First Chromosomal Analysis in Hepsetidae (Actinopterygii, Characiformes): Insights into Relationship between African and Neotropical Fish Groups

Abstract

Hepsetidae is a small fish family with only the genus Hepsetus, with six described species distributed throughout the South, Central and Western regions of Africa, showing a close relationship with the Alestidae and some Neotropical fish families. However, no cytogenetic information is available for both Hepsetidae and Alestidae species, thus preventing any evolutionary comparative studies at the chromosomal level. In the present study, we are providing new cytogenetic data for Hepsetus odoe, including the standard karyotype, C-banding, repetitive DNAs mapping, comparative genomic hybridization (CGH) and whole chromosome painting (WCP), providing chromosomal patterns and subsidies for comparative cytogenetics with other characiform families. Both males and females H. odoe have 2n = 58 chromosomes (10m + 28sm + 20st/a), with most of the C-band positive heterochromatin localized in the centromeric and subtelomeric regions. Only one pair of chromosomes bears proximal 5S rDNA sites in the short arms, contrasting with the 18S rDNA sequences which are located in the terminal regions of four chromosome pairs. Clear interstitial hybridization signals are evidenced for the U1 and U2 snDNA probes, but in only one and two chromosome pairs, respectively. Microsatellite motifs are widely distributed in the karyotype, with exception for the (CGG)10, (GAA)10 and (GAG)10 probes, which highlight conspicuous interstitial signals on an unique pair of chromosomes. Comparative data from conventional and molecular cytogenetics, including CGH and WCP experiments, indicate that H. odoe and some Erythrinidae species, particularly Erythrinus erythrinus, share similar chromosomal sequences suggesting some relatedness among them, although bearing genomic specificities in view of their divergent evolutionary histories.

Chromosome-level genome assembly of the African pike, Hepsetus odoe

“…The final African pike genome assembly spanned 862.1 Mb and 29 chromosomes, accounting for 86.6 % of the estimated genome size, with contig and scaffold N50 of 347.4 kb and 25.8 Mb, respectively. The constructed 29 chromosomes agreed with the previous karyotype analysis of H. odoe 6 .…”

“…This distribution across the Atlantic Ocean displays asymmetry in the number of species, with circa 220 reported species in Africa and over 1,700 species in South America. High fragmentation has been reported in the South American species, compared to the lower fragmentation and variability in African ones 4,5 . However, quite limited genomic information has been available to study the Characiformes vicariance.…”

“…African pike, Hepsetus odoe , is a representative African Characiformes that belongs to the family Hepsetidae . It is a torpedo-shaped predatory and piscivorous species distributed in the freshwater basins in central and western Africa 6 , bearing a striking resemblance to the European pike. One of the most striking features is their dentition with the lower jaw filled with two rows of sharp point teeth while the upper with only one raw.…”

“…H . odoe was reported the only species in the Hepsetidae family, until recently five additional species were described by recent studies 6,7 . Despite of the high economic and evolutionary importance, no genome data are available for this group.…”

Molecular Analysis and Chromosome Mapping of Repetitive DNAs in the Green TerrorAndinoacara rivulatus(Cichlidae: Cichlasomatini)

“…15 Fish cytogenetics is a very active research area that provides information for taxonomy and for the understanding of the phylogenetic relationships among taxa. [16][17][18][19][20][21][22][23] The most recent checklist of cytogenetically analyzed fish species reveals that only *8% of cichlid fishes are included. 24 The diploid number in the group ranges from 2n = 32 to 2n = 60, but in neotropical cichlids, the modal diploid number is 2n = 48.…”