Allopatric speciation is the norm in sexually reproducing taxa. Ever since the mid-1900s, the prevailing worldview was that species normally arise during or immediately following geographic separation. Populations either undergo full speciation in allopatry, or they quickly complete the process by reinforcement selection for prezygotic RIBs (reproductive isolating barriers) after regaining secondary geographic contact. Strictly sympatric speciation, by contrast, was deemed to be rare or atypical at best.
adaptive speciation; sympatry
Allopatric speciation is the norm in sexually reproducing taxa. Ever since the mid-1900s (see Chapter 20), the prevailing worldview was that species normally arise during or immediately following geographic separation. Populations either undergo full speciation in allopatry, or they quickly complete the process by reinforcement selection for prezygotic RIBs (reproductive isolating barriers) after regaining secondary geographic contact. Strictly sympatric speciation, by contrast, was deemed to be rare or atypical at best.
Beginning mostly in the 1980s, a shifting attitude emerged in which ecological and behavioral selective factors are deemed to be prime drivers of biological speciation, sometimes even in sympatry. Under this view, diversifying selection on resource utilization or mate choice frequently eventuates in reproductively isolated populations worthy of full species recognition. Some famous putative examples involve insects that rapidly shifted hosts or switched habitats, and fish species flocks that apparently arose quickly within particular bodies of water. In 2004, Ulf Dieckmann and his colleagues compiled many such examples of what they termed “adaptive speciation”.
We are currently in the midst of this ongoing scientific revolution, so it is too early to know how it will unfold. In any event, it is appropriate to conclude this book by using this as the penultimate example of paradigm shifts in evolutionary genetics, because it brings us back to the Darwinian revolution (see Chapter 1) that opened this book. Darwin too envisioned that species arise by means of natural selection operating during ecological plays on the evolutionary stage. Thus, in a sense we have come conceptually full circle!
1. Berlocher SH, Bush GL. An electrophoretic analysis of Rhagoletis (Diptera: Tephritidae) phylogeny. Syst Zool. 1982;31:136–155.
2. West-Eberhard M. Sexual selection, social competition, and speciation. Q Rev Biol. 1983;58:155–183.
3. Echelle AA, Kornfield I, eds. Evolution of Fish Species Flocks. Orono, ME: University of Maine Press; 1984.
4. Kondrashov AS, Mina MV. Sympatric speciation: When is it possible? Biol J Linn Soc. 1986;27:201–223.
5. Schluter D. The Ecology of Adaptive Radiation Oxford, UK: Oxford University Press; 2000.
6. Schluter D. Ecology and the origin of species. Trends Ecol Evol. 2001;16:372–380.
7. Dieckmann U, Doebeli M, Metz JAJ, Tautz D, eds. Adaptive Speciation. Cambridge, UK: Cambridge University Press; 2004.