The differentiation observed between
groups of haplotypes of both islands appears to result mostly from
the barrier represented by the sea that separates the Isla de la
Juventud and the main Cuban island. To our knowledge
R. cylindraceus has low salt water tolerance, which would effectively
reduce its dispersal ability across marine barriers. The Cuban
archipelago was formed during the latest Eocene–early Oligocene
(35–33 Ma). During most of this time the western part of Cuba
was two major lands masses which today are the Isla de la Juventud
and the Guaniguanico mountain range.