Environment, population, and biology: a short history of modern epidemiology

Since its origin in the 19th century, epidemiology has faced an internal tension between an approach oriented toward biology and the study of mechanisms, and an approach oriented toward populations and their interactions with the environment. Initially, this tension took the form of an opposition between microbiology and statistics. We describe the early roots of the quantitative approach to health and disease and several historical examples of the above tension. The search for the causes of pellagra exemplifies our thesis. In Italy, where pellagra was endemic, contrasting opinions coexisted between the hypothesis of contaminated maize, supported by Cesare Lombroso, and the hypothesis of a prevailing role of poverty and poor nutrition. In the United States, Joseph Goldberger found no evidence for the hypothesis of contaminated maize or for a microbiological agent, but recognized the central role of nutrition. The "cure" Goldberger proposed was land reform, but he continued studying the disease from a mechanistic point of view; shortly after his death, niacin deficiency was identified as the cause of pellagra. The tension between mechanistic and population-based studies is still present within epidemiology and is in fact essential for the success of the discipline.     

Development and utilization of a population growth history of Red Lake walleye, Stizostedion vitreum

Synopsis An environmental growth history of commercially harvested walleye, Stizostedion vitreum, in Red Lakes, Minnesota, was constructed for the years 1944–1992. This was accomplished using a linear model which was fitted to annular scale increment measurements. Increment size was separated into one component due to a combination of environmental factors, an environmental growth coefficient, and one due to the age of the fish. Our hypothesis was that variables such as air temperature, walleye year-class strength, catch-per-unit-effort (CPUE) of walleye, and CPUE of yellow perch, Perca flavescens, affect walleye growth, and therefore a historical series of these variables would show coherence to the series of walleye growth coefficients. Multiple regression techniques were used to test these hypotheses. Significant predictors of the growth of walleye after age one were average February temperature, cumulative degree days in July, walleye year-class strength, and growth of young-of-the-year (YOY) walleye. We hypothesized that YOY walleye respond to a different set of factors than walleye after age one, thus, a series of YOY growth measurements would show coherence to a different set of environmental factors. Significant predictors of YOY walleye growth were May, June, and August cumulative degree days, as well as the growth of older walleye. We expected the set of factors which affect freshwater drum, Aplodinotus grunniens, to include factors that affect walleye, such as temperature, shared prey availability, and abundance of both walleye and drum. As a test, environmental growth coefficients computed by Pereira (1992) for freshwater drum were compared to walleye growth coefficients. The growth coefficients of drum were significantly positively correlated with the walleye coefficients, and the significance increased if the poorest walleye growth years were excluded.     

XtalView, protein structure solution and protein graphics, a short history

From a user's point-of-view we are in the Golden Age of protein crystallographic software. In the past few decades, solving protein structures has gone from a task requiring man-months of effort to a process requiring minutes on an ordinary laptop with no human intervention required. The birth of XtalView coincided with the mainstream use of synchrotron radiation, seleno-Met phasing and it continues to be used in this age of robotic crystallization, Fed-Ex data collection and fully automated structure solution "pipelines". This article is a retrospective history of protein crystallographic computing and a discussion of the current state of the art.     

Life history of a neotropical marsupial: Evaluating potential contributions of survival and reproduction to population growth rate

The relative effect of survival and reproductive rates to population growth rate is expected to be similar across species with similar life-histories. We employed a matrix population model and sensitivity and elasticity analysis to assess the absolute and relative importance of age-specific survival and fertility to population growth rate of Didelphis aurita (Didelphimorphia, Didelphidae) in a rural area of Rio de Janeiro, southeastern Brazil. The results were compared to expectations for mammals that mature early and have short generation time, such as D. aurita. Prospective analysis showed that changes in pouch young and juveniles survival would have large effects on population growth rate, relative to other vital rates, being the most critical time periods in the life cycle of D. aurita, whereas the effect of fertilities were always low. These findings do not fit to the observed pattern in mammals that mature early, where reproductive parameters have the largest relative influence on population growth rate. Although reproductive rates were characterized by a relatively small influence on population growth rate, they are still relevant because of their high variability and response to potential environmental disturbances. The first application of matrix population models to a neotropical rainforest marsupial provides information on marsupial demography and life-history strategy, increasing comprehension of this unknown group.     

Dupuytren's disease: history, diagnosis, and treatment

LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. Describe the clinical features of the disease. 2. Describe the pathoanatomical structures in Dupuytren's disease. 3. Outline the various factors associated with Dupuytren's disease. 4. Describe the modalities for surgical and nonsurgical treatment of the condition. 5. Outline recent biomolecular knowledge about the basis of Dupuytren's disease. SUMMARY: Dupuytren's disease is characterized by nodule formation and contracture of the palmar fascia, resulting in flexion deformity of the fingers and loss of hand function. The authors review the historical background, clinical features, and current therapy of Dupuytren's disease; preview treatment innovations; and present molecular data related to Dupuytren's disease. These new findings may improve screening for Dupuytren's disease and provide a better understanding of the disease's pathogenesis.     

Nutrition, hormones and life history in burying beetles

Nutrition, hormones and the allocation of physiological resources are intricately related. To investigate these inter-relationships in female burying beetles (Nicrophorus spp.), we examined the effect of diet quality on juvenile hormone (JH) levels and reproduction, and the effect of JH supplementation on reproduction and resistance to starvation. Nicrophorus orbicollis adult females fed a less preferred mealworm larvae diet gained less body mass, had smaller ovaries and had lower titers of JH in their hemolymph than females fed a preferred blowfly diet. When presented a carcass for breeding, females on a less preferred diet oviposited 33% fewer eggs, and eggs were of 18% less mass. Females on the less preferred diet also took longer to begin oviposition as indicated indirectly by the time when their eggs hatched. To investigate the effects of JH, independent of nutrition, JH was topically applied to single and paired females of Nicrophorus tomentosus. When presented a carcass, JH-treated paired females oviposited more eggs (28%-year 1, 44%-year 2) than control females, and also showed a trend toward faster oviposition. JH supplementation had a greater effect on single females. JH treatment increased the proportion of single females attempting reproduction (at least one viable larva), increased the number of eggs (69%-year 1, 123%-year 2), and increased the proportion of females ovipositing early. In separate experiments, treatment with JH or a JH analog negatively affected resistance to starvation in three species. Treatment with JH reduced starvation survival by 10.3% days in N. tomentosus females. Treatment with the JH analog methoprene reduced starvation survival 17.8% in N. orbicollis females and by 18% in Ptomascopus morio females. These results suggest that JH has positive and negative effects on different components of life history.     

Photosynthesis: a short history of some modern experimental approaches.

This paper presents a personal interpretation of a chapter of plant physiology beginning from the early 1930s to the early 1940s, when plant physiologists tried to find the missing link between the two (dark and light) phases of photosynthesis. As initially inferred by Richard Willst?tter and Arthur Stoll in the 1910s, and then stated by Robert Emerson and William Arnold in 1932, the most accredited theory proposed that carbon dioxide must combine with chlorophyll in the dark. Successive light flashes activated the complex chlorophyll-carbon dioxide with oxygen evolution, and carbon dioxide was reduced to formaldehyde and successively polymerised into hexose. Arthur Stool in 1932 and Cornelius v. Niel in 1935 gave the first stroke to this theory suggesting that carbon dioxide must be reduced and assimilated by means of a process of water oxidation. Robert Hill showed the existence of an indissoluble link between the light phase, water oxidation and possibly oxygen evolution. Two physicists, Sam Ruben and Martin Kamen proposed the assembly of photosynthesis into a unitary process occurring as a sequence of several steps in the first 1940s. By utilising for the first time radioactive carbon (11C), they elaborated a new theory according to which carbon dioxide reduction was a repeated "cyclic" mechanism. This "heretical" view abolished the old, but still considered, theory of formaldehyde. Hill, Ruben and Kamen were able to exploit at best the possibility offered by a very advanced technology, thus confirming once again that ideas stand upon the powerful legs of technology.     

Human cardiomyocyte progenitor cells: a short history of nearly everything

The high occurrence of cardiac disease in the Western world has driven clinicians and cardiovascular biologists to look for alternative strategies to treat patients. A challenging approach is the use of stem cells to repair the heart, in itself an inspiring thought. In the past 10 years, stem cells from different sources have been under intense investigation and, as a result, a multitude of studies have been published on the identification, isolation, and characterization, of cardiovascular progenitor cells and repair in different animal models. However, relatively few cardiovascular progenitor populations have been identified in human hearts, including, but not limited to, cardiosphere-derived cells, cKit+ human cardiac stem cells , Isl1+ cardiovascular progenitors, and, in our lab, cardiomyocyte progenitor cells (CMPCs). Here, we aim to provide a comprehensive summary of the past findings and present challenges for future therapeutic potential of CMPCs.     

Muskrat life history: a comparison of a northern and southern population

Muskrats Ondatra zibethicus were studied at Old Crow flats Yukon Territory (68°05'N, 140°05W) and Tiny Marsh, Ontario (44°35'N, 79°52'W) during the summers of 1985 and 1986 Life–history traits of these two populations were compared Litter size was not significantly different between the two sites However average annual productivity was significantly greater at Tiny Marsh where individuals produced more litters per season Growth rates of juvenile and adult muskrats were significantly greater at Tiny Marsh, as was juvenile and adult weight However overwinter survival of juvenile muskrats was significantly greater at Old Crow than at Tiny Marsh We suggest that the shorter growing season and proximate energetic limitations on growth and reproduction favour a conservative reproductive strategy by the northern muskrat population For the southern muskrat population a long growing season and high quality food resources allow for a more productive reproductive strategy     

Influence of pH,lactose and lactic acid on the growth of Streptococcus cremoris: a kinetic study

Summary The effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l^-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l^-1 demonstrated. With the product yield of 0.9 g·g^-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l^-1 could not explain the low growth rates obtained, implicating a nutritional limitation.Symbols t _f fermentation duration (h) - X Biomass concentration (g·l^-1) - X _m maximum biomass concentration (g·l^-1) - S lactose concentration (g·l^-1) - S _r residual lactose concentration (g·l^-1) - P produced lactic acid concentration (g·l^-1) - P _a added lactic acid concentration (g·l^-1) - P _c critical lactic acid concentration (g·l^-1) - specific growth rate (h^-1) - _max maximum specific growth rate (h^-1) - R _x/S biomass yield (g·g^-1) calculated when =0 - R _P/S product yield (g·g^-1)     

Bacterial growth on lactose: an experimental investigation

A wild-type strain of Klebsiella oxytoca growing aerobically in batch culture has exhibited intermittent or oscillatory growth while growing on lactose at concentrations on the order of 1 g/L or less. In two-substrate experiments, preferred growth on glucose followed by growth on lactose also produced oscillatory growth behavior during the lactose growth phase at lactose concentrations of 1 g/L or less. Only oscillations in cell density have currently been observed. Alkalinization of the medium during growth on lactose indicated the presence of lactose active transport. The observed intermittent growth was reduced or removed during growth on lactose after preferred growth on galactose or in a medium containing 50 mM NaCl. Results suggested that the presence of an intracellular energy source or a sufficient DeltapH buffer may alleviate growth inhibition when transport and growth processes compete for essential energy resources during growth on lactose.     

Effects of branching spatial structure and life history on the asymptotic growth rate of a population

The dendritic structure of a river network creates directional dispersal and a hierarchical arrangement of habitats. These two features have important consequences for the ecological dynamics of species living within the network. We apply matrix population models to a stage-structured population in a network of habitat patches connected in a dendritic arrangement. By considering a range of life histories and dispersal patterns, both constant in time and seasonal, we illustrate how spatial structure, directional dispersal, survival, and reproduction interact to determine population growth rate and distribution. We investigate the sensitivity of the asymptotic growth rate to the demographic parameters of the model, the system size, and the connections between the patches. Although some general patterns emerge, we find that a species’ modes of reproduction and dispersal are quite important in its response to changes in its life history parameters or in the spatial structure. The framework we use here can be customized to incorporate a wide range of demographic and dispersal scenarios.     

Mineral nutrition of plants: a short history of plant physiology.

The development of the knowledge on the mineral nutrition of plants begins between the 17th and 18th centuries when some European naturalists gave the first experimental evidences of what had been empirically known for about two millennia. The works of Hales and Ingenhousz were of absolute importance in relation to the transport of water and solutes, and assimilation of "fixed air" (carbon dioxide), respectively. The early chemistry introduced by Lavoisier benefited the first physiologists Senebier and De Saussure to reject the "theory of humus", which imposed the soil as the unique source of carbon. During the first half of the 19th century, Sprengel and Liebig investigated on the problems related to some indispensable mineral salts, while Boussingault and Ville attempted to prove the nitrogen fixation from air without giving any convincing evidence. Liebig was the pioneer of the agricultural chemistry: he epitomised the knowledge of that period by imposing the so-called "law of the minima", already acknowledged by Sprengel, and patronised the use of mineral fertilisers in Europe by devising several formulas of mineral manure. He, however, did not recognise the needs of external supplies of nitrogen salts for the crops, in open dispute with the English school of Lawes and Gilbert, who were instead convinced assertors of such needs. At the end of the 19th century Hellriegel showed that leguminous plants presenting peculiar nodules on their roots could really fix the gaseous nitrogen. From these nodules Beijerinck and Prazmowski isolated for the first time some bacteria which were recognised as the real agents fixing nitrogen. This discovery was of fundamental importance for plant nutrition, only second to the discovery of photosynthesis. Another basic contribution came from early research of Sachs on plants grown on aqueous solutions: these techniques allowed to impose the concept of "essential elements", which was fixed as a principle by Arnon and Stout in 1939. This principle benefited further research concerning the effects of states of deficiency on plant growth and development through investigation on the anatomical, histologic and biochemical nutritional disorders of plants.     

Genetic diversity, population structure, effective population size and demographic history of the Finnish wolf population

The Finnish wolf population (Canis lupus) was sampled during three different periods (1996-1998, 1999-2001 and 2002-2004), and 118 individuals were genotyped with 10 microsatellite markers. Large genetic variation was found in the population despite a recent demographic bottleneck. No spatial population subdivision was found even though a significant negative relationship between genetic relatedness and geographic distance suggested isolation by distance. Very few individuals did not belong to the local wolf population as determined by assignment analyses, suggesting a low level of immigration in the population. We used the temporal approach and several statistical methods to estimate the variance effective size of the population. All methods gave similar estimates of effective population size, approximately 40 wolves. These estimates were slightly larger than the estimated census size of breeding individuals. A Bayesian model based on Markov chain Monte Carlo simulations indicated strong evidence for a long-term population decline. These results suggest that the contemporary wolf population size is roughly 8% of its historical size, and that the population decline dates back to late 19th century or early 20th century. Despite an increase of over 50% in the census size of the population during the whole study period, there was only weak evidence that the effective population size during the last period was higher than during the first. This may be caused by increased inbreeding, diminished dispersal within the population, and decreased immigration to the population during the last study period.