What is Phylogeography?

Wikipedia (the one who knows everything!) defines phylogeography as “the study of the historical processes that may be responsible for the contemporary geographic distributions of individuals … distribution of individuals in light of the patterns associated with a gene genealogy”. I have found more complex definitions, from renamed authors, and even using different words, all authors agree that phylogeography is concerned with processes driving distributions of genealogical lineages (population or intraspecific levels). Moreover, they agree that phylogeography is positively related to the development of recent molecular techniques. Finally, I will define phylogeography as a field of study concerned in understands microevolution and speciation in its geographic or spatiotemporal context based on molecular studies.

 

The phylogeography approach began in the late 1980s, with the development of the molecular techniques. With the advanced of the polymerase chain reaction (PCR), phylogenetic and population genetic studies have increased fast in the last years. The newly developing molecular approaches provide bases for mapping the spread of lineages (within populations or close related species) during the evolution.

 

The studies are based mainly on mitochondrial DNA, this DNA is small (about 16,500 bases), circular, and has high rate of evolution. Also, it is usually passed without recombination to the next generation, making it perfect for intraspecific studies. (In the majority of the species).

 

Organellar genomes (as mitochondrial or chloroplast ones) exist as haploid rather than diploid. Individuals within species have different genotypes, or in this case called haplotype and transmitted between generations exclusively through the female. The analysis of the haplotype distribution, frequencies across different geographical regions, quantification of the genetic divergence between haplotypes, and the evaluation of genetic relationship between haplotypes will be the base of phylogeographic studies (Weising et al.  .

 

Phylogeographyc has been used not only in taxa distribution and lineage studies, but deeper studies have come out in the last years.

 

Carstens & Richards (2007) studied the influence of stochastic variance inherent to genetic processes that could interfere in formation of population genetic structure. Statistical approaches to testing phylogeography hypotheses accommodate this stochasticity by evaluating competing models of putative historical population structure.

 

Hewitt (2001) provides many examples of studies using mtDNA for biogeography applications. For example: DNA sequences that have been used for the phylogeography of volcanic archipelagos like Hawaii and Canaries. He cites the studied conducted by Carson, in 1983, based on Hawaiian Drosophila. Others like Remington used the technique in understanding hybrid zones in Europe. Moreover, Hewitt (2001) affirms that advances in molecular genetics providing DNA markers for the study of subspecific divergence there has been much progress in paleoclimatology. In southem Europe and south-east USA molecular phylogeographies reveal that species contain divergent genomes and are often greatly subdivided geographically, in marked contrast to northward expansions. Climatic changes in Pleistocene are also cleared in light of phylogeography.

 

In conclusion, phylogeography is a rapidly growing discipline that aims at studying the principles and historical processes governing the geographical distributions of genealogical lineages. In contrast to classical population genetics, which is based on allele frequency distributions, phylogeographic procedures are supposed to separate population structure from population history (Weising et al. 2005).

 

 

 

Weising, K., Nybom, H., Wolff, K. & Kahl, G. (2005). DNA Fingerprinting in plants: Principles, methods, and applications. Second edition. CRC Press, Taylor & Francis Group. 470pp

 

Hewitt, G. (2001). Speciation, hybrid zones and phylogeography – or seeing genes in space and time. Molecular Ecology, 10, 537-549.

 

Carstens, B. C. & Richards, C. L. (2007). Integrating coalescent and Ecological niche modeling in comparative phylogeography. Evolution, 61 (6), 1439-1454.

 

Others:

Wikipedia

Text book.

Advertisements

2 Comments »

  1. amnoelleb Said:

    That is a good overview of phylogeography. I have to admit that I knew NOTHING about the topic until this class, but I think that it’s a really important field of study and I’m glad that it seems to be growing. As someone who is more of an evolutionary biologist, I think that evolution often misses out on the historical context of the processes that we’re interested in studying. Previously, I think that this was mostly because there weren’t any methods for identifying historical ranges of species, that might indicate different interactions or pressures that may have contributed to speciation events. I think that this work will be really important in the further development of the evolution and ecology disciplines. Cool stuff!! =)

  2. cwaichert Said:

    Thanks! =)


{ RSS feed for comments on this post} · { TrackBack URI }

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: