Chromosomal NOR Phenotype and C-Banded Karyotype of Olympic Mudminnow, Novumbra hubbsi (Euteleostei: Umbridae)

Chromosomes of Novumbra hubbsi were analyzed by Giemsa staining, C-banding, silver staining, CMA₃ fluorescence and fluorescence in situ hybridization (FISH). Diploid chromosome number of 2n = 48 was confirmed. The karyotype consists of two pairs of metacentric, five pairs of submetacentric, seven pairs of subtelocentric, and 10 pairs of acrocentric chromosomes (FN = 62). Nucleolar organizer regions are situated in the telomeric regions of the shorter arms of the largest and smallest subtelocentric pairs. Four additional CMA3-positive (but silver negative) sites also are present. Results of FISH (rDNA probe) suggest that all CMA₃-positive sites represent rDNA cistrons. C-positive blocks of heterochromatin are situated primarily in the short arms of biarmed chromosomes, providing a distinct banding pattern for most chromosomes. The karyotype of N. hubbsi may be derived from that of a hypothetical esocoid ancestor (with 2n = 48, FN = 48) by pericentromeric inversions and amplifications of NOR sites. The karyotype of N. hubbsi may link the simple karyotype of such ancestor with the unusual karyotype of Dallia pectoralis. Novumbra and Dallia may be more closely related to one another than either is to Umbra. Extant umbrid species cytotaxonomically may represent two distinct lineages, which differ by the type of karyotype differentiation: the polyploid/fusion branch that includes three species of the genus Umbra and an inversion/fission branch that includes N. hubbsi and one species (and possibly all three) of Dallia.

Fig. 1.

Metaphase cell of Novumbra hubbsi (left) stained with Giemsa (upper spread) and sequentially stained with silver (lower spread); karyotype (right) arranged from the same cell. NOR-bearing pairs of chromosomes are indicated by arrows on silver stained spread (lower left) and framed in the karyotype; note two larger and two smaller Ag-positive signals in the interphase nucleus in lower spread; m, metacentric; sm, submetacentric; st, subtelocentric; and a, acrocentric chromosomes. Bars = 5 μm

Fig. 2.

Metaphase cell (upper left) and cell nucleus (lower left) stained with CMA₃. Drawings (right) indicate more clearly location of eight CMA₃-positive signals

Fig. 3.

Interphase nucleus of Novumbra hubbsi subjected to fluorescence in situ hybridization (FISH) with a rDNA probe. Two major signals (large arrowheads) and six minor signals are indicated

Fig. 4.

C-banded karyotype of Novumbra hubbsi (left) and ordered chromosomes (right). Note distinctive banding pattern of NOR-bearing pairs #8 and #14. m, metacentric; sm, submetacentric; st, subtelocentric; and a, acrocentric chromosomes. Bars = 5 μm

Accepted: 21 Nov 2000