Individual Characters (individual + character)

Distribution by Scientific Domains

Selected Abstracts

Metamorphosis of cinctoblastula larvae (Homoscleromorpha, porifera)

Alexander V. Ereskovsky
Abstract The metamorphosis of the cinctoblastula of Homoscleromorpha is studied in five species belonging to three genera. The different steps of metamorphosis are similar in all species. The metamorphosis occurs by the invagination and involution of either the anterior epithelium or the posterior epithelium of the larva. During metamorphosis, morphogenetic polymorphism was observed, which has an individual character and does not depend on either external or species specific factors. In the rhagon, the development of the aquiferous system occurs only by epithelial morphogenesis and subsequent differentiation of cells. Mesohylar cells derive from flagellated cells after ingression. The formation of pinacoderm and choanoderm occurs by the differentiation of the larval flagellated epithelium. This is possibly due to the conservation of cell junctions in the external surface of the larval flagellated cells and of the basement membrane in their internal surface. The main difference in homoscleromorph metamorphosis compared with Demospongiae is the persistence of the flagellated epithelium throughout this process and even in the adult since exo- and endopinacoderm remain flagellated. The antero-posterior axis of the larva corresponds to the baso-apical axis of the adult in Homoscleromorpha. J. Morphol., 2007. 2007 Wiley-Liss, Inc. [source]


EVOLUTION, Issue 7 2010
Douglas J. Futuyma
One of the most important shifts in evolutionary biology in the past 50 years is an increased recognition of sluggish evolution and failures to adapt, which seem paradoxical in view of abundant genetic variation and many instances of rapid local adaptation. I review hypotheses of evolutionary constraint (or restraint), and suggest that although constraints on individual characters or character complexes may often reside in the structure or paucity of genetic variation, organism-wide stasis, as described by paleontologists, might better be explained by a hypothesis of ephemeral divergence, according to which the spatial or temporal divergence of populations is often short-lived because of interbreeding with nondivergent populations. Among the many consequences of acknowledging evolutionary constraints, community ecology is being transformed as it takes into account phylogenetic niche conservatism and the strong imprint of deep history. [source]


EVOLUTION, Issue 6 2000
Kevin E. Omland
Abstract. Several empirical studies suggest that sexually selected characters, including bird plumage, may evolve rapidly and show high levels of convergence and other forms of homoplasy. However, the processes that might generate such convergence have not been explored theoretically. Furthermore, no studies have rigorously addressed this issue using a robust phylogeny and a large number of signal characters. We scored the appearance of 44 adult male plumage characters that varied across New World orioles (Icterus). We mapped the plumage characters onto a molecular phylogeny based on two mitochondrial genes. Reconstructing the evolution of these characters revealed evidence of convergence or reversal in 42 of the 44 plumage characters. No plumage character states are restricted to any groups of species higher than superspecies in the oriole phylogeny. The high frequency of convergence and reversal is reflected in the low overall retention index (RI = 0.66) and the low overall consistency index (CI = 0.28). We found similar results when we mapped plumage changes onto a total evidence tree. Our findings reveal that plumage patterns and colors are highly labile between species of orioles, but highly conserved within the oriole genus. Furthermore, there are at least two overall plumage types that have convergently evolved repeatedly in the three oriole clades. This overall convergence leads to significant conflict between the molecular and plumage data. It is not clear what evolutionary processes lead to this homoplasy in individual characters or convergence in overall pattern. However, evolutionary constraints such as developmental limitations and genetic correlations between characters are likely to play a role. Our results are consistent with the belief that avian plumage and other sexually selected characters may evolve rapidly and may exhibit high homoplasy. The overall convergence in oriole plumage patterns is an interesting evolutionary phenomenon, but it cautions against heavy reliance on plumage characters for constructing phylogenies. [source]

Risk as a Window to Agency: A Case Study of Three Decorators

Nancy H. Blossom M.A.
ABSTRACT This paper explores the idea of "risk" by examining the role of three women in interior design in the twentieth century (Elsie de Wolfe, 1865,1950; Dorothy Draper, 1888,1969; and Sister Parish, 1929,1994). Women's roles as arbiters of taste were consistent with the social construction of the female gender at the turn of the century; that these roles involved risk,the perception of possible loss or injury,is, for the most part, overlooked by social historians. Our theoretical framework is built upon three keywords from the vocabularies of postmodern social history and women's history: discourse, experience, and agency. These three terms represent the important recognition that the collective understanding of history is not static, but is dependent on the social constructs of the period, as well as (1) how individuals experienced, interpreted, and acted within these constructs and (2) how historians understand and interpret the individual actions in the context of the same constructs. These concepts suggest that individual characters have agency (i.e., power or choice) in framing or reframing an event, based on their unique view of the world. It is through agency that we explore unique qualities of de Wolfe, Draper, and Parish. The stories of de Wolfe, Draper, and Parish demonstrate that risk of traditional values, risk of public persona, and risk of financial security all influenced the ways that they navigated the social and economic circumstances that surrounded them. Each risk, whether imposed on or undertaken by our protagonists, was a seed of change that ultimately affected the social and professional construct of the field of interior design. [source]

Relationship of cranial robusticity to cranial form, geography and climate in Homo sapiens

Karen L. Baab
Abstract Variation in cranial robusticity among modern human populations is widely acknowledged but not well-understood. While the use of "robust" cranial traits in hominin systematics and phylogeny suggests that these characters are strongly heritable, this hypothesis has not been tested. Alternatively, cranial robusticity may be a response to differences in diet/mastication or it may be an adaptation to cold, harsh environments. This study quantifies the distribution of cranial robusticity in 14 geographically widespread human populations, and correlates this variation with climatic variables, neutral genetic distances, cranial size, and cranial shape. With the exception of the occipital torus region, all traits were positively correlated with each other, suggesting that they should not be treated as individual characters. While males are more robust than females within each of the populations, among the independent variables (cranial shape, size, climate, and neutral genetic distances), only shape is significantly correlated with inter-population differences in robusticity. Two-block partial least-squares analysis was used to explore the relationship between cranial shape (captured by three-dimensional landmark data) and robusticity across individuals. Weak support was found for the hypothesis that robusticity was related to mastication as the shape associated with greater robusticity was similar to that described for groups that ate harder-to-process diets. Specifically, crania with more prognathic faces, expanded glabellar and occipital regions, and (slightly) longer skulls were more robust than those with rounder vaults and more orthognathic faces. However, groups with more mechanically demanding diets (hunter-gatherers) were not always more robust than groups practicing some form of agriculture. Am J Phys Anthropol, 2010. 2009 Wiley-Liss, Inc. [source]

Evolutionarily independent genes and genomes and insights on genetic structure, evolution and conservation of the collis group of darters

K. J. Oswald
Abstract Comparing variation across evolutionarily independent characters, notably nuclear and mitochondrial genes, yields a more robust estimate of diversification than is generally recovered from individual characters. Patterns of variation across multiple molecular markers from the mitochondrial (16SrRNA, cytochrome b) and nuclear (ldhA6 and aldB) genomes were examined from six populations of Etheostoma collis and two populations of Etheostoma saludae, species aligned in the collis groups. Phylogenetic analyses revealed that sequence variation among individuals from the Roanoke, Tar and Neuse Rivers and the Catawba and Pee Dee Rivers, respectively, form highly supported, deeply divergent clades. Relationships of alleles sampled from Saluda River E. saludae and Cape Fear River E. collis to these lineages are unresolved, but all groups are reciprocally monophyletic for both nuclear and mtDNA loci. Phylogenetic analyses suggest that historical factors have had a strong influence on the distribution of genetic variation among populations. Genetic variation within the collis group is consistent with all previously proposed taxonomic hypotheses for the collis group, providing no taxonomic insights. From a conservation standpoint, each population of the collis group is an ESU, thereby warranting a drainage-specific management strategy. [source]