bluuebunny/crossref_metadata_2025 huggingface dataset:
Epicardial development in lamprey supports an evolutionary origin of the vertebrate epicardium from an ancestral pronephric external glomerulus
Authors: Pombal Manuel A. , Carmona Rita , Megías Manuel , Ruiz Alejandro , Pérez‐Pomares José María , Muñoz‐Chápuli Ramón
Published: August 2010

SUMMARY
The epicardium is the outer layer of the vertebrate heart. Both the embryonic epicardium and its derived mesenchyme are critical to heart development, contributing to the coronary vasculature and modulating the proliferation of the ventricular myocardium. The embryonic epicardium arises from an extracardiac, originally paired progenitor tissue called the proepicardium, a proliferation of coelomic cells found at the limit between the liver and the sinus venosus. Proepicardial cells attach to and spread over the cardiac surface giving rise to the epicardium. Invertebrate hearts always lack of epicardium, and no hypothesis has been proposed about the origin of this tissue and its proepicardial progenitor in vertebrates. We herein describe the epicardial development in a representative of the most basal living lineage of vertebrates, the agnathan Petromyzon marinus (lamprey). The epicardium in lampreys develops by migration of coelomic cells clustered in a paired structure at the roof of the coelomic cavity, between the pronephros and the gut. Later on, these outgrowths differentiate into the pronephric external glomerulus (PEG), a structure composed of capillary networks, mesangial cells, and podocytes. This observation is consistent with the conclusion that the primordia of the most anterior pair of PEG in agnathans have been retained and transformed into the proepicardium in gnathostomes. Glomerular progenitor cells are highly vasculogenic and probably allowed for the vascularization of a cardiac tube primarily devoid of coronary vessels. This new hypothesis accounts for the striking epicardial expression of Wt1 and Pod1, two transcription factors essential for development of the excretory system.
Phylogenetic, functional, and structural components of variation in bone growth rate of amniotes
Authors: Cubo Jorge , Legendre Pierre , De Ricqlès Armand , Montes Laëtitia , De Margerie Emmanuel , Castanet Jacques , Desdevises Yves
Published: August 2010

SUMMARYThe biological features observed in every living organism are the outcome of three sets of factors: historical (inherited by homology), functional (biological adaptation), and structural (properties inherent to the materials with which organs are constructed, and the morphogenetic rules by which they grow). Integrating them should bring satisfactory causal explanations of empirical data. However, little progress has been accomplished in practice toward this goal, because a methodologically efficient tool was lacking. Here we use a new statistical method of variation partitioning to analyze bone growth in amniotes. (1)Historical component. The variation of bone growth rates contains a significant phylogenetic signal, suggesting that the observed patterns are partly the outcome of shared ancestry. (2)Functional causation. High growth rates, although energy costly, may be adaptive (i.e., they may increase survival rates) in taxa showing short growth periods (e.g., birds). In ectothermic amniotes, low resting metabolic rates may limit the maximum possible growth rates. (3)Structural constraint. Whereas soft tissues grow through a multiplicative process, growth of mineralized tissues is accretionary (additive, i.e., mineralization fronts occur only at free surfaces). Bone growth of many amniotes partially circumvents this constraint: it is achieved not only at the external surface of the bone shaft, but also within cavities included in the bone cortex as it grows centrifugally. Our approach contributes to the unification of historicism, functionalism, and structuralism toward a more integrated evolutionary biology.
Emerging model systems in evo‐devo: cavefish and microevolution of development
Authors: Jeffery William R.
Published: August 2010

SUMMARY
Cavefish and their conspecific surface‐dwelling ancestors (Astyanax mexicanus) are emerging as a model system to study the microevolution of development. Here we describe attributes that make this system highly promising for such studies. We review how the Astyanax system is being used to understand evolutionary forces underlying loss of eyes and pigmentation in cavefish. Pigment regression is probably explained by neutral mutations, whereas natural selection is a likely mechanism for loss of eyes. Finally, we discuss several research frontiers in which Astyanax is poised to make significant contributions in the future: evolution of constructive traits, the craniofacial skeleton, the central nervous system, and behavior.
Species‐specific recognition of beetle cues by the nematode Pristionchus maupasi
Authors: Hong Ray L. , Svatoš Aleš , Herrmann Matthias , Sommer Ralf J.
Published: August 2010

SUMMARY
The environment has a strong effect on development as is best seen in the various examples of phenotypic plasticity. Besides abiotic factors, the interactions between organisms are part of the adaptive forces shaping the evolution of species. To study how ecology influences development, model organisms have to be investigated in their environmental context. We have recently shown that the nematode Pristionchus pacificus and its relatives are closely associated with scarab beetles with a high degree of species specificity. For example, P. pacificus is associated with the oriental beetle Exomala orientalis in Japan and the northeastern United States, whereas Pristionchus maupasi is primarily isolated from cockchafers of the genus Melolontha in Europe. Here, we investigate how Pristionchus nematodes identify their specific insect hosts by using chemotaxis studies originally established in Caenorhabditis elegans. We observed that P. maupasi is exclusively attracted to phenol, one of the sex attractants of Melolontha beetles, and that attraction was also observed when washes of adult beetles were used instead of pure compounds. Furthermore, P. maupasi chemoattraction to phenol synergizes with plant volatiles such as the green leaf alcohol and linalool, demonstrating that nematodes can integrate distinct chemical senses from multiple trophic levels. In contrast, another cockchafer‐associated nematode, Diplogasteriodes magnus, was not strongly attracted to phenol. We conclude that interception of the insect communication system might be a recurring strategy of Pristionchus nematodes but that different nematodes use distinct chemical cues for finding their beetle hosts.
Ancestral variation and the potential for genetic accommodation in larval amphibians: implications for the evolution of novel feeding strategies
Authors: Ledon‐Rettig Cris C. , Pfennig David W. , Nascone‐Yoder Nanette
Published: August 2010

SUMMARY
Few studies provide empirical evidence for phenotypic plasticity's role in the evolution of novel traits. One way to do so is to test whether latent plasticity is present in an ancestor that can be refined, enhanced, or diminished by selection in derived taxa (through “genetic accommodation”), thereby producing novel traits. Here, we evaluated whether gut plasticity preceded and promoted the evolution of a novel feeding strategy in spadefoot toad tadpoles. We studied Scaphiopus couchii, whose tadpoles develop an elongate gut and consume only detritus, and two derived species, Spea multiplicata and Sp. bombifrons, whose tadpoles also express a novel, short‐gut phenotype in response to a novel resource (anostracan shrimp). Consistent with the expectations of plasticity‐mediated trait evolution, we found that shrimp induced a range of phenotypes in Scaphiopus that were not produced with detritus. This plasticity was either suppressed or exaggerated in Spea depending on whether the induced phenotypes were adaptive. Moreover, in contrast to its effects on morphology, shrimp induced little or no functional plasticity, as assessed by gut cell proliferation, in Scaphiopus. Shrimp did, however, induce substantial proliferation in Sp. bombifrons, the species that consumes the most shrimp and that produces the short‐gut phenotype the most frequently. Thus, if Spea had ancestral morphological plasticity in response to a novel diet, their shrimp‐induced short‐gut morphology may have undergone subsequent genetic accommodation that improved its functionality. Hence, diet‐induced phenotypic plasticity may have preceded and even promoted the evolution of a novel phenotype.
Deciphering the fossil record of early bilaterian embryonic development in light of experimental taphonomy
Authors: Gostling Neil J. , Thomas Ceri‐Wyn , Greenwood Jenny M. , Dong Xiping , Bengtson Stefan , Raff Elizabeth C. , Raff Rudolf A. , Degnan Bernard M. , Stampanoni Marco , Donoghue Philip C. J.
Published: August 2010

SUMMARY
Experimental analyses of decay in a tunicate deuterostome and three lophotrochozoans indicate that the controls on decay and preservation of embryos, identified previously based on echinoids, are more generally applicable. Four stages of decay are identified regardless of the environment of death and decay. Embryos decay rapidly in oxic and anoxic conditions, although the gross morphology of embryos is maintained for longer under anoxic conditions. Under anoxic reducing conditions, the gross morphology of the embryos is maintained for the longest period of time, compatible with the timescale required for bacterially mediated mineralization of soft tissues. All four stages of decay were encountered under all environmental conditions, matching the spectrum of preservational qualities encountered in all fossil embryo assemblages. The preservation potential of embryos of deuterostomes and lophotrochozoans is at odds with the lack of such embryos in the fossil record. Rather, the fossil record of embryos, as sparse as it is, is dominated by forms interpreted as ecdysozoans, cnidarians, and stem‐metazoans. The dearth of deuterostome and lophotrochozoan embryos may be explained by the fact that ecdysozoans, at least, tend to deposit their eggs in the sediment rather than through broadcast spawning. However, fossil embryos remain very rare and the main controlling factor on their fossilization may be the unique conspiracy of environmental conditions at a couple of sites. The preponderance of fossilized embryos of direct developers should not be used in evidence against the existence of indirect development at this time in animal evolutionary history.
The dynamics of developmental system drift in the gene network underlying wing polyphenism in ants: a mathematical model
Authors: Nahmad Marcos , Glass Leon , Abouheif Ehab
Published: August 2010

SUMMARY
Understanding the complex interaction between genotype and phenotype is a major challenge of Evolutionary Developmental Biology. One important facet of this complex interaction has been called “Developmental System Drift” (DSD). DSD occurs when a similar phenotype, which is homologous across a group of related species, is produced by different genes or gene expression patterns in each of these related species. We constructed a mathematical model to explore the developmental and evolutionary dynamics of DSD in the gene network underlying wing polyphenism in ants. Wing polyphenism in ants is the ability of an embryo to develop into a winged queen or a wingless worker in response to an environmental cue. Although wing polyphenism is homologous across all ants, the gene network that underlies wing polyphenism has evolved. In winged ant castes, our simulations reproduced the conserved gene expression patterns observed in the network that controls wing development in holometabolous insects. In wingless ant castes, we simulated the suppression of wings by interrupting (up‐ or downregulating) the expression of genes in the network. Our simulations uncovered the existence of four groups of genes that have similar effects on target gene expression and growth. Although each group is comprised of genes occupying different positions in the network, their interruption produces vestigial discs that are similar in size and shape. The implications of our results for understanding the origin, evolution, and dissociation of the gene network underlying wing polyphenism in ants are discussed.
Developmental bias in evolution: evolutionary accessibility of phenotypes in a model evo‐devo system
Authors: Psujek Sean , Beer Randall D.
Published: August 2010

SUMMARY
The success of the modern synthesis has resulted in forces of evolutionary change other than natural selection being marginalized. However, recent work has attempted to show the importance of non‐selective influences in shaping organic form. One such force is developmental bias, in which phenotypes are differentially produced. We use a simulation model of neural development to explore questions of general interest about developmental systems. From this analysis, we find that the pattern of developmental bias varies strongly with the genotype even among phenotypically‐neutral genotypes. In addition to this genotype‐dependent developmental bias (local bias), an intrinsic bias exists in the developmental system (global bias). We also show that developmental bias varies among related genotypes that produce the same phenotype. Finally, we illustrate how a pattern of bias emerges from the manner in which mutations affect the regulatory structure of the wild‐type genotype. These results suggest that developmental bias could have a strong influence on the direction of evolutionary modification.
An examination of the Chiropteran HoxD locus from an evolutionary perspective
Authors: Ray Russell , Capecchi Mario
Published: August 2010

SUMMARY
Duplications of Hox gene clusters have been suggested as a mechanism whereby new Hox functions can be developed while preserving critical ancestral roles. However, in tetrapods, particularly in mammals, there is great variability in limb structure morphologies that are known to be affected by Hox genes without further Hox cluster duplications. The lack of further duplications suggests that if Hox genes have played a direct role in the morphological elaboration of tetrapod limbs, the changes must have come about from Hox protein sequence changes or from changes regarding the amount, time, and place of Hox gene expression. To investigate whether such changes to Hox genes could play a role in limb elaboration, we examined the HoxD locus in bats, which have both highly elaborated fore‐ and hindlimbs. We found that while the Chiropteran HoxD13 protein was highly conserved, there was an expansion of HoxD13 expression in the posterior portion of the Chiropteran forelimb and into the leading edge of the wing membrane. We were also able to uncover a number of unique lineage‐specific sequence changes to a known HoxD limb enhancer, the Global Control Region (GCR). Further, mouse transgenic assays showed that the Chiropteran GCR has new limb enhancer activity domains beyond that reported for the Human GCR. These results suggest that modulation of Hox gene expression may be a mechanism for effecting morphological change in lineage‐specific manner while maintaining ancestral constraints and cluster integrity.
Abundant genetic variation in transcript level during early Drosophila development
Authors: Nuzhdin Sergey V. , Tufts Danielle M. , Hahn Matthew W.
Published: August 2010

SUMMARY
Variation in gene expression may underlie many important evolutionary traits. However, it is not known at what stage in organismal development changes in gene expression are most likely to result in changes in phenotype. One widely held belief is that changes in early development are more likely to result in changes in downstream phenotypes. In order to discover how much genetic variation for transcript level is present in natural populations, we studied zygotic gene expression in nine inbred lines of Drosophila melanogaster at two time points in their development. We find abundant variation for transcript level both between lines and over time; close to half of all expressed genes show a significant line effect at either time point. We examine the contribution of maternally loaded genes to this variation, as well as the contribution of variation in upstream genes to variation in their downstream targets in two well‐studied gene regulatory networks. Finally, we estimate the dimensionality of gene expression in these two networks and find that—despite large numbers of varying genes—there appear to be only two factors controlling this variation.
The chelifores of sea spiders (Arthropoda, Pycnogonida) are the appendages of the deutocerebral segment
Authors: Brenneis Georg , Ungerer Petra , Scholtz Gerhard
Published: August 2010

SUMMARY
Within the last decade, gene expression patterns and neuro‐anatomical data have led to a new consensus concerning the long‐debated association between anterior limbs and neuromeres in the arthropod head. According to this new view, the first appendage in all extant euarthropods is innervated by the second neuromere, the deutocerebrum, whereas the anterior‐most head region bearing the protocerebrum lacks an appendage. This stands in contrast to the clearly protocerebrally targeted “antennae” of Onychophora and to some evidence for protocerebral limbs in fossil euarthropod representatives. Yet, the latter “frontal appendages” or “primary antennae” have most likely been reduced or lost in the lineage, leading to extant taxa. Surprisingly, a recent neuro‐anatomical study on a pycnogonid challenged this evolutionary scenario, reporting a protocerebral innervation of the first appendages, the chelifores. However, this interpretation was soon after questioned by Hox gene expression data. To re‐evaluate the unresolved controversy, we analyzed neuro‐anatomy and neurogenesis in four pycnogonid species using immunohistochemical techniques. We clearly show the postprotocerebral innervation of the chelifores, which is resolved as the plesiomorphic condition in pycnogonids when evaluated against a recently published comprehensive phylogeny. By providing direct morphological support for the deutocerebral status of the cheliforal ganglia, we reconcile morphological and gene expression data and argue for a corresponding position between the anterior‐most appendages in all extant euarthropods. Consequently, other structures have to be scrutinized to illuminate the fate of a presumptive protocerebral appendage in recent euarthropods. The labrum and the “frontal filaments” of some crustaceans are possible candidates for this approach.
The mammalian myotome: a muscle with no innervation
Authors: Deries Marianne , Collins Jennifer J. P. , Duxson Marilyn J.
Published: August 2010

SUMMARY
The segmented muscular myotome is the first muscle to form in all vertebrates. In fish and amphibian embryos, the myotome becomes innervated very early and is essential for larval swimming. Its role in birds and mammals, however, is not clear. Using immunohistochemistry on sections and whole mounts of rat embryos, we demonstrate that the mammalian myotome differentiates and develops over a period of 3 days without being invaded by the outgrowing spinal nerves. In contrast, the limb muscle masses become filled with fine nerve branches from the first time that myocyte differentiation can be detected. Additionally, we show that the mammalian myotome does not express clustered acetylcholine receptors until after embryonic day 13.5, which corresponds to the beginning of its transformation into the adult epaxial muscles, showing that there are no functional myotomal neuromuscular junctions before this age. We suggest that the mammalian myotome has entirely lost the function of neurally controlled muscular contraction: its remaining functions are likely to be as a signaling tissue, as a structural scaffold, and as an incubator for myogenic precursors of the deep back, abdominal, and intercostal muscles.
Evolution of morphogenesis in 360‐million‐year‐old conodont chordates calibrated in days
Authors: Dzik Jerzy
Published: August 2010

SUMMARY
Highly rhythmic increments of crown tissue are identifiable in conodont oral apparatus elements from the Late Devonian of the Holy Cross Mountains, Poland; individual laminae being of thickness comparable with daily increments of vertebrate tooth enamel and fish otoliths. Abundant occurrence of such specimens enables bed‐by‐bed (stratophenetic) studies of the process of evolution at the population level and quantitative presentation of the evolution of ontogeny in the sampled geological section covering several million years. The morphologic transformation is expressed as expansion of a juvenile asymmetry to later stages of the ontogeny and in decrease of the mature element width, which was due to a change of the mineral tissue secretion rate. It was not just a simple extension of a juvenile character into the later stage of the ontogeny (heterochrony) but rather a true developmental novelty. The evolution was gradual and very slow. The proposed quantitative approach to growth increments in the mineral skeleton of ancient chordates introduces real‐time units to evolutionary developmental studies connected with direct paleontological evidence on the course of evolution.
Molecular signaling in zebrafish development and the vertebrate phylotypic period
Authors: Comte Aurélie , Roux Julien , Robinson‐Rechavi Marc
Published: August 2010

SUMMARY
During development vertebrate embryos pass through a stage where their morphology is most conserved between species, the phylotypic period (approximately the pharyngula). To explain the resistance to evolutionary changes of this period, one hypothesis suggests that it is characterized by a high level of interactions. Based on this hypothesis, we examined protein–protein interactions, signal transduction cascades and miRNAs over the course of zebrafish development, and the conservation of expression of these genes in mouse development. We also investigated the characteristics of genes highly expressed before or during the presumed phylotypic period. We show that while there is a high diversity of interactions during the phylotypic period (protein–DNA, RNA–RNA, cell–cell, and between tissues), which is well conserved with mouse, there is no clear difference with later, more morphologically divergent, stages. We propose that the phylotypic period may rather be the expression at the morphological level of strong conservation of molecular processes earlier in development.
Are palaeoscolecids ancestral ecdysozoans?
Authors: Harvey Thomas H. P. , Dong Xiping , Donoghue Philip C. J.
Published: August 2010

SUMMARYThe reconstruction of ancestors is a central aim of comparative anatomy and evolutionary developmental biology, not least in attempts to understand the relationship between developmental and organismal evolution. Inferences based on living taxa can and should be tested against the fossil record, which provides an independent and direct view onto historical character combinations. Here, we consider the nature of the last common ancestor of living ecdysozoans through a detailed analysis of palaeoscolecids, an early and extinct group of introvert‐bearing worms that have been proposed to be ancestral ecdysozoans. In a review of palaeoscolecid anatomy, including newly resolved details of the internal and external cuticle structure, we identify specific characters shared with various living nematoid and scalidophoran worms, but not with panarthropods. Considered within a formal cladistic context, these characters provide most overall support for a stem‐priapulid affinity, meaning that palaeoscolecids are far‐removed from the ecdysozoan ancestor. We conclude that previous interpretations in which palaeoscolecids occupy a deeper position in the ecdysozoan tree lack particular morphological support and rely instead on a paucity of preserved characters. This bears out a more general point that fossil taxa may appear plesiomorphic merely because they preserve only plesiomorphies, rather than the mélange of primitive and derived characters anticipated of organisms properly allocated to a position deep within animal phylogeny.
A placozoan affinity for Dickinsonia and the evolution of late Proterozoic metazoan feeding modes
Authors: Sperling Erik A. , Vinther Jakob
Published: August 2010

SUMMARY
Dickinsonia is one of the most recognizable forms in the Ediacaran fauna, but its phylogenetic position has been contentious, and it has been placed in almost every kingdom of life. Here, it is hypothesized that the affinities of Dickinsonia lie with the Placozoa (Metazoa), an understudied phylum that is widespread in tropical seas worldwide. Modern placozoans show obvious differences in size and axial organization compared with Dickinsonia, but these differences can be accounted for by the stem‐group/crown‐group distinction. The affinity with placozoans is evidenced primarily by the unique feeding mode of Dickinsonia, which is demonstrated by a series of feeding traces. These traces indicate that Dickinsonia moved over the Ediacaran matgrounds, and digested the mat using its entire lower sole. The ability of Dickinsonia to move negates an algal, fungal, or sponge affinity, while the feeding mode, external digestion with a ventral sole, rules out placement within any sponge or eumetazoan lineage. The only organisms that both move and feed in this manner are placozoans. Recent molecular phylogenetic studies have demonstrated that placozoans lie above sponges but below Eumetazoa. We hypothesize that Dickinsonia and other externally digesting Ediacaran forms are either stem‐placozoans, or a series of extinct lineages above sponges and below eumetazoans on the metazoan tree. We discuss the potential evolutionary transitions between the main metazoan feeding modes in the context of the emerging molecular phylogeny, and suggest that aspects of the sponge and placozoan feeding strategies are relicts of nonuniformitarian Proterozoic ocean conditions.
You Can’t Not Choose: Embracing the Role of Choice in Ecological Restoration
Authors: Allison Stuart K.
Published: August 2010

From the moment of its inception, human choice about how to treat the environment is a key part of ecological restoration. Because many, if not most, restoration projects require continual management once established, human choice remains a vital component of restoration projects for their entire life. But ecological restorationists often downplay the role of choice in restoration, partly because we see the choice to restore as obvious and inherently good and partly because we feel the restoration of more natural conditions for a habitat will lessen the impact of human choice over time. Some critics feel the role of human choice in restoration degrades the value of restoration. However, another response to human choice in restoration is to embrace choice, even with the problems it brings, and use choice as a way to more fully engage humans with the environment. If such choices are approached carefully, with recognition of the potential for poor choices, then restorationists can arrive at restorations that are better for both the environment and us.
Two‐Sided Edge Effect Studies and the Restoration of Endangered Ecosystems
Authors: Fonseca Carlos R. , Joner Fernando
Published: August 2010

Edge effect is the modification of ecological patterns and processes that occur around the edge of two adjacent ecosystems. Depending on their aim, edge effect studies have adopted one of the following methodological approaches: (1) the one‐sided approach—which studies ecological patterns and processes from an edge to the interior of just one of the habitats and (2) the two‐sided approach—which studies ecological patterns and processes across the whole gradient from the interior of one habitat to the interior of the other habitat, passing through the edge zone. A database containing information on 317 published papers revealed that both methodological approaches were equally used until the end of the 1980s. During the 1990s, the question of how organisms respond to habitat destruction and fragmentation led to an abrupt increase in the number of one‐sided studies. Recently, however, two‐sided studies have become more frequent. In this review, we put forth theoretical arguments of why the two‐sided edge effect approach can produce a broader understanding of the ecological processes associated with edges. We highlight that two‐sided edge effect studies must become more experimental and predictive, focusing on the factors controlling edge dynamics. Finally, we point out that two‐sided edge effect studies have the potential to create a positive research agenda for the restoration and expansion of endangered ecosystems.
Effectiveness of Turf Stripping as a Measure for Restoring Species‐Rich Fen Meadows in Suboptimal Hydrological Conditions
Authors: Van der Hoek Dick , Heijmans Monique M. P. D.
Published: August 2010

Most species‐rich fen meadows in nature reserves in The Netherlands are acidified due to weaker upwelling of base‐rich groundwater. The present study investigated whether and why turf stripping combined with superficial drainage might promote the long‐term recovery of such meadows and restore the nutrient‐poor, buffered conditions they require. In a field experiment, we analyzed changes in vegetation composition, soil parameters, and soil water chemistry in stripped plots of degraded Cirsio‐Molinietum vegetation over 12 years. After the first five years, many species from the target communities occurred in stripped plots. Both vegetation and soil data showed positive effects of turf stripping on the acid‐buffering capacity. Because sulfate concentration in the soil water decreased over time, whereas the bicarbonate concentration increased, we inferred that there was internal alkalinization driven by sulfate reduction in low‐lying stripped plots. However, the succession toward more acidophilus plant communities, in both control and stripped plots, indicated gradual acidification. This may be caused by a continuing weakening of the upward seepage of base‐rich groundwater as shown by declining calcium concentrations in the soil water. Though turf stripping exposed a nutrient‐poor soil layer with a greater acid‐buffering capacity, these positive effects might not be sufficient to combat the ongoing acidification in the long term.
Selective and Non‐Selective Control of Invasive Plants: The Short‐Term Effects of Growing‐Season Prescribed Fire, Herbicide, and Mowing in Two Texas Prairies
Authors: Simmons Mark T. , Windhager Steve , Power Paula , Lott Jason , Lyons Robert K. , Schwope Carl
Published: August 2010

Conservation of North American grasslands is hampered by the impact of invasive herbaceous species. Selective control of these plants, although desirable, is complicated by the shared physiology and phenology of the invader and the native components of the invaded plant community. Fortunately, there is evidence that some management practices, such as prescribed fire, herbicide, and mowing, can cause differential responses in native and invasive grassland species. However, timing of treatment is critical, and fire has been shown to increase rates of invasion when implemented during the dormant season. Bothriochloa ischaemum, an introduced C4 Eurasian grass is an increasing problem in grasslands, particularly in southern and central regions of North America. To date, there has been little success in effective selective control. Two invaded grassland sites representative of Blackland Prairie and Edwards Plateau ecoregions were subjected to two growing‐season prescribed fire treatments, single and double herbicide applications, and single and double mowing treatments. Mowing had no effect on either B. ischaemum or other dominant species at either site one‐year posttreatment. However, growing‐season fire and herbicide were both effective at reducing the abundance of B. ischaemum, with other codominant species responding either negatively to herbicide or neutrally or positively to fire. The vulnerability of B. ischaemum to growing‐season fire may be associated with the ecology of its native range. The negative growth response to growing‐season fire, combined with its lower implementation costs, indicates that this method warrants further investigation as a selective management tool for other problematic species in invaded grasslands.
Short‐Term Response of Land Birds to Ponderosa Pine Restoration
Authors: Gaines William L. , Haggard Maryellen , Lehmkuhl John F. , Lyons Andrea L. , Harrod Richy J.
Published: August 2010

We monitored the short‐term (>3 years) response of land birds to forest restoration treatments in Ponderosa pine forests located on the east slope of the North Cascade Range. Restoration treatments were designed to create stand structure and composition similar to pre‐settlement forests, which were influenced by a frequent fire regime. Overall, avian community composition was changed as a result of the treatments. Cassin’s Finch, Chipping Sparrow, and Yellow‐rumped Warbler were found at higher densities in treated stands, whereas Mountain Chickadee, Western Tanager, and Red‐breasted Nuthatch had higher densities in untreated stands. White‐headed Woodpecker and Western Bluebird were only detected in the treated stands. Brown‐headed Cowbird showed no response to treatments. We detected changes in the density of four of five foraging guilds in response to restoration treatments. Tree seedeaters, low understory and ground insectivores, and aerial insectivores all increased in density in treated stands. Overall, bark insectivores showed no density response to treatments. Tree foliage insectivore density was lower in treated than in untreated stands. Overall avian density, density of neotropical migrants, and density of some focal species were higher in treated stands. Monitoring should be continued to understand the longer‐term (5–10 year) responses of land birds and to guide future forest restoration efforts.
Vegetation Control Treatments to Favor Naturally RegeneratedBetula alleghaniensisSaplings Following Seed‐Tree Cut: Sapling Monitoring Two Years after Treatment
Authors: Bouffard Daniel , Nolet Philippe , Delagrange Sylvain , Lorenzetti François , Yamasaki Stephen
Published: August 2010

Control of competing vegetation is recommended to ensure successful Yellow birch (Betula alleghaniensisBritton) regeneration within juvenile stands that do not sustain high enough sapling densities of this species. Four contrasting vegetation control treatments were tested to determine their effect on the growth and vigor of eight‐year‐oldB. alleghaniensissaplings regenerating after final cutting of a shelterwood seed cut. Vegetation control treatments were TC (total circular removal), PC (circular removal of codominant competing vegetation), TS (total semicircular removal on 180° section), and NC (no vegetation control). Two years after treatment application, diameter growth significantly improved in response to vegetation control treatments, whereas sapling height growth did not. This pattern of biomass allocation was directly related to sapling etiolation, which increased with decreasing severity of vegetation removal. As a result, application of vegetation control, especially TC and PC treatments, was valuable in reducing signs of stress in saplings. However, increasing the severity of vegetation removal also made saplings more conspicuous to herbivores, which increased browsing, especially in the TC and PC treatments. Browsing was sufficient in some plots of the TC and PC treatments to overcome the vigor and diameter growth enhancements observed when browsing was negligible. In contrast to the TC and PC treatments, the TS treatment kept browsing very low while largely removing competition. The results suggest thatB. alleghaniensissaplings established after final cutting of a shelterwood seed cut do take advantage of vegetation control treatments, but the decision to apply these treatments must include consideration of local herbivore population densities.
Polytrichum strictum as a Nurse‐Plant in Peatland Restoration
Authors: Groeneveld Elisabeth V. G. , Massé Ariane , Rochefort Line
Published: August 2010

Polytrichum strictum is a pioneer plant frequently found on bare peat substrate after perturbations (fire, peat extraction). Can this moss facilitate the return of Sphagnum species or other boreal plants after disturbances? Field surveys of abandoned peatlands after peat extraction revealed that Sphagnum was always found in association with P. strictum carpets. We conducted field experiments in abandoned peatlands and showed that P. strictum carpets were able to keep Sphagnum fragments more humid than bare peat but only when the P. strictum carpets were not totally bone dry. In general, daytime temperatures beneath P. strictum carpets and fragments were reduced during the day and increased during the night compared to bare peat. Polytrichum strictum carpets acted as a seed trap, retaining more artificial seeds than bare peat. Polytrichum strictum can be a nurse‐plant: after 16 months, vascular plants transplanted in the P. strictum carpet were healthier than the ones planted on bare peat. The use of P. strictum as a nurse‐plant in boreal forest or peatland restoration is recommended for sites prone to frost heaving and with harsh microclimatic conditions.
Alcoa’s Mining and Restoration Process in South Western Australia
Authors: Koch John M.
Published: August 2010

This paper describes the sequence of Alcoa’s bauxite mining and restoration operations in Western Australia, commencing with pre‐mining surveys and geological exploration through to the preparation and extraction of the bauxite ore, the restoration process, and then monitoring. These methods have changed continually since operations commenced in 1963 as knowledge improved; however, this paper only describes the current procedures.
Restoring Jarrah Forest Trees after Bauxite Mining in Western Australia
Authors: Koch John M. , Samsa Glen P.
Published: August 2010

The overstory of the jarrah forest is dominated by Jarrah (Eucalyptus marginata) with a smaller proportion of Marri (Corymbia calophylla). There are also several smaller tree species in the areas where Alcoa mines. Alcoa’s restoration aims to restore all these species at densities similar to the unmined forest. This paper describes the establishment, survival, and growth of these trees with particular focus on Jarrah. Factors affecting the growth and form of Jarrah are also discussed. Establishment of Jarrah from seed in restored sites is variable (mean 10%), and once established, survival is high over two summer droughts (96%) and still high (mean 83%) after about a decade regardless of the presence of the Jarrah dieback disease Phytophthora cinnamomi. High establishment densities (10,000 stems/ha) show mortality rates of 22% after a decade. Growth rates of Jarrah trees are high (1.5–2.7 m2·ha−1·yr−1 basal area), similar to tree growth in unmined forest following clear‐fell operations. Jarrah responds to both N and P fertilizers when very young but the response to early N application is not significant after approximately one decade. Between one‐ and two‐thirds of Jarrahs established from seed grow into saplings, but this proportion decreases with increasing tree density. Closer tree spacing results in more single‐stemmed Jarrah trees at the expense of growth. Tree seed used for restoration should be sourced from northern Jarrah forest areas with similar soil type and rainfall. Seed from outlier populations and coastal plain vegetation types should not be used.
Development of a Winged Tine to Relieve Mining‐Related Soil Compaction after Bauxite Mining in Western Australia
Authors: Croton James T. , Ainsworth Glen L.
Published: August 2010

Deep ripping, using a conventional chisel‐tine to a nominal depth of 1.4 m, was introduced to Alcoa’s operations on the Darling Plateau in 1969 following windthrow of a number of trees. Although research into mine floor compaction showed that this ripping depth was sufficient to remove the mining compaction, tillage studies showed that plastic failure around the point of a conventional tine ripping to this depth was actually adding to deep compaction rather than removing it. To improve tillage at depth, wing‐like structures were attached to the shank of a conventional chisel‐tine directly behind the point. These wings lift and till the soil across a broad front. Wingspans between 0.75 and 1.8 m were tested, and a final design of 1.8‐m wingspan adopted for ripping during the 1980s and 1990s. Availability of suitable steels in the late 1990s allowed the winged tines to be fabricated from scratch, enabling the fitting of wear plates to almost completely eliminate shank wear and breakage problems, though these additions have resulted in some loss of tillage efficiency. Modification of the bulldozer ripping box is highly desirable for ripper design to be improved further, particularly to overcome lateral sliding when contour ripping is undertaken on steep slopes. An alternative is to divide the ripping process in two: a pre‐rip up and down the slope followed by shallow ripping on contour. A two‐step ripping process is now being used at Alcoa’s Western Australian bauxite mines.
Root Architecture of Jarrah (Eucalyptus marginata) Trees in Relation to Post‐Mining Deep Ripping in Western Australia
Authors: Szota Christopher , Veneklaas Erik J. , Koch John M. , Lambers Hans
Published: August 2010

This research aimed to investigate coarse root systems of Jarrah (Eucalyptus marginata Donn ex Sm.) trees at a 13‐year‐old restored bauxite mine site in south‐western Australia. Excavations in an area with small trees (low‐quality site) revealed that deep ripping equipment failed to penetrate the cemented lateritic subsoil, restricting coarse roots (roots >5 mm in diameter) to the top 0.5 m of the soil profile, resulting in fewer (1,344 stems/ha) and smaller (mean height 4.5 m) Jarrah trees. An adjacent area within the same pit (high‐quality site), with a stand density of 3,256 stems/ha and a mean height of 8.0 m, had a kaolinitic clay subsoil which coarse roots penetrated to the average ripping depth (1.5 m). Trees at the low‐quality site did not penetrate the subsoil with their taproot, relying instead on a large number of lateral (5.3–8.0/tree) and sinker (12.0–16.5/tree) roots. Taproots of trees on crests at the high‐quality site also did not penetrate the subsoil, and in contrast to trees at the low‐quality site, they produced fewer lateral and sinker roots (2.3 and 2.0/tree, respectively). Taproots of trees in riplines at the high‐quality site directly penetrated the ripline and these trees also produced fewer lateral and sinker roots (5.0 and 3.7/tree, respectively) than those at the low‐quality site. Jarrah trees appear to have opportunistic root systems capable of responding to a variety of soil conditions encountered in the post‐mining landscape.
Beneficial Soil Microorganisms of the Jarrah Forest and Their Recovery in Bauxite Mine Restoration in Southwestern Australia
Authors: Jasper David A.
Published: August 2010

Beneficial soil microorganisms are integral to nutrient availability and uptake for plants in restoration. They include mycorrhizal fungi and nitrogen‐fixing bacteria, together with the soil microbial populations which contribute to nutrient availability. Around 70% of jarrah forest plant species form arbuscular mycorrhizas, and approximately a quarter also form ectomycorrhizas. Many are also legumes. In addition, around 70 orchid species depend on mycorrhizal symbioses. Therefore, symbiotic soil microorganisms are important in the ecosystem. Arbuscular mycorrhizal fungi recover to pre‐mining levels in bauxite restoration in five years. Ectomycorrhizal fungi are poorly adapted to disturbance; however, they are able to reinvade through wind‐blown spores. The density of ectomycorrhizal fungi has been found to be equivalent in seven‐year‐old restoration and adjacent forest, but both abundance and diversity are correlated with development of a litter layer. Fortunately, rhizobia are known to be tolerant of soil disturbance, and failure of N‐fixation by legumes has not been reported in restoration. Other N‐fixing symbioses, such as between Allocasuarina and Frankia or Macrozamia and Nostoc, have not been investigated in restored mines. Soil microbial biomass C achieves near equivalence after about eight years and appears to be driven by vegetation productivity and related inputs of C into the soil. There is little field evidence that the absence, or very low levels, of soil microbial symbionts will have a substantial impact on plant growth in restoration. Therefore, deliberate reintroduction of these microorganisms does not appear justified. However, soil management to enhance the survival of soil biological components is recommended.
What If the Leader of the Central Bank Told Hilarious Jokes and Did Card Tricks? A Panel of Experts
Authors: Mehrling Perry , Moss Laurence S. , Pixley Jocelyn , Tavlas George S.
Published: August 2010

Abstract. A panel of distinguished experts discuss the linkages (if any) between monetary policy and the personality of the nation's central banker. Why is the personality of a central banker important to monetary stability and financial leadership? What follows is a written edited version of the short papers that were presented at this panel. The panel was held in Olin Auditorium on Tuesday, April 25, 2006, as part of the Carpenter Lecture Series at Babson College.
Reconciling Weber and Mises on Understanding Human Action
Authors: Callahan Gene
Published: August 2010

Abstract.  Max Weber and Ludwig von Mises were two of the 20th century's foremost theorists of human action. Mises held Weber, his senior by some 17 years, in great esteem and often discussed his theories, even weaving some, such as Weber's model of ideal types, deeply into the fabric of his own social thought. However, at least at first glance, there seems to be a deep rift between the two men's conceptions about the rationality of action. Weber classified “social actions” into several distinct categories, some of which he saw as exhibiting little, if any, rationality. Mises, in contrast, held that all action is rational by conceptual necessity. Various writers have taken their views to be obviously incompatible, among them, Mises himself. This article suggests that the appearance of a conflict is produced by the failure to discern that Weber and Mises were addressing different sorts of questions and constructing frameworks to support different modes of analyzing social phenomena. I contend that, if that divergence of aim is properly understood, then the apparent contradiction will be seen as illusory.
The Impact of the Americans with Disabilities Act on Per‐Student Public Education Expenditures at the State Level: 1987–2000
Authors: Gius Mark P.
Published: August 2010

Abstract.  Section 504 of the Rehabilitation Act of 1973 and the Americans with Disabilities Act (ADA) of 1990 are designed to protect the civil rights of individuals with disabilities. These two laws have had a major impact on public schools, their offerings of services, and their budgets. The purpose of the present study is to determine if passage of the ADA in 1990 has resulted in a statistically significant increase in per‐student public education expenditures at the state level. Although numerous studies have estimated educational cost functions, no prior study has examined the impact of the ADA on per‐capita educational spending. Results of the present study indicate that the ADA increased per‐student educational spending at the state level, but by less than 2 percent. By way of comparison, Rothstein and Miles (1995) noted in their study that desegregation added 4.1 percent to per‐pupil spending and bilingual education added 3.9 percent.