Origin Of Genus Research Articles

Darwin’s dark matter: utter extinction

ABSTRACT Species that died without leaving descendants Darwin called ‘utterly extinct’. They far outnumber the ancestors of all living things, so they resemble the dark matter of modern cosmology, which far outweighs visible matter. He realized in 1837 that their absence is what creates the groups in a natural classification. In his Notebook B he combined the idea that species multiply with the idea that ancestors' relatives must mostly be extinct. The fossil Megatherium was utterly extinct. The iconic branching ‘I think’ diagram shows extinction causing the origin of genera by eliminating intermediate species. Darwin’s concept of taxonomic ranks, starting with the genus, was informed by his interaction with taxonomists. Based on his familiarity with demography, Darwin reasoned that the survival of transitional forms was unlikely, which helped him decide to focus at the species level. When drafting his theory in the 1840s, he left out these speculative ideas, but they emerged again in the 1850s when he realized his theory needed a cause for branches to diverge. His ecological answer worked at the species level, but his Principle of Divergence was unconvincing at higher taxonomic levels. In the Origin, Darwin repeatedly insisted on the importance of utter extinction.

Selective extinction at the end-Cretaceous and appearance of the modern Decapoda

Abstract Extinction and origination of genera and families of marine Decapoda at the end of the Cretaceous established the modern fauna. Podotrematous crabs suffered high extinction levels, whereas heterotrematous crabs experienced both extinction and radiation. Anomuran decapods exhibited high extinction levels at the generic but not family level. In general, family extinctions predominantly occurred among podotrematous and heterotrematous crabs, which also exhibit overall shorter family ranges. Possible refugia promoted survival of genera and families into the Paleocene, whereas habitation of the Western Interior Seaway ensured high levels of extinction. Areas proximal to the Chicxulub impact site experienced moderate levels of extinction. Habitat specialists preferentially survived the end-Cretaceous extinction in some clades. Heterotrematous crabs recovered rapidly in the Paleocene, especially in the siliciclastic environments of the Americas. Because decapod crustaceans are highly variable in morphology, habitat, and ecology, no one pattern of extinction and recovery can explain the end-Cretaceous decapod extinction event. Rather, a mosaic of responses in various decapod groups led to their differential survival.

Coffee Quality Profile of Jimma Zone, South Western Ethiopia

Coffee is one of the most important crops in Ethiopia and the world. Ethiopia is the genus's origin and the focal point of Arabica coffee. The objective of this research study was to assess the raw, cup and biochemical composition of Jimma coffee and it ssoil and environmental variables in the Jimma zone. The survey was conducted in seven major coffee growing woredas of Jimma zone. Seven kebeles were selected from each woreda and 5kg of red coffee cherries and soil samples were collected from each kebele. Red coffee cherries were processed using a dry or wet method of processing. Raw and cup quality was assessed. Determination of caffeine (CAF), trigonelline (TRG) and chlorogenic acids (CGA) were done using the HPLC. Soil analysis of total available nitrogen, cation exchange capacity (CEC), soil pH were done coffee shade type, coffee based major crops production, etc., were recorded. Over all quality of samples from the kebeles Atnago, Yeddo, Komma, Kuralebu, Debello, Wollensu, Kechotrtra, Dengajasole, Kellagebiss, Dorra Omofuntule, Qota, Tesosedecha, Choche, and Omoboqo kebeles and all Gomma, Manna, Gummay, Gera, and Shebe-Sombo woredas were very good and highly acceptable. Typical spicy flavor were obtained from Atnago, Yeddo and Omofuntale kebeles sample. While Kilokirkr samples have a fruity flavor, those taken from Gatogore and Gerenaso kebele have a winy flavor. Biochemicals compositions were ranged from 0.64 to 1.51; from 3.82 to 6.10 and from 0.81 to 1.16 percent of TRG, CGA and CAF respectively. Nito-sol and clay make up the soil. Soil analysis results revealed that pH, total N (%) and CEC ranges of 4.37 - 6.0, 0.12 -0.6, and 6.24-30.78, respectively. Coffee quality profile of Jimma zone showed good to very good quality with acceptable to highly acceptable in their overall quality standards, with a unique typicity of spicy, fruity and winy.

Tropical and Temperate: Evolutionary History of Páramo Flora

Biogeography of the tropical alpine flora of South and Central America, the paramo flora, has been studied by dividing genera into tropical, temperate, and cosmopolitan chorological flora elements. Published molecular phylogenies of paramo genera are reviewed to summarize knowledge about evolutionary history of the paramo flora and to assess congruence between chorological and phylogenetic approaches. Molecular phylogenies suggest that both the tropical and temperate regions have been important source areas for evolution of the paramo flora. Conclusions derived from chorological patterns regarding origin of genera in paramo are mostly supported by phylogenetic data. Nevertheless, in Chuquiraga, Halenia, Huperzia, and Perezia the chorological scenario is rejected, and in Chusquea-Neurolepis, Elaphoglossum, Gunnera, Halenia, Jamesonia-Eriosorus, and Lasiocephalus independent colonization events from one or several source areas are suggested. Tropical and temperate genera contributed equally to modern species richness of the paramo flora. Among temperate genera, the northern hemisphere genera gave rise to more species in paramo than did genera from the southern hemisphere. So far, no unequivocal evidence has been provided for migration of paramo genera to the temperate zones.

Distributional patterns and possible origin of leafhoppers (Homoptera, Cicadellidae)

The zoogeographical distribution of 42 cicadellid subfamilies and their assigned tribes and genera is compiled with distributional maps and proposed dispersal pathways of genera that are shared interzoogeographically. Possible origin of the subfamilies and tribes is proposed in an ancestral context from which the more modern extant groups evolved whereas origin of genera is in a more modern context. Notwithstanding their complex biogeography, the distributional data of the higher groups indicate that all of the cosmopolitan and near cosmopolitan subfamilies arose during early Cretaceous or possibly the late Jurassic period (140-116 m.y.a.) when continental drift was in its early stages. Nearly all of the New World and some Old World subfamilies are considered of more recent origin (late Cretaceous-Tertiary). Ninety percent of the known genera (2,126) are endemic to their respective zoogeographical region and subregion, thus indicating relatively high host specificity and low rate of dispersal. The majority (76%) of known extant genera are pantropical in origin, suggesting early or possible Gondwanaland origin of their ancestors. Dispersal pathways of genera shared by more than one zoogeographical region were generally south to north (Neotropical/Nearctic, Oriental/Palaearctic) or west to east (Palaearctic/Nearctic, Oriental/Australian), from regions of high diversity to regions of low diversity and from warmer climates to cooler climates. The most diverse and richest leafhopper fauna are present in the Neotropical and Ethiopian regions although taxal affinities between them are poorest. The most depauperate fauna are in the Nearctic region and in Australia, reflecting the impact of isolating and ecological factors on distribution and radiation. Ecological barriers were more evident between the Ethiopian and Oriental fauna than between any other zoogeographical combination. Taxal affinities appeared to be correlated with close continental proximities. Vicariance (physical) was the principal event that appealed to explain the distribution of many subfamilies and tribes whereas dispersal accounted for distribution of the majority of interzoogeographical genera.

Chromosome Number Variation in the Myrtaceae and Its Taxonomic Implications

New chromosome number determinations are reported for some 150 Western Australian species of the Myrtaceae. These include the lowest number (n = 5) so far recorded in the family and several newly recorded descending dysploid series. Dysploid chromosome numbers are far less common than the base chromosome number of n = 11 but parallel dysploid series have occurred in many groups and some have played a role in the origin of genera. Polyploidy has been successful at the intraspecific and interspecific levels but is of limited evolutionary potential. The cytoevolutionary trends in the Myrtaceae are examined in relation to taxonomic problems within the family and in relation to cytoevolution in the woody Australian flora as a whole. Smith- White's suggestion that a more natural generic classification in the Chamelauciinae could be obtained by grouping species with the same base chromosome numbers is found to be untenable.

Chronospecies' longevities, the origin of genera, and the punctuational model of evolution

Taxonomists working with late Cenozoic faunas tend to view living species as starting points for the evaluation of chronospecies (i.e., segments of evolutionary lineages subjectively designated as species) that extend backward in time from the Recent. This practice makes it possible to construct a survivorship curve for late Cenozoic chronospecies by evaluating all fossil lineages believed to have survived to the present day. A survivorship curve is produced by plotting the fraction of these lineages existing at any time that have not undergone enough phyletic evolution that their extant representatives are assigned to new species. This kind of surviviorship curve has been plotted for chronospecies of mammals using the beginning of the Würm, rather than the Recent, as an endpoint in order to avoid the effects of the Würm and post-Würm mass extinction. The survivorship curve reveals that all but a small fraction of established chronospecies have long durations relative to intervals of time during which distinctive higher taxa have arisen. Phyletic turnover of species has been remarkably slow. Most net evolutionary change must have been associated with saltational speciation. Even the large majority of genera must have arisen rapidly by one or more divergent speciation events. Estimates of rates of extinction suggest that the bottleneck effect, in which constriction of a lineage is followed by re-expansion as a distinct species, cannot be a major source of evolutionary change. These conclusions, based on the evaluation of mammalian phylogeny, seem also to apply to other taxa of animals, supporting the punctuational model of evolution. The long durations of hominid species imply that the evolution of humans, like that of other mammals, conforms to this model.

BIOSYSTEMATICS: AN AVENUE TOWARDS UNDERSTANDING EVOLUTION

SummaryThe distinctive feature of biosystematics is considered to be its emphasis upon the processes responsible for differences between taxa, rather than the differences themselves. A progress report on our knowledge of these processes can be summarized as follows. With respect to divergent adaptations to different environments, we understand well their genetic basis, and are now ready to analyze them in terms of gene action in development and metabolism. A valuable new tool for this purpose is the study of isozyme differences by gel electrophoresis. With respect to the origin of barriers of reproductive isolation that play a large role in the origin of species, we need further tests of the hypothesis that chromosomal repatterning is established through the action of natural selection, because of the different adaptive values of differing clusters of linked genes. A new hypothesis that also needs testing is that hybrid inviability or sterility may be produced by disharmonious interaction between genes that code for different subunits of the same multimer enzyme. Valuable studies of hybridization are directed toward determining the importance of transgressive segregation in the origin of new characters. Our understanding of differences in karyotypes must now be based upon the demonstrated fact that even diploid organisms contain large stretches of chromosomal DNA that is duplicated in tandem fashion. With respect to major trends of evolution, several examples are cited which indicate that the origin of genera and other higher categories can take place through an extension of the processes mentioned earlier. An important fact in this connection is that many natural populations of plants contain hidden genetic variation with respect to such basic characteristics as the number of parts of a flower.

The Origin of Genera *

ALTHOUGH it is now two years since the publication of Prof. Cope's “fragmentary essay,”as he modestly terms it, bearing the above title, it may not be out of place, in the present stage of the theory of Evolution, to give our readers some idea of its scope. It ought to be in the possession of every naturalist. Although already so condensed that anything like an analysis of it is impossible, the following tabular sketch may serve to give our readers an idea of the mode in which the Origin of Genera is treated:—