Abstract
Harttia comprises an armored catfish genus endemic to the Neotropical region, including 27 valid species with low dispersion rates that are restricted to small distribution areas. Cytogenetics data point to a wide chromosomal diversity in this genus due to changes that occurred in isolated populations, with chromosomal fusions and fissions explaining the 2n number variation. In addition, different multiple sex chromosome systems and rDNA loci location are also found in some species. However, several Harttia species and populations remain to be investigated. In this study, Harttia intermontana and two still undescribed species, morphologically identified as Harttia sp. 1 and Harttia sp. 2, were cytogenetically analyzed. Harttia intermontana has 2n = 52 and 2n = 53 chromosomes, while Harttia sp. 1 has 2n = 56 and 2n = 57 chromosomes in females and males, respectively, thus highlighting the occurrence of an XX/XY1Y2 multiple sex chromosome system in both species. Harttia sp. 2 presents 2n = 62 chromosomes for both females and males, with fission events explaining its karyotype diversification. Chromosomal locations of the rDNA sites were also quite different among species, reinforcing that extensive rearrangements had occurred in their karyotype evolution. Comparative genomic hybridization (CGH) experiments among some Harttia species evidenced a shared content of the XY1Y2 sex chromosomes in three of them, thus pointing towards their common origin. Therefore, the comparative analysis among all Harttia species cytogenetically studied thus far allowed us to provide an evolutionary scenario related to the speciation process of this fish group.
Highlights
Fishes exhibit the greatest biodiversity among the vertebrates, constituting a useful model for studying several evolutionary questions [1]
We provide a set of conventional and molecular cytogenetic approaches (Giemsa staining, C-banding, repetitive DNA mapping by Fluorescence In Situ Hybridization (FISH), comparative genomic hybridization (CGH)), in an attempt to advance the knowledge of the processes that have shaped the chromosomal evolution in the genus Harttia
Our study provided additional evidence on the evolutionary pathways followed by fish species of the genus Harttia, highlighting both shared and specific chromosomal features that have emerged throughout their life story
Summary
Fishes exhibit the greatest biodiversity among the vertebrates, constituting a useful model for studying several evolutionary questions [1]. Species inhabiting small streams, with limited migration opportunities, tend to present an increased rate of speciation [3], even in parapatric populations [4]. One of these examples relies on the genus Harttia (Siluriformes, Loricariidae, Loricariinae), an endemic and widespread group throughout many South American river basins [5]. These species have a sedentary lifestyle and reduced vagility, leading them to inhabit specific sections of the river and to form small local populations [6]
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