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Character Matrix (character + matrix)

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Life Sciences	100%

Selected Abstracts

EXHAUSTION OF MORPHOLOGIC CHARACTER STATES AMONG FOSSIL TAXA

EVOLUTION, Issue 2 2000
Peter J. Wagner
Abstract., Frequencies of new character state derivations are analyzed for 56 fossil taxa. The hypothesis that new character states are added continuously throughout clade history can be rejected for 48 of theses clades. Two alternative explanations are considered: finite states and ordered states. The former hypothesizes a limited number of states available to each character and is tested using rarefaction equations. The latter hypothesizes that there are limited possible descendant morphologies for any state, even if the character has infinite potential states. This is tested using power functions. The finite states hypothesis explains states: steps relationships significantly better than does the ordered states hypothesis in 14 cases; the converse is true for 14 other cases. Under either hypothesis, trilobite clades show appreciably more homoplasy after the same numbers of steps than do molluscs, echinoderms, or vertebrates. The prevalence of the exhaustion pattern among different taxonomic groups implies that worker biases are not to blame and instead implicates biological explanations such as intrinsic constraints or persistent selective trends. Regardless of the source of increased homoplasy, clades appear to exhaust their available character spaces. Nearly all examined taxa show significant increases in proportions of incompatible character pairs (i.e., those necessarily implying homoplasy) as progressively younger taxa are added to character matrices. Thus, a deterioration of hierarchical structure accompanies character state exhaustion. Exhaustion has several implications: (1) the basic premise of cladistic analyses (i.e., that maximum congruence reflects homology rather than homoplasy) becomes increasingly less sound as clades age; (2) sampling high proportions of taxa probably is needed for congruence to discern homoplasy from homology; (3) stratigraphic data might be necessary to discern congruent homoplasy from congruent homology; and (4) in many cases, character states appear to have evolved in ordered patterns. [source]

Phylogenetic analyses of marine sponges within the order Verongida: a comparison of morphological and molecular data

INVERTEBRATE BIOLOGY, Issue 3 2007
Patrick M. Erwin
Abstract. Because the taxonomy of marine sponges is based primarily on morphological characters that can display a high degree of phenotypic plasticity, current classifications may not always reflect evolutionary relationships. To assess phylogenetic relationships among sponges in the order Verongida, we examined 11 verongid species, representing six genera and four families. We compared the utility of morphological and molecular data in verongid sponge systematics by comparing a phylogeny constructed from a morphological character matrix with a phylogeny based on nuclear ribosomal DNA sequences. The morphological phylogeny was not well resolved below the ordinal level, likely hindered by the paucity of characters available for analysis, and the potential plasticity of these characters. The molecular phylogeny was well resolved and robust from the ordinal to the species level. We also examined the morphology of spongin fibers to assess their reliability in verongid sponge taxonomy. Fiber diameter and pith content were highly variable within and among species. Despite this variability, spongin fiber comparisons were useful at lower taxonomic levels (i.e., among congeneric species); however, these characters are potentially homoplasic at higher taxonomic levels (i.e., between families). Our molecular data provide good support for the current classification of verongid sponges, but suggest a re-examination and potential reclassification of the genera Aiolochroia and Pseudoceratina. The placements of these genera highlight two current issues in morphology-based sponge taxonomy: intermediate character states and undetermined character polarity. [source]

Comparative sperm ultrastructure in Nemertea

JOURNAL OF MORPHOLOGY, Issue 7 2010
J. von Döhren
Abstract Although the monophyly of Nemertea is strongly supported by unique morphological characters and results of molecular phylogenetic studies, their ingroup relationships are largely unresolved. To contribute solving this problem we studied sperm ultrastructure of 12 nemertean species that belong to different subtaxa representing the commonly recognized major monophyletic groups. The study yielded a set of 26 characters with an unexpected variation among species of the same genus (Tubulanus and Procephalothrix species), whereas other species varied in metric values or only one character state (Ramphogordius). In some species, the sperm nucleus has grooves (Zygonemertes virescens, Amphiporus imparispinosus) that may be twisted and give a spiral shape to the sperm head (Paranemertes peregrina, Emplectonema gracile). To make the characters from sperm ultrastructure accessible for further phylogenetic analyses, they were coded in a character matrix. Published data for eight species turned out to be sufficiently detailed to be included. Comparative evaluation of available information on the sperm ultrastructure suggests that subtaxa of Heteronemertea and Hoplonemertea are supported as monophyletic by sperm morphology. However, the data do not provide information on the existing contradictions regarding the internal relationships of "Palaeonemertea." Nevertheless, our study provides evidence that sperm ultrastructure yields numerous potentially informative characters that will be included in upcoming phylogenetic analyses. J. Morphol. 2010. © 2010 Wiley-Liss, Inc. [source]

On the evolution and morphology of the rotiferan trophi, with a cladistic analysis of Rotifera

JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 3 2002
M. V. SØrensen
Abstract The phylogeny of Rotifera was examined in different computer-generated cladistic analyses, including Seisonidea, Bdelloidea, Flosculariacea, Collothecacea and all ploimids treated on family level. The analyses were based on a character matrix solely dealing with morphological characters, primarily based on the trophi morphology. Limnognathia maerski (Micrognathozoa), Rastrognathia macrostoma and Gnathostomula paradoxa (Gnathostomulida) were used as outgroups. The cladistic analysis performed by paup produced 288 most parsimonious trees. peewee analyses produced between 140 and 432 trees, depending on the concavity value. The monophyly of Eurotatoria, Monogononta and Ploima was confirmed in all obtained trees. All analyses suggested a division of Ploima into major clades. One clade corresponded to Transversiramida while the other contained all other ploimid taxa and recognized Antrorsiramida as a monophylum. Based on the obtained results a scenario for the trophi evolution is proposed. The analyses suggested that the presence of an incus is synapomorphic for Gnathifera while mallei are synapomorphic for Micrognathozoa and Rotifera. The ancestral rotifer trophi probably resembled those in Harringia (Asplanchnidae). Zusammenfassung Die Phylogenie der Rotatorien wurde mit verschiedenen kladistischen Computeranalysen, unter Einbezug der Seisonidea, Bdelloidea, Flosculariacea, Collothecacea und aller Taxa von Ploima auf Familienebene, untersucht. Die Analyse basierte auf einer Mekmalsmatrix, die nur morphologische Merkmale, vorwiegend aus der Morphologie der Kiefer, enthielt. Limnognathia maerski (Micrognathozoa), Rastrognathia macrostoma und Gnathostomula paradoxa (Gnathostomulida) wurden als Außengruppe benutzt. Die mit paup durchgeführte Analyse ergab 288 ,,sparsamste'' Kladogramme. PeeWee Analysen produzierten in Abhängigkeit vom Konkavitäts-Wert 140 bzw. 432 Bäume. Die Monophylie der Eurotatoria, Monogononta und Ploima wurde in allen Kladogrammen bestätigt. Alle Analysen schlugen auch eine Teilung von Ploima in zwei große Kladen vor. Eine der Kladen entspricht den Transversiramida, die andere enthält alle anderen Ploima-Taxa und weist Antrorsiramida als Monophylum aus. Gestützt auf die gefundenen Ergebnisse wird ein Szenarium für die Evolution der Kiefer vorgeschlagen. Die Analysen lassen vermuten, daß der Besitz eines Incus eine Synapomorphie der Gnathifera ist, während der eines Malleus eine Synapomorphie der Mikrognathozoa und derRotifera darstellt. Die ursprünglichen Kiefer waren vermutlich dem von Harringia (Asplanchnidae) ähnlich. [source]

Higher-level phylogenetics of linyphiid spiders (Araneae, Linyphiidae) based on morphological and molecular evidence

CLADISTICS, Issue 3 2009
Miquel A. Arnedo
This study infers the higher-level cladistic relationships of linyphiid spiders from five genes (mitochondrial CO1, 16S; nuclear 28S, 18S, histone H3) and morphological data. In total, the character matrix includes 47 taxa: 35 linyphiids representing the currently used subfamilies of Linyphiidae (Stemonyphantinae, Mynogleninae, Erigoninae, and Linyphiinae (Micronetini plus Linyphiini)) and 12 outgroup species representing nine araneoid families (Pimoidae, Theridiidae, Nesticidae, Synotaxidae, Cyatholipidae, Mysmenidae, Theridiosomatidae, Tetragnathidae, and Araneidae). The morphological characters include those used in recent studies of linyphiid phylogenetics, covering both genitalic and somatic morphology. Different sequence alignments and analytical methods produce different cladistic hypotheses. Lack of congruence among different analyses is, in part, due to the shifting placement of Labulla, Pityohyphantes, Notholepthyphantes, and Pocobletus. Almost all combined analyses agree on the monophyly of linyphioids, Pimoidae, Linyphiidae, Erigoninae, Mynogleninae, as well as Stemonyphantes as a basal lineage within Linyphiidae. Our results suggest independent origins of the desmitracheate tracheal system in micronetines and erigonines, and that erigonines were primitively haplotracheate. Cephalothoracic glandular specializations of erigonines and mynoglenines apparently evolved independently. Subocular sulci of mynoglenines and lateral sulci (e.g. Bathyphantes) evolved independently but glandular pores in the prosoma proliferated once. The contribution of different character partitions and their sensitivity to changes in traditional analytical parameters is explored and quantified. ,© The Willi Hennig Society 2009. [source]