Inferring hybrid zone history


Where the ranges of closely related species meet they may hybridize. The regions where this occurs are called hybrid zones. A balance of selection against hybrids and dispersal of parental species determines the width of the hybrid zone, but the environmental background also influences its positon. Via the hybrid zone, alleles from one species can be incorporated into the genome of the other: a process known as introgression. From the pattern of gene flow between the two species it is possible to determine where the hybrid zone is positioned and whether the hybrid zone has been stable or shifted position over time.


Ben Wielstra


Period and duration

c. 6-9 months

Study and level

Biology, MSc.

Objectives and

It is not always obvious where a hybrid zone is positioned. Closely related species are often morphologically similar and separation gets only more complicated when genetically admixed offspring are present. Furthermore, introgression of individual markers means that not all markers show the same geographical transition between the two parental species. Such patterns can be used to infer the history of the hybrid zone. Genetic data are key here. You will use genetic data to delineate the hybrid zone and determine potential differences among individual genetic markers.

Methods, tasks
and approach

Individuals from transects across hybrid zones are available. After DNA extraction, you will sequence over 6,000 nuclear DNA markers using target enrichment by sequence capture (or ‘hybseq’). Lab work entails the extraction of DNA, library preparation, and capture. Next-generation sequencing will be done commercially. Bioinformatics is required to prepare the data for analysis. Data analysis encompasses determining the degree of genetic admixture for each individual newt from the overall genotypic data. Next, geographical cline analysis is conducted to determine gene flow patterns for each individual marker.


Successfully completed the Evolutionary Biology 2 course (or equivalent). 

Currently only MSc students studying Biology at Leiden University can apply for this project.