Karyotypic Variation in the Genus Megaelosia (Anura, Hylodinae) with the First Description of a B-Chromosome in a Leptodactylid Frog

Three species of the genus Megaelosia (Megaelosia massarti, Megaelosia boticariana, and Megaelosia lutzae) were studied karyotypically using conventional Giemsa staining, C-banding, and NOR techniques. Megaelosia lutzae had 2n = 32 chromosomes, a new diploid number for this genus and for the subfamily Hylodinae. Two morphotypes of B-chromosomes were found in two specimens of M. massarti. C-banding patterns and NOR location varied among the species. Nevertheless, some chromosome pairs, as well as the NOR-bearing secondary constriction and the large pericentromeric C-block on the short arm of chromosome 10, were consistent among the three species. Megaelosia differs markedly from other Hylodinae and Dendrobatidae in terms of karyotype.

Fig. 1.

Giemsa stained karyotypes of Megaelosia boticariana (A) and Megaelosia lutzae (B). Note the conspicuous secondary constriction (arrowheads) in the two karyotypes. Bar = 5μm

Fig. 2.

Ideograms of the Megaelosia boticariana (A) and Megaelosia lutzae (B) karyotypes. Dark sectors indicate C-bands. Dotted areas represent the secondary constrictions. The gray areas indicate NOR sites

Fig. 3.

Karyotypes of three females of Megaelosia massarti with 28 (A) and 29 chromosomes (B and C). The inset shows the small supernumerary in specimen ZUEC 11396 (B) and the large supernumerary in specimen ZUEC 11397 (C). In C, note the difference in morphology of chromosomes 1 and 2 compared to the standard 28-chromosome karyotype. The arrowheads indicate the conspicuous secondary constrictions. Bar = 5μm

Fig. 4.

Ideograms of the 28 (A) and 29-chromosome karyotypes of Megaelosia massarti with small (B) and large (C) supernumerary chromosomes. The dotted areas show the secondary constrictions and the gray areas represent the NOR. Dark sectors denote the C-band regions

Fig. 5.

C-banded chromosomes of females Megaelosia massarti (A), and tadpoles of Megaelosia boticariana (B) and M. lutzae (C). Note that most of centromeric region are C-banded. Note also the presence in the three karyotypes of a large C-block coincident with the secondary constriction and a dark pericentromeric and centromeric band on the short arm of pair 10. Bar = 5μm

Fig. 6.

Banding pattern of 29-chromosome karyotypes of two females of Megaelosia massarti. The inset shows the fully heterochromatic small B chromosome (A) and the large B chromosome with weakly stained telomeric C-bands (B). Bar = 5μm

Fig. 7.

NOR-bearing chromosome pairs in females of Megaelosia massarti from a standard karyotype, karyotype with small and large supernumerary chromosomes; and tadpoles of Megaelosia boticariana and Megaelosia lutzae. Bar 5 = μm

Received: 17 Sept 2001

Accepted: 30 Jul 2002