CHROMOSOMAL INVESTIGATION OF 3 COSTA-RICAN FROGS FROM THE 30-CHROMOSOME RADIATION OF HYLA WITH THE DESCRIPTION OF A UNIQUE GEOGRAPHIC-VARIATION IN NUCLEOLUS ORGANIZER REGIONS

A cytogenetic investigation of Hyla ebraccata Cope, H. microcephala Co pe, and H. phlebodes Stejneger revealed that the karyotypes of these 3 0-chromosome Hyla are very conservative. With the exception of some st ructural rearrangements, only few differences in chromosomal morpholog y could be discerned. Based on our results, we hypothesize that the te lomeric position of nucleolus organizer regions (NOR) on chromosome no . 10 may represent a derived condition in 30-chromosome Hyla. This cyt otype was found only in the Caribbean population of H. ebraccata. Such within-species disparity has not been observed previously among amphi bians. This phenomenon can most readily be explained by a translocatio n or insertion that rapidly drifted to high frequency in a small popul ation.