The Karyotype of the Hoatzin (<b><i>Opisthocomus hoazin</i></b>) - A Phylogenetic Enigma of the Neornithes

Abstract

The hoatzin (Opisthocomus hoazin Müller, 1776) is a folivorous bird, endemic to the Amazonian region. It presents some unique characteristics, including wing claws and foregut fermentation, which make its phylogenetic relationship to other birds difficult to determine. There have been various attempts to place it among the Galliformes, Gruiformes, Musophagiformes, Cuculiformes, and Charadriiformes, but phylogenetic analyses always show low supporting values. Nowadays, the hoatzin is included in the monotypic order Opisthocomiformes, but the relationship of this order to other groups of birds is still unclear. Although its karyotype resembles the typical avian model, fissions of the syntenic groups corresponding to chicken chromosomes 1 and 2 and 2 fusions were found. The presence of 18S rDNA clusters in 2 pairs of microchromosomes is another derived character. Hence, different rearrangements were detected in the karyotype of the hoatzin, indicating it has been derived from the putative ancestral karyotype by the occurrence of fissions and fusions. However, as these rearrangements are not exclusive to O. hoazin, they do not clarify the phylogenetic position of this enigmatic species.

A Comprehensive Cytogenetic Analysis of Several Members of the Family Columbidae (Aves, Columbiformes)

“…passerina , including a fusion between GGA6/GGA8. Interchromosomal fusions are exceptionally rare in birds, and evidence of fusion between GGA6/GGA8 has only been previously described in three not-closely related species, Tetrao urogallus (Galliformes), Falco columbarius (Falconiformes) and Opisthocomus hoazin (Opisthocomiformes) [ 23 , 24 , 25 ], hence, this fusion in C . talpacoti and C .…”

“…talpacoti and C . passerina , since this fusion is not common in birds [ 2 , 25 ]. However, if the phylogeny proposed by Pereira et al [ 7 ] is correct, this fusion is likely to be a convergent chromosome rearrangement in S. decaocto and in C .…”

“…Whole chromosome paints derived from GGA1-10 produced identical results in C. talpacoti and C. passerina, including a fusion between GGA6/GGA8. Interchromosomal fusions are exceptionally rare in birds, and evidence of fusion between GGA6/GGA8 has only been previously described in three not-closely related species, Tetrao urogallus (Galliformes), Falco columbarius (Falconiformes) and Opisthocomus hoazin (Opisthocomiformes) [23][24][25], hence, this fusion in C. talpacoti and C. passerina likely occurred in their common ancestor. This hypothesis is reinforced by the absence of this fusion in other species of the same genus, C. picui [16].…”

Revising the Chromosome-Specific Probes of White Hawk (Leucopternis albicollis)

“…However, the fact that the five previously chromosomes of L. albicollis identified as homologous to GGA1 did not cover the entire chromosome 1 of Columbiformes species raised the suspicions that at least one more chromosome of L. albicollis should be assigned to GGA1 [5]. Similar results were observed in Opisthocomiformes and Cuculiformes [7,8]. Hence, the aim of this study was to generate a new set of chromosome paints of L. albicollis in order to obtain a better coverage of GGA chromosomes.…”

Unusual parasite from an enigmatic host – a new group of mites infesting feather quills of the hoatzin

“…Its phylogenetic position among Neornithes still constitutes one of the biggest mysteries in the avian systematics (Sibley & Ahlquist 1973Sorenson et al 2003;Ericson et al 2006;Kimball et al 2013;McCormack et al 2013;Prum et al 2015;Dos Santos et al 2018;Houde et al 2019). There have been various attempts to place it in different parts of the bird tree, but phylogenetic analyses mostly have shown low supporting values (Dos Santos et al 2018). However, the most recent molecular phylogeny with robust statistical support placed hoatzin as the sister taxon of the Caprimulgiformes in basal landbirds clade (Kuhl et al 2020); only future researches can confirm this position.…”