Abstract
Pipidae is a clade of Anura that diverged relatively early from other frogs in the phylogeny of the group. Pipids have a unique combination of morphological features, some of which appear to represent a mix of adaptations to aquatic life and plesiomorphic characters of Anura. The present study describes the karyotype of Pipa carvalhoi Miranda-Ribeiro, 1937, including morphology, heterochromatin distribution, and location of the NOR site. The diploid number of P. carvalhoi is 2n=20, including three metacentric pairs (1, 4, 8), two submetacentric (2 and 7), three subtelocentric (3, 5, 6), and two telocentric pairs (9 and 10). C-banding detected centromeric blocks of heterochromatin in all chromosome pairs and the NOR detected in chromosome pair 9, as confirmed by FISH using the rDNA 28S probe. The telomeric probes indicated the presence of interstitial telomeric sequences (ITSs), primarily in the centromeric region of the chromosomes, frequently associated with heterochromatin, suggesting that these repeats are a significant component of this region. The findings of the present study provide important insights for the understanding of the mechanisms of chromosomal evolution in the genus Pipa, and the diversification of the Pipidae as a whole.
Highlights
Chromosome studies provide important insights into the diversification of karyotypes and represent an effective approach for the identification of homologies among species (Targueta et al 2018)
Interstitial heterochromatin blocks were detected in the long arms of pair 5 (Fig. 1B)
Mezzasalma et al (2015) proposed that the ancestral karyotype of Pipidae had a diploid number of 2n = 20, based on the conserved diploid numbers observed in Xenopus (= Silurana) tropicalis and Hymenochirus boettgeri + Pseudhymenochirus merlini
Summary
Chromosome studies provide important insights into the diversification of karyotypes and represent an effective approach for the identification of homologies among species (Targueta et al 2018). This approach provides a systematic understanding of the rearrangements of the genome that have occurred during the evolutionary history of the target group. The frogs of the family Pipidae dwell in freshwater environments and have behavioral and physiological features that are unique in anuran amphibians, making this group an excellent model for evolutionary studies (Cannatella and Trueb 1988, Cannatella and De Sá 1993, Pough et al 2001). The family currently includes four genera: Hymenochirus Boulenger, 1896 (4 species), Pseudohymenochirus Chabanaud, 1920 (1 species), Xenopus Wagler, 1827 (29 species), and Pipa Laurenti, 1768 (7 species), which are distributed in sub-Saharan Africa and South America (Frost 2019)
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