Sibling species (also known as aphanic species) are species that are very similar in appearance, in behavior and in other characteristics, but they are reproductively isolated. In other words, sibling species are pairs or groups of genetically closely related species which are often morphologically indistinguishable, but are reproductively isolated, meaning that while they may interbreed, the offspring cannot reproduce.
Sibling species may arise as a result of allopatric speciation through geographic isolation, parapatric speciation, or sympatric speciation. The important thing to note is that sibling species are in fact separate biological species. The biological species concept, proposed by Ernst Mayr in 1942, emphasizes reproductive isolation as the basis of defining a species. The definition states: "A species is defined as a population or group of populations whose members have the potential to interbreed with one another in nature and to produce viable offspring, but cannot produce viable, fertile offspring with members of other species." Mayr, a proponent of allopatric speciation, hypothesized that adaptive genetic changes that accumulate between allopatric populations cause negative epistasis in hybrids, resulting in sterility of the offspring.
Scientists traditionally pairs or groups of species as sibling species based upon morphology, biogeography, and anatomical studies, but recent advances in DNA testing and molecular phylogeny have made it possible to better determine whether two or more species are in reality sibling species.
- George C. Steyskal (1972). "The meaning of the term 'sibling species'" (PDF). Systematic Zoology 21 (4): 446. doi:10.1093/sysbio/21.4.446.
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- Ernst Mayr (1970). "Morphological species characters and sibling species". Populations, Species, and Evolution. Cambridge, MA: The Belknap Press of Harvard University Press. pp. 21–36. ISBN 0-674-69013-3.
- Nicolas Puillandre, Christopher P. Meyer, Philippe Bouchet & Baldomero M. Olivera (2011). "Genetic divergence and geographical variation in the deep-water Conus orbignyi complex (Mollusca: Conoidea)". Zoologica Scripta 40 (4): 350–363. doi:10.1111/j.1463-6409.2011.00478.x. PMID 21712968.