Cyclic Reproduction Research Articles

Variation in reproductive parameters of Rhinella arenarum (Hensel, 1867) (Anura: Bufonidae) between the reproductive and post-reproductive periods

We compared reproductive parameters of Rhinella arenarum in a wetland of the Monte in Argentina during reproductive and post-reproductive seasons. Individuals were collected at random, monthly from November 2001 to October 2002. August through November was considered the reproductive period, and December through April was considered the post-reproductive period. Of the 116 adults, 75 were males and 41 were females. The reproductive parameters measured included body mass, fat body mass, number of mature ova, ova size, and testicular volume. There were significant differences between the reproductive and post-reproductive periods in females for body mass, fat body mass, and number of mature ova. Likewise, males also had significant differences between these periods for body mass and fat body mass. Apparently, R. arenarum has an opportunistic and continuous reproductive strategy. Entering dormancy with large fat bodies and testes in apparent spermatogenesis allows males to reproduce immediately after emerging in the spring. However, females have mature but fewer ova during this period, which is a reproductive feature shared by most temperate amphibians. Our data, and the primarily tropical distribution of R. arenarum, suggest that this species recently invaded the temperate region wherein males retained acyclic reproductive activity and females, owing to their higher reproductive costs, have evolved cyclic reproduction.

Spatio-temporal profile of atomic oxygen in a 1 kHz repetition atmospheric-pressure plasma jet in He–O2–H2O mixture

Atomic oxygen (O) is one of the essential reactive species in plasma oxidation processes. We investigated the behavior of atomic oxygen in a 1 kHz-repetition pulsed plasma jet in atmospheric-pressure He/O2/H2O mixture. By two-photon absorption laser-induced fluorescence, the spatio-temporal profiles of O density were measured under various conditions. In the dry ([H2O] 100 ppm) condition, the rate of O production did not depend on the [O2] fraction in the range of [O2] = 275–8600 ppm. The analysis of the O-production rate indicates that the atomic oxygen in this plasma jet arises from electron-impact dissociation and quenching of O(1 D), similar to the O-production mechanism in radio-frequency plasma jet. The dependence of O-production in each discharge pulse (Δ[O]) on the discharge energy and [O2] in the plasma region at dry condition is formulated as . The decay rate of atomic oxygen was not explained by self-recombination or ozone-generation reactions; it was consistent with the reaction rate of O + OH O2 + H at [OH] = cm−3. This result suggests that the small amount of [OH] with 1013 cm−3 density is more responsible for O behavior than [O2] with large fraction of 1015 cm−3. We conducted a chemical reaction simulation considering the measured results of [O] and [OH] production, resulting in good agreement with the spatial distribution of [O]. Chemical reaction analysis revealed that the cyclic reproduction of OH via chain reaction with O and O2 is important, therefore a small amount of OH catalytically consumes atomic oxygen with two-order higher density.

МОДЕЛЮВАННЯ РІВНЯ ІННОВАТИВНОСТІ ПІДПРИЄМСТВА ЯК ІНФОРМАЦІЙНО-АНАЛІТИЧНЕ ЗАБЕЗПЕЧЕННЯ СТРАТЕГІЇ ІННОВАЦІЙНОГО РОЗВИТКУ

The issues of determining the level of enterprises. The research methods were statistical, methods of scientific knowledge, dialectical, induction and deduction, and economic and mathematical modeling to determine the influence of the level of innovation of enterprises on their development. The review of the theoretical foundations of the category of innovativeness of enterprises, intended components of innovation, such as innovative susceptibility; cyclical reproduction of innovative potential; the nature of innovative behavior; the level of research potential. It is proposed to consider innovation from the point of view of M. Porter's “concept of a diamond”. A methodological approach has been developed to assess the impact of the degree of innovation on the development of enterprises based on the integral index. The developed methodological approach consists of a sequence of the following stages: formation of a sample of statistical information on the degree of innovation of enterprises, selection of a reference indicator, statistical processing of input data, selection of indicators for inclusion in the model based on correlation analysis, after which the additive form of the integral index is constructed, assignment weighting coefficients for the components of innovation, raising indicators to a comparable type. The developed methodological approach will allow to timely and quickly assess the impact of the degree of innovation on the development of enterprises and make appropriate management decisions aimed at increasing the level of innovation of socio-economic systems of various levels and scales. The existing parameters of the growth of enterprises are based on innovation. The issues of assessing the effectiveness of economic development of enterprises on the basis of innovation are considered. Further research will be aimed at finding and improving modern methodological methods for assessing the impact of the innovatization of enterprises on their economic development, as well as the formation and accumulation of best experiences in accordance with the indicated problems and categories.

Digital Cyclical Ecological Regional Self-Sufficient Economy

The economy is sphere of public work and the set of relations that form in the system of production, distribution, exchange and consumption. The paper examines the digital, cyclical, environmental and regional aspects of a cyclical digital environmental regional economy. The digital direction of the economy uses digital twins and robots as assistants to improve its quality, productivity and efficiency. The cyclical economy uses savings and profits to boost its competition and development. The environmental direction of the economy maintains the viability of the environment. The regional economy increases diversification and capacity of local production and preserves the environment in its territory regardless of the type of economic activity. Cyclical aspects of the economy of self-sufficiency mainly concern the financial round-up, and the closed reproduction cycle. Business models of cyclic reproduction realize its economic self-sufficiency. At present, Russia, China, the United States and EU integration education have achieved the optimal level of national economic self-sufficiency. Russia, the United States, and the EU have the necessary financial and human resources. At the same time, China, with excessive human resources, is pursuing a policy of expansion into developing and underdeveloped countries. The main reason for countries to abandon autarky policies in favor of globalization of research activities is the decline in profit levels. The reason for this situation lies in the availability of cheap labour and favourable economic conditions, and production in countries is therefore cheaper. The reason for globalization and the international division of labour lies in maximizing profits, and autarks in maximizing national production, i.e. self-sufficiency. The unity of the Autarky State must be ensured by the existence of economic, historical, cultural ties, as well as by national equilibrium.

Digital Cyclical Ecological Regional Self-Sufficient Economy

The economy is sphere of public work and the set of relations that form in the system of production, distribution, exchange and consumption. The paper examines the digital, cyclical, environmental and regional aspects of a cyclical digital environmental regional economy. The digital direction of the economy uses digital twins and robots as assistants to improve its quality, productivity and efficiency. The cyclical economy uses savings and profits to boost its competition and development. The environmental direction of the economy maintains the viability of the environment. The regional economy increases diversification and capacity of local production and preserves the environment in its territory regardless of the type of economic activity. Cyclical aspects of the economy of self-sufficiency mainly concern the financial round-up, and the closed reproduction cycle. Business models of cyclic reproduction realize its economic self-sufficiency. At present, Russia, China, the United States and EU integration education have achieved the optimal level of national economic self-sufficiency. Russia, the United States, and the EU have the necessary financial and human resources. At the same time, China, with excessive human resources, is pursuing a policy of expansion into developing and underdeveloped countries. The main reason for countries to abandon autarky policies in favor of globalization of research activities is the decline in profit levels. The reason for this situation lies in the availability of cheap labour and favourable economic conditions, and production in countries is therefore cheaper. The reason for globalization and the international division of labour lies in maximizing profits, and autarks in maximizing national production, i.e. self-sufficiency. The unity of the Autarky State must be ensured by the existence of economic, historical, cultural ties, as well as by national equilibrium.

Chloronium Cations in Dichloromethane Solutions as Catalysts for the Conversion of CH2Cl2 to CHCl3/CCl4 and CH3Cl/CH4

AbstractThe mechanism of homogeneous acidic catalytic conversion of CH2Cl2 to CHCl3 and CCl4 and simultaneously to CH3Cl and CH4 in solutions of the H(CHB11Cl11) superacid in dichloromethane was identified. The role of the catalysts is played by the chloronium cations formed in the solutions. The processes proceed through the exchange of the Cl atoms of the CH2Cl‐ group of cations CH2Cl‐Cl+‐CH2Cl and CH2Cl‐Cl+‐CH3 for the H atoms of the CH2Cl2 molecules, transforming them initially to CHCl3 and then to CCl4. Simultaneously, the CH3‐group of cations CH3‐Cl+‐CH2Cl and CH3‐Cl+‐CH3 exchanges its H atom for the Cl atom of CH2Cl2 molecules, transforming them to CH3Cl and further to CH4. The processes of chlorination and dechlorination lead to cyclic reproduction of chloronium cations.

Reproductive biology of Philodryas patagoniensis (Snakes: Dipsadidae) in south Brazil: Female reproductive cycle

AbstractIn this study, we describe the female reproductive cycle of Philodryas patagoniensis in south Brazil, which was described through morpho‐anatomical and histological analyses. The peak of secondary vitellogenesis occurred during winter–spring (July–December), ovulation in spring (October–December), mating and fertilization in spring–summer (October–February), oviposition in spring–autumn (October–May) and births from late spring to autumn (December–July). The diameter of vitellogenic follicles/eggs was larger in winter–spring than in other seasons. The diameter of the shell glands was also larger in winter–spring. In spite of the clear reproductive peak, gonads only showed reduced activity in the autumn. Therefore, at the individual level, females have a discontinuous cyclical reproduction; in the populational level, the reproductive cycle is seasonal semisynchronous. We support the hypothesis that P. patagoniensis have the ability to produce multiple clutches with long‐term stored sperm. Sexual dimorphism in body size was evident, and females are significantly larger and heavier than males. Larger females were able to produce follicles and eggs in larger amount and size. The maternal body size was positively related to the reproductive effort and fecundity. To conclude, we deliberated about the proximal and distal causes that influence the reproductive traits and patterns of P. patagoniensis.

The adaptive significance of phasic colony cycles in army ants

Army ants are top arthropod predators in tropical forests around the world. The colonies of many army ant species undergo stereotypical behavioral and reproductive cycles, alternating between brood care and reproductive phases. In the brood care phase, colonies contain a cohort of larvae that are synchronized in their development and have to be fed. In the reproductive phase larvae are absent and oviposition takes place. Despite these colony cycles being a striking feature of army ant biology, their adaptive significance is unclear. Here we use a modeling approach to show that cyclic reproduction is favored under conditions where per capita foraging costs decrease with the number of larvae in a colony (“High Cost of Entry” scenario), while continuous reproduction is favored under conditions where per capita foraging costs increase with the number of larvae (“Resource Exhaustion” scenario). We argue that the former scenario specifically applies to army ants, because large raiding parties are required to overpower prey colonies. However, once raiding is successful it provides abundant food for a large cohort of larvae. The latter scenario, on the other hand, will apply to non-army ants, because in those species local resource depletion will force workers to forage over larger distances to feed large larval cohorts. Our model provides a quantitative framework for understanding the adaptive value of phasic colony cycles in ants.

Reproduction and development in some species of the weakly electric genus Campylomormyrus (Mormyridae, Teleostei)

Reproduction in captivity of four species of the mormyrid genus Campylomormyrus was investigated. Cyclical reproduction was provoked by changing water conductivity (C) alone: decreasing C led to gonadal recrudescence, an increase induced gonad regression. Data on the reproduction and development of three species are presented. All three species are indeterminate fractional spawners. Spawning intervals ranged from 6 to 66 days in C. rhynchophorus, 10–75 days in C. tshokwe, and 18 days in C. compressirostris (calculated values). Fecundities (eggs per fractional spawning) ranged from 70 to 1570 eggs in C. rhynchophorus, 100–1192 in C. tshokwe, and 38–246 in C. compressirostris. Spawnings/ovipositions occurred during the second half of the night; no parental care was observed; no special spawning substrates were necessary. C. compressirostris successfully spawned in breeding groups, C. rhynchophorus as pair. Agonistic behavior in the C. tshokwe pair forced us to divide the breeding tank; therefore, only ovipositions occurred. However, injection of an artificial GnRH hormone allowed us to obtain ripe eggs and sperm and to perform successful artificial reproduction. All three species produce yolky, slightly sticky eggs. Egg diameter ranges from 2.3–3.0 mm. Hatching occurred on day 3, feeding started on day 11. Transition from larval to juvenile stage occurred at around 20 mm total length (TL). At this size C. rhynchophorus developed a higher body than the two other species and differences between the species in the melanin pigmentation of the unpaired fins occurred. Between 32 and 35 mm TL the upper and lower jaws started to elongate.

Reproductive biology of Philodryas patagoniensis (Snakes: Dipsadidae) in south Brazil: male reproductive cycle

AbstractThe male reproductive cycle of Philodryas patagoniensis in south Brazil was described through morpho‐anatomical and histological analysis of individuals deposited in zoological collections. Spermatogenesis occurred during late autumn–winter (June–September) and spermiogenesis occurred in spring–summer (October–March). The volume of the testes was smaller (quiescent) in winter, while the tubular diameter and the epithelial height of the seminiferous tubule were larger in summer (January–March). The ductus deferens presented spermatozoa all over the year and had no seasonal variation in diameter. The length of the kidney was larger in winter–spring (July–December), although the tubular diameter and epithelium height of the sexual segment of the kidney (SSK) were larger only in winter (July–September). Total testicular regression was observed in late autumn (May), simultaneously with the peak in SSK. Therefore, at the individual level, males exhibit a discontinuous cyclical reproduction. Considering the population level, the reproductive cycle is seasonal semisynchronous, with most of the individuals showing a reproductive peak in spring–summer (October–March). Here, we present evidence to support the importance of the microscopic approach to reproductive cycle studies. Finally, we discuss the intrinsic and extrinsic factors influencing P. patagoniensis reproductive patterns.

Exercising Privilege: The Cyclical Reproduction of Capital through Swim Club Membership

According to cultural theorist Pierre Bourdieu, social class is defined by the interplay and operation of various forms of capital, within the set of durable and objective relations in which the classed subject is located. Informed by Bourdieu's understanding of social class, this article details the empirical dimensions of upper‐middle‐class familial involvement at the Valley View Swim and Tennis Club. An institution prefigured on the practice and development of important physical skills, Valley View represents a site for the complex interplay of capitals (economic, social, cultural, and physical) complicit in the preservation and reproduction of members' upper‐middle‐class habitus, and corresponding elevated and privileged social status. Specifically, we discuss the findings of ethnographic fieldwork focused on the acquisition, transmission, and conversion of economic, social, cultural, and physical capital in and through member families' club involvement. We argue that Valley View operates as a distinctive cultural field, wherein embodied techniques and expressions of class‐based power and privilege contribute to the reproduction of social class differences, boundaries, and hierarchies, in such a way as to render them natural, and largely unacknowledged, effects of being.

LPXRFamide peptide stimulates growth hormone and prolactin gene expression during the spawning period in the grass puffer, a semi-lunar synchronized spawner

Gonadotropin-inhibitory hormone (GnIH) plays as a multifunctional neurohormone that controls reproduction in birds and mammals. LPXRFamide (LPXRFa) peptide, the fish ortholog of GnIH, has been shown to regulate the secretion of not only gonadotropin (GTH) but also growth hormone (GH) and prolactin (PRL), which are potentially important for gonadal function. To investigate the role of LPXRFa peptide on reproduction of the grass puffer, which spawns in semilunar cycles, we examined changes in the levels of gh and prl expression over the several months during the reproductive cycle, and the effects of goldfish LPXRFa peptide-1 (gfLPXRFa-1) on their expression were examined using primary pituitary cultures. The expression levels of both gh and prl showed significant changes during the reproductive cycle in both sexes with one peak in the spawning and pre-spawning periods for gh and prl, respectively. Particularly, gh showed substantial increase in expression in the spawning and post-spawning periods, indicative of its essentiality in the advanced stage of reproduction. gfLPXRFa-1 stimulated the expression of both gh and prl but there was a marked difference in response between them: gfLPXRFa-1 stimulated gh expression at a relatively low dose but little effect was observed on prl. Combined with the previous results of daily and circadian oscillations of lpxrfa expression, the present results suggest that LPXRFa peptide is important in the control of the cyclic reproduction by serving as a multifunctional hypophysiotropic factor that regulates the expression of gh and prl as well as GTH subunit genes.

Cyclical Parthenogenetic Reproduction in the Russian Wheat Aphid (Hemiptera: Aphididae) in the United States: Sexual Reproduction and Its Outcome on Biotypic Diversity

In 1986, the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), became an invasive species of United States. Nearly 20 yr later, new biotypes appeared that were capable of overcoming most sources of resistance and became a renewed threat to wheat, Triticum aestivum L., production. Cyclical (CP) and obligate (OP) parthenogenesis enables aphids to both adapt to changing environments and exploit host resources. We documented these forms of reproduction for Russian wheat aphid in wheat and wild grasses in the Central Great Plains and Rocky Mountain regions during falls 2004-2009. Colonies from sample sites also were held under unheated greenhouse conditions and observed for the presence of sexual morphs and eggs through the winter. Russian wheat aphid populations were mainly OP and attempted to overwinter as adults, regardless of region sampled. A few populations contained oviparae but no males (gynocyclic) and were not specific to any particular region. Observation of the Russian wheat aphid colonies under greenhouse conditions failed to produce males or eggs. In spring 2007, CP was confirmed in a small population of Russian wheat aphid that eclosed from eggs (fundatricies) on wild grasses and wheat near Dove Creek, CO, in the Colorado Plateau region where other aphid species undergo CP. Lineages from ninety-three fundatricies were screened against 16 resistant and susceptible cereal entries to determine their biotypic classification. A high degree of biotypic diversity (41.4%) was detected in this population. Although CP was a rare in Russian wheat aphid populations, genetic recombination during the sexual cycle creates new biotypes and can have significant effects on population genetics.

The “divided time illusion” in musicians: From puzzling data to evidence for a rate limit.

The divided time illusion (DTI) is the finding that brief intervals seem longer when they are subdivided by one or more additional events than when they are empty. Two previous multiexperiment studies using different synchronization-continuation tapping tasks demonstrated the DTI in musicians' perception and production of beat tempo (Repp, 2008; Repp & Bruttomesso, 2009): Subdivided seem slower than undivided beats. Each study, however, contained a single condition that yielded puzzling results inconsistent with the DTI; each had intermixed trials with duple and triple metrical subdivision of interbeat intervals (IBIs). Our attempt to replicate the deviant 2008 result failed, now yielding data consistent with the DTI. However, we did replicate the deviant 2009 result and then followed it up by assigning different forms of subdivision (duple, triple, quadruple) to separate trial blocks and varying IBI duration within each block. The results turned out to be quite systematic and consistent with the DTI. Moreover, they revealed that the DTI decreases as IBI duration decreases and vanishes when the subdivision event rate reaches 5- 6 Hz. We tentatively attribute the puzzling 2009 result to attenuation of the DTI by mental subdivision of undivided beats, due to memory requirements of the earlier task design.Keywords: divided time illusion, filled duration illusion, synchronization, tempo perception, rate limitsMany studies, some conducted as long ago as the 19th century, have demonstrated that brief temporal intervals are perceived to be longer when they contain one or more additional stimulus events than when they are empty (Adams, 1977; Buffardi, 1971; Craig, 1973; Goldfarb & Goldstone, 1963; Hall & Jastrow, 1886; Meumann, 1896; Ornstein, 1969; Thomas & Brown, 1974; Wearden, Norton, Martin, & Montford-Bebb, 2007). This divided time illusion (DTI; ten Hoopen, Miyauchi, & Nakajima, 2008) is one kind of filled duration illusion, another kind being the finding that continuous sounds are perceived as longer than equally long silent intervals (called the sustained sound illusion by Repp & Marcus, 2010). Most research on these effects used single intervals, though Grondin and collaborators (Gamache, Bisson, Hawke, Roussel, & Grondin, 2008; Grondin, 1992; Grondin, Guay, Lapointe, & Poulin, 2008; Grondin, Metthe, & Koren, 1994), who were primarily interested in timing variability, investigated cyclic reproduction of relatively long intervals from cyclic models containing various forms of metrical subdivision and found some evidence of the DTI for the shorter intervals used (1-1.2 s).In two recent studies, Repp (2008) and Repp and Bruttomesso (2009) similarly investigated whether the DTI is found in rhythmic contexts, where an isochronous sequence of presents the same interval repeatedly, with or without metrical subdivisions. These authors were specifically interested in the constant error occurring in musicians' judgment or reproduction of beat rates within a range characteristic of music (600-1,000 ms), the hypothesis being that subdivided would be perceived as being slower than undivided beats. (The term beats here refers simply to the sounds whose onsets delimit the successive intervals that are to be judged or reproduced.) Each of these previous studies yielded strong evidence in support of the DTI hypothesis in several experiments, but each contained one experiment or condition in which results were obtained that were inconsistent with the DTI hypothesis. The purpose of the present study was to try to replicate and possibly explain these puzzling exceptions.In Repp (2008), the deviant results occurred in Condition 4 of Experiment 2. In this condition, a synchronization-continuation paradigm was used where during the synchronization phase participants tapped with their right hand in synchrony with an isochronous auditory beat that was either undivided or divided by one or two left-hand taps, according to cues provided at the onset of the computer-produced beat sequence. …

Reproductive Mode of Fejervarya limnocharis (Anura: Ranidae) Caught from Mae Sot, Thailand Based on Its Gonadosomatic Indices.

Amphibians show a variety of reproductive modes and strategies. The cyclicity and continuity of reproduction can often be predicted from the annual gonadosomatic index trends in a species specific manner. This research aims to document the female and male gonadosomatic index profiles and to ascertain the reproductive cyclicity or continuity of Fejervarya limnocharis (Anura: Ranidae) caught in Mae Sot, Tak Province, Thailand. Frogs were collected monthly between November 2007 and October 2009 in rice fields and their surrounding areas in the study site. For each frog, total weight and ovarian/testicular weight were measured to obtain the female and male gonadosomatic index. The number of female individuals with mature eggs (postvitellogenic eggs) was also counted. The results showed that female frogs had two main surges of increased GSI in March and September of 2008. Alternatively, male frogs showed a more gradual increase and decrease in gonadosomatic index, thus the index remaining high throughout the year. This study concluded that while F. limnocharis in this area is essentially a continuous breeder, it is more optimized for a cyclic reproduction mode with two breeding cycles during the rainy season.

Cyclical Reproduction in Females of the Cuban Lizard Anolis lucius (Polychrotidae)

Abstract We describe the gonadal and fat-body cycles and their relationship to environmental factors for Cuban female Anolis lucius (Polychrotidae). We obtained monthly samples of lizards from the karstic caves at Boca de Jaruco, Havana, Cuba. The lizards reached sexual maturity at 45.0 mm snout–vent length and at approximately 7 mo of age. Female A. lucius showed seasonal reproduction from March to August. The nonreproductive season occurred from September to February, as identified by the absence of active ovogenesis. Vitellogenic ovaries, and almost all females having one or two oviductal eggs, characterized the peak reproductive interval from May to August. In contrast, fat-body mass diminished from May to July and reached its highest values from September to January. The clutch size is one egg per oviposition, and oviposition events occurred from July to September. Increased photoperiod and environmental temperature induced ovarian activity.

Niggers no more: a critical race counternarrative on Black male student achievement at predominantly White colleges and universities

A methodological approach popularized by critical race theorists is used in this article to oppose dominant discourse concerning the social and educational status of Black men in America. Specifically, this counternarrative on student achievement was derived from face‐to‐face individual interviews with 143 Black male undergraduates at 30 predominantly White colleges and universities across the USA. Exemplified via five composites constructed from the overall sample are resistant responses to subordination and racist stereotyping; confrontations with the cyclical reproduction of low expectations for Black male leadership and achievement; and an industrious rejection of what I refer to throughout the article as ‘niggering’. Also offered herein are implications for postsecondary faculty, administrators, and researchers.

Role of diapause in coexistence of zooplankton species: Model analysis

Many species of zooplankton form dormant eggs, which is a widespread phenomenon in aquatic ecosystems [1]. This is a common way in which populations survive unfavorable environmental conditions. Dormant eggs are resistant to drying and freezing [7], and they retain viability during a long storage [9]; therefore, they play an important role in the dynamics and evolution of aquatic ecosystems [3]. Dormant egg formation is traditionally regarded as an adaptive response to adverse factors that are potentially lethal for a population. The fact that species inhabiting temporary water bodies are the most sensitive to the environmental factors confirms this hypothesis [2]. At the same time, dormant egg formation may serve as a mechanism for supporting species diversity in the ecosystems in a relatively stable environment. The long-term coexistence of many phyto- and zooplanktonic species, their numbers exceeding the number of growth-limiting factors, is a well-known phenomenon referred to as the planktonic paradox [10]. In aquatic ecology, this phenomenon is in conflict with an axiom of modern ecology, Gause’s principle, according to which, in stationary environment, one out of two species competing for the same resource becomes extinct. The conditions meeting this axiom are extremely rare in nature; hence, the species diversity in real ecosystems often contradicts Gause’s principle, which may seem a paradox. To explain this paradox, a concept has been developed suggesting that water column serves as a multi-dimensional ecological niche where coexistence of species competing for the same resource is possible due to nonuniformity of the medium and periodicity of processes. Dormant egg formation may be regarded as a mechanism that supports species coexistence. For example, Caceres has reported that two close Daphnia species differing in reproductive strategy coexist in the same lake [5]: one species has a diapause in its life cycle, whereas the other species has no diapause. We studied the results of species competition for the same resource to estimate the possibility of the coexistence of two zooplanktonic species with different reproductive strategies: a species that forms dormant eggs and a species that does not form them. In this study, we used a discrete model of cyclic reproduction in Cladocera, which had been developed previously [13]. This model simulates a laboratory Cladocera batch culture with a continuous flow of fresh media and nutrition. Species competition was modeled in the space of natural values of zooplankton growth rate (0.004‐0.04 h ‐1 ) [11]. The region of modeling was divided into 81 cells using a grid with a spacing parameter of 0.004 cm (Fig. 1). Ten calculations were made for each cell. The initial density of both populations was 0.18 (mg wet biomass) l ‐1 . The calculation continued until one of the populations became extinct. The results of competition (the death of one or the other population) and the total number of dormant eggs were recorded at the end of each calculation. The possibility of coexistence was evaluated under the assumption that, during seasonal zooplankton growth, reactivation of dormant eggs occurred at the beginning of the next season. It was assumed that only 10% or even fewer dormant eggs were capable of reactivating [6].

Geographical Variation in the Ecology of Populations of Some Brazilian Species of Cnemidophorus (Squamata, Teiidae)

We investigated geographical variation in ecological parameters among populations of Cnemidophorus cryptus, Cnemidophorus gramivagus, Cnemidophorus lemniscatus, Cnemidophorus ocellifer, and Cnemidophorus parecis, from three Brazilian biomes (Cerrado, Caatinga, and Amazonian Savannas). Lizards used mainly the open ground, with a high similarity in microhabitat use among populations. Differences in microhabitat use probably resulted from the availability of microhabitats and not from microhabitat preferences. Body temperatures were high and little influenced by environmental temperatures, there being no differences among populations. There were significant differences in diet among populations, with C. ocellifer from Caatinga and Cerrado consuming large quantities of termites, whereas Amazonian Savanna species used primarily ants and insect larvae. The data on reproductive seasonality indicated cyclical reproduction in seasonal biomes and continuous reproduction in unpredictable climate regions. We found significant differences in mean clutch size among populations, independent of body size, with C. lemniscatus having the smallest clutch size (1.50) and C. ocellifer from Cerrado the largest (2.10). There were fewer differences in clutch size among species from Amazonian Savannas, than between populations of C. ocellifer from Caatinga and Cerrado. Apparently, populations under seasonal climates concentrate their reproductive effort during the short reproductive season, producing larger clutches, whereas those under more stable or unpredictable climates reproduce continuously, yielding smaller clutches, corroborating the hypothesis that environmental conditions exert an important influence upon life-history parameters. There were significant differences in body shape among populations, but most of the variation was related to sex. We also observed significant differences in body size among populations, seemingly unrelated to differences in community structure, but the highly conservative morphology of Cnemidophorus species suggests the presence of historical constraints.

Changes in the extracellular matrix surface network during cyclic reproduction of proembryonic cell complexes in the Fagopyrum tataricum (L.) gaertn callus.

Changes in the extracellular matrix surface network during cyclic reproduction of proembryonic cell complexes in the Fagopyrum tataricum (L.) gaertn callus.