Κυριακή, 12 Μαΐου 2019

Biology

Longitudinal Stolon Pulsations in the Colonial Hydroid Dynamena pumila (Linnaeus, 1758)

Abstract

It is established via time-lapse video microscopy that the zone of longitudinal extension of the stolon coenosarc in the colonial hydroid Dynamena pumila can extend over two interstitial sites (modules). The stretching occurs in the form of oscillations with a period corresponding to the growth pulsations of the stolon tip. Consequently, the growth zone is not restricted to one stolon module, and the main condition for longitudinal growth of the coenosarc appears to be the stretching created by the advancing growth tip, not only by the increasing number of cells in the growth zone, as the main cause of coenosarc elongation.



Impact of Spatial Heterogeneity on Drosophila melanogaster Adaptation to Unfavourable Food Media: The Results of an Experimental Evolution Study

Abstract

The spatiotemporal variability of environmental conditions is assumed to have a strong impact on the course of microevolution processes, including the efficiency of adaptation to unfavourable conditions and the probability of ecological specialization or, conversely, generalization (the acquisition of multipurpose adaptations). The experimentаl research on these effects is still at the initial stage, and the temporal, rather than spatial, heterogeneity of the environment is analyzed in most studies. We performed an evolution experiment that involved the adaptation of Drosophila melanogaster lines to two unfavourable media: a high-salt (S) medium and a starch-based (St) medium of low nutritional value. Some of the experimental lines had access to one of the two unfavourable media only (homogeneous environment), whereas the others had access to both media and could choose between them (heterogeneous environment). The control lines were reared on a normal laboratory medium (N) that provided favourable conditions for the species. The degree of adaptation of lines obtained on the S, St, and N media was assessed after one and a half years of adaptation. The reproduction efficiency (the amount of adult progeny derived from a pair of parents within a specified time interval), adult lifespan, oviposition rate, and ageing-related changes in the former were assessed. Flies reared in a heterogeneous environment were superior to those reared in a homogeneous one with regard to most adaptation parameters on all three media. The results agree with the hypothesis concerning the promotion of generalization and more efficient adaptation to unfavourable conditions upon spatial heterogeneity of the environment. The obtained data do not support the hypothesis of antagonistic pleiotropy, which leads to "evolutionary trade-offs" and a lower competitiveness of generalists than that of specialists under stable conditions.



Growth, Coenosarc Pulsations, and Hydroplasm Movement in the Colonial Hydroid Dynamena pumila (L., 1758) Placed in Flow-Through and Nonflow Cuvettes

Abstract

The coenosarc pulsations of the stolon and hydroplasmic flows (HFs) in the colonial hydroid Dynamena pumila (L., 1758) have been recorded in flow-through and nonflow, shallow cuvettes via time-lapse video microscopy. The water in the flow-through cuvette was refreshed during every 24 s. Each episode was video recorded for 2 h. Eleven indicators were used to compare hydroid reactions to maintenance in flowing and nonflowing water: the period and amplitude of pulsations of the stolon growing tip; the hourly stolon growth; the period and amplitude of transverse coenosarc pulsations; the period of unidirectional HF rate pulsations; the maximum velocity of HFs to and from the stolon tip; the distance of particle transfer per act of unidirectional HF; the volume of displaced hydroplasm per HF; and the percentage of the rest ratio in coenosarc pulsations and hydroplasm movement. On the whole, no significant changes in the coenosarc pulsations or in the growth and displacement of the hydroplasm were detected when they were compared sequentially in the same colonies in nonflowing and flowing water. At the same time, there were no changes in the growth, the frequency and amplitude of the transverse pulsations of the coenosarc, or the activity and extent of the hydroplasm currents. However, it was found that the period of growth pulsations increases by 20% in the regime with water exchange in comparison with the previous regime without flowing water. The period of HFs in the stolon increases by 42%, and the maximum current velocity decreases by 20% in flowing water. As a result, the calculated volume of moved hydroplasm in the stolon for one HF decreased by 30% in flow conditions.



Parasitic Manipulations of the Host Phenotype: Effects in Internal and External Environments

Abstract

Parasites can influence their hosts in various ways. When a parasite changes the phenotype of its host to increase its own fitness, it is called parasitic manipulation of host phenotype. Perhaps, not all parasites are manipulators, but manipulations are undoubtedly a widespread natural phenomenon and well-established scientific concept. Parasites can manipulate the host phenotype to ensure their additional safety within the host body, create optimal conditions for their growth and development, and promote transmission from one host to another. Parasitic manipulative strategies are highly diverse and tightly connected with the parasite's life cycle. The review gives insight into the most common types of manipulative strategies and discusses (i) the evolutionary advantages of these strategies, (ii) why some strategies are more common than others, and (iii) how manipulative strategies change in the course of parasite growth and development. Recently, it has become clear that parasitic manipulations can be an important factor influencing the relationships in both the parasitic infracommunity within the host and the ecosystem in general. The last two sections of the review describe the conflicts and cooperation within the parasitic infrapopulation and the role of parasitic manipulations in ecosystems. The review concludes with a short, imaginary journey into the future that discusses how climate change may influence the role of parasites and their manipulations in the ever-changing environment.



Trends of Intraspecific Differentiation in the Beaked Redfish Sebastes mentella (Scorpaenidae) from the Atlantic Ocean and Adjacent Waters

Abstract

Based on studies of the population structure of the beaked redfish Sebastes mentella in the Atlantic and Arctic oceans, a conclusion has been made about the existence of another, epigenetic, trend of its intraspecific differentiation, in addition to the population trend. Analysis of the vast array of our data and those available in literature, which were obtained by the methodological approaches accepted in population biology, made it possible to distinguish three isolated populations of beaked redfish: the North Atlantic, the Norwegian Barents Sea, and the Flemish Cap. The first two are subdivided into demersal and pelagic epigenetic groups that differ morphophysiologically and ecologically. One of the main factors of the epigenetic differentiation of beaked redfish is ontogenetic—individuals reach sexual maturity at different times. Based on the dynamics of the physiological condition of gonads, two groups of fish are identified: early maturing individuals that mainly inhabit the ocean pelagic zone and late-maturing fish that predominantly live in the near-bottom layer along the continental slope. In the first group, the mass maturation of redfish (50% of individuals) occurs at an FL of 29–33 cm and the age of 9–12 years; in the second group, it occurs at an FL of 35–43 cm and the age of 14–19 years. Another factor of epigenetic differentiation is biotopic; it is manifested as the association of discrete groups with different biotopes. Late-maturing redfish stay in the near-bottom layer of the continental and island slopes throughout the year, while early maturing individuals tend to live in the pelagic zone of open ocean areas. The biotopic epigenetic differentiation is closely related to the onset of return migrations from the nursery grounds of juveniles upon their reaching maturity. Juvenile beaked redfish stay in the nursery ground, which is located in the shelf and shallow coastal waters, up to the age 6–10 years. Early maturing individuals are the first to leave the juvenile grounds and move to the ocean pelagic waters. Late-maturing fish, as they grow during prolonged (up to 5–7 years) migration, are recruited to demersal aggregations in deep-sea areas on continental slopes. The complication of the species' ecological structure due to the differentiation of epigenetic groups by biotopes has led to trophic specialization and weakening of the competitive interactions between them. Their habitation in different biotopes and the physiological polymorphism of redfish have not affected the unity of species populations. In the breeding season, there is no spatiotemporal isolation between the epigenetic groups, and the demersal and pelagic aggregations are replenished by common sources.



Modeling of the Damage Sustained by Forest Coenoses and Their Destruction under the Impact of Point Contamination Sources

Abstract

This paper addresses novel approaches to the description of ecosystem changes under the impact of contaminants, depending on their local concentration and impact duration. It is shown that, with quite simple assumptions about the biotic effects of a contaminant, this process can be considered an environmental analog of a second-order phase transition. Data on forest ecosystems in the vicinity of major point sources of contamination (copper smelting plants) were used for the analysis and verification of the proposed model.



Analyzing the Fine-Scale Dynamics of Two Dominant Species in a Polytrichum–Myrtillus Pine Forest. II. An Inhomogeneous Markov Chain and Averaged Indices

Abstract

Data from six repeated observations in a Polytrichum-type Scots pine forest are used to construct a nonautonomous Markov model of fine-scale dynamics of the two dominant species, bilberry (Vaccinium myrtillus) and lingonberry (V. vitis-idaea), at the late stages of postfire succession. The model consists of five transition matrices dependent on the observation year, and transition to the average matrix results in a homogeneous model. The design of the field experiment featured a large sample size on permanent transects (2000 quadrats × 6 observations), a 5-year reexamination interval, and the use of species rooting frequency on 20 × 20 cm quadrats over 25 years. The discrete Markov chain used to model the observed process of species alternation on the quadrats consists of four states: an absence of both species from the quadrat, the presence of one species of the two, and the joint presence of both species. The model time step coincides with the interval between the observations. The data allow for a unique calibration of the transition matrix for each pair of sequential observations, and the formulas of finite Markov chain theory yield the vectors of steady-state square distributions for each of the five temporal transitions. Fluctuations in the species rooting frequency among the observations are shown to exert substantial effects on the values of certain elements in the transition matrices and the components of the corresponding steady-state vectors (for particular pairs of observations), but there are no major changes in the conclusions concerning the dominating components (dominating states of the quadrats), regardless of the fluctuations. The geometric mean of five transition matrices recapitulates the spatial and temporal characteristics of the process over the entire observation period. We show that the stable terminal outcome of species dynamics is expected to involve the following distribution of quadrats among the states: 37% of the quadrats with V. myrtillus alone, 11% with V. vitis-idaea alone, 38% quadrats with both species present, and 14% "empty" quadrats. It is shown for the first time that the share of quadrats with V. vitis-idaea alone decreases considerably in the course of succession, whereas the share of quadrats with both species growing together increases. The averaged characteristics of the cyclicity and stage duration of the fine-scale dynamics make it possible to estimate the total duration of the secondary postfire succession (to reach a nearly terminal state) at 46–50 years. The quadrats with V. vitis-idaea alone have the shortest average lifetime among the described states (9 years), and those with both V. myrtillus and V. vitis-idaea have the longest average lifetime (18 years), which is partly explained by the different lifetimes of the species' shoots.



The Relation between the Species Diversity Index and Characteristics of Organism Communities in Waterbodies

Abstract

Based on literature data and our own, changes in the Shannon diversity index for the communities of organisms under changing environmental factors are considered. The eutrophication and pollution of waterbodies are shown to reduce the diversity of the communities; they become simpler, and the ratio of steno- to eurybiotic species decreases.



Estuarine Ecosystems and Their Place in Natural River Mouth Complexes of the Arctic: A Case Study of the Yenisei Mouth Area

Abstract

The estuarine ecosystem is characterized by the mixing of seawater and freshwater with a resulting salinity of 0.5 to 22–26‰, which is preserved for no less than 2–3 weeks, and by the presence of specific brackish water species. The distinguishing features of Arctic estuarine ecosystems are a sharp thermohaline stratification of the waters and, as a consequence, a difference in the boundaries of the brackish water biota distribution near the bottom and in the pelagic zone. Note that only the bottom estuarine biocenoses are characteristic of the river mouth area. The most important factor in the Arctic estuarine ecosystems is the longitudinal migrations of the halocline, especially seasonal ones. The coincidence of the borders of distribution of the true brackish water species with the borders of hydrological and morphological regions of the Yenisei River estuary defined according to long-term observations is noteworthy. Given the relative similarity of the Arctic estuarine ecosystems in their physical, chemical, and biotic components associated with the latitudinal uniformity of the mouths, we assume the presence of this correlation in other estuarine areas as well. In this case, a single survey of the benthos may give the same result as multiyear series of hydrological observations in the regionalization of an estuarine ecosystem.



In vitro Callus as a Model System for the Study of Plant Stress-Resistance to Abiotic Factors (on the Example of Cereals)

Abstract

The data on various aspects of the use of cereals callus cultures in vitro as model systems for the study of the plant stress-resistance to abiotic factors are presented. The focus is on studies of in vitro calli for the assessment of plant stress-resistance to drought stress. The advantages and limitations of callus cultures in vitro are considered as experimental methods to obtain stress-resistant regenerants. The issue of studying anti-stress effects in callus cultures in vitro is analyzed. The prospects of studying the mechanisms of the action of abiotic stressors and their resistance in plants at the cellular and tissue levels in the model conditions of in vitro callus culture are shown. It is emphasized that the basis for the use of calli as model systems is both the important role of the cell in all of the morphogenetic events of the plant organism in vivo and in vitro and the similarity of responses of plants in vivo, calli in vitro, and calli regenerants in vitro and ex vitro.



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