THE GENETIC BASIS OF INCIPIENT SPECIATION IN ARABIDOPSIS LYRATA, ACTA UNIVERSITATIS OULUENSIS A Scientiae Rerum Naturalium 568
|ISBN-13:||978-951-42-9356-6 || |
|Kustantaja:||Oulun yliopisto|| |
|Sijainti:||Print Tietotalo|| |
|Tekijät:||LEPPÄLÄ JOHANNA|| |
The study of speciation has been an area of primary interest in evolutionary biology from Darwinto the present day. Understanding the processes that give rise to new species requires knowledgeon how reproductive isolation develops between diverging populations. An irreversible andtherefore important component of reproductive isolation is intrinsic postzygotic isolation.Postzygotic incompatibilities often manifest themselves through hybrid inviability or sterility, anddistort allelic transmission ratios in hybrid progenies. The genetic basis of such incompatibilitieshas often been found to be negative interactions between two or more loci, also known as Bateson-Dobzhansky-Muller incompatibilities. During the last decade some genes involved in this type ofincompatibilities have been identified, but especially in plants our knowledge remains scarce. Inthis thesis I examined whether intrinsic postzygotic isolation had developed between allopatricpopulations of a perennial, outcrossing plant; Arabidopsis lyrata.
The studied populations of A. lyrata were found to be genetically highly differentiated. In F2progenies of crosses between populations many molecular markers reveal non-Mendeliangenotype ratios, that is, show transmission ratio distortion (TRD). By contrast, TRD was found tobe nearly absent in progenies of within population crosses. The degree of TRD clearly increasedwith genetic distance between the crossed populations, and origin for TRD was often in F1 gameteformation, instead of F2 zygotic level. The genetic basis of TRD appeared due to interactionsbetween nuclear loci, and between nuclear and cytoplasmic factors.
In addition to transmission ratio distortion, reduced male fertility and cytoplasmic malesterility was found in the F2 hybrids between A. lyrata subspecies petraea and lyrata. Quantitativetrait loci for reduced male fertility were polymorphic within populations, and dependent oncytoplasm. Thus, the findings in this thesis underline the role of cytonuclear interactions, and thepossibility of development of genic incompatibilities through genomic conflicts due to divergencelikely unrelated to local adaptation.