Geographic variation in life cycle strategies of a progenetic trematode

Numerous parasite species have evolved complex life cycles with multiple, subsequent hosts. In trematodes, each transmission event in multi-host life cycles selects for various adaptations, one of which is facultative life cycle abbreviation. This typically occurs through progenesis, i.e., precocious maturity and reproduction via self-fertilization within the second intermediate host. Progenesis eliminates the need for the definitive host and facilitates life cycle completion. Adopting a progenetic cycle may be a conditional strategy in response to environmental cues related to low probability of transmission to the definitive host. Here, the effects of environmental factors on the reproductive strategy of the progenetic trematode Stegodexamene anguillae were investigated using comparisons among populations. In the 3-host life cycle, S. anguillae sexually reproduces within eel definitive hosts, whereas in the progenetic life cycle, S. anguillae reproduces by selfing within the metacercaria cyst in tissues of small fish intermediate hosts. Geographic variation was found in the frequency of progenesis, independent of eel abundance. Progenesis was affected by abundance and length of the second intermediate fish host as well as encystment site within the host. The present study is the first to compare life cycle strategies among parasite populations, providing insight into the often unrecognized plasticity in parasite developmental strategies and transmission.     

On the survival of populations in a heterogeneous and variable environment

Summary The survival time of small and isolated populations will often be relatively low, by which the survival of species living in such a way will depend on powers of dispersal sufficiently high to result in a rate of population foundings that about compensates the rate of population extinctions. The survival time of composite populations uninterruptedly inhabiting large and heterogeneous areas, highly depends on the extent to which the numbers fluctuate unequally in the different subpopulations. The importance of this spreading of the risk of extinction over differently fluctuating subpopulations is demonstrated by comparing over 19 years the fluctuation patterns of the composite populations of two carabid species, Pterostichus versicolor with unequally fluctuating subpopulations, and Calathus melanocephalus with subpopulations fluctuating in parallel, both uninterruptedly occupying the same large heath area. The conclusions from the field data are checked by simulating the fluctuation patterns of these populations, and thus directly estimating survival times. It thus appeared that the former species can be expected to survive more than ten times better than the latter (other things staying the same). These simulations could also be used to study the possible influence of various density restricting processes in populations already fluctuating according to some pattern. As could be expected, the survival time of a population, which shows a tendency towards an upward trend in numbers, will be favoured by some kind of density restriction, but the degree to which these restrictions are density-dependent appeared to be immaterial. Density reductions that are about adequate on the average need even not occur at high densities only, if only the chance of occurrence at very low densities is low. The density-level at which a population is generally fluctuating appeared to be less important for survival than the fluctuation pattern itself, except for very low density levels, of course. The different ways in which deterministic and stochastic processes may interact and thus determine the fluctuations of population numbers are discussed. It is concluded that some stochastic processes will operate everywhere and will thus necessarily result in density fluctuations; such an omnipresence is much less imperative, however, for density-dependent processes, by which population models should primarily be stochastic models. However, if density-dependent processes are added to model populations, that are already fluctuating stochastically the effects are taken up into the general, stochastic fluctuation pattern, without altering it fundamentally.Communication No. 228 of the Biological Station WijsterDedicated to Professor Michael Evenari     

Basking and torpor in a rock-dwelling desert marsupial: survival strategies in a resource-poor environment

Australian deserts are characterized by unpredictability, low primary productivity, and high temperature fluctuations. Despite these adverse conditions the diversity of small insectivorous marsupials of the family Dasyuridae is surprisingly high. We quantified the thermal biology of the dasyurid Pseudantechinus madonnellensis (body mass ∼30 g) in the wild to gain some understanding of whether the success of dasyurids in the arid zone may be related to some extent to their use of energy conservation strategies. In winter, most free-ranging Pseudantechinus frequently (58.3% of 131 animal days) entered daily torpor after midnight (mean 0157 hours) in rock crevices when outside ambient temperatures (T _a) were low. Most animals remained torpid until the next morning when they moved while still torpid from rock crevices to sun-exposed basking sites. We visually observed basking during rewarming from torpor (mean commencement at 0943 hours) at body temperatures (T _b) as low as 19.3°C when radiant heat was high and T _a was rising. Basking continued for the rest of the day. Torpor use was not strongly correlated with T _a, but the temporal organization of daily torpor and activity were apparently linked to the thermal characteristics of basking sites. Our study suggests that by frequently employing daily torpor and basking and by appropriately coordinating their thermal biology with that of specific locations in their environment, Pseudantechinus can reduce daily energy expenditure and thus can live and reproduce in a challenging environment. It is likely that the success of other small dasyurids and perhaps many other small mammals living in deserts is linked to employment of torpor and basking for energy conservation.     

Bet hedging in desert winter annual plants: optimal germination strategies in a variable environment

In bet hedging, organisms sacrifice short‐term success to reduce the long‐term variance in success. Delayed germination is the classic example of bet hedging, in which a fraction of seeds remain dormant as a hedge against the risk of complete reproductive failure. Here, we investigate the adaptive nature of delayed germination as a bet hedging strategy using long‐term demographic data on Sonoran Desert winter annual plants. Using stochastic population models, we estimate fitness as a function of delayed germination and identify evolutionarily stable strategies for 12 abundant species in the community. Results indicate that delayed germination meets the criteria as a bet hedging strategy for all species. Density‐dependent models, but not density‐independent ones, predicted optimal germination strategies that correspond remarkably well with observed patterns. By incorporating naturally occurring variation in seed and seedling dynamics, our results present a rigorous test of bet hedging theory within the relevant environmental context.     

Irradiating the environment: Radiological impacts in life cycle assessment

One of the main shortcomings of Life Cycle Assessment (LCA) when applied to the Nuclear Fuel Cycle, is that there is currently no recognised procedure to deal with radionuclide emissions in the Impact Assessment stage. A framework which considers both human and environmental impacts is required and a methodology which is compatible with the other impact assessment approaches in LCA must be developed. It is important that the discussion is not only restricted to concepts, but that a working methodology is developed which can be readily applied by LCA practitioners. A provisional method is available for assessing radiological impacts on human health, but no consideration has been given to potential effects on the environment. A methodology is proposed in this paper which assesses irradiation of the environment using Environmental Increments (EI) as the quality standard. This approach is based on the same principles as for the Ecotoxicity classification group, and it represents a working methodology which can be continuously improved as knowledge in the area increases.     

Aquatic hyphomycetes in a changing environment

In 1942, Ingold documented an ecologically defined group of fungi, aquatic hyphomycetes, on autumn-shed leaves decaying in streams. They were shown to be vital intermediaries between the nutritionally poor leaf substratum and leaf-eating invertebrates. Research has subsequently emphasized functional aspects such as leaf decomposition and nutritional conditioning by fungi. Structural aspects (community composition) have attracted less attention, partly because of the difficulties of identifying fungal mycelia in situ. Extraction, amplification (PCR, qPCR) and characterization of DNA and RNA, and, more recently, of proteins, allow much greater insights into the presence of fungal taxa, their metabolic status (dead, dormant or active), and their potential and actual participation in decomposition processes. This approach can yield huge amounts of data, and major challenges today are the development and application of suitable bioinformatics techniques. The complexity of data collection and evaluation favour interdisciplinary teams of researchers. Fungi are major players in most ecosystems and are increasingly affected by human impacts. Changing land use, eutrophication/pollution and climate change are among the major factors that affect diversity and ecological functions of aquatic hyphomycetes.     

Alternative life cycle strategies in the West African reed frog Hyperolius nitidulus: the answer to an unpredictable environment?

The West African reed frog Hyperolius nitidulus, mainly known for its extraordinary aestivation behaviour and physiology, is able to vary its reproductive strategy in response to environmental conditions. We found indirect as well as direct evidence for individuals not following the generally assumed one year-one generation life cycle including an extended aestivation phase during the dry season, but leading very short lives for only a part of that rainy season in which the frogs were born. Second-generation frogs (males and females that reproduced in the season in which they were born) were significantly smaller than all other adults and their egg diameter was reduced. As the pattern and amount of rainfall and thus the span of time suitable for reproduction in H. nitidulus varies strongly between years in this savannah region, a flexible reproductive strategy may be highly adaptive for risk spreading. Alternative reproduction strategies probably contribute to the great success of H. nitidulus in terms of the extension of its geographical range and its often very high local abundance.     

Habitat selection in a variable environment

A Monte Carlo simulation scheme was utilized to determine optimal strategies of habitat utilization in a variable environment. The model allows for differences in quality among habitats at any one time and for varying levels of environmental variance and autocorrelation. When habitats are on the average equal in quality, tracking of temporal fluctuations in environment through variable habitat selection is universally advantageous with the gain in fitness limited by environmental variance, autocorrelation, and number of available habitats. Average differences in quality among habitats will restrict the advantage of variable habitat utilization (over complete usage of the average better habitat) to cases of high environmental autocorrelation or high ratios of enviromental variance to mean habitat separation. Extending an earlier prediction of Levins (1965), the average heterozygosity per individual in a natural population should increase with increasing environmental variance.     

ICT for environment in life cycle applications openLCA — A new open source software for life cycle assessment

This paper is a two-fold introduction. For one, it introduces a new, open source, LCA software. Second, it is to establish a new section in Int J LCA named ‘LCA Software’. Herewith, the editors of the journal recognise the growing possibilities and the impact of software, meaning both databases and calculation as well as modelling software, for practical applications as well as for the scientific development in LCA. This section is designed to house a broad variety of papers to beLCA focused and related to ICT (Information and Communication Technology). In this sense, announcements (as this one), conference reports, but also peer-reviewed papers on methodology and case studies, are most welcome.     

Integration of working environment into life cycle assessment framework

Background, aim, and scope  Life cycle assessment (LCA) has been considered one of the tools for supporting decision-making related to the environmental aspects of a product system. It has mainly been used to evaluate the potential impacts associated with relevant inputs and outputs to/from a given product system throughout its life cycle. In most cases, LCA has not considered the impacts on the internal environment, i.e. working environment, but only the external environment. Recently, it has been recognized that the consideration of the impacts on the working environment as well as on the external environment, is needed in order to assess all aspects of the effects on human well-being. To this end, this study has developed a total environmental assessment methodology which enables one to integrate both the working environment and the external environment into the conventional LCA framework. Materials and methods  In general, the characteristics of the impacts on the external environment are different from those on the working environment. In order to properly integrate the two types into total environmental impacts, it is necessary to define identical system boundaries and select impact category indicators at the same level. In order to define the identical system boundary and reduce the uncertainties of LCI results, the hybrid IOA (input–output analysis) method, which integrates the advantages between conventional LCI method and IOA method, is introduced to collect input and output data throughout the entire life cycle of a given product. For the impact category indicators at the endpoint level, LWD (Lost Work Days) is employed to evaluate the damage to human health and safety in the working environment, while DALY (disability-adjusted life years) and PAF (Potentially Affected Fraction) are selected to evaluate the damage to human health and eco-system quality in the external environment, respectively. Results and discussion  The environmental intervention factors (EIFs) are developed not only for the data categories of resource use, air emissions, and water emissions, but also for occupational health and safety to complete a life cycle inventory table. For the development of the EIFs on occupational health and safety, in particular, the number of workers affected by i hazardous items and the number of workers affected at the i magnitude of disability are collected. For the characterization of the impact categories in the working environment, such as occupational health and safety, the exposure factors, effect factors, and damage factors are developed to calculate the LWD of each category. For normalization, the normalization reference is defined as the total LWD divided by the total number of workers. A case study is presented to illustrate the applicability of the proposed method for the integration of the working environment into the conventional LCA framework. Conclusions  This study is intended to develop a methodology which enables one to integrate the working environmental module into the conventional LCA framework. The hybrid IOA method is utilized to extend the system boundary of both the working environment module and the external environment module to the entire life cycle of a product system. In this study, characterization models and category indicators for occupational health and safety are proposed, respectively, while the methodology of Eco-indicator 99 is used for the external environment. In addition to aid further understanding on the results of this method, this study introduced and developed the category indicators such as DALY, and LWD, which can be expressed as a function of time, and introduced PAF, which can be expressed as a probability. Recommendations and perspectives  The consideration of the impacts not only on the external environment, but also on the working environment, is very important, because the best solution for the external environment may not necessarily be the best solution for the working environment. It is expected that the integration of occupational health and safety matters into the conventional LCA framework can bring many benefits to individuals, as well as industrial companies, by avoiding duplicated measures and false optimization.     

Egg development, nymphal growth and life cycle strategies in Plecoptera

Interspecific and intraspecific differences in egg development, nymphal growth and the life cycles of Fennoscandian stoneflies are examined in relation to zoogeographical aspects and evolutionary trends. Data on other European and North American species are also considered.
Egg development shows considerable diversity, the main categories being ovovivipary, egg development with diapause and non-diapause development. Egg development in species in the non-diapause category can be classified as eurythermal, cold stenothermal or warm stenothermal. Temperature has a marked effect on nymphal growth of some species but not others. The distribution of several species can be explained by their temperature relationships, either in the egg or nymphal stage. Several species modify their life cycle to fit local climatic conditions. In some species, such as Leuctra hippopus , environmental selection has been so strong that they have probably recently evolved into subspecies and/or species in northern Europe.
Morphological and ecological variations in the Plecoptera have facilitated their colonization of the variety of freshwater biotopes that occur in Fennoscandia.     

On the boundary between economy and environment in life cycle assessment

Purpose

We investigate how the boundary between product systems and their environment has been delineated in life cycle assessment and question the usefulness and ontological relevance of a strict division between the two.

Methods

We consider flows, activities and impacts as general terms applicable to both product systems and their environment and propose that the ontologically relevant boundary is between the flows that are modelled as inputs to other activities (economic or environmental)—and the flows that—in a specific study—are regarded as final impacts, in the sense that no further feedback into the product system is considered before these impacts are applied in decision-making. Using this conceptual model, we contrast the traditional mathematical calculation of the life cycle impacts with a new, simpler computational structure where the life cycle impacts are calculated directly as part of the Leontief inverse, treating product flows and environmental flows in parallel, without the need to consider any boundary between economic and environmental activities.

Results and discussion

Our theoretical outline and the numerical example demonstrate that the distinctions and boundaries between product systems and their environment are unnecessary and in some cases obstructive from the perspective of impact assessment, and can therefore be ignored or chosen freely to reflect meaningful distinctions of specific life cycle assessment (LCA) studies. We show that our proposed computational structure is backwards compatible with the current practice of LCA modelling, while allowing inclusion of feedback loops both from the environment to the economy and internally between different impact categories in the impact assessment.

Conclusions

Our proposed computational structure for LCA facilitates consistent, explicit and transparent modelling of the feedback loops between environment and the economy and between different environmental mechanisms. The explicit and transparent modelling, combining economic and environmental information in a common computational structure, facilitates data exchange and re-use between different academic fields.

     

Integrating life cycle assessment and life cycle cost: a review of environmental-economic studies

The International Journal of Life Cycle Assessment - The purpose of this document is to carry out a critical review of the existing literature by specifically addressing the following: (i) the...     

The life form concept and the use in the analysis of life cycle evolutionary strategies

The life form is a generalized morphoecological characteristic of an animal giving an idea of the organism as a whole, its position and function and functional role in the ecosystem. This characteristic is inherent to a species or to a group of congeneric species (for applied goal it is better to use a genus, not species) considered in the framework of higher taxon (from family to type). The principal contradiction of life form concept is determined by the existence of ontogenetic stages and changes of life forms during the whole life of individual. It is usually assumed that the concept of life form should be applied only to the adult stage, thus ignoring the integral character of the life cycle as indivisible unit of selection, evolution and functioning in ecosystem. We propose that a morphologically specific ontogenetic of a given species should be used as an elementary lowest unit in the classification of life forms. Thus it can be considered as integrated internally structured morphoecological unit in time and multidimensional space of abiotic and biotic environmental factors. As an example we describe the types of reproductive strategies and classification of elementary (ontogenetic) life forms in cephalopods. We present characteristics of the life cycle of some typical cephalopod species inhabiting different biotopes and having different models of locomotion, feeding, reproduction and development.     

Consequential life cycle assessment: a review

Purpose  

Over the past two decades, consequential life cycle assessment (CLCA) has emerged as a modeling approach for capturing environmental impacts of product systems beyond physical relationships accounted for in attributional LCA (ALCA). Put simply, CLCA represents the convergence of LCA and economic modeling approaches.     

Fitness and physiology in a variable environment

The relationship between physiological traits and fitness often depends on environmental conditions. In variable environments, different species may be favored through time, which can influence both the nature of trait evolution and the ecological dynamics underlying community composition. To determine how fluctuating environmental conditions favor species with different physiological traits over time, we combined long-term data on survival and fecundity of species in a desert annual plant community with data on weather and physiological traits. For each year, we regressed the standardized annual fitness of each species on its position along a tradeoff between relative growth rate and water-use efficiency. Next, we determined how variations in the slopes and intercepts of these fitness-physiology functions related to year-to-year variations in temperature and precipitation. Years with a relatively high percentage of small rain events and a greater number of days between precipitation pulse events tended to be worse, on average, for all desert annual species. Species with high relative growth rates and low water-use efficiency had greater standardized annual fitness than other species in years with greater numbers of large rain events. Conversely, species with high water-use efficiency had greater standardized annual fitness in years with small rain events and warm temperatures late in the growing season. These results reveal how weather variables interact with physiological traits of co-occurring species to determine interannual variations in survival and fecundity, which has important implications for understanding population and community dynamics.