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Warming temperatures are altering communities and trophic networks across Earth's ecosystems. While the overall influence of warming on food webs is often context-dependent, increasing temperatures are predicted to change communities in two fundamental ways: (1) by reducing average body size and (2) by increasing individual metabolic rates. These warming-induced changes have the potential to influence the distribution of food web fluxes, food web stability, and the relative importance of deterministic and stochastic ecological processes shaping community assembly. Here, we quantified patterns and the relative distribution of organic matter fluxes through stream food webs spanning a broad natural temperature gradient (5-27°C). We then related these patterns to species and community trait distributions of mean body size and population biomass turnover (P:B) within and across streams. We predicted that (1) communities in warmer streams would exhibit smaller body size and higher P:B and (2) organic matter fluxes within warmer communities would increasingly skew toward smaller, higher P:B populations. Across the temperature gradient, warmer communities were characterized by smaller body size (~9% per °C) and higher P:B (~7% faster turnover per °C) populations on average. Additionally, organic matter fluxes within warmer streams were increasingly skewed toward higher P:B populations, demonstrating that warming can restructure organic matter fluxes in both an absolute and relative sense. With warming, the relative distribution of organic matter fluxes was decreasingly likely to arise through the random sorting of species, suggesting stronger selection for traits driving high turnover with increasing temperature. Our study suggests that a warming world will favor energy fluxes through "smaller and faster" populations, and that these changes may be more predictable than previously thought., (© 2024 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

A tenet of ecology is that temporal variability in ecological structure and processes tends to decrease with increasing spatial scales (from locales to regions) and levels of biological organization (from populations to communities). However, patterns in temporal variability across trophic levels and the mechanisms that produce them remain poorly understood. Here we analyzed the abundance time series of spatially structured communities (i.e., metacommunities) spanning basal resources to top predators from 355 freshwater sites across three continents. Specifically, we used a hierarchical partitioning method to disentangle the propagation of temporal variability in abundance across spatial scales and trophic levels. We then used structural equation modeling to determine if the strength and direction of relationships between temporal variability, synchrony, biodiversity, and environmental and spatial settings depended on trophic level and spatial scale. We found that temporal variability in abundance decreased from producers to tertiary consumers but did so mainly at the local scale. Species population synchrony within sites increased with trophic level, whereas synchrony among communities decreased. At the local scale, temporal variability in precipitation and species diversity were associated with population variability (linear partial coefficient, β = 0.23) and population synchrony (β = -0.39) similarly across trophic levels, respectively. At the regional scale, community synchrony was not related to climatic or spatial predictors, but the strength of relationships between metacommunity variability and community synchrony decreased systematically from top predators (β = 0.73) to secondary consumers (β = 0.54), to primary consumers (β = 0.30) to producers (β = 0). Our results suggest that mobile predators may often stabilize metacommunities by buffering variability that originates at the base of food webs. This finding illustrates that the trophic structure of metacommunities, which integrates variation in organismal body size and its correlates, should be considered when investigating ecological stability in natural systems. More broadly, our work advances the notion that temporal stability is an emergent property of ecosystems that may be threatened in complex ways by biodiversity loss and habitat fragmentation., (© 2023 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Intraspecific interactions within predator populations can affect predator-prey dynamics and community structure, highlighting the need to better understand how these interactions respond to anthropogenic change. To this end, we used a half-century (1969-2018) of abundance and size-at-age data from Lake Erie's walleye (Sander vitreus) population to determine how anthropogenic alterations have influenced intraspecific interactions. Before the 1980s, the length-at-age of younger walleye (ages 1 and 2) negatively correlated with older (age 3 +) walleye abundance, signaling a 'density feedback' in which intraspecific competition limited growth. However, after the early 1980s this signal of intraspecific competition disappeared. This decoupling of the density feedback was related to multiple anthropogenic changes, including a larger walleye population resulting from better fisheries management, planned nutrient reductions to improve water quality and transparency, warmer water temperatures, and the proliferation of a non-native fish with novel traits (white perch, Morone americana). We argue that these changes may have reduced competitive interactions by reducing the spatial overlap between older and younger walleye and by introducing novel prey. Our findings illustrate the potential for anthropogenic change to diminish density dependent intraspecific interactions within top predator populations, which has important ramifications for predicting predator dynamics and managing natural resources., (© 2023. The Author(s).)

Understanding the observed temperature dependence of decomposition (i.e., its "apparent" activation energy) requires separation of direct effects of temperature on consumer metabolism (i.e., the "inherent" activation energy) from those driven by indirect seasonal patterns in phenology and biomass, and by longer-term, climate-driven shifts in acclimation, adaptation, and community assembly. Such parsing is important because studies that relate temperature to decomposition usually involve multi-season data and/or spatial proxies for long-term shifts, and so incorporate these indirect factors. The various effects of such factors can obscure the inherent temperature dependence of detrital processing. Separating the inherent temperature dependence of decomposition from other drivers is important for accurate prediction of the contribution of detritus-sourced greenhouse gases to climate warming and requires novel approaches to data collection and analysis. Here, we present breakdown rates of red maple litter incubated in coarse- and fine-mesh litterbags (the latter excluding macroinvertebrates) for serial approximately one-month increments over one year in nine streams along a natural temperature gradient (mean annual: 12.8°-16.4°C) from north Georgia to central Alabama, USA. We analyzed these data using distance-based redundancy analysis and generalized additive mixed models to parse the dependence of decomposition rates on temperature, seasonality, and shredding macroinvertebrate biomass. Microbial decomposition in fine-mesh bags was significantly influenced by both temperature and seasonality. Accounting for seasonality corrected the temperature dependence of decomposition rate from 0.25 to 0.08 eV. Shredder assemblage structure in coarse-mesh bags was related to temperature across both sites and seasons, shifting from "cold" stonefly-dominated communities to "warm" communities dominated by snails or crayfish. Shredder biomass was not a significant predictor of either coarse-mesh or macroinvertebrate-mediated (i.e., coarse- minus fine-mesh) breakdown rates, which were also jointly influenced by temperature and seasonality. Unlike fine-mesh bags, however, temperature dependence of litter breakdown did not differ between models with and without seasonality for either coarse-mesh (0.36 eV) or macroinvertebrate-mediated (0.13 eV) rates. We conclude that indirect (non-thermal) seasonal and site-level effects play a variable and potentially strong role in shaping the apparent temperature dependence of detrital breakdown. Such effects should be incorporated into studies designed to estimate inherent temperature dependence of slow ecological processes., (© 2021 by the Ecological Society of America.)

Climate warming is predicted to alter routing and flows of energy through food webs because of the critical and varied effects of temperature on physiological rates, community structure, and trophic dynamics. Few studies, however, have experimentally assessed the net effect of warming on energy flux and food web dynamics in natural intact communities. Here, we test how warming affects energy flux and the trophic basis of production in a natural invertebrate food web by experimentally heating a stream reach in southwest Iceland by ~4°C for 2 yr and comparing its response to an unheated reference stream. Previous results from this experiment showed that warming led to shifts in the structure of the invertebrate assemblage, with estimated increases in total metabolic demand but no change in annual secondary production. We hypothesized that elevated metabolic demand and invariant secondary production would combine to increase total consumption of organic matter in the food web, if diet composition did not change appreciably with warming. Dietary composition of primary consumers indeed varied little between streams and among years, with gut contents primarily consisting of diatoms (72.9%) and amorphous detritus (19.5%). Diatoms dominated the trophic basis of production of primary consumers in both study streams, contributing 79-86% to secondary production. Although warming increased the flux of filamentous algae within the food web, total resource consumption did not increase as predicted. The neutral net effect of warming on total energy flow through the food web was a result of taxon-level variation in responses to warming, a neutral effect on total invertebrate production, and strong trophic redundancy within the invertebrate assemblage. Thus, food webs characterized by a high degree of trophic redundancy may be more resistant to the effects of climate warming than those with more diverse and specialized consumers., (© 2019 by the Ecological Society of America.)

A central question at the interface of food-web and climate change research is how secondary production, or the formation of heterotroph biomass over time, will respond to rising temperatures. The metabolic theory of ecology (MTE) hypothesizes the temperature-invariance of secondary production, driven by matched and opposed forces that reduce biomass of heterotrophs while increasing their biomass turnover rate (production : biomass, or P:B) with warming. To test this prediction at the whole community level, we used a geothermal heat exchanger to experimentally warm a stream in southwest Iceland by 3.8°C for two years. We quantified invertebrate community biomass, production, and P : B in the experimental stream and a reference stream for one year prior to warming and two years during warming. As predicted, warming had a neutral effect on community production, but this result was not driven by opposing effects on community biomass and P:B. Instead, warming had a positive effect on both the biomass and production of larger-bodied, slower-growing taxa (e.g., larval black flies, dipteran predators, snails) and a negative effect on small-bodied taxa with relatively high growth rates (e.g., ostracods, larval chironomids). We attribute these divergent responses to differences in thermal preference between small- vs. large-bodied taxa. Although metabolic demand vs. resource supply must ultimately constrain community production, our results highlight the potential for idiosyncratic community responses to warming, driven by variation in thermal preference and body size within regional species pools., (© 2017 by the Ecological Society of America.)

Animals can be important in modulating ecosystem-level nutrient cycling, although their importance varies greatly among species and ecosystems. Nutrient cycling rates of individual animals represent valuable data for testing the predictions of important frameworks such as the Metabolic Theory of Ecology (MTE) and ecological stoichiometry (ES). They also represent an important set of functional traits that may reflect both environmental and phylogenetic influences. Over the past two decades, studies of animal-mediated nutrient cycling have increased dramatically, especially in aquatic ecosystems. Here we present a global compilation of aquatic animal nutrient excretion rates. The dataset includes 10,534 observations from freshwater and marine animals of N and/or P excretion rates. These observations represent 491 species, including most aquatic phyla. Coverage varies greatly among phyla and other taxonomic levels. The dataset includes information on animal body size, ambient temperature, taxonomic affiliations, and animal body N:P. This data set was used to test predictions of MTE and ES, as described in Vanni and McIntyre (2016; Ecology DOI: 10.1002/ecy.1582)., (© 2017 by the Ecological Society of America.)

Variation in resource supply can cause variation in temperature dependences of metabolic processes (e.g., photosynthesis and respiration). Understanding such divergence is particularly important when using metabolic theory to predict ecosystem responses to climate warming. Few studies, however, have assessed the effect of temperature-resource interactions on metabolic processes, particularly in cases where the supply of limiting resources exhibits temperature dependence. We investigated the responses of biomass accrual, gross primary production (GPP), community respiration (CR), and N2 fixation to warming during biofilm development in a streamside channel experiment. Areal rates of GPP, CR, biomass accrual, and N2 fixation scaled positively with temperature, showing a 32- to 71-fold range across the temperature gradient (approximately 7 degrees-24 degrees C). Areal N2-fixation rates exhibited apparent activation energies (1.5-2.0 eV; 1 eV = approximately 1.6 x 10(-19) J) approximating the activation energy of the nitrogenase reaction. In contrast, mean apparent activation energies for areal rates of GPP (2.1-2.2 eV) and CR (1.6-1.9 eV) were 6.5- and 2.7-fold higher than estimates based on metabolic theory predictions (i.e., 0.32 and 0.65 eV, respectively) and did not significantly differ from the apparent activation energy observed for N2 fixation. Mass-specific activation energies for N2 fixation (1.4-1.6 eV), GPP (0.3-0.5 eV), and CR (no observed temperature relationship) were near or lower than theoretical predictions. We attribute the divergence of areal activation energies from those predicted by metabolic theory to increases in N2 fixation with temperature, leading to amplified temperature dependences of biomass accrual and areal rates of GPP and R. Such interactions between temperature dependences must be incorporated into metabolic models to improve predictions of ecosystem responses to climate change.

The elemental composition of solutes transported by rivers reflects combined influences of surrounding watersheds and transformations within stream networks, yet comparatively little is known about downstream changes in effects of watershed loading vs. in-channel processes. In the forested watershed of a river under a mediterranean hydrologic regime, we examined the influence of longitudinal changes in environmental conditions on water-column nutrient composition during summer base flow across a network of sites ranging from strongly heterotrophic headwater streams to larger, more autotrophic sites downstream. Small streams (0.1-10 km2 watershed area) had longitudinally similar nutrient concentration and composition with low (approximately 2) dissolved nitrogen (N) to phosphorus (P) ratios. Abrupt deviations from this pattern were observed in larger streams with watershed areas > 100 km2 where insolation and algal abundance and production rapidly increased. Downstream, phosphorus and silica concentrations decreased by > 50% compared to headwater streams, and dissolved organic carbon and nitrogen increased by approximately 3-6 times. Decreasing dissolved P and increasing dissolved N raised stream-water N:P to 46 at the most downstream sites, suggesting a transition from N limitation in headwaters to potential P limitation in larger channels. We hypothesize that these changes were mediated by increasing algal photosynthesis and N fixation by benthic algal assemblages, which, in response to increasing light availability, strongly altered stream-water nutrient concentration and stoichiometry in larger streams and rivers.

Animals commonly experience spatial and temporal variation in resource quality, thus experiencing temporally variable diets. Methods for scaling up growth in component patches to long‐term growth across heterogeneity are seldom explicitly considered. Long‐term growth is sometimes considered to be a weighted average of growth rates on component diets (growth integration). However, if animals integrate resources across high‐ and low‐quality diets, their long‐term growth may be greater than predicted from diet‐specific growth rates (resource integration). We measured biomass growth rates of seven Daphnia species exposed to different types of diet variation in algal phosphorus (P) content. Support for resource integration was found for four of the seven species, which achieved near maximal growth when high‐P food was available for at least 12 h. In contrast, no support for resource integration was found for the other three species. These three species achieved only one‐half maximal growth rate under the same conditions and could be considered growth integrators. The type of integration could be predicted from the degree of stoichiometric homeostasis. Species with weak homeostatic regulation exhibited a capacity for resource integration. Resource integrators should have an advantage in heterogeneous environments.

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6-176 molar). At the reach scale, fish excretion could meet >75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool in <0.3 km. Areal N excretion estimates varied 47-fold among channel units, suggesting that fish distributions could influence local N availability. P excretion rates varied 14-fold among units but were low relative to ambient concentrations. Spatial variation in aggregate nutrient excretion by fish reflected the effects of habitat characteristics (depth, water velocity) on community structure (body size, density, species composition), and the preference of large-bodied species for deep runs was particularly important. We conclude that the spatial distribution of fish could indeed create hotspots of nutrient recycling during the dry season in this species-rich tropical stream. The prevalence of patchy distributions of stream fish and invertebrates suggests that hotspots of consumer nutrient recycling may often occur in stream ecosystems.

Background: Open abdominal aortic aneurysm (AAA) repair is associated with cardiac and respiratory complications and an overall mortality rate of 2 to 8%. We hypothesised that excessive fluid administration during the perioperative period contributes to complications and poor outcome after AAA repair., Methods: This was a retrospective cohort study. Medical records were analysed for fluid balance and complications in 100 consecutive patients treated by open AAA repair at a single centre between 2002-2005. Mortality and all major adverse events (MAE) such as myocardial infarction (MI), cardiac arrhythmia (Arr), pulmonary oedema (PO), pulmonary infection (PI), and acute renal failure (ARF) were included in the analysis. Level of care and hospital stay, were also recorded., Results: There were no in-hospital deaths. MAE occurred in 40/100 (40%): MI (6%); Arr (14%); PO (14%); PI (25%); ARF (8%). Complications were not predicted by preoperative cardiovascular risk factors, operative and clamp time, or blood loss. Patients with complications had significantly greater cumulative positive fluid balance on postoperative day 0 (p<0.01), day 1 (p<0.05), day 2 (p<0.03) and day 3 (p<0.04). This relationship also existed for individual complications such as MI, and pulmonary oedema. These patients had significantly longer ICU/HDU (p<0.002) and hospital stay (p<0.0001)., Conclusions: Serious complications are common after elective open AAA repair, and we have shown that positive fluid balance is predictive of major adverse events increased HDU/ICU and overall hospital stay.

Introduction: Complex lower limb vascular injuries (CLVIs) in high-energy penetrating or blunt trauma are associated with an unacceptably high incidence of complications including amputation. Traumatic ischaemia and ischaemia-reperfusion injury (IRI) of skeletal muscle often lead to limb loss, the systemic inflammatory response syndrome (SIRS) which affects remote organs and even the potentially fatal multiple organ dysfunction syndrome (MODS). Surgical care of CLVIs everywhere, including Northern Ireland until 1978, was governed by an anxiety to restore arterial flow quickly often using expedient and flawed repair techniques while a damaged major vein was frequently ligated., Materials and Methods: A new policy centred on early intraluminal shunting of both artery and vein, restoring arterial inflow and venous outflow, respectively, was introduced at the Regional Vascular Surgery Unit of The Royal Victoria Hospital, Belfast in 1979. It imposed a disciplined one-stage comprehensive approach to treatment involving a sequence of operative manoeuvres in which all damaged anatomical elements receive meticulous and optimal attention unshackled by time constraints., Results: Comparisons drawn between the pre-shunt period of unplanned treatment (1969-1978) and the post-shunt period centred on the use of shunts (1979-2000) showed that early shunting of both artery and vein in both penetrating (P) and blunt (B) injuries significantly reduced the necessity for fasciotomy (P: p=0.016, B: p=0.02) and caused a significant fall in the incidence of contracture (P: p=0.018, B: p=0.02) and of amputation (P: p=0.009, P: p=0.012)., Conclusions: The policy of early shunting of artery and vein in CLVIs has proved to be of great benefit in terms of significantly improved outcomes, better operative discipline and harmonious collaboration among the specialists involved.

In ecosystems where excretion by fish is a major flux of nutrients, the nitrogen (N) to phosphorus (P) ratio released by fish can be important in shaping patterns of algal biomass, community composition, primary production, and nutrient limitation. Demand for N and P as well as energy influences N/P excretion ratios and has broad implications in ecosystems where nutrient recycling by fishes is substantial. Bioenergetics and stoichiometric models predict that natural fish populations are generally energy-limited and therefore N/P recycling by fishes is relatively invariant. Yet, the potential for P limitation of growth has not been examined in herbivorous fishes, which are common in many aquatic habitats. We examined N/P excretion ratios and P demand in two P-rich herbivorous catfishes of the family Loricariidae, Ancistrus triradiatus (hereafter Ancistrus) and Chaetostoma milesi (hereafter Chaetostoma). Both fishes are common grazers in the Andean piedmont region of Venezuela where we conducted this study. Mass balance (MB) models indicate that these fishes have a high P demand. In fact, our Ancistrus' P MB model predicted negative P excretion rates, indicating that Ancistrus did not consume enough P to meet its P demand for growth. Direct measurement of excretion rates showed positive, but very low P excretion rates and high N/P excretion ratios for both taxa. To obtain measured P excretion rates of Ancistrus from the MB model, gross growth efficiency must be reduced by 90%. Our results suggest that growth rates of both of these herbivorous and P-rich fish are likely P-limited. If P limitation of growth is common among herbivorous fish populations, herbivorous fishes recycle likely at high N/P ratios and act to diminish the quality of their food.

Seasonal and circadian variation in the incidence of ruptured abdominal aortic aneurysm (RAAA) has been reported. We explored the role of atmospheric pressure changes on rupture incidence and its relationship to cardiovascular risk factors. During a three year-period, 1st April 1998 and 31st March 2001, data was prospectively acquired on 144 Ruptured Abdominal Aortic Aneurysm (RAAA) presenting to the Regional Vascular Surgery Unit at the Royal Victoria Hospital, Belfast, Northern Ireland. For each patient the chronology of acute onset of symptoms and presentation to the regional vascular unit was recorded, along with details of standard cardiovascular risk factors. During the same period meteorological data including atmospheric pressure and air temperature were recorded daily at the regional meteorological research unit, Armagh. We then analyzed the monthly mean values for daily rupture incidence in relation to the monthly values for atmospheric pressure, pressure change and temperature. Furthermore atmospheric pressure on the day of rupture, and day preceding rupture, were also analyzed in relation to days without rupture presentation and between individual ruptures for various cardiovascular risk factors. Data demonstrated a significant monthly variation in aneurysm rupture frequency, (p<0.03, ANOVA). There was also a significant monthly variation in mean barometric atmospheric pressure, (p<0.0001, ANOVA), months with high rupture frequency also exhibiting low average pressures in the months of April (0.24 +/- 0.04 ruptures per day and 1007.78 +/- 1.23 mB) and September (0.16 +/- 0.04 ruptures per day and 1007.12 +/- 1.14 mB), respectively. The average barometric pressures were found to be significantly lower on those days when ruptures occurred (n=1127) compared to days when ruptures did not occur (n=969 days), (1009.98 +/- 1.11 versus 1012.09 +/- 0.41, p<0.05). Full data on risk factors was available on 103 of the 144 rupture patients and was further analyzed. Interestingly, RAAA with a known history of hypertension, (n=43), presented on days with significantly lower atmospheric pressure than those without, (n=60), (1008.61 +/- 2.16 versus 1012.14 +/- 1.70, p<0.05). Further analysis of ruptures grouped into those occurring on days above or below mean annual atmospheric pressure 1013.25 (approximately 1 atmosphere), by Chi-square test, revealed three cardiovascular risk factors significantly associated with low-pressure rupture, (p<0.05). Data represents mean +/- SEM, statistical comparisons with Student t-test and ANOVA. These data demonstrate a significant association between periods of low barometric pressure and high incidence of ruptured aneurysm, especially in those patients with known hypertension. The association between rupture incidence and barometric pressure warrants further study as it may influence the timing of elective AAA repair.

Objective: To assess the reliability of intramucosal pH (pHi) of the sigmoid colon, IL-6 concentration and the APACHE II score in predicting outcome in patients undergoing elective abdominal aortic aneurysm repair., Design: Prospective study., Methods: In 42 patients, measurements were made of the sigmoid pHi with the silicone tonometer and plasma IL-6 by enzyme linked immuno-sorbent assay (ELISA). The daily postoperative APACHE II scores were also calculated. In 29 patients a preoperative left ventricular ejection fraction was determined by gated radionuclide angiography., Results: Four out of 42 patients who were studied died. The lowest perioperative pHi, the peak postoperative IL-6 concentration and APACHE II scores were significantly different in the survivors in comparison to the non-survivors. In the non-survivors, the fall in pHi preceded the time of patient's demise by at least 4 days. Significant correlations were observed between changes in pHi, IL-6 and APACHE II. Using receiver operating characteristic curves, pHi was shown to be the most predictive of mortality compared to the other variables. The simplicity, speed and practicality of using the tonometer adds to its superiority over the latter measurements. No relationship was found between ventricular ejection fraction, pHi and outcome., Conclusion: Although the number of patients is small, these results support pHi as a valuable predictor of outcome and also suggest a role for the gut in initiating the IL-6 and physiological responses.

The aim of this study was to determine whether free radical-induced lipid peroxidation occurs following transient carotid clamping. Jugular vein plasma levels of malondialdehyde (MDA) and diene conjugates (DC) were estimated in 24 patients undergoing carotid endarterectomy, at the beginning of the operation (To), just prior to clamping the carotid artery before the shunt was removed for closure of the arteriotomy (Ts), and at 30 (T30), 60 (T60), 120 (T120), 180 (T180) and 300 (T300) seconds after the clamps were released. Carotid clamp times were recorded. Significant elevations in the concentrations of both MDA and DC were observed at T60 after clamp release (MDA = 559 +/- 64 pmol/ml, DC = 428 +/- 32 units/ml), in comparison to concentrations at To (MDA = 408 +/- 34 pmol/ml, p < 0.01; DC = 374 +/- 28 units/ml, p < 0.05), returning to baseline at T300. There was a significant correlation between the percentage rise in MDA concentration and the duration of clamp-induced ischaemia (r = 0.45, p = 0.03). The significance of this burst of MDA and DC is unclear especially as the one patient who sustained a postoperative neurological deficit displayed no rise in the concentration of either. If this rise is related to free radical generation following ischaemia-reperfusion injury it may play an important role in influencing the clinical outcome in the patients.

Preoperative acid studies and early postoperative insulin tests in 275 patients undergoing various forms of vagotomy have been related to recurrent ulceration. Follow-up time has been from two to nine years, mean 4-3 years. Recurrence is directly related to basal acidity in both tests but is not related to stimulated acid levels preoperatively. In the insulin tests higher levels of acidity after insulin are associated with a higher incidence of recurrence. When positive, Hollander's and multiple criteria are both associated with a higher recurrence rate.

A Monte Carlo-type simulation of the evolution of a multigene family was performed. The model was designed to study the selective forces which may control the size of a multigene family. As expected, we find that direct selection on the size of the multigene family can control its size. More important, we find that selection acting upon the family as a single functional unit, in conjunction with homologous but unequal crossing over, can also control the size of a multigene family.

Structural and functional analyses of myeloma immunoglobulins from inbred BALB/c mice and humans have provided important insights into the structure of the antibody molecule and the expression and evolution of antibody genes. One important question concerning these analyses is whether the myeloma process selects, in a nonrandom manner, the lymphocytes to be transformed. The availability of myeloma tumors in a second inbred strain of mouse, NZB, permits us to approach this question. In this respect. the NH2-terminal amino acid sequences of 27 kappa light chains as well as data relating to the antigen-binding properties and immunoglobulin class distribution of NZB myeloma proteins are presented and compared with similar data from the BALB/c mouse. These studies suggest that the myeloma proteins from the BALB/c and NZB mice constitute two populations of immunoglobulins with distinct functional and structural properties. The implication of this observation are discussed.

In this article, we develop a mathematical approach for the analysis of diversity in antibody gene families. This approach is arrived at by examing two general questions about protein populations: (1) What is a relative measure of the diversity exhibited by one protein family when compared with a second? (2) What is the probability that two protein populations were derived from a single common population? These quantitative approaches permit a variety of precise evolutionary, genetic, and developmental questions to be asked of antibody gene families. Using this methodology, we demonstrate that the diversity in mouse K-immunoglobulin chains is considerably greater than in their human K counterparts. We also show that the variable (Vl) regions of light chains associated with IgG and IgA immunoglobulins in the mouse appear to have been derived from a common population of Vl genes. This approach also can be used to analyse sequence data from other informational multigene families.

The amino acid sequence of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) has been compared to itself and to other proteins. Two segments, each of about 380 amino acids, comprising the first three-fourths of the polypeptide chain, were found to be very similar to each other. It is concluded that they are homologous. The carboxyl-terminal fourth has a high percentage of amino acid identities with dihydrofolate reductase of Escherichia coli, suggesting these sequences also are homologous. A model for the origin of beta-galactosidase is presented. The overall similarity of beta-galactosidase to lac repressor does not appear to be significant.