Maternal effect on seed survival and emergence in Cytisus scoparius: an experimental approach

The role of the individual origin of seeds in the variability of demographic parameters within a seed-bank has been little studied despite the recognition of its important contribution to species adaptation strategies to environmental constraints. This study analyzed the seed-bank dynamics of Cytisus scoparius, a small woody species with a high aptitude for colonization and dominance. Our experimental setup made it possible to monitor seed emergence dynamics in situ for maternal individuals within the study population. In addition to the characteristic traits of the species (maximum seed life span between 4 and 5 years in 75 % of the cases), there was a high variability of the emergence dynamics between individuals, distinguished both by their total emergence rate and profile. The total emergence rate of seeds was correlated with their quality (seed weight and number of seeds per pod), but was unrelated to either maternal age or fecundity. Different emergence profiles can be recognized between two distinct patterns: on one hand, a strategy that concentrates on emergence in the second year and, on the other, a regular decrease of the germinant number over time. The coexistence of different seed-bank strategies between individuals results in the ability for the population to face to disturbances and environmental variability.     

Probit and survival analysis of tooth emergence ages in a mixed-longitudinal sample of chimpanzees (Pan troglodytes).

Tooth emergence data from a mixed-longitudinal sample of 58 chimpanzees of known age were analyzed using probit and survival techniques to produce median emergence ages, ranges of variability, and emergence sequences for primary and permanent teeth. Between-group comparisons were made to test for statistically significant differences in emergence ages. No such differences were found between right and left sides, or between maxilla and mandible, for any primary or permanent teeth. Male-female comparisons did demonstrate significant emergence-age differences for some teeth, although they were not always bilaterally symmetrical. More complete data are required to further clarify the nature of sex differences in tooth emergence in chimpanzees. Regression models for age prediction from the number of emerged teeth were generated and indicate that males achieve a given number of emerged teeth at a significantly later age than females. However, when fewer than five teeth have emerged, males are predicted to be younger than females. The sizable root mean square error values for these models suggest that this method of age prediction has limited usefulness owing to the amount of variability in timing of tooth emergence in chimpanzees. The implications of these data for studies on tooth emergence in early hominids are addressed.     

Analysis of emergence stage facilitates the evaluation of chickpea (Cicer arietinum L.) genotypes for salinity tolerance imparted by mycorrhizal colonization

Salinity is an ever-increasing constraint limiting crop production in arid and semi-arid regions. Arbuscular mycorrhiza (AM) helps host plant to cope with detrimental effects of salinity. Experiments were aimed to examine the hypothesis that emergence is a better stage to determine salt tolerance of chickpea genotypes than germination and genotypic variability in their tolerance ability at emergence and subsequent vegetative growth is the manifestation of differential benefits imparted by mycorrhiza. Investigations were carried out at germination and emergence stage of genotypes (PBG 5, GPF 2, PBG 1, BG 1053, L 550) at 0, 40, 60, 80 mM NaCl. Significant genotypic variations in salt tolerance were observed at emergence rather than germination because of greater inhibitory effects on seedling emergence. Percent mycorrhizal colonization (MC) and its resulting impact on respiration rate (RR) and salt tolerance index (STI) at emergence indicated that PBG 5, with lowest RR, highest STI and mycorrhiza benefit percentage was the most tolerant whereas, L 550 the most sensitive genotype. Genotypic variability recorded at 30 days was consistent with that at emergence stage. Superior salt tolerance of PBG 5 than L 550 could be attributed to higher correlation between MC and physio-biochemical traits (RWC, chlorophyll a/b, proline accumulation, antioxidant activities). The study supported the hypothesis that both emergence stage and mycorrhizal effectiveness are important determinants of salt tolerance in chickpea genotypes. Evaluation of genotypes for relative adaptation to salinity should include estimation of their differential salt tolerance at different growth stages and symbiotic effectiveness of AM .     

Chrono–geographical approach to analysis of variability of bicyclic <Emphasis Type="Italic">Erebia ligea</Emphasis> (L.) (Lepidoptera: Satyridae) species in the Urals

The phenotypic variability of a complex of metric traits (the length of fore and hind wings and diameters of wing pattern spots) in populations of trans-Eurasian Erebia ligea species in different landscape–zonal and climatic conditions of the Ural region has been analyzed. It is demonstrated that protandry, bicyclicity, and imago emergence, mainly in odd years, are inherent for the E. ligea in the Ural territory. The geographical variability of sizes is characterized by a cline consisting in a gradual increase in imago sizes in the direction from north to south. The chrono–geographical approach allowed us to establish the scale of observed differences: differences of a complex of analyzed traits caused by chronographic variability are the largest, followed by those caused by sexual, geographical, and—only at the very end—seasonal variability (that is, the time of imago emergence during generation flight).     

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.     

Environmental variation enables invasions of environmental opportunist pathogens

Emerging infectious diseases are a persistent threat to humans and food production but the mechanisms promoting the emergence of novel pathogens are not fully understood. The widely discussed explanations for pathogen emergence include range shifts, coincidental evolution of virulence, and host immunity variation. Here we propose a novel mechanism of virulence evolution that relies on environmental variability. Our model combines an environmental community experiencing random or periodic variability, to a classical SIR epidemiological model. We assume that environmentally growing, potentially infective variants arise at low frequency from a resident, non‐infective (benign microbial) strain through random variation on genetic material. We found that environmental perturbations commonly promote establishment of sporadic infections or persistent epidemics, by creating transient periods of low competition, which can in turn be exploited by an infective strain. Given the ubiquitous nature of potentially pathogenic environmental micro‐organisms and environmental variability, this mechanism provides a plausible explanation for emerging diseases.     

A comparison of methods for evaluating seed quality in carrots (Daucus carota)

Comparisons of embryo length, ISTA (International Seed Testing Association), cold (10 ^oC), controlled-deterioration, and slope tests for estimating seedling size variability and percentage seedling emergence were made using eighteen stocks of carrot seeds. The coefficient of variation (C.V.) of seedling weight was closely correlated with the C.V. of embryo length (r = 0–87 D.F., 16) and also with the C.V. of root length from the slope test (r = 0–63 D.F., 16). Poorer estimates of percentage seedling emergence were obtained from the cold test in all three sowings (correlation coefficients were between 0–65 and 0–70 D.F., 16) compared with the ISTA, controlled deterioration, and slope tests. For these three tests the correlation coefficients varied between 0–80 and 0–87 (D.F., 16) for all sowings. The embryo test is a rapid (1 man hour per seed lot) and accurate method of assessing potential variability between seed lots. The slope test could provide a less labour demanding method of assessing potential variability than the embryo length test though the results would not be available immediately. However, the slope test could also provide as good an estimate of seedling emergence in the field as the ISTA or controlled-deterioration tests.     

Large-Scale Temperature Patterns in Past Centuries: Implications for North American Climate Change

Recent climate reconstructions are analyzed specifically for insights into those patterns of climate variability in past centuries with greatest impact on the North American region. Regional variability, largely associated with the El Nino/Southern Oscillation (ENSO) phenomenon, the North Atlantic Oscillation (NAO), and multidecadal patterns of natural variability, are found to mask the emergence of an anthropogenic temperature signal in North America. Substantial recent temperature anomalies may however indicate a possible recent emergence of this signal in the region. Multidecadal North Atlantic variability is likely to positively reinforce any anthropogenic warming over substantial parts of North America in coming decades. The recent magnitudes of El Nino events appear to be unprecedented over the past several centuries. These recent changes, if anthropogenic in nature, may outweigh the projection of larger-scale climate change patterns onto the region in a climate change scenario. The implications of such changes for North America, however, are not yet clear. These observations suggest caution in assessing regional climate change scenarios in North America without a detailed consideration of possible anthropogenic changes in climate patterns influencing the region.     

Timing of the Departure of Ocean Biogeochemical Cycles from the Preindustrial State

Changes in ocean chemistry and climate induced by anthropogenic CO₂ affect a broad range of ocean biological and biogeochemical processes; these changes are already well underway. Direct effects of CO₂ (e.g. on pH) are prominent among these, but climate model simulations with historical greenhouse gas forcing suggest that physical and biological processes only indirectly forced by CO₂ (via the effect of atmospheric CO₂ on climate) begin to show anthropogenically-induced trends as early as the 1920s. Dates of emergence of a number of representative ocean fields from the envelope of natural variability are calculated for global means and for spatial ‘fingerprints’ over a number of geographic regions. Emergence dates are consistent among these methods and insensitive to the exact choice of regions, but are generally earlier with more spatial information included. Emergence dates calculated for individual sampling stations are more variable and generally later, but means across stations are generally consistent with global emergence dates. The last sign reversal of linear trends calculated for periods of 20 or 30 years also functions as a diagnostic of emergence, and is generally consistent with other measures. The last sign reversal among 20 year trends is found to be a conservative measure (biased towards later emergence), while for 30 year trends it is found to have an early emergence bias, relative to emergence dates calculated by departure from the preindustrial mean. These results are largely independent of emission scenario, but the latest-emerging fields show a response to mitigation. A significant anthropogenic component of ocean variability has been present throughout the modern era of ocean observation.     

Quality assessment of selected commercially available whitefly and aphid biological control agents in the United States

This study assessed the quality of three commercially available natural enemies used for pest management in greenhouses: the whitefly parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae), the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae), and the aphid predatory midge Aphidoletes aphidimlyza (Rondani) (Diptera: Cecidomyiidae). Shipment packaging was consistent for all natural enemies. However, there was high variability in delivery punctuality, product cost, and product information provided by each of the six selected companies. Product quantity, percentage of emergence upon arrival, percentage of total emergence, percentage of females, and percentage of flying insects were assessed using International Organization for Biological Control (IOBC) recommended procedures. The parameters with greatest variability between companies were percentage of emergence upon arrival (0.9-10.5%) and percentage of flying insects (35.4-85.0%) for E. formnosa; product quantity (623.3-833.8 aphid mummies), percentage of emergence upon arrival (6.1-41.2%) and percentage of females (51.1-54.8%) for A. colemani; and percentage of emergence upon arrival (0.0-7.7%) and percentage of females (54.6-76.2%) for A. aphlidimyza. Results are discussed in terms of the value to consumers and compared with IOBC standards.     

Disentangling the paradox of insect phenology: are temporal trends reflecting the response to warming?

The strength and direction of phenological responses to changes in climate have been shown to vary significantly both among species and among populations of a species, with the overall patterns not fully resolved. Here, we studied the temporal and spatial variability associated with the response of several insect species to recent global warming. We use hierarchical models within a model comparison framework to analyze phenological data gathered over 40 years by the Japan Meteorological Agency on the emergence dates of 14 insect species at sites across Japan. Contrary to what has been predicted with global warming, temporal trends of annual emergence showed a later emergence day for some species and sites over time, even though temperatures are warming. However, when emergence data were analyzed as a function of temperature and precipitation, the overall response pointed out an earlier emergence day with warmer conditions. The apparent contradiction between the response to temperature and trends over time indicates that other factors, such as declining populations, may be affecting the date phenological events are being recorded. Overall, the responses by insects were weaker than those found for plants in previous work over the same time period in these ecosystems, suggesting the potential for ecological mismatches with deleterious effects for both suites of species. And although temperature may be the major driver of species phenology, we should be cautious when analyzing phenological datasets as many other factors may also be contributing to the variability in phenology.     

Production and chronobiology of emergence of the cercariae of Euparyphium albuferensis (Trematoda: Echinostomatidae)

The production and the chronobiology of emergence of the cercariae of Euparyphium albuferensis from Gyraulus chinensis experimentally infected with a single miracidium were established during 28 consecutive days from the first day of cercarial shedding. Moreover, the effect of a sudden change in light-dark cycling was investigated. Although the daily cercarial shedding rates show great variability, a progressive increase in cercarial production was observed in the first weeks of the cercarial shedding periods, probably in relation to the demography of intramolluscan larval stages. Under 12:12 light-dark cycling conditions, E. albuferensis cercariae emerged in the light, and the rhythm was circadian. The sudden change in the light-dark cycle resulted in corresponding alterations in emergence patterns, which shows that cercarial emergence was correlated to light-dark alternation. The ecological consequences of daily emergence by mobile cercariae whose target hosts are organisms that regularly occur in the same habitat with the molluscan emitting host, such as those of E. albuferensis, are discussed with reference to the hypotheses proposed to date, and an alternative hypothesis is proposed.     

Schistosoma intercalatum from Cameroon and Za?re: chronobiological differentiation of cercarial emergence

An experimental study of the cercarial emergence rhythm was conducted to compare 2 geographical strains of Schistosoma intercalatum from Cameroon and Za?re. For the Cameroon strain, the peak emergence time was between 1300 hr and 1400 hr, and the mean emergence time was 1359 hr. For the Za?re strain, the peak emergence time was between 1200 hr and 1300 hr, and the mean emergence time was 1213 hr. These results were shown to be significantly different by statistical analysis. Thus, the chronobiology of the emergence rhythms of the cercariae seems to be an additional marker to estimate the genetic variability of this species and to characterize the 2 strains.     

Cellular heterogeneity: yeast-side story

A major challenge for cells lies in their ability to detect, respond and adapt to changing environments that may threaten their survival. Among the numerous evolutionary strategies, cell-to-cell heterogeneity allows the emergence of different phenotypes within a population. This variability in cellular behaviors can be essential for a small fraction of cells to adapt and survive in various environments. Analyses at the single-cell level have allowed to highlight the great variability that is present between cells within an isogenic population. Numerous molecular mechanisms have been uncovered, allowing to understand the emergence and the role of cellular heterogeneity. These attempts at identifying the source of cellular noise have also provided clues for strategies needed to control heterogeneity. In this review, S. cerevisiae is used as an example to illustrate the different factors leading to cell heterogeneity, ranging from intracellular processes to environmental constraints. In addition, some recent strategies developed to modulate cell-to-cell variability are discussed.     

THE CYST OF THE POTATO-ROOT EELWORM (HETERODERA ROSTOCHIENSIS WOLLENWEBER) AS A HATCHING UNIT

Two series of experiments are described: in one, the hatching of half and whole cysts is compared, in some cases after they have been subjected to tryptic digestion; in the second series, the hatching of free eggs is considered.
Total emergence from halved cysts was very much greater than that from intact cysts. Emergence from trypsin-treated halved cysts was greater than emergence from control halved cysts, suggesting that the enzyme affects the egg shell or the larva inside; it is possible, however, that the enzyme also affects the cyst wall, for treated whole cysts shrink more rapidly and to a greater extent when exposed to air.
Total emergence from trypsin-treated whole cysts did not differ significantly from that of untreated whole cysts, unlike previous findings (Ellenby, 1946 a); however, emergence began sooner from these cysts. Halving the cysts also resulted in earlier emergence, the biggest effect being produced by a combination of both trypsin and subsequent halving.
The variability shown by the intact cysts was considerably greater than that shown by the halved cysts; halving the cysts reduced the coefficient of variation from 0·55 for whole untreated cysts, to 0·19 for untreated halved cysts, and to 0·13 for trypsin-treated halved cysts. Apparently some of the variability in emergence, like the limitation of total emergence, is bound up with the nature of the cyst as a more or less closed system.
In two experiments the hatching of eggs freed from half-cysts was compared with that of eggs in their fellow intact halves. In one experiment there was no difference; in the other it was possible to show that a higher proportion of free eggs hatched. Evidently factors limiting hatching may operate among eggs in a mass, even though they are no longer completely enclosed in a cyst.     

Emergence of deciduous teeth in Punjabi children, north India.

Data on deciduous tooth emergence of 312 children aged 4 to 31 months of Punjabi parentage are presented. Probit analysis was used to derive the median age of tooth emergence. Female children are found to be advanced with respect to tooth emergence than their male counterparts. While comparing the present data with those from other populations it is found that, in general, the mean number of emerged teeth in Punjabi children is more at most ages, with lower median age of eruption for most teeth. Magnitude of interage variability in the eruption times is noticed to be maximum in the 16-17 and 20-21 months age groups. The findings of the study suggest that number of teeth can be used as a parameter for the estimation of age.     

Intraspecific variability of the phenology and morphology of three protected dragonflies between natural and artificial habitats

Changes in phenology and in body size are two of the three main consequences of global warming on organisms. We investigated whether living in a warm artificial habitat would induce changes in the phenology and body size of dragonflies. We monitored in natura the emergence pattern of three protected and red-listed dragonfly species in three geographically close systems which differ in thermal profiles: a medium-sized river, one of its tributaries and an artificial lake fed by the water of the tributary. We also investigated the morphological variability of one of the species between the three systems. We showed an asynchrony of emergence for the three species, as well as morphological variability between the lake and the two rivers. Individuals from the lake emerged earlier and were smaller than those from the two rivers. These results are in agreement with a temperature-induced response hypothesis as the lake is warmer than the two rivers. Asynchrony of emergence between neighbouring populations triggers questions related to metapopulation functioning and about the fitness and the fate of the early-emerging individuals. Understanding the response of these species to local thermal conditions will help to improve population monitoring and conservation.     

Effects of timing of precipitation and acorn harvest date on emergence of Quercus emoryi

Abstract. Germination of semi-arid Quercus is strongly correlated with the rainy season. However, the timing and amount of summer precipitation in the southwestern United States is extremely variable. Ongoing and impending changes in global and regional climates are likely to increase this variability. Specifically, anthropogenically induced changes in general circulation patterns may alter the seasonal distribution of precipitation in a directional manner. In addition to climatic variability, the inter- and intra-annual variability of Quercus emoryi Torr. (Emory oak) acorn maturation also is high. Therefore, in light of existing climatic variability and potential future climate change, we conducted a greenhouse experiment to investigate the effects of acorn maturation date and the timing of the onset of the ‘monsoon’ on emergence of Q. emoryi seedlings. Acorns were collected at weekly intervals in July of 1995 and 1996, planted in a greenhouse, and subjected to different watering treatments. Watering treatments were (1) acorns watered the same day as planting; (2) acorns watered two weeks after planting; (3) acorns watered four weeks after planting. Emergence in 1995 was significantly greater in the last week of acorn maturation and decreased significantly as time to the onset of the ‘monsoon’ increased. Emergence in 1996 was very low, presumably because of soil moisture contents that were lower than those observed in 1995. The dependence of Q. emoryi on water for emergence has profound implications for Q. emoryi recruitment in the face of current climatic variability and future climate change. Summers with a delayed ‘monsoon’ and decreased soil moisture may severely constrain recruitment of this woody plant.     

Emergence rhythms and protandry in relation to daily patterns of locomotor activity inTrichogramma species

Summary In insect parasitoids, the mating structure of the population depends on the emergence pattern of adults and on their behaviour after emergence. In order to study some aspects of these characteristics in four species of egg parasitoid of the genusTrichogramma, laboratory experiments using automatic video analysis are performed. Adult emergence is concentrated in the morning, with an earlier time for males. The variability of the time of emergence is under genetic control. The relationships between the emergence pattern and the locomotor activity are considered by measuring individually: first, the delay between the emergence and the first locomotion which is significantly greater in females than in males and, second, the activity of newly emerged males, which is maximum at the time of the emergence of females. The locomotor activity is influenced by mating; mated females are much more active than virgin ones, mated males are less active than virgin ones. The adaptive values of the rhythmicity of emergence and of protandry are discussed together with their relationship with the patterns of locomotor activity. The results are also considered with respect to mating strategies in insect parasitoids; they actually support the hypothesis of mating occurring principally among individuals native to the same host patch inTrichogramma species.     

Assessing maternal effects on metabolic rate dynamics along early development in brown trout (Salmo trutta): an individual-based approach

Routine metabolic rate (oxygen consumption) of individual eggs and larvae of brown trout (Salmo trutta) originating from different families were monitored from fertilisation to the onset of emergence by means of flow through micro-respirometry. This measuring system revealed an accurate tool to measure oxygen consumption on small organisms at the individual level, and daily consumption proved to be very stable. The mass-specific metabolic rate remained low from fertilisation to hatching, and then increased quickly until the age of emergence. A Bayesian modelling approach was used to adequately infer maternal effects on metabolic rate dynamics all along the development period. Substantial differences were found between families, affecting average metabolic rate as well as intra-family variance. That is, offspring originating from different females may have different energetic needs at emergence from gravel. Moreover, between siblings, variability in metabolic rate is also under the influence of maternal effects. Implications of this metabolic rate variability are discussed with regard to life history strategies and early behaviours.