Defining ‘Evolutionarily Significant Units’ for conservation
TL;DR: With the explicit recognition of the genetic component of biodiversity in conservation legislation of many countries and in the Convention on Biological Diversity, the ESU concept is set to become increasingly significant for conservation of natural as well as captive populations.
Abstract: writing in the first issue of TREE, Ryder’ brought the term ‘Evolutionarily Significant Unit’ (ESU) to the attention of a broad audience of ecologists and evolutionary biologists. The ESU concept was developed to provide a rational basis for prioritizing taxa for conservation effort (e.g. captive breeding), given that resources are limited and that existing taxonomy may not adequately reflect underlying genetic diversity*. With the explicit recognition of the genetic component of biodiversity in conservation legislation of many countries and in the Convention on Biological Diversity, the ESU concept is set to become increasingly significant for conservation of natural as well as captive populations.
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TL;DR: A unified species concept can be achieved by treating existence as a separately evolving metapopulation lineage as the only necessary property of species and the former secondary species criteria as different lines of evidence relevant to assessing lineage separation.
Abstract: The issue of species delimitation has long been confused with that of species conceptualization, leading to a half century of controversy concerning both the definition of the species category and methods for inferring the boundaries and numbers of species. Alternative species concepts agree in treating existence as a separately evolving metapopulation lineage as the primary defining property of the species category, but they disagree in adopting different properties acquired by lineages during the course of divergence (e.g., intrinsic reproductive isolation, diagnosability, monophyly) as secondary defining properties (secondary species criteria). A unified species concept can be achieved by treating existence as a separately evolving metapopulation lineage as the only necessary property of species and the former secondary species criteria as different lines of evidence (operational criteria) relevant to assessing lineage separation. This unified concept of species has several consequences for species delimitation, including the following: First, the issues of species conceptualization and species delimitation are clearly separated; the former secondary species criteria are no longer considered relevant to species conceptualization but only to species delimitation. Second, all of the properties formerly treated as secondary species criteria are relevant to species delimitation to the extent that they provide evidence of lineage separation. Third, the presence of any one of the properties (if appropriately interpreted) is evidence for the existence of a species, though more properties and thus more lines of evidence are associated with a higher degree of corroboration. Fourth, and perhaps most significantly, a unified species concept shifts emphasis away from the traditional species criteria, encouraging biologists to develop new methods of species delimitation that are not tied to those properties.
2,875 citations
Cites background from "Defining ‘Evolutionarily Significan..."
...For example, the existence of separate species is commonly inferred from reciprocal monophyly of the alleles at a given locus in allopartically or parapatrically distributed sets of populations (e.g., Moritz, 1994; Avise and Wollenberg, 1997)....
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TL;DR: This work argues for a broader categorization of population distinctiveness based on concepts of ecological and genetic exchangeability (sensu Templeton), which are more relevant for conservation.
Abstract: Conservation biologists assign population distinctiveness by classifying populations as evolutionarily significant units (ESUs). Historically, this classification has included ecological and genetic data. However, recent ESU concepts, coupled with increasing availability of data on neutral genetic variation, have led to criteria based exclusively on molecular phylogenies. We argue that the earlier definitions of ESUs, which incorporated ecological data and genetic variation of adaptive significance, are more relevant for conservation. Furthermore, this dichotomous summary (ESU or not) of a continuum of population differentiation is not adequate for determining appropriate management actions. We argue for a broader categorization of population distinctiveness based on concepts of ecological and genetic exchangeability ( sensu Templeton).
1,852 citations
Cites background from "Defining ‘Evolutionarily Significan..."
...Moritz 1994: populations that are reciprocally monophyletic for mtDNA alleles and show signifi cant divergence of allele frequencies at nuclear loci3....
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TL;DR: The methods proposed to identify prior- ity areas for conservation of the genetic resources of the argan tree are compared to those sometimes advo- cated in the case of reserve design, where one of the goals is to maximize species richness.
Abstract: To select candidate populations of wild species to be given priority for conservation, genetic criteria gained from the study of molecular markers may be useful. Traditionally, diversity measures such as ex- pected heterozygosity or percentage of polymorphic loci have been considered. For conservation we propose instead that priority should be given to measures of allelic richness. To standardize the results of allelic rich- ness across populations, we used the technique of rarefaction. This technique allows evaluation of the ex- pected number of different alleles among equal-sized samples drawn from several different populations. We also show how the contribution of each population to total diversity can be partitioned into two components. The first is related to the level of diversity of the population and the second to its divergence from the other populations. For conservation purposes the uniqueness of a population-in terms of its allelic composition- may be at least as important as its diversity level. These new descriptors are illustrated by means of isozyme and chloroplast DNA data obtainedfor an endangered tree species, the argan tree of Morocco (Argania spinosa (L.) Skeels). With these analyses the conservation value of the argan tree populations, especially those of two isolates present in the north of the country, can be better appreciated. The methods proposed to identify prior- ity areas for conservation of the genetic resources of the argan tree are compared to those sometimes advo- cated in the case of reserve design, where one of the goals is to maximize species richness.
1,621 citations
Cites background from "Defining ‘Evolutionarily Significan..."
...According to Moritz (1994), both types of information should be included to identify evolutionarily significant units (ESUs)....
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TL;DR: It is suggested several quantitative criteria that might be used to determine when groups of individuals are different enough to be considered ‘populations’, and a simple algorithm based on a multilocus contingency test of allele frequencies in pairs of samples has high power to detect the true number of populations but requires more rigorous statistical evaluation.
Abstract: We review commonly used population definitions under both the ecological paradigm (which emphasizes demographic cohesion) and the evolutionary paradigm (which emphasizes reproductive cohesion) and find that none are truly operational. We suggest several quantitative criteria that might be used to determine when groups of individuals are different enough to be considered ‘populations’. Units for these criteria are migration rate ( m ) for the ecological paradigm and migrants per generation ( Nm ) for the evolutionary paradigm. These criteria are then evaluated by applying analytical methods to simulated genetic data for a finite island model. Under the standard parameter set that includes L = 20 High mutation (microsatellitelike) loci and samples of S = 50 individuals from each of n = 4 subpopulations, power to detect departures from panmixia was very high (∼ 100%; P < 0.001) even with high gene flow ( Nm = 25). A new method, comparing the number of correct population assignments with the random expectation, performed as well as a multilocus contingency test and warrants further consideration. Use of Low mutation (allozyme-like) markers reduced power more than did halving S or L . Under the standard parameter set, power to detect restricted gene flow below a certain level X (H 0 : Nm < X ) can also be high, provided that true Nm ≤ 0.5 X . Developing the appropriate test criterion, however, requires assumptions about several key parameters that are difficult to estimate in most natural populations. Methods that cluster individuals without using a priori sampling information detected the true number of populations only under conditions of moderate or low gene flow ( Nm ≤ ≤ ≤ 5), and power dropped sharply with smaller samples of loci and individuals. A simple algorithm based on a multilocus contingency test of allele frequencies in pairs of samples has high power to detect the true number of populations even with Nm = 25 but requires more rigorous statistical evaluation. The ecological paradigm remains challenging for evaluations using genetic markers, because the transition from demographic dependence to independence occurs in a region of high migration where genetic methods have relatively little power. Some recent theoretical developments and continued advances in computational power provide hope that this situation may change in the future.
1,465 citations
Cites methods from "Defining ‘Evolutionarily Significan..."
...Finally, genetic data are increasingly being used to inform conservation and management (Moritz 1994; Waples 1995; Crandall et al ....
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...Finally, genetic data are increasingly being used to inform conservation and management (Moritz 1994; Waples 1995; Crandall et al . 2000; Allendorf et al . 2004)....
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TL;DR: Seven guidelines are proposed to help integrative taxonomists recognize cases when species are supported by broad biological evidence and therefore are deserving of an official name and to prevent the over-abundance of both synonyms and names of doubtful application from worsening.
Abstract: Delineating species boundaries correctly is crucial to the discovery of life’s diversity because it determines whether or not different individual organisms are members of the same entity. The gap in communication between the different disciplines currently involved in delimiting species is an important and overlooked problem in the so-called ‘taxonomy crisis’. To solve this problem, it is suggested that taxonomy become integrative, and this integration is seen as the real challenge for the future of taxonomy. ‘Integrative taxonomy’ is defined as the science that aims to delimit the units of life’s diversity from multiple and complementary perspectives (phylogeography, comparative morphology, population genetics, ecology, development, behaviour, etc.). Some workers have already collaborated and successfully adopted an integrative approach to taxonomy. However, it is now time for the whole discipline to evolve. A radical change in mentality is needed concerning the creation of names in order to achieve this integration and to prevent the over-abundance of both synonyms and names of doubtful application from worsening. Integrative taxonomy gives priority to species delineation over the creation of new species names. Furthermore, it is emphasized that describing morphological diversity, referred to as ‘morphodiversity’, does not require the naming of any single set of specimens. Seven guidelines are proposed to help integrative taxonomists recognize cases when species are supported by broad biological evidence and therefore are deserving of an official name. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 407‐415. ADDITIONAL KEYWORDS: biodiversity ‐ character variation ‐ DNA barcoding ‐ ecology ‐ morphodiversity ‐ phylogenetics ‐ phylogeography ‐ population biology ‐ species delineation ‐ systematics.
1,451 citations
References
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Book•
01 Jan 1994
TL;DR: A history of Molecular Phylogenetics and applications of individuality and Parentage, issues of Heterozygosity, and special Approaches to Phylageny Estimation are reviewed.
Abstract: Preface. Part I: Background: 1. Introduction. Why Employ Molecular Genetic Markers? Why Not Employ Molecular Genetic Markers? 2. History of Molecular Phylogenetics. Debates and Diversions from Molecular Systematics. Molecular Phylogenetics. 3. Molecular Tools. Protein Assays. DNA Assays. References to Laboratory Protocols. 4. Interpretative Tools. Categorical Subdivisions of Molecular Genetic Data. Molecular Clocks. Procedures for Phylogeny Reconstruction. Gene Trees versus Species Trees. Part II: Applications: 5. Individuality and Parentage. Genetic Identity versus Non-Identity. Parentage. 6. Kinship and Intraspecific Phylogeny. Close Kinship and Family Structure. Geographic Population Structure and Gene Flow. Phylogeography. Microtemporal Phylogeny. 7. Speciation and Hybridization. The Speciation Process. Hybridization and Introgression. 8. Species Phylogenies and Macroevolution. Rationales for Phylogeny Estimation. Special Approaches to Phylogeny Estimation. Prospectus for a Global Phylogeny. Special Topics in Molecular Phylogenetics. 9. Conservation Genetics. Issues of Heterozygosity. Issues of Phylogeny. Literature Cited. Index to Taxonomic Genera. General Index.
4,727 citations
2,783 citations
01 Jan 1983
TL;DR: A new mechanistic taxonomy of speciation is needed before population genetics, which deals with evolutionary mechanisms, can be properly integrated with speciation theory; that is, the various modes of Speciation should be characterized according to the various forces and genetic mechanisms that underly the evolution of isolating barriers.
Abstract: Systematic biologists have directed much attention to species concepts because they realize that the origin of taxonomic diversity is the fundamental problem of evolutionary biology. Questions such as, What are the units of evolution? and, How do these units originate? thus continually capture the attention of many. It is probably no exaggeration to say that most believe the “systematic” aspects of the problem have been solved to a greater or lesser extent, whereas the task before us now is to understand the “genetic” and “ecologic” components of differentiation, i. e., those aspects often perceived to constitute the “real mechanisms” of speciation:
A study of speciation is, to a considerable extent, a study of the genetics and evolution of reproductive isolating mechanisms (Bush, 1975, p. 339).
... a new mechanistic taxonomy of speciation is needed before population genetics, which deals with evolutionary mechanisms, can be properly integrated with speciation theory; that is, the various modes of speciation should be characterized according to the various forces and genetic mechanisms that underly [sic] the evolution of isolating barriers (Templeton 1980, p. 720).
1,346 citations
1,124 citations
TL;DR: It is found that the power of the test is substantial with samples of size 50, when 4Nm less than 10, where N is the subpopulation size and m is the fraction of migrants in each subpopulation each generation.
Abstract: A statistical test for detecting genetic differentiation of subpopulations is described that uses molecular variation in samples of DNA sequences from two or more localities. The statistical significance of the test is determined with Monte Carlo simulations. The power of the test to detect genetic differentiation in a selectively neutral Wright-Fisher island model depends on both sample size and the rates of migration, mutation, and recombination. It is found that the power of the test is substantial with samples of size 50, when 4Nm less than 10, where N is the subpopulation size and m is the fraction of migrants in each subpopulation each generation. More powerful tests are obtained with genes with recombination than with genes without recombination.
937 citations