The cytogenetic analysis of Brachygalaxias gothei, B. bullocki and their hybrids showed differences in the number of biarmed and monoarmed chromosomes, as like as, in their c-banding patterns. The basic karyotype consists in 2n=40 with a FN=58 in B. gothei, and 66 in B. bullocki, and 2n= 38 + 1 and FN =51 in the hybrids. B. bullocki presents a larger quantity of constitutive heterochromatin than B. gothei, and present a polymorphism in the location of one pair of NOR. The taxonomic status of B. gothei is discussed in relation of chromosome results and the hybrid sterility.
Karyotypes of Diplomystes camposensis and Dipfomystes nahuelbutaensis were the same diploid number (n = 56). The chromosome formula for D. camposensis was 16 metacentric + 24 submetacentric + 8 subtelocentric + 8 telocentric chromosomes and for D. nahuelbutaensis was 14 metacentric + 26 submetacentric + 8 subtelocentric .t 8 telocentric chromosomes. In contrast, the differences in the chromosomal C-banding patterns between these species was large. For instance, chromosome pairs 5, 6, and 7 of D. nahuelbutaensis showed heterochromatic centromeres and pairs 23, 24, 27, and 28 were entirely heterochromatic. Diplomystes camposensis showed conspicuous C-banded blocks in pairs 7, 24, and 25 (chromosome pair 7 had one heterochromatic arm, chromosome pair 24 was entirely heterochromatic, and chromosome pair 25 had heterochromatin close to centromere). Comparison with other ostariophysan karyotypes (e.g. gymnotiforms, characiforms, and cypriniforms), does not allow any conclusions about the plesiomorphic catfish condition, because the karyotypes of the outgroups are too variable. A synapomorphy shared by characiforms, gymnotiforms, and diplomystid catfishes is the presence of more metacentric to submetacentric than subtelocentric to telocentric chromosomes. Cypriniforms are more primitive because they have more subtelocentric to telocentric than metacentric to submetacentric chromosomes.
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