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- Volume 52, 2021
Annual Review of Ecology, Evolution, and Systematics - Volume 52, 2021
Volume 52, 2021
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Plant Communication
Vol. 52 (2021), pp. 1–24More LessCommunication occurs when a sender emits a cue perceived by a receiver that changes the receiver's behavior. Plants perceive information regarding light, water, other nutrients, touch, herbivores, pathogens, mycorrhizae, and nitrogen-fixing bacteria. Plants also emit cues perceived by other plants, beneficial microbes, herbivores, enemies of herbivores, pollinators, and seed dispersers. Individuals responding to light cues experienced increased fitness. Evidence for benefits of responding to cues involving herbivores and pathogens is more limited. The benefits of emitting cues are also less clear, particularly for plant–plant communication. Reliance on multiple or dosage-dependent cues can reduce inappropriate responses, and plants often remember past cues. Plants have multiple needs and prioritize conflicting cues such that the risk of abiotic stress is treated as greater than that of shading, which is in turn treated as greater than that of consumption. Plants can distinguish self from nonself and kin from strangers. They can identify the species of competitor or consumer and respond appropriately. Cues involving mutualists often contain highly specific information.
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The Ecological Importance of Allelopathy
Vol. 52 (2021), pp. 25–45More LessAllelopathy (i.e., chemical interaction among species) was originally conceived as inclusive of positive and negative effects of plants on other plants, and we adopt this view. Most studies of allelopathy have been phenomenological, but we focus on studies that have explored the ecological significance of this interaction. The literature suggests that studies of allelopathy have been particularly important for three foci in ecology: species distribution, conditionality of interactions, and maintenance of species diversity. There is evidence that allelopathy influences local distributions of plant species around the world. Allelopathic conditionality appears to arise through coevolution, and this is a mechanism for plant invasions. Finally, allelopathy promotes species coexistence via intransitive competition, modifications of direct interactions, and (co)evolution. Recent advances additionally suggest that coexistence might be favored through biochemical recognition. The preponderance of phenomenological studies notwithstanding, allelopathy has broad ecological consequences.
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Why Are Species’ Traits Weak Predictors of Range Shifts?
Vol. 52 (2021), pp. 47–66More LessWe examine the evidence linking species’ traits to contemporary range shifts and find they are poor predictors of range shifts that have occurred over decades to a century. We then discuss reasons for the poor performance of traits for describing interspecific variation in range shifts from two perspectives: (a) factors associated with species’ traits that degrade range-shift signals stemming from the measures used for species’ traits, traits that are typically not analyzed, and the influence of phylogeny on range-shift potential and (b) issues in quantifying range shifts and relating them to species’ traits due to imperfect detection of species, differences in the responses of altitudinal and latitudinal ranges, and emphasis on testing linear relationships between traits and range shifts instead of nonlinear responses. Improving trait-based approaches requires a recognition that traits within individuals interact in unexpected ways and that different combinations of traits may be functionally equivalent.
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From Insects to Frogs, Egg–Juvenile Recruitment Can Have Persistent Effects on Population Sizes
Vol. 52 (2021), pp. 67–86More LessUnderstanding what regulates population sizes of organisms with complex life cycles is challenging because limits on population sizes can occur at any stage or transition. We extend a conceptual framework to explore whether numbers of successfully laid eggs determine densities of later stages in insects, fish, amphibians, and snails inhabiting marine, freshwater, or terrestrial habitats. Our review suggests novel hypotheses, which propose characteristics of species or environments that create spatial variation in egg densities and predict when such patterns are maintained throughout subsequent life-cycle stages. Existing data, although limited, suggest that persistent, strong associations between egg and subsequent juvenile densities are likely for species where suitable egg-laying habitat is in short supply. Those associations are weakened in some environments and for some species by density-dependent losses of eggs or hatchlings. Such cross-ecosystem comparisons are fundamental to generality in ecology but demand place-based understandings of species’ biology and natural history.
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The Biology of Chernobyl
Vol. 52 (2021), pp. 87–109More LessEnvironmental disasters offer the unique opportunity for landscape-scale ecological and evolutionary studies that are not possible in the laboratory or small experimental plots. The nuclear accident at Chernobyl (1986) allows for rigorous analyses of radiation effects on individuals and populations at an ecosystem scale. Here, the current state of knowledge related to populations within the Chernobyl region of Ukraine and Belarus following the largest civil nuclear accident in history is reviewed. There is now a significant literature that provides contrasting and occasionally conflicting views of the state of animals and how they are affected by this mutagenic stressor. Studies of genetic and physiological effects have largely suggested significant injuries to individuals inhabiting the more radioactive areas of the Chernobyl region. Most population censuses for most species suggest that abundances are reduced in the more radioactive areas.
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Ancient Invaders: How Paleogenetic Tools Help to Identify and Understand Biological Invasions of the Past
Vol. 52 (2021), pp. 111–129More LessPast biological invasions have contributed to shaping our present day biodiversity. For many island ecosystems, they are the only source of terrestrial life. At the same time, biological invasions, in particular when caused by human activity, are a major concern for the conservation of native species. It is therefore essential to understand the drivers of biological invasions as well as the role invasions have played in different ecosystems. Molecular tools have provided valuable data to reconstruct biological invasions, their drivers, and their impacts. Recent technological developments have further increased the potential of molecular tools to track past shifts in biodiversity. Here, we provide a perspective on how such molecular tools have influenced our understanding of past biological invasions and discuss how they may further help to shape our understanding and management of biological invasions.
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A Genetic Perspective on Cetacean Evolution
Vol. 52 (2021), pp. 131–151More LessStudies of cetacean evolution using genetics and other biomolecules have come a long way—from the use of allozymes and short sequences of mitochondrial or nuclear DNA to the assembly of full nuclear genomes and characterization of proteins and lipids. Cetacean research has also advanced from using only contemporary samples to analyzing samples dating back thousands of years, and to retrieving data from indirect environmental sources, including water or sediments. Combined, these studies have profoundly deepened our understanding of the origin of cetaceans; their adaptation and speciation processes; and of the past population change, migration, and admixture events that gave rise to the diversity of cetaceans found today.
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Evolvability: A Quantitative-Genetics Perspective
Vol. 52 (2021), pp. 153–175More LessThe concept of evolvability emerged in the early 1990s and soon became fashionable as a label for different streams of research in evolutionary biology. In evolutionary quantitative genetics, evolvability is defined as the ability of a population to respond to directional selection. This differs from other fields by treating evolvability as a property of populations rather than organisms or lineages and in being focused on quantification and short-term prediction rather than on macroevolution. While the term evolvability is new to quantitative genetics, many of the associated ideas and research questions have been with the field from its inception as biometry. Recent research on evolvability is more than a relabeling of old questions, however. New operational measures of evolvability have opened possibilities for understanding adaptation to rapid environmental change, assessing genetic constraints, and linking micro- and macroevolution.
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Effects of Selection at Linked Sites on Patterns of Genetic Variability
Vol. 52 (2021), pp. 177–197More LessPatterns of variation and evolution at a given site in a genome can be strongly influenced by the effects of selection at genetically linked sites. In particular, the recombination rates of genomic regions correlate with their amount of within-population genetic variability, the degree to which the frequency distributions of DNA sequence variants differ from their neutral expectations, and the levels of adaptation of their functional components. We review the major population genetic processes that are thought to lead to these patterns, focusing on their effects on patterns of variability: selective sweeps, background selection, associative overdominance, and Hill–Robertson interference among deleterious mutations. We emphasize the difficulties in distinguishing among the footprints of these processes and disentangling them from the effects of purely demographic factors such as population size changes. We also discuss how interactions between selective and demographic processes can significantly affect patterns of variability within genomes.
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The Invisible Hand of the Periodic Table: How Micronutrients Shape Ecology
Vol. 52 (2021), pp. 199–219More LessBeyond the better-studied carbohydrates and the macronutrients nitrogen and phosphorus, a remaining 20 or so elements are essential for life and have distinct geographical distributions, making them of keen interest to ecologists. Here, I provide a framework for understanding how shortfalls in micronutrients like iodine, copper, and zinc can regulate individual fitness, abundance, and ecosystem function. With a special focus on sodium, I show how simple experiments manipulating biogeochemistry can reveal why many of the variables that ecologists study vary so dramatically from place to place. I conclude with a discussion of how the Anthropocene's changing temperature, precipitation, and atmospheric CO2 levels are contributing to nutrient dilution (decreases in the nutrient quality at the base of food webs).
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Demographic Consequences of Phenological Shifts in Response to Climate Change
Vol. 52 (2021), pp. 221–245More LessWhen a phenological shift affects a demographic vital rate such as survival or reproduction, the altered vital rate may or may not have population-level consequences. We review the evidence that climate change affects populations by shifting species’ phenologies, emphasizing the importance of demographic life-history theory. We find many examples of phenological shifts having both positive and negative consequences for vital rates. Yet, few studies link phenological shifts to changes in vital rates known to drive population dynamics, especially in plants. When this link is made, results are largely consistent with life-history theory: Phenological shifts have population-level consequences when they affect survival in longer-lived organisms and reproduction in shorter-lived organisms. However, there are just as many cases in which demographic mechanisms buffer population growth from phenologically induced changes in vital rates. We provide recommendations for future research aiming to understand the complex relationships among climate, phenology, and demography, which will help to elucidate the extent to which phenological shifts actually alter population persistence.
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Multispecies Coalescent: Theory and Applications in Phylogenetics
Vol. 52 (2021), pp. 247–268More LessSpecies tree estimation is a basic part of many biological research projects, ranging from answering basic evolutionary questions (e.g., how did a group of species adapt to their environments?) to addressing questions in functional biology. Yet, species tree estimation is very challenging, due to processes such as incomplete lineage sorting, gene duplication and loss, horizontal gene transfer, and hybridization, which can make gene trees differ from each other and from the overall evolutionary history of the species. Over the last 10–20 years, there has been tremendous growth in methods and mathematical theory for estimating species trees and phylogenetic networks, and some of these methods are now in wide use. In this survey, we provide an overview of the current state of the art, identify the limitations of existing methods and theory, and propose additional research problems and directions.
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Biotic and Abiotic Controls on the Phanerozoic History of Marine Animal Biodiversity
Vol. 52 (2021), pp. 269–289More LessDuring the past 541 million years, marine animals underwent three intervals of diversification (early Cambrian, Ordovician, Cretaceous–Cenozoic) separated by nondirectional fluctuation, suggesting diversity-dependent dynamics with the equilibrium diversity shifting through time. Changes in factors such as shallow-marine habitat area and climate appear to have modulated the nondirectional fluctuations. Directional increases in diversity are best explained by evolutionary innovations in marine animals and primary producers coupled with stepwise increases in the availability of food and oxygen. Increasing intensity of biotic interactions such as predation and disturbance may have led to positive feedbacks on diversification as ecosystems became more complex. Important areas for further research include improving the geographic coverage and temporal resolution of paleontological data sets, as well as deepening our understanding of Earth system evolution and the physiological and ecological traits that modulated organismal responses to environmental change.
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Are Terrestrial Biological Invasions Different in the Tropics?
Vol. 52 (2021), pp. 291–314More LessMost biological invasion literature—including syntheses and meta-analyses and the resulting theory—is reported from temperate regions, drawing only minimally from the tropics except for some island systems. The lack of attention to invasions in the tropics results from and reinforces the assumption that tropical ecosystems, and especially the continental tropics, are more resistant to invasions. We have critically assessed biological invasions in the tropics and compared them with temperate regions, finding relatively weak evidence that tropical and temperate regions differ in their invasibility and in the traits that determine invader success and impacts. Propagule pressure and the traits that promote adaptation to disturbances (e.g., high fecundity or fast growth rates) are generally favorable to invasions in both tropical and temperate regions. We emphasize the urgent need for greater investment and regional cooperation in the study, prevention, and management of biological invasions in the tropics.
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Evolution of Mimicry Rings as a Window into Community Dynamics
Vol. 52 (2021), pp. 315–341More LessMimicry rings are communities of mimetic organisms that are excellent models for ecological and evolutionary studies because the community composition, the nature of the species interactions, the phenotypes under selection, and the selective agents are well characterized. Here, we review how regional and ecological filtering, density- and frequency-dependent selection, toxicity of prey, and age of mimicry rings shape their assembly. We synthesize findings from theoretical and empirical studies to generate the following hypotheses: (a) the degree of unpalatability and age of mimicry rings increase mimicry ring size and (b) the degree of unpalatability, generalization of the aposematic signal, and availability of alternative prey are positively related to the breadth of the protection umbrella for an aposematic signal and negatively related to the degree of mimetic resemblance. We also provide a phylogenetic framework in which key aspects of mimicry ring diversification may be studied.
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A Dual Role for Behavior in Evolution and Shaping Organismal Selective Environments
Vol. 52 (2021), pp. 343–362More LessThe hypothesis that evolved behaviors play a determining role in facilitating and impeding the evolution of other traits has been discussed for more than 100 years with little consensus beyond an agreement that the ideas are theoretically plausible in accord with the Modern Synthesis. Many recent reviews of the genomic, epigenetic, and developmental mechanisms underpinning major behavioral transitions show how facultative expression of novel behaviors can lead to the evolution of obligate behaviors and structures that enhance behavioral function. Phylogenetic and genomic studies indicate that behavioral traits are generally evolutionarily more labile than other traits and that they help shape selective environments on the latter traits. Adaptive decision-making to encounter resources and avoid stress sources requires specific sensory inputs, which behaviorally shape selective environments by determining those features of the external world that are biologically relevant. These recent findings support the hypothesis of a dual role for behavior in evolution and are consistent with current evolutionary theory.
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The Ecology and Evolution of Model Microbial Mutualisms
Vol. 52 (2021), pp. 363–384More LessMutually beneficial interspecific interactions are abundant throughout the natural world, including between microbes. Mutualisms between microbes are critical for everything from human health to global nutrient cycling. Studying model microbial mutualisms in the laboratory enables highly controlled experiments for developing and testing evolutionary and ecological hypotheses. In this review, we begin by describing the tools available for studying model microbial mutualisms. We then outline recent insights that laboratory systems have shed on the evolutionary origins, evolutionary dynamics, and ecological features of microbial mutualism. We touch on gaps in our current understanding of microbial mutualisms, note connections to mutualism in nonmicrobial systems, and call attention to open questions ripe for future study.
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Evolution of the Mode of Nutrition in Symbiotic and Saprotrophic Fungi in Forest Ecosystems
Vol. 52 (2021), pp. 385–404More LessIn this review, we highlight the main insights that have been gathered from recent developments using large-scale genomics of fungal saprotrophs and symbiotrophs (including ectomycorrhizal and orchid and ericoid mycorrhizal fungi) inhabiting forest ecosystems. After assessing the goals and motivations underlying our approach, we explore our current understanding of the limits and future potential of using genomics to understand the ecological roles of these forest fungi. Comparative genomics unraveled the molecular machineries involved in lignocellulose decomposition in wood decayers, soil and litter saprotrophs, and mycorrhizal symbionts. They also showed that transitions from saprotrophy to mutualism entailed widespread losses of lignocellulose-degrading enzymes; diversification of novel, lineage-specific symbiosis-induced genes; and convergent evolution of genetic innovations that facilitate the accommodationof mutualistic symbionts within their plant hosts. We also identify the major questions that remain unanswered and propose new avenues of genome-based research to understand the role of soil fungi in sustainable forest ecosystems.
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Dynamics of Ecological Communities Following Current Retreat of Glaciers
Vol. 52 (2021), pp. 405–426More LessGlaciers are retreating globally, and the resulting ice-free areas provide an experimental system for understanding species colonization patterns, community formation, and dynamics. The last several years have seen crucial advances in our understanding of biotic colonization after glacier retreats, resulting from the integration of methodological innovations and ecological theories. Recent empirical studies have demonstrated how multiple factors can speed up or slow down the velocity of colonization and have helped scientists develop theoretical models that describe spatiotemporalchanges in community structure. There is a growing awareness of how different processes (e.g., time since glacier retreat, onset or interruption of surface processes, abiotic factors, dispersal, biotic interactions) interact to shape community formation and, ultimately, their functional structure through succession. Here, we examine how these studies address key theoretical questions about community dynamics and show how classical approaches are increasingly being combined with environmental DNA metabarcoding and functional trait analysis to document the formation of multitrophic communities, revolutionizing our understanding of the biotic processes that occur following glacier retreat.
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The Emerging Phylogenetic Perspective on the Evolution of Actinopterygian Fishes
Vol. 52 (2021), pp. 427–452More LessThe emergence of a new phylogeny of ray-finned fishes at the turn of the twenty-first century marked a paradigm shift in understanding the evolutionary history of half of living vertebrates. We review how the new ray-finned fish phylogeny radically departs from classical expectations based on morphology. We focus on evolutionary relationships that span the backbone of ray-finned fish phylogeny, from the earliest divergences among teleosts and nonteleosts to the resolution of major lineages of Percomorpha. Throughout, we feature advances gained by the new phylogeny toward a broader understanding of ray-finned fish evolutionary history and the implications for topics that span from the genetics of human health to reconsidering the concept of living fossils. Additionally, we discuss conceptual challenges that involve reconciling taxonomic classification with phylogenetic relationships and propose an alternate higher-level classification for Percomorpha. Our review highlights remaining areas of phylogenetic uncertainty and opportunities for comparative investigations empowered by this new phylogenetic perspective on ray-finned fishes.
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Previous Volumes
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Volume 55 (2024)
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Volume 54 (2023)
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Volume 53 (2022)
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Volume 52 (2021)
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Volume 51 (2020)
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Volume 50 (2019)
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Volume 49 (2018)
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Volume 48 (2017)
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Volume 47 (2016)
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Volume 46 (2015)
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Volume 45 (2014)
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Volume 44 (2013)
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Volume 43 (2012)
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Volume 42 (2011)
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Volume 41 (2010)
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Volume 40 (2009)
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Volume 39 (2008)
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Volume 38 (2007)
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Volume 37 (2006)
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Volume 36 (2005)
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Volume 35 (2004)
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Volume 34 (2003)
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Volume 33 (2002)
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Volume 32 (2001)
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Volume 31 (2000)
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Volume 30 (1999)
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Volume 29 (1998)
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Volume 28 (1997)
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Volume 27 (1996)
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Volume 26 (1995)
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Volume 25 (1994)
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Volume 24 (1993)
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Volume 23 (1992)
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Volume 22 (1991)
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Volume 21 (1990)
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Volume 20 (1989)
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Volume 19 (1988)
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Volume 18 (1987)
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Volume 17 (1986)
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Volume 16 (1985)
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Volume 15 (1984)
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Volume 14 (1983)
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Volume 13 (1982)
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Volume 12 (1981)
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Volume 11 (1980)
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Volume 10 (1979)
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Volume 9 (1978)
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Volume 8 (1977)
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Volume 7 (1976)
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Volume 6 (1975)
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Volume 5 (1974)
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Volume 4 (1973)
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Volume 3 (1972)
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Volume 2 (1971)
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Volume 1 (1970)
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Volume 0 (1932)