Fasciole pathways in spatangoid echinoids: a new source of phylogenetically informative characters

Fascioles are important early-forming structures that play a key role in allowing irregular echinoids to burrow. They have traditionally been grouped into a small number of types according to their general position on the test, but this masks some significant differences that exist. The precise course that fasciole bands follow over the test plating has been mapped in detail for 89 species of spatangoid echinoids, representing the great majority of fasciole-bearing genera both living and fossil. Within each fasciole type, discrete and conserved patterns can be distinguished, differing both in which plates they are initiated on, and on whether they cross plate growth centres or are late-stage bands positioned towards the edge of the plate. Fasciole position is most highly conserved in the anterior and lateral interambulacral plates and on the earliest forming bands. The existence of different subanal fasciole patterns in the Micrasteridae and Brissidae suggests that these may have evolved independently. Schizasterid and hemiasterine spatangoids can each be subdivided into two major clades, and brissid spatangoids into three clades based on detailed patterns of their fascioles. Plotting fasciole pathways over test architecture provides a rich new source of phylogenetically informative characters.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 15−35.     

Early post-metamorphic ontogenesis of deep-sea spatangoids (Echinoidea, Spatangoida) of the NE Atlantic Ocean

Abstract. The early juvenile development of 3 species of irregular deep-sea echinoids of the NE Atlantic was examined using scanning electron microscopy. Although the post-metamorphic development of these 3 spatangoids is very similar, the morphology and development of fascioles (specialized bands of heavily ciliated minute spines) facilitates distinguishing the species. In Hemiaster expergitus and Spatangus raschi , the fascioles present in the early juvenile develop to form adult fascioles. In Brissopsis lyrifera , a juvenile fasciole of unknown function disappears during ontogenesis, and new adult subanal and periproct fascioles arise. Fascioles of S. raschi and B. lyrifera are present at a very early stage of development (∼0.7 mm test length), whereas in H. expergitus the fasciole appears much later (∼3 mm test length). Animals smaller than 0.8 mm test diameter have not yet developed a functional mouth and are still considered as endotrophic postlarval stages. Mouth development is similar for all spatangoids examined.     

Carrying on regardless: the echinoid genus Cyclaster at the Cretaceous–Tertiary boundary

A taxonomic revision and subsequent cladistic analysis show that Maastrichtian and Palaeocene species of the genus Cyclaster are split into three clades. Members of all three are present before and after the Cretaceous-Tertiary boundary, demonstrating that the genus Cyclaster as a whole was unaffected by the crisis at the end of the Cretaceous. Unlike most spatangoids, Cyclaster has the characteristic crystallographic signature of a lecithotrophic larval stage. Further work on other groups will determine whether larval strategy affected survivorship at this time.     

Biodiversity dynamics and their driving factors during the Cretaceous diversification of Spatangoida (Echinoidea, Echinodermata)

Variations in recorded diversity over time present a scrambled signal that is modulated by a large number of variables: the potential of particular life forms to generate evolutionary innovations, external constraints induced by the environment in its broad sense, the heterogeneity of the fossil record and the analytical artefacts due to sampling bias. A key question is how to characterise and quantify the separate input of any given factor in the overall diversity signal. This paper explores the structure of diversity data for spatangoid heart urchins and the sensitivity of recorded diversity to different factors of analytical bias (length of geological periods, proportion of palaeogeographical realms explored, accessible area of outcrops and historical determinism). Unexpectedly, recorded diversity of spatangoids is not proportional to the duration of stages. Bias implied by time scale is negligible compared to bias of sampling or historical determinism. Diversity at any given time is dependent on its recent history (autocorrelation). For spatangoids, a high correlation between diversity at time t_i and t_i−1 suggests that recorded diversity has an evolutionary significance. A nearly constant rate of diversification is hypothesised for the Cretaceous. A relative poor fossil record during the Turonian and the Coniacian interrupts the main trend of diversification. The number of species counted for a single time interval depends on the number of palaeogeographical realms considered. In conjunction with ecological and phylogenetic data, this relation suggests an evolutionary signal in which western Tethys acted as a centre of origination. Diversity at a single location is constrained ecologically and diversification is controlled by migration into new realms. Recorded diversity and available area of outcrop seem to be correlated, but alternative interpretations can be drawn, including large-scale bias in the fossil record or operation of similar causes (e.g., effect of sea-level fluctuation). Comparing recorded diversity with separate factors independently leads to conflicting results. A multivariate approach suggests that the main trend in recorded diversity might be partially related to evolutionary signal or biases connected with the heterogeneity of the fossil record. Results from other approaches (phylogeny, morphological disparity) are consistent with and emphasise the evolutionary significance of the recorded diversity of spatangoids.     

Continuous characters analyzed as such

Quantitative and continuous characters have rarely been included in cladistic analyses of morphological data; when included, they have always been discretized, using a variety of ad hoc methods. As continuous characters are typically additive, they can be optimized with well known algorithms, so that with a proper implementation they could be easily analyzed without discretization. The program TNT has recently incorporated algorithms for analysis of continuous characters. One of the problems that has been pointed out with existing methods for discretization is that they can attribute different states to terminals that do not differ significantly—or vice versa. With the implementation in TNT, this problem is diminished (or avoided entirely) by simply assigning to each terminal a range that goes from the mean minus one (or two) SE to the mean plus one (or two) SE; given normal distributions, terminals that do not overlap thus differ significantly (more significantly if using more than 1 SE). Three real data sets (for scorpions, spiders and lizards) comprising both discrete and quantitative characters are analyzed to study the performance of continuous characters. One of the matrices has a reduced number of continuous characters, and thus continuous characters analyzed by themselves produce only poorly resolved trees; the support for many of the groups supported by the discrete characters alone, however, is increased when the continuous characters are added to the analysis. The other two matrices have larger numbers of continuous characters, so that the results of separate analyses for the discrete and the continuous characters can be more meaningfully compared. In both cases, the continuous characters (analyzed alone) result in trees that are relatively similar to the trees produced by the discrete characters alone. These results suggest that continuous characters carry indeed phylogenetic information, and that (if they have been observed) there is no real reason to exclude them from the analysis. © The Willi Hennig Society 2006.     

Phylogeny of Early Cretaceous spatangoids (Echinodermata: Echinoidea) and taxonomic implications

A phylogenetic analysis of 36 species provides a test for the taxonomy and the history of Early Cretaceous spatangoids. Most taxonomic units from genera to suborders are consistent with the proposed phylogenetic framework. We retain Hemiasterina, Micrasterina, Hemiasteridae, Schizasteridae, Hemiaster , Heteraster , Mecaster , and Periaster as original monophyletic groups. However, all of these clades originate without the classical apomorphies normally ascribed to them. We suggest a revision of their diagnoses and of the generic attributions of basal species. Some ill-defined, 'primitive', and paraphyletic taxa are recognised: Toxaster , Epiaster , Palhemiaster , and Toxasteridae. Even if they do not have phylogenetic meaning, they are retained here, pending a more complete revision.     

Domes,arches and urchins: The skeletal architecture of echinoids (Echinodermata)

Summary A combination of simple membrane theory and statical analysis has been used to determine how stresses are carried in echinoid skeletons. Sutures oriented circumferentially are subject principally to compression. Those forming radial zig-zags are subject to compression near the apex and tension near the ambitus. Radial and circumferential sutures in Eucidaris are equally bound with collagen fibers but in Diadema, Tripneustes, Psammechinus, Arbacia and other regular echinoids, most radial sutures are more heavily bound, and thus stronger in tension. Psammechinus, Tripneustes and several other echinoids have radial sutures thickened by ribs which increase the area of interlocking trabeculae. Ribs also increase flexural stiffness and carry a greater proportion of the stress. Further, ribs effectively draw stress from weaker areas pierced by podial pores, and increase the total load which can be sustained.Allometry indicates that regular echinoids become relatively higher at the apex as size increases, thus reducing ambital stresses. Some spatangoids with very high domes (eg Agassizia) maintain isometry, but others (eg Meoma) become flatter with size. Both holectypoids (Echinoneus) and cassiduloids (Apatopygus) maintain a constant height to diameter relationship. Flattening, and consequently ambital tensile stress, is greatest in the clypeasteroids. In this group the formation of internal buttresses which preferentially carry stress, reaches maximum development. A notable exception, however, is the high domed Clypeaster rosaceus.In this analysis it was assumed that local buckling or bending does not occur. The test of some echinoids (e.g. Diadematoida) have relatively wide sutures swathed in collagen, which allows local deformation. Others (e.g. Arbacia) have rigid sutures with reduced collagen. In Psammechinus and other members of the Order Echinoida, in addition to rib formation, inner and outer surface trabeculae are thickened so that the individual plates are stiffened. Some spatangoids (Meoma, Paleopneustes) have extensive sutural collagen, but the cassiduloid Apatopygus has collagen confined to junctions of sutures, and elsewhere the joints are strengthened and stiffened by fusion of trabeculae. Fusion of surface trabeculae is almost complete in the holectypoid, Echinoneus, and the sutures are obscured.     

Tuberculation in spatangoid fascioles: Delineating plausible homologies

The existing definition of spatangoid fascioles as a narrow band of minute tubercles (miliaries) is inadequate. One reason is that many intermediates between the presence of indisputable fascioles and their total absence are known. Although fascioles are widely used in the classification of spatangoids, diversity of fasciole tuberculation has largely been ignored. We examine fascioles in about 100 spatangoid species, focusing on the earliest manifestations of fascioles (both developmentally and phylogenetically) and on their variable tuberculation. Qualitative observations are complemented by quantitative analyses (ANOVA and PCA) of 21 species. Three types of fascioles are defined according to tubercle pattern: protofascioles for localized concentrations of miliaries; parafascioles for bands of miliaries with a progressive transition to the surrounding tuberculation; orthofascioles for strongly differentiated, well-circumscribed bands of miliaries. Ontogenetic, architectural, ecological, and taxonomic variations of these three patterns are qualitatively and quantitatively investigated. We attempt to delineate plausible homologies, origins, and subsequent evolution of the different kinds of fascioles.     

Circularity and Independence in Phylogenetic Tests of Ecological Hypotheses

It has been asserted that in order to avoid circularity in phylogenetic tests of ecological hypotheses, one must exclude from the cladistic analysis any characters that might be correlated with that hypothesis. The argument assumes that selective correlation leads to lack of independence among characters and may thus bias the analysis. This argument conflates the idea of independence between the ecological hypothesis and the phylogeny with independence among characters used to construct the tree. We argue that adaptation or selection does not necessarily result in the non-independence of characters, and that characters for a cladistic analysis should be evaluated as homology statements rather than functional ones. As with any partitioning of data, character exclusion may lead to weaker phylogenetic hypotheses, and the practice of mapping characters onto a tree, rather than including them in the analysis, should be avoided. Examples from pollination biology are used to illustrate some of the theoretical and practical problems inherent in character exclusion.     

The mouse skull as a source of morphometric data for phylogeny inference

Brownian motion has been a model widely used for describing phenotypic evolution of continuous characters under random drift. Evolution of traits evolving under weak stabilizing selection, together with drift, can also be modeled by the Ornstein-Uhlenbeck process, in which a population moves at random on an adaptive peak under the influence of drift with selection returning the population towards the optimum. Obviously, reliability of an evolutionary model stands or falls with the extent to which the underlying assumptions are supported or violated. Another potential problem of continuous characters as a source of data for phylogeny inference is the correlation between them. To assess whether the Brownian motion model or the Ornstein-Uhlenbeck model are suitable for modeling the evolution of continuous cranial and dental characters and to what extent these characters are correlated with one another, 11 measurements encompassing various aspects of the mouse skull morphology were collected and subjected to a comparative analysis using the generalized least squares method. It could be shown that only about one-half of the characters evolved according to the Brownian motion model or the Ornstein-Uhlenbeck model. Moreover, about 44% of the correlation coefficients exceeded 0.8, suggesting a need for removing at least phenotypic covariances from the data prior to a phylogenetic analysis. Finally, ancestral states of the characters under study were estimated with the generalized least square method. There has been a general trend towards enlarging the overall size of the skull and increasing the braincase volume in the species of the genus Mus.     

THE USEFULNESS OF BEHAVIOR FOR PHYLOGENY ESTIMATION: LEVELS OF HOMOPLASY IN BEHAVIORAL AND MORPHOLOGICAL CHARACTERS

It is widely believed that behavior is more evolutionarily labile and/or more difficult to characterize than morphology, and thus that behavioral characters are not as useful as morphological characters for estimating phylogenetic relationships. To examine the relative utility of behavior and morphology for estimating phylogeny, we compared levels of homoplasy for morphological and behavioral characters that have been used in systematic studies. In an analysis of 22 data sets that contained both morphological and behavioral characters we found no significant difference between mean consistency indices (CIs, which measure homoplasy) within data sets for the two types of characters. In a second analysis we compared overall CIs for 8 data sets comprised entirely of behavioral characters with overall CIs for 32 morphological data sets and found no significant difference between the two types of data sets. For both analyses, 95% confidence limits on the difference between the two types of characters indicate that, even if given the benefit of the doubt, morphological characters could not have substantially higher mean CIs than behavioral characters. These results do not support the idea that behavioral characters are less useful than morphological characters for the estimation of phylogeny.     

Lateral variations of size-frequency distribution in a fossil echinoid community and their palaeoecological significance

The analysis of size-frequency spatial distribution of three species of Cenomanian echinoids in a single fossil assemblage shows both intraspecific and interspecific horizontal segregation of the individuals parallel to the variations in silt and organic matter levels of the substrate. The exceptional preservation of echinoids. fossilized in the living position with part of their spines. and their multimodal size-frequency distribution, with no evidence of physical transportation. suggest that a catastrophic event resulted in the fossilization of the demographic structure of the populations. The assemblage. being the result of mass mortality of a community, corresponds to a census assemblage. Thus the patchy segregation of echinoids could not primarily be influenced by size-selective taphonomy (current winnowing, biological or mechanical destruction) but more likely determined by biological phcnomena like mortality and recruitment patterns, high juvenile growth, substrate selection and herd mode of life. Recent examples of spatial separation of adults and juveniles. given for different species of echinoids. show that these patchy distributions are widespread, and therefore may be a privileged source of fossil preservation of cohort's size-frequency distribution in catastrophic mortality. □ Palaeoecology, size-frequency distribution, demography, echinoids. spatangoids, cassiduloids, M ecaster , C atopygus , N ucleopygus .     

Cladistic and phenetic studies of genera of Afrotropical Cryptobiina (Coleoptera,Staphylinidae, Paederinae) II. The phenetic approach

The phenetics of 12 genera of Afrotropical Cryptobiina have been analysed by multivariate statistics. Three analyses (principal component analysis, canonical discriminant analysis and cluster analysis) have been used to determine the relative positions of the taxa in a morphospace. These analyses have allowed us to confirm the generic divisions based on alpha-systematic and phylogenetic grounds. While phenetic systematics and cladistic systematics have often been opposed, this study shows that both approaches are, in the end, complementary. Phenetical analysis allow, in addition to a quantitative definition of the genera, the isolation of ethological or ecological characters, while the cladistic approch gives to them precision and a phylogenetic sense. The three types of analyses point out the importance in Cryptobiina of the size, length of the scapus and width of the neck, all three characters which were also designated as significant characters by the phylogenetic analysis.     

The origin of echinoid shell beds in siliciclastic shelf environments: three examples from the Miocene of Sardinia,Italy

Three mass accumulations of sea urchins from the Miocene of Sardinia show a number of taphonomic features which set them apart from previously described echinoid assemblages from the Cenozoic in which they represent: (1) monotypic assemblages; (2) include very well‐preserved remains of either regular or spatangoid echinoids; and (3) originate in deeper water environments. These accumulations are compared using a detailed sedimentological and taphonomic analysis including preservational fabrics, taphonomic signatures, size frequency distributions, density of occurrences and preferred orientations. The possible role of gregarious behaviour contributing to mass occurrences and the specific sedimentary events leading to the excellent preservation are discussed. The interpreted depositional environment of all three deposits is that of a storm‐dominated, siliciclastic shelf environment. A phymosomatid assemblage represents rapid burial through obrution of a highly dense, freshly dead community. A Brissopsis‐dominated spatangoid assemblage represents a mixed accumulation of parautochthonous and transported skeletons. The third assemblage consisting of regular echinoid spines and rare tests represents a composite tempestite. Differences in the depositional environments are related to their position along onshore–offshore gradient with the first two beds originated in a deeper setting than that of the spine accumulation. This study shows that the preservation of assemblages containing complete regular echinoids and spatangoids is higher in deeper water settings than in shallow water environments.     

缺失数据和贝叶斯系统发育分析精确度之探索

The effect of missing data on phylogenetic methods is a potentially important issue in our attempts to reconstruct the Tree of Life. If missing data are truly problematic, then it may be unwise to include species in an analysis that lack data for some characters (incomplete taxa) or to include characters that lack data for some species. Given the difficulty of obtaining data from all characters for all taxa (e.g., fossils), missing data might seriously impede efforts to reconstruct a comprehensive phylogeny that includes all species. Fortunately, recent simulations and empirical analyses suggest that missing data cells are not themselves problematic, and that incomplete taxa can be accurately placed as long as the overall number of characters in the analysis is large. However, these studies have so far only been conducted on parsimony, likelihood, and neighbor-joining methods. Although Bayesian phylogenetic methods have become widely used in recent years, the effects of missing data on Bayesian analysis have not been adequately studied. Here, we conduct simulations to test whether Bayesian analyses can accurately place incomplete taxa despite extensive missing data. In agreement with previous studies of other methods, we find that Bayesian analyses can accurately reconstruct the position of highly incomplete taxa (i.e., 95% missing data), as long as the overall number of characters in the analysis is large. These results suggest that highly incomplete taxa can be safely included in many Bayesian phylogenetic analyses.     

Statistical Genetics of an Annual Plant, Impatiens Capensis. I. Genetic Basis of Quantitative Variation

Analysis of quantitative genetics in natural populations has been hindered by computational and methodological problems in statistical analysis. We developed and validated a jackknife procedure to test for existence of broad sense heritabilities and dominance or maternal effects influencing quantitative characters in Impatiens capensis. Early life cycle characters showed evidence of dominance and/or maternal effects, while later characters exhibited predominantly environmental variation. Monte Carlo simulations demonstrate that these jackknife tests of variance components are extremely robust to heterogeneous error variances. Statistical methods from human genetics provide evidence for either a major locus influencing germination date, or genes that affect phenotypic variability per se. We urge explicit consideration of statistical behavior of estimation and testing procedures for proper biological interpretation of statistical results.     

Adaptation and functional integration in primate phylogenetics

In two areas of phylogenetics, contrary predictions have been developed and maintained for character analysis and weighting. With regard to adaptation, many have argued that adaptive characters are poorly suited to phylogenetic analysis because of a propensity for homoplasy, while others have argued that complex adaptive characters should be given high weight because homoplasy in complex characters is unlikely. Similarly, with regard to correlated sets of characters, one point of view is that such sets should be collapsed into a single character-a single piece of phylogenetic evidence. Another point of view is that a suite of correlated characters should be emphasized in phylogenetics, again because recurrence of detailed similarity in the same suite of features is unlikely. In this paper, I discuss the theoretical background of adaptation and functional integration with respect to phylogenetic systematics of primates. Several character examples are reviewed with regard to their functional morphology and phylogenetic signal: postorbital structures, tympanic morphology, fusion of the mandibular symphysis, the tooth comb, strepsirrhine talar morphology, and the prehensile tail. It is clear when considering characters such as these that some characters are synapomorphic of major clades and at the same time functionally important. This appears particularly to be the case when characters are integrated into a complex and maintained as stable configurations. Rather than being simply a problem in character analysis, processes of integration may help to explain the utility of phylogenetically informative characters. On the other hand, the character examples also highlight the difficulty in forming a priori predictions about a character's phylogenetic signal. Explanations of patterns of character evolution are often clade-specific, which does not allow for a simple framework of character selection and/or weighting.     

Genetic Correlations and Maternal Effect Coefficients Obtained from Offspring-Parent Regression

Additive genetic variances and covariances of quantitative characters are necessary to predict the evolutionary response of the mean phenotype vector in a population to natural or artificial selection. Standard formulas for estimating these parameters, from the resemblance between relatives in one or two characters at a time, are biased by natural selection on the parents and by maternal effects. We show how these biases can be removed using a multivariate analysis of offspring-parent regressions. A dynamic model of maternal effects demonstrates that, in addition to the phenotypic variance-covariance matrix of the characters, sufficient parameters for predicting the response of the mean phenotype vector to weak selection are the additive genetic variance-covariance matrix and a set of causal coefficients for maternal effects. These can be simultaneously estimated from offspring-parent regressions alone, in some cases just from the daughter-mother regressions, if all of the important selected and maternal characters have been measured and included in the analysis.     

Conflict between Amino Acid and Nucleotide Characters

Slowly evolving characters, such as amino acids and replacement substitutions, have generally been favored over faster evolving characters for inferring phylogenetic relationships. However, amino acids constitute composite characters and, because of the degenerate genetic code, are subject to convergence. Based on an analysis of atpB and rbcL in 567 seed plants, we show that silent substitutions may be more phylogenetically informative than replacement substitutions and that artifacts caused by composite characters and/or convergence cause clades on amino acid trees to conflict with nucleotide trees and independent evidence. These findings indicate that coding nucleotide sequences only as amino acid characters for phylogenetic analysis provides little benefit and may yield misleading results.