Phylogenetic position of the saola <i>(Pseudoryx nghetinhensis)</i> inferred from cytogenetic analysis of eleven species of Bovidae

Abstract

Previous morphological and molecular analyses failed to resolve the phylogenetic position of the critically endangered saola (Pseudoryx nghetinhensis) with respect to its placement in Bovina (cattle, bison, and yak) or Bubalina (Asian and African buffaloes). In the present study, G- and C-banding, Ag-staining and FISH with 28S and telomeric probes was undertaken for 17 bovid species. An analysis of these data allowed us to identify 49 structural rearrangements that included autosomes, gonosomes and 17 different NOR sites. The combined data set was subjected to a cladistic analysis aimed at: (i) providing new insights on phylogenetic relationships of the saola and other species within the subfamily Bovinae, and (ii) testing the suitability of different classes of chromosomal characters for phylogenetic reconstruction of the family Bovidae. The study revealed that nucleolar organizing regions (NORs) are phylogenetically informative. It was shown that at least one, or sometimes two of these characters punctuate divergences that include nodes that are the most basal in the tree, to those that are the most recent. In this context, the shared presence of three NORs in saola and species of Syncerus and Bubalus strongly suggests the saola’s placement within the subtribe Bubalina. This contrasts with Robertsonian rearrangements which are informative only at the generic level. These findings suggest that NORs are an important and frequently overlooked source of additional phylogenetic information within the Bovidae that may also have applicability at higher taxonomic levels, possibly even for Pecora.

Cytotypes of Kirk’s Dik-Dik (<i>Madoqua kirkii</i>,Bovidae) Show Multiple Tandem Fusions

“…The A cytotype has retained the Caprini type. Three structural variants of the X chromosome were detected among bovids according to studies supporting previous findings [see for example Robinson et al, 1997Robinson et al, , 1998Gallagher et al, 1999;Rubes et al, 2007;Nguyen et al, 2008]. The intrachromosomal rearrangements which differentiated the X chromosomes of the Bovinae from the Caprinae were described by Iannuzzi et al [2000] using comparative FISH mapping with 17 markers.…”

Chromosome Evolution in Domestic Bovids as Revealed by Chromosome Banding and FISH-Mapping Techniques

“…At present, we still do not know whether these variations in number and position of the NORs offer any selective advantage to the species; however, they seem to evolve independently of the centric fusions and may represent a useful source of information for studying evolutionary relationships among species, as suggested by Gallagher et al [1999] and demonstrated recently by Nguyen et al [2008].…”

Chromosomal dynamics of nucleolar organizer regions (NORs) in the house mouse: micro-evolutionary insights

“…In phylogenetic reconstructions, such results have sometimes been interpreted as a signature of homoplasy, when in fact they may correspond to hemiplasy or lineage sorting (Robinson et al, 2008). An illustration of this may be found in a recent phylogenetic analysis of Bovidae using chromosomal characters, 17 of which were NORs (Gallagher et al, 1999;Nguyen et al, 2008). Several of the individuals analyzed were heterozygous at seven NOR-bearing chromosomes, four of which were homoplasic in the reconstructed tree.…”

“…The vast majority of these investigations are based on the silverstaining method which presents two drawbacks: it reveals only the active fraction of the rRNA genes, that is, those that were transcribed during the previous interphase, and in some cases, it may lead to nonspecific staining of heterochromatic regions (Dobigny et al, 2003;Cabrero and Camacho, 2008;Carvalho et al, 2009). Access to the genes themselves by the fluorescence in situ hybridization (FISH) technique has provided a cytogenetic tool to explore the extent of NOR diversity between species irrespective of their expression status (Matsubara et al, 2004;Datson and Murray, 2006;Nguyen et al, 2008). However, many of these studies involve comparisons between species, and thus provide little information on the evolutionary processes acting on variation at the intraspecific level.…”