Abstract
The freshwater fish species Dormitator latifrons, commonly named the Pacific fat sleeper, is an important food resource in CentralSouth America, yet almost no genetic information on it is available. A cytogenetic analysis of this species was undertaken by standard and molecular techniques (chromosomal mapping of 18S rDNA, 5S rDNA, and telomeric repeats), aiming to describe the karyotype features, verify the presence of sex chromosomes described in congeneric species, and make inferences on chromosome evolution in the genus. The karyotype (2n = 46) is mainly composed of metacentric and submetacentic chromosomes, with nucleolar organizer regions (NORs) localized on the short arms of submetacentric pair 10. The presence of XX/XY sex chromosomes was observed, with the X chromosome carrying the 5S rDNA sequences. These heterochromosomes likely appeared before 1 million years ago, since they are shared with another derived Dormitator species (Dormitator maculatus) distributed in the Western Atlantic. Telomeric repeats hybridize to the terminal portions of almost all chromosomes; additional interstitial sites are present in the centromeric region, suggesting pericentromeric inversions as the main rearrangement mechanisms that has driven karyotypic evolution in the genus. The data provided here contribute to improving the cytogenetics knowledge of D. latifrons, offering basic information that could be useful in aquaculture farming of this neotropical fish.
Highlights
Freshwater habitats, covering a small proportion of the Earth’s surface [1], host rich biodiversity, largely represented by freshwater fishes [2]—about 40% of global fish diversity [3].The Neotropical Region shows remarkable diversification of species and hosts more than three-quarters of the world’s fish functional diversity [4]
C-positive blocks are recognizable on the short arms of chromosome pair 10 carrying nucleolar organizer regions (NORs) and on those of the X chromosome; in the Y chromosome, besides the short arms, heterochromatin can be observed in the long arms, close to the pericentromeric area
Double fluorescence in situ hybridization (FISH) assays with ribosomal genes showed that 18S rDNA sequences are localized on a single chromosome pair in both males and females, whereas
Summary
Freshwater habitats, covering a small proportion of the Earth’s surface (about 1%) [1], host rich biodiversity, largely represented by freshwater fishes [2]—about 40% of global fish diversity [3].The Neotropical Region shows remarkable diversification of species and hosts more than three-quarters of the world’s fish functional diversity [4]. For the continental Neotropical Region 20 orders, 69 families and 5160 freshwater fishes have been described, accounting for about 40% of worldwide freshwater biodiversity [5]. Research on fish systematics and evolution has expanded over time, including, in recent decades, molecular taxonomy, developmental biology, and new tools like 3D imaging [2]. Cytogenetic analyses join these new tools, providing new evidence of the existence of cryptic species and evolutionary divergence ([7] and references therein) and giving rise to a prosperous field focused on neotropical species [8,9]
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