Wojciech Waga

Sympatric speciation as intrinsic property of the expanding population

Sympatric speciation is still debatable, though some well documented empirical data that support it already exist. Our computer modeling reveals that sympatric speciation is an intrinsic property of the expanding populations with differentiated inbreeding—higher at the edges and lower inside the territory. At the edges of expanding populations, the probability of forming deleterious phenotypes by placing two defective alleles in the corresponding loci is relatively high even with low genetic load. Thus, the winning strategy is to use rather the complementary haplotypes to form zygotes. This strategy leads to a very fast sympatric speciation and specific distribution of recombination activity along the chromosomes—higher at the subtelomeric regions (close to the ends of chromosomes) and lower in the middle of chromosomes, which is also observed in all human chromosomes (excluding Y).

PHASE TRANSITION IN THE GENOME EVOLUTION FAVORS NONRANDOM DISTRIBUTION OF GENES ON CHROMOSOMES

We have used the Monte Carlo-based computer models to show that selection pressure could affect the distribution of recombination hotspots along the chromosome. Close to the critical crossover rate, where genomes may switch between the Darwinian purifying selection or complementation of haplotypes, the distribution of recombination events and the force of selection exerted on genes affect the structure of chromosomes. The order of expression of genes and their location on chromosome may decide about the extinction or survival of competing populations.

The Role Of Haplotype Complementation And Purifying Selection In The Genome Evolution

We discuss two different ways of evolution for chromosomes and genomes. Purifying selection dominates in large panmictic populations, where the Mendelian law of independent gene assortment is valid. If instead the populations are small, recombination processes are not effective enough to ensure an independent assortment of linked genes, and larger clusters of genes could be inherited as genetic units. There are whole clusters of genes which tend to complement in such conditions instead of single pairs of alleles like in the case of purifying selection. Computer simulations have shown that switching between complementation and purification strategies has the characteristic of a phase transition. This is also responsible for specific distribution of recombination events observed along eukaryotic chromosomes (a higher recombination rate is observed in subtelomeric regions than in central parts of chromosomes) and for sympatric speciation.