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Evolutionary Biology
Phylogeography
| Question | Answer |
|---|---|
| What is phylogeography? | ‘the field of study concerned with the principles and processes governing the geographical distribution of genealogical lineages, especially those at the intraspecific level’ |
| Biogeography | • Biogeography is the study of the patterns and causes of the distribution of living things • Almost all taxa are restricted geographically to some degree • Some are very restricted - endemic to a particular area |
| Biogeography | • Major historical factors that influence current distributions include vicariance and dispersal • Vicariance is the splitting of distributions, when ancient landmasses split and separate due to continental drift |
| Biogeography | • Dispersal is movement of organisms or their propagules (e.g. seeds) • The relative contribution of vicariance and dispersal to current distributions can be investigated using phylogeographic methods |
| Wallace's line | Divides two regions that have separate tectonic histories that have only recently come into contact |
| What does phylogeography do? | Uses genetic information to examine genealogical history and patterning within species and populations This information is used to infer relationships of biogeographic areas and species histories |
| What does phylogeography do? | It also concerns the relationships between gene geneologies, phylogenetics and geography Aim of understanding the factors contributing to the formation of genetic population structure |
| What does phylogeography do? | Can explain the consequences of major historical events that had continent-wide impacts |
| Hedgehogs | Refugia and colonisation routes of other species Mountain ranges are barriers for some species but not others Main southern refugia are Iberia, Italy, Balkans and Greece |
| Molecular markers for phylogeographic studies: types of markers used | – Mitochondrial (mtDNA) or chloroplast (cpDNA) vs genomic markers |
| Molecular markers for phylogeographic studies: considerations | – Polymorphism, recombination, mode of inheritance |
| Molecular markers for phylogeographic studies: methods used | Coalescent theory – Nested Clade Analysis (not much any more) - case studies |
| Advantages to mtDNA | • Effectively neutral markers • High mutation rate means that variation will usually be present • High copy number allows for ease of amplification from limited or archived samples |
| However... | • Uniparentally inherited so if there are differences between sexes then no information about one sex • In plants mtDNA is less variable and recombines |
| Nuclear DNA | • Nuclear DNA markers are recombining and can be under selection • More complete but far more complicated picture • More difficult to obtain from archived specimens (fewer copies) |
| Coalescent theory | • The tracing of allelic ancestries back to their most recent common ancestor |
| Statistical phylogeography | Typically, a summary statistic is calculated from simulated data sets under each model to obtain a distribution of the summary statistic under each respective model |
| Single populations | • Equilibrium between mutation and drift (lineage sorting) • Lineage sorting effect greatest with small population sizes (more likely to lose alleles by chance) |
| Network of mtDNA haplotypes | - in the centre: most common and widespread allele - outside: single mutation steps |
| Multiple populations | • Few species exist as single, undifferentiated populations • Vicariance and dispersal - more complex pattern involving a barrier to gene flow |
| Factors affecting divergence between populations | • Genetic drift and gene flow – Isolation by distance – Physical barriers • Gene flow between species (inter-specific hybridization |
| Use of haplotype trees in phylogeograpy | Correlations between haplotype trees and geographical information can allow inference to be made about genetic processes occurring between populations |
| Haplotype networks | A haplotype network in which each number represents a different haplotype, and the size of a circle is approximately proportional to the number of individuals sequenced containing that haplotype |
| Haplotype networks | Solid circles represent haplotypes that were either not sampled, or are extinct Lines connecting haplotypes indicate single mutational differences Circles are coloured for reference to their geographic distribution (other shapes on ppt) |
| Case studies on ppts |
Created by:
rose.coo
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