Nancy Knowlton

Smithsonian Institution, Washington, Washington, D.C., United States

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Publications (88)680.1 Total impact

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    ABSTRACT: Modern coral taxonomy has begun to resolve many long-standing problems in traditional systematics stemming from its reliance on skeletal macromorphology. By integrating examinations of colony, corallite, and subcorallite morphology with the molecular sequence data that have proliferated in the last decade, many taxa spread across the scleractinian tree of life have been incorporated into a rigorous classification underpinned by greater phylogenetic understanding. This monograph focuses on one of the most challenging clades recovered to date – its disarray epitomized by the informal name ‘Bigmessidae’. This group of predominantly Indo-Pacific species previously comprised families Merulinidae, Faviidae, Pectiniidae, and Trachyphylliidae, but in a recent study these have been incorporated within Merulinidae. We studied 84 living merulinid species by examining morphological traits at three different scales of coral skeletal structure − macromorphology, micromorphology, and microstructure − to construct a morphological matrix comprising 44 characters. Data were analysed via maximum parsimony and also transformed onto a robust molecular phylogeny under the parsimony and maximum likelihood criteria. Comparisons amongst morphological character types suggest that although many characters at every scale are homoplastic, some to a greater extent than others, several can aid in distinguishing genus-level clades. Our resulting trees and character analyses form the basis of a revised classification that spans a total of 139 species contained within 24 genera. The tree topologies necessitate the synonymization of Barabattoia as Dipsastraea, and Phymastrea as Favites. Furthermore, Astrea and Coelastrea are resurrected, and one new genus, Paramontastraea Huang & Budd gen. nov., is described. All the genera in Merulinidae, along with the monotypic Montastraeidae and Diploastraeidae, are diagnosed based on the characters examined. The integrative classification system proposed here will form the framework for more accurate biodiversity estimates and guide the taxonomic placement of extinct species. © 2014 The Linnean Society of London
    Zoological Journal of the Linnean Society 06/2014; 171(2). · 2.58 Impact Factor
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    ABSTRACT: Explaining patterns of commonness and rarity is fundamental for understanding and managing biodiversity. Consequently, a key test of biodiversity theory has been how well ecological models reproduce empirical distributions of species abundances. However, ecological models with very different assumptions can predict similar species abundance distributions, whereas models with similar assumptions may generate very different predictions. This complicates inferring processes driving community structure from model fits to data. Here, we use an approximation that captures common features of “neutral” biodiversity models—which assume ecological equivalence of species—to test whether neutrality is consistent with patterns of commonness and rarity in the marine biosphere. We do this by analyzing 1,185 species abundance distributions from 14 marine ecosystems ranging from intertidal habitats to abyssal depths, and from the tropics to polar regions. Neutrality performs substantially worse than a classical nonneutral alternative: empirical data consistently show greater heterogeneity of species abundances than expected under neutrality. Poor performance of neutral theory is driven by its consistent inability to capture the dominance of the communities’ most-abundant species. Previous tests showing poor performance of a neutral model for a particular system often have been followed by controversy about whether an alternative formulation of neutral theory could explain the data after all. However, our approach focuses on common features of neutral models, revealing discrepancies with a broad range of empirical abundance distributions. These findings highlight the need for biodiversity theory in which ecological differences among species, such as niche differences and demographic trade-offs, play a central role.
    Proceedings of the National Academy of Sciences 05/2014; early edition. · 9.81 Impact Factor
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    Science 05/2014; 344(6186):814-815. · 31.20 Impact Factor
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    Science 05/2014; 344(6186):814-815. · 31.20 Impact Factor
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    Science 05/2014; 344(6186):814-815. · 31.20 Impact Factor
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    ABSTRACT: Over 95% of all metazoan (animal) species comprise the “invertebrates,” but very few genomes from these organisms have been sequenced. We have, therefore, formed a “Global Invertebrate Genomics Alliance” (GIGA). Our intent is to build a collaborative network of diverse scientists to tackle major challenges (e.g., species selection, sample collection and storage, sequence assembly, annotation, analytical tools) associated with genome/transcriptome sequencing across a large taxonomic spectrum. We aim to promote standards that will facilitate comparative approaches to invertebrate genomics and collaborations across the international scientific community. Candidate study taxa include species from Porifera, Ctenophora, Cnidaria, Placozoa, Mollusca, Arthropoda, Echinodermata, Annelida, Bryozoa, and Platyhelminthes, among others. GIGA will target 7000 noninsect/nonnematode species, with an emphasis on marine taxa because of the unrivaled phyletic diversity in the oceans. Priorities for selecting invertebrates for sequencing will include, but are not restricted to, their phylogenetic placement; relevance to organismal, ecological, and conservation research; and their importance to fisheries and human health. We highlight benefits of sequencing both whole genomes (DNA) and transcriptomes and also suggest policies for genomic-level data access and sharing based on transparency and inclusiveness. The GIGA Web site (http://giga.nova.edu) has been launched to facilitate this collaborative venture.
    Journal of Heredity 01/2014; 105(1):1-18. · 2.00 Impact Factor
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    ABSTRACT: Over 95% of all metazoan (animal) species comprise the “invertebrates,” but very few genomes from these organisms have been sequenced. We have, therefore, formed a “Global Invertebrate Genomics Alliance” (GIGA). Our intent is to build a collaborative network of diverse scientists to tackle major challenges (e.g., species selection, sample collection and storage, sequence assembly, annotation, analytical tools) associated with genome/transcriptome sequencing across a large taxonomic spectrum. We aim to promote standards that will facilitate comparative approaches to invertebrate genomics and collaborations across the international scientific community. Candidate study taxa include species from Porifera, Ctenophora, Cnidaria, Placozoa, Mollusca, Arthropoda, Echinodermata, Annelida, Bryozoa, and Platyhelminthes, among others. GIGA will target 7000 noninsect/nonnematode species, with an emphasis on marine taxa because of the unrivaled phyletic diversity in the oceans. Priorities for selecting invertebrates for sequencing will include, but are not restricted to, their phylogenetic placement; relevance to organismal, ecological, and conservation research; and their importance to fisheries and human health. We highlight benefits of sequencing both whole genomes (DNA) and transcriptomes and also suggest policies for genomic-level data access and sharing based on transparency and inclusiveness. The GIGA Web site (http://giga.nova.edu) has been launched to facilitate this collaborative venture.
    Journal of Heredity 12/2013; 105(1):1-18. · 2.00 Impact Factor
  • C Hurt, K Silliman, A Anker, N Knowlton
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    ABSTRACT: Divergent natural selection driven by competition for limited resources can promote speciation, even in the presence of gene flow. Reproductive isolation is more likely to result from divergent selection when the partitioned resource is closely linked to mating. Obligate symbiosis and host fidelity (mating on or near the host) can provide this link, creating ideal conditions for speciation in the absence of physical barriers to dispersal. Symbiotic organisms often experience competition for hosts, and host fidelity ensures that divergent selection for a specific host or host habitat can lead to speciation and strengthen pre-existing reproductive barriers. Here, we present evidence that diversification of a sympatric species complex occurred despite the potential for gene flow and that partitioning of host resources (both by species and by host habitat) has contributed to this diversification. Four species of snapping shrimps (Alpheus armatus, A. immaculatus, A. polystictus and A. roquensis) are distributed mainly sympatrically in the Caribbean, while the fifth species (A. rudolphi) is restricted to Brazil. All five species are obligate commensals of sea anemones with a high degree of fidelity and ecological specificity for host species and habitat. We analysed sequence data from 10 nuclear genes and the mitochondrial COI gene in 11-16 individuals from each of the Caribbean taxa and from the only available specimen of the Brazilian taxon. Phylogenetic analyses support morphology-based species assignments and a well-supported Caribbean clade. The Brazilian A. rudolphi is recovered as an outgroup to the Caribbean taxa. Isolation-migration coalescent analysis provides evidence for historical gene flow among sympatric sister species. Our data suggest that both selection for a novel host and selection for host microhabitat may have promoted diversification of this complex despite gene flow.
    Molecular Ecology 07/2013; · 6.28 Impact Factor
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    ABSTRACT: Ancient DNA (aDNA) provides powerful evidence for detecting the genetic basis for adaptation to environmental change in many taxa. Among the greatest of changes in our biosphere within the last century is rapid anthropogenic ocean warming. This phenomenon threatens corals with extinction, evidenced by the increasing observation of widespread mortality following mass bleaching events. There is some evidence and conjecture that coral-dinoflagellate symbioses change partnerships in response to changing external conditions over ecological and evolutionary timescales. Until now, we have been unable to ascertain the genetic identity of Symbiodinium hosted by corals prior to the rapid global change of the last century. Here, we show that Symbiodinium cells recovered from dry, century old specimens of 6 host species of octocorals contain sufficient DNA for amplification of the ITS2 subregion of the nuclear ribosomal DNA, commonly used for genotyping within this genus. Through comparisons with modern specimens sampled from similar locales we show that symbiotic associations among several species have been static over the last century, thereby suggesting that adaptive shifts to novel symbiont types is not common among these gorgonians, and perhaps, symbiotic corals in general.
    PLoS ONE 01/2013; 8(2):e55057. · 3.73 Impact Factor
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    ABSTRACT: The United States is an ocean nation—our past, present, and future are inextricably connected to and dependent on oceans and marine resources. Marine ecosystems provide many important services, including jobs, food, transportation routes, recreational opportunities, health benefits, climate regulation, and cultural heritage that affect people, communities, and economies across the United States and internationally every day. There is a wealth of information documenting the strong linkages between the planet’s climate and ocean systems, as well as how changes in the climate system can produce changes in the physical, chemical, and biological characteristics of ocean ecosystems on a variety of spatial and temporal scales. There is relatively little information on how these climate-driven changes in ocean ecosystems may have an impact on ocean services and uses, although it is predicted that ocean-dependent users, communities, and economies will likely become increasingly vulnerable in a changing climate. Based on our current understanding and future projections of the planet’s ocean systems, it is likely that marine ecosystems will continue to be affected by anthropogenic-driven climate change into the future. This review describes how these impacts are set in motion through a suite of changes in ocean physical, chemical, and biological components and processes in U.S. waters and the significant implications of these changes for ocean users and the communities and economies that depend on healthy oceans. U.S. international partnerships, management challenges, opportunities, and knowledge gaps are also discussed. Effectively preparing for and responding to climate-driven changes in the ocean will require both limiting future change through reductions of greenhouse gases and adapting to the changes that we can no longer avoid.
    Oceanography and marine biology 01/2013; 51:71-192. · 6.91 Impact Factor
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    ABSTRACT: In broadcast spawners, prezygotic reproductive isolation depends on differences in the spatial and temporal patterns of gamete release and gametic incompatibility. Typically, gametic incompatibility is measured in no-choice crosses, but conspecific sperm precedence (CSP) can prevent hybridization in gametes that are compatible in the absence of sperm competition. Broadcast spawning corals in the Montastraea annularis species complex spawn annually on the same few evenings. Montastraea franksi spawns an average of 110 min before M. annularis, with a minimum gap of approximately 40 min. Gametes are compatible in no-choice heterospecific assays, but it is unknown whether eggs exhibit choice when in competition. Hybridization depends on either M. franksi eggs remaining unfertilized and in proximity to M. annularis when the latter species spawns or M. franksi sperm remaining in sufficient viable concentrations when M. annularis spawns. We found that the eggs of the early spawning M. franksi demonstrate strong CSP, whereas CSP appears to be lacking for M. annularis eggs. This study provides evidence of diverging gamete affinities between these recently separated species and suggests for the first time that selection may favour CSP in earlier spawning species when conspecific sperm is diluted and aged and is otherwise at a numeric and viability disadvantage with heterospecific sperm.
    Journal of Evolutionary Biology 10/2012; · 3.48 Impact Factor
  • Nancy Knowlton
    Proceedings of the National Academy of Sciences 10/2012; · 9.81 Impact Factor
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    ABSTRACT: Molecular analyses are transforming our understanding of the evolution of scleractinian corals and conflict with traditional classification, which is based on skeletal morphology. A new classification system, which integrates molecular and morphological data, is essential for documenting patterns of biodiversity and establishing priorities for marine conservation, as well as providing the morphological characters needed for linking present-day corals with fossil species. The present monograph is the first in a series whose goal is to develop such an integrated system. It addresses the taxonomic relationships of 55 Recent zooxanthellate genera (one new) in seven families (one new), which were previously assigned to the suborder Faviina (eight genera are transferred to incertae sedis). The present monograph has two objectives. First, we introduce the higher-level classification system for the 46 genera whose relationships are clear. Second, we formally revise the taxonomy of those corals belonging to the newly discovered family-level clade (restricted today to the western Atlantic and Caribbean regions); this revised family Mussidae consists of ten genera (one of which is new) and 26 species that were previously assigned to the 'traditional' families Faviidae and Mussidae. To guide in discovering morphologic characters diagnostic of higher-level taxa, we mapped a total of 38 morphologic characters [19 macromorphology, eight micromorphology, 11 microstructure] onto a molecular tree consisting of 67 species [22 Indo-Pacific and seven Atlantic species in the traditional family Faviidae; 13 Indo-Pacific and ten Atlantic species in the traditional family Mussidae; 13 species in the traditional families Merulinidae (5), Pectiniidae (7), and Trachyphylliidae (1); two Atlantic species of traditional Montastraea], and trace character histories using parsimony. To evaluate the overall effectiveness of morphological data in phylogeny reconstruction, we performed morphology-based phylogenetic analyses using 27 (80 states) of the 38 characters, and compared morphological trees with molecular trees. The results of the ancestral state reconstructions revealed extensive homoplasy in almost all morphological characters. Family-and subfamily-level molecular clades [previously identified as XVII-XXI] are best distinguished on the basis of the shapes of septal teeth and corresponding microstructure. The newly revised family Mussidae (XXI) has septal teeth with regular pointed tips (a symplesiomorphy) and a stout blocky appearance. It has two subfamilies, Mussinae and Faviinae. The subfamily Mussinae is distinguished by spine-shaped teeth and widely spaced costoseptal clusters of calcification centres. The subfamily Faviinae is distinguished by blocky, pointed tricorne or paddle-shaped teeth with elliptical bases, transverse structures such as carinae that cross the septal plane, and well-developed aligned granules. Defining diagnostic characters for the broader data set is more challenging. In analyses of taxonomic subsets of the data set that were defined by clade, morphological phylogenetic analyses clearly distinguished the families Mussidae (XXI) and Lobophylliidae (XIX), as well as the two subfamilies of Mussidae (Mussinae, Faviinae), with one exception (Homophyllia australis). However, analyses of the entire 67-species data set distinguished the family Lobophylliidae (XIX), but not the Merulinidae (XVII) and not the newly defined Mussidae (XXI), although the subfamily Mussinae was recovered as monophyletic. Some lower-level relationships within the Merulinidae (XVII) agree with molecular results, but this particular family is especially
    Zoological Journal of the Linnean Society 01/2012; · 2.58 Impact Factor
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    Ryuji J Machida, Matthew Kweskin, Nancy Knowlton
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    ABSTRACT: Assessment of the biodiversity of communities of small organisms is most readily done using PCR-based analysis of environmental samples consisting of mixtures of individuals. Known as metagenetics, this approach has transformed understanding of microbial communities and is beginning to be applied to metazoans as well. Unlike microbial studies, where analysis of the 16S ribosomal DNA sequence is standard, the best gene for metazoan metagenetics is less clear. In this study we designed a set of PCR primers for the mitochondrial 12S ribosomal DNA sequence based on 64 complete mitochondrial genomes and then tested their efficacy. A total of the 64 complete mitochondrial genome sequences representing all metazoan classes available in GenBank were downloaded using the NCBI Taxonomy Browser. Alignment of sequences was performed for the excised mitochondrial 12S ribosomal DNA sequences, and conserved regions were identified for all 64 mitochondrial genomes. These regions were used to design a primer pair that flanks a more variable region in the gene. Then all of the complete metazoan mitochondrial genomes available in NCBI's Organelle Genome Resources database were used to determine the percentage of taxa that would likely be amplified using these primers. Results suggest that these primers will amplify target sequences for many metazoans. Newly designed 12S ribosomal DNA primers have considerable potential for metazoan metagenetic analysis because of their ability to amplify sequences from many metazoans.
    PLoS ONE 01/2012; 7(4):e35887. · 3.73 Impact Factor
  • Ryuji J Machida, Nancy Knowlton
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    ABSTRACT: Metagenetic analysis using second-generation sequencing offers a novel methodology for measuring the diversity of metazoan communities. Among commercially available second-generation sequencers, the 454 GS FLX Titanium (Roche Diagnostics) offers by far the longest read length and can produce one million sequences from a single run. Compared to the large number of sequences produced from single run, however, number of samples these machines can process is rather low. In this chapter, we describe the use of MID adapters to mix multiple PCR amplicons into a single 454 run. This strategy is rather easy to use and up to 132 samples can be multiplexed into a single 454 run. If a large number of samples are going to be mixed into a single 454 run, however, high cost might be next bottleneck. In this context, we also discuss other ways of multiplexing, including the use of fusion primers and Parallel Tagged Sequencing and weigh their advantages and disadvantages.
    Methods in molecular biology (Clifton, N.J.) 01/2012; 858:355-61. · 1.29 Impact Factor
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    Ryuji J Machida, Nancy Knowlton
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    ABSTRACT: Metagenetic analyses, which amplify and sequence target marker DNA regions from environmental samples, are increasingly employed to assess the biodiversity of communities of small organisms. Using this approach, our understanding of microbial diversity has expanded greatly. In contrast, only a few studies using this approach to characterize metazoan diversity have been reported, despite the fact that many metazoan species are small and difficult to identify or are undescribed. One of the reasons for this discrepancy is the availability of universal primers for the target taxa. In microbial studies, analysis of the 16S ribosomal DNA is standard. In contrast, the best gene for metazoan metagenetics is less clear. In the present study, we have designed primers that amplify the nuclear 18S and 28S ribosomal DNA sequences of most metazoan species with the goal of providing effective approaches for metagenetic analyses of metazoan diversity in environmental samples, with a particular emphasis on marine biodiversity. Conserved regions suitable for designing PCR primers were identified using 14,503 and 1,072 metazoan sequences of the nuclear 18S and 28S rDNA regions, respectively. The sequence similarity of both these newly designed and the previously reported primers to the target regions of these primers were compared for each phylum to determine the expected amplification efficacy. The nucleotide diversity of the flanking regions of the primers was also estimated for genera or higher taxonomic groups of 11 phyla to determine the variable regions within the genes. The identified nuclear ribosomal DNA primers (five primer pairs for 18S and eleven for 28S) and the results of the nucleotide diversity analyses provide options for primer combinations for metazoan metagenetic analyses. Additionally, advantages and disadvantages of not only the 18S and 28S ribosomal DNA, but also other marker regions as targets for metazoan metagenetic analyses, are discussed.
    PLoS ONE 01/2012; 7(9):e46180. · 3.73 Impact Factor
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    ABSTRACT: In marine ecosystems, rising atmospheric CO2 and climate change are associated with concurrent shifts in temperature, circulation, stratification, nutrient input, oxygen content, and ocean acidification, with potentially wide-ranging biological effects. Population-level shifts are occurring because of physiological intolerance to new environments, altered dispersal patterns, and changes in species interactions. Together with local climate-driven invasion and extinction, these processes result in altered community structure and diversity, including possible emergence of novel ecosystems. Impacts are particularly striking for the poles and the tropics, because of the sensitivity of polar ecosystems to sea-ice retreat and poleward species migrations as well as the sensitivity of coral-algal symbiosis to minor increases in temperature. Midlatitude upwelling systems, like the California Current, exhibit strong linkages between climate and species distributions, phenology, and demography. Aggregated effects may modify energy and material flows as well as biogeochemical cycles, eventually impacting the overall ecosystem functioning and services upon which people and societies depend.
    Annual Review of Marine Science 01/2012; 4:11-37. · 14.37 Impact Factor

Publication Stats

6k Citations
680.10 Total Impact Points

Institutions

  • 2008–2014
    • Smithsonian Institution
      • Department of Invertebrate Zoology
      Washington, Washington, D.C., United States
    • Kyoto University
      • Advanced Education and Research Center of Energy Science
      Kyoto, Kyoto-fu, Japan
    • University of Queensland 
      • Centre for Marine Studies
      Brisbane, Queensland, Australia
    • San Diego State University
      • Department of Biology
      San Diego, CA, United States
  • 2013
    • Carnegie Institution for Science
      Washington, West Virginia, United States
  • 1997–2013
    • University of Miami
      • • Department of Biology
      • • Rosenstiel School of Marine and Atmospheric Science
      كورال غيبلز، فلوريدا, Florida, United States
  • 2012
    • Academia Sinica
      • Biodiversity Research Center
      T’ai-pei, Taipei, Taiwan
  • 2000–2012
    • University of California, San Diego
      • • Center for Marine Biodiversity and Conservation
      • • Marine Biology Research Division
      San Diego, California, United States
  • 2011
    • University of Geneva
      Genève, Geneva, Switzerland
  • 2004–2011
    • Florida State University
      • Department of Biological Science
      Tallahassee, FL, United States
  • 1992–2006
    • Smithsonian Tropical Research Institute
      Ciudad de Panamá, Panamá, Panama
  • 2001–2003
    • National University (California)
      San Diego, California, United States
  • 2002
    • Natural History Museum, London
      • Department of Zoology
      London, ENG, United Kingdom
  • 1998–1999
    • Universität Basel
      • Zoological Institute
      Basel, BS, Switzerland
  • 1995
    • Australian Institute of Marine Science
      Townsville, Queensland, Australia