Academic literature on the topic 'Species delimitation'

Abstract This paper provides an overview and a tutorial of the BPP program, which is a Bayesian MCMC program for analyzing multi-locus genomic sequence data under the multispecies coalescent model. An example dataset of five nuclear loci from the East Asian brown frogs is used to illustrate four different analyses, including estimation of species divergence times and population size parameters under the multispecies coalescent model on a fixed species phylogeny (A00), species tree estimation when the assignment and species delimitation are fixed (A01), species delimitation using a fixed guide tree (A10), and joint species delimitation and species-tree estimation or unguided species delimitation (A11). For the joint analysis (A11), two new priors are introduced, which assign uniform probabilities for the different numbers of delimited species, which may be useful when assignment, species delimitation, and species phylogeny are all inferred in one joint analysis. The paper ends with a discussion of the assumptions, the strengths and weaknesses of the BPP analysis.

Garnett and Christidis (2017) [hereafter GC] recently proposed that the International Union of the Biological Sciences should centrally regulate the taxonomy of complex organisms. Their proposal was met with much criticism (e.g. Hołyński 2017; Thomson et al., 2018), and perhaps most extensively from Raposo et al. (2017) in this journal. The main target of this criticism was GC’s call to, first, “restrict the freedom of taxonomic action”, and, second, to let social, political and conservation values weigh in on species classification. Some commentators even went as far as to draw a comparison with the infamous Lysenko-case of state-controlled and heavily restricted science (Raposo et al. 2017, 181; Hołyński 2017, 12). This comment will argue, without thereby endorsing GC’s position, that these two aspects of their views need not be as threatening as this comparison suggests, and indeed are very reasonable.

Statistical species delimitation usually relies on singular data, primarily genetic, for detecting putative species and individual assignment to putative species. Given the variety of speciation mechanisms, singular data may not adequately represent the genetic, morphological and ecological diversity relevant to species delimitation. We describe a methodological framework combining multivariate and clustering techniques that uses genetic, morphological and ecological data to detect and assign individuals to putative species. Our approach recovers a similar number of species recognized using traditional, qualitative taxonomic approaches that are not detected when using purely genetic methods. Furthermore, our approach detects groupings that traditional, qualitative taxonomic approaches do not. This empirical test suggests that our approach to detecting and assigning individuals to putative species could be useful in species delimitation despite varying levels of differentiation across genetic, phenotypic and ecological axes. This work highlights a critical, and often overlooked, aspect of the process of statistical species delimitation—species detection and individual assignment. Irrespective of the species delimitation approach used, all downstream processing relies on how individuals are initially assigned, and the practices and statistical issues surrounding individual assignment warrant careful consideration.

Zoanthidea (Cnidaria, Anthozoa, Hexacorallia) are common on tropical rocky shores and coral reefs. Large numbers of nominate species exist and many are difficult to identify. I used a genetic approach to examine population structure and taxonomy of zoanthids from the Great Barrier Reef and Torres Strait regions of Australia. Genetic population structure was investigated over two different spatial scales, using allozyme electrophoresis at seven polymorphic loci. I collected Palythoa caesia samples from 20 reefs spread over 1800 km. Results show that genetic differentiation among reefs is low but statistically significant, primarily due to variation in two populations. Population structure is characterised by genetic patchiness against a background of high gene flow. In a second study I collected Zoanthus coppingeri samples from three localities. Populations show evidence of asexual reproduction but are not dominated by successful clones. Sites separated by 50 m are genetically differentiated. Gene flow prevents fixed gene differences arising among populations of both these species. Fixed differences in taxonomic surveys (below) are therefore strong indicators of species boundaries. Eight species, from 19 localities throughout the Great Barrier Reef and Torres Strait, were genetically delimited using allozyme analysis of 14 loci. These species are separated by fixed gene differences. Genotype frequencies within species conform to Hardy-Weinberg predicted ratios. There is considerable morphological variation within species. Five species are identified in the family Zoanthidae: Palythoa caesia, Protopalythoa mutuki, Sphenopus marsupialis, Zoanthus coppingeri and Z. vietnamensis. These are probable senior synonyms of eighteen nominate species. Two Protopalythoa species remain unidentified. The eighth species, Parazoanthus dichroicus, is in the Parazoanthidae. A key to species is given. Phylogenetic analysis of zoanthid species used allozyme data and sequence data from 28S rDNA. I discuss results in the light of previous views of zoanthid systematics.

Hintergrund Zu den grundlegendsten Fragestellungen in der Biologie gehört die Frage nach der Natur und Entstehung biologischer Arten. Dieses Problem der Artdefinition (Engl. "Species Problem") war der Ursprung weitläufiger und kontroverser Diskussionen seit der Formulierung der Darwin'schen Evolutionstheorie. Bis heute wurden etwa 30 verschiedene und zum Teil gegensätzliche Konzepte zur Definition und wissenschaftlichen Abgrenzung der Art veröffentlicht. Eine Einigung ist nicht in Sicht. Gleichzeitig ist die Taxonomie mit der Herausforderung konfrontiert, dass ein immenser Teil der weltweiten Artenvielfalt wissenschaftlich noch nicht erfasst und beschrieben ist. Dies erfordert Methoden, die die Beschreibung neuer Arten beschleunigen und gleichzeitig deren Zuverlässigkeit und Nachvollziehbarkeit wahren. DNA-Barcoding, d.h. Artbestimmung an Hand eines kurzen standardisierten Fragments der DNA, soll die Erfassung der Artenvielfalt und das Erkennen unbekannter Arten beschleunigen. Die so genannte "Cybertaxonomie" erlaubt leichteren und schnelleren Zugriff auf vorhandene taxonomische Informationen, indem Daten online und kostenfrei zur Verfügung gestellt werden. Dies trägt zur Steigerung der Effizienz taxonomischer Prozesse bei. Integrative Taxonomie kombiniert verschiedene Beweislinien, wie zum Beispiel morphologische, molekulare und ökologische Daten, um die Zuverlässigkeit und Nachvollziehbarkeit bei der Abgrenzung und Beschreibung von Arten zu erhöhen. In dieser Dissertation untersuche ich zwei verschiedene Studiensysteme, um derzeit als gültig angesehene Modelle der Artbildung und Methoden der Artabgrenzung zu testen. Bei diesen Systemen handelt es sich um die Reptilien der Komoren, einer Gruppe ozeanischer Inseln im westlichen Indischen Ozean, und australische Wasserkäfer. Die Biogeographie dieser beiden Gruppen ist durch höchst unterschiedliche Faktoren geprägt: Die Komoren sind vergleichsweise junge vulkanische Inseln, deren einheimische, landbewohnende und flugunfähige Faunenelemente ausschließlich auf Besiedelung durch Drift über das offene Meer zurückgehen. Dagegen stellt Australien eine alte und isolierte Landmasse dar, deren Lebensgemeinschaften durch Klimaveränderungen in der Erdgeschichte geprägt sind. Ozeanische Inseln wurden schon von frühen Forschern als wichtige Systeme zum Studium der Biogeographie erkannt, und meine Untersuchung dieser beiden so unterschiedlichen Systeme stellt sowohl die Gemeinsamkeiten als auch die Unterschiede der Biogeographie von Inseln und Kontinenten heraus. Methoden und wesentliche Ergebnisse Als Fallbeispiele zur Untersuchung im Rahmen dieser Dissertation wählte ich zwei Teilgruppen der komorischen Reptilien (Geckos der Gattung Paroedura und Schlangen der Gattung Lycodryas) sowie drei Teilgruppen der australischen Wasserkäfer (die Familie Hygrobiidae und die Gattungen Antiporus und Sternopriscus aus der Familie Dytiscidae) aus. In beiden Fällen wurde der Grundstein für weitere Untersuchungen durch DNA-Barcoding gelegt, wie für die Reptilien als Teil dieser Dissertation beschrieben. Als nächsten Schritt führte ich Untersuchungen an mehreren mitochondrialen und nukleären Genmarkern durch, um die Phylogenien der jeweiligen Gruppen zu rekonstruieren und, im Fall der Hygrobiidae, das Alter der Phylogenie durch eine molekulare Uhr abzuschätzen. Ich versuchte, die Phylogenien komorischer Reptilien mit geologischen Daten über die erdgeschichtliche Entstehung der Inseln sowie die Ausbreitungsmöglichkeiten zu und zwischen den Inseln in Verbindung zu bringen. Bei Phylogenien australischer Käfer der Gattungen Antiporus und Sternopriscus suchte ich nach Korrelationen zu Klimaveränderungen in der Erdgeschichte, der Entstehung der australischen Trockengebiete und den Eiszeiten im Pleistozän. Diese Hypothesen konnte ich durch Belege für die ökologische Diversifikation australischer Käfer aus meinen Ökologischen Nischenmodellierungen untermauern. Auf der Grundlage der Ergebnisse von DNA-Barcoding und molekularen Phylogenien unternahm ich taxonomische Revisionen der betreffenden Gruppen nach Methoden der integrativen Taxonomie. Als Beweislinien verwendete ich Daten aus morphologischen Untersuchungen, mitochondrialen und nukleären Genen, sowie kategorische und quantitative ökologische Daten. Dieser Ansatz führte zur Beschreibung einer neuen Art von Käfern (Antiporus occidentalis HAWLITSCHEK, HENDRICH, PORCH, & BALKE, 2011), zweier neuer Arten (Paroedura stellata HAWLITSCHEK & GLAW, 2012 and Lycodryas cococola HAWLITSCHEK, NAGY & GLAW, 2012) und einer Unterart von Reptilien (Lycodryas cococola innocens HAWLITSCHEK, NAGY & GLAW, 2012), sowie zur Bestätigung oder Wiederherstellung der Gültigkeit der zuvor beschriebene Taxa Lycodryas maculatus (GÜNTHER, 1858) und Lycodryas maculatus comorensis (PETERS, 1874). Alle taxonomischen Handlungen wurden gemäß dem Konzept der Cybertaxonomie ausgeführt: es wurden LSID-Nummern vergeben, Einträge in Online-Datenbanken vorgenommen, und nach Möglichkeit Publikationsmodi mit freiem Zugang für Leser gewählt. Zudem verwendete ich die im Rahmen meiner Dissertation gesammelten Daten zur Abschätzung des artenschutzfachlichen Status der Reptilien der Komoren. Außerdem dienten sie als Basis für die Entwicklung von SmartHerper Comoros, einem Naturführer zur Herpetofauna der Komoren als Applikation für Smartphone. Schlussfolgerungen Die Ergebnisse meiner Untersuchungen weisen auf komplexe biogeographische Muster sowohl im insulären als auch im kontinentalen Untersuchungsgebiet hin. Demzufolge haben die Stammformen der dort heimischen Reptilien die Komoren in einem sehr komplizierten Muster besiedelt, das z.B. im Fall der Gecko-Gattung Paroedura mehrere Aussterbe- und Wiederbesiedlungsereignisse beinhaltet und kaum mit der geographischen Lage und dem geologischen Alter der Inseln korreliert. Viele endemische Arten zeigen mögliche morphologische Anpassungen an den Insellebensraum. Molekulare Daten komorischer Reptilien legen nahe, dass Grand Comoro, zuvor als geologisch jüngste Insel angesehen, möglicherweise weit älter ist als bislang angenommen. Über australische Wasserkäfer erhobene Daten zeigten, dass Artbildungsereignisse innerhalb dieser Gruppe von höchst unterschiedlichem erdgeschichtlichem Alter sind und vom Mesozoikum (Hygrobiidae) über das Pleistozän (Antiporus) bis in die jüngste erdgeschichtliche Vergangenheit (Sternopriscus) reichen. Molekulare Unterschiede weisen darauf hin, dass die "Sternopriscus tarsalis radiation" einen der am schnellsten verlaufenen bislang beschriebenen Artbildungsprozesse innerhalb der Insekten darstellt. Der integrativ-taxonomische Ansatz erwies sich in meinen Augen bei der Abgrenzung aller neu beschriebenen Taxa wie auch bei der Bestätigung bestehender Taxa als höchst erfolgreich. Durch diesen Ansatz standen Belege für die Artabgrenzung auch bei unzureichender morphologischer oder genetischer Differenzierung in ausreichendem Maße zur Verfügung. Ökologische Daten, insbesondere solche, die bei Ökologischer Nischenmodellierung gewonnen wurden, haben sich in diesen Fällen als höchst aussagekräftig bei der Artabgrenzung erwiesen. Bei der Anwendung des integrativ-taxonomischen Ansatzes auf Schlangen der Gattung Lycodryas argumentierte ich, den Rang der Unterart auf infraspezifische Einheiten mit einem gewissen Grad der Differenzierung anzuwenden. Schlussendlich liefern die Ergebnisse der Untersuchungen in meiner Dissertation nur einen kleinen, aber meiner Meinung nach dennoch nützlichen Beitrag zu unserem Verständnis darüber, wie biologische Arten entstehen und wie sie wissenschaftlich erfasst werden können. Meine Dissertation präsentiert diese Ergebnisse im Kontext der Debatte über die Artdefinition und stellt auch meine Meinung und Position darin dar. Meiner Ansicht nach ist diese äußerst fruchtbare Debatte von hoher Bedeutung für die zeitgenössische Entwicklung der Evolutionsbiologie und Biodiversitätsforschung.
Background The question of the nature and the origin of biological species is one of the most fundamental issues in biology. This so-called 'species problem' has been intensely debated since the formulation of the theory of evolution by Darwin. To date, about 30 concepts have been published that attempt to define, often conflictingly, what a species is and how it can be recognized by scientists, and a general agreement is not in sight. At the same time, taxonomy faces the challenge of a huge amount of global biodiversity that remains to be scientifically described. Therefore, taxonomic methods are required that make the description of new species faster and at the same time make them more reliable and reproducible. DNA barcoding, i.e., the use of a short standardized fragment of DNA for species identification, means to accelerate biodiversity inventories and the recognition of new species. Cybertaxonomy makes the access to taxonomic information easier and faster and helps increasing the efficiency of the taxonomic workflow by making data available online and free. Integrative taxonomy combines different lines of evidence, such as morphological, molecular, and ecological data, to make species delimitation and species descriptions more reliable and reproducible. In this dissertation I explore two different zoological study systems in order to test current models of speciation and methods of species delimitation. These study systems are the reptiles of the Comoros Archipelago, a group of oceanic islands in the Western Indian Ocean, and aquatic beetles of Australia. The biogeographical backgrounds of these two groups are very different: The Comoros are relatively young volcanic islands whose native terrestrial and non-flying fauna originates exclusively from overseas dispersal. In contrast, Australia is an old isolated landmass whose biota were shaped by past climate change. Oceanic islands have been recognized as prime study systems even by early biogeographers, and my study of these two different systems highlights the common grounds as well as the differences between insular and continental biogeography. Methods and principal findings I selected two groups out of the Comoran reptiles (Paroedura geckos and Lycodryas snakes) and three groups out of the Australian aquatic beetles (family Hygrobiidae and genera Antiporus and Sternopriscus, Dytiscidae) as study groups for this dissertation. In both cases, the data fundament for subsequent studies was laid by DNA barcoding, as included for reptiles in this dissertation. I then conducted analyses of several mitochondrial and nuclear genetic markers to reconstruct the phylogenies of the study groups and, in Hygrobiidae, estimate the divergence times within the phylogeny in a molecular clock approach. In Comoran reptiles, I attempted to correlate phylogenetic hypotheses with the geological history of island emergence and dispersal to and within the archipelago. In Australian Antiporus and Sternopriscus beetles, I attempted to correlate phylogenies with past climate change, the genesis of the Australian arid zone, and the Pleistocene climate oscillations. I used Ecological Niche Modeling to corroborate these hypotheses with evidence for ecological diversification in Australian beetles. Based on the results of DNA barcoding and molecular phylogenies, I used an integrative taxonomic approach to revise the taxonomy of the study groups accordingly. The lines of evidence I used were morphological data, mitochondrial molecular markers, nuclear molecular markers, and categorical and quantitative ecological data. This approach led to the description of one new species of beetle (Antiporus occidentalis HAWLITSCHEK, HENDRICH, PORCH, & BALKE, 2011) and two new species (Paroedura stellata HAWLITSCHEK & GLAW, 2012 and Lycodryas cococola HAWLITSCHEK, NAGY & GLAW, 2012), and one subspecies (Lycodryas cococola innocens HAWLITSCHEK, NAGY & GLAW, 2012), of reptiles, as well as to the confirmation or resurrection of the previously described taxa Lycodryas maculatus (GÜNTHER, 1858) and Lycodryas maculatus comorensis (PETERS, 1874). All taxonomic acts followed a cybertaxonomic concept by using LSID numbers, online databases, and, as far as possible, open access publication. Additionally, I used data collected in the course of this dissertation for estimating the conservation status of Comoran reptiles and for the development of SmartHerper Comoros, a field guide to the herpetofauna of the Comoros as a mobile application for smartphone. Conclusions The results of my studies show complex biogeographic patterns in both the insular and the continental study system. According to these results, the ancestors of native reptiles have colonized the Comoros Archipelago in a very complex pattern, including several events of extinction and re-colonization, e.g., in the case of the gecko genus Paroedura, with little correlation to the geographic positions or geological ages of the islands. Many endemic species show possible morphological adaptations to the island environment. Molecular data of reptiles suggest that Grand Comoro, the presumably geologically youngest island, may be considerably older than previously estimated. In Australian aquatic beetles, speciation events were shown to be of very different ages from Mesozoic (Hygrobiidae) to Pleistocene (Antiporus) and very recent (Sternopriscus). Molecular divergences indicate that speciation in the Sternopriscus tarsalis radiation was one of the fastest speciation events so far described among insects. I applied an integrative taxonomical approach in the delimitation of all newly described taxa and in the confirmation of previously described taxa. This approach provided sufficient evidence for species delimitation even in the absence of morphological differentiation (Antiporus), or when genetic data did not provide any clear evidence (Sternopriscus tarsalis radiation). In these cases, ecological data, particularly such data from Ecological Niche Modeling, was shown to be highly useful in integrative species delimitation. In the same approach applied to Lycodryas snakes, I argued for the usefulness of the subspecies rank for infraspecific entities with some degree of differentiation. I conclude that my research in the study systems I investigated in this dissertation are but small pieces that nevertheless advance our understanding of speciation and species delimitation by contributing to the ongoing debate on the species problem. My dissertation presents these results and represents my position in the debate. I see this debate as a very fruitful process that is highly important for the current development of evolutionary biology and biodiversity research.

The plant family Gesneriaceae is represented in Sri Lanka by six genera: Aeschynanthus, Epithema, Championia, Henckelia, Rhynchoglossum and Rhynchotechum, with 13 species (plus one subspecies/variety) of which ten are endemic including the monotypic genus Championia, according to the last revision in 1981. They are exclusively distributed in undisturbed habitats, and some have high ornamental value. The species are morphologically diverse, but face a problem of taxonomic delineation, which is further complicated by the presence of putative hybrids. Sri Lanka and Indian Peninsula, represent the Deccan plate of the ancient Gondwanan supercontinent. The presence of a relict flora may indicate the significance of the geological history of the Deccan plate for the evolution of angiosperms. The high degree of endemism here, along with their affinities to the global angiosperm flora paints a complex picture, but its biogeographic history is still unclear. The pantropical family Gesneriaceae distributed in Sri Lanka and South India is therefore an appropriate study group in this context. Besides, the family itself has a complex but largely unresolved biogeographical history especially concerning the origin and diversification of Old World Gesneriaceae. Modern approaches for the taxonomic studies were applied, integrating morphological and molecular data. Multiple samples were collected for each species across their geographical distribution. Nuclear ITS and chloroplast trnL-F sequences for the taxa from Sri Lanka were used to generate regional genus phylogenies of all six genera, using maximum parsimony. The rate of evolution of the nuclear ITS region versus chloroplast trnL-F was varied greatly across the six genera studied. Molecular delimitations were mostly congruent with the classical taxonomy. Over 65 taxonomic characters were studied in detail to recognize synapomorphies for clades and taxa. A complete taxonomic revision of Gesneriaceae in Sri Lanka, including lectotypification, was conducted based on both, the molecular and morphological data. This resulted in the recognition of 14 species in the six genera, including one newly described species H. wijesundarae Ranasinghe and Mich. Möller. Henckelia communis and H. angusta were not supported molecularly as two separate entities but are recognized as two species because of consistent morphological differences between them. Henckelia humboldtiana is proposed to represent a species complex due to its highly variable and inconsistent molecular and morphological diversity and overlap with H. incana and H. floccosa; more research is needed here. National conservation assessments were conducted, and all 14 species were recognized as threatened. Biogeographic affinities of Sri Lankan Gesneriaceae were elucidated, generating a dated phylogeny using an existing matrix of four plastid gene regions; trnL-F, matK, rps16 and ndhF, amended by sequences generated in this study. The final combined matrix included 175 taxa including newly generated sequences for the 13 Sri Lankan taxa. Phylogenetic trees were generated using parsimony, maximum likelihood and Bayesian inference. Molecular dating was carried out using BEAST and ancestral area reconstruction using BioGeoBears. These analyses indicated that the six genera of Gesneriaceae arrived in Sri Lanka separately and sometimes different time periods. One lineage dated back to the early diversification of the subfamily Didymocarpoideae (generally regarded as the Old World Gesneriaceae), which occurred around the KT boundary, before the Deccan plate was connected to Asia.

Heteromys pictus-spectabilis is a species complex within the subfamily Heteromyinae (Family: Heteromyidae) that is distributed along the western and southern Mexican coast and surrounding environments. Currently, the species complex is accepted as being 2 separate species (H. pictus and H. spectabilis), but this also renders H. pictus paraphyletic. Therefore, the species complex requires re-evaluation in order to resolve the paraphyly. Mitochondrial DNA sequences from a previously existing ~720 specimen database compiled by Victoria Vance were used in conjunction with new nuclear DNA sequences sequenced for the purpose of this study to generate multiple phylogenetic trees via the software programs RAxML, BEAST, and MrBayes to evaluate how different haplotype networks were related to each other. Using these molecular datasets in consideration with Kimura two-parameter values, time calibrations via BEAST, and the relative geographic locations of the haplotype networks, the results strongly indicate this species complex is composed of multiple cryptic species and potentially multiple genera. This was a preliminary exploration into this species complex however, and future research will be required to verify these findings.

BACKGROUND:Traditional morphological and biological species concepts are difficult to apply to closely related, asexual taxa because of the lack of an active sexual phase and paucity of morphological characters. Phylogenetic species concepts such as genealogical concordance phylogenetic species recognition (GCPSR) have been extensively used
however, methods that incorporate gene tree uncertainty into species recognition may more accurately and objectively delineate species. Using a worldwide sample of Alternaria alternata sensu lato, causal agent of citrus brown spot, the evolutionary histories of four nuclear loci including an endo-polygalacturonase gene, two anonymous loci, and one microsatellite flanking region were estimated using the coalescent. Species boundaries were estimated using several approaches including those that incorporate uncertainty in gene genealogies when lineage sorting and non-reciprocal monophyly of gene trees is common.RESULTS:Coalescent analyses revealed three phylogenetic lineages strongly influenced by incomplete lineage sorting and recombination. Divergence of the citrus 2 lineage from the citrus 1 and citrus 3 lineages was supported at most loci. A consensus of species tree estimation methods supported two species of Alternaria causing citrus brown spot worldwide. Based on substitution rates at the endo-polygalacturonase locus, divergence of the citrus 2 and the 1 and 3 lineages was estimated to have occurred at least 5, 400 years before present, predating the human-mediated movement of citrus and associated pathogens out of SE Asia.CONCLUSIONS:The number of Alternaria species identified as causing brown spot of citrus worldwide using morphological criteria has been overestimated. Little support was found for most of these morphospecies using quantitative species recognition approaches. Correct species delimitation of plant-pathogenic fungi is critical for understanding the evolution of pathogenicity, introductions of pathogens to new areas, and for regulating the movement of pathogens to enforce quarantines. This research shows that multilocus phylogenetic methods that allow for recombination and incomplete lineage sorting can be useful for the quantitative delimitation of asexual species that are morphologically indistinguishable. Two phylogenetic species of Alternaria were identified as causing citrus brown spot worldwide. Further research is needed to determine how these species were introduced worldwide, how they differ phenotypically and how these species are maintained.

Cryptic species are organisms which look identical, but which represent distinct evolutionary lineages. They are an emerging trend in organismal biology across all groups, from flatworms, insects, amphibians, primates, to vascular plants. This book critically evaluates the phenomenon of cryptic species and demonstrates how they can play a valuable role in improving our understanding of evolution, in particular of morphological stasis. It also explores how the recognition of cryptic species is intrinsically linked to the so-called 'species problem', the lack of a unifying species concept in biology, and suggests alternative approaches. Bringing together a range of perspectives from practicing taxonomists, the book presents case studies of cryptic species across a range of animal and plant groups. It will be an invaluable text for all biologists interested in species and their delimitation, definition, and purpose, including undergraduate and graduate students and researchers.

Interest in the first hunter-gatherer populations of Mexico has increased in the last fifteen years. Exploration of the Late Pleistocene localities involved in the early peopling of Mexico, including the discovery of new ones and reanalysis of known ones, and the application of new methods and techniques (e.g. AMS radiocarbon dating, stable isotopes, scanning electron microscopy, palaeobotanical analysis) have increased. Archaeozoology has contributed to this expansion by increasing the record of terrestrial vertebrates, improving understanding of the record and delimitation of distributional ranges of extinct species. There is now more information on the type of diet of some extinct herbivores and hypotheses about the status of local palaeoenvironments have been provided. Questions remain about the interactions between human migrations and the environments, specifically the degree of influence that humans had in the extinction of mega- and mesofaunas, and the diversity of subsistence strategies employed by hunter-gatherers in the Late Pleistocene.

Human activities have taken place in the world's oceans and seas for most of human history. With such a vast number of ways in which the oceans can be used for trade, exploited for natural resources and fishing, as well as concerns over maritime security, the legal systems regulating the rights and responsibilities of nations in their use of the world's oceans have long been a crucial part of international law. The United Nations Convention on the Law of the Sea comprehensively defined the parameters of the law of the sea in 1982, and since the Convention was concluded it has seen considerable development. This book provides an analysis of its current debates and controversies, both theoretical and practical. It consists of forty chapters divided into six parts. First, it explains the origins and evolution of the law of the sea, with a particular focus upon the role of key publicists such as Hugo Grotius and John Selden, the gradual development of state practice, and the creation of the 1982 UN Convention. It then reviews the components which comprise the maritime domain, assessing their definition, assertion, and recognition. It also analyzes the ways in which coastal states or the international community can assert control over areas of the sea, and the management and regulation of each of the maritime zones. This includes investigating the development of the mechanisms for maritime boundary delimitation, and the decisions of the International Tribunal for the Law of the Sea. The book also discusses the actors and intuitions that impact on the law of the sea, considering their particular rights and interests, in particular those of state actors and the principle law of the sea institutions. Then it focuses on operational issues, investigating longstanding matters of resource management and the integrated oceans framework. This includes a discussion and assessment of the broad and increasingly influential integrated oceans management governance framework that interacts with the traditional law of the sea. It considers six distinctive regions that have been pivotal to the development of the law of the sea, before finally providing a detailed analysis of the critical contemporary issues facing the law of the sea. These include threatened species, climate change, bioprospecting, and piracy.

The aim of this paper is to compare the superlexical prefixes of Russian and Bulgarian. The main focus is on delimitative and attenuative po- in derived PF forms as well as in secondary IPF verbs. Using the Russian-Bulgarian parallel corpus, I show that there is a functional parallelism between PF and IPF delimitatives in Russian and Bulgarian. The semantic similarity between delimitative and attenuative meaning is the basis for expressing special pragmatic functions by means of both PF and IPF poattenuatives in Bulgarian, while attenuative po-verbs in Russian express specific pragmatic meanings primarily via PF forms.