Diversification In Time Research Articles

The first evidence of saprophytic Tetraploa on Siwalik (Late Miocene) monocot leaf from western Himalaya and its role in palaeoecology reconstruction

Even though the records of Tetraploa spores from Mesozoic and Cenozoic sedimentary strata along with spore-pollen assemblages are numerous and well documented, no foliicolus Tetraploa macroconidia have been reported to date. Here, we report the first occurrence of conidia assignable to modern Tetraploa Berk. & Broome (Tetraplosphaeriaceae: Pleosporales: Dothideomycetes) on cuticular fragments of compressed monocot leaf recovered from the middle Siwalik sediments (Late Miocene; 12–8 Ma) of Himachal Himalaya, India. We determine their taxonomic position based on detailed macromorphological comparison with similar modern and fossil taxa and discuss their palaeoecological significance in terms of the present-day ecological conditions of modern analogues. This finding also represents an essential data source for understanding Tetraploa's evolution and diversification in deep time.

Optimizing the Nitrogen Use Efficiency in Vegetable Crops

Nitrogen (N) is the most limiting nutrient for the production of vegetable crops, but anthropogenic sources pose risks due to its transformation into several reactive forms and movement throughout the environment. The bulk of the N research to date to improve Nitrogen Use Efficiency (NUE) has followed a reductionist factorial approach focused on synthetic N application rates and crop growth response, under monocultures. The increased adoption of diversified cropping systems, organic N sources, and alternative management practices makes it more challenging to unravel N form transformation, movement, and crop uptake dynamics, in time and space. Here, based on a selected review of the recent literature, we propose a holistic approach of nutrient management to highlight key management and production variables as well as multilevel cropping system, genetic, environmental, ecological, and socioeconomic interactions to improve the N cycle and NUE. The best management strategies to improve NUE include both organic and inorganic N rate calibration studies, germplasm selection, crop rotations, identification of nutrient x nutrient interactions, and pest and water management. Agroecological practices that may improve NUE include vegetational diversification in time and space, integrated crop–livestock systems, conservation tillage, organic amendment inputs, legume-based cropping systems, as well as a landscape approach to nutrient management.

Diversification in time and space and how it is perceived: Applying a folk linguistic listening task with Tver’ Karelians

AbstractIn this article we apply a folk linguistic listening task to examine how the Tver’ Karelians in Russia recognise a sample of their own dialect and a sample of Border Karelian (spoken in Finland), both recorded about 60 years ago. Tver’ Karelian and Border Karelian have a shared origin in Proto-Karelian but have been diverging from each other since the seventeenth century; the former has had strong influence from Russian and the latter from Finnish. The study investigates the Tver’ Karelians’ awareness of and observations about the Karelian language and shows that they easily recognise their own dialect, whereas the Border Karelian sample is harder to recognise and describe. However, the respondents observed and described lexical and phonetic features of this sample, and two thirds of them located the sample in the republic of Karelia or in Finland, mostly based on the ‘accent’ of the speaker.

Homeotic transformations suggest mechanisms for rapid evolution diversification in Drosophila sex combs.

Evolutionary innovations refer to the emergence of new traits, functions, or behaviors in organisms and lineages over time. Although research has demonstrated that such innovations can arise gradually or through small steps (Chouard 2010), the mechanisms by which rapid morphological diversification takes place remain poorly understood (Bailey et al. 2019). To explore this question, we used the evolution of sex combs, as a system (Ho et al. 2018). We used this male-specific row of leg bristles, comprising sex combs as a system, because it displays spectacular morphological diversification in a short time (Kopp 2011). Homeotic mutations in the fruit fly, Drosophila melanogaster, are those which create modifications in one part of a fly to resemble another region. Here we describe effects of some of these mutations which transform the D. melanogaster fly sex comb morphology to closely resemble sex comb morphology in other species. These findings support previous research indicating that minor alterations to regulatory elements can play a significant role in explaining morphological evolution (Atallah et al. 2004). Thus, our results suggest that rapid diversification may not require starting from scratch, but rather may require minor modifications to the sex comb ground plan, which may account for its rapid morphological evolution (Lee et al. 2011).

Lineage-specific protein repeat expansions and contractions reveal malleable regions of immune genes.

Functional diversification, a higher evolutionary rate, and intense positive selection help a limited number of immune genes interact with many pathogens. Repeats in protein-coding regions are a well-known source of functional diversification, adaptive variation, and evolutionary novelty in a short time. Repeats play a crucial role in biochemical functions like functional diversification of transcription regulation, protein kinases, cell adhesion, signaling pathways, morphogenesis, DNA repair, recombination, and RNA processing. Repeat length variation can change the associated protein's interaction, efficacy, and overall protein network. Repeats have an intrinsic unstable nature and can potentially evolve rapidly and expedite the acquisition of complex phenotypic traits and functions. Because of their ability to generate rapid, adaptive variations over short evolutionary distances, repeats are considered "tuning knobs." Repeat length variation in specific genes, like RUNX2 and ALX4, is associated with morphological and physiological changes across vertebrates. Here we study repeat length variation as a potent source of species-specific immune diversification across several clades of tetrapods. Moreover, we provide a clade-wise comprehensive list of immune genes with repeat types for future studies of morphological/evolutionary changes within species groups. We observe significant repeat length variation of FASLG and C1QC in Rodentia and Primates' contrasting species groups, respectively.

The influence of palaeogeography and tectonic events on trilobite distributions in Morocco and northwestern Algeria

AbstractThe effects of sea-level changes and anoxia on Devonian trilobites have been studied for a long time, but the importance of palaeogeographic and tectonic events in this key-period is still not well understood. In the Devonian Period, trilobites invaded many different marine environments and areas in North Africa where important palaeogeographic changes occurred. Distribution patterns of trilobites through time and space have been analysed using a hierarchical cluster analysis and diversity indices. Our examination of the literature suggests that trilobites were scarce during Lochkovian time before an important diversification in Pragian time. Trilobites flourished in many North African regions without there being important taxonomic differences between basins, because of free migration in relatively flat palaeo-topography and homogeneous environments. During Middle Devonian time, early Variscan tectonic movements transformed the eastern Anti-Atlas area into a basin with a platform topography. Geographical barriers such as deep basins prevented trilobite migrations. At the beginning of Eifelian time, the reduction in migration between the different regions of this area coincided with a decrease in diversity. Consequently, tectonic events played an important role in the decline of trilobites during Middle Devonian time, especially when these were combined with sea-level changes and anoxic/hypoxic events. A recovery occurred in Famennian time involving only new genera. As at the global scale, cyrtosymbolines developed in shallow seas, whereas phacopids evolved in deeper environments. The basin and platform system still hampered migrations, although sea-level variations led to episodic exchanges. The late Famennian regression reduced trilobite diversity dramatically in the study area.

Climate Change and Adaptation Strategies of Arable Crop Farmers In Abia State, Nigeria

This study was set up to examine climate change and adaptation strategies of arable crop farmers in Abia State. The study adopted the cross-sectional research design with a sample population of 392 farmers across the seventeen Local Government Areas of Abia State. Chi Square statistics was used to test the study hypothesis. The study revealed that Climate change impact on arable crops is affecting farmer’s economy in Abia State. Evidences of climate change in the area, could be seen in the form of increase in temperature, change in rainfall pattern and intensity which has brought about a change in planting seasons, the study further revealed that The techniques/strategies adopted by arable crop famers in Abia State include cultivation of early maturing breeds of arable crop, crop diversification, changes in time of farm operation, change of farm location, rain water harvesting, diversification of income-generating activities and planting of drought-resistant varieties. The most predominant adaptation strategies practiced by arable crop farmers in Abia State are cultivation of early maturing breeds of arable crops, crop diversification and changes in time of farm operation and that there was seasonal variation in the choice of adaptation strategy adopted by farmers. The study however recommends that climate change impacts on arable crops as such agricultural activities that enhance climate change such as bush burning, total forest clearing should be discouraged. There is a need to adopt agro based environmental friendly techniques in crop production such as alley farming and that farmers should be encouraged to adopt the identified effective adaptation technique that are practicable for their location.

Astrochronology of the Ediacaran Shuram carbon isotope excursion, Oman

The Ediacaran is a highly dynamic period in terms of large perturbations in Earth's atmosphere, biosphere, and climate. Among these perturbations, a pronounced negative carbon isotope excursion, known as the Shuram excursion (SE), is characterized by the most depleted δ13C values (-12‰) that have ever been observed in the geological record. A poorly determined chronostratigraphic framework makes the SE difficult to correlate and compare globally. Therefore, it is hard to study the potential connection between the SE and coeval climate and biological variations. Here, we present a high-resolution astrochronological study of the Ediacaran Shuram and Buah Formations, Nafun Group, Oman, in which the SE is reported for the first time. Power spectral analysis of the 600-m long gamma ray log of the Miqrat-1 Well shows that a hierarchy of astronomically-forced climate cycles (eccentricity, obliquity, and precession) is accurately-preserved. Using multiple statistical tests, we constructed a sedimentation rate variation profile that covers the entire SE, which is characterized by low rates in shale-dominated layers and high rates in shale-carbonate interbedded layers. The duration of the SE in Oman is suggested to be 7.7 ± 0.2 Myr, which agrees with estimates from South Australia, South China, and the United States. An identical duration of the SE supports its global synchroneity and indicates a primary origin of the depleted δ13C values. Combined with the newly proposed termination age (562.5 ± 1.1 Ma) of the SE, our astrochronological results suggest that the onset age of the excursion is 570.2 ± 1.1 Ma. The astrochronology of the SE delineates the tempo of the excursion, with a rapid decrease (∼ 1 Myr) from the onset to its isotopic nadir followed by a more gradual recovery (∼ 6–7 Myr) towards the termination. The new chronostratigraphic framework permits further investigations of the potential causal links between the global carbon cycle and the widespread glaciation, the oceanic oxygenation, and the biological diversification in Ediacaran time.

Diversification rate vs. diversification density: Decoupled consequences of plant height for diversification of Alooideae in time and space.

While biodiversity hotspots are typically identified on the basis of species number per unit area, their exceptional richness is often attributed, either implicitly or explicitly, to high diversification rates. High species concentrations, however, need not reflect rapid diversification, with the diversity of some hotspots accumulating at modest rates over long timespans. Here we explore the relationship between diversification in time vs. diversification in space and develop the concept of diversification density to describe the spatial scale of species accumulation in a clade. We investigate how plant height is associated with both aspects of diversification in Alooideae, a large plant subfamily with its center of diversity in the Greater Cape Floristic Region. We first reconstruct a time-calibrated phylogeny for Alooideae and demonstrate an evolutionary tendency towards reduced plant height. While plant height does not correlate with diversification rate across Alooideae it does so with diversification per unit space: clades of small plants tend to have the highest diversification densities. Furthermore, we find that diversification in time vs. space are uncorrelated. Our results show that diversification rate and density can be decoupled, and suggest that while some biodiversity hotspots might have been generated by high diversification rates, others are the product of high diversification density.

Scale-invariant topology and bursty branching of evolutionary trees emerge from niche construction

Phylogenetic trees describe both the evolutionary process and community diversity. Recent work has established that they exhibit scale-invariant topology, which quantifies the fact that their branching lies in between the two extreme cases of balanced binary trees and maximally unbalanced ones. In addition, the backbones of phylogenetic trees exhibit bursts of diversification on all timescales. Here, we present a simple, coarse-grained statistical model of niche construction coupled to speciation. Finite-size scaling analysis of the dynamics shows that the resultant phylogenetic tree topology is scale-invariant due to a singularity arising from large niche construction fluctuations that follow extinction events. The same model recapitulates the bursty pattern of diversification in time. These results show how dynamical scaling laws of phylogenetic trees on long timescales can reflect the indelible imprint of the interplay between ecological and evolutionary processes.

Conceptual and statistical problems with the DEC+J model of founder‐event speciation and its comparison with DEC via model selection

AbstractPhylogenetic studies of geographic range evolution are increasingly using statistical model selection methods to choose among variants of the dispersal‐extinction‐cladogenesis (DEC) model, especially between DEC and DEC+J, a variant that emphasizes “jump dispersal,” or founder‐event speciation, as a type of cladogenetic range inheritance scenario. Unfortunately, DEC+J is a poor model of founder‐event speciation, and statistical comparisons of its likelihood with DEC are inappropriate. DEC and DEC+J share a conceptual flaw: cladogenetic events of range inheritance at ancestral nodes, unlike anagenetic events of dispersal and local extinction along branches, are not modelled as being probabilistic with respect to time. Ignoring this probability factor artificially inflates the contribution of cladogenetic events to the likelihood, and leads to underestimates of anagenetic, time‐dependent range evolution. The flaw is exacerbated in DEC+J because not only is jump dispersal allowed, expanding the set of cladogenetic events, its probability relative to non‐jump events is assigned a free parameter, j, that when maximized precludes the possibility of non‐jump events at ancestral nodes. DEC+J thus parameterizes the mode of speciation, but like DEC, it does not parameterize the rate of speciation. This inconsistency has undesirable consequences, such as a greater tendency towards degenerate inferences in which the data are explained entirely by cladogenetic events (at which point branch lengths become irrelevant, with estimated anagenetic rates of 0). Inferences with DEC+J can in some cases depart dramatically from intuition, e.g. when highly unparsimonious numbers of jump dispersal events are required solely because j is maximized. Statistical comparison with DEC is inappropriate because a higher DEC+J likelihood does not reflect a more close approximation of the “true” model of range evolution, which surely must include time‐dependent processes; instead, it is simply due to more weight being allocated (via j) to jump dispersal events whose time‐dependent probabilities are ignored. In testing hypotheses about the geographic mode of speciation, jump dispersal can and should instead be modelled using existing frameworks for state‐dependent lineage diversification in continuous time, taking appropriate cautions against Type I errors associated with such methods. For simple inference of ancestral ranges on a fixed phylogeny, a DEC‐based model may be defensible if statistical model selection is not used to justify the choice, and it is understood that inferences about cladogenetic range inheritance lack any relation to time, normally a fundamental axis of evolutionary models.

Aporosa Blume from the paleoequatorial rainforest of Bikaner, India: Its evolution and diversification in deep time

The Gondwanan origin, northward migration and subsequent collision with Asia means that the Indian subcontinent is of particular interest regarding the origin and dispersal of numerous plants and animal species. With this in mind, we describe a fossil leaf of Aporosa Blume (Phyllanthaceae) from the Paleogene of the Indian subcontinent and discuss its evolution and diversification with respect to the moving Indian plate and its connection with Southeast Asia since the early Cenozoic. At present, Aporosa Blume is confined to Southeast Asia with a few species in India and New Guinea. It is represented by six endemic species growing in the evergreen forests of India and Sri Lanka, including Aporosa acuminata Thwaites, which is morphologically close to the here described fossil from Bikaner, Rajasthan, India. From the age of the fossil and the distribution of its modern comparable form, it is assumed that Aporosa originated on the Indian subcontinent and then was distributed to Southeast Asia, supporting the ‘Out of India’ hypothesis. Diversification of the genus might have taken place either in the Paleogene or Neogene. Our fossil leaf material also indicates the existence of palaeoequatorial (<10° N) tropical rain forests in western India during the Paleogene in contrast to dry and desertic climate occurring today.

Evolution of opercle shape in cichlid fishes from Lake Tanganyika - adaptive trait interactions in extant and extinct species flocks.

Phenotype-environment correlations and the evolution of trait interactions in adaptive radiations have been widely studied to gain insight into the dynamics underpinning rapid species diversification. In this study we explore the phenotype-environment correlation and evolution of operculum shape in cichlid fishes using an outline-based geometric morphometric approach combined with stable isotope indicators of macrohabitat and trophic niche. We then apply our method to a sample of extinct saurichthyid fishes, a highly diverse and near globally distributed group of actinopterygians occurring throughout the Triassic, to assess the utility of extant data to inform our understanding of ecomorphological evolution in extinct species flocks. A series of comparative methods were used to analyze shape data for 54 extant species of cichlids (N = 416), and 6 extinct species of saurichthyids (N = 44). Results provide evidence for a relationship between operculum shape and feeding ecology, a concentration in shape evolution towards present along with evidence for convergence in form, and significant correlation between the major axes of shape change and measures of gut length and body elongation. The operculum is one of few features that can be compared in extant and extinct groups, enabling reconstruction of phenotype-environment interactions and modes of evolutionary diversification in deep time.

Enhancing Yields in Organic Crop Production by Eco-Functional Intensification

&lt;p&gt;Organic agriculture faces challenges to enhance food production per unit area and simultaneously reduce the environmental and climate impacts, e.g. nitrate leaching per unit area and greenhouse gas (GHG) emissions per unit mass produced. Eco-functional intensification is suggested as a means to reach these objectives. Eco-functional intensification involves activating more knowledge and refocusing the importance of ecosystem services in agriculture. Organic farmers manage agrobiodiversity by crop rotation (diversification in time). However, sole cropping (SC) of genetically identical plants in organic agriculture may limit resource use efficiency and yield per unit area. Intercropping (IC) of annual grain species, cultivar mixes, perennial grains, or forage species and forestry and annual crops (agroforestry) are examples of spatial crop diversification. Intercropping is based on eco-functional intensification and may enhance production by complementarity in resource use in time and space. Intercropping is based on the ecological principles of competition, facilitation and complementarity, which often increases the efficiency in acquisition and use of resources such as light, water and nutrients compared to sole crops, especially in low-input systems. Here we show that IC of cereals and grain legumes in European arable organic farming systems is an efficient tool for enhancing total grain yields compared to their respective sole crops. Simultaneously, we display how intercropping of cereals and legumes can be used as an efficient tool for weed management and to enhance product quality (i.e. cereal grain protein concentration). We discuss how intercropping contributes to efficient use of soil N sources and minimizes losses of N by nitrate leaching via &lt;em&gt;Ecological Precision Farming&lt;/em&gt;. It is concluded that intercropping has a strong potential to increase yield and hereby reduce global climate impacts such as GHG kg&lt;sup&gt;-1&lt;/sup&gt; grain. Finally, we discuss likely barriers and lock-in effects for increased use of intercropping in organic farming and suggest a roadmap for innovation and implementation of IC strategies in organic agriculture.&lt;/p&gt;

A multi-gene dataset reveals a tropical New World origin and Early Miocene diversification of croakers (Perciformes: Sciaenidae)

Widely distributed groups of living animals, such as the predominantly marine fish family Sciaenidae, have always attracted the attention of biogeographers to document the origins and patterns of diversification in time and space. In this study, the historical biogeography of the global Sciaenidae is reconstructed within a molecular phylogenetic framework to investigate their origin and to test the hypotheses explaining the present-day biogeographic patterns. Our data matrix comprises six mitochondrial and nuclear genes in 93 globally sampled sciaenid species from 52 genera. Within the inferred phylogenetic tree of the Sciaenidae, we identify 15 main and well-supported lineages; some of which have not been recognized previously. Reconstruction of habitat preferences shows repeated habitat transitions between marine and euryhaline environments. This implies that sciaenids can easily adapt to some variations in salinity, possibly as the consequence of their nearshore habitats and migratory life history. Conversely, complete marine/euryhaline to freshwater transitions occurred only three times, in South America, North America and South Asia. Ancestral range reconstruction analysis concomitant with fossil evidence indicates that sciaenids first originated and diversified in the tropical America during the Oligocene to Early Miocene before undergoing two range expansions, to Eastern Atlantic and to the Indo-West Pacific where a maximum species richness is observed. The uncommon biogeographic pattern identified is discussed in relation to current knowledge on origin of gradients of marine biodiversity toward the center of origin hypothesis in the Indo-West Pacific.

Actionable sequence data on infectious diseases in the clinical workplace.

Among the wide variety of diagnostic and therapeutic challenges in the clinical workplace, infectious diseases pose unusually difficult problems. First, the diversity of disease-causing agents is prodigious, and infectious agents may disseminate to and invade almost any host anatomic compartment. Second, these agents, because of their short generation times and, in some cases, high mutation rates, evolve quickly, resulting in evasion of host defenses, inter- and intrahost diversification in real time, and acquired resistance to antimicrobial drugs. Third, some infectious diseases progress quickly, i.e., within hours or days, and offer only a fleeting, narrow window of opportunity for successful therapeutic intervention early in the course of disease. Thus, to be actionable, diagnostic tests must be broad in their range, specific, sensitive, and rapid. These needs have not been adequately met by current, routine approaches, such as cultivation, serology, and specific PCR assays. As a result, inappropriately broad or mistargeted antimicrobial agents are used, resulting in drug resistance and other adverse effects, and important diseases are untreated or treated too late. A recently published case report by Wilson et al. (1) highlights the potential impact of DNA sequencing technology on infectious disease diagnosis, and illustrates in a best-case scenario how this technology may address these needs. The report describes a 14-year-old boy with severe combined immunodeficiency, who had undergone bone marrow transplantation and was maintained on monthly intravenous infusions of immune globulin and antibiotic prophylaxis against Pneumocystis pneumonia. Approximately 1 month after a trip to Puerto Rico, he experienced 10 days of unexplained fever, headache, and conjunctivitis. Over the course of the following 12 months, he suffered from uveitis, thrombocytopenia, and 2 more acute episodes of fever, headache, and photophobia and developed a lymphocyte-predominant cerebrospinal fluid (CSF) pleocytosis, as well as biopsy-proven granulomatous leptomeningitis. All routine tests for infectious disease agents …

Biogeography: Where do we go from here?

AbstractBiogeography is a multidisciplinary science concerned with how and why organisms are distributed as they are on Earth. It links fields such as systematics, ecology, paleontology, and climatology, and occupies a central position in evolutionary biology, being fundamental to the study of processes such as speciation and adaptive radiation. Here we provide a brief overview of some particularly dynamic areas of inquiry and offer some perspectives on future directions for the field. We hope that some historical debates, such as those over the importance of dispersal, or the validity of molecular dating, are finally being put to rest. Over the last decade, biogeography has become increasingly integrative, and has benefited from advances in statistical methods for inferring geographic range dynamics in a phylogenetic context, molecular estimation of lineage divergence times, and modeling lineage birth and death. These are enabling greater insights into patterns of organismal diversification in time and space. In the next decade, analytical challenges are emerging on several fronts. For example, phylogenies are increasing in size and taxonomic breadth and new sequencing technologies enabling phylogenetic and phylogeographic datasets are increasingly genomic in depth. In addition, geographic occurrence data are accumulating in online repositories, yet tools for data mining and synthetic analysis are lacking for comparative multi‐lineage studies. Biogeography is thus entering an era characterized by phylogenomic datasets, increasingly comprehensive sampling of clades, and interdisciplinary synthesis. We anticipate continued progress in our understanding of biodiversity patterns at regional and global scales, but this will likely require greater collaboration with specialists in bioinformatics and computational science. Finally, it is clear that biogeography has an increasingly important role to play in the discovery and conservation of biodiversity. Lessons learned from biogeographic studies of islands are being applied to better understand extinction dynamics as continental ecosystems become more fragmented, and phylogeography and ecological niche modeling offer innovative paths toward the discovery of previously unknown species distributions and priority areas for conservation. The future of biogeography is bright and filled with exciting challenges and opportunities.

Multi-variate models are essential for understanding vertebrate diversification in deep time.

Statistical models are helping palaeontologists to elucidate the history of biodiversity. Sampling standardization has been extensively applied to remedy the effects of uneven sampling in large datasets of fossil invertebrates. However, many vertebrate datasets are smaller, and the issue of uneven sampling has commonly been ignored, or approached using pairwise comparisons with a numerical proxy for sampling effort. Although most authors find a strong correlation between palaeodiversity and sampling proxies, weak correlation is recorded in some datasets. This has led several authors to conclude that uneven sampling does not influence our view of vertebrate macroevolution. We demonstrate that multi-variate regression models incorporating a model of underlying biological diversification, as well as a sampling proxy, fit observed sauropodomorph dinosaur palaeodiversity best. This bivariate model is a better fit than separate univariate models, and illustrates that observed palaeodiversity is a composite pattern, representing a biological signal overprinted by variation in sampling effort. Multi-variate models and other approaches that consider sampling as an essential component of palaeodiversity are central to gaining a more complete understanding of deep time vertebrate diversification.

Superheavy pyrite ( 34Spyr &gt; 34SCAS) in the terminal Proterozoic Nama Group, southern Namibia: A consequence of low seawater sulfate at the dawn of animal life

Sulfur isotope analysis (δ^(34)S) of well-preserved carbonates spanning an ~10 Ma interval of the terminal Proterozoic Nama Group reveals that disseminated pyrite is consistently enriched in ^(34)S relative to coeval seawater sulfate as preserved in carbonate-associated sulfate (CAS). This observation is not consistent with the current paradigm for interpreting the geologic record of sulfur isotopes, which assumes that pyrite δ^(34)S (δ^(34)S_(pyr)) will be equal to or less than co-occurring CAS δ^(34)S (δ^(34)S_(CAS)) due to the kinetic isotope effect of bacterial sulfate reduction (BSR) that favors the lighter isotope of sulfur (^(32)S) during sulfur-oxygen bond breakage. Although the precise mechanism of pyrite sulfur isotope enrichment is debatable, our combined observations of extremely ^(34)S-enriched pyrite, low bulk-rock concentrations of sulfur from CAS and pyrite, and high-frequency fluctuations in δ^(34)S_(CAS) and δ^(34)S_(pyr) throughout the Nama Group carbonates point to very low concentrations of sulfate in portions of the terminal Proterozoic ocean. The additional occurrence of ^(34)S-enriched pyrite in contemporaneous terminal Proterozoic sections from Poland and Canada reveal that low seawater sulfate may have been widespread in the oceans at this time. However, the absence of such extremely 34S-enriched pyrite from well-preserved, coeval carbonate sections in Oman suggests that such conditions were not globally uniform. Low, geographically varied concentrations of marine sulfate in terminal Proterozoic time are consistent with elevated, geographically varied concentrations of reactive, nonpyritized iron in marine shales recently reported for this interval, suggesting that high dissolved Fe(II) and low O_2 persisted in a range of marine facies as late as 543 Ma -— tens of millions of years after the origin of animals, yet prior to their major diversification in Early Cambrian time.

EXPRESSING PRODUCT DIVERSIFICATION — CATEGORIZING AND CLASSIFYING VARIABILITY IN SOFTWARE PRODUCT FAMILY ENGINEERING

In a software product family context, software architects design architectures that support product diversification in both space (multiple contexts) and time (changing contexts). Product diversification is based on the concept of variability: a single architecture and a set of components support a family of products. Software product families have to support increasing amounts of variability, thereby making variability engineering a primary concern in software product family development. The first part of this paper (1) suggests a two-dimensional, orthogonal categorization of variability realization techniques and classifies these variability categories into system maturity levels. The second part (2) discusses a case study of an industrial software product family of mobile communication infrastructure for professional markets such as the military. The study categorizes and classifies the variability in this product family according to criteria common to virtually all software development projects.