scholarly journals What limits the morphological disparity of clades?

2015 ◽  
Vol 5 (6) ◽  
pp. 20150042 ◽  
Author(s):  
Jack W. Oyston ◽  
Martin Hughes ◽  
Peter J. Wagner ◽  
Sylvain Gerber ◽  
Matthew A. Wills
Keyword(s):  
Character State ◽  
Simple Relationship ◽  
Curve Shape ◽  
Evolutionary Time ◽  
Internal Constraints ◽  
Morphological Disparity ◽  
Centre Of Gravity ◽  
Significant Relationships ◽  
Higher Taxa ◽  
New States

The morphological disparity of species within major clades shows a variety of trajectory patterns through evolutionary time. However, there is a significant tendency for groups to reach their maximum disparity relatively early in their histories, even while their species richness or diversity is comparatively low. This pattern of early high-disparity suggests that there are internal constraints (e.g. developmental pleiotropy) or external restrictions (e.g. ecological competition) upon the variety of morphologies that can subsequently evolve. It has also been demonstrated that the rate of evolution of new character states decreases in most clades through time (character saturation), as does the rate of origination of novel bodyplans and higher taxa. Here, we tested whether there was a simple relationship between the level or rate of character state exhaustion and the shape of a clade's disparity profile: specifically, its centre of gravity (CG). In a sample of 93 extinct major clades, most showed some degree of exhaustion, but all continued to evolve new states up until their extinction. Projection of states/steps curves suggested that clades realized an average of 60% of their inferred maximum numbers of states. Despite a weak but significant correlation between overall levels of homoplasy and the CG of clade disparity profiles, there were no significant relationships between any of our indices of exhaustion curve shape and the clade disparity CG. Clades showing early high-disparity were no more likely to have early character saturation than those with maximum disparity late in their evolution.

scholarly journals Early bursts of disparity and the reorganization of character integration

2018 ◽  
Vol 285 (1891) ◽  
pp. 20181604 ◽  
Author(s):  
Peter J. Wagner
Keyword(s):  
Fossil Record ◽  
Developmental Theory ◽  
Inverse Modelling ◽  
Character State ◽  
Change Model ◽  
Morphological Disparity ◽  
Change Models ◽  
Higher Taxa ◽  
Constrained Evolution

‘Early bursts' of morphological disparity (i.e. diversity of anatomical types) are common in the fossil record. We typically model such bursts as elevated early rates of independent character change. Developmental theory predicts that modules of linked characters can change together, which would mimic the effects of elevated independent rates on disparity. However, correlated change introducing suboptimal states should encourage breakup (parcellation) of character suites allowing new (or primitive) states to evolve until new suites arise (relinkage). Thus, correlated change–breakup–relinkage presents mechanisms for early bursts followed by constrained evolution. Here, I analyse disparity in 257 published character matrices of fossil taxa. For each clade, I use inverse-modelling to infer most probably rates of independent change given both time-homogeneous and separate ‘early versus late' rates. These rates are used to estimate expected disparity given both independent change models. The correlated change–breakup–relinkage model also predicts elevated frequencies of compatible character state-pairs appearing out of order in the fossil record (e.g. 01 appearing after 00 and 11; = low stratigraphic compatibility), as one solution to suboptimal states induced by correlated change is a return to states held before that change. As predicted by the correlated change–breakup–relinkage model, early disparity in the majority of clades both exceeds the expectations of either independent change model and excess early disparity correlates with low stratigraphic compatibility among character-pairs. Although it is possible that other mechanisms for linking characters contribute to these patterns, these results corroborate the idea that reorganization of developmental linkages is often associated with the origin of groups that biologists recognize as new higher taxa and that such reorganization offers a source of new disparity throughout the Phanerozoic.

Morphological disparity in Ordovician-Devonian crinoids and the early saturation of morphological space

Paleobiology ◽  
1994 ◽  
Vol 20 (3) ◽  
pp. 320-344 ◽  
Author(s):  
Mike Foote
Keyword(s):  
Design Space ◽  
Full Range ◽  
Taxonomic Diversity ◽  
Character State ◽  
Early Paleozoic ◽  
Evolutionary Patterns ◽  
Morphological Disparity

It has been argued that many clades originating in the early Paleozoic filled their design space rapidly while still at low taxonomic diversity. Standardization of morphology for analytical purposes facilitates testing of this claim. Here I document evolutionary patterns of morphological disparity in Ordovician-Devonian crinoids, using a set of 75 discrete characters covering the principal features of the crinoid stem, cup, tegmen, and arms. Disparity is measured as the average dissimilarity among species, the range of morphospace occupied, and the number of realized character-state combinations. Comparison with generic richness reveals that the full range of form was essentially attained by the early part of the Caradocian, long before the time of maximal taxonomic diversity. Despite subsequent taxonomic diversification, the variety of crinoid form did not expand appreciably; increased diversity was accommodated by the evolution of variations upon the spectrum of designs established earlier. The data discussed here do not definitively imply specific sources of constraint, but the effective stasis in disparity supports previous arguments that some morphological limits were reached early in crinoid history.

On The Mechanism of Interstitial Cluster Migration in α -FE

1998 ◽  
Vol 540 ◽  
Author(s):  
A.V. Barashev ◽  
Yu.N. Osetsky ◽  
D.J. Bacon
Keyword(s):  
Molecular Dynamics ◽  
Computer Simulations ◽  
Microstructure Evolution ◽  
Pure Copper ◽  
Simple Relationship ◽  
Statistical Accuracy ◽  
Jump Frequency ◽  
Temperature Range ◽  
Thermally Activated ◽  
Centre Of Gravity

AbstractRecent molecular dynamics (MD) computer simulations have shown that clusters consisting of up to a few tens of self-interstitial atoms (SIAs) are highly mobile along closed-packed crystallographic directions in pure copper and iron. This effect has important consequences for microstructure evolution in irradiated metals and so it is desirable to investigate the mechanisms of the cluster motion. In the present paper the results of MD modelling of the thermally-activated motion of clusters of 3, 9 and 17 SIAs in α-Fe in the temperature range from 90 to 1400 K are analyzed. The extensive MD data has enabled the migration of clusters, as well as that of individual SIAs in the clusters, to be treated with high statistical accuracy. The correlation between the motion of the centre of gravity of a cluster and the jumps of individual SIAs in the cluster is revealed. It is found that the SIAs in a cluster jump almost independently and their jump frequency depends on the number of SIAs in the cluster. This leads to a simple relationship between the jump frequency of a cluster and the number of SIAs in it. The cluster jump frequency exhibits a deviation from the Arrhenius relationship. The reason for this is discussed.

scholarly journals Glacial Stream Ecology: Structural and Functional Assets

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 376 ◽  
Author(s):  
Leopold Füreder ◽  
Georg H. Niedrist
Keyword(s):  
Stream Ecology ◽  
Harsh Environments ◽  
Feeding Strategies ◽  
European Alps ◽  
Simple Relationship ◽  
Significant Relationships ◽  
Glacial Stream ◽  
Alpine Stream ◽  
Alpine Streams ◽  
Functional Components

High altitude glacier-fed streams are harsh environments inhabiting specialized invertebrate communities. Most research on biotic aspects in glacier-fed streams have focused on the simple relationship between presence/absence of species and prevailing environmental conditions, whereas functional strategies and potentials of glacial stream specialists have been hardly investigated so far. Using new and recent datasets from our investigations in the European Alps, we now demonstrate distinct functional properties of invertebrates that typically dominate glacier-fed streams and show significant relationships with declining glacier cover in alpine stream catchments. In particular, we present and argue about cause-effect relationships between glacier cover in the catchment and temperature, community structure, diversity, feeding strategies, early life development, body mass, and growth of invertebrates. By concentrating on key taxa in glacial and non-glacial alpine streams, the relevance of distinct adaptations in these functional components becomes evident. This clearly demonstrates that further studies of functional characteristics are essential for the understanding of peculiar diversity patterns, successful traits and their plasticity, evolutionary triggered species adaptions, and flexibilities.

SOME PRO- AND MESOTHORACIC STRUCTURES IMPORTANT FOR PHYLOGENETIC ANALYSIS OF HYMENOPTERA, WITH A REVIEW OF TERMS USED FOR THE STRUCTURES

1985 ◽  
Vol 117 (11) ◽  
pp. 1395-1443 ◽  
Author(s):  
Gary A.P. Gibson
Keyword(s):  
Phylogenetic Analysis ◽  
Character State ◽  
Ancestral State ◽  
State Distribution ◽  
Higher Taxa ◽  
Prior Use ◽  
Attachment Mechanism ◽  
Single Set

AbstractThe character-state distribution of various external and internal pro- and mesothoracic structures of Hymenoptera is described. Structures discussed are the transscutal articulation, axillae, notauli, median mesoscutal sulcus, parapsidal lines, pronotal lobe, postspiracular sclerite, prepectus, netrion, epicnemium, basalare, pronotal-mesothor-acic attachment mechanism, and 2 mesothoracic muscles, viz. mesotrochanteral depressor and second-phragmal flexor. Ancestral state and transformation of the characters are hypothesized, and shared derived states of higher taxa are determined. Hypotheses of synapomorphy are based on the shared derived states, and these hypotheses used to test previous hypotheses of relationship and classification. Relationships of Symphyta to Apocrita and of Aculeata to Terebrantes are discussed, and various aspects of classification of Symphyta and Terebrantes are examined. Finally, prior use of terms is reviewed for the thoracic structures studied. A single set of terms is selected for use throughout the order based on original use of each term and on hypotheses of homology.

Morphological diversification of Paleozoic crinoids

Paleobiology ◽  
1995 ◽  
Vol 21 (3) ◽  
pp. 273-299 ◽  
Author(s):  
Mike Foote
Keyword(s):  
Taxonomic Diversity ◽  
Character State ◽  
Similar Species ◽  
Average Difference ◽  
Maximal Level ◽  
Morphological Diversification ◽  
Evolutionary Pattern ◽  
Higher Taxa ◽  
Additional Support ◽  
Do So

Several metrics, including average difference among species, range of occupied morphological space, and number of character-state combinations, are used to investigate morphological diversification in Paleozoic crinoids. Despite several phases of taxonomic diversification, the maximal level of disparity reached in the Ordovician remained essentially unsurpassed. Although new regions in morphological space were occupied after the Devonian, these were not as extensive as those that had been evacuated prior to the Carboniferous. This discordance between extensive total morphological change and limited net change further supports previous arguments for the importance of morphological constraints in crinoid evolution. Major changes in the occupation of morphological space correspond with changes in taxonomic diversity within certain higher taxa. The extent to which advanced cladids (Poteriocrinina) appear to expand into new morphological space is exaggerated by the large number of very similar species in this group. If fewer species are sampled, by considering only those forms that differ from each other by at least some prescribed amount, poteriocrines appear to be less extreme morphologically. In contrast, other groups that seem to occupy unique regions in morphological space continue to do so even if fewer of them are sampled. Major crinoid clades—Camerata and Cladida+Flexibilia—do not show the same evolutionary pattern as Crinoidea, but instead exhibit a more gradual diversification of morphology. This observation provides additional support for the existence of qualitative differences among taxa of different rank.

scholarly journals PHYLOGENY AND CLASSIFICATION OF EUPELMIDAE, WITH A REVISION OF THE WORLD GENERA OF CALOSOTINAE AND METAPELMATINAE (HYMENOPTERA: CHALCIDOIDEA)

1989 ◽  
Vol 121 (S149) ◽  
pp. 3-121 ◽  
Author(s):  
Gary A. P. Gibson
Keyword(s):  
Sister Group ◽  
Structural Features ◽  
Character State ◽  
Type Specimens ◽  
Higher Taxa ◽  
Biogeographic Region ◽  
State Evolution ◽  
The World ◽  
Made In

AbstractThree subfamilies are classified in Eupelmidae: Calosotinae Bouček, Eupelminae Walker, and Metapelmatinae Bouček. Diagnoses of these three subfamilies and of Tanaostigmatidae are given, together with a key to distinguish members from each other and from other Chalcidoidea. Genera of Calosotinae and Metapelmatinae are revised for the world, with a key to genera given for both subfamilies. For each genus the following is provided: synonymy, description of structural features of males and females, notes on distribution and hosts, available keys to species listed by biogeographic region, and a catalog of species. New generic combinations are made in the catalogs of species based on examination of type specimens of the species. Eight genera are included in Calosotinae [type species in brackets]: Archaeopelma gen.nov. [A. tropeotergum sp.nov.], Licrooides gen.nov. [L. umbilicatus sp.nov.], Paraeusandalum gen.nov. [P. chilense sp.nov.], Eusandalum Ratzeburg, Chirolophus Haliday, Calosota Curtis, Balcha Walker, and Tanythorax gen.nov. [T. spinosus sp.nov.]. Four genera are included in Metapelmatinae: Metapelma Westwood, Neanastatus Girault, Eopelma gen.nov. [E. mystax sp.nov.], and Lambdobregma gen.nov. [L. schwarzii (Ashmead) comb.nov.]. The following are proposed as new synonymies: Notosandalum De Santis and Exosandalum Bouček = Eusandalum Ratzeburg, and Metacalosoter Masi = Calosota Curtis. Eighteen structural features of adults of the three eupelmid subfamilies, and of other Chalcidoidea including Tanaostigmatidae, Encyrtidae, Aphelinidae, and Pteromalidae, are studied to delimit character states and determine their distribution among the higher taxa. Twenty-two additional features of adults of Calosotinae and Metapelmatinae are studied for supplemental evidence of relationships among the genera in these two subfamilies. Observed character-state distributions are used to postulate character polarity and homoplastic states, and hypotheses of monophyly and relationships among taxa are based on proposed synapomorphic states. Aphelinidae sensu lato (including the subfamily Eriaporinae) are indicated as either a paraphyletic or polyphyletic taxon if the Eriaporinae are included but the Signiphoridae are excluded. Tanaostigmatidae sensu lato (including the genus Cynipencyrtus Ishii) are indicated as the sister group of Encyrtidae based on a relatively long mesoscutal process for the muscle pl2–t2c, and structure of the articulation between the mesoscutum and scutellar-axillar complex. The genus Cynipencyrtus Ishii is indicated to be most closely related to Encyrtidae based on common possession of transverse axillae and mesotibial apical pegs. Possible relationships among Calosotinae, Metapelmatinae, and Eupelminae, and among these and Tanaostigmatidae + Encyrtidae remain unresolved. There are no derived character states unique to either Eupelmidae, or Eupelmidae + (Tanaostigmatidae + Encyrtidae), so that these taxa and relationships are not definitively supported as monophyletic. Eupelmidae may represent a grade-level taxon with membership determined by similar suites of apomorphic states that function to enhance jumping ability. Cladograms are used to illustrate alternate hypotheses of character-state evolution and relationships among the genera of Calosotinae and Metapelmatinae. Distribution of character states for the higher taxa and for each genus of Calosotinae and Metapelmatinae is summarized in two tables. Scanning electron photomicrographs are used to illustrate structural features.

Speech-Language Pathologists' Perceptions of Their Preparation and Confidence for Providing Dysphagia Services

2020 ◽  
Vol 5 (6) ◽  
pp. 1666-1682
Author(s):  
Lena G. Caesar ◽  
Merertu Kitila
Keyword(s):  
Service Delivery ◽  
Graduate School ◽  
Online Survey ◽  
The United States ◽  
Academic Preparation ◽  
Speech Language Pathologists ◽  
Confidence Levels ◽  
Graduate School Preparation ◽  
Graduate Preparation ◽  
Significant Relationships

Purpose The purpose of this study was to investigate the perceptions of speech-language pathologists (SLPs) regarding their academic preparation and current confidence levels for providing dysphagia services, and the relationship between their perceptions of graduate school preparation and their current levels of confidence. Method This study utilized an online survey to gather information from 374 American Speech-Language-Hearing Association–certified SLPs who currently provide dysphagia services in the United States. Surveys were primarily distributed through American Speech-Language-Hearing Association Special Interest Group forums and Facebook groups. The anonymous survey gathered information regarding SLPs' perceptions of academic preparation and current confidence levels for providing dysphagia services in 11 knowledge and skill areas. Results Findings indicated that more than half of respondents did not feel prepared following their graduate academic training in five of the 11 knowledge and skill areas related to dysphagia service delivery. However, about half of respondents indicated they were currently confident about their ability to provide services in eight of the 11 knowledge and skill areas. Findings also indicated that their current confidence levels to provide dysphagia services were significantly higher than their perceptions of preparation immediately following graduate school. However, no significant relationships were found between respondents' self-reported current confidence levels and their perceptions of the adequacy of their academic preparation. Conclusions Despite SLPs' low perceptions of the adequacy of their graduate preparation for providing dysphagia services in specific knowledge and skill areas immediately following graduation, they reported high confidence levels with respect to their actual service delivery. Implications of these findings are discussed.

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