems with dimensionless measurement models of synchrony in biological systems

Synchrony is surprisingly complex even in the simplest cases. One strategy for simplifying complex phenomena is to define a dimensionless measurement model with the aim of (1) finding order, (2) comparing complex phenomena, and (3) making decisions about statistical significance. However, a model is only as good as its assumptions. In this paper, several types of dimensionless measurement models of synchrony among biological states are evaluated using the preceding criteria. These dimensionless measurement models are found to be inadequate even in the simplest cases of N individuals cycling through k non-overlapping states. Moreover, independent of their adequacy as measures of synchrony, there is the additional problem of the applicability of biological-state measurement models to rhythmic biological processes. Biological states are often just quantized observations of the phases of rhythmic biological processes. With the help of a concrete example, it is shown that quantizing the phases of a process into discrete states can lead to serious errors. These conclusions do not imply that the study of synchrony in biological systems is intractable. There are statistical approaches for detecting synchrony in groups and researchers are making progress towards understanding the general mechanisms of rhythmic phenomena in biological systems. Am. J. Primatol. 41:65–85, 1997. © 1997 Wiley-Liss, Inc.     

Logical problems and misunderstandings in “problems with dimensionless measurement models of synchrony in biological systems”

A model for the standardized measurement of synchrony in behavioral or biological states was proposed for use in comparative analyses of synchrony's adaptive significance. A recent critique attempts to discredit dimensionless (unitless) or standardized measures of synchrony in general and the proposed model in particular. Although the critique helps define and sharpen thinking about the measurement of synchrony and makes some well‐taken points, it also arrives at questionable conclusions based upon dubious assumptions. The critique proceeds from a fictional example in which all biological states being considered always have exactly the same durations for all individuals and always start or end for all individuals at exactly the same instants in time. These unreal, biologically meaningless premises, together with other questionable assumptions, are the basis of inappropriate analyses of standardized measures. The critique's arguments reveal a failure to understand the basic underlying principle of the standardized method and are dependent upon faulty logic. A statistical discussion contains both worthy points and arguable comments based not on data or actual probabilities of real events but on irrelevant chance outcomes derived from the biologically meaningless assumptions. The critique's conclusions are not credible, and its basic question probably is not scientifically answerable. Am. J. Primatol. 47:29–42, 1999. © 1999 Wiley‐Liss, Inc.     

A model for the adaptive significance of partial reproductive synchrony within social units

Summary Synchronized breeding in social units of animals (like colonies and herds) is often interpreted as a strategy against predators (predator satiation), and one might expect to find little variation in the relative date of starting reproduction. However, data on many colonies or herds show only partial synchrony. Our hypothesis is that this is not simply unavoidable variance but may be an adaption against predators. We consider the case where the members of a social unit can avoid predation actively by cooperation. If the contribution to this predator avoidance is different for individuals engaged in different phases of reproduction, our model shows that partial synchrony is of adaptive significance. Data on the black-headed gull (Larus ridibundus) are used to test the model's predictions.     

Population synchrony in small-world networks

Network topography ranges from regular graphs (linkage between nearest neighbours only) via small-world graphs (some random connections between nodes) to completely random graphs. Small-world linkage is seen as a revolutionary architecture for a wide range of social, physical and biological networks, and has been shown to increase synchrony between oscillating subunits. We study small-world topographies in a novel context: dispersal linkage between spatially structured populations across a range of population models. Regular dispersal between population patches interacting with density-dependent renewal provides one ecological explanation for the large-scale synchrony seen in the temporal fluctuations of many species, for example, lynx populations in North America, voles in Fennoscandia and grouse in the UK. Introducing a small-world dispersal kernel leads to a clear reduction in synchrony with both increasing dispersal rate and small-world dispersal probability across a variety of biological scenarios. Synchrony is also reduced when populations are affected by globally correlated noise. We discuss ecological implications of small-world dispersal in the frame of spatial synchrony in population fluctuations.     

Proximity and estrous synchrony in Mahale chimpanzees

Since McClintock [Nature 229:244-255, 1971] first reported menstrual synchrony in women, a number of studies have reported similar phenomena. Many researchers have suggested that one of the proximate factors leading to synchrony is spatial proximity among females (e.g., close friends or roommates). However, most studies on menstrual synchrony have been conducted in limited spaces, and it remains to be determined whether controlled environments, such as those used in experiments, actually exist in the wild. In this study, we analyzed the relationship between proximity and estrous synchrony using data from wild female chimpanzees at Mahale, Tanzania. In the cycling females, we observed two pairs that spent a large amount of time together. We compared the estrous synchrony indices (ESIs) between these two pairs and the other females. Our results showed that the ESIs of the high-proximity pairs did not differ from those of other pairs. .     

Latitudinal variation in monthly-scale reproductive synchrony among Acropora coral assemblages in the Indo-Pacific

Early research into coral reproductive biology suggested that spawning synchrony was driven by variations in the amplitude of environmental variables that are correlated with latitude, with synchrony predicted to break down at lower latitudes. More recent research has revealed that synchronous spawning, both within and among species, is a feature of all speciose coral assemblages, including equatorial reefs. Nonetheless, considerable variation in reproductive synchrony exists among locations and the hypothesis that the extent of spawning synchrony is correlated with latitude has not been formally tested on a large scale. Here, we use data from 90 sites throughout the Indo-Pacific and a quantitative index of reproductive synchrony applied at a monthly scale to demonstrate that, despite considerable spatial and temporal variation, there is no correlation between latitude and reproductive synchrony. Considering the critical role that successful reproduction plays in the persistence and recovery of coral reefs, research is urgently needed to understand the drivers underpinning variation in reproductive synchrony.

     

The occurrence of synchrony in the North American fireflyPhotinus carolinus (Coleoptera: Lampyridae)

Synchronous flashing has been described for some Southeast Asian fireflies but has rarely been reported in North American fireflies. Our field observations indicated thatPhotinus carolinus flash synchronously. The flash pattern of individualP. carolinus was characterized by a burst of five to eight flashes over a period of approximately 4 s. These flash bursts were repeated about every 12 s. Groups of fireflies comprised individuals exhibiting this species-specific flash pattern. Remarkably, members of the group flashed synchronously: Flash bursts started and stopped at the same time and the flashes among individuals occurred at the same time as well. We used low-light level videography to examine this behavior in caged groups of (3 or 10) fireflies for synchronic flashing. The occurrence of concurrent rhythmic group flashing satisfies the criteria for synchrony as defined by Buck (1988). The intermittent nature of the bursts of flashes shown byP. carolinus makes this a discontinuous synchrony. The mechanisms underlying discontinuous synchrony are not known.     

Estimating reproductive success of primates and other animals with long and incompletely known reproductive life spans

Lifetime reproductive success is difficult to obtain for adequate numbers of wild, long-lived animals because of incomplete knowledge of reproductive life histories and fates of offspring. A procedure is described that provides a standard estimate of lifetime reproductive success from either complete or incomplete reproductive life spans. For this procedure, reproductive success is defined as the following ratio: the number of offspring living to a criterion age in a given time period divided by the number expected for that age and period. The number expected is based upon the mean inter-birth interval of the population, the length of the time period, the age criterion of reproductive success chosen by the researcher (e.g., the average age of menarche), and the probability that an offspring will live to the criterion age. The effect of error upon the estimation of parameters is analyzed using the yellow baboons of Mikumi National Park as an example. The method can be used for both sexes, any litter (clutch) size, any mating system, any mean length of interbirth interval, any age criterion of reproductive success, and any study length that allows a reasonably sized sample of individuals for each of whom a substantial proportion of their reproductive life span is known. © 1992 Wiley-Liss, Inc.     

Dispersal and spatial scale affect synchrony in spatial population dynamics

A large body of theoretical studies has shown that synchrony among populations is critical for the long-term persistence of species in fragmented habitats. Although the effects of dispersal and environmental factors on synchrony have been investigated theoretically, empirical studies of these relationships have been lacking. We explored the interplay between environmental and demographic factors (fecundity, survival, dispersal) on population synchrony for 53 species of birds. We show that the interspecific differences in mean synchrony were determined by global environmental factors whose action was probably mediated by the abundance of each species. After removing the effect of these global factors on synchrony, the residual synchrony was strongly correlated with dispersal distance. The relationship between dispersal and synchrony was stronger for the species nesting in wet habitats than for those nesting in dry habitats. Our results indicate that different factors synchronize bird populations at different spatial scales, thus highlighting the role of scale in understanding spatial population dynamics and extinction risks.     

Fourteen-month-old infants use interpersonal synchrony as a cue to direct helpfulness

Musical behaviours such as dancing, singing and music production, which require the ability to entrain to a rhythmic beat, encourage high levels of interpersonal coordination. Such coordination has been associated with increased group cohesion and social bonding between group members. Previously, we demonstrated that this association influences even the social behaviour of 14-month-old infants. Infants were significantly more likely to display helpfulness towards an adult experimenter following synchronous bouncing compared with asynchronous bouncing to music. The present experiment was designed to determine whether interpersonal synchrony acts as a cue for 14-month-olds to direct their prosocial behaviours to specific individuals with whom they have experienced synchronous movement, or whether it acts as a social prime, increasing prosocial behaviour in general. Consistent with the previous results, infants were significantly more likely to help an experimenter following synchronous versus asynchronous movement with this person. Furthermore, this manipulation did not affect infant''s behaviour towards a neutral stranger, who was not involved in any movement experience. This indicates that synchronous bouncing acts as a social cue for directing prosociality. These results have implications for how musical engagement and rhythmic synchrony affect social behaviour very early in development.     

Searching for mechanisms of synchrony in spatially structured gamebird populations

1.  Time series data on five species of gamebird from the Dolomitic Alps were used to examine the relative importance of dispersal and common stochastic events in causing synchrony between spatially structured populations.
2.  Cross-correlation analysis of detrended time series was used to describe the spatial pattern of fluctuations in abundance, while standardized time series were used to describe both fluctuations and the trend in abundance. There were large variations in synchrony both within and between species and only weak negative relationships with distance.
3.  Species in neighbouring habitats were more likely to be in synchrony than species separated by several habitats. Species with similar density-dependent structure were more likely to be in synchrony.
4.  In order to estimate the relative importance of dispersal and environmental stochasticity, we modelled the spatial dynamics of each species using two different approaches. First, we used estimating functions and bootstrapping of time series data to calculate the relative importance of dispersal and stochastic effects for each species. Second, we estimated the intensity of environmental stochasticity from climatic records during the breeding season and then modelled the dispersal rate and dispersal distance for each species. The two models exhibited similar results for rock ptarmigan, black grouse, hazel grouse and rock partridge, while contrasting patterns were observed for capercaillie.
5.  The results suggest that environmental stochasticity plays the dominant role in synchronizing the fluctuations of these galliform species, although there will also be some dispersal between populations.     

Spatial synchrony in host-parasitoid models using aggregation of variables

We consider a host-parasitoid system with individuals moving on a square grid of patches. We study the effects of increasing movement frequency of hosts and parasitoids on the spatial dynamics of the system. We show that there exists a threshold value of movement frequency above which spatial synchrony occurs and the dynamics of the system can be described by an aggregated model governing the total population densities on the grid. Numerical simulations show that this threshold value is usually small. This allows using the aggregated model to make valid predictions about global host-parasitoid spatial dynamics.     

The effects of density-dependent offspring mortality on the synchrony of reproduction

Mortality rates often depend on the size of a population. Using ideal free theory to model the optimal timing of reproduction in model populations, I considered how the specific relationship between density-dependent offspring mortality and population size affects the optimal temporal distribution of reproduction. The results suggest that the specific form of the relationship between density-dependent mortality and the number of offspring produced determines the degree to which reproduction within a population is synchronous. Specifically, reproductive synchrony decreases as density-dependent mortality becomes increasingly inversely related to the number of offspring produced and is highest when density-dependent mortality is directly density-dependent. These findings support the suggestion that predation pressure selects for greater reproductive synchrony in species where mortality is directly density-dependent, but does not affect the timing of reproduction in species with density-independent rates of mortality. This revised version was published online in July 2006 with corrections to the Cover Date.     

Extrapair paternity, migration, and breeding synchrony in birds

To understand interspecific patterns in the strength of sexualselection, variation in the costs and benefits of exercisingmate choice needs to be evaluated. One manifestation of sexualselection in birds is the occurrence of greatly variable levelsof extrapair paternity (EPP). A proposed general explanationfor this variation is that the benefits to females in seekingextrapair copulations vary in a predictable manner accordingto the degree of breeding synchrony because females are betterable to assess potential extrapair partners when males are simultaneouslyin breeding condition. This hypothesis predicts a latitudinaltrend in EPP because birds tend to breed more synchronouslyaway from the equator. Expanding on previous geographicallyand taxonomically restricted tropical/temperate comparisons,we used phylogenetically independent standardized linear contraststo show that this positive relationship persists when all birdspecies for which EPP estimates currently exist are considered.However, if a third factor covaries with latitude in the sameway as breeding synchrony and EPP, this relationship need notbe causal. Migration could also account for latitudinal variationin the benefits to females of pursuing EPP, if migration isassociated with (1) hasty or (2) inaccurate mate choice, (3)facilitated assessment of male quality through the condition-dependenceof arrival time, or (4) increased genetic variance in male quality.We show that migration distance is positively related to theproportion of EPP and that migration can statistically explainthe latitudinal trend in EPP, even when confounding factorsare simultaneously controlled. Hence, alternative explanationsfor latitudinal variation in EPP may be feasible, and carefulintraspecific tests are needed to assess their relative importanceand their implications for geographical variation in life-historyevolution.