Polymorphism of Sooty-fronted Spinetail (Synallaxis frontalis Aves: Furnariidae): Evidence of chromosomal rearrangements by pericentric inversion in autosomal macrochromosomes

Abstract

The Passeriformes is the most diverse and cytogenetically well-known clade of birds, comprising approximately 5,000 species. The sooty-fronted spinetail (Synallaxis frontalis Aves: Furnariidae) species, which belongs to the order Passeriformes, is typically found in South America, where it is widely distributed. Polymorphisms provide genetic variability, important for several evolutionary processes, including speciation and adaptation to the environment. The aim of this work was to analyze the possible cytotypes and systemic events involved in the species polymorphism. Of the sampled 19 individuals, two thirds were polymorphic, an event supposedly linked to mutations resulting from genomic evolution that can be transmitted hereditarily. A chromosomal polymorphism was detected between the 1st and 3rdpairs of autosomal macrochromosomes. This type of polymorphism is related to a pericentric inversion in regions involving chromosomal rearrangements. Differently from other polymorphism studies that report a link between polymorphic chromosomes and phenotypic changes, S. frontalis did not present any morphological variation in the sampled individuals.

Figure 1. Classical cytogenetics techniques in Synallaxis frontalis (SFR). (A) Conventional staining of metaphases from a male; arrows indicate the sexual chromosome Z. (B) Partial karyotype containing macrochromosomes, microchromosomes, and sex chromosomes. (C). C-banding of a female showing the W sex chromosome, entirely heterochromatic. (D) Five distinct cytotypes found in samples.

Figure 2. G-banding patterns found in standard and polymorphic individuals. Metaphasis of a standard (A) and polymorphic (B) bird; arrows indicate the first chromosome pair expanded in the box. (C) Schematic illustration of pericentric inversion.

Figure 3. Heredogram of the SFR family. Circles represent the females and squares, the males. The numbers refer to chromosome pairs. t: telocentric; st: subtelocentric; sm: submetacentric.