Home About us Contact
|
Home About us Contact | ||
|
|
||
Taxon
Kinds of Taxon Terms modified by Taxon Selected AbstractsThe concept of the taxon cycle in biogeographyGLOBAL ECOLOGY, Issue 5 2002Robert E. Ricklefs Abstract Taxon cycles are sequential phases of expansion and contraction of the ranges of species, associated generally with shifts in ecological distribution. The important contribution of the taxon cycle to biogeographical analysis is its emphasis on evolutionary and ecological interactions among colonizing and resident species, which influence their extinction dynamics and establish patterns of geographical distribution. Taxon cycles were inferred originally from the distribution of species across island archipelagos, where a correlation was noted between gaps in island occupancy and the degree of phenotypic differentiation. This pattern implied that phases of colonization were followed by range contraction, while endemic Antillean species that were undifferentiated between islands suggested secondary expansion and the beginning of a new cycle. This interpretation was met with scepticism, but reconstruction of phylogenetic relationships from gene sequences has now permitted us to characterize taxon cycles in Lesser Antillean birds. The relative timing of phases of the cycle can be deduced from genetic divergence between island populations. We have found that taxon cycles have periods in the order of 106 years and that cycles in different lineages occur independently of each other and independently of Pleistocene climate cycles. Individual island populations may persist for several millions of years on the larger islands of the Lesser Antilles; occasional expansion phases lead to the replacement of island populations that have disappeared, thus reducing the archipelago-wide rate of extinction to nil. What drives taxon cycles is unknown, but we speculate that they may be caused by co-evolution with enemy populations, and a probable mechanism would involve infrequent mutations influencing parasite virulence and avian host disease resistance. Taxon cycles undoubtedly occur on continents, but the geographical configuration of island archipelagos reveals more clearly their presence and invites their study. [source] Phylogeny of Dicranophoridae (Rotifera: Monogononta) , a maximum parsimony analysis based on morphological charactersJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 1 2009O. Riemann Abstract This study presents the first phylogenetic analysis of Dicranophoridae (Rotifera: Monogononta), a species rich rotifer family of about 230 species currently recognized. It is based on a maximum parsimony analysis including 77 selected ingroup and three outgroup taxa and a total of 59 phylogenetically informative morphological characters. Character coding is based on personal investigation of material collected by the authors and an extensive survey of the literature. Apart from covering general body organization, character coding primarily relies on scanning electron microscopic preparations of the mastax jaw elements. Our study suggests monophyly of Dicranophoridae with a clade of Dicranophorus and Dorria as the sister taxon of all other dicranophorid species. Monophyly of Encentrum, the most species rich genus within Dicranophoridae, cannot be demonstrated. Within Dicranophoridae our study identifies the monophyletic taxa Caudosubbasifenestrata, Intramalleata, Praeuncinata and Proventriculata, each based on unambiguous character transformations evolved in their stem lineages. However, resolution within Praeuncinata and Proventriculata is very limited. Although some terminal clades within Praeuncinata and Proventriculata are recognized, basal splits remain obscure. Probably, other characters such as DNA sequence data are needed to further our understanding of phylogenetic relationships within these poorly resolved taxa. Zusammenfassung Die hier vorgelegte Studie stellt die erste phylogenetische Analyse des Taxons Dicranophoridae (Rotifera: Monogononta) dar, einer artenreichen Familie der Rotiferen mit zurzeit etwa 230 validen Arten. Die resultierenden phylogenetischen Verwandtschaftsbeziehungen fußen auf einer Maximum Parsimonie Analyse mit 77 ausgewählten Vertretern der Innen, und 3 Vertretern der Außengruppe bei insgesamt 59 Parsimonie,informativen Merkmalen. Die Kodierung der Merkmale basiert einerseits auf Material, das von den Autoren selbst gesammelt und bestimmt wurde und andererseits auf einem ausgedehnten Studium der relevanten Literatur. Neben der Erfassung von Merkmalen zur allgemeinen Körperorganisation stützt sich die Merkmalskodierung vor allem auf rasterelektronenmikroskopische Präparationen der Hartelemente des Mastax. Das Ergebnis der Analyse stützt die Monophylie der Dicranophoridae. Innerhalb der Dicranophoridae stellt ein monophyletisches Taxon, das die Gattungen Dicranophorus und Dorria umfasst, die Schwestergruppe aller übrigen Dicranophoridae dar. Die bei weitem artenreichste Gattung Encentrum lässt sich nicht als Monophylum begründen. Als monophyletische Teilgruppen innerhalb der Dicranophoridae identifiziert unsere Analyse die Taxa Caudosubbasifenestrata, Intramalleata, Praeuncinata und Proventriculata, die jeweils durch mindestens eine unzweideutige Merkmalstransformation in ihren Stammlinien begründet werden. Innerhalb der Taxa Praeuncinata und Proventriculata bietet unsere Analyse nur sehr begrenzte Auflösung. Obgleich sich einzelne Teilgruppen über unzweideutige Merkmalstransformationen als Monophyla begründen lassen, fehlen Merkmale für die Auflösung der basalen Verzweigungen innerhalb der Praeuncinata und Proventriculata. Es ist zu erwarten, dass andere Merkmalssysteme, wie zum Beispiel DNA Sequenzdaten, bei der Aufklärung der Verwandtschaftsbeziehungen innerhalb dieser Teilgruppen Klärung erbringen. [source] Phylogenetic analysis of the Brachyura (Crustacea, Decapoda) based on characters of the foregut with establishment of a new taxonJOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 1 2007A. Brösing Abstract The Brachyura, within the decapod crustaceans, is one of the most species-rich taxa with up to 10 000 species. However, its phylogenetic history, evolution and fossil record remain subjects of controversy. In our study, we examined the phylogenetic relationships of the Brachyura based on morphological characters of the foregut. The cladistic analysis supports a monophyletic Brachyura including the Dromiidae and Raninidae. A clade comprising Dromiidae and Dynomenidae forms the most basal assemblage within the Brachyura, followed by the Homolidae and Latreilliidae. As a result, neither Podotremata nor Archaeobrachyura form a clade. In contrast, foregut data suggest that the classical taxon Oxystomata, comprising Calappidae, Parthenopidae, Dorippidae, Leucosiidae, Cymonomidae and Raninidae, is monophyletic. This makes the Heterotremata paraphyletic or polyphyletic. A newly established taxon, Neobrachyura, embraces some representatives of the Heterotremata and the monophyletic Thoracotremata. Zusammenfassung Das Taxon Brachyura stellt innerhalb der decapoden Krebse eines der artenreichsten Taxa mit bis zu 10000 Arten dar. Seine Stammesgeschichte, Evolution und Fossilbericht ist Thema vieler Diskussionen. In unserer Studie wurden die phylogenetischen Verwandtschaftsbeziehungen der Brachyura auf der Grundlage morphologischer Merkmale des Vorderdarmes untersucht. Die kladistische Analyse unterstützt ein monophyletisches Taxon Brachyura, einschließlich der Taxa Dromiidae und Raninidae. Ein Taxon, welches die Taxa Dromiidae und Dynomenidae enthält, stellt die basalste Gruppierung innerhalb der Brachyura dar, gefolgt von den Taxa Homolidae und Latreilliidae. Weder das Taxon ,Podotremata, noch ein Taxon ,Archaeobrachyura, stellen eine natürliche Einheit im Sinne eines Monophylums dar. Die Merkmale der Vorderdarmstrukturen deuten weiterhin darauf hin, dass das klassische Taxon Oxystomata mit den Taxa Calappidae, Parthenopidae, Dorippidae, Leucosiidae, Cymonomidae und Raninidae ein Monophylum darstellt. Dies hat ein para- oder polyphyletisches Taxon Heterotremata zur Folge. Ein in dieser Studie neu etabliertes Taxon Neobrachyura vereint sowohl Vertreter der ursprünglichen Heterotremata als auch der Thoracotremata. [source] Beyond Species Richness: Community Similarity as a Measure of Cross-Taxon Congruence for Coarse-Filter ConservationCONSERVATION BIOLOGY, Issue 1 2004JEFFREY C. SU Species richness is only one measure of species diversity, however, and recent studies suggest that investigations of cross-taxon congruence should consider a broader range of assessment techniques. The cross-taxon congruence of community similarity between sites among taxa has rarely been examined and may be the most relevant measure of species diversity in the context of coarse-filter conservation strategies. We examined cross-taxon congruence patterns of species richness and community similarity (Bray-Curtis similarity) among birds, butterflies, and vascular plants in montane meadow habitats in the Greater Yellowstone Ecosystem. Although patterns of species richness (Spearman rank correlation) varied between taxa, we consistently found a positive correlation in community similarity (Mantel test) between all pair-wise comparisons of the three taxa (e.g., sites with similar bird communities also had similar butterfly communities). We suggest that the success of a surrogate taxon depends on the technique used to assess surrogacy and the specific approach to conservation planning. In the context of coarse-filter conservation, measures of community similarity may be more appropriate than measures of species richness. Furthermore, the cross-taxon congruency of community similarity in our study suggests that coarse-filter conservation may be tenable in montane meadow communities. Resumen:,El uso de un taxón sustituto en la planeación de la conservación se ha vuelto cuestionable porque información reciente sugiere que la correlación de riqueza de especies entre pares de taxones es altamente variable taxonómica y geográficamente. Sin embargo, la riqueza de especies es solo una medida de la diversidad de especies, y estudios recientes sugieren que las investigaciones de congruencia trans-taxón debieran considerar una mayor variedad de técnicas de evaluación. La congruencia trans-taxón de la similitud de comunidades entre sitios entre taxones rara vez se ha examinado y puede ser la medida de diversidad de especies más relevante en el contexto de las estrategias de conservación de grano grueso. Examinamos patrones de congruencia trans-taxón de riqueza de especies y similitud de comunidades (similitud Bray-Curtis) en aves, mariposas y plantas vasculares en hábitats de praderas montanas en el Ecosistema Greater Yellowstone. Aunque los patrones de riqueza de especies (correlación Spearman de rangos) variaron entre especies, encontramos consistentemente una correlación positiva en la similitud de la comunidad (prueba de Mantel) entre todas las comparaciones de pares de los tres taxones (es decir, los sitios con comunidades similares de aves también tenían comunidades similares de mariposas). Sugerimos que el éxito de un taxón sustituto depende de la técnica utilizada para evaluar la sustitución y el abordaje específico de la planeación de conservación. En el contexto de la conservación de grano grueso, pueden ser más apropiadas las medidas de similitud de comunidades que las medidas de riqueza de especies. Más aun, la congruencia trans-taxón de similitud de comunidades en nuestro estudio sugiere que la conservación de grano grueso puede ser justificable en comunidades de praderas montanas. [source] Performance of Sub-Saharan Vertebrates as Indicator Groups for Identifying Priority Areas for ConservationCONSERVATION BIOLOGY, Issue 1 2003Joslin L. Moore Often, these sets of important areas, referred to as priority sets, have been identified through use of data on a single taxon (e.g., birds), which is assumed to act as an indicator for all biodiversity. Using a database of the distributions of 3882 vertebrate species in sub-Saharan Africa, we conducted one of very few large-scale tests of this assumption. We used six potential indicator groups,birds, mammals, amphibians, snakes, threatened birds, and threatened mammals,to find priority sets of 200 areas that best represent the species in that group. Priority sets of grid cells designed to maximize representation of a single indicator group captured 83,93% of species in the other groups. This high degree of representation is consistent with observed high levels of overlap in the patterns of distribution of species in different groups. Those species of highest conservation interest were more poorly represented, however, with only 75,88% of other groups' threatened species and 63,76% of other groups' narrow-range species represented in the priority sets. We conclude that existing priority sets based on indicator groups provide a pragmatic basis for the immediate assessment of priorities for conservation at a continental scale. However, complete and efficient representation,especially of narrow-range species,will not be achieved through indicator groups alone. Therefore, priority-setting procedures must remain flexible so that new areas important for other taxa can be incorporated as data become available. Resumen: La meta de la identificación de prioridades globales y continentales de conservación es la identificación de áreas particularmente valiosas para la conservación en las cuales enfocar esfuerzos más detallados. A menudo, estos conjuntos de áreas importantes (referidas como conjuntos prioritarios) han sido identificados utilizando datos de un solo taxón (e. g. aves), el cual se supone que actúa como indicador de toda la biodiversidad. Utilizando una base de datos de la distribución de 3882 especies de vertebrados en África sub-Sahara, realizamos una de las pocas pruebas a gran escala de este supuesto. Utilizamos seis grupos de indicadores potenciales (aves, mamíferos, anfibios, serpientes, aves amenazadas y mamíferos amenazados ) para encontrar conjuntos prioritarios de 200 áreas que mejor representan las especies de ese grupo. Conjuntos prioritarios de celdas matriciales diseñadas para maximizar la representatividad de un grupo indicador capturaron 83,93% de las especies de los otros grupos. Este alto grado de representatividad es consistente con los altos niveles de superposición observados en los patrones de distribución de especies en los diferentes grupos. Sin embargo, las especies de mayor interés para la conservación estaban poco representadas, con solo 75,88% de las especies amenazadas de otros grupos y 63,76% de las especies de distribución restringida de otros grupos representados en los conjuntos prioritarios. Concluimos que los conjuntos prioritarios existentes, basados en grupos indicadores, proporcionan una base pragmática para la evaluación inmediata de las prioridades de conservación a escala continental. Sin embargo, no se logrará la representación completa y eficiente,especialmente de especies de distribución restringida,solo con grupos indicadores. Por lo tanto, los procedimientos de definición de prioridades deben permanecer flexibles para que se puedan incorporar nuevas áreas importantes para otros taxones a medida que se obtienen los datos. [source] Phylogenetic Reanalysis of the Saudi Gazelle and Its Implications for ConservationCONSERVATION BIOLOGY, Issue 4 2001Robert L. Hammond The Saudi gazelle ( Gazella saudiya) was endemic to the Arabian peninsula but is now considered extinct in the wild and is potentially a candidate for captive breeding and reintroduction. Using 375 base pairs of mitochondrial DNA (mtDNA) cytochrome b gene derived from museum samples collected from the wild prior to the presumed extinction of this species, we show that G. saudiya is the sister taxon of the African dorcas gazelle ( G. dorcas). Reciprocal monophyly of G. saudiya mtDNA haplotypes with G. dorcas, coupled with morphological distinctiveness, suggests that it is an evolutionarily significant unit. These data indicate that captive populations identified previously as potential sources of G. saudiya for captive breeding appear incorrectly designated and are irrelevant to the conservation of G. saudiya. The polymerase chain reaction,restriction fragment length polymorphism ( PCR-RFLP) analysis of several private collections of living gazelles in Saudi Arabia provides no evidence for the survival of G. saudiya. We recommend that field surveys be undertaken to establish whether G. saudiya is indeed extinct in the wild and that other private collections within the Arabian peninsula be screened genetically. We urge caution when captive animals of unknown provenance are used to investigate the phylogenetics of cryptic species groups. Resumen: La identificación de poblaciones taxonómicamente apropiadas de especies en peligro para programas de reproducción en cautiverio y de reintroducción es fundamental para su éxito. La Gacela Saudi (Gazella saudiya) fue endémica a la península de Arabia pero ahora está considerada como extinta en su medio y es un candidato potencial para reproducción en cautiverio y reintroducción. Utilizando 375 pares de bases de ADN mitocondrial (ADNmt) del gene citocromo b derivados de muestras de museos colectadas en el medio silvestre antes de la extinción de la especie, mostramos que G. saudiya es el taxón hermano de la gacela dorcas africana (G. dorcas). La monofilia recíproca de haplotipos de ADNmt de G. saudiya con G. dorcas, aunado a diferencias morfológicas, sugiere que es una unidad evolutiva significativa. Estos datos indican que las poblaciones cautivas identificadas previamente como fuente potencial de G. saudiya para reproducción en cautiverio están incorrectamente identificadas y son irrelevantes para la conservación de G. saudiya. El análisis PCR-RFLP de varias colecciones privadas de gacelas vivas en Arabia Saudita no proporcionan evidencia para la supervivencia de G. saudiya. Recomendamos que se realicen muestreos en el campo para establecer si en efecto G. saudiya está extinta en su hábitat y que se examinen genéticamente las otras colecciones privadas en la península Arábiga. Recomendamos precaución cuando animales cautivos de origen desconocido son utilizados para investigar la filogenia de grupos de especies crípticas. [source] 566. RATIBIDA COLUMNIFERA var. PULCHERRIMACURTIS'S BOTANICAL MAGAZINE, Issue 4 2006Compositae Summary The new combination Ratibida columnifera var. pulcherrima is made and the taxon illustrated in colour. A full synonymy (of both the species and variety), description, cultivation and distribution notes, along with line drawings of the dissections of the taxon, is provided. [source] Embryogenesis and ossification of Emydura subglobosa (Testudines, Pleurodira, Chelidae) and patterns of turtle developmentDEVELOPMENTAL DYNAMICS, Issue 11 2009Ingmar Werneburg Abstract Using the Standard Event System (SES) to study patterns of vertebrate development, we describe a series of 17 embryos of the pleurodire turtle Emydura subglobosa. Based on a sequence heterochrony analysis including 23 tetrapod taxa, we identified autapomorphic developmental shifts that characterise Testudines, Cryptodira, and Pleurodira. The main results are that Testudines are characterised by an autapomorphic late neck development, whereas pleurodires and cryptodires show a different developmental timing of the mandibular process. Additionally, we described the ossification pattern of E. subglobosa and compared the data to those of five other turtles. Pleurodires show the epiplastron to ossify before or simultaneously with maxilla and dentary. In contrast, cryptodires show a later ossification of this bone. Because evolutionary developmental studies on turtles have previously focused only on "model organisms" that all belong to Cryptodira, we underline the necessity to include a pleurodire taxon for a more comprehensive, phylogenetically more informative approach. Developmental Dynamics 238:2770,2786, 2009. © 2009 Wiley-Liss, Inc. [source] Evolution of invertebrate nervous systems: the Chaetognatha as a case studyACTA ZOOLOGICA, Issue 1 2010Steffen Harzsch Abstract Harzsch, S. and Wanninger, A. 2010. Evolution of invertebrate nervous systems: the Chaetognatha as a case study. ,Acta Zoologica (Stockholm) 91: 35,43 Although recent molecular studies indicate that Chaetognatha may be one of the earliest Bilaterian offshoots, the phylogenetic position of this taxon still is a matter of ongoing debate. In this contribution, we review recent attempts to contribute phylogenetic information on the Chaetognatha by analysing structure and development of their nervous system (neurophylogeny). Analysing this group of organisms also has a major impact on our understanding of nervous system evolution in Bilateria. We review recent evidence from this field and suggest that Urbilateria already was equipped with the genetic toolkit required to build a complex, concentrated central nervous system (CNS), although this was not expressed phenotypically so that Urbilateria was equipped with a nerve plexus and not a CNS. This implies that in the deep metazoan nodes, concentration of the ancestral plexus occurred twice independently, namely once after the protostome,deuterostome split on the branch leading to the protostomes (resulting in a ventrally positioned nerve cord) and once along the chordate line (with a dorsal nerve cord). [source] Are there general rules governing parasite diversity?DIVERSITY AND DISTRIBUTIONS, Issue 3 2007Small mammalian hosts, gamasid mite assemblages ABSTRACT Parasite biodiversity varies on several scales, and in particular among different host species. Previous attempts at finding relationships between host features and the diversity of the parasite assemblages they harbour have yielded inconsistent results, suggesting strongly that any patterns might be taxon-specific. Here, we examined the potential of three host characteristics (host body mass, basal metabolic rate, and area of the geographical range) as determinants of parasite diversity in one group of ectoparasites, gamasid mites (superfamily Dermanyssoidea), using data from 63 species of small mammalian hosts. Our analyses used three measures of parasite diversity (species richness, the Shannon diversity index, and average taxonomic distinctness), and controlled for sampling effort and phylogenetic influences. Although several significant relationships were observed, they depended entirely on which diversity measure was used, or on which host taxon was investigated (insectivores vs. rodents and lagomorphs). In addition, the present results on patterns of mite diversity were not consistent with those of an earlier study involving roughly the same host taxa and the same biogeographical area, but a different group of ectoparasites, i.e. fleas. Thus, there appears to be no universal determinant of parasite diversity, and associations between host features and parasite diversity probably evolve independently in different host,parasite systems. [source] An enigmatic gnathostome vertebrate skull from the Middle Devonian of BoliviaACTA ZOOLOGICA, Issue 2009Alan Pradel Abstract A new taxon, Ramirosuarezia boliviana n. gen., n. sp. is erected for a single, articulated jawed fish (gnathostome) skull from the Middle Devonian (Eifelian) Icla Formation of Bolivia. The specimen displays an elasmobranch-like braincase, but lacks unambiguous elasmobranch and even chondrichthyan characters, although its peculiar tooth-bearing ,labial' elements evoke certain stem-holocephalans. Its endoskeletal elements seem lined with either perichondral bone or non-prismatic calcified cartilage, but show no evidence of endochondral bone. Although devoid of large dermal bones and scales, R. boliviana shares with certain ,ostracoderms', placoderms and holocephalans the lack of an otico-occipital fissure, but lacks a hypophysial fenestra. Certain features (elongated braincase, ,labial elements', sharp denticles and teeth) are also suggestive of the equally enigmatic coeval stensioellids, once regarded as either primitive placoderms or stem holocephalans. The jaws are armed with platelets that bear blunt to pointed and sharp teeth, in which synchrotron radiation microtomography yields evidence of a large pulp cavity, a possibly osteichthyan-like character. No character clearly supports affinities of R. boliviana to any of the currently known major gnathostome groups. Tenuous hints suggest a relationship to the enigmatic fossil Zamponiopteron, from the Eifelian of Bolivia, known by peculiar calcified ,fin plates' and isolated shoulder girdles. [source] Why are ferns regularly over-represented on state and provincial rare plant lists?DIVERSITY AND DISTRIBUTIONS, Issue 6 2006Matthew Wild ABSTRACT Several recent studies have suggested that rare species are not randomly distributed throughout plant taxa. This would appear to apply to North American ferns, which are frequently over-represented on local lists of rare plant species. However, such lists often paint a skewed portrait of the true situation because of our tendency to recognize the rarity of well-known and charismatic species while ignoring that of lesser-known or less-appreciated species. In order to verify if this over-representation of ferns is a real and consistent trend throughout local floras in North America, we used data from what we consider to be the most complete and objective available database: NatureServe Explorer (http://www.natureserve.org/explorer/). We compiled data on total vascular plant species, total fern species, as well as rare vascular plant species and rare fern species for each North American subnational (Canadian province or US state) flora. Rare species were defined as those belonging to one of NatureServe's ,at risk' categories. The null hypothesis that the contribution of rare ferns to total rare species did not differ from their contribution to the total vascular flora was assessed using ,2. Out of 64 subnational floras, we obtained significantly higher values than expected in 28 cases, and significantly lower in only one case. Similar trends hold true for individual fern families. These tendencies could be related to several factors of anthropogenic, biological, climatological, evolutionary, and geographical origin. However, we believe that the main reason is related to scale, namely the geopolitical units at which rarity is often studied. Our results illustrate one of the problems of a parochial approach to conservation, where the perceived rarity of an entire taxon is exaggerated because of the scale at which rarity is addressed. [source] A new tooth-plated lungfish from the Middle Devonian of Yunnan, China, and its phylogenetic relationshipsACTA ZOOLOGICA, Issue 2009Tuo Qiao Abstract A new genus and species of tooth-plated lungfish, Sinodipterus beibei gen. et sp. nov., is described from the Qujing Formation (Middle Devonian, late Eifelian) of Zhaotong, Yunnan, China. The new form resembles Dipterus in the skull table, but differs in its tooth-plate: cosmine-like tissue absent near the midline, tooth rows fewer in number (7 to 8) and less divergent radiating, and no reparative dentine layers. Phylogenetic analysis of Devonian lungfish based on a dataset of 150 characters and 33 taxa indicates that the new taxon is more crownward than Dipterus and the clade comprising Adololopas, Sorbitorhynchus and Pillararhynchus. Our results agree broadly with previous cladistic solutions. Diabolepis is placed as a sister group to all other Devonian lungfish. The species referred to Chirodipterus fail to form a monophyletic group. The result shows a large number of convergences corresponding to early radiation of lungfish compressed in time. [source] Naturalization and invasion of alien plants: concepts and definitionsDIVERSITY AND DISTRIBUTIONS, Issue 2 2000David M. Richardson Abstract., Much confusion exists in the English-language literature on plant invasions concerning the terms ,naturalized' and ,invasive' and their associated concepts. Several authors have used these terms in proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology. Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction (approximate scales: > 100 m over < 50 years for taxa spreading by seeds and other propagules; > 6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers. We propose that the term ,invasive' should be used without any inference to environmental or economic impact. Terms like ,pests' and ,weeds' are suitable labels for the 50,80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed ,transformers'. [source] Morpho-anatomy of the lobopod Magadictyon cf. haikouensis from the Early Cambrian Chengjiang Lagerstätte, South ChinaACTA ZOOLOGICA, Issue 4 2007Jianni Liu Abstract Magadictyon haikouensis (Luo and Hu, 1999) from the Early Cambrian Chengjiang Lagerstätte, an incomplete specimen of a large lobopod with strong appendages, has been regarded as related to the lobopods Microdictyon and Onychodictyon. Newly discovered complete specimens of Magadictyon cf. haikouensis (found by the Early Life Institute field team) show that the taxon, in addition to its strong appendages with appendicules, also had a head bearing similar caecum-like structures to those of the arthropod Naraoia and Chelicerate, ,Peytoia'-like mouthparts and frontal appendages. Because of their similarity, the caecum-like structures of Magadictyon cf. haikouensis are considered to be homologous with those of stem-group arthropods. The ,Peytoia'-like mouthparts and the frontal appendages are similar to those of the AOPK (Anomalocaris,Opabinia,Pambdelurion,Kerygmachela) group. In addition, the appendages with appendicules show that Magadictyon cf. haikouensis is closely related to Onychodictyon. Therefore, Magadictyon cf. haikouensis is regarded here as a rare transitional form between lobopods and arthropods. Besides, together with other lobopods, the morphology of Magadictyon cf. haikouensis demonstrates that the Cambrian lobopods appear to have been diverse and not particularly closely related to one another, and do not seem to represent a monophyletic clade. [source] The origin of higher taxa: macroevolutionary processes, and the case of the mammalsACTA ZOOLOGICA, Issue 1 2007T. S. Kemp Abstract The origin of a new higher taxon is characterized by a long-term phylogenetic trend, involving evolutionary changes in a large number of characters. At this phylogenetic level, the conflict between internal integration of the phenotype and its evolvability can be resolved by the correlated progression model, in which many disparate traits evolve by a sequence of small increments in loose correlation with one another, rather than by the modularity model. The trend leading to the new higher taxon implies the existence of a long ridge in an adaptive landscape. An evolutionary lineage tracking it requires adaptive changes in broad biological characteristics, involving many traits. Species selection is a possible additional driver of the trend. These conclusions are tested against the synapsid fossil record of the origin of mammals. The reconstructed sequence of acquisition of mammalian traits supports the correlated progression model. The adaptive ridge involved is postulated to have been a sequence of overlapping niches requiring increasing ability to remain active in daily and seasonally fluctuating environments by means of increasing internal regulation. An inferred speciation bias in favour of relatively small, relatively more progressive carnivores indicates that species selection was also involved in driving the trend. Palaeoenvironmental evidence indicates that ecological opportunity probably played a role at certain points along the lineage. [source] The musculature of three species of gastrotrichs surveyed with confocal laser scanning microscopy (CLSM)ACTA ZOOLOGICA, Issue 3 2006Francesca Leasi Abstract The muscular system of gastrotrichs consists of circular, longitudinal and helicoidal bands that when analysed with confocal laser scanning microscopy, provide new insights into their functional organization and phylogenetic importance. We therefore undertook a comparative study of the muscle organization in three species of Gastrotricha from the orders Macrodasyida (Paradasys sp., Lepidodasyidae; Turbanella sp., Turbanellidae) and Chaetonotida (Polymerurus nodicaudus, Chaetonotidae). The general muscle organization of the marine interstitial macrodasyidans, Paradasys and Turbanella, not only confirms earlier observation on other species but also adds new details concerning the organization and number of helicoidal, longitudinal and other muscle bands (e.g. semicircular band). The freshwater, epibenthic,epiphytic chaetonotid, Polymerurus nodicaudus, has a similar muscular organization to other species of Chaetonotidae, especially species of Chaetonotus, Halichaetonotus and Lepidodermella. Perhaps unique to Polymerurus is the combined presence of an unbranched Rückenhautmuskel (also in Halichaetonotus and Lepidodermella) and a specialized dorsoventral caudal muscle, which flank the splanchnic component of the longitudinal muscles (only in Chaetonotus and Lepidodermella). This combination, together with the presence of splanchnic dorsoventral muscles, known only in Xenotrichulidae, implies a unique phylogenetic position for Polymerurus, and indicates a potential basal position of this taxon among the Chaetonotidae studied so far (i.e. Aspidiophorus, Chaetonotus, Halichaetonotus and Lepidodermella). [source] Integrating highly diverse invertebrates into broad-scale analyses of cross-taxon congruence across the PalaearcticECOGRAPHY, Issue 6 2009Andreas Schuldt Our knowledge on broad-scale patterns of biodiversity, as a basis for biogeographical models and conservation planning, largely rests upon studies on the spatial distribution of vertebrates and plants, neglecting large parts of the world's biodiversity. To reassess the generality of these patterns and better understand spatial diversity distributions of invertebrates, we analyzed patterns of species richness and endemism of a hyperdiverse insect taxon, carabid beetles (ca 11 000 Palaearctic species known), and its cross-taxon congruence with well-studied vertebrates (amphibians, reptiles) and plants across 107,units of the Palaearctic. Based on species accumulation curves, we accounted for completeness of the carabid data by separately examining the western (well-sampled) and eastern (partly less well-sampled) Palaearctic and China (deficient data). For the western Palaearctic, we highlight overall centers of invertebrate, vertebrate and plant diversity. Species richness and endemism of carabids were highly correlated with patterns of especially plant and amphibian diversity across large parts of the Palaearctic. For the well-sampled western Palaearctic, hotspots of diversity integrating invertebrates were located in Italy, Spain and Greece. Only analysis of Chinese provinces yielded low congruence between carabids and plants/vertebrates. However, Chinese carabid diversity is only insufficiently known and China features the highest numbers of annual new descriptions of carabids in the Palaearctic. Even based on the incomplete data, China harbors at least 25% of all Palaearctic carabid species. Our study shows that richness and endemism patterns of highly diverse insects can exhibit high congruence with general large scale patterns of diversity inferred from plants/vertebrates and that hotspots derived from the latter can also include a high diversity of invertebrates. In this regard, China qualifies as an outstanding multi-taxon hotspot of diversity, requiring intense biodiversity research and conservation effort. Our findings extend the limited knowledge on broad-scale invertebrate distributions and allow for a better understanding of diversity patterns across a larger range of the world's biodiversity than usually considered. [source] Spatial and temporal variation in the morphology (and thus, predicted impact) of an invasive species in AustraliaECOGRAPHY, Issue 2 2006Ben L. Phillips The impact of an invasive species is unlikely to be uniform in space or time, due to variation in key traits of the invader (e.g. morphology, physiology, behaviour) as well as in resilience of the local ecosystem. The weak phylogeographic structure typical of an invasive population suggests that much of the variation in an invading taxon is likely to be generated by the environment and recent colonisation history. Here we describe effects of the environment and colonisation history on key morphological traits of an invader (the cane toad Bufo marinus). These "key traits" (body size and relative toxicity) mediate the impact of toads on Australian native predators, which often die as a consequence of ingesting a fatal dose of toad toxin. Measurements of museum specimens collected over >60 yr from a wide area show that seasonal variation in toad body size (due to seasonal recruitment) effectively swamps much of the spatial variance in this trait. However, relative toxicity of toads showed strong spatial variation and little seasonal variation. Thus, the risk to a native predator ingesting a toad will vary on both spatial and temporal scales. For native predators capable of eating a wide range of toad sizes (e.g. quolls, varanid lizards), seasonal variation in overall toad size will be the most significant predictor of risk. In contrast, gape-limited predators restricted to a specific range of toad sizes (such as snakes) will be most strongly affected by the relative toxicity of toads. Gape-limited predators will thus experience strong spatial variation in risk from toad consumption. [source] Fungivore host-use groups from cluster analysis: patterns of utilisation of fungal fruiting bodies by ciid beetlesECOLOGICAL ENTOMOLOGY, Issue 6 2005Glenda M. Orledge Abstract., 1.,Ciid beetles typically live and breed in the fruiting bodies of lignicolous basidiomycete fungi. This study was undertaken to address the lack of an objective examination of patterns of host use by ciids. 2.,Cluster analysis of ciid host-use datasets from Britain, Germany, North America, and Japan, and subsequent cross-dataset comparisons, demonstrated the existence of ciid host-use patterns of wide geographical occurrence. These patterns were formalised as ciid host-use groups. 3.,Six Holarctic ciid host-use groups, and two host-use subgroups, were identified, and are described. Each host-use group comprises an assemblage of fungal genera and the breeding ciids that it supports. Each taxon belongs to only a single host-use group, but may be associated with several members of that group. There is a strong tendency for closely related taxa to belong to the same host-use group. 4.,It is suggested that ciid host-use groups are defined ultimately by host chemistry, with the ciids that belong to a particular group recognising, and responding positively to, emitted volatiles characterising the fungi belonging to that group. 5.,The idea of the host-use group bears comparison with the concepts of niche and guild, but is not equivalent to either. 6.,Ciid host-use groups have a valuable role to play in underpinning future studies of ciid ecology, also the systematics of both ciids and their fungal hosts. [source] Beyond macronutrients: element variability and multielement stoichiometry in freshwater invertebratesECOLOGY LETTERS, Issue 12 2006Roxanne Karimi Abstract We contrasted concentrations of macronutrients (C, N and P), essential (As, Cu, Zn and Se) and non-essential metals (Pb, Hg and Cd) in invertebrates across five lakes and June to October in one lake. We predicted that somatic concentrations of tightly regulated elements would be less variable than weakly and unregulated elements. Within each taxon, variation was lowest in macronutrients, intermediate in essential micronutrients, and highest in non-essential metals, which corresponded in rank to homeostatic regulation strength for the same elements calculated from the literature. Hence, homeostatic regulation may strongly influence variation in element concentrations of biota in situ. Of the individual elements, only taxonomic differences in C and N were consistent across lakes and over a season. Nevertheless, canonical discriminant analyses successfully discriminated among taxa based on taxonomic multielement composition. Thus, relative taxonomic differences in multielement composition appear more informative than absolute stoichiometric formulae when considering the role of inherently variable trace elements in ecological investigations. [source] Metabolic responses of novel cellulolytic and saccharolytic agricultural soil Bacteria to oxygenENVIRONMENTAL MICROBIOLOGY, Issue 4 2010Stefanie Schellenberger Summary Cellulose is the most abundant biopolymer in terrestrial ecosystems and is degraded by microbial communities in soils. However, relatively little is known about the diversity and function of soil prokaryotes that might participate in the overall degradation of this biopolymer. The active cellulolytic and saccharolytic Bacteria in an agricultural soil were evaluated by 16S rRNA 13C-based stable isotope probing. Cellulose, cellobiose and glucose were mineralized under oxic conditions in soil slurries to carbon dioxide. Under anoxic conditions, these substrates were converted primarily to acetate, butyrate, carbon dioxide, hydrogen and traces of propionate and iso-butyrate; the production of these fermentation end-products was concomitant with the apparent reduction of iron(III). [13C]-cellulose was mainly degraded under oxic conditions by novel family-level taxa of the Bacteroidetes and Chloroflexi, and a known family-level taxon of Planctomycetes, whereas degradation under anoxic conditions was facilitated by the Kineosporiaceae (Actinobacteria) and cluster III Clostridiaceae and novel clusters within Bacteroidetes. Active aerobic sub-communities in oxic [13C]-cellobiose and [13C]-glucose treatments were dominated by Intrasporangiaceae and Micrococcaceae (Actinobacteria) whereas active cluster I Clostridiaceae (Firmicutes) were prevalent in anoxic treatments. A very large number (i.e. 28) of the detected taxa did not closely affiliate with known families, and active Archaea were not detected in any of the treatments. These collective findings suggest that: (i) a large uncultured diversity of soil Bacteria was involved in the utilization of cellulose and products of its hydrolysis, (ii) the active saccharolytic community differed phylogenetically from the active cellulolytic community, (iii) oxygen availability impacted differentially on the activity of taxa and (iv) different redox guilds (e.g. fermenters and iron reducers) compete or interact during cellulose degradation in aerated soils. [source] Population dynamics of the ectomycorrhizal fungal species Tricholoma populinum and Tricholoma scalpturatum associated with black poplar under differing environmental conditionsENVIRONMENTAL MICROBIOLOGY, Issue 5 2006Hervé Gryta Summary Fungi combine sexual reproduction and clonal propagation. The balance between these two reproductive modes affects establishment dynamics, and ultimately the evolutionary potential of populations. The pattern of colonization was studied in two species of ectomycorrhizal fungi: Tricholoma populinum and Tricholoma scalpturatum. The former is considered to be a host specialist whereas T. scalpturatum is a generalist taxon. Fruit bodies of both basidiomycete species were mapped and collected over several years from a black poplar (Populus nigra) stand, at two different sites. Multilocus genotypes (= genets) were identified based on the analysis of random amplified polymorphic DNA (RAPD) patterns, inter-simple sequence repeat (ISSR) patterns and restriction fragment length polymorphisms (RFLPs) in the ribosomal DNA intergenic spacer (rDNA IGS). The genetic analyses revealed differences in local population dynamics between the two species. Tricholoma scalpturatum tended to capture new space through sexual spores whereas T. populinum did this by clonal growth, suggesting trade-offs in allocation of resources at the genet level. Genet numbers and sizes strongly differ between the two study sites, perhaps as a result of abiotic disturbance on mycelial establishment and genet behaviour. [source] Summer changes in cyanobacterial bloom composition and microcystin concentration in eutrophic Czech reservoirsENVIRONMENTAL TOXICOLOGY, Issue 3 2006Petr Znachor Abstract In mid-July and August 2003 and 2004, 18 reservoirs in the Czech Republic were sampled for phytoplankton species composition and concentration of intracellular microcystins (MCs). As a consequence of high nutrient loading, most of the reservoirs experienced cyanobacterial blooms of various intensities, with the prevalence of cyanobacteria increasing markedly in August, along with a conspicuous shift in species composition toward dominance of Microcystis spp. Microcystins were detected in 90% of the samples, and their amount also increased considerably in August, reflecting the cyanobacterial biomass. In Microcystis -dominated samples, a significantly higher amount of MCs (p < 0.001) occurred than in samples in which other taxa prevailed. Microcystins were positively correlated with chlorophyll a and cyanobacterial biovolume (p < 0.05, R2 = 0.61 and 0.66, respectively), with the strongest correlation found for Microcystis spp. biovolume (p < 0.001, R2 = 0.87). This taxon was the most important producer of MCs in Czech reservoirs. The main structural variants of MCs were MC-LR, MC-RR, and MC-YR. This study's data also indicate that the relative share of MC variants (MC-LR and MC-RR) varies considerably with time, most likely as a consequence of different species and strain compositions during the summer. This study clearly demonstrates a high prevalence of MC-producing cyanobacteria in Czech reservoirs. Therefore, regular monitoring of these reservoirs is highly desirable in an effort to minimize potential health risks to the human population. © 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 236,243, 2006. [source] Evolution of Courtship Behaviour Patterns and Reproductive Isolation in the Desmognathus ochrophaeus ComplexETHOLOGY, Issue 5 2002Louise S. Mead The extent to which differences in courtship behaviour patterns act as mechanisms of reproductive isolation is critical to understanding both speciation and the evolution of these behaviour patterns. While numerous studies have investigated intraspecific and interspecific differences in courtship, fewer interpret results in a phylogenetic framework. We describe and analyse geographic variation in the courtship behaviour patterns of the Allegheny Dusky salamander (Desmognathus ochrophaeus). We then examine courtship among closely related species in the D. ochrophaeus complex in a phylogenetic context. We found that populations of D. ochrophaeus separated by extensive geographic distances show little variation in courtship behaviour patterns and are sexually compatible. This contrasts with significant levels of sexual isolation between D. ochrophaeus and other species in the complex. Mapping behaviour patterns onto a phylogeny that we generated from cytochrome b sequences indicates that two behaviour patterns present in the courtship sequence of other members in the complex have either been lost in D. ochrophaeus or gained independently in other species in the complex. Loss of these behaviour patterns may result in reproductive isolation between D. ochrophaeus and its sister taxon, D. orestes. [source] TAIL SHEDDING IN ISLAND LIZARDS [LACERTIDAE, REPTILIA]: DECLINE OF ANTIPREDATOR DEFENSES IN RELAXED PREDATION ENVIRONMENTSEVOLUTION, Issue 5 2009Panayiotis Pafilis The ability of an animal to shed its tail is a widespread antipredator strategy among lizards. The degree of expression of this defense is expected to be shaped by prevailing environmental conditions including local predation pressure. We test these hypotheses by comparing several aspects of caudal autotomy in 15 Mediterranean lizard taxa existing across a swath of mainland and island localities that differ in the number and identity of predator species present. Autotomic ease varied substantially among the study populations, in a pattern that is best explained by the presence of vipers. Neither insularity nor the presence of other types of predators explain the observed autotomy rates. Final concentration of accumulated tail muscle lactate and duration of movement of a shed tail, two traits that were previously thought to relate to predation pressure, are in general not shaped by either predator diversity or insularity. Under conditions of relaxed predation selection, an uncoupling of different aspects of caudal autotomy exists, with some elements (ease of autotomy) declining faster than others (duration of movement, lactate concentration). We compared rates of shed tails in the field against rates of laboratory autotomies conducted under standardized conditions and found very high correlation values (r > 0.96). This suggests that field autotomy rates, rather than being a metric of predatory attacks, merely reflect the innate predisposition of a taxon to shed its tail. [source] EVOLUTIONARY POTENTIAL OF A LARGE MARINE VERTEBRATE: QUANTITATIVE GENETIC PARAMETERS IN A WILD POPULATIONEVOLUTION, Issue 4 2009Joseph D. DiBattista Estimating quantitative genetic parameters ideally takes place in natural populations, but relatively few studies have overcome the inherent logistical difficulties. For this reason, no estimates currently exist for the genetic basis of life-history traits in natural populations of large marine vertebrates. And yet such estimates are likely to be important given the exposure of this taxon to changing selection pressures, and the relevance of life-history traits to population productivity. We report such estimates from a long-term (1995,2007) study of lemon sharks (Negaprion brevirostris) conducted at Bimini, Bahamas. We obtained these estimates by genetically reconstructing a population pedigree (117 dams, 487 sires, and 1351 offspring) and then using an "animal model" approach to estimate quantitative genetic parameters. We find significant additive genetic (co)variance, and hence moderate heritability, for juvenile length and mass. We also find substantial maternal effects for these traits at age-0, but not age-1, confirming that genotype,phenotype interactions between mother and offspring are strongest at birth; although these effects could not be parsed into their genetic and nongenetic components. Our results suggest that human-imposed selection pressures (e.g., size-selective harvesting) might impose noteworthy evolutionary change even in large marine vertebrates. We therefore use our findings to explain how maternal effects may sometimes promote maladaptive juvenile traits, and how lemon sharks at different nursery sites may show "constrained local adaptation." We also show how single-generation pedigrees, and even simple marker-based regression methods, can provide accurate estimates of quantitative genetic parameters in at least some natural systems. [source] SONG LEARNING ACCELERATES ALLOPATRIC SPECIATIONEVOLUTION, Issue 9 2004R. F. Lachlan Abstract The songs of many birds are unusual in that they serve a role in identifying conspecific mates, yet they are also culturally transmitted. Noting the apparently high rate of diversity in one avian taxon, the songbirds, in which song learning appears ubiquitous, it has often been speculated that cultural transmission may increase the rate of speciation. Here we examine the possibility that song learning affects the rate of allopatric speciation. We construct a population-genetic model of allopatric divergence that explores the evolution of genes that underlie learning preferences (predispositions to learn some songs over others). We compare this with a model in which mating signals are inherited only genetically. Models are constructed for the cases where songs and preferences are affected by the same or different loci, and we analyze them using analytical local stability analysis combined with simulations of drift and directional sexual selection. Under nearly all conditions examined, song divergence occurs more readily in the learning model than in the nonlearning model. This is a result of reduced frequency-dependent selection in the learning models. Cultural evolution causes males with unusual genotypes to tend to learn from the majority of males around them, and thus develop songs compatible with the majority of the females in the population. Unusual genotypes can therefore be masked by learning. Over a wide range of conditions, learning therefore reduces the waiting time for speciation to occur and can be predicted to accelerate the rate of speciation. [source] PHYLOGENETIC RELATIONSHIPS AND MORPHOLOGICAL DIVERSITY IN DARWIN'S FINCHES AND THEIR RELATIVESEVOLUTION, Issue 6 2002Kevin J. Burns Abstract Despite the importance of Darwin's finches to the development of evolutionary theory, the origin of the group has only recently been examined using a rigorous, phylogenetic methodology that includes many potential outgroups. Knowing the evolutionary relationships of Darwin's finches to other birds is important for understanding the context from which this adaptive radiation arose. Here we show that analysis of mitochondrial DNA sequence data from the cytochrome b gene confirm that Darwin's finches are monophyletic. In addition, many taxa previously proposed as the sister taxon to Darwin's finches can be excluded as their closest living relative. Darwin's finches are part of a well-supported monophyletic group of species, all of which build a domed nest. All but two of the non-Darwin's finches included in this clade occur on Caribbean islands and most are Caribbean endemics. These close relatives of Darwin's finches show a diversity of bill types and feeding behaviors similar to that observed among Darwin's finches themselves. Recent studies have shown that adaptive evolution in Darwin's finches occurred relatively quickly. Our data show that among the relatives of Darwin's finches, the evolution of bill diversity was also rapid and extensive. [source] THE EVOLUTION OF THE VERTEBRATE ,-GLOBIN GENE PROMOTEREVOLUTION, Issue 2 2002Nadia A. Chuzhanova Abstract Complexity analysis is capable of highlighting those gross evolutionary changes in gene promoter regions (loosely termed "promoter shuffling") that are undetectable by conventional DNA sequence alignment. Complexity analysis was therefore used here to identify the modular components (blocks) of the orthologous ,-globin gene promoter sequences of 22 vertebrate species, from zebrafish to humans. Considerable variation between the ,-globin gene promoters was apparent in terms of block presence/absence, copy number, and relative location. Some sequence blocks appear to be ubiquitous, whereas others are restricted to a specific taxon. Block similarities were also evident between the promoters of the paralogous human ,-like globin genes. It may be inferred that a wide variety of different mutational mechanisms have operated upon the ,-globin gene promoter over evolutionary time. Because these include gross changes such as deletion, duplication, amplification, elongation, contraction, and fusion, as well as the steady accumulation of single base-pair substitutions, it is clear that some redefinition of the term "promoter shuffling" is required. This notwithstanding, and as previously described for the vertebrate growth hormone gene promoter, the modular structure of the ,-globin promoter region and those of its paralogous counterparts have continually been rearranged into new combinations through the alteration, or shuffling, of preexisting blocks. Some of these changes may have had no influence on promoter function, but others could have altered either the level of gene expression or the responsiveness of the promoter to external stimuli. The comparative study of vertebrate ,-globin gene promoter regions described here confirms the generality of the phenomenon of sequence block shuffling and thus supports the view that it could have played an important role in the evolution of differential gene expression. [source] | ||||||||||||||||||||||||||||||||||||||||||||||