Hybrid Speciation

by

Michael L. Arnold

• LAST REVIEWED: 09 March 2021
• LAST MODIFIED: 13 January 2014
• DOI: 10.1093/obo/9780199941728-0005

Introduction

The process of hybrid speciation—the formation of evolutionarily independent lineages from genetic exchange events between divergent taxa—has been a hotly debated topic since at least the Neo-Darwinian Synthesis. Though it was recognized hundreds of years before the time of the Synthesis that some lineages might have arisen via matings between divergent lineages, the 1930s through the1960s saw a paradigm established that argued for a minor role for hybrid formation in the evolutionary history of organisms (especially animals). In contrast, the occurrence of hybrid speciation is now well documented across many taxonomic groups, including prokaryotes and eukaryotes, and in the latter group within both plants and animals. Such observations reflect not only the frequent occurrence of hybrid lineage formation, but also that lineages often evolve while exchanging genes, rather than in the geographic and genetic isolation (i.e., “allopatry”) incorporated as another tenet of the Neo-Darwinian Synthesis. With the ease of collection of large genomic data sets, tests for hybrid speciation should continue to multiply.

General Overviews

Unlike the literature on many processes and concepts in evolutionary biology (e.g., adaptation, natural selection, migration), most of the general works discussing hybrid speciation have appeared within the past fifteen or so years. This appearance reflects a renewed interest in this process, and thus an exponential increase in reported studies. The general works have included review articles and book chapters concerning hybrid speciation in plants, such as Rieseberg 1997 and Soltis and Soltis 2009. Taxonomically broader discussions of the process of hybrid speciation have been presented in Mallet 2007 and Coyne and Orr 2004. Finally, Arnold 2006 focuses on the process of reticulate evolution, and thus extensively on hybrid speciation. Two earlier works that described the mechanisms and outcomes of hybrid speciation and considered its importance in either plants or animals were Grant 1981, the book Plant Speciation, and Mayr 1963, the treatise Animal Species and Evolution. Though more recent analyses and reviews, such as Arnold 2006, have emphasized the role of ecological selection in hybrid species formation, Grant 1981 and others such as Rieseberg 1997 have pointed to the importance of genomic recombination and stabilization of the resulting hybrid lineage.

• Arnold, M. L. 2006. Evolution through genetic exchange. Oxford: Oxford Univ. Press.

  As the title indicates, this book explores the variety of mechanisms and outcomes that can occur when divergent lineages exchange genetic material. In the context of hybrid speciation, examples of hybrid bisexual, unisexual, homoploid, and polyploid plant and animal lineages are presented.

• Coyne, J. A., and H. A. Orr. 2004. Speciation. Sunderland, MA: Sinauer.

  This general work provides a good overview of natural hybridization and hybrid speciation, but largely in the vein of the Neo-Darwinian Synthesis paradigm.

• Grant, V. 1981. Plant speciation. New York: Columbia Univ. Press.

  In large sections of his seminal work Grant explores the various mechanisms and outcomes of natural hybridization between divergent plant lineages—including the formation of allopolyploid, homoploid, and asexual hybrid species.

• Mallet, J. 2007. Hybrid speciation. Nature 446:279–283.

  DOI: 10.1038/nature05706

  This review emphasizes the notion that hybrid speciation is important in both plant and animal clades. It argues that the role of homoploid hybrid speciation in particular has been greatly underappreciated. Available online for purchase or by subscription.

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

  Written from the perspective that new species arise almost exclusively in allopatry, and that natural hybridization between animal lineages is an evolutionarily unimportant process, this work represents the Neo-Darwinian Synthesis viewpoint concerning hybrid speciation.

• Rieseberg, L. H. 1997. Hybrid origins of plant species. Annual Review of Ecology and Systematics 28:359–389.

  DOI: 10.1146/annurev.ecolsys.28.1.359

  This review provides a critical evaluation of the theoretical and empirical evidence for and against homoploid hybrid speciation in plants, thereby establishing a framework for hypothesis testing in not only plants, but animal clades as well. Available online for purchase or by subscription.

• Soltis, P. S., and D. E. Soltis. 2009. The role of hybridization in plant speciation. Annual Review of Plant Biology 60:561–588.

  DOI: 10.1146/annurev.arplant.043008.092039

  This review article has a broad focus. The topics covered include a consideration of species concepts, isolating mechanisms and ancient and recent hybrid speciation events involving allopolyploidy and homoploidy. Available online for purchase or by subscription.