Cytogenetic and biochemical differences between Apodemus sylvaticus and Apodemus flavicollis, possibly responsible for the failure to interbreed

TLDR: Interspecific hybrids never occurred, neither within the population nor in the laboratory interbreeding experiments with or without hormonal pretreatment, and this failure may be due to the genetic differences between both species.

Abstract: 1. 1. In the two closely related rodent species, Apodemus sylvaticus and Apodemus flavicollis , thirty-three different protein markers and the chromosome banding pattern as produced by special staining techniques were compared. Breeding and interbreeding experiments were also performed. 2. 2. Both species differ in the electrophoretic position of twelve out of thirty-three protein markers and in the existence of telomeric heterochromatin on five chromosome pairs. 3. 3. Interspecific hybrids never occurred, neither within the population nor in the laboratory interbreeding experiments with or without hormonal pretreatment. This failure may be due to the genetic differences between both species.