What, if anything, is sympatric speciation?

Abstract

in part because it challenges us to synthesize ecology, genetics and behaviour when attempting to understand how it might occur in nature. Both proponents and skeptics agree on the importance of understanding the contexts and processes influencing the likelihood of sympatric divergence, and of identifying the kinds of evidence necessary to diagnose individual case studies. However, sympatric speciation is not always clearly defined, and not all clear definitions describe the same set of phenomena. In fact, some of the disagreement over the prevalence and importance of sympatric speciation rests on disagreement over what sympatric speciation is. Such arguments do little to advance the study of evolution, and we advocate research aimed at understanding mechanisms of divergence, rather than classifying cases into a taxonomy of 'modes of speciation ' (sensu Mayr, 1942' (sensu Mayr, , 1963.The problem is most severe in host-specific parasites, phytophagous insects and other situations where ecological differentiation necessarily involves spatial structure. Differentiated populations, 'host races' or descendant species that occur in different, discrete habitat patches may have broadly overlapping geographical ranges and yet never encounter one another at the same time and place because of their distinct ecological niches. Such situations were dubbed 'microallopatric' by Smith (1955Smith ( , 1965, who was dissatisfied with the simple dichotomy between allopatry and sympatry advocated by Mayr (1942Mayr ( , 1963. Several recent authors have raised concerns over conceptual and evidential confusion between 'microallopatry' and 'sympatry ' (Berlocher & Feder, 2002;Dres & Mallet, 2002;Dieckmann & Doebeli, 2004;Provine, 2004;Mallet, 2005).The definition of sympatric speciation is important in the interpretation of case studies. For example, regarding Rice & Salt's (1990) classic experimental demonstration of speciation by habitat selection in Drosophila, Coyne & Orr (2004, pp. 140-141) argued that the strong selection levied against females that switched habitats made the allopatry; biogeography; migration; parapatry; population genetics; selection; speciation; sympatry. AbstractSympatric speciation has always fascinated evolutionary biologists, and for good reason; it pits diversifying selection directly against the tendency of sexual reproduction to homogenize populations. However, different investigators have used different definitions of sympatric speciation and different criteria for diagnosing cases of sympatric speciation. Here, we explore some of the definitions that have been used in empirical and theoretical studies. Definitions based on biogeography do not always produce the same conclusions as definitions based on population genetics. The most precise definitions make sympatric speciation an infinitesimal end point of a continuum. Because it is virtually impossible to demonstrate the occurrence of such a theoretical extreme, we argue that testing whether a case fits a particular definition is less informative...

Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North Atlantic

“…However, both the species concept and the processes driving speciation represent sliding windows along continuums, rather than discrete categories (Butlin et al, 2008). For example, it is now recognized that speciation can occur despite incomplete reproductive isolation (=adaptive speciation); similarly, very low levels of gene flow are ''allowed'' to breach the ''complete'' barriers of allopatry (Schluter, 2001(Schluter, , 2009Hey, 2006;Butlin et al, 2008;Fitzpatrick et al, 2008).…”

Repeated evolution of reproductive isolation in a marine snail: unveiling mechanisms of speciation

“…Following Bolnick & Fitzpatrick (2007) (see also discussions in Mallet et al 2009 andFitzpatrick et al 2009), we consider the spatial context of speciation to be important, because it reflects the level of connectivity/independence of populations although we do not expect to find complete sympatry nor complete allopatry in nature Fitzpatrick et al 2008). As underlined by Rieseberg & Burke (2001), levels of migration that are much smaller than what is needed to prevent divergence of populations by drift (i.e.…”

Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

“…allopatric speciation). However, a number of theoretical models and examples of speciation in the face of gene flow have now emerged (for recent reviews see Schluter, 2001, 2009, Hey, 2006, Butlin et al 2008, Fitzpatrick et al 2008. Sympatric speciation driven by disruptive selection while populations are still exchanging genes, also referred to as 'adaptive speciation,' is now considered a possible mechanism of speciation, where the evolution of reproductive isolation is a response to selection and not a simple byproduct of divergence.…”