A Unified Model of Phylogeography

Identify barriers to gene flow.	Investigate events of speciation.
Develop phylogenic hypotheses.	Visualize genetic pathways.

Creating Genetic Isolines from Georeferenced DNA

This study introduces a unified model of phylogeography to better understand biodiversity and how it relates to the spatial distribution of species and evolutionary processes. The unified model uses ArcGIS to integrate an analysis of habitat suitability with information on phylogenic relationships derived from the analysis of mitochondrial DNA. The neotropical bat, Uroderma bilobatum, was chosen to test the model. This particular bat was chosen because of the large amount of genetic and ecological information available for the species. The information analyzed in the present study is the product of more than 30 years of work by researchers at Texas Tech University.

Genetic variation was calculated by comparing the DNA sequence from each sample population to the DNA sequence of an outgroup. The genetic distance values were then georeferenced to specimen localities. Using cokriging in ArcGIS Geostatistical Analyst, a genetic distance surface was interpolated using the GARP model of habitat suitability as a variable. The genetic isolines represent the genetic distance from the outgroup and provide a cartographic representation of the genetic variation within a species.

Interpretation and Significance of Genetic Isolines

The unified model provides a better understanding of biodiversity in different ways. Genetic isolines allow researchers to identify physical barriers to gene flow, investigate events of divergence and speciation, develop new phylogeographic hypotheses, and visualize genetic pathways.

Physical barriers to gene flow are associated with closely spaced isolines indicating a steep gradient in genetic distance. A concentric pattern of isolines is associated with genetic divergence or the generation of new taxa. The concentric pattern in Venezuela suggests strong divergence in an isolated population. Moreover, the direction of genetic isolines indicates the primary direction of gene flow. In this case, the isolines reflect a stronger gene flow in a north-south direction.