Speciation Genetics and Genomics

by

Chris Jiggins, Catherine Peichel

• LAST REVIEWED: 29 September 2014
• LAST MODIFIED: 29 September 2014
• DOI: 10.1093/obo/9780199941728-0055

Introduction

Speciation is the evolutionary process that generates biodiversity and has been a central focus for evolutionary biologists since Darwin. Studies of the genetic basis of speciation date back to the early days of the modern synthesis, when Mendelian Genetics was first integrated into Darwinian evolution. An early area of interest was the role of chromosomal rearrangements in generating reproductive isolation, known as Chromosomal Speciation. This is an area that has received a resurgence of interest due to the influence of chromosomal rearrangements on rates of recombination. Historically, there has also been a strong tradition of studies of hybrid incompatibilities (the causes of hybrid sterility or inviability), ultimately leading to the Genetic Basis for Hybrid Sterility and Inviability. This work has led to the formulation of the Two Rules of Speciation. However early-21st-century developments in sequencing technology now make genetic studies of a much wider diversity of traits possible, and in particular there is now much more focus on the Genetic Basis for Behavioral and Ecological Isolation. Hybrid zones have long been recognized as natural systems where the genetic basis for ecological and reproductive traits can be studied. One exciting approach with great promise for the future is admixture mapping, in which natural variation segregating in a hybrid zone can be used to identify genetic loci controlling traits of interest (Hybrid Zones and Admixture Mapping). Genomic studies also permit the characterization of patterns of divergence across genomes during speciation, which has become an exciting area of current research (Genome-Wide Patterns of Divergence). In summary, the genetic basis of speciation has much in common with the genetics of adaptation, but with a critical focus on those genetic changes that underlie reproductive isolation and thus permit species divergence and coexistence.

Books on Speciation

There has been a wealth of books and monographs on the topic of speciation over the last 150 years, many of them primarily or partly concerned with genetics. Although Darwin 1859 lacked a clear understanding of the mechanisms of heredity, his work nonetheless remains relevant to our current understanding of speciation genetics. In particular he understood speciation to result as a consequence of divergence by natural selection between populations. The relative importance of natural selection and drift in speciation remains an important topic. The incorporation of Mendelian genetics and Darwinian evolution occurred in the early 20th century, and one of the pioneers was a Russian-American biologist, Dobzhansky, who incorporated both field and laboratory studies into his work on speciation. Dobzhansky 1937 remains a classic and is well worth reading. In the second half of the 20th century, speciation biology was dominated by the writing of Ernst Mayr, notably Mayr 1963, which strongly emphasized divergence in allopatry. However, a contrasting view can be seen among plant biologists, for example in Grant 1971, with a much stronger emphasis on hybridization and gene flow during speciation. In the early 21st century, the perspective of the botanists seems more contemporary, with a renewed interest among zoologists in the role of hybridization during speciation. Perhaps the single most comprehensive treatment of speciation in recent times is the book Coyne and Orr 2004, offering a remarkable overview of the field. Nonetheless, the authors’ perspective on speciation contrasts with a shift in emphasis in recent years toward the importance of ecology, exemplified in Schluter 2000 and Nosil 2012, and from a more theoretical perspective, as in Gavrilets 2004.

• Coyne, Jerry A., and H. Allen Orr. 2004. Speciation. Sunderland, MA: Sinauer Associates.

  A definitive review of the field as it stood at the time. This book gives a different perspective to that of Schluter 2000, with more of a focus on genetic incompatibility and less on ecology.

• Darwin, Charles. 1859. On the origin of species by means of natural selection, or the preservation of favored races in the struggle for life. London: John Murray.

  Although Darwin did not have a clear understanding of the mechanism of heredity, his work is nonetheless relevant to our current understanding of speciation genetics. In particular Darwin argued for a prominent role of natural selection in causing species differences, a hypothesis that can now be tested with molecular data.

• Dobzhansky, Theodosius. 1937. Genetics and the origin of species. New York: Columbia Univ. Press.

  Dobzhansky was a Russian-American biologist who combined field and laboratory studies, mainly of Drosophila. This book was an influential and readable account of speciation biology early in the modern synthesis.

• Gavrilets, Sergey. 2004. Fitness landscapes and the origin of species. Princeton, NJ: Princeton Univ. Press.

  This is theoretical and a challenging read but also an important overview of the theoretical basis for speciation research. Gavrilets argues that incompatibilities can evolve between lineages through evolution along fitness ridges, leading to the metaphor of the “holey” adaptive landscape. The term “magic trait” was coined in this book.

• Grant, Verne. 1971. Plant speciation. New York: Columbia Univ. Press.

  Grant reviewed speciation from a botanical perspective, with a particular emphasis on hybridization and reticulate evolution. This is a perspective that was rare in the animal literature at the time but is increasingly recognized (see also Homoploid Hybrid Speciation).

• Mayr, Ernst. 1963. Animal species and evolution. Cambridge, MA: Belknap.

  DOI: 10.4159/harvard.9780674865327

  Mayr’s opinions were hugely influential for several decades after publication of this book, and the history of speciation research can only really be understood in light of this. However Mayr’s perspective has been heavily criticized for an overly strong emphasis on the role of allopatry.

• Nosil, Patrik. 2012. Ecological speciation. Oxford: Oxford Univ. Press.

  A recent review of the importance of ecological processes in driving species divergence.

• Schluter, Dolph. 2000. The ecology of adaptive radiation. Oxford: Oxford Univ. Press.

  This book was a rallying call for a renewed interest in the role of ecological selection in speciation, that has dominated speciation research ever since.