Heterozygosity and its unexpected correlations with hybrid sterility

Area of Science:

• Evolutionary biology
• Genetics
• Speciation

Background:

• Heterozygosity is generally advantageous by masking deleterious alleles.
• However, heterozygotes can experience reduced fitness due to heterospecific pairing (interspecies hybrids).
• Unfit hybrids contribute to species isolation, but the mechanism of directional sterility in backcrosses is unknown.

Purpose of the Study:

• To investigate the mechanism underlying directional sterility in later-generation backcross hybrids.
• To determine if the amount of heterospecific genome correlates with observed sterility patterns.

Main Methods:

• Analysis of heterospecific genome content in offspring from different backcross directions.
• Correlation of heterospecific genome levels with hybrid sterility.

Main Results:

• One direction of backcross consistently produces offspring with a higher proportion of heterospecific genome.
• This higher heterospecific genome content is correlated with increased sterility in that backcross direction.
• Interspecies laboratory backcrosses generally yield an excess of heterospecific individuals across taxa.

Conclusions:

• Directional hybrid sterility is likely caused by differing amounts of heterospecific genome in backcross offspring.
• The prevalence of excess heterospecific individuals in lab backcrosses suggests a broader phenomenon in hybrid zones.
• These findings provide insight into mechanisms maintaining species isolation.