Founder Effect Speciation

by

Alan R. Templeton

• LAST REVIEWED: 23 March 2023
• LAST MODIFIED: 23 March 2023
• DOI: 10.1093/obo/9780199941728-0044

Introduction

The origin of species (speciation)—the process by which two or more species evolve from a single ancestral species—is a central problem in evolutionary biology. During the evolutionary synthesis of the twentieth century, the dominant theory of speciation for those working on sexually reproducing animals was allopatric speciation. Allopatric speciation posits that an ancestral species becomes subdivided into two or more geographical subpopulations by changing climates, colonization of new areas, the erection of geological barriers, etc. If these geographical subpopulations have little to no genetic interchange, they will begin to evolve separately. Speciation then arises as an incidental by-product of the independent evolution occurring within the geographical isolates. Evolution within species (microevolution) was often envisioned as being dominated by natural selection leading to adaptive divergence between the geographical isolates. However, the modern synthesis made it clear that microevolution involved many processes in addition to natural selection. One of these processes was genetic drift, the random changes in a population’s gene pool (the set of alleles or gametes collectively shared by a reproducing population) that inevitably arise from random sampling of a finite number of gametes to form the next generation. Just by chance, a particular form of a gene can decrease or increase in frequency in the population, including being completely lost or fixed. The impact of random sampling increases as the population size decreases. One special case of strong genetic drift is the founder effect, in which a population is established by a small number of founding individuals from a much larger ancestral population. Strong genetic drift in the founder population could lead to an immediate evolutionary divergence from the ancestral population. This accelerated divergence is the essence of founder effect speciation models. Founder effect speciation is a special case of allopatric speciation in which one of the geographical isolates was established from a small number of individuals. This does not mean that other microevolutionary forces, such as natural selection, are not operating, but rather that the founder effect enhances and accelerates microevolutionary divergence in concert with natural selection and other microevolutionary forces, thereby making speciation more likely.

General Overviews

A general overview of founder effect speciation can be found in the articles published in Giddings, et al. 1989. Pro and con back-to-back reviews are found in Carson and Templeton 1984 and Barton and Charlesworth 1984. Templeton 2008 provides a review of the various theories of founder effect speciation as well as a review and meta-analysis of the empirical studies on founder effect speciation. Gavrilets 2004 presents population genetic analyses of many mechanisms of speciation, including founder speciation.

• Barton, Nicholas H., and Brian Charlesworth. 1984. Genetic revolutions, founder effects, and speciation. Annual Review of Ecology and Systematics 15:133–164.

  DOI: 10.1146/annurev.es.15.110184.001025

  Founder speciation models are equated to adaptive peak shifts in which genetic drift causes a population to evolve across a low-fitness state (an adaptive valley). The authors deem this scenario as unlikely. They also argue that the natural examples can be explained without invoking founder events.

• Carson, Hampton L., and Alan R. Templeton. 1984. Genetic revolutions in relation to speciation phenomena: The founding of new populations. Annual Review of Ecology and Systematics 15:97–131.

  DOI: 10.1146/annurev.es.15.110184.000525

  This review covers the three basic theories of founder speciation and provides natural examples, with a special focus on the Hawaiian Drosophila.

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

  DOI: 10.1515/9780691187051

  This monograph covers many speciation mechanisms, including founder speciation, mainly from a theoretical population genetic perspective. Confirms the objections of Barton, Charlesworth, and others to founder speciation by evolving through an adaptive valley, but he shows other mechanisms that make founder populations more likely to speciate.

• Giddings, Luther V., Kenneth Y. Kaneshiro, and Wyatt W. Anderson, eds. 1989. Genetics, speciation and the founder principle. New York: Oxford Univ. Press.

  Contains chapters on the theory of founder effect speciation, natural examples, and genetic studies. An interview with Hampton Carson (chapter 1) and a historical perspective by William Provine (chapter 2) are valuable general introductions to this model of speciation and how it was developed.

• Templeton, Alan R. 2008. The reality and importance of founder speciation in evolution. BioEssays 30.5: 470–479.

  DOI: 10.1002/bies.20745

  The most recent review of this area. The three major theories of founder speciation are summarized, showing that none of them are based on adaptive peak shifts. A detailed statistical analysis of the empirical literature shows that the predictions and assumptions of founder effect speciation are strongly supported.