Reproductive isolation occurs due to all of the following EXCEPT

Reproductive isolation refers to the intrinsic biological mechanisms (pre-zygotic and post-zygotic barriers) that prevent two populations from interbreeding and producing fertile offspring. These mechanisms include changes in genetic material, structural differences in genital organs (mechanical isolation), and changes in the gene pool that lead to behavioral or temporal isolation.

Barriers such as glaciers, mountains, or rivers cause geographical isolation, which is an extrinsic physical barrier. While geographical isolation can eventually lead to reproductive isolation over time due to independent evolution of the separated populations, it is not a reproductive isolation mechanism itself.

Answer: Barriers like glacier