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Parsimonious Hypothesis (parsimonious + hypothesis)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Phylogeny of the sea spiders (Arthropoda, Pycnogonida) based on direct optimization of six loci and morphology

CLADISTICS, Issue 3 2007
Claudia P. Arango
Higher-level phylogenetics of Pycnogonida has been discussed for many decades but scarcely studied from a cladistic perspective. Traditional taxonomic classifications are yet to be tested and affinities among families and genera are not well understood. Pycnogonida includes more than 1300 species described, but no systematic revisions at any level are available. Previous attempts to propose a phylogeny of the sea spiders were limited in characters and taxon sampling, therefore not allowing a robust test of relationships among lineages. Herein, we present the first comprehensive phylogenetic analysis of the Pycnogonida based on a total evidence approach and Direct Optimization. Sixty-three pycnogonid species representing all families including fossil taxa were included. For most of the extant taxa more than 6 kb of nuclear and mitochondrial DNA and 78 morphological characters were scored. The most parsimonious hypotheses obtained in equally weighted total evidence analyses show the two most diverse families Ammotheidae and Callipallenidae to be non-monophyletic. Austrodecidae + Colossendeidae + Pycnogonidae are in the basal most clade, these are morphologically diverse groups of species mostly found in cold waters. The raising of the family Pallenopsidae is supported, while Eurycyde and Ascorhynchus are definitely separated from Ammotheidae. The four fossil taxa are grouped within living Pycnogonida, instead of being an early derived clade. This phylogeny represents a solid framework to work towards the understanding of pycnogonid systematics, providing a data set and a testable hypothesis that indicate those clades that need severe testing, especially some of the deep nodes of the pycnogonid tree and the relationships of ammotheid and callipallenid forms. The inclusion of more rare taxa and additional sources of evidence are necessary for a phylogenetic classification of the Pycnogonida. © The Willi Hennig Society 2006. [source]

Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic Region

DIVERSITY AND DISTRIBUTIONS, Issue 3 2002
R. M. Cowling
Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source]

How much can cladistics tell us about early hominid relationships?

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2004
John Hawks
Abstract Although cladistic analysis has been used to compare hypotheses of relationships among early hominids, the outcomes of different studies have depended entirely on the assumptions made by different investigators. Problems include the close genetic relationship of early hominid taxa, small fossil sample sizes, possible correlations among characters, and a lack of understanding about the evolutionary factors affecting characters. This study investigates the interaction of some of these problems affecting early hominid phylogenetics. Monte Carlo simulations of character state evolution in closely related taxa demonstrate that the sample sizes and close genetic relationships of early hominids do not permit cladistic analyses to obtain unequivocal results. Even with unrealistically good assumptions about the evolutionary dynamics affecting characters, the probability of the most parsimonious hypothesis being true is unacceptably small. In the face of these problems, even phylogenetic statements that are supported by a strong consensus of cladistic studies may nevertheless be in error, and such errors are likely to confound the placement of new specimens and taxa. Advancement in our knowledge of hominid phylogeny can depend only on a fuller understanding of the natural history and evolutionary dynamics of traits. Am J Phys Anthropol, 2004. © 2004 Wiley-Liss, Inc. [source]

Distinguishing "or" from "and" and the case for historical identification

CLADISTICS, Issue 6 2002
Arnold G Kluge
The adequacy of a probabilistic interpretation must be judged according to the nature of the event, or thing, being inferred. For example, conditional (frequency) probability is not admissible in the inference of phylogeny, because basic statements of common ancestry do not fulfill the requirements of the relations specified by the probability calculus. The probabilities of the situation peculiar to the time and place of origin of species are unique. Moreover, according to evolutionary theory, an event of species diversification is necessarily unique, because species are parts of a replicator continuum,species arise from ancestral species. Also, these probabilities cannot be ascertained, because the relevant situation cannot be repeated,it is unique. Finally, the applicability of conditional (frequency) probability is denied, because events of common ancestry have already occurred,there is nothing to predict. However, hypotheses of species relationships can be identified objectively according to the degree to which they have survived simultaneous testing with critical evidence, not with generally confirming evidence. The most parsimonious hypothesis of species relationships represents the least disconfirmed, best supported, proposition among the alternatives being compared. That hypothesis does not, however, deserve any special epistemological status beyond serving as the focus of the next round of testing. [source]