Species Delimitation

2022 ◽  
Keyword(s):  
Species Delimitation ◽  
Genetic Data ◽  
Species Boundaries ◽  
Dna Barcodes ◽  
Multispecies Coalescent ◽  
Statistical Framework ◽  
Dramatic Rise ◽  
Invaluable Tool ◽  
Taxonomic Groups ◽  
Over Time

Species delimitation is the process of determining whether a group of sampled individuals belong to the same species or to different species. The criteria used to delimit species differ across taxonomic groups, and the methods for delimiting species have changed over time, with a dramatic rise in the popularity of genomic approaches recently. Because inferred species boundaries have ramifications that extend beyond systematics, affecting all fields that rely upon species as a foundational unit, controversy has unsurprisingly surrounded not only the practices used to delimit species boundaries, but also the idea of what species are, which varies across taxa (e.g., the use of subspecies varies across the tree of life). This lack of consensus has no doubt contributed to the appeal of genetic-based delimitation. Specifically, genomic data can be collected from any taxon. Moreover, it can be analyzed in a common statistical framework (as popularized by the multispecies coalescent as a model for species delimitation). With the ease of collecting genetic data, the power of genomics, and the purported standardization for diagnosing species limits, genetic-based species delimitation is displacing traditional time-honored (albeit time-consuming) taxonomic practices of species diagnosis. It has also become an invaluable tool for discovering species in understudied groups, and genetic-based approaches are the foundation of international endeavors to generate a catalogue of DNA barcodes to illuminate biodiversity for all of life on the planet. Yet, genomic applications, and especially the sole reliance upon genetic data for inferring species boundaries, are not without their own set of challenges.

scholarly journals Incorporating the speciation process into species delimitation

2021 ◽  
Vol 17 (5) ◽  
pp. e1008924
Author(s):  
Jeet Sukumaran ◽  
Mark T. Holder ◽  
L. Lacey Knowles
Keyword(s):  
Gene Flow ◽  
Species Delimitation ◽  
Subsequent Development ◽  
Genetic Data ◽  
Distinct Species ◽  
Species Boundaries ◽  
Multispecies Coalescent ◽  
Speciation Process ◽  
Other Information ◽  
Species Population

The “multispecies” coalescent (MSC) model that underlies many genomic species-delimitation approaches is problematic because it does not distinguish between genetic structure associated with species versus that of populations within species. Consequently, as both the genomic and spatial resolution of data increases, a proliferation of artifactual species results as within-species population lineages, detected due to restrictions in gene flow, are identified as distinct species. The toll of this extends beyond systematic studies, getting magnified across the many disciplines that rely upon an accurate framework of identified species. Here we present the first of a new class of approaches that addresses this issue by incorporating an extended speciation process for species delimitation. We model the formation of population lineages and their subsequent development into independent species as separate processes and provide for a way to incorporate current understanding of the species boundaries in the system through specification of species identities of a subset of population lineages. As a result, species boundaries and within-species lineages boundaries can be discriminated across the entire system, and species identities can be assigned to the remaining lineages of unknown affinities with quantified probabilities. In addition to the identification of species units in nature, the primary goal of species delimitation, the incorporation of a speciation model also allows us insights into the links between population and species-level processes. By explicitly accounting for restrictions in gene flow not only between, but also within, species, we also address the limits of genetic data for delimiting species. Specifically, while genetic data alone is not sufficient for accurate delimitation, when considered in conjunction with other information we are able to not only learn about species boundaries, but also about the tempo of the speciation process itself.

scholarly journals The challenge of delimiting cryptic species, and a supervised machine learning solution

2021 ◽  
Author(s):  
Shahan Derkarabetian ◽  
James Starrett ◽  
Marshal Hedin
Keyword(s):  
Machine Learning ◽  
Cryptic Species ◽  
Species Delimitation ◽  
Genetic Data ◽  
Biological Characteristics ◽  
Supervised Machine Learning ◽  
Training Dataset ◽  
Dispersal Ability ◽  
Data Types ◽  
Multispecies Coalescent

The diversity of biological and ecological characteristics of organisms, and the underlying genetic patterns and processes of speciation, makes the development of universally applicable genetic species delimitation methods challenging. Many approaches, like those incorporating the multispecies coalescent, sometimes delimit populations and overestimate species numbers. This issue is exacerbated in taxa with inherently high population structure due to low dispersal ability, and in cryptic species resulting from nonecological speciation. These taxa present a conundrum when delimiting species: analyses rely heavily, if not entirely, on genetic data which over split species, while other lines of evidence lump. We showcase this conundrum in the harvester Theromaster brunneus, a low dispersal taxon with a wide geographic distribution and high potential for cryptic species. Integrating morphology, mitochondrial, and sub-genomic (double-digest RADSeq and ultraconserved elements) data, we find high discordance across analyses and data types in the number of inferred species, with further evidence that multispecies coalescent approaches over split. We demonstrate the power of a supervised machine learning approach in effectively delimiting cryptic species by creating a "custom" training dataset derived from a well-studied lineage with similar biological characteristics as Theromaster. This novel approach uses known taxa with particular biological characteristics to inform unknown taxa with similar characteristics, and uses modern computational tools ideally suited for species delimitation while also considering the biology and natural history of organisms to make more biologically informed species delimitation decisions. In principle, this approach is universally applicable for species delimitation of any taxon with genetic data, particularly for cryptic species.

The Multispecies Coalescent Over-Splits Species in the Case of Geographically Widespread Taxa

2019 ◽  
Vol 69 (1) ◽  
pp. 184-193 ◽  
Author(s):  
E Anne Chambers ◽  
David M Hillis
Keyword(s):  
Species Delimitation ◽  
Isolation By Distance ◽  
A Priori ◽  
Genetic Data ◽  
Species Group ◽  
Recent Analysis ◽  
Multispecies Coalescent ◽  
Species Complexes ◽  
Taxonomic Changes ◽  
Recent Species

AbstractMany recent species delimitation studies rely exclusively on limited analyses of genetic data analyzed under the multispecies coalescent (MSC) model, and results from these studies often are regarded as conclusive support for taxonomic changes. However, most MSC-based species delimitation methods have well-known and often unmet assumptions. Uncritical application of these genetic-based approaches (without due consideration of sampling design, the effects of a priori group designations, isolation by distance, cytoplasmic–nuclear mismatch, and population structure) can lead to over-splitting of species. Here, we argue that in many common biological scenarios, researchers must be particularly cautious regarding these limitations, especially in cases of well-studied, geographically variable, and parapatrically distributed species complexes. We consider these points with respect to a historically controversial species group, the American milksnakes (Lampropeltis triangulum complex), using genetic data from a recent analysis (Ruane et al. 2014). We show that over-reliance on the program Bayesian Phylogenetics and Phylogeography, without adequate consideration of its assumptions and of sampling limitations, resulted in over-splitting of species in this study. Several of the hypothesized species of milksnakes instead appear to represent arbitrary slices of continuous geographic clines. We conclude that the best available evidence supports three, rather than seven, species within this complex. More generally, we recommend that coalescent-based species delimitation studies incorporate thorough analyses of geographic variation and carefully examine putative contact zones among delimited species before making taxonomic changes.

scholarly journals Molecular species delimitation in the primitively segmented spider genus Heptathela endemic to Japanese islands

2019 ◽  
Author(s):  
Xin Xu ◽  
Matjaž Kuntner ◽  
Jason E. Bond ◽  
Hirotsugu Ono ◽  
Simon Y. W. Ho ◽  
...  
Keyword(s):  
Molecular Species ◽  
Species Delimitation ◽  
Computational Time ◽  
Species Boundaries ◽  
Biological Research ◽  
Morphological Evidence ◽  
Data Sets ◽  
Bayesian Approaches ◽  
Multispecies Coalescent ◽  
Japanese Islands

ABSTRACTDetermining species boundaries forms an important foundation for biological research. However, the results of molecular species delimitation can vary with the data sets and methods that are used. Here we use a two-step approach to delimit species in the genus Heptathela, a group of primitively segmented trapdoor spiders that are endemic to Japanese islands. Morphological evidence suggests the existence of 19 species in the genus. We tested this initial species hypothesis by using six molecular species-delimitation methods to analyse 180 mitochondrial COI sequences of Heptathela sampled from across the known range of the genus. We then conducted a set of more focused analyses by sampling additional genetic markers from the subset of taxa that were inconsistently delimited by the single-locus analyses of mitochondrial DNA. Multilocus species delimitation was performed using two Bayesian approaches based on the multispecies coalescent. Our approach identified 20 putative species among the 180 sampled individuals of Heptathela. We suggest that our two-step approach provides an efficient strategy for delimiting species while minimizing costs and computational time.

scholarly journals Multispecies coalescent delimits structure, not species

2017 ◽  
Vol 114 (7) ◽  
pp. 1607-1612 ◽  
Author(s):  
Jeet Sukumaran ◽  
L. Lacey Knowles
Keyword(s):  
Genetic Structure ◽  
Species Delimitation ◽  
Population Level ◽  
Species Boundaries ◽  
Data Types ◽  
Population Isolation ◽  
Species Discovery ◽  
Multispecies Coalescent ◽  
Units Of Analysis ◽  
Multiple Data

The multispecies coalescent model underlies many approaches used for species delimitation. In previous work assessing the performance of species delimitation under this model, speciation was treated as an instantaneous event rather than as an extended process involving distinct phases of speciation initiation (structuring) and completion. Here, we use data under simulations that explicitly model speciation as an extended process rather than an instantaneous event and carry out species delimitation inference on these data under the multispecies coalescent. We show that the multispecies coalescent diagnoses genetic structure, not species, and that it does not statistically distinguish structure associated with population isolation vs. species boundaries. Because of the misidentification of population structure as putative species, our work raises questions about the practice of genome-based species discovery, with cascading consequences in other fields. Specifically, all fields that rely on species as units of analysis, from conservation biology to studies of macroevolutionary dynamics, will be impacted by inflated estimates of the number of species, especially as genomic resources provide unprecedented power for detecting increasingly finer-scaled genetic structure under the multispecies coalescent. As such, our work also represents a general call for systematic study to reconsider a reliance on genomic data alone. Until new methods are developed that can discriminate between structure due to population-level processes and that due to species boundaries, genomic-based results should only be considered a hypothesis that requires validation of delimited species with multiple data types, such as phenotypic and ecological information.

The Evolutionary Biology of Species

2019 ◽  
Author(s):  
Timothy G. Barraclough
Keyword(s):  
Evolutionary Biology ◽  
Biological Diversity ◽  
Distinct Species ◽  
Species Boundaries ◽  
Central Thesis ◽  
Species Accumulation ◽  
Multicellular Organisms ◽  
Broad Approach ◽  
Over Time

‘Species’ are central to understanding the origin and dynamics of biological diversity; explaining why lineages split into multiple distinct species is one of the main goals of evolutionary biology. However, the existence of species is often taken for granted, and precisely what is meant by species and whether they really exist as a pattern of nature has rarely been modelled or critically tested. This novel book presents a synthetic overview of the evolutionary biology of species, describing what species are, how they form, the consequences of species boundaries and diversity for evolution, and patterns of species accumulation over time. The central thesis is that species represent more than just a unit of taxonomy; they are a model of how diversity is structured as well as how groups of related organisms evolve. The author adopts an intentionally broad approach to consider what species constitute, both theoretically and empirically, and how we detect them, drawing on a wealth of examples from microbes to multicellular organisms.

Revision of Banded Knifefishes of the Gymnotus carapo and G. tigre clades (Gymnotidae Gymnotiformes) from the Southern Neotropics

Zootaxa ◽  
2018 ◽  
Vol 4379 (1) ◽  
pp. 47 ◽  
Author(s):  
JACK M. CRAIG ◽  
LUIZ R. MALABARBA ◽  
WILLIAM G. R. CRAMPTON ◽  
JAMES S. ALBERT
Keyword(s):  
Lateral Line ◽  
Electric Organ ◽  
Valid Species ◽  
Species Boundaries ◽  
Multivariate Statistical ◽  
Widespread Species ◽  
Statistical Framework ◽  
Fin Ray ◽  
Taxonomic Confusion ◽  
Electric Organ Discharges

Banded Knifefishes (Gymnotus, Gymnotidae) comprise the most species-rich, ecologically tolerant (eurytopic), and geographically widespread genus of Neotropical electric fishes (Gymnotiformes), with 40 valid species occupying most habitats and regions throughout the humid Neotropics. Despite substantial alpha-taxonomic work in recent years, parts of the genus remain characterized by taxonomic confusion. Here we describe and delimit species of the G. carapo and G. tigre clades from the southern Neotropics, using body proportions (caliper-based morphometrics), fin-ray, scale and laterosensory-pore counts (meristics), quantitative shape differences (geometric morphometrics), osteology, color patterns and electric organ discharges. We report these data from 174 Gymnotus specimens collected from 100 localities throughout the southern Neotropics, and delimit species boundaries in a multivariate statistical framework. We find six species of the G. carapo clade (G. carapo australis, G. cuia n. sp., G. chimarrao, G. omarorum, G. pantanal, and G. sylvius), and two species of the G. tigre clade (G. inaequilabiatus and G. paraguensis) in the southern Neotropics. The new species G. cuia is readily distinguished from the morphologically similar and broadly sympatric G. c. australis by a shorter head and deeper head and body, and from the morphologically similar and sympatric G. omarorum by fewer lateral-line ventral rami and fewer pored lateral-line scales anterior to the first ventral ramus. We also review the geographic distributions of all eight species of the G. carapo and G. tigre clades in the southern Neotropics, showing that G. cuia is the most widespread species in the region. These results affirm the importance of understanding the structure of variation within and between species, both geographic and ontogenetic, in delimiting species boundaries. 

scholarly journals Current limitations and future prospects of detection and biomonitoring of NIS in the Mediterranean Sea through environmental DNA

NeoBiota ◽  
2021 ◽  
Vol 70 ◽  
pp. 151-165
Author(s):  
Francesco Zangaro ◽  
Benedetta Saccomanno ◽  
Eftychia Tzafesta ◽  
Fabio Bozzeda ◽  
Valeria Specchia ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Dna Barcode ◽  
Environmental Dna ◽  
Special Focus ◽  
Indigenous Species ◽  
Dna Barcodes ◽  
Identification Of Species ◽  
The Mediterranean ◽  
Taxonomic Groups ◽  
Non Indigenous Species

The biodiversity of the Mediterranean Sea is currently threatened by the introduction of Non-Indigenous Species (NIS). Therefore, monitoring the distribution of NIS is of utmost importance to preserve the ecosystems. A promising approach for the identification of species and the assessment of biodiversity is the use of DNA barcoding, as well as DNA and eDNA metabarcoding. Currently, the main limitation in the use of genomic data for species identification is the incompleteness of the DNA barcode databases. In this research, we assessed the availability of DNA barcodes in the main reference libraries for the most updated inventory of 665 confirmed NIS in the Mediterranean Sea, with a special focus on the cytochrome oxidase I (COI) barcode and primers. The results of this study show that there are no barcodes for 33.18% of the species in question, and that 45.30% of the 382 species with COI barcode, have no primers publicly available. This highlights the importance of directing scientific efforts to fill the barcode gap of specific taxonomic groups in order to help in the effective application of the eDNA technique for investigating the occurrence and the distribution of NIS in the Mediterranean Sea.

scholarly journals A new species of Pima Hulst, 1888 from China (Lepidoptera, Pyralidae, Phycitinae), with a key to Holarctic species

ZooKeys ◽  
2020 ◽  
Vol 975 ◽  
pp. 111-124
Author(s):  
Linlin Yang ◽  
Yingdang Ren
Keyword(s):  
New Species ◽  
Species Delimitation ◽  
Dna Barcodes ◽  
Neighbor Joining ◽  
Distribution Map ◽  
Autonomous Region ◽  
Ningxia Hui Autonomous Region ◽  
Lepidoptera Pyralidae ◽  
A New Species ◽  
Holarctic Species

Pima tristriatasp. nov. is described as new to science based on specimens collected from the Ningxia Hui Autonomous Region, China, and P. boisduvaliella (Guenée, 1845) is also treated here for comparison. DNA barcodes of the two species are provided, together with a neighbor-joining tree for species delimitation. A key to the Holarctic species and a distribution map of the Chinese species are presented.

scholarly journals Species delimitation and life stage association of Propsilocerus Kieffer, 1923 (Diptera, Chironomidae) using DNA barcodes

ZooKeys ◽  
2020 ◽  
Vol 975 ◽  
pp. 79-86
Author(s):  
Hai-Jun Yu ◽  
Xiao-Long Lin ◽  
Rui-Lei Zhang ◽  
Qian Wang ◽  
Xin-Hua Wang
Keyword(s):  
Species Delimitation ◽  
Life Stage ◽  
Dna Barcodes ◽  
Neighbor Joining ◽  
Index Numbers ◽  
Nj Tree ◽  
Barcode Gap

The utility of COI DNA barcodes in species delimitation is explored as well as life stage associations of five closely related Propsilocerus species: Propsilocerus akamusi (Tokunaga, 1938), Propsilocerus paradoxus (Lundström, 1915), Propsilocerus saetheri Wang, Liu et Paasivirta, 2007, Propsilocerus sinicus Sæther et Wang, 1996, and Propsilocerus taihuensis (Wen, Zhou et Rong, 1994). Results revealed distinctly larger interspecific than intraspecific divergences and indicated a clear “barcode gap”. In total, 42 COI barcode sequences including 16 newly generated DNA barcodes were applied to seven Barcode Index Numbers (BINs). A neighbor-joining (NJ) tree comprises five well-separated clusters representing five morphospecies. Comments on how to distinguish the larvae of P. akamusi and P. taihuensis are provided.

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