SPECIATION IN MAMMALS AND THE GENETIC SPECIES CONCEPT

By R. Baker, R. Bradley. Journal of Mammalogy, 2006

768 citations recorded by the source corpus.

Abstract We define a genetic species as a group of genetically compatible interbreeding natural populations that is genetically isolated from other such groups. This focus on genetic isolation rather than reproductive isolation distinguishes the Genetic Species Concept from the Biological Species Concept. Recognition of species that are genetically isolated (but not reproductively isolated) results in an enhanced understanding of biodiversity and the nature of speciation as well as speciation-based issues and evolution of mammals. We review criteria and methods for recognizing species of mammals and explore a theoretical scenario, the Bateson–Dobzhansky–Muller (BDM) model, for understanding and predicting genetic diversity and speciation in mammals. If the BDM model is operating in mammals, then genetically defined phylogroups would be predicted to occur within species defined by morphology, and phylogroups experiencing stabilizing selection will evolve genetic isolation without concomitant morphological diversification. Such species will be undetectable using classical skin and skull morphology (Morphological Species Concept). Using cytochrome-b data from sister species of mammals recognized by classical morphological studies, we estimated the number of phylogroups that exist within mammalian species and hypothesize that there will be >2,000 currently unrecognized species of mammals. Such an underestimation significantly affects conclusions on the nature of speciation in mammals, barriers associated with evolution of genetic isolation, estimates of biodiversity, design of conservation initiatives, zoonoses, and so on. A paradigm shift relative to this and other speciation-based issues will be needed. Data that will be effective in detecting these “morphologically cryptic genetic species” are genetic, especially DNA-sequence data. Application of the Genetic Species Concept uses genetic data from mitochondrial and nuclear genomes to identify species and species boundaries, the extent to which the integrity of the gene pool is protected, nature of hybridization (if present), and introgression. Genetic data are unique in understanding species because the use of genetic data 1) can quantify genetic divergence from different aspects of the genome (mitochondrial and nuclear genes, protein coding genes, regulatory genes, mobile DNA, microsatellites, chromosomal rearrangements, heterochromatin, etc.); 2) can provide divergence values that increase with time, providing an estimate of time since divergence; 3) can provide a population genetics perspective; 4) is less subject to convergence and parallelism relative to other sets of characters; 5) can identify monophyly, sister taxa, and presence or absence of introgression; and 6) can accurately identify hybrid individuals (kinship and source of hybrid individuals, F1s, backcrosses, direction of hybridization, and in concert with other data identify which hybrids are sterile or fertile). The proposed definition of the Genetic Species Concept is more compatible with a description of biodiversity of mammals than is “reproductively isolated species.” Genetic profiles of mammalian species will result in a genetic description of species and mammalian diversity, and such studies are being accelerated by technological advances that reduce cost and increase speed and efficiency of generating genetic data. We propose that this genetic revolution remain museum- and voucher specimen–based and that new names are based on a holotype (including associated tissues) deposited in an accredited museum.

Subfields: Genetics, Molecular Biology

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Citations in the corpus

Systematics of the Platyrrhinus helleri species complex (Chiroptera: Phyllostomidae), with descriptions of two new species (2010, background): “…species of the P. helleri complex and close relatives (P. matapalensis and P. recifinus) do not meet the > 5% rule for sister species proposed by Baker & Bradley (2006) in their ‘genetic species concept’, the specific distinction of these bats is corroborated by several marked qualitative…”
Assessing the Value of Natural History Collections and Addressing Issues Regarding Long-Term Growth and Care (2014, methodology): “Baker and Bradley (2006) postulated that, on the basis of the rate of new species names being described in the recent literature, approximately 40% of mammal species remained to be described by scientists.”
Mammals of Italy: an annotated checklist (2019, background): “…and Rannala, 2014); 4) presence of chromosomal differences, which may be directly involved in the reproductive isolation between populations (meiotic aberrations in hybrids or recombination suppression associated to chromosomal heterozygosity; Baker and Bradley, 2006; Pavlova and Searle, 2018).”
Cosmopolitan polychaetes – fact or fiction? Personal and historical perspectives (2018, background): “The concept of phylogenetic (sensu Cracraft 1989) species based on recognition of monophyletic groups (clades) and the genetic species (sensu Baker and Bradley 2006) concept that uses levels of sequence variation for determination of genetic isolation as indications of species boundaries, became…”
How to fail at species delimitation (2013, methodology): “Rather than equating gene trees with a species tree or basing species status on some genetic threshold (e.g. Baker & Bradley 2006), the relationship between the gene trees and the lineage history is modelled probabilistically using coalescent theory (Hudson 1991; Rosenberg 2002).”
Lemur Diversity in Madagascar (2008, background): “…a Genetic Species as “a group of genetically compatible interbreeding natural populations that is genetically isolated from other such groups” (Baker and Bradley 2006, p. 645), and they reiterate that, though based on the idea that “speciation is the accumulation of genetic changes in 2…”
Mammalian Response to Cenozoic Climatic Change (2009, background): “Mammalian molecular data show divergences between extant sister species that are roughly in agreement with fossil estimates, on the order of 3 to 10 million years (Avise et al. 1998, Baker & Bradley 2006).”
Keys to the Bats (Mammalia: Chiroptera) of East Africa (2012, methodology): “Two species concepts now commonly used in mammalogy—the phylogenetic (Cracraft, 1989) and genetic (Baker & Bradley, 2006) species concepts— have been used to revalidate many names formerly considered synonyms.”