In this project we propose to thoroughly examine a hybrid zone between two metacentric races of the house mouse inhabiting Madeira. There are six metacentric races on Madeira, two of which come into contact and hybridise in a 4 km wide zone in the western part of the island. Given their chromosomal differences, these races are expected to produce unfit metacentric hybrids. Interestingly, such hybrids are extremely scarce in the hybrid zone, which is in fact dominated by a telocentric form with the race-specific chromosomes in the ancestral telocentric condition. In essence, instead of a single contact between metacentric races there are two contacts between the telocentric form and the metacentric race on either side, each with hybrids of much higher fitness than the metacentric hybrids.
As a result, this 'double hybrid zone' may in fact be less of a barrier to gene flow on grounds of hybrid fitness, but a greater barrier to gene flow on grounds of recombination suppression, than a single hybrid zone between the metacentric races. Such a situation raises several questions: i) Is a double hybrid zone more or less efficient than a standard single hybrid zone in reducing gene flow between chromosomal races? ii) What is the contribution of hybrid unfitness versus recombination suppression to the gene flow barrier? iii) Can behavioural isolation develop in such a system? In summary, are the two races ‘speciating with gene flow' [12] or 'despeciating'? The hybrid zone formed by these two races represents a fascinating system to investigate fundamental aspects of the speciation process involving chromosomal rearrangements.
This project builds on a huge amount of previous work conducted on the Madeiran system of chromosomal variation in the house mouse.

CESAM members on this project

Ana Mota Cerveira
Researcher

Researcher

Joaquim Tapisso
Research fellow

Maria da Luz Mathias
Principal Investigator

Sofia Isabel Vieira Gabriel
Researcher