Adaptive Shift Research Articles

Eccentric Loading Increases Peak Torque Angle of the Ankle Plantar Flexors in Healthy Volunteers

Eccentric loading of the ankle plantar Flexor’s (PF) has demonstrated clinical efficacy in the conservative treatment of Achilles tendinopathy, however, its mechanism of therapeutic benefit remains unclear. The purpose of this study was to examine the effects of PF eccentric loading on PF angle to peak torque (AtPT), peak torque (PT) and lower limb vertical stiffness. Thirty healthy volunteers were randomised to an eccentric (n=15) or concentric (n=13) exercise group. A 10-week loading programme of the ankle plantar flexors was completed. AtPT, PT and vertical stiffness were compared within and between groups before and after the interventions. AtPT increased in the eccentric group by 3.2 ° dorsiflexion (p=0.001) and decreased by 0.7 ° dorsiflexion (p=0.528) for the concentric group with significant post-intervention group differences (p 0.2); however, postintervention the eccentric group showed a greater PT than the concentric group (p>0.05). Between group comparison showed no significant difference in vertical stiffness (p>0.5). However, the concentric group demonstrated a vertical stiffness increase of 765kNm ¹ (p ≥ 0.05). This study demonstrates that a clinicallyderived eccentric loading programme can produce an adaptive shift in AtPT of the ankle plantar flexors in a healthy population. These results support the theory that in part, eccentric loading derives its therapeutic benefit from mechanisms that influence plantar flexor motor performance.

Alterations in the mitochondrial responses to PENAO as a mechanism of resistance in ovarian cancer cells

ObjectiveThe purpose of this study was to test PENAO, a promising new organoarsenical that is in phase 1 testing in patients with solid tumours, on a range of ovarian cancer cell lines with different histotypes, and to understand the molecular basis of drug resistance exhibited by the endometrioid ovarian cancer cell line, SKOV-3. MethodsProliferation arrest and cell death induced by PENAO in serous (OVCAR-3), endometrioid (SKOV-3, TOV112D), clear cell (TOV21G) and mucinous (EFO27) ovarian cancer cells in culture, and anti-tumour efficacy in a murine model of SKOV-3 and OVCAR-3 tumours, were measured. Cells were analysed for cell cycle arrest, cell death mechanisms, reactive oxygen species production, mitochondrial depolarisation, oxygen consumption and acid production. ResultsPENAO demonstrated promising anti-proliferative activity on the most common (serous, endometrioid) as well as on rare (clear cell, mucinous) subtypes of ovarian cancer cell lines. No cross-resistance with platinum-based drugs was evident. Endometrioid SKOV-3 cells were, however, shown to be resistant to PENAO in vitro and in a xenograft mouse model. This resistance was due to an ability to cope with PENAO-induced oxidative stress, notably through heme oxygenase-1 induction, and a shift in metabolism towards glycolysis. The adaptive glycolytic shift in SKOV-3 was targeted using a mTORC1 inhibitor in combination with PENAO. This strategy was successful with the two drugs acting synergistically to inhibit cell proliferation and to induce cell death via apoptosis and autophagy. ConclusionMitochondria/mTOR dual-targeting therapy may constitute a new approach for the treatment of recurrent/resistant forms of epithelial ovarian cancer.

The joint evolution of traits and habitat: ontogenetic shifts in leaf morphology and wetland specialization in Lasthenia.

The interplay between functional traits and habitat associations drives species' evolutionary responses to environmental heterogeneity, including processes such as adaptation, ecological speciation, and niche evolution. Seasonal variation is an aspect of the environment that varies across habitats, and could result in adaptive shifts in trait values across the life cycle of a plant. Here, we use phylogenetic comparative methods to evaluate the joint evolution of plant traits and habitat associations in Lasthenia (Asteraceae), a small clade of predominantly annual plants that have differentiated into an ecologically diverse range of habitats, including seasonal ephemeral wetlands known as vernal pools. Our results support the hypothesis that there is a link between the evolution of leaf morphology and the ecohydrological niche in Lasthenia, and, in the formation of aerenchyma (air space), differentiation between vernal pool and terrestrial taxa is fine-tuned to specific stages of plant ontogeny that reflects the evolution of heterophylly. Our findings demonstrate how the relationships between traits and habitat type can vary across the development of an organism, while highlighting a carefully considered comparative approach for examining correlated trait and niche evolution in a recently diversified and ecologically diverse plant clade.

Sexual signalling by females: do unmated females increase their signalling effort?

Theory predicts that females should invest least in mate searching when young, but increase their effort with age if they remain unmated. Few studies have examined variation in female sexual signalling. Female Dawson's burrowing bees (Amegilla dawsoni) search for males by signalling their receptivity on emergence, but many leave the emergence site unmated and must attract males at feeding sites. Female bees prevented from mating on emergence had more extreme versions of cuticular hydrocarbon profiles that make them attractive to males, lending empirical evidence of adaptive shifts in female mating effort.

Biochemical adaptation to ocean acidification

The change in oceanic carbonate chemistry due to increased atmospheric PCO2 has caused pH to decline in marine surface waters, a phenomenon known as ocean acidification (OA). The effects of OA on organisms have been shown to be widespread among diverse taxa from a wide range of habitats. The majority of studies of organismal response to OA are in short-term exposures to future levels of PCO2 . From such studies, much information has been gathered on plastic responses organisms may make in the future that are beneficial or harmful to fitness. Relatively few studies have examined whether organisms can adapt to negative-fitness consequences of plastic responses to OA. We outline major approaches that have been used to study the adaptive potential for organisms to OA, which include comparative studies and experimental evolution. Organisms that inhabit a range of pH environments (e.g. pH gradients at volcanic CO2 seeps or in upwelling zones) have great potential for studies that identify adaptive shifts that have occurred through evolution. Comparative studies have advanced our understanding of adaptation to OA by linking whole-organism responses with cellular mechanisms. Such optimization of function provides a link between genetic variation and adaptive evolution in tuning optimal function of rate-limiting cellular processes in different pH conditions. For example, in experimental evolution studies of organisms with short generation times (e.g. phytoplankton), hundreds of generations of growth under future conditions has resulted in fixed differences in gene expression related to acid-base regulation. However, biochemical mechanisms for adaptive responses to OA have yet to be fully characterized, and are likely to be more complex than simply changes in gene expression or protein modification. Finally, we present a hypothesis regarding an unexplored area for biochemical adaptation to ocean acidification. In this hypothesis, proteins and membranes exposed to the external environment, such as epithelial tissues, may be susceptible to changes in external pH. Such biochemical systems could be adapted to a reduced pH environment by adjustment of weak bonds in an analogous fashion to biochemical adaptation to temperature. Whether such biochemical adaptation to OA exists remains to be discovered.

Building up a Bio-Inspired Visual Attention Model by Integrating Top-Down Shape Bias and Improved Mean Shift Adaptive Segmentation

The driver-assistance system (DAS) becomes quite necessary in-vehicle equipment nowadays due to the large number of road traffic accidents worldwide. An efficient DAS detecting hazardous situations robustly is key to reduce road accidents. The core of a DAS is to identify salient regions or regions of interest relevant to visual attended objects in real visual scenes for further process. In order to achieve this goal, we present a method to locate regions of interest automatically based on a novel adaptive mean shift segmentation algorithm to obtain saliency objects. In the proposed mean shift algorithm, we use adaptive Bayesian bandwidth to find the convergence of all data points by iterations and the k-nearest neighborhood queries. Experiments showed that the proposed algorithm is efficient, and yields better visual salient regions comparing with ground-truth benchmark. The proposed algorithm continuously outperformed other known visual saliency methods, generated higher precision and better recall rates, when challenged with natural scenes collected locally and one of the largest publicly available data sets. The proposed algorithm can also be extended naturally to detect moving vehicles in dynamic scenes once integrated with top-down shape biased cues, as demonstrated in our experiments.

Resilience vs. historical contingency in microbial responses to environmental change.

How soil processes such as carbon cycling will respond to future climate change depends on the responses of complex microbial communities, but most ecosystem models assume that microbial functional responses are resilient and can be predicted from simple parameters such as biomass and temperature. Here, we consider how historical contingencies might alter those responses because function depends on prior conditions or biota. Functional resilience can be driven by physiological, community or adaptive shifts; historical contingencies can result from the influence of historical environments or a combination of priority effects and biotic resistance. By modelling microbial population responses to environmental change, we demonstrate that historical environments can constrain soil function with the degree of constraint depending on the magnitude of change in the context of the prior environment. For example microbial assemblages from more constant environments were more sensitive to change leading to poorer functional acclimatisation compared to microbial assemblages from more fluctuating environments. Such historical contingencies can lead to deviations from expected functional responses to climate change as well as local variability in those responses. Our results form a set of interrelated hypotheses regarding soil microbial responses to climate change that warrant future empirical attention.

Reduction of Energetic Demands through Modification of Body Size and Routine Metabolic Rates in Extremophile Fish.

Variation in energy availability or maintenance costs in extreme environments can exert selection for efficient energy use, and reductions in organismal energy demand can be achieved in two ways: reducing body mass or metabolic suppression. Whether long-term exposure to extreme environmental conditions drives adaptive shifts in body mass or metabolic rates remains an open question. We studied body size variation and variation in routine metabolic rates in locally adapted populations of extremophile fish (Poecilia mexicana) living in toxic, hydrogen sulfide-rich springs and caves. We quantified size distributions and routine metabolic rates in wild-caught individuals from four habitat types. Compared with ancestral populations in nonsulfidic surface habitats, extremophile populations were characterized by significant reductions in body size. Despite elevated metabolic rates in cave fish, the body size reduction precipitated in significantly reduced energy demands in all extremophile populations. Laboratory experiments on common garden-raised fish indicated that elevated routine metabolic rates in cave fish likely have a genetic basis. The results of this study indicate that adaptation to extreme environments directly impacts energy metabolism, with fish living in cave and sulfide spring environments expending less energy overall during routine metabolism.

MORPHOFUNCTIONAL CHANGES IN LONG-TIME ADAPTATION PROCESS OBSERVED IN NATIVES OF INTERCONTINENTAL AREAS OF RUSSIA’S NORTHEAST

Based on the study of parameters of physical development, cardio-vascular system, external respiration and gas exchange comparative study of 88 young males among European migrants and those born in 1 and 2 generation, natives of continental area of Magadan region was carried. Found that formation of adaptive shifts are typical of some physiological systems of European newcomers; the direction of these shifts does not change in further generations. This fact allow considering it as an organism response of people residing under more extreme conditions of continental natural-climatic area of the region (in comparison with seaside area), when many parameters of functional systems change and weakly depend on duration of residence under such conditions.

Automated MRI brain tissue segmentation based on mean shift and fuzzy c-means using a priori tissue probability maps

This paper presents a novel fully automated unsupervised framework for the brain tissue segmentation in magnetic resonance (MR) images. The framework is a combination of Bayesian-based adaptive mean shift, a priori spatial tissue probability maps and fuzzy c-means. Mean shift is employed to cluster the tissues in the joint spatial-intensity feature space and then a fuzzy c-means is applied with initialization by a priori spatial tissue probability maps to assign the clusters into three tissue types; white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF). The proposed framework is validated on a synthetic T1-weighted MR image with varying noise characteristics and spatial intensity inhomogeneity, obtained from the BrainWeb database as well as on 38 real T1-weighted MR images, obtained from the IBSR repository. The performance of the proposed framework is evaluated relative to the three widely used brain segmentation toolboxes: FAST, SPM and PVC, and the adaptive mean shift (AMS) and classical fuzzy c-means methods. The experimental results demonstrate the robustness of the proposed framework, and that it exhibits a higher degree of segmentation accuracy in segmenting both synthetic and real T1-weighted MR images compared to all competing methods.

A segmentation system based on clustering method for pediatric DTI images

ABSTRACTA system is presented for the segmentation of white matter fiber tracts in pediatric diffusion tensor magnetic resonance imaging (DTI) images. DTI is an in vivo method to delineate the connectivity of white matter fiber tracts in human brain by fiber tractography. Fiber tractography is a promising method to visualize the whole bundles of fiber tracts. Fiber tractography is unable to provide a quantitative analysis and description of specific white matter fiber tracts. Obviously, segmenting and clustering the fiber tracts into anatomical bundles play an important role in fiber tracts analysis. Traditional manual segmentation method requires neuroanatomical expertise and significant time. It can not be a standardized and widely used method for segmentation of complicated fiber tracts in pediatric DTI images. Hence, an image segmentation system with an adaptive mean shift (AMS) clustering method is proposed to cluster fiber tracts into bundles automatically in this article. In the image segmentation system, fiber similarity measure based on Euclidean distance is used in the clustering method. Since the increase of children's mental illness in recent years, segmentation of pediatric DTI images by clustering methods is focused in our research. The effectiveness and robustness of adaptive mean shift clustering algorithm for segmentation of fiber tracts are also evaluated by error analysis experiments. In addition, the experiment results show that adaptive mean shift method used in our system is more efficient and effective than K‐means and Fuzzy C‐means (FCM) clustering methods for the segmentation of fiber tracts in real pediatric DTI images. © 2015 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 25, 102–113, 2015

Quantitative trait locus mapping identifies candidate alleles involved in adaptive introgression and range expansion in a wild sunflower.

The wild North American sunflowers Helianthus annuus and H. debilis are participants in one of the earliest identified examples of adaptive trait introgression, and the exchange is hypothesized to have triggered a range expansion in H. annuus. However, the genetic basis of the adaptive exchange has not been examined. Here, we combine quantitative trait locus (QTL) mapping with field measurements of fitness to identify candidate H. debilis QTL alleles likely to have introgressed into H. annuus to form the natural hybrid lineage H. a. texanus. Two 500-individual BC1 mapping populations were grown in central Texas, genotyped for 384 single nucleotide polymorphism (SNP) markers and then phenotyped in the field for two fitness and 22 herbivore resistance, ecophysiological, phenological and architectural traits. We identified a total of 110 QTL, including at least one QTL for 22 of the 24 traits. Over 75% of traits exhibited at least one H. debilis QTL allele that would shift the trait in the direction of the wild hybrid H. a. texanus. We identified three chromosomal regions where H. debilis alleles increased both female and male components of fitness; these regions are expected to be strongly favoured in the wild. QTL for a number of other ecophysiological, phenological and architectural traits colocalized with these three regions and are candidates for the actual traits driving adaptive shifts. G × E interactions played a modest role, with 17% of the QTL showing potentially divergent phenotypic effects between the two field sites. The candidate adaptive chromosomal regions identified here serve as explicit hypotheses for how the genetic architecture of the hybrid lineage came into existence.

Explicit and implicit components of visuo-motor adaptation: An analysis of individual differences.

Adaptation to visuo-motor rotations embraces implicit and explicit components. We contrast this two-component model with a three-component model by means of an individual-differences approach. Adaptive changes were tested under four conditions: (1) closed-loop test, presence of the rotation cued (initial adaptive shift), (2) open-loop test, presence of the rotation cued (adaptive shift), (3) open-loop test, absence of the rotation cued (after-effect), (4) test of explicit knowledge (explicit shift). After-effects and explicit shifts were uncorrelated. After regression on after-effects and explicit shifts, the residuals of the initial adaptive shifts and the adaptive shifts remained correlated, suggesting an additional implicit component of adaptation found only in the cued presence of the visuo-motor rotation. The two implicit components are consistent with the distinction between a change of the body schema giving rise to after-effects, and the development of an internal model of a tool that is applied only when the transformation is present.

COMPILATION AND ANALYSIS OF PRE-COLUMBIAN SETTLEMENT DATA IN THE BASIN OF MEXICO

AbstractA key component of archaeological research in the Basin of Mexico was a series of systematic regional surveys conducted between 1960 and 1975. This essay discusses efforts to finalize settlement data generated by those surveys, and preliminary analyses of the resulting dataset that include geographic information system applications to examine patterns of settlement over time. The paper begins by reviewing the surveys and the information they produced for more than 3,900 sites. Analyses of demographics, settlement hierarchies, and environmental patterning reveal periods of slow population increase and decrease that indicate no major demographic events, but noteworthy shifts in settlement types and environmental focus. Analyses of spatial patterning reveal evidence of considerable geographic shifts in settlement over time, probable widespread reliance on irrigation throughout much of the pre-Columbian basin, likely major shifts in adaptation to the central lake system in the region, and intraregional migration as a key demographic process in settlement patterning. Amid growing understanding of pre-Columbian settlement patterns in the Basin of Mexico, this paper also defines key research problems involving demographic mobility, the role of water control in adaptation and sociocultural evolution, and implications of changing environmental emphasis in settlement patterning.

Unsupervised Segmentation of Head Tissues from Multi-modal MR Images for EEG Source Localization.

In this paper, we present and evaluate an automatic unsupervised segmentation method, hierarchical segmentation approach (HSA)-Bayesian-based adaptive mean shift (BAMS), for use in the construction of a patient-specific head conductivity model for electroencephalography (EEG) source localization. It is based on a HSA and BAMS for segmenting the tissues from multi-modal magnetic resonance (MR) head images. The evaluation of the proposed method was done both directly in terms of segmentation accuracy and indirectly in terms of source localization accuracy. The direct evaluation was performed relative to a commonly used reference method brain extraction tool (BET)-FMRIB's automated segmentation tool (FAST) and four variants of the HSA using both synthetic data and real data from ten subjects. The synthetic data includes multiple realizations of four different noise levels and several realizations of typical noise with a 20% bias field level. The Dice index and Hausdorff distance were used to measure the segmentation accuracy. The indirect evaluation was performed relative to the reference method BET-FAST using synthetic two-dimensional (2D) multimodal magnetic resonance (MR) data with 3% noise and synthetic EEG (generated for a prescribed source). The source localization accuracy was determined in terms of localization error and relative error of potential. The experimental results demonstrate the efficacy of HSA-BAMS, its robustness to noise and the bias field, and that it provides better segmentation accuracy than the reference method and variants of the HSA. They also show that it leads to a more accurate localization accuracy than the commonly used reference method and suggest that it has potential as a surrogate for expert manual segmentation for the EEG source localization problem.

The physiological analysis of cross adaptation to regular cold exposure and physical activities

Research is devoted to the comparative analysis of results of cold adaptation and physical training. The adaptive shifts occurring in an organism under the influence of a hardening (douche by a cold shower 2 times a day 2 minutes long within 6 weeks) and running training on the treadmill (30 minutes at 70-80% of individual VO2max, 3 times a week, within 6 weeks) were compared at 6 the same subjects. The interval between the two cycles of training was no less than 3 months. The indicators registered during ramp test and standard cold exposure test before and after each cycle of trainings were compared. It is shown that patterns of adaptive shifts at adaptation to factors of various modality strongly differ. Shifts at adaptation to physical activities were as a whole more expressed, than at adaptation to regular cold exposition. An individual variety of adaptive reactions suggests the feasibility of developing new approaches to the theory of the adaptation, connected with studying of physiological individuality.

Road Centerline Extraction in Complex Urban Scenes From LiDAR Data Based on Multiple Features

Automatic extraction of roads from images of complex urban areas is a very difficult task due to the occlusions and shadows of contextual objects, and complicated road structures. As light detection and ranging (LiDAR) data explicitly contain direct 3-D information of the urban scene and are less affected by occlusions and shadows, they are a good data source for road detection. This paper proposes to use multiple features to detect road centerlines from the remaining ground points after filtering. The main idea of our method is to effectively detect smooth geometric primitives of potential road centerlines and to separate the connected nonroad features (parking lots and bare grounds) from the roads. The method consists of three major steps, i.e., spatial clustering based on multiple features using an adaptive mean shift to detect the center points of roads, stick tensor voting to enhance the salient linear features, and a weighted Hough transform to extract the arc primitives of the road centerlines. In short, we denote our method as Mean shift, Tensor voting, Hough transform (MTH). We evaluated the method using the Vaihingen and Toronto data sets from the International Society for Photogrammetry and Remote Sensing Test Project on Urban Classification and 3-D Building Reconstruction. The completeness of the extracted road network on the Vaihingen data and the Toronto data are 81.7% and 72.3%, respectively, and the correctness are 88.4% and 89.2%, respectively, yielding the best performance compared with template matching and phase-coded disk methods.

The geography of morphological convergence in the radiations of Pacific Sebastes rockfishes.

The evolution of convergent phenotypes in lineages subject to similar selective pressures is a common feature of adaptive radiation. In geographically replicated radiations, repeated convergence occurs between clades occupying distinct regions or islands. Alternatively, a clade may repeatedly reach the same adaptive peaks in broadscale sympatry, resulting in extensive convergence within a region. Rockfish (Sebastes sp.) have radiated in both the northeast and northwest Pacific, allowing tests of the extent and geographic pattern of convergence in a marine environment. We used a suite of phylogenetically informed methods to test for morphological convergence in rockfish. We examined patterns of faunal similarity using nearest neighbor distances in morphospace and the frequency of morphologically similar yet distantly related species pairs. The extent of convergence both between regions and within the northeast Pacific exceeds the expectation under a Brownian motion null model, although constraints on trait space could account for the similarity. We then used a recently developed method (SURFACE) to identify adaptive peak shifts in Sebastes evolutionary history. We found that the majority of convergent peak shifts occur within the northeast Pacific rather than between regions and that the signal of peak shifts is strongest for traits related to trophic morphology. Pacific rockfish thus demonstrate a tendency toward morphological convergence within one of the two broad geographic regions in which they have diversified.

Fiducial marker and marker-less soft-tissue detection using fast MV fluoroscopy on a new generation EPID: investigating the influence of pulsing artifacts and artifact suppression techniques.

Because frame rates on current clinical available electronic portal imaging devices (EPID's) are limited to 7.5 Hz, a new commercially available PerkinElmer EPID (XRD 1642 AP19) with a maximum frame rate of 30 Hz and a new scintillator (Kyokko PI200) with improved sensitivity (light output) for megavolt (MV) irradiation was evaluated. In this work, the influence of MV pulse artifacts and pulsing artifact suppression techniques on fiducial marker and marker-less detection of a lung lesion was investigated, because target localization is an important component of uncertainty in geometrical verification of real-time tumor tracking. Visicoil™ markers with a diameter of 0.05 and 0.075 cm were used for MV marker tracking with a frame rate of, respectively, 7.5, 15, and 30 Hz. A 30 Hz readout of the detector was obtained by a 2 × 2 pixel binning, reducing spatial resolution. Static marker detection was conducted in function of increasing phantom thickness. Additionally, marker-less tracking was conducted and compared with the ground-truth fiducial marker motion. Performance of MV target detection was investigated by comparing the least-square sine wave fit of the detected marker positions with the predefined sine wave motion. For fiducial marker detection, a Laplacian-of-Gaussian enhancement was applied after which normalized cross correlation was used to find the most probable marker position. Marker-less detection was performed by using the scale and orientation adaptive mean shift tracking algorithm. For each MV fluoroscopy, a free running (FR-nF) (ignoring MV pulsing during readout) acquisition mode was compared with two acquisition modes intending to reduce MV pulsing artifacts, i.e., combined wavelet-FFT filtering (FR-wF) and electronic readout synchronized with respect to MV pulses. A 0.05 cm Visicoil marker resulted in an unacceptable root-mean square error (RMSE) > 0.2 cm with a maximum frame rate of 30 Hz during FR-nF readout. With a 30 Hz synchronized readout (S-nF) and during 15 Hz readout (independent of readout mode), RMSE was submillimeter for a static 0.05 cm Visicoil. A dynamic 0.05 cm Visicoil was not detectable on the XRD 1642 AP19, despite a fast synchronized readout. For a 0.075 cm Visicoil, deviations of sine wave motion were submillimeter (RMSE < 0.08 cm), independent of the acquisition mode (FR, S). For marker-less tumor detection, FR-nF images resulted in RMSE > 0.3 cm, while for MV fluoroscopy in S-mode RMSE < 0.1 cm for 15 Hz and RMSE < 0.16 cm for 30 Hz. Largest consistency in target localization was experienced during 15 Hz S-nF readout. In general, marker contrast decreased in function of higher frame rates, which was detrimental for marker detection success. In this work, Visicoils with a thickness of 0.075 cm were showing best results for a 15 Hz frame rate, while non-MV compatible 0.05 cm Visicoil markers were not visible on the new EPID with improved sensitivity compared to EPID models based on a Kodak Lanex Fast scintillator. No noticeable influence of pulsing artifacts on the detection of a 0.075 cm Visicoil was observed, while a synchronized readout provided most reliable detection of a marker-less soft-tissue structure.

Evolution of pollination niches in a generalist plant clade.

It is widely assumed that floral diversification occurs by adaptive shifts between pollination niches. In contrast to specialized flowers, identifying pollination niches of generalist flowers is a challenge. Consequently, how generalist pollination niches evolve is largely unknown. We apply tools from network theory and comparative methods to investigate the evolution of pollination niches among generalist species belonging to the genus Erysimum. These species have similar flowers. We found that the studied species may be grouped in several multidimensional niches separated not by a shift of pollinators, but instead by quantitative variation in the relative abundance of pollinator functional groups. These pollination niches did not vary in generalization degree; we did not find any evolutionary trend toward specialization within the studied clade. Furthermore, the evolution of pollination niche fitted to a Brownian motion model without phylogenetic signal, and was characterized by frequent events of niche convergences and divergences. We presume that the evolution of Erysimum pollination niches has occurred mostly by recurrent shifts between slightly different generalized pollinator assemblages varying spatially as a mosaic and without any change in specialization degree. Most changes in pollination niches do not prompt floral divergence, a reason why adaptation to pollinators is uncommon in generalist plants.