Cytogenetics of beavers: a case of speciation by monobrachial centric fusions

Abstract

A comparison of G-banded chromosomes of four North American beavers, Castor canadensis (two males, two females), and four Eurasian beavers, Castor fiber (two males, two females), revealed that extensive monobrachial centric fusions distinguished the karyotypes of the two species. The complex multivalent formations that would occur in meiosis of a hypothetical hybrid would be expected to produce unbalanced gametes and postmating reproductive isolation. Thus, neither species was derived from the other; rather, they likely were derived from isolated populations in which some of the acrocentrics fused independently to produce monobrachial homology.Key words: beaver, chromosomes, karyotype evolution, monobrachial rearrangements, reproductive isolation.