Comparative Cytogenetics between Two Important Songbird, Models: The Zebra Finch and the Canary

Abstract

Songbird species (order Passeriformes, suborder Oscines) are important models in various experimental fields spanning behavioural genomics to neurobiology. Although the genomes of some songbird species were sequenced recently, the chromosomal organization of these species is mostly unknown. Here we focused on the two most studied songbird species in neuroscience, the zebra finch (Taeniopygia guttata) and the canary (Serinus canaria). In order to clarify these issues and also to integrate chromosome data with their assembled genomes, we used classical and molecular cytogenetics in both zebra finch and canary to define their chromosomal homology, localization of heterochromatic blocks and distribution of rDNA clusters. We confirmed the same diploid number (2n = 80) in both species, as previously reported. FISH experiments confirmed the occurrence of multiple paracentric and pericentric inversions previously found in other species of Passeriformes, providing a cytogenetic signature for this order, and corroborating data from in silico analyses. Additionally, compared to other Passeriformes, we detected differences in the zebra finch karyotype concerning the morphology of some chromosomes, in the distribution of 5S rDNA clusters, and an inversion in chromosome 1.

Chromosome Painting in Tyrant Flycatchers Confirms a Set of Inversions Shared by Oscines and Suboscines (Aves, Passeriformes)

“…Besides the confirmation of breakpoints of ancient syntenic groups, one of the most interesting findings is the detection of both paracentric and pericentric inversions in the ancestral pair 1 (GGA1q), observed both in Oscines and Suboscines [Kretschmer et al, 2014dos Santos et al, 2015dos Santos et al, , 2017. As the results in Suboscines were based on only 1 species, E. spectabilis , our data confirm that these inversions are present in different subfamilies among Tyrannidae and must have occurred before the separation of Suboscines and Oscines, 20 million years ago [Ohlson et al, 2013].…”

“…sulphuratus and S. subcristata have macrochromosomes with the same morphology, despite different diploid numbers. The analyses of classical cytogenetic data and FISH experiments show that these species retain a chromosome formula which is similar not only to other Tyrannidae, but also to other Oscines, with the first pair being submetacentric (corresponding to GGA2) and the presence of a centric fission in the ancestral pair 1, followed by a number of paracentric inversions, especially in the segment corresponding to GGA1q [Gunski et al, 2000;Kretschmer et al, 2014Kretschmer et al, , 2015dos Santos et al, 2015dos Santos et al, , 2017. Thus, the difference of diploid numbers must be due to rearrangements involving microchromosomes.…”

“…Hence, the mapping of BAC probes is a worthwhile approach that could reveal further intrachromosomal rearrangements that represent synapomorphies in these 2 suborders, or even within them. In fact, 2 different patterns of inversion have been described in oscine species, involving chromosomes homologous to GGA1q [Kretschmer et al, 2014;dos Santos et al, 2015dos Santos et al, , 2017, that probably represent a sequence of inversion events. Additionally, morphological differences due to the centromere position are visible by conventional staining, and while most macrochromosomes in Tyrannidae are biarmed [Gunski et al, 2000;Kretschmer et al, 2015], in the putative ancestral avian karyotype most of them were probably acrocentric/telocentric [Deakin and Ezaz, 2014], suggesting the occurrence of pericentric inversions during evolution.…”

“…The results showed a chromosomal organization similar to other Passeriformes belonging to the suborder Oscines, suggesting that the fissions and paracentric inversions detected by FISH had occurred before the divergence of Passeriformes into 2 groups . Hence, the fission of the ancestral syntenic group corresponding to chicken ( Gallus gallus ) chromosome 1 (GGA1), and the occurrence of numerous inversions, both paracentric and pericentric in GGA1q, may be a cytogenetic signature for Passeriformes [Kretschmer et al, 2014dos Santos et al, 2015dos Santos et al, , 2017. The analysis of other species of tyrants is necessary to corroborate this notion and define the chromosomal evolutionary history of Passeriformes.…”

Introducing the Bird Chromosome Database: An Overview of Cytogenetic Studies in Birds

“…The domestic fowl, Gallus gallus (GGA), 2n = 78, was the first bird species from which WCPs were isolated [Griffin et al, 1999]. These GGA probes have been used successfully to determine the chromosomal homologies between distantly related species such as ostrich ( Struthio camelus ), American rhea ( Rhea americana ), canary ( Serinus canaria ), and zebra finch ( Taeniopygia guttata ) [Nishida-Umehara et al, 2007;dos Santos et al, 2017]. For example, chromosome painting with GGA probes in eagles (Accipitridae) has shown that the macrochromosomes of these birds evolved through interchromosomal rearrangements such as fusions, fissions, and chromosome transloca-tions, leading to a decrease in the diploid number to 58-68 [de Oliveira et al, 2005].…”