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Species Concepts (species + concept)
Kinds of Species Concepts Selected AbstractsMATHEMATICAL CONSEQUENCES OF THE GENEALOGICAL SPECIES CONCEPTEVOLUTION, Issue 8 2002Richard R. Hudson Abstract A genealogical species is defined as a basal group of organisms whose members are all more closely related to each other than they are to any organisms outside the group ("exclusivity'), and which contains no exclusive group within it. In practice, a pair of species is so defined when phylogenies of alleles from a sample of loci shows them to be reciprocally monophyletic at all or some specified fraction of the loci. We investigate the length of time it takes to attain this status when an ancestral population divides into two descendant populations of equal size with no gene exchange, and when genetic drift and mutation are the only evolutionary forces operating. The number of loci used has a substantial effect on the probability of observing reciprocal monophyly at different times after population separation, with very long times needed to observe complete reciprocal monophyly for a large number of loci. In contrast, the number of alleles sampled per locus has a relatively small effect on the probability of reciprocal monophyly. Because a single mitochondrial or chloroplast locus becomes reciprocally monophyletic much faster than does a single nuclear locus, it is not advisable to use mitochondrial and chloroplast DNA to recognize genealogical species for long periods after population divergence. Using a weaker criterion of assigning genealogical species status when more than 50% of sampled nuclear loci show reciprocal monophyly, genealogical species status depends much less on the number of sampled loci, and is attained at roughly 4,7 N generations after populations are isolated, where N is the historically effective population size of each descendant. If genealogical species status is defined as more than 95% of sampled nuclear loci showing reciprocal monophyly, this status is attained after roughly 9,12 N generations. [source] The implications of different species concepts for describing biodiversity patterns and assessing conservation needs for African birdsECOGRAPHY, Issue 5 2005Shaun Dillon It has been suggested that switching from the widely used Biological Species Concept to a Phylogenetic Species Concept, would result in the appearance of hitherto neglected patterns of endemism. The problem has mainly been analyzed with respect to endemic taxa and for rather limited geographical regions, but will here be analysed for the entire resident avifauna of sub-Saharan Africa. A database of African bird distributions was re-edited to create two new datasets representing 1572 biological species and 2098 phylogenetic species. Species richness patterns were virtually identical with the two taxonomies, and only subtle changes were found in the geographical variation in range-size rarity sum. However, there were some differences in the most range-restricted species, with increased complexity of long-recognized centres of endemism. Overall, then, the large-scale biogeographic patterns are robust to changes in species concepts. This reflects the aggregated nature of endemism, with certain areas acting as "species pumps" and large intervening areas being characterised by a predominance of widespread species which distribute themselves in accordance with contemporary environmental conditions. The percentages of phylogenetic and threatened species captured in a BSC near-minimum set of 64 grid-cells and a PSC near-maximum set, with the same number of grid-cells, are very similar. [source] World-wide genetic differentiation of Eubalaena: questioning the number of right whale speciesMOLECULAR ECOLOGY, Issue 11 2000H. C. Rosenbaum Abstract Few studies have examined systematic relationships of right whales (Eubalaena spp.) since the original species descriptions, even though they are one of the most endangered large whales. Little morphological evidence exists to support the current species designations for Eubalaena glacialis in the northern hemisphere and E. australis in the southern hemisphere. Differences in migratory behaviour or antitropical distribution between right whales in each hemisphere are considered a barrier to gene flow and maintain the current species distinctions and geographical populations. However, these distinctions between populations have remained controversial and no study has included an analysis of all right whales from the three major ocean basins. To address issues of genetic differentiation and relationships among right whales, we have compiled a database of mitochondrial DNA control region sequences from right whales representing populations in all three ocean basins that consist of: western North Atlantic E. glacialis, multiple geographically distributed populations of E. australis and the first molecular analysis of historical and recent samples of E. glacialis from the western and eastern North Pacific Ocean. Diagnostic characters, as well as phylogenetic and phylogeographic analyses, support the possibility that three distinct maternal lineages exist in right whales, with North Pacific E. glacialis being more closely related to E. australis than to North Atlantic E. glacialis. Our genetic results provide unequivocal character support for the two usually recognized species and a third distinct genetic lineage in the North Pacific under the Phylogenetic Species Concept, as well as levels of genetic diversity among right whales world-wide. [source] Empirical tests for ecological exchangeabilityANIMAL CONSERVATION, Issue 3 2005Russell B. Rader The concept of ecological exchangeability, together with genetic exchangeability, is central to both the Cohesion Species Concept as well as to some definitions of Evolutionarily Significant Units. While there are well-established criteria for measuring genetic exchangeability, the concept of ecological exchangeability has generated considerable confusion. We describe a procedure that uses the complementary strengths, while recognising the limitations, of both molecular genetic data and ecological experiments to determine the ecological exchangeability of local populations within a species. This is the first synthesis of a combined approach (experiments and genetics) and the first explicit discussion of testing ecological exchangeability. Although it would be ideal to find functional genes that interact to influence quantitative traits resulting in ecological differences (e.g. growth, size, fecundity), we suggest that our current knowledge of functional markers is too limited for most species to use them to differentiate adaptively different local populations. Thus, we argue that ecological experiments using whole organisms combined with neutral markers that indicate evolutionary divergence, provide the strongest case for detecting adaptive differences among local populations. Both genetic divergence and ecological experiments provide the best information for infering ecological exchangeability. This procedure can be used to decide which local populations should be preserved to maintain intraspecific variation and to determine which populations would enhance captive-breeding programs, augment endangered local populations and could best be used to re-introduce native species into historically occupied areas. [source] Species concepts: the basis for controversy and reconciliationFISH AND FISHERIES, Issue 3 2002Michael T Ghiselin Abstract Some of the disputes about species concepts can be resolved through clarification of the conceptual issues. Others are intractable because incompatible preferences are being optimized. According to the current biological consensus species (taxa) are populations rendered cohesive by sex. The philosophical consensus has it that the species and other categories are (abstract) classes, whereas particular species and other taxa are (concrete) individuals (in the ontological sense). Natural kinds are classes that have the properties they do because of laws of nature. Individuals such as species and clades owe their properties to history, not laws of nature; they are not kinds at all and calling them natural kinds is, therefore, grossly misleading. Having the species of taxonomy be equivalent to the species of evolutionary theory facilitates the integration of history and laws of nature within biology. Efforts to define the species category on the basis of similarity create misleading impressions about the laws and mechanisms of speciation processes. A diversity of incompatible species concepts (pluralism) is undesirable because the various kinds of units that are called ,species' differ with respect to the underlying laws of nature that make them natural kinds. [source] Species concepts and species reality: salvaging a Linnaean rankJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2003M. S. Y. Lee Abstract The validity of the species category (rank) as a distinct level of biological organization has been questioned. Phenetic, cohesion and monophyletic species concepts do not delimit species-level taxa that are qualitatively distinct from lower or higher taxa: all organisms throughout the tree of life exhibit varying degrees of similarity, cohesion, and monophyly. In contrast, interbreeding concepts delimit species-level taxa characterized by a phenomenon (regular gene flow) not found in higher taxa, making the species category a distinct level of biological organization. Only interbreeding concepts delimit species-level taxa that are all comparable according to a biologically meaningful criterion and qualitatively distinct from entities assigned to other taxonomic categories. Consistent application of interbreeding concepts can result in counterintuitive taxonomies , e.g. many wide polytypic species in plants and narrow cryptic species in animals. However, far from being problematic, such differences are biologically illuminating , reflecting differing barriers to gene flow in different clades. Empirical problems with interbreeding concepts exist, but many of these also apply to other species concepts, whereas others are not as severe as some have argued. A monistic view of species using interbreeding concepts will encounter strong historical inertia, but can save the species category from redundancy with other categories, and thus justify continued recognition of the species category. [source] Species concepts and floras: what are species for?BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2008SANDRA KNAPP In 1992, in a special paper in the American Journal of Botany, Ernst Mayr attempted to ,prove' the biological species concept (BSC) worked as well in plants as it did in animals by analyzing the flora of the Concord region of northern Massachusetts. He concluded that there were minimal difficulties when applying the BSC for the plants of this particular area, and concluded that botanists were misguided in not accepting the BSC. He suggested that what he called ,typological' thinking was prevalent in the taxonomic community, and that this was a factor in botanical resistance to the BSC. Typology, as defined by Mayr in his 1992 foray into botany, is to a certain extent a straw-man and, by the late 20th Century, no longer a way of thinking in widespread use in the taxonomic community in any organismal group. Here, I examine his analysis in the light of current interest in plant diversity. Species can be characterized as hypotheses about the distribution of variation in nature, subject to test with new data of many kinds. Species concepts like the BSC, although of interest philosophically and to researchers looking at mechanisms of speciation, may actually get in the way of achieving a baseline understanding of the diversity of life on Earth. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 17,25. [source] THE BIOLOGY OF SPECIATIONEVOLUTION, Issue 2 2010James M. Sobel Since Darwin published the "Origin," great progress has been made in our understanding of speciation mechanisms. The early investigations by Mayr and Dobzhansky linked Darwin's view of speciation by adaptive divergence to the evolution of reproductive isolation, and thus provided a framework for studying the origin of species. However, major controversies and questions remain, including: When is speciation nonecological? Under what conditions does geographic isolation constitute a reproductive isolating barrier? and How do we estimate the "importance" of different isolating barriers? Here, we address these questions, providing historical background and offering some new perspectives. A topic of great recent interest is the role of ecology in speciation. "Ecological speciation" is defined as the case in which divergent selection leads to reproductive isolation, with speciation under uniform selection, polyploid speciation, and speciation by genetic drift defined as "nonecological." We review these proposed cases of nonecological speciation and conclude that speciation by uniform selection and polyploidy normally involve ecological processes. Furthermore, because selection can impart reproductive isolation both directly through traits under selection and indirectly through pleiotropy and linkage, it is much more effective in producing isolation than genetic drift. We thus argue that natural selection is a ubiquitous part of speciation, and given the many ways in which stochastic and deterministic factors may interact during divergence, we question whether the ecological speciation concept is useful. We also suggest that geographic isolation caused by adaptation to different habitats plays a major, and largely neglected, role in speciation. We thus provide a framework for incorporating geographic isolation into the biological species concept (BSC) by separating ecological from historical processes that govern species distributions, allowing for an estimate of geographic isolation based upon genetic differences between taxa. Finally, we suggest that the individual and relative contributions of all potential barriers be estimated for species pairs that have recently achieved species status under the criteria of the BSC. Only in this way will it be possible to distinguish those barriers that have actually contributed to speciation from those that have accumulated after speciation is complete. We conclude that ecological adaptation is the major driver of reproductive isolation, and that the term "biology of speciation," as proposed by Mayr, remains an accurate and useful characterization of the diversity of speciation mechanisms. [source] Charles Darwin, ichthyology and the species conceptFISH AND FISHERIES, Issue 3 2002Daniel Pauly Abstract This contribution presents the ichthyological writings of Charles Darwin (1809,1882), by periods, viz. ,the years prior to the voyage of the Beagle' (about 1825,1830); ,the Beagle years' (1831,1836); ,from the return of the Beagle to the Foundation of Origin' (1837,1844); and ,the mature Darwin' (1845,1882). Overall, this material covers 45 000 words penned by Darwin, but represents only 0.7% of his lifetime output of about 6 million words, indicating a limited interest in fish. However, this sample, briefly described here, but analysed in great detail in a forthcoming volume on Darwin's Fishes, allows drawing inferences on Darwin's working style that were missed in conventional biographies. On the other hand, it is suggested, based on a close reading of the 6th (1876) edition of Origin, that Darwin was not particularly interested in the theoretical issues now associated with the species concept, nor indeed with other levels of the Linnean system. [source] Assortative mating also indicates that common crossbill Loxia curvirostra vocal types are speciesJOURNAL OF AVIAN BIOLOGY, Issue 1 2008Pim Edelaar Compared to most other birds, the taxonomy of crossbills (Loxia) is still highly unsettled. However, much progress seems to be achievable when data on vocalisations is included. In a recent paper, Summers et al. (2007) argued that strong assortative mating indicated that parrot crossbill Loxia pytyopsittacus, Scottish crossbill Loxia scotica and common crossbill Loxia curvirostra behave as good species when breeding in sympatry. Here I argue that their data, when placed in the context of other studies, also indicate that three vocally differentiated European populations within the common crossbill are species (following the biological species concept of Mayr (1963): species are groups of interbreeding natural populations that are reproductively isolated from other such groups). If this tentative conclusion remains to be upheld, it might have large repercussions for our understanding of the speciation process as well as for a number of more applied issues such as the discovery and description of biodiversity and the conversation of mobile, cryptic species. [source] Niche partitioning of closely related symbiotic dinoflagellatesMOLECULAR ECOLOGY, Issue 17 2007EUGENIA M. SAMPAYO Abstract Reef-building corals are fundamental to the most diverse marine ecosystems, yet a detailed understanding of the processes involved in the establishment, persistence and ecology of the coral,dinoflagellate association remains largely unknown. This study explores symbiont diversity in relation to habitat by employing a broad-scale sampling regime using ITS2 and denaturing gradient gel electrophoresis. Samples from Pocillopora damicornis, Stylophora pistillata and Seriatopora hystrix all harboured host-specific clade C symbiont types at Heron Island (Great Barrier Reef, Australia). While Ser. hystrix associated with a single symbiont profile along its entire depth distribution, both P. damicornis and Sty. pistillata associated with multiple symbiont profiles that showed a strong zonation with depth. It is shown that, with an increased sampling effort, previously identified ,rare' symbiont types within this group of host species are in fact environmental specialists. A multivariate approach was used to expand on the common distinction of symbionts by a single genetic identity. It shows merit in its capacity not only to include all the variability present within the marker region but also to reliably represent ecological diversification of symbionts. Furthermore, the cohesive species concept is explored to explain how niche partitioning may drive diversification of closely related symbiont lineages. This study provides thus evidence that closely related symbionts are ecologically distinct and fulfil their own niche within the ecosystem provided by the host and external environment. [source] Gene trees: A powerful tool for exploring the evolutionary biology of species and speciationPLANT SPECIES BIOLOGY, Issue 3 2000Alan R. Templeton Abstract Evolutionary trees can be constructed from the haplotypes observed with molecular surveys of sequence or restriction site variation. Such gene trees can be constructed regardless of whether or not all of the individual specimens came from one or many species. Hence, these gene trees can straddle the species/population interface, thereby providing a powerful tool for studying the meaning of species and the process of speciation. We illustrate how historical approaches using gene trees can be used to separate the effects of population structure from population history, in order to rigorously test the species status of a group, and to test hypotheses about the process of speciation. A worked example of species status in the Piriqueta caroliniana complex is presented. Species status is evaluated under the cohesion species concept that defines a species as an evolutionary lineage with boundaries arising from the forces that create reproductive communities. Such forces are collectively called cohesion mechanisms and consist of two main subtypes: (i) genetic exchangeability, and (ii) ecological interchangeability. To make this definition operational, populations that behave as separate evolutionary lineages are first identified. A method is reviewed for inferring lineages using explicit statistical criteria from geographic overlays upon gene trees. Once lineages have been identified, the next step is to use the cohesion mechanisms to identify candidate traits that should contribute to genetic exchangeability and/or ecological interchangeability. The cohesion species are then identified by performing overlays upon gene trees in order to identify significant transitions in the candidate traits. Cohesion species are recognized only when statistically significant reproductive/ecological transitions occur that are concordant with the lineages defined earlier. This data-rich method of recognizing species automatically generates much information about the biogeography, population structure, historical events, and ecology and/or reproductive biology of the group under study. In turn, this information provides much insight into the process of speciation. It also makes the criteria, data, methods of analysis and degree of support for the species inference completely explicit, thereby avoiding confusion, inconsistency and artificial controversies that plague much of the literature on species concepts. [source] Taxon combinations, parsimony analysis (PAUP*), and the taxonomy of the yellow-tailed woolly monkey, Lagothrix flavicaudaAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2008Luke J. Matthews Abstract The classifications of primates, in general, and platyrrhine primates, in particular, have been greatly revised subsequent to the rationale for taxonomic decisions shifting from one rooted in the biological species concept to one rooted solely in phylogenetic affiliations. Given the phylogenetic justification provided for revised taxonomies, the scientific validity of taxonomic distinctions can be rightly judged by the robusticity of the phylogenetic results supporting them. In this study, we empirically investigated taxonomic-sampling effects on a cladogram previously inferred from craniodental data for the woolly monkeys (Lagothrix). We conducted the study primarily through much greater sampling of species-level taxa (OTUs) after improving some character codings and under a variety of outgroup choices. The results indicate that alternative selections of species subsets from within genera produce various tree topologies. These results stand even after adjusting the character set and considering the potential role of interobserver disagreement. We conclude that specific taxon combinations, in this case, generic or species pairings, of the primary study group has a biasing effect in parsimony analysis, and that the cladistic rationale for resurrecting the Oreonax generic distinction for the yellow-tailed woolly monkey (Lagothrix flavicauda) is based on an artifact of idiosyncratic sampling within the study group below the genus level. Some recommendations to minimize the problem, which is prevalent in all cladistic analyses, are proposed. Am J Phys Anthropol, 2008. © 2008 Wiley-Liss, Inc. [source] Species: towards new, well-grounded practicesBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009SARAH SAMADI Velasco recently criticized our formal definition of the species concept, arguing for its inappropriateness both in fundamental and practical aspects [Velasco JD (2008) Biological Journal of the Linnean Society, 93, 865,869]. Here, we clarify some misunderstandings that are at the basis of Velasco's paper. First, we show why and how the definition of the species concept can be grounded in the theory of evolution and what that implies. Then, we explain why Velasco's formal criticisms are unjustified. Finally, we point out the practical and methodological consequences of a rigorous conceptual framework for species study, and we show that today's development of species delimitation methods fully agrees with our proposal. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 217,222. [source] Speciation mirrors geomorphology and palaeoclimatic history in African laminate-toothed rats (Muridae: Otomyini) of the Otomys denti and Otomys lacustris species-complexes in the ,Montane Circle' of East AfricaBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009PETER J. TAYLOR We adopted an integrated systematic approach to delimit evolutionary species and describe phylogeographic, morphometric and ecological relationships in Otomys denti (from the Albertine Rift, Southern Rift in Malawi and the northern Eastern Arc Mountains) and Otomys lacustris (from the Southern Rift in Tanzania and Zambia, and the southern Eastern Arc Mountains). Molecular [cytochrome (cyt) b sequences, 1143 bp, N = 18], craniometric (classical, N = 100 and geometric, N = 60) and ecological (Partial Least Squares regression of shape and ecogeographic variables) approaches show a profound, parallel disjunction between two groups: (1) Eastern Arc and Southern Rift (including the Malawi Rift) (O. lacustris and Otomys denti sungae) and (2) Albertine Rift (Otomys denti denti and Otomys denti kempi) taxa. Within both groups, cyt b sequences or craniometric analysis provided evidence for the differentiation of both southern and northern Eastern Arc from Southern Rift lineages (across the so-called Makambako Gap). Within the Albertine Rift (denti,kempi) lineage, populations from individual mountain ranges differed significantly in skull shape (but not size), but were similar genetically. Over-reliance in the past on very few morphological characters (e.g. number of molar laminae) and a polytypic species concept has obscured phylogenetic relationships and species discrimination in this group. We recognize at least three species in this group, and distinct lineages within two of these species. Each species or lineage was endemic to one of three regions: the Albertine Rift, the Malawi Rift or the Eastern Arc. Our result echo conclusions of recent studies of other mammalian and bird taxa and reflect the geomorphology and palaeoclimatic history of the region. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96, 913,941. [source] Species concepts and floras: what are species for?BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2008SANDRA KNAPP In 1992, in a special paper in the American Journal of Botany, Ernst Mayr attempted to ,prove' the biological species concept (BSC) worked as well in plants as it did in animals by analyzing the flora of the Concord region of northern Massachusetts. He concluded that there were minimal difficulties when applying the BSC for the plants of this particular area, and concluded that botanists were misguided in not accepting the BSC. He suggested that what he called ,typological' thinking was prevalent in the taxonomic community, and that this was a factor in botanical resistance to the BSC. Typology, as defined by Mayr in his 1992 foray into botany, is to a certain extent a straw-man and, by the late 20th Century, no longer a way of thinking in widespread use in the taxonomic community in any organismal group. Here, I examine his analysis in the light of current interest in plant diversity. Species can be characterized as hypotheses about the distribution of variation in nature, subject to test with new data of many kinds. Species concepts like the BSC, although of interest philosophically and to researchers looking at mechanisms of speciation, may actually get in the way of achieving a baseline understanding of the diversity of life on Earth. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 17,25. [source] Molecular and morphological data reveal cryptic taxonomic diversity in the terrestrial slug complex Arion subfuscus/fuscus (Mollusca, Pulmonata, Arionidae) in continental north-west EuropeBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2004J. PINCEEL The importance and abundance of cryptic species among invertebrate taxa is well documented. Nowadays, taxonomic, phylogenetic and conservation biological studies frequently use molecular markers to delineate cryptic taxa. Such studies, however, often face the problem of the differential resolution of the molecular markers and techniques involved. This issue is explored in the present study of cryptic taxa within the terrestrial slug complex Arion subfuscus/fuscus in continental north-west Europe. To this end, morphological, allozyme and mitochondrial 16S rDNA sequence data have been jointly evaluated. Using allozyme data and gonad type, two distinct groups were consistently delineated, even under sympatric conditions. The 16S rDNA data strongly supported both those groups and even suggested the presence of three distinct taxa within one of them. However, in view of: (1) the allopatric distribution of three OTUs, (2) the lack of allozyme or morphological differentiation, and (3) the extremely high degree of intraspecific mtDNA variation reported in pulmonate gastropods, they are, for the time being, not regarded as valid species under the biological species concept. By means of 16S rDNA and allozyme data, the position of type and topotype material of A. subfuscus s.s. and A. fuscus relative to the newly defined OTUs was determined, thus clarifying the nomenclature of this species complex. Additionally, gonad type proved to be a useful character for distinguishing the two species in north-west Europe. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 23,38. [source] Phylogenetic Species, Nested Hierarchies, and Character FixationCLADISTICS, Issue 4 2000Paul Z. Goldstein Cladistic mechanics and ramifications of various species concepts rooted in phylogenetic theory are explored. Published discussions of the phylogenetic species concept (PSC) have been hampered by persistent misconceptions surrounding its ontology and applicability, and by confusion of various incompatible versions of species concepts claiming to follow from Hennig's (1966), Phylogenetic Systematics, Univ. of Illinois Press, Urbana work. Especially problematic are topology- or tree-based versions of species diagnosis, which render diagnoses dependent on relationships depicted as hierarchically structured regardless of any lack of underlying hierarchy. Because the applicability of concepts such as monophyly, paraphyly, and polyphyly rests ultimately on the underlying hierarchical distribution of characters, representations of tokogenetic or reticulating systems as nested hierarchies are necessarily inaccurate. And since hierarchical representations,even if accurate,of nonrecombining genetic elements need not coincide with the organisms that bear them, tree-based diagnoses are further hampered, except potentially as retrospective tools. The relationship between tree-based species delineations and the criterion of character fixation is explored. Fixation of characters by which one identifies phylogenetic species is further distinguished from the fixation of character state differences, and the implications of that distinction are explored with reference to the interpretation of speciation events. It is demonstrated that character fixation in alternative species need not coincide with the achievement of reciprocal monophyly. While the PSC retains shortcomings, some of the more frequently criticized aspects of the PSC are functions of sampling that are no more problematic than for any basic systematic endeavor. [source] Mayr's view of Darwin: was Darwin wrong about speciation?BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2008JAMES MALLET We commonly read or hear that Charles Darwin successfully convinced the world about evolution and natural selection, but did not answer the question posed by his most famous book, ,On the Origin of Species ,'. Since the 1940s, Ernst Mayr has been one of the people who argued for this point of view, claiming that Darwin was not able to answer the question of speciation because he failed to define species properly. Mayr undoubtedly had an important and largely positive influence on the study of evolution by stimulating much evolutionary work, and also by promoting a ,polytypic species concept' in which multiple, geographically separated forms may be considered as subspecies within a larger species entity. However, Mayr became seduced by the symmetry of a pair of interlocking ideas: (1) that coexistence of divergent populations was not possible without reproductive isolation and (2) reproductive isolation could not evolve in populations that coexist. These beliefs led Mayr in 1942 to reject evidence of the importance of intermediate stages in speciation, particularly introgression between hybridizing species, which demonstrates that complete reproductive isolation is not necessary, and the existence of ecological races, which shows that ecological divergence can be maintained below the level of species, in the face of gene flow. Mayr's train of thought led him to the view that Darwin misunderstood species, and that species were fundamentally different from subspecific varieties in nature. Julian Huxley, reviewing similar data at the same time, came to the opposite conclusion, and argued that these were the intermediate stages of speciation expected under Darwinism. Mayr's arguments were, however, more convincing than Huxley's, and this caused a delay in the acceptance of a more balanced view of speciation for many decades. It is only now, with new molecular evidence, that we are beginning to appreciate more fully the expected Darwinian intermediates between coexisting species. © The Author. Journal compilation © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 3,16. [source] The implications of different species concepts for describing biodiversity patterns and assessing conservation needs for African birdsECOGRAPHY, Issue 5 2005Shaun Dillon It has been suggested that switching from the widely used Biological Species Concept to a Phylogenetic Species Concept, would result in the appearance of hitherto neglected patterns of endemism. The problem has mainly been analyzed with respect to endemic taxa and for rather limited geographical regions, but will here be analysed for the entire resident avifauna of sub-Saharan Africa. A database of African bird distributions was re-edited to create two new datasets representing 1572 biological species and 2098 phylogenetic species. Species richness patterns were virtually identical with the two taxonomies, and only subtle changes were found in the geographical variation in range-size rarity sum. However, there were some differences in the most range-restricted species, with increased complexity of long-recognized centres of endemism. Overall, then, the large-scale biogeographic patterns are robust to changes in species concepts. This reflects the aggregated nature of endemism, with certain areas acting as "species pumps" and large intervening areas being characterised by a predominance of widespread species which distribute themselves in accordance with contemporary environmental conditions. The percentages of phylogenetic and threatened species captured in a BSC near-minimum set of 64 grid-cells and a PSC near-maximum set, with the same number of grid-cells, are very similar. [source] Testing for endemism, genotypic diversity and species concepts in Antarctic terrestrial microalgae of the Tribonemataceae (Stramenopiles, Xanthophyceae)ENVIRONMENTAL MICROBIOLOGY, Issue 3 2009Nataliya Rybalka Summary The genetic diversity of all available culture strains of the Tribonemataceae (Stramenopiles, Xanthophyceae) from Antarctica was assessed using the chloroplast-encoded psbA /rbcL spacer region sequences, a highly variable molecular marker, to test for endemism when compared with their closest temperate relatives. There was no species endemic for Antarctica, and no phylogenetic clade corresponded to a limited geographical region. However, species of the Tribonemataceae may have Antarctic populations that are distinct from those of other regions because the Antarctic strain spacer sequences were not identical to sequences from temperate regions. Spacer sequences from five new Antarctic isolates were identical to one or more previously available Antarctic strains, indicating that the Tribonemataceae diversity in Antarctic may be rather limited. Direct comparisons of the spacer sequences and phylogenetic analyses of the more conserved rbcL gene revealed that current morphospecies were inadequate to describe the actual biodiversity of the group. For example, the genus Xanthonema, as currently circumscribed, was paraphyletic. Fortunately, the presence of distinctive sequence regions within the psbA/rbcL spacer, together with differences in the rbcL phylogeny, provided significant autoapomorphic criteria to re-define the Tribonemataceae species. [source] Species concepts: the basis for controversy and reconciliationFISH AND FISHERIES, Issue 3 2002Michael T Ghiselin Abstract Some of the disputes about species concepts can be resolved through clarification of the conceptual issues. Others are intractable because incompatible preferences are being optimized. According to the current biological consensus species (taxa) are populations rendered cohesive by sex. The philosophical consensus has it that the species and other categories are (abstract) classes, whereas particular species and other taxa are (concrete) individuals (in the ontological sense). Natural kinds are classes that have the properties they do because of laws of nature. Individuals such as species and clades owe their properties to history, not laws of nature; they are not kinds at all and calling them natural kinds is, therefore, grossly misleading. Having the species of taxonomy be equivalent to the species of evolutionary theory facilitates the integration of history and laws of nature within biology. Efforts to define the species category on the basis of similarity create misleading impressions about the laws and mechanisms of speciation processes. A diversity of incompatible species concepts (pluralism) is undesirable because the various kinds of units that are called ,species' differ with respect to the underlying laws of nature that make them natural kinds. [source] Species concepts and species reality: salvaging a Linnaean rankJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2003M. S. Y. Lee Abstract The validity of the species category (rank) as a distinct level of biological organization has been questioned. Phenetic, cohesion and monophyletic species concepts do not delimit species-level taxa that are qualitatively distinct from lower or higher taxa: all organisms throughout the tree of life exhibit varying degrees of similarity, cohesion, and monophyly. In contrast, interbreeding concepts delimit species-level taxa characterized by a phenomenon (regular gene flow) not found in higher taxa, making the species category a distinct level of biological organization. Only interbreeding concepts delimit species-level taxa that are all comparable according to a biologically meaningful criterion and qualitatively distinct from entities assigned to other taxonomic categories. Consistent application of interbreeding concepts can result in counterintuitive taxonomies , e.g. many wide polytypic species in plants and narrow cryptic species in animals. However, far from being problematic, such differences are biologically illuminating , reflecting differing barriers to gene flow in different clades. Empirical problems with interbreeding concepts exist, but many of these also apply to other species concepts, whereas others are not as severe as some have argued. A monistic view of species using interbreeding concepts will encounter strong historical inertia, but can save the species category from redundancy with other categories, and thus justify continued recognition of the species category. [source] PHYLOGENETIC AND BIOGEOGRAPHIC AFFINITIES OF THE HALYMENIALES AND RHODYMENIALES (RHODOPHYTA) FROM THE GULF OF MEXICOJOURNAL OF PHYCOLOGY, Issue 2000B. Gavio Generic and species concepts within the red algal assemblages Halymeniales and Rhodymeniales are discussed for taxa inhabiting the western Gulf of Mexico. Two principal biogeographic assemblages occur: an off-shore deep-water group (including Coelarthrum cliftonii, Halymenia spp., Botryocladia spp., Gloiocladia) representing remnants of a Tethyan distribution, and a near-shore intertidal flora (comprising Rhodymenia, Grateloupia and Prionitis) which instead reveals biogeographic affinities with the Carolinian Province. These two distinct marine floras will be contrasted phylogenetically based on DNA sequence analysis inferred from chloroplast-encoded rbcL. The generic descriptions of Grateloupia and Prionitis are in need of taxonomic revision based on a survey of species from Caribbean and Pacific Mexico. [source] Phylogenetic biogeography and taxonomy of disjunctly distributed bryophytesJOURNAL OF SYSTEMATICS EVOLUTION, Issue 5 2009Jochen HEINRICHS Abstract, More than 200 research papers on the molecular phylogeny and phylogenetic biogeography of bryophytes have been published since the beginning of this millenium. These papers corroborated assumptions of a complex genetic structure of morphologically circumscribed bryophytes, and raised reservations against many morphologically justified species concepts, especially within the mosses. However, many molecular studies allowed for corrections and modifications of morphological classification schemes. Several studies reported that the phylogenetic structure of disjunctly distributed bryophyte species reflects their geographical ranges rather than morphological disparities. Molecular data led to new appraisals of distribution ranges and allowed for the reconstruction of refugia and migration routes. Intercontinental ranges of bryophytes are often caused by dispersal rather than geographical vicariance. Many distribution patterns of disjunct bryophytes are likely formed by processes such as short distance dispersal, rare long distance dispersal events, extinction, recolonization and diversification. [source] Genetic tests of the taxonomic status of the ring-tailed lemur (Lemur catta) from the high mountain zone of the Andringitra Massif, MadagascarJOURNAL OF ZOOLOGY, Issue 1 2000Anne D. Yoder Abstract A recent survey of the high-mountain zone of the Madagascar Parc National (PN) d'Andringitra revealed the presence of an apparently isolated troop of the ring-tailed lemur Lemur catta. These animals display phenotypic and ecological characteristics that are unusual for the monotypic genus Lemur, thus raising the possibility that they are members of a different undescribed species. We present analyses of two mitochondrial genes to test the hypothesis that L. catta from Andringitra should be considered a distinct species. The results indicate that taxonomic revision is not warranted under the expectations of the phylogenetic, coalescent, or biological species concepts. Rather, the genetic patterns observed among the Andringitra and lowland mitochondrial haplotypes are consistent with those expected for a single species. [source] Adaptive evolutionary conservation: towards a unified concept for defining conservation unitsMOLECULAR ECOLOGY, Issue 12 2001Dylan J. Fraser Abstract Recent years have seen a debate over various methods that could objectively prioritize conservation value below the species level. Most prominent among these has been the evolutionarily significant unit (ESU). We reviewed ESU concepts with the aim of proposing a more unified concept that would reconcile opposing views. Like species concepts, conflicting ESU concepts are all essentially aiming to define the same thing: segments of species whose divergence can be measured or evaluated by putting differential emphasis on the role of evolutionary forces at varied temporal scales. Thus, differences between ESU concepts lie more in the criteria used to define the ESUs themselves rather than in their fundamental essence. We provide a context-based framework for delineating ESUs which circumvents much of this situation. Rather than embroil in a befuddled debate over an optimal criterion, the key to a solution is accepting that differing criteria will work more dynamically than others and can be used alone or in combination depending on the situation. These assertions constitute the impetus behind adaptive evolutionary conservation. [source] ANACORACID SHARKS FROM THE ALBIAN (LOWER CRETACEOUS) PAWPAW SHALE OF TEXASPALAEONTOLOGY, Issue 4 2007MIKAEL SIVERSON Abstract:, Recent collecting from the Pawpaw Shale in north-east Texas has yielded several hundred teeth of anacoracid sharks. The material allows for a much-needed revision of the Late Albian anacoracids from North America. The previously recognized Squalicorax sp., also referred to as S. volgensis in more recent publications, is a mix of two different species: S. priscoserratus sp. nov. and S. pawpawensis sp. nov. In addition to these two new species, a single tooth is assigned to S. aff. S. baharijensis. Our data indicate that anacoracids were a considerably more diverse group in the North American Cretaceous than previously thought. We attribute much of the underestimation of diversity to vague species concepts, poor preparation techniques and the associated lack of attention to certain dental features, in particular neck morphology, root surface porosity and the root's vascularization. [source] Gene trees: A powerful tool for exploring the evolutionary biology of species and speciationPLANT SPECIES BIOLOGY, Issue 3 2000Alan R. Templeton Abstract Evolutionary trees can be constructed from the haplotypes observed with molecular surveys of sequence or restriction site variation. Such gene trees can be constructed regardless of whether or not all of the individual specimens came from one or many species. Hence, these gene trees can straddle the species/population interface, thereby providing a powerful tool for studying the meaning of species and the process of speciation. We illustrate how historical approaches using gene trees can be used to separate the effects of population structure from population history, in order to rigorously test the species status of a group, and to test hypotheses about the process of speciation. A worked example of species status in the Piriqueta caroliniana complex is presented. Species status is evaluated under the cohesion species concept that defines a species as an evolutionary lineage with boundaries arising from the forces that create reproductive communities. Such forces are collectively called cohesion mechanisms and consist of two main subtypes: (i) genetic exchangeability, and (ii) ecological interchangeability. To make this definition operational, populations that behave as separate evolutionary lineages are first identified. A method is reviewed for inferring lineages using explicit statistical criteria from geographic overlays upon gene trees. Once lineages have been identified, the next step is to use the cohesion mechanisms to identify candidate traits that should contribute to genetic exchangeability and/or ecological interchangeability. The cohesion species are then identified by performing overlays upon gene trees in order to identify significant transitions in the candidate traits. Cohesion species are recognized only when statistically significant reproductive/ecological transitions occur that are concordant with the lineages defined earlier. This data-rich method of recognizing species automatically generates much information about the biogeography, population structure, historical events, and ecology and/or reproductive biology of the group under study. In turn, this information provides much insight into the process of speciation. It also makes the criteria, data, methods of analysis and degree of support for the species inference completely explicit, thereby avoiding confusion, inconsistency and artificial controversies that plague much of the literature on species concepts. [source] Past President's Address: Protistan Biogeography: Why All The Fuss?,THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2009DAVID A. CARON ABSTRACT. Conflicting hypotheses regarding the distribution of protistan species on our planet have led to rather impassioned arguments in the recent literature, and heated discussions at scientific meetings. Both sides of this debate have mounted seemingly credible arguments for endemism on the one hand, or ubiquitous dispersal of protists on the other. At present, the controversy appears unending, perhaps because it is fueled by a convergence of unresolvable issues involving the enormous phylogenetic breadth of species presently encompassed by the term "protist," the application of multiple species concepts to these taxa, the inability of extant techniques and technology to plumb the depths of microbial diversity in natural ecosystems, and a lack of knowledge regarding the relationship between dispersal rates and rates of evolution of protists. These issues have made it difficult to erect and test hypotheses concerning the distribution of protists. In the absence of definitive experimental or observational information, preconceived attitudes regarding protistan distributions have dominated the interpretation of the available data. On the positive side, the debate has led to the development and application of new approaches to the study of protistan diversity, and stimulated discussions involving how (and why) we define protistan species. [source] | ||||||||||||||||||||||||||||