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\"Piecing together a fractured European continent after World War I, the Versailles Peace Treaty stipulated the long-term occupation of the Rhineland by Allied troops. This occupation, perceived as a humiliation by the political right, caused anger and dismay in Germany and an aggressive propaganda war broke out--heightened by an explosion of vicious racist propaganda against the use of non-European colonial troops by France in the border area.\"--Dust jacket.

Convergence is central to the study of evolution because it demonstrates the power of natural selection to deterministically shape phenotypic diversity. However, the conditions under which a common morphology repeatedly evolves may be restrictive. Many factors, such as differing genetic and environmental backgrounds and many-to-one mapping of form to function, contribute to variability in responses to selection. Nevertheless, lineages may evolve similar, even if not identical, forms given a shared selective regime, providing opportunities to examine the relative importance of natural selection, constraint, and contingency. Here, we show that following 10 transitions to durophagy (eating hard-shelled prey) in moray eels (Muraenidae), cranial morphology repeatedly evolved toward a novel region of morphological space indicative of enhanced feeding performance on hard prey. Disparity among the resulting 15 durophagous species, however, is greater than disparity among ancestors that fed on large evasive prey, contradicting the pattern expected under convergence. This elevated disparity is a consequence of lineage-specific responses to durophagy, in which independent transitions vary in the suites of traits exhibiting the largest changes. Our results reveal a pattern of imperfect convergence, which suggests shared selection may actually promote diversification because lineages often differ in their phenotypic responses to similar selective demands.

Proximity to an adaptive peak influences a lineage's potential to diversify. We tested whether piscivory, a high quality but functionally demanding trophic strategy, represents an adaptive peak that limits morphological diversification in the teleost fish clade, Centrarchidae. We synthesized published diet data and applied a well-resolved, multilocus and time-calibrated phylogeny to reconstruct ancestral piscivory. We measured functional features of the skull and performed principal components analysis on species' values for these variables. To assess the role of piscivory on morphological diversification, we compared the fit of several models of evolution for each principal component (PC), where model parameters were allowed to vary between lineages that differed in degree of piscivory. According to the best-fitting model, two adaptive peaks influenced PC 1 evolution, one peak shared between highly and moderately piscivorous lineages and another for nonpiscivores. Brownian motion better fit PCs 2, 3, and 4, but the best Brownian models infer a slow rate of PC 2 evolution shared among all piscivores and a uniquely slow rate of PC 4 evolution in highly piscivorous lineages. These results suggest that piscivory limits feeding morphology diversification, but this effect is most severe in lineages that exhibit an extreme form of this diet.

The demand that anatomical structures work together to perform biological functions is thought to impose strong limits on morphological evolution. Breakthroughs in diversification can occur, however, when functional integration among structures is relaxed. Although such transitions are expected to generate variation in morphological diversification across the tree of life, empirical tests of this hypothesis are rare. Here we show that transitions between suction-based and biting modes of prey capture, which require different degrees of coordination among skull components, are associated with shifts in the pattern of skull diversification in eels (Anguilliformes). Biting eels have experienced greater independence of the jaws, hyoid and operculum during evolution and exhibit more varied morphologies than closely related suction feeders, and this pattern reflects the weakened functional integration among skull components required for biting. Our results suggest that behavioural transitions can change the evolutionary potential of the vertebrate skeleton by altering functional relationships among structures. Functional integration limits the potential for morphological differences to evolve. Here, the authors show an association between changes in skull morphology and evolutionary integration with feeding behaviour in eels.

Despite almost 50 years of research on the functional morphology and biomechanics of suction feeding, no consensus has emerged on how to characterize suction-feeding performance, or its morphological basis. We argue that this lack of unity in the literature is due to an unusually indirect and complex linkage between the muscle contractions that power suction feeding, the skeletal movements that underlie buccal expansion, the sharp drop in buccal suction pressure that occurs during expansion, the flow of water that enters the mouth to eliminate the pressure gradient, and the forces that are ultimately exerted on the prey by this flow. This complexity has led various researchers to focus individually on suction pressure, flow velocity, or the distance the prey moves as metrics of suction-feeding performance. We attempt to integrate a mechanistic view of the ability of fish to perform these components of suction feeding. We first discuss a model that successfully relates aspects of cranial morphology to the capacity to generate suction pressure in the buccal cavity. This model is a particularly valuable tool for studying the evolution of the feeding mechanism. Second, we illustrate the multidimensional nature of suction-feeding performance in a comparison of bluegill, Lepomis macrochirus, and largemouth bass, Micropterus salmoides, two species that represent opposite ends of the spectrum of performance in suction feeding. As anticipated, bluegills had greater accuracy, lower peak flux into the mouth, and higher flow velocity and acceleration of flow than did bass. While the differences between species in accuracy of strike and peak water flux were substantial, peak suction velocity and acceleration were only about 50% higher in bluegill, a relatively modest difference. However, a hydrodynamic model of the forces that suction feeders exert on their prey shows that this difference in velocity is amplified by a positive effect of the smaller mouth aperture of bluegill on force exerted on the prey. Our model indicates that the pressure gradient in front of a fish that is feeding by suction, associated with the gradient in water velocity, results in a force on the prey that is larger than drag or acceleration reaction. A smaller mouth aperture results in a steeper pressure gradient that exerts a greater force on the prey, even when other features of the suction flow are held constant. Our work shows that some aspects of suction-feeding performance can be determined from morphology, but that the complexity of the behavior requires a diversity of perspectives to be used in order to adequately characterize performance.

The association between diversification and evolutionary innovations has been well documented and tested in studies of taxonomic richness but the impact that such innovations have on the diversity of form and function is less well understood. Using phylogenetically rigorous techniques, we investigated the association between morphological diversity and two design breakthroughs within the jaws of parrotfish. Similar intramandibular joints and other modifications of the pharyngeal jaws have evolved repeatedly in teleost fish and are frequently hypothesized to promote diversity. We quantified morphological diversity within six functionally important oral jaw traits using the Brownian motion rate of evolution to correct for phylogenetic and time-related biases and compared these rates across clades that did and did not possess the intramandibular joint and the parrotf ish pharyngeal jaw. No change in morphological diversity was associated with the pharyngeal jaw modification alone but rates of oral jaw diversification were up to 8 ÷ faster in parrotf ish species that possessed both innovations. Interestingly, this morphological diversity may not have led to differential resource uses as available data suggest that members of this clade show remarkable homogeneity of diet.

Trade-offs are believed to impose major constraints on adaptive evolution, and they arise when modification of a trait improves one aspect of performance but incurs a cost in another. Here we show that performance costs that result from competing demands on one trait can be mitigated by compensatory changes in other traits, so long as performance has a complex basis. Numerical simulations indicate that increases in the number of traits that determine performance decrease the strength of performance trade-offs. In centrarchid fishes, multiple traits underlie suction feeding performance, and experimental data and hydrodynamic modeling show that combinations of traits evolve to increase the ability to feed on attached prey while mitigating costs to performance on evasive prey. Diet data for centrarchid species reveal a weak trade-off between these prey types, corroborating the results based on hydrodynamic modeling and suggesting that complexity in the functional basis of suction feeding performance enhances trophic diversification. Complexity may thus permit the evolution of combinations of high-performance behaviors that appear to violate underlying trade-offs, such as the ability to exert high suction forces with large gape. This phenomenon may promote morphological, functional, and ecological diversification in the face of the myriad selective demands organisms encounter.

Morphological diversity is routinely used to infer ecological variation among species because differences in form underlie variation in functional performance of ecological tasks like capturing prey, avoiding predators, or defending territories. However, many functions have complex morphological bases that can weaken associations between morphological and functional diversification. We investigate the link between these levels of diversity in a mechanically explicit model of fish suction-feeding performance, where the map of head morphology to feeding mechanics is many-to-one: multiple, alternative forms can produce the same mechanical property. We show that many-to-one mapping leads to discordance between morphological and mechanical diversity in the freshwater fish family, the Centrarchidae, despite close associations between morphological changes and their mechanical effects. We find that each of the model's five morphological variables underlies evolution of suction capacity. Yet, the major centrarchid clades exhibit an order of magnitude range in diversity of suction mechanics in the absence of any clear difference in diversity of the morphological variables. This cryptic pattern of mechanical diversity suggests an evolutionary history for suction performance that is unlike the one inferred from comparisons of morphological diversity. Because many-to-one mapping is likely to be common in functional systems, this property of design may lead to widespread discordance between functional and morphological diversity. Although we focus on the interaction between morphology and mechanics, many-to-one mapping can decouple diversity between levels of organization in any hierarchical system.

Morphological diversification does not proceed evenly across the organism. Some body parts tend to evolve at higher rates than others, and these rate biases are often attributed to sexual and natural selection or to genetic constraints. We hypothesized that variation in the rates of morphological evolution among body parts could also be related to the performance consequences of the functional systems that make up the body. Specifically, we tested the widely held expectation that the rate of evolution for a trait is negatively correlated with the strength of biomechanical trade-offs to which it is exposed. We quantified the magnitude of trade-offs acting on the morphological components of three feeding-related functional systems in four radiations of teleost fishes. After accounting for differences in the rates of morphological evolution between radiations, we found that traits that contribute more to performance trade-offs tend to evolve more rapidly, contrary to the prediction. While ecological and genetic factors are known to have strong effects on rates of phenotypic evolution, this study highlights the role of the biomechanical architecture of functional systems in biasing the rates and direction of trait evolution.

Background Amyloid-β imaging through positron emission tomography (PET) has significantly transformed Alzheimer’s disease (AD) research. [ 11 C]PiB has been widely used for imaging β-amyloid plaques due to its high affinity and selectivity for amyloid deposits. [ 18 F]AZD4694 is a more recently developed amyloid-PET imaging agent, which structurally resembles PiB and has less non-specific binding in the white matter than other 18 F-labeled compounds. The purpose of this study is to compare the in vitro binding properties of the amyloid-PET radiotracers [ 11 C]PiB and [ 18 F]AZD4694 in post-mortem human brain tissue. Total binding was assessed by autoradiography in prefrontal, inferior parietal, posterior cingulate cortices and hippocampal sections of healthy control (HC) and AD autopsy-confirmed brain tissues. Furthermore, the displacement of [ 18 F]AZD4694 by unlabeled PiB was evaluated in the above-mentioned sections of AD brain tissues. Results For both radiotracers, we found significant differences (p < 0.0001) between HC and AD tissues binding in the prefrontal cortex ([ 11 C]PiB Cohen’s d = 3.424, [ 18 F]AZD4694 Cohen’s d = 5.070), inferior parietal cortex ([ 11 C]PiB Cohen’s d = 3.156, [ 18 F]AZD4694 Cohen’s d = 3.959), posterior cingulate cortex ([ 11 C]PiB Cohen’s d = 1.781, [ 18 F]AZD4694 Cohen’s d = 3.434), and hippocampus ([ 11 C]PiB Cohen’s d = 1.320, [ 18 F]AZD4694 Cohen’s d = 3.696). Higher binding was detected for [ 18 F]AZD4694 compared to [ 11 C]PiB in AD prefrontal, inferior parietal and posterior cingulate cortices, while binding in the hippocampus was comparable for both radioligands. Strong correlations between [ 18 ]AZD4694 and [ 11 C]PiB were found in the prefrontal (R = 0.959, p  < 0.0001), inferior parietal (R = 0.893, p  < 0.0001), posterior cingulate (R = 0.838, p  = 0.0006) cortices and hippocampus (R = 0.750, p  < 0.0001). Bland–Altman analyses revealed strong agreement between [ 11 C]PiB and [ 18 F]AZD4694 in the prefrontal, inferior parietal, and posterior cingulate cortices, but lower agreement in the hippocampus. Displacement studies confirmed high binding affinity of PiB in all tissues, indicating that both amyloid-PET agents compete for the same binding sites. Conclusions This head-to-head study provides evidence that while [ 18 F]AZD4694 and [ 11 C]PiB bindings are highly correlated with both tracers competing for the same binding sites, [ 18 F]AZD4694 has a slightly higher effect size when comparing between neuropathologically-confirmed AD and HC brain tissues.