Natural Reproduction Research Articles

Rational nature management: problems and prospects of Ukraine in the global system of nature restoration activities

The paper is devoted to studying the current state of nature management in Ukraine, considering the key factors that create problems in the global system of natural reproduction in Ukraine. The purpose of the study is to identify the key place, problems, and prospects of national nature management in Ukraine compared with other countries of the world and to determine the prospects for developing nature management in the post-war recovery period. For the research, general scientific methods of cognition were used, particularly methods of induction, deduction, analysis, synthesis, grouping, and systematization. The research results are based on the study of global environmental management ratings, including the environmental performance rating, the Happy Planet Index, the Global Green Economy Index, and the sustainable economic development assessment. The study of Ukraine's place among all countries in the world in terms of environmental management has highlighted a number of key problems, including deforestation, pollution, inefficient waste management, water use, etc. Furthermore, the report considers ways to improve natural resource management based on improving the natural resource management system and reducing corruption in all areas of natural resource management. The priority areas for the conservation and development of natural resources are the use of alternative, renewable energy sources, improvement of the processing industry, and introduction of modern standards and technologies for using natural resources. The practical significance of the study lies in the possibility of its use in the development of sustainable development strategies for the next periods.

Комплекс рыбоохранных сооружений Багаевского гидроузла на реке Дон

Purpose: to develop a technical justification of fish protection structures arranged as part of the Bagaevsky hydroelectric com-plex on the Don River. Materials and methods. The research was based on data on fish science, topographic, hydraulic and tech-nological conditions of the Bagaevsky hydroelectric complex. The methods of scientific analysis and technology of search design were used in the development of fish and security structures of the hydroelectric power plant. Results and discussion. The com-position, type, location and parameters of the fish protection facilities of the Bagaevsky hydroelectric complex have been estab-lished. A continuous fish-passing lock provides up to 16-20 cycles of attracting, accumulating and locking fish per day. The fish-spawning channel provides for the passage of fish with different swimming ability. Conditions for recreation and spawning of rheophilic and lithophilic fish species are formed in its tract, and phytophiles spawn in the ponds of the tract. Conclusions. 1. Tak-ing into account the fish-breeding significance and responsibility of the Bagaevsky hydroelectric complex, its technical solution provides for the creation of conditions for the passage and spawning of fish. 2. The adopted technical solutions for the construc-tion of a hydroelectric power plant, a fish-passing gateway, a fish-spawning channel and spawning ponds meet modern fish-breeding requirements and provide conditions for the natural reproduction of fish.

Germplasm Rescue of Postmortem Critically Endangered Yangtze Sturgeon (Acipenser dabryanus) by Cell Preservation

With the growing sophistication of cloning technology, rescuing cell resources is of great significance for the protection of endangered animals. The Yangtze sturgeon (Acipenser dabryanus), one of the three Acipenseriformes species in the Yangtze River, is critically endangered. Natural reproduction of the Yangtze sturgeon has not been detected since 2000. Less than 20 wild individuals are kept in husbandry, and all are too old to breed. Therefore, it is urgent to rescue the genetic resources of every wild Yangtze sturgeon. Here, we isolated and preserved viable cells from critically endangered postmortem Yangtze sturgeon for the first time. Attempts to rescue and preserve cell resources were carried out from 8 tissues, brain, kidney, gonad, fin, liver, skin, spleen, and muscle of an over 35-year-old female wild Yangtze sturgeon between 11 and 14 hours after death at 19.8°C in an outdoor concrete pond, and only muscle tissue cells could be successfully subcultured and preserved. Furthermore, the cultured cells showed high post-thaw cell viability and normal growth with a population doubling time of 52.98 h. Moreover, they were fibronectin- and desmin-positive, characterizing them as fibroblastic confirmed muscle cells with fibroblastic properties and myogenic origin. Tests for microbial contamination of the cell lines were negative. Chromosome analysis demonstrated that muscle cells possess a modal polyploid chromosome number of 264. The mitochondrial sequence data of COI genes and 12S rRNA confirmed that the developed cell line originated from A. dabryanus. Furthermore, transfection results indicate that muscle cells could be used for gene manipulation and functional studies. These results suggest that viable muscle cells could also be successfully isolated and cryopreserved from the wild Yangtze sturgeon in a short time after death. This report is not only of great significance for the germplasm rescue of critically endangered Yangtze sturgeon but also provides some scientific reference for the germplasm preservation of other endangered fish.

Transformation of Volga river runoff in multiyear aspect

The article describes in detail all the most significant components of the hydrological regime in the lower reaches of the Volga. As a result of the regulation of the Volga runoff by the Volgograd hydroelectric dam in 1958, the ecological conditions of natural reproduction of fish changed significantly: the areas of spawning grounds decreased, the hydrological regime was violated, which led to deformation of the spring flood regime, intra-annual redistribution of runoff. Their size is of fundamental importance for the fisheries of the Volga-Caspian basin. Attention is drawn to the deep deformation of all flood indicators that occurred after the regulation of the Volga runoff on the Lower Volga, while in the worse direction for the reproduction of aquatic biological resources. The process of degradation of aquatic biological resources of the Volga-Caspian reflects the lack of the minimum hydroecological conditions necessary to ensure the formation of resilient juvenile fish in the process of their natural reproduction in the overwhelming number of years. The modern operation of the Volga-Kama cascade of reservoirs does not meet the requirements of the Volga-Caspian fisheries. There is a tendency to increase intraannual redistribution of runoff, due to high winter releases of water into the lower reaches of the Volgograd hydroelectric complex and low spring releases. The system of management and intersectoral distribution of water resources during the flood does not currently meet the necessary hydroecological conditions under which it is possible to form resilient fish offspring and, as a consequence, preserve and increase stocks of the most valuable commercial fish species. The main reasons for the decrease in water reserves are determined by the regulation of the Volga runoff and as a result of this reduction in the volume of water supply to the lower reaches of the Volgograd hydroelectric complex. Especially this negative manifestation of a sharp deterioration in the flooding of spawning grounds occurs in low-water years, when the priority is to fill the reservoirs of the cascade to a normal retaining level in order to ensure the generation of hydroelectric power during the inter-war period (summer, autumn, winter), the operation of water transport, the implementation of water intake for irrigation, utility purposes, etc.

Fish-spawning channel consisting of Kochetovsky waterworks facility on the Don river (variants of layout and design solutions)

The relevance of the development of technical solutions for the Kochetovsky fish-spawning channel is predetermined by the ongoing degradation of populations and a decrease in commercial fish stocks in the Azov-Don fishery basin. One of the reasons for the current and deteriorating fishing conditions on the Lower Don is a decrease in the volume of natural reproduction of passing and semi-passing fish. The necessary volumes of natural reproduction of commercial herds can be provided by creating conditions for spawning migrations and spawning of fish in the Don River. This task can be solved to a certain extent by the creation of the Kochetovsky fish-spawning channel, which predetermined the purpose of the study to develop a technical justification for the possibility of its device and layout and design solutions. The factual basis was the data of surveys and studies carried out at the Kochetovsky waterworks facility. Surveys, surveys and studies were carried out in compliance with generally accepted methods, and the development of layout and structural solutions of structures using search design technologies. Two competing versions of the canal arrangement with its location along the bank of the Don River and along the riverbed of the Barsovka River have been developed. Both of the proposed solutions take into account the conditions of their device and ensure their functioning according to their intended purpose — to create conditions for the passage and spawning of fish. Each of the options has certain technical and fish science advantages, characterized by different possibilities for attracting fish to the channel, their passage from the lower reaches of the hydroelectric power plant to the upper and spawning in the channel tract. The work was carried out in the order of pre-design study, which determines the technical feasibility of the fish-spawning channel and establishes its hydrometric parameters. The choice of the option from the two proposed is proposed to be carried out by specialists of the fisheries sector, taking into account the ratio of the potential possibilities of channels for passing and spawning certain species and quantities of fish, and their technical and economic indicators.

Fish reproduction in Krasnoarmeysk district of Saratov region in 2022

One of the main factors influencing the efficiency of reproduction of limnophilic fish is the height of water level and the duration of spring flood with uniform water heating. Work was carried out to assess the natural reproduction of fish in the area of the middle zone of the Volgograd reservoir, near the villages Akhmat and Zolotoye, Krasnoarmeysk district, Saratov region, in 2022. In total, juveniles of 11 fish species were caught in the surveyed areas in 2022. There is a significant decrease in species diversity compared to previous years. Due to the unfavorable level regime during the spawning period, very unfavorable conditions for the reproduction of fish have developed in 2022. For the first time in 6 years of research in the waters under consideration, it was possible to record the reproduction of catfish (Silurus glanis) and carp (Cyprinus carpio). In 2022, in the area near Akhmat village, an anomaly was observed: underyearlings of bleak (Alburnus alburnus), which usually dominates catches, and perch (Perca fluviatilis), which is also common in this area, were absent in the catches (despite the fact that individuals of these fish of older ages were encountered). In the water area near Zolotoye village still recorded the reproduction of Black Sea-Caspian sprat (Clupeonella cultriventris), the early larvae of which are common there in the catches and are not found in the water area near Akhmat village. In the water area near Zolotoye village underyearlings of asp (Aspius aspius) are still common, and they dominate the catches in 2022. In the water area near Akhmat village, the catches of 2022 are dominated by crucian carp (Carassius gibelio).

Parentage-based tagging and parentage analyses of stocked sea trout in Vistula River commercial catches

The longest Baltic River, the Vistula, historically hosted numerous sea trout populations. However, dam construction in the twentieth century drastically reduced the spawning migration rate. Reduced natural reproduction has resulted in a population collapse and, consequentially, a substantial reduction in catches. In response, like other Baltic countries, Poland has initiated an intensive stocking program, mainly involving smolt. Initially, stocking was conducted primarily with offspring of sea trout caught during spawning migration. Currently, due to difficulties in obtaining fish, most stocking involves fish from breeding stocks. Therefore, determining the proportion of fish derived from stocking has become an important issue. Experiments based on traditional tagging did not provide sufficient material for analysis; hence, we decided to use genetic methods based on analysis of relatedness. In this study, we performed parentage-based tagging and an analysis of the origins of parent animals used for artificial spawning in 2013, and offspring returning to the Vistula in subsequent years. We based the analysis on three different algorithms and compared the results, showing that the presented methods were effective for estimating mass stocking success. The study also indicated that a certain level of natural reproduction in the Vistula continues to occur. The proportion of sea trout from spawning in 2013 in Vistula sea trout catches from 2017 to 2018 was approximately 30%.

Consistent Monthly Reproduction and Completion of a Brooding Coral Life Cycle through Ex Situ Culture

The continuing impact of local and global stressors on coral reefs worldwide is prompting the exploration of novel approaches aimed at mitigating and improving the bleak future projections for corals. Ex situ aquaculture has the potential to provide a standardized supply of source corals to support active intervention-based research endeavours as well as complementary reef restoration initiatives. To effectively achieve this supply of coral, however, ex situ aquaculture systems need to be able to efficiently maintain reproducing colonies, and have the capacity to support each coral life stage. We monitored the monthly reproduction of the brooding coral, Pocillopora acuta, for one year in two distinct aquaculture systems: a natural seawater-supplied flow-through system (FTS) and an artificial seawater-supplied recirculating aquaculture system (RAS). The coral colonies in both aquaculture systems showed relatively consistent reproduction over time (on average > 70% of all colonies reproducing each month) and maintained natural diel reproduction patterns even after 1 year of ex situ culture. Coral colony reproductive output and timing (i.e., lunar day of release) differed between aquaculture systems in some, but not all, seasons. Planulae released from colonies settled and grew to reproductive size after ~16 months of culture, resulting in the ex situ production of an F2 generation of a brooding coral within two distinct aquaculture systems. This demonstrated that the use of ex situ aquaculture could be directly applied to research, restoration, and conservation aimed at mitigating coral decline in a future marred by climate change and local impacts.

Long‐term data of maintained salmonid populations show alarming conditions, albeit signs of natural reproduction

AbstractHealthy populations of salmonids are integral for the functioning of ecosystems and a valuable part of sociocultural identities. Past declines were attributed to anthropogenic stressors, raising concern about the sustainability of populations. Accordingly, many salmonids are listed on red lists and protected by national legislation. One region where salmonid populations are threatened is Northern Spain, the most southern distribution of both the Atlantic salmon (protected under the EU Habitat Directive) and the brown trout. Here, we collated ~700 biomonitoring samples of both species collected across 177 sites over a 10‐year period (2010–2019) to describe ongoing trends in these species and to relate them to site characteristics and potential drivers which may modulate these trends. We showed that both species have declined substantially, with stocked individuals constituting the majority of both populations. Natural reproduction was almost entirely absent for the brown trout (<1%), but present in the Atlantic salmon (~20%). Both species expressed distinct spatial patterns, likely related to their stocking and habitat preferences. As a result, we not only underline alarming conditions of both species, but also question the effectiveness of currently employed stocking efforts. Given that both species are of increasing conservation concern, river basin‐specific analyses are required to identify limiting factors on which conservation actions can be taken. In the evaluated river systems, identified targets include dam removal and pollution reduction, concomitant to the implementation of more effective stocking practices to reduce dependency and maximise conservation benefits for aquatic populations.

Grass Carp Reproduction in Small Tributaries of Harry S. Truman Reservoir, Missouri: Implications for Establishment in Novel Habitats

AbstractSubstantial work has been conducted to estimate the river length required for recruitment of invasive Grass Carp Ctenopharyngodon idella and bigheaded carps (Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix); however, the distance upstream and size of stream required for spawning remain unclear. Adult Grass Carp are regularly captured in Harry S. Truman Reservoir, Missouri, although there have been only unconfirmed sightings of Silver Carp. Fertile diploid Grass Carp are used legally for vegetation control in Missouri; however, it is uncertain whether Grass Carp in Harry S. Truman Reservoir are the result of natural reproduction or escapees. We used ichthyoplankton tows and environmental DNA (eDNA) to investigate which carp species were present in the reservoir basin and to determine whether these carps were spawning in reservoir tributaries. Grass Carp eggs were collected in four of five tributaries during June 2014. We did not detect eggs, larvae, or eDNA of Bighead Carp or Silver Carp. The occurrence of Grass Carp eggs generally coincided with rapid increases in discharge and turbidity. These tributaries may be the smallest rivers worldwide in which spawning of Grass Carp has been documented. We infer from the developmental stages captured and the distance from the reservoir that sufficient river length exists for egg survival. These results have broad implications concerning the establishment of Grass Carp in other novel habitats, including other reservoirs and lake basins, smaller rivers, and the Laurentian Great Lakes ecosystem.

Chelonian challenge: three alien species from North America are moving their reproductive boundaries in Central Europe

Biological invasions by alien species have substantial economic impacts and are a major driver of the ongoing decline and loss of biodiversity. Through humans, the North American pond slider (Trachemys scripta) has acquired a global distribution over the last decades and is currently listed among the worst invasive reptile species. However, in more recent times, other freshwater chelonian species have increasingly been recorded far outside their native distribution ranges as well, not only on the same continent but also on others. Despite that, the impact of alien chelonians on their respective new ecosystems remains unclear. The long-term effects and severity of impacts of alien populations mostly depend on whether they ultimately succeed in establishing themselves. This is not entirely resolved for chelonians in Central Europe. To answer that, we investigated wild populations of three non-native chelonian species from North America in Germany (Pseudemys concinna, Graptemys pseudogeographica and Trachemys scripta) applying population genetic approaches. We revealed the successful reproduction of all three species in Germany and provide the very first record for the reproduction of P. concinna and G. pseudogeographica in a temperate continental climate zone outside their native distribution. Based on our unambiguous evidence of natural reproduction, we call for dedicated studies to verify how widespread established populations are and to investigate the existing and potential impacts of all three species in a range of ecosystems along a climatic gradient. Such data is urgently needed to revise the current risk assessments of non-native chelonians, especially in Central European countries.

Effect of the alveolate parasite Perkinsus olseni infection on sexual maturation and spawning efficiency of the clam Ruditapes decussatus.

The effect of Perkinsus olseni infection on the reproduction ability of clams has been underestimated so far. Although some studies found evidence of reduction of egg production and delay in gonad maturation after infection, the total effect of the infection is still unclear. In this study, Ruditapes decussatus clams from a naïve population were injected with two different doses of P. olseni parasites, a low dose leading to a light infection and a high dose leading to a heavy infection. Clams were maintained during 2 months for maturation, and at the end of the experiment, the spawning was induced, the number of larvae release and mortality were evaluated. During the maturation period, infection level, gonadal stage, condition index, gross biochemical composition and oxidative status of progenitors were evaluated at days 0, 30 and 60 post-injection. The effects of P. olseni infection on clams showed alterations on biochemical parameters, namely lipid peroxidation, a significant mortality and a delayed gonad maturation, with a greater effect in the highly infected individuals. The reproductive capacity of the clams was impaired in both infected groups showing a lower production and a higher mortality rate of larvae. Finally, this study indicates that the production of natural beds with a high prevalence of P. olseni could be compromised by a deregulation of the natural reproduction cycle and a decrease in larvae production by infected animals, probably due to a combination of lower egg production and lower lipid reserves in larvae from infected clams.

The evolution of age-specific resistance to infectious disease.

Innate, infection-preventing resistance often varies between host life stages. Juveniles are more resistant than adults in some species, whereas the opposite pattern is true in others. This variation cannot always be explained by prior exposure or physiological constraints and so it has been hypothesized that trade-offs with other life-history traits may be involved. However, little is known about how trade-offs between various life-history traits and resistance at different life stages affect the evolution of age-specific resistance. Here, we use a mathematical model to explore how trade-offs with natural mortality, reproduction and maturation combine to affect the evolution of resistance at different life stages. Our results show that certain combinations of trade-offs have substantial effects on whether adults or juveniles are more resistant, with trade-offs between juvenile resistance and adult reproduction inherently more costly than trade-offs involving maturation or mortality (all else being equal), resulting in consistent evolution of lower resistance at the juvenile stage even when infection causes a lifelong fecundity reduction. Our model demonstrates how the differences between patterns of age-structured resistance seen in nature may be explained by variation in the trade-offs involved and our results suggest conditions under which trade-offs tend to select for lower resistance in juveniles than adults.

MULTIPLICACIÓN in vitro DE Phalaenopsis sp. USANDO REGULADORES DE CRECIMIENTO VEGETAL, AGUAMIEL Y PULQUE (COMPLEJOS ORGÁNICOS)

<p><strong>Background:</strong> <em>Phalaenopsis</em> is an orchid of economic importance worldwide. Its natural reproduction is slow due to its monopodial growth (a single apical meristem). Therefore, it is necessary to make <em>in vitro</em> propagation protocols more efficient. <strong>Objectives:</strong> 1. To evaluate three concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) in combination with three of 6-Benzyl Adenine (BA) in the <em>in vitro</em> induction of protocormic like bodies (PLBs) at from leaf explants of <em>Phalaenopsis</em> sp. var. Dudu, under three periods of darkness, 2. To test the effect of four concentrations of honey water and fermented sap, as organic complexes (CO), on the <em>in vitro</em> multiplication rate of PLBs. <strong>Methodology:</strong> Two tests were carried out: Test 1. Three concentrations of 2,4-D (3, 4, 5 mgL<sup>-1</sup>) and three of BA (1, 2, 3 mgL<sup>-1</sup>) were evaluated in leaf explants of <em>Phalaenopsis</em> sp., combined with three periods of darkness 14, 21, 28 days in a completely randomized design with a trifactorial arrangement (27x10). Test 2. Four concentrations of honey water and fermented sap (0, 10, 50, 100 mlL<sup>-1</sup>) were evaluated, arranged in a completely random design (8x10). <strong>Results:</strong> The best combination of plant growth regulators (PGR) for the formation of PLBs (14 PLBs/explant) was with 5 mgL<sup>-1</sup> of 2,4-D and 2 mgL<sup>-1</sup> of BA, during 21 days of darkness. Regarding the use of CO, the addition of 10 mlL<sup>-1</sup> of fermented sap and 50 mlL<sup>-1</sup> of honey water induced the highest rates of multiplication of PLBs/explant (41.4 and 39.6 PLBs). The regeneration of <em>Phalaenopsis</em> sp. from PLBs occurred in 225 days. <strong>Implications:</strong> The results obtained in the two trials are the basis for establishing a protocol for the multiplication of <em>Phalaenopsis</em> sp. <strong>Conclusions:</strong> The combination of 5 mgL<sup>-1</sup> of 2,4-D and 2 mgL<sup>-1</sup> of BA produced the highest number of PLBs/explant (14) at 21 days of darkness and subsequent light exposure for six weeks. On the other hand, the addition of 10 mlL<sup>-1</sup> of fermented sap and 50 mlL<sup>-1</sup> of honey water as CO induced the highest rates of PLBs multiplication (41.4 and 39.6 PLBs, respectively). 100% survival of seedlings was observed after 21 days of acclimatization, under greenhouse conditions.</p>

Sperm selection by the oviduct: perspectives for male fertility and assisted reproductive technologies†.

The contribution of sperm to embryogenesis is gaining attention with up to 50% of infertility cases being attributed to a paternal factor. The traditional methods used in assisted reproductive technologies for selecting and assessing sperm quality are mainly based on motility and viability parameters. However, other sperm characteristics, including deoxyribonucleic acid integrity, have major consequences for successful live birth. In natural reproduction, sperm navigate the male and female reproductive tract to reach and fertilize the egg. During transport, sperm encounter many obstacles that dramatically reduce the number arriving at the fertilization site. In humans, the number of sperm is reduced from tens of millions in the ejaculate to hundreds in the Fallopian tube (oviduct). Whether this sperm population has higher fertilization potential is not fully understood, but several studies in animals indicate that many defective sperm do not advance to the site of fertilization. Moreover, the oviduct plays a key role in fertility by modulating sperm transport, viability, and maturation, providing sperm that are ready to fertilize at the appropriate time. Here we present evidence of sperm selection by the oviduct with emphasis on the mechanisms of selection and the sperm characteristics selected. Considering the sperm parameters that are essential for healthy embryonic development, we discuss the use of novel in vitro sperm selection methods that mimic physiological conditions. We propose that insight gained from understanding how the oviduct selects sperm can be translated to assisted reproductive technologies to yield high fertilization, embryonic development, and pregnancy rates.

ДЕМОГРАФИЧЕСКИЕ ПРОЦЕССЫ В РЕГИОНАХ АРКТИЧЕСКОЙ ЗОНЫ РОССИЙСКОЙ ФЕДЕРАЦИИ В ПЕРИОД 2014–2022 ГГ.

The article examines the demographic processes of the regions whose territories are fully included in the Arctic (Murmansk region, Nenets Autonomous Okrug, Chukotka Autonomous Okrug, Yamalo- Nenets Autonomous Okrug) from 2014, from the year the land territories of the Arctic zone of the Russian Federation were determined by the Decree of the President of the Russian Federation, to 2022. The study was conducted as a whole for the period 2014-2022, including three three-year periods 2014-2016, 2017-2019, 2020-2022. in two directions 1) dynamics of changes in the number of the regions permanent population, taking into account recalculation from the results of the All-Russian Population Census - 2020 (VPN-2020); 2) dynamics of changes in the general characteristics of the population natural reproduction. The study determined: changes in the size of the permanent population of the regions by components; structure for recalculating the dynamics of changes in the permanent population of regions from the results of the VPN - 2020; trends in the processes of natural reproduction of the population of the regions as a whole for the period 2014-2022, including three three-year periods 2014-2016, 2017-2019; 2020-2022. Positive periods of the population natural reproduction processes development in the regions of the Arctic zone of the Russian Federation have been defined.

Instrumental potential of monetary valuation in managing natural ecosystems reproduction sustainability

The basic approaches to comprehension of economic nature and the subject content of the process of market transformation of natural ecosystem into nature-economy in the course of which there is a disturbing system of the formed geobiocenosis, human intrusion which creates artificial nature-ecosystem, which needs constant poly-resource support, are described in the paper. Scientific conceptualisation of the transition from the consumer attitude of man to nature as a natural "pantry" of production resources and free environmental benefits as gifts of nature to the understanding of the creative nature of partner interaction with nature and the commodity-market nature of ecosystem services rendered by it required an appropriate accounting and cost estimate of them as a tool to regulate this transition and manage the reproductive mode of functioning of the nature management system.

A Method for Natural Spectral Reproduction Based on Fully Connected Neural Network

A Method for Natural Spectral Reproduction Based on Fully Connected Neural Network

Changes of natural reproduction of fish producing drifting eggs in downstream Shashi section, middle reaches of Yangtze River during the ten-year (2011-2020) ecological operation of Three Gorges Reservoir

Changes of natural reproduction of fish producing drifting eggs in downstream Shashi section, middle reaches of Yangtze River during the ten-year (2011-2020) ecological operation of Three Gorges Reservoir

Transmission dynamics and high infectiousness of Coronavirus Disease 2019

<p style='text-indent:20px;'>Coronavirus disease 2019 (COVID-19) has rapidly spread around the world since the early 2020. Recently, a second wave of COVID-19 has resurged in many countries. The transmission dynamics and infectiousness of the COVID-19 pandemic remain unclear, and developing strategies to mitigate the severity of the pandemic is a top priority for global public health. According to the infection mechanism of COVID-19, a novel susceptible-asymptomatic-symptomatic-recovered (SASR) model with control variables in a patchy environment was proposed not only to consider the key characteristics of asymptomatic infection and the effects of seasonal variation but also to incorporate different control measures for multiple transmission routes. The basic reproduction number <inline-formula><tex-math id="M1">\begin{document}$ R_{0} $\end{document}</tex-math></inline-formula> was established to describe the spreading behavior in the natural state over a long time horizon, and the natural reproduction number <inline-formula><tex-math id="M2">\begin{document}$ R_{n} $\end{document}</tex-math></inline-formula>, which describes the development trend of the disease during a short time in the future, was defined according to the actual propagation characteristics. In addition, the effective reproduction number <inline-formula><tex-math id="M3">\begin{document}$ R_{e} $\end{document}</tex-math></inline-formula> considering the control strategies was proposed to evaluate the impact of non-pharmaceutical interventions. The results of numerical simulations for COVID-19 cases in Wuhan, China, based on the SASR model indicate that <inline-formula><tex-math id="M4">\begin{document}$ R_{0} $\end{document}</tex-math></inline-formula> was 3.58, <inline-formula><tex-math id="M5">\begin{document}$ R_{n} $\end{document}</tex-math></inline-formula> ranged from 2.37 to 4.91, and <inline-formula><tex-math id="M6">\begin{document}$ R_{e} $\end{document}</tex-math></inline-formula> decreased gradually from 4.83 on December 8, 2019 to 0.31 on March 8, 2020, reaching 1.40 on January 23, 2020, when the lockdown was lifted in Wuhan. We further concluded that the total number of infections, including asymptomatic infections, was approximately 301, 804 as of March 8, 2020, in Wuhan, China. In particular, this article proposes a dynamic method to distinguish the impact of natural factors and human interventions on the development of the pandemic, and provides a theoretical basis for fighting the global COVID-19 pandemic.</p>