Further insights on chromosomal evolution of the genus Enyalius with karyotype description of Enyalius boulengeri Etheridge, 1969 (Squamata, Leiosauridae)

The genus Enyalius is composed of 10 described species inhabiting forest areas in Amozônia, Cerrado and Atlantic forest biomes. Currently, eight species with high levels of chromosome variation have been karyotyped. The study aims to characterize the karyotype of Enyalius boulengeri, with classical and molecular techniques, and improve knowledge about the karyotype evolution of the lizard genus Enyalius. The species has 2n = 36 chromosomes (8m + 4sm + 24mc), FN = 24; NORs and 18S rDNA were subtelomeric and located on chromosome pair 2. Repetitive DNA probes (CAT)10 accumulated on centromeric and terminal regions of some macrochromosomes. (GA)15 probe showed conspicuous accumulation on the pericentromeric region of chromosome pairs 1 and 6. Repetitive FISH patterns obtained with (GC)15 probe marked the pericentromeric region of the first chromosome pair. All probes showed accumulation in the microchromosomes. The chromosomal formula found on E. boulengeri has been considered the ancestral karyotype for pleurodont Iguania. The genus Enyalius is characterized by two distinctive chromosomal groups; one with highly conserved karyotypes, whereas the other is karyotypically diverse. Our molecular cytogenetics data are promising and will increase knowledge about the genus Enyalius chromosome evolution.

Chromosomal relationships among the native rodents (Cricetidae: Oryzomyini) of the Galápagos Islands, Ecuador

Although the Galápagos Islands are recognized for their contribution to our understanding of evolutionary theory and have received the attention of scientists for over 185 years, our understanding of the native rodents there has been minimal relative to many other groups of organisms. Much of what we knew through most of the 20th century was based solely on species descriptions. Chromosome data has been limited to only Nesoryzomys narboroughi (2n = 32, FN (number of autosomal arms) = 50) and Aegialomys galapagoensis (2n = 56; FN = 58). We present the karyotypes of the only remaining extant species in the genus, N. swarthi (2n = 56; FN = 54) and N. fernandinae (2n = 44; FN = 54). Chromosomal banding reveals that extensive rearrangement has occurred within Nesoryzomys, including Robertsonian fusion and tandem fusion events but these alone cannot account for the diverse diploid numbers found within the genus. We propose that 1) N. swarthi represents the ancestral karyotype for the genus, similar to A. galapagoensis, 2) N. swarthi and N. fernandinae share the same fundamental number, suggesting divergence by Robertsonian fusions, and 3) N. narboroughi has the most derived karyotype, based on banding morphology and low diploid number.

First cytogenetic information for five Nilotic elephantfishes and a problem of ancestral karyotype of the family Mormyridae (Osteoglossiformes)

The elephantfish family Mormyridae is the most diverse lineage of the primitive teleostean clade Osteoglossomorpha distributed in inland waters of all continents except Antarctica and Europe. The family Mormyridae is endemic to Africa and includes 22 genera and almost 230 species. The evolutionary radiation of mormyrids most probably should be attributed to their capability of both generating and receiving weak electric signals. Up-to-date cytogenetic studies have revealed substantial karyotype differentiation among the nine investigated elephantfish species and genera (a single species studied per each genus). In the present study, karyotypes of five species representing five mormyrid genera (four unexplored ones) collected from the White Nile system in southwestern Ethiopia are described for the first time. The results show substantial variety of the diploid chromosome and fundamental numbers: 2n = 48 and FN = 54 in Brevimyrus niger (Günther, 1866), 2n = 50 and FN = 72 in Cyphomyrus petherici (Boulenger, 1898), 2n = 50 and FN = 78 in Hippopotamyrus pictus (Marcusen, 1864), 2n = 50 and FN = 76 in Marcusenius cyprinoides (Linnaeus, 1758), 2n = 52 and FN = 52 in Mormyrops anguilloides (Linnaeus, 1758). Karyotype structure in the latter species seems to be close to the ancestral condition for the family. This hypothesis is discussed in the light of available data on karyotype diversity and phylogeny of mormyrids.

Extensive chromosomal fissions and repetitive DNA accumulation shaped the atypical karyotypes of two Ramphastidae (Aves: Piciformes) species

In contrast to the ‘avian-like’ diploid number (2n = 80), most toucans and aracaris (Piciformes: Ramphastidae) have divergent karyotypes, exhibiting a higher 2n. To identify the chromosomal rearrangements that shaped the karyotype of these species, we applied chicken macrochromosome paints 1–10 and 11 microsatellite sequences to the chromosomes of two representative species, Pteroglossus inscriptus and Ramphastos tucannus tucannus. Paints of chicken chromosomes revealed that at least the first five ancestral chromosomes have undergone fissions, and a fusion between a segment of chicken chromosome 1 and a segment from chromosome 3 occurred in both species. The microsatellite sequences were accumulated mainly in the Z chromosome and in several microchromosomes in both species. These results suggest that the genomes of the Ramphastidae have been shaped by extensive fissions and repetitive DNA accumulation as the main driving forces leading to the higher 2n as found in these species. Furthermore, our results suggest that the putative ancestral karyotype of Ramphastidae already had a high diploid number, probably close to 2n = 112, similar to that observed in P. inscriptus and R. t. tucannus.

Phylogenetic Analysis and Karyotype Evolution in Two Species of Core Gruiformes: Aramides cajaneus and Psophia viridis

Gruiformes is a group with phylogenetic issues. Recent studies based on mitochondrial and genomic DNA have proposed the existence of a core Gruiformes, consisting of five families: Heliornithidae, Aramidae, Gruidae, Psophiidae and Rallidae. Karyotype studies on these species are still scarce, either by conventional staining or molecular cytogenetics. Due to this, this study aimed to analyze the karyotype of two species (Aramides cajaneus and Psophia viridis) belonging to families Rallidae and Psopiidae, respectively, by comparative chromosome painting. The results show that some chromosome rearrangements in this group have different origins, such as the association of GGA5/GGA7 in A. cajaneus, as well as the fission of GGA4p and association GGA6/GGA7, which place P. viridis close to Fulica atra and Gallinula chloropus. In addition, we conclude that the common ancestor of the core Gruiformes maintained the original syntenic groups found in the putative avian ancestral karyotype.

The wax gourd genomes offer insights into the genetic diversity and ancestral cucurbit karyotype

The botanical family Cucurbitaceae includes a variety of fruit crops with global or local economic importance. How their genomes evolve and the genetic basis of diversity remain largely unexplored. In this study, we sequence the genome of the wax gourd (Benincasa hispida), which bears giant fruit up to 80 cm in length and weighing over 20 kg. Comparative analyses of six cucurbit genomes reveal that the wax gourd genome represents the most ancestral karyotype, with the predicted ancestral genome having 15 proto-chromosomes. We also resequence 146 lines of diverse germplasm and build a variation map consisting of 16 million variations. Combining population genetics and linkage mapping, we identify a number of regions/genes potentially selected during domestication and improvement, some of which likely contribute to the large fruit size in wax gourds. Our analyses of these data help to understand genome evolution and function in cucurbits.

Comparative Chromosome Painting in Two Brazilian Stork Species with Different Diploid Numbers

Despite the variation observed in the diploid chromosome number of storks (Ciconiiformes, Ciconiidae), from 2n = 52 to 2n = 78, most reports have relied solely on analyses by conventional staining. As most species have similar macrochromosomes, some authors propose that karyotype evolution involves mainly fusions between microchromosomes, which are highly variable in species with different diploid numbers. In order to verify this hypothesis, in this study, the karyotypes of 2 species of storks from South America with different diploid numbers, the jabiru (Jabiru mycteria, 2n = 56) and the maguary stork (Ciconia maguary, 2n = 72), were analyzed by chromosome painting using whole chromosome probes from the macrochromosomes of Gallus gallus (GGA) and Leucopternis albicollis (LAL). The results revealed that J. mycteria and C. maguary share synteny within chromosome pairs 1-9 and Z. The syntenies to the macrochromosomes of G. gallus are conserved, except for GGA4, which is homologous to 2 different pairs, as in most species of birds. A fusion of GGA8 and GGA9 was observed in both species. Additionally, chromosomes corresponding to GGA4p and GGA6 are fused to other segments that did not hybridize to any of the macrochromosome probes used, suggesting that these segments correspond to microchromosomes. Hence, our data corroborate the proposed hypothesis that karyotype evolution is based on fusions involving microchromosomes. In view of the morphological constancy of the macrochromosome pairs in most Ciconiidae, we propose a putative ancestral karyotype for the family, including the GGA8/GGA9 fusion, and a diploid number of 2n = 78. The use of probes for microchromosome pairs should be the next step in identifying other synapomorphies that may help to clarify the phylogeny of this family.