Biomedical subjects

Peter J Wagner

Publications and source records attributed to Peter J Wagner.

7 recordsLinked to original sources

PubMed2007

The effects of taxonomic standardization on sampling-standardized estimates of historical diversity.

Occurrence-based databases such as the Palaeobiology database (PBDB) provide means of accommodating the heterogeneities of the fossil record when evaluating historical diversity patterns. Although palaeontologists have given ample attention to the effects of taxonomic practice on diversity patterns derived from synoptic databases (those using first and last appearances of taxa), workers have not examined the effects of taxonomic error on occurrence-based diversity studies. Here, we contrast diversity patterns and diversity dynamics between raw data and taxonomically vetted data in the PBDB to evaluate the effects of taxonomic errors. We examine three groups: Palaeozoic gastropods, Jurassic bivalves and Cenozoic bivalves. We contrast genus-level diversity patterns based on: (i) all occurrences assigned to a genus (i.e. both species records and records identifying only the genus), (ii) only occurrences for which a species is identified, and (iii) only occurrences for which a species is identified, but after vetting the genus to which the species is assigned. Extensive generic reassignments elevate origination and extinction rates within Palaeozoic gastropods and origination rates within Cenozoic bivalves. However, vetting increases generic richness markedly only for Cenozoic bivalves, and even then the increase is less than 10%. Moreover, the patterns of standing generic richness are highly similar under all three data treatments. Unless our results are unusual, taxonomic standardization can elevate diversity dynamics in some cases, but it will not greatly change inferred richness over time.

Animals↗

PubMed2006

Abundance distributions imply elevated complexity of post-Paleozoic marine ecosystems.

Likelihood analyses of 1176 fossil assemblages of marine organisms from Phanerozoic (i.e., Cambrian to Recent) assemblages indicate a shift in typical relative-abundance distributions after the Paleozoic. Ecological theory associated with these abundance distributions implies that complex ecosystems are far more common among Meso-Cenozoic assemblages than among the Paleozoic assemblages that preceded them. This transition coincides not with any major change in the way fossils are preserved or collected but with a shift from communities dominated by sessile epifaunal suspension feeders to communities with elevated diversities of mobile and infaunal taxa. This suggests that the end-Permian extinction permanently altered prevailing marine ecosystem structure and precipitated high levels of ecological complexity and alpha diversity in the Meso-Cenozoic.

Animals↗

PubMed2006

Evolutionary patterns in early tetrapods. II. Differing constraints on available character space among clades.

Radiations of large clades often accompany rapid morphological diversification. Evolutionary biologists debate the impact of external restrictions imposed by ecology, and intrinsic constraints imposed by development and genetics, on the rate at which morphological innovations are gained. These issues are particularly interesting for groups such as tetrapods, which evolved novel body plans relative to their piscine ancestors and which also invaded new ecosystems following terrestrialization. Prior studies have addressed these issues by looking at either ranges of morphological variation or rates of character change. Here, we address a related but distinct issue: the numbers of characters that freely vary within a clade. We modify techniques similar to those used by ecologists to infer species richnesses to estimate the number of potentially varying characters given the distributions of changes implied by a model phylogeny. Our results suggest both increasing constraints/restrictions and episodes of 'character release' (i.e. increasing the number of potentially varying characters). In particular, we show that stem lissamphibians had a restricted character space relative to that of stem amniotes, and that stem amniotes both had restrictions on some parts of character space but also invaded new character space that had been unavailable to stem tetrapods.

Amphibians↗

PubMed2006

Evolutionary patterns in early tetrapods. I. Rapid initial diversification followed by decrease in rates of character change.

Although numerous studies have examined morphological diversification during major radiations of marine taxa, much less attention has been paid to terrestrial radiations. Here, we examine rates of character change over phylogeny and over time for Palaeozoic limbed tetrapods. Palaeozoic tetrapods show significant decreases in rates of character change whether the rate is measured per sampled cladistic branch or per million years along phylogeny. Given changes per branch, rates decrease significantly from the Devonian through the Pennsylvanian, but not from the Pennsylvanian through the Permian. Given changes per million years, rates decrease significantly over each boundary, although the decrease is least significant over the Pennsylvanian-Permian boundary. Decreasing rates per million years through the Permian might be an artefact of the method being able to ascribe longer durations to Permian branches than to Carboniferous ones; however, it is difficult to ascribe the general pattern of decreasing rates of change over time to sampling biases or methodological biases. Thus, the results implicate biological explanations for this pattern.

Amphibians↗

PubMed2006

Statistical independence of escalatory ecological trends in Phanerozoic marine invertebrates.

Ecological interactions, such as predation and bioturbation, are thought to be fundamental determinants of macroevolutionary trends. A data set containing global occurrences of Phanerozoic fossils of benthic marine invertebrates shows escalatory trends in the relative frequency of ecological groups, such as carnivores and noncarnivorous infaunal or mobile organisms. Associations between these trends are either statistically insignificant or interpretable as preservational effects. Thus, there is no evidence that escalation drives macroecological trends at global and million-year time scales. We also find that taxonomic richness and occurrence data are cross-correlated, which justifies the traditional use of one as a proxy of the other.

Animals↗

PubMed2006

Electronic effects of ring substituents on triplet benzylic biradicals.

[reaction: see text] UV irradiation of alpha-(o-alkylphenyl)acetophenones with a methoxy or cyano substituent para to the o-alkyl group of the alpha-aryl ring has revealed that a methoxy group slightly increases the stereoselectivity but not the quantum yield of indanol formation, whereas a cyano group greatly lowers both diastereoselectivity and quantum efficiency, confirming the likelihood that hydrogen-bonding of the hydroxy group to the alpha-phenyl ring plays an important role in the cyclization of the photogenerated triplet 1,5-biradical intermediates.

Journal Article↗

PubMed2002

Light-induced decarboxylation of (o-acylphenyl)acetic acids.

Near-UV irradiation of both o-acetylphenyl- and o-benzoylphenylacetic acids in benzene solution results in their efficient decarboxylation. Their meta and para isomers do not undergo this process. The O-deuterated acids yield deuterated o-acyltoluene products, suggesting the possibility of an intramolecular proton transfer step in the decarboxylation process, although intermolecular deuteration would achieve the same result. The corresponding esters and amides are essentially photoinert and, like the acids, do not undergo the benzocyclobutenol formation expected of o-alkylphenyl ketones.

Journal Article↗