Comparative Studies On Autotetraploid And Allotetraploid

Inbreeding depression is the decrease of offspring fitness after inbreeding and is one of the primary forces selecting against the evolution of self-fertilization. Researches suggest that inbreeding depression is mainly caused by the expression of recessive deleterious alleles as homozygotes whose frequency will increase because of self-fertilization or mating among relatives. Inbreeding depression has important effects on many aspects of evolutionary biology, such as selfing avoidance, evolution and maintenance of sexual system and polyploid. Researches have shown that the level of inbreeding depression may be related to the individual's age, population structure, history of species expansion, the degree of environmental stress, and so on. Polyploidy has also been hypothesized to affect magnitude of inbreeding depression, and studies imply that polyploids exhibit less inbreeding depression than its diploidy ancestors.In this paper, we studied the differences of the relative fitness and inbreeding depression between autotetraploid and allotetraploid. The results show that no matter what kind of reproductive method they may use, autotetraploids have lower fitness than allotetraploid after the early formation of tetraploid. However, the fitness advantage of allotetraploid disappears after a short period, and then the fitness of autotetraploid is greater than that of allotetraploid, until finally they both reach equilibrium. The inbreeding depression of autotetraploid is lower than allotetraploid in the first few generations after the formation of tetraploid. But, after a few generations of purge, inbreeding depression of autotetraploid will be higher than allotetraploid, until they both reach equilibrium.Level of dominance and natural selection against deleterious allele is more important than mating system in affecting the magnitude of fitness and inbreeding depression of tetraploid.Without new mutations, fitness of autotetraploid and allotetraploid increase with generations, but inbreeding depression decrease with generations regardless of the mating system. This article supports the role of purge of recessive deleterious allele, our results show that under self-fertilization, deleterious recessive alleles can be purged more quickly by natural selection. The above-mentioned results indicate that the formation of autopolyploid and allopolyploid may be related to the level of inbreeding depression.