Abstract
Chromosomal rearrangements are an important process in the evolution of species. It is assumed that these rearrangements occur near repetitive sequences and heterochromatic regions. Avian karyotypes have diverse chromosomal band patterns and have been used as the parameters for phylogenetic studies. Although the group has a high diversity of species, no more than 12% has been analyzed cytogenetically, and the Parulidae family are extremely underrepresented in these studies. The aim of this study was to detect independent or simultaneous chromosomal rearrangements, and also to analyze chromosomal banding convergences and divergences of three Wood-Warblers species (Myiothlypis leucoblephara, Basileuterus culicivorus, and Setophaga pitiayumi). Our CBG-band results reveal an unusual W sex chromosome in the three studied species, containing a telomeric euchromatic region. The GTG and RBG bands identify specific regions in the macrochromosomes involved in the rearrangements. Cytogenetic data confirm the identification of speciation processes at the karyotypic of this group.
Highlights
The Avian Class is characterized by a bimodal karyotype, composed of many pairs of microchromosomes and just a few macrochromosomes (Christidis 1990)
The karyotypic structure of the three analyzed species in this study is similar to the typical avian karyotype (Figure 1 and Table 1), containing few pairs of macrochromosomes, many microchromosomes, a ZW heterogametic sexual system for females and ZZ homogametic for males (Christidis 1990)
In Passeriformes, it was shown by fluorescent in situ hybridization (FISH) results that all species studied shared a fission of GGA1 (Kretschmer et al 2018b)
Summary
The Avian Class is characterized by a bimodal karyotype, composed of many pairs of microchromosomes and just a few macrochromosomes (Christidis 1990). Some classical cytogenetic techniques provide patterns of positive and negative bands, exposing points of reference on the full length of the chromosome and enabling the creation of ideograms (Ladjali et al 1999). Changes in these patterns suggest the possible types of rearrangements caused by chromosomal differences that may have occurred during the evolution of the genome (Griffin et al 2007). Examples of this are the chromosomal rearrangements already reported by GTG and RBG bands in Gallus gallus (Galliformes), which identified a paracentric inversion in the long arm of chromosome 2 (Nanda et al 1994). Chromosomal polymorphisms were identified by GTG bands in Synallaxis frontalis (Passeriformes), where pericentric inversion involving the first and third pairs was observed (de Souza et al 2019), and in Treron phoenicoptera (Columbiformes) in the first and second pairs (Gupta and Kaul 2014)
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