Multiple forms of selection shape reproductive isolation in a primate hybrid zone

Area of Science:

• Evolutionary Biology
• Genomics
• Speciation Research

Background:

• Speciation involves populations becoming reproductively isolated.
• Natural selection is a key driver, often assumed to cause reproductive isolation as a byproduct of adaptation in allopatry.
• Reinforcement can strengthen reproductive isolation upon secondary contact, but its prevalence is debated.

Purpose of the Study:

• To investigate genomic signatures of selection related to reproductive isolation in a natural primate hybrid zone.
• To differentiate between allopatric divergence and reinforcement as drivers of reproductive isolation.
• To analyze how locus-specific differentiation and introgression patterns relate to reproductive isolation.

Main Methods:

• Analysis of reduced-representation sequencing data in a howler monkey hybrid zone.
• Quantification of admixture and population structure.
• Examination of the relationship between locus-specific differentiation and introgression.

Main Results:

• Extensive admixture was observed, primarily within the narrow hybrid zone.
• Loci with reduced introgression (indicating selection against hybrids) were more differentiated between parental populations than neutral loci.
• Loci with reduced introgression showed increased differentiation in sympatry compared to allopatry, suggesting reinforcement.

Conclusions:

• Reproductive isolation in this primate system likely originated from divergence in allopatry.
• Reinforcement by divergent selection in sympatry further contributed to reproductive isolation.
• The study highlights the interplay of different selection forms in shaping speciation.