Karyotype Evolution and Distinct Evolutionary History of the W Chromosomes in Swallows (Aves, Passeriformes)

Abstract

As in many other bird groups, data on karyotype organization and distribution of repetitive sequences are also lacking in species belonging to the family Hirundinidae. Thus, in the present study, we analyzed the karyotypes of 3 swallow species (Progne tapera, Progne chalybea, and Pygochelidon cyanoleuca) by Giemsa and AgNOR staining, C-banding, and FISH with 11 microsatellite sequences. The diploid chromosome number was 2n = 76 in all 3 species, and NORs were observed in 2 chromosome pairs each. The microsatellite distribution pattern was similar in both Progne species, whereas P. cyanoleuca presented a distinct organization. These repetitive DNA sequences were found in the centromeric, pericentromeric, and telomeric regions of the macrochromosomes, as well as in 2 interstitial blocks in the W chromosome. Most microchromosomes had mainly telomeric signals. The Z chromosome displayed 1 hybridization signal in P. tapera but none in the other species. In contrast, the W chromosome showed an accumulation of different microsatellite sequences. The swallow W chromosome is larger than that of most Passeriformes. The observed enlargement in chromosome size might be explained by these high amounts of repetitive sequences. In sum, our data highlight the significant role that microsatellite sequences may play in sex chromosome differentiation.

Comparative analyses of three swallow species (Aves, Passeriformes, Hirundinidae): Insights on karyotype evolution and genomic organization

“…Nevertheless, recent studies using classical and molecular cytogenetics have shown a greater similarity between the P. tapera and P. chalybea when compared to P. cyanoleuca (Barcellos et al, 2019). Taken together, these examples and our data support the current phylogeny of the genus Progne, which puts all Progne species into a single genus (Sheldon et al, 2005;Moyle et al, 2008;Barcellos et al, 2019).…”

“…The diploid number is 76 for the three swallow species, which corroborate previous studies (Barcellos et al, 2019). The 1st, 4th, 10th pairs and also the Z chromosome are metacentric, pairs 2 and 3 are acrocentric, while 8th, 9th, 11th and all microchromosomes are telocentric.…”

“…The swallow karyotypes presented a diploid number and morphology typically found in most Passeriformes (Tegelström and Ryttman, 1981;Santos and Gunski, 2006), with 76 chromosomes and many microchromosome pairs, as observed in Barcellos et al (2019). However, these species have a W chromosome relatively bigger than the W of most Passeriformes species due to a highly repetitive sequences accumulation, such as microsatellites (Berlin and Ellegren, 2004;Chen et al, 2012;Zhang et al, 2014;Barcellos et al, 2019).…”

“…As the other members from this class, it presents small genome, high chromosomal number, a few pairs of macrochromosomes and several microchromosome pairs. Furthermore, birds have a sexual system ZZ/ZW, where the female is heterogametic (Griffin et al, 2007;Barcellos et al, 2019).…”

“…Progne tapera (Linnaeus, 1766), Progne chalybea (Gmelin, 1789) and Pygochelidon cyanoleuca (Vieillot, 1817) have similar karyotypical organization with the same diploid number (2n=76) and distribution of repetitive DNA. Furthermore, recent studies with these species found an interesting characteristic, an enlarged W chromosome (Barcellos et al, 2019). Despite recent research, the cytogenetics of swallows is still poorly defined.…”