Genetic isolate

A genetic isolate is population of organisms that has little genetic mixing with other organisms within the same species. This may result in speciation, but this is not necessarily the case. Genetic isolates may form new species in several ways:

• allopatric speciation, in which two populations of the same species are geographically isolated from one another by an extrinsic barrier, and evolve intrinsic (genetic) reproductive isolation
• peripatric speciation, in which a small group of a population is separated from the main population, and experiences genetic drift
• parapatric speciation, in which zones of two diverging populations are separate, but do overlap somewhat; partial separation is afforded by geography, so individuals of each species may come in contact from time to time, but selection for specific behaviours or mechanisms may prevent breeding between the two groups.
• sympatric speciation, a contentious method of speciation in which species diverge while inhabiting the same place.

Human influences on genetic isolates include restricted breeding of dogs, or a community living secluded away from others (such as Tristan da Cunha or Pitcairn Islands). Far larger and less secluded human genetic isolates are peoples like Sardinians or also the Finns, natives of Finland.

Genetic Isolation and the Giraffa camelopardalis

Genetic isolation can happen in a variety of different ways. There are many ongoing, current research projects evaluating how various species have diverged through the process of genetic isolation, the giraffe, Giraffa camelopardalis, being one example. Giraffe are recognized to have nine separate subspecies, each varying in their coloration and patterns.^[1] After much research, it is accepted that genetic isolation is at fault for allowing the G. camelopardalis species to diverge. There are various ideas behind how genetic isolation has occurred within the giraffe species. Extant giraffe populations have been studied to make small-scale migratory movements based upon wet and dry seasons within the African climate.^[2] The feeding ecology of giraffe is highly researched and it has shown that giraffe will follow the growth patterns of the Acacia tree based upon seasonal change, changing giraffe locations from mountain ranges to desert range.^[3] Though this is not evidence for current day genetic isolation, it suggests evidence for past large-scale migrations that may have caused separation within the species, caused genetic isolation, and led to the beginnings of the subspeciation of the giraffe population. Giraffe also tend to travel in loose social herds. However, these loose social herds have been researched to be based upon a non-random system. This non-random system follows a trend of kinship, or the sharing of similar genes between individuals. These loose-social herds that keep kin and familiar individuals within the same group, with only small movements of individuals from the herd, only for them to return to the same group.^[4] This is evidence for genetic isolation by interaction only between familiar individuals. This is cause for interbreeding and the accumulation of certain alleles, alleles that could potentially code for pelage color and pattern, within a population, causing differences between populations and ultimately the subspeciation of the giraffe species. Geographic separation has also been studied to play a role in the genetic isolation of the giraffe. The mitochondrial DNA of giraffe has been studied for mutations and loci substitutions between subspecies and suggests diversification around the Late Pleistocene, where geographic isolation was likely.^[5] The giraffe is a great example of how genetic isolation can happen in a number of ways and can lead to the diversification of a species.

Allopatric Speciation

The giraffe, Giraffa camelopardalis, can be seen as a representation of the allopatric speciation that occurs due to genetic isolation of a population. Several clades of giraffe show differentiation within their mitochondrial DNA, varying between regions throughout Africa. These differences date back to the middle of the Pleistocene epoch, and coincide with genetic isolation due to climatic and geographical separations within the population, allowing for the evolution and subspeciation of the separate subspecies of giraffe and differences in their pelage.^[6]

See also

• Language isolate
• Linkage disequilibrium

References

1. "Giraffe Subspecies". Giraffe Conservation Foundation. Retrieved 23 October 2014.
2. Pellew, R (1984). "The feeding ecology of a selective browser, the giraffe (Giraffa camelopardalis tippelskirchi". Journal of Zoology. 202: 57–81. doi:10.1111/j.1469-7998.1984.tb04288.x.
3. Fennessy, J (2009). "Home range and seasonal movements of Giraffa camelopardalis angolensis in the northern Namib Desert". African Journal of Ecology. 47: 318–327. doi:10.1111/j.1365-2028.2008.00963.x.
4. Bercovitch, F.B. (2013). "Herd composition, kinship and fission–fusion social dynamics among wild giraffe". African Journal of Ecology. 51: 206–216. doi:10.1111/aje.12024.
5. Hassanin, A (2007). "Mitochondrial DNA variability in Giraffa camelopardalis: consequences for taxonomy, phylogeography and conservation of giraffes in West and central Africa". Comptes rendus biologies: 265–274.
6. Brown, D. M.; Brenneman, R. A.; Koepfli, K. P.; Pollinger, J. P.; Milá, B.; Georgiadis, N. J.; Wayne, R. K. (2007). "Extensive population genetic structure in the giraffe". BMC Biology. 5 (1): 57. doi:10.1186/1741-7007-5-57. PMC 2254591. PMID 18154651.