What is an Incipient Species?[]
When populations have diverged and they are mostly isolated from each other in terms of gene flow, though some interbreeding my occur, they are said to be incipient species. Incipient speciation may be the first stage of what would be considered true and complete speciation in which populations are no longer able to interbreed.
Freeman, S., & Herron, J. C. (2004). Evolutionary analysis (pp. xiv-802). Upper Saddle River (NJ): Pearson Education.
An Example of Incipient Speciation[]
European Blackcaps (Sylvia atricapilla)
- Named for the male's distinctive black head coloration, this species is common throughout Europe.
- European Blackcaps are migratory. They spend their summers in northern Europe and overwinter in southern Europe and northern Africa.
- Recently, researchers have taken notice of a migratory divide between populations of blackcaps (Rolshausen et al., 2009; Santiago-Alarcon, 2011).
- The Northwest Migratory Route
- These blackcaps overwinter in England where it's noted that humans offer them food (i.e. bird feeders).
- This migratory route is shorter and does not involve crossing the Alps.
- The Southwest Migratory Route
- These blackcaps overwinter in Spain and other areas of the Mediterranean.
- These birds feed primarily on native berries and insects.
- The Northwest Migratory Route
- Blackcaps that overwinter in England return to the breeding grounds earlier than the group that overwinters in Spain and therefore, they mate with each other. This timing difference has resulted in unequal mixing of the genes from the two populations and may be an initial step towards speciation (Bearhop et al., 2005; Rolshausen et al., 2009).
- Though the two populations are not incapable of interbreeding, gene flow has been inhibited.
- Scientists speculate that the migratory divide could, within a few short generations, cause the two populations to be reproductively isolated (Bearhop et at., 2005).
Sources:
Bearhop, S., Fiedler, W., Furness, R. W., Votier, S. C., Waldron, S., Newton, J., ... & Farnsworth, K. (2005). Assortative mating as a mechanism for rapid evolution of a migratory divide. Science, 310(5747), 502-504.
Rolshausen, G., G. Segelbacher, K. A. Hobson, and H. M. Schaefer. (2009). Contemporary evolution of reproductive isolation and phenotypic divergence in sympatry along a migratory divide. Current Biology 19:1-5.
Santiago-Alarcon, D., Bloch, R., Rolshausen, G., Schaefer, H. M., & Segelbacher, G. (2011). Prevalence, diversity, and interaction patterns of avian haemosporidians in a four-year study of blackcaps in a migratory divide. Parasitology, 138(07), 824-835.
Image Credit: Vassen, F. (2010). Flicker. Available at http://www.flickr.com/photos/42244964@N03/3944661073/