Trends in Ecology & Evolution
ReviewSympatric speciation in animals: the ugly duckling grows up
Section snippets
The ugly duckling is born (1930s–1966) and cast out (1966–1981)
The idea that natural selection can lead to divergence and speciation of sympatric populations dates back to Darwin (Ref. 1). However, sympatric speciation was not particularly controversial until the general acceptance of the allopatric mode of speciation as articulated by Mayr 2. In the 1960s, several researchers answered Mayr's 2 call for evidence that speciation could occur under sympatric conditions: First, Thoday and Gibson's laboratory study 11 purported to show that disruptive selection
Empirical evidence for sympatric speciation
Despite an increasing sense that sympatric speciation is plausible, it remains exceptionally difficult to prove that speciation in a given pair of taxa has occurred in an exclusively sympatric manner. This is not surprising, because it is usually easier to document that an evolutionary process could have occurred than it is to conclusively show that it is the only possible explanation in a particular case, particularly given how few systems have been studied in detail. There are two main types
Phylogenetic and other historical signatures of sympatric speciation
Several phylogenetic and population genetic analyses have recently been proposed as retrospective tests of sympatric speciation (Table 3). Reconstruction of the phylogenetic history of divergent taxa can provide an important, but not foolproof, line of empirical evidence for sympatric speciation. For example, the monophyly of taxa from small isolated environments, such as crater lakes, is powerful evidence that speciation has occurred sympatrically 51, 52, 53. However, in larger lakes, islands
Is it productive to continue to distinguish sympatric speciation as a unique mode?
Kondrashov has separated the process of sympatric speciation into two phases 23, 24, 25, 78. The first phase involves the initiation of genetic divergence within a population exposed to disruptive selection, whereas the second involves the conditions under which speciation between partially isolated sympatric groups can proceed to completion. ‘Multiple-niche’-type population genetics models have shown that establishing a stable polymorphism under disruptive selection is relatively
Towards a mechanistic classification of speciation modes?
Recent insights into sympatric speciation suggest that the mechanisms that produce it are neither improbable nor rare. The evidence summarized here certainly supports the contention that speciation can be initiated and/or go to completion in sympatry, and many of the same factors that facilitate this process are also likely to facilitate allopatric speciation when driven by selection. In all, ecological interactions, and the natural and sexual selection that they cause, might be responsible for
Prospects
Although the process of sympatric speciation now appears plausible and even probable under some circumstances, there is still much to be done (Box 2). It will be important to generalize models of speciation as much as possible and to estimate crucial model parameters in natural populations. In addition, the study of reproductive isolation in taxa along the entire continuum of divergence, from locally adapted ecotypes to very recent species, will be central to future analyses of speciation 95.
Acknowledgements
I thank D. Futuyma, J. Feder, R. Highton, A. Kondrashov, J. Mallet, K. Shaw, D. Schluter, D. Schemske, P. Danley and K. Filchak for useful discussion and comments on this article (although they do not all agree with it). I have great admiration for G. Bush's tenacity, as well as that of other long-time supporters of sympatric speciation. This work was supported by US National Science Foundation grant DEB9629081.
References (95)
Modes of animal speciation
Annu. Rev. Ecol. Syst.
(1975)- et al.
Enchenopa binotata complex: Sympatric speciation?
Science
(1983) - W.R. Rice, Speciation via habitat specialization: the evolution of reproductive isolation as a correlated character,...
Ecology returns to speciation studies
Science
(1999)Sympatric speciation driven by beneficial mutations
Proc. R. Soc. London B Biol. Sci.
(1996)Reproductive isolation between divergent races of pea aphids on two hosts. II. Selection against migrants and hybrids in the parental environments
Evolution
(2000)On the Origin of Species
(1859)Animal Species and Evolution
(1963)The population genetics of speciation: the evolution of hybrid incompatibilities
Genetics
(1995)Theory and speciation
Trends Ecol. Evol.
(2001)