Ant genomics sheds light on the molecular regulation of social organization

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.     

Profile of micronucleus frequencies and nuclear abnormalities in different species of electric fishes (Gymnotiformes) from the Eastern Amazon

The frequency of spontaneous micronucleus (MN) formation in fish species needs to be determined to evaluate their usefulness for genotoxic biomonitoring. The definition of a good bioindicator takes into account the current knowledge of its metabolic traits as well as other factors including its feeding behavior and relationship to the environment. In this study, we compared the basal frequencies of micronucleated erythrocytes and nuclear abnormalities (NA) among different species of the fish Order Gymnotiformes (Rhamphichthys marmoratus, Steatogenys elegans, Sternopygus macrurus, Parapteronotus hasemani, Gymnotus mamiraua, Gymnotus arapaima, Brachyhypopomus beebei, Brachyhypopomus n. sp. BENN) sampled in several localities of the Eastern Amazon. A baseline of MN and NA frequency in these fish was determined, enabling the identification of potentially useful species as models for genotoxicity studies. Only one impacted sample collected at a site in the River Caripetuba showed a significant number of NAs, which may be due to the release of wastewater by neighbouring mining industries and by the burnt fuel released by the small boats used by a local community. Our results may provide support for further studies in areas of the Eastern Amazon affected by mining, deforestation and other anthropogenic activities.     

Phylogenetic analysis of the tenascin gene family: evidence of origin early in the chordate lineage

Background  

Tenascins are a family of glycoproteins found primarily in the extracellular matrix of embryos where they help to regulate cell proliferation, adhesion and migration. In order to learn more about their origins and relationships to each other, as well as to clarify the nomenclature used to describe them, the tenascin genes of the urochordate Ciona intestinalis, the pufferfish Tetraodon nigroviridis and Takifugu rubripes and the frog Xenopus tropicalis were identified and their gene organization and predicted protein products compared with the previously characterized tenascins of amniotes.     

Clues on Syntenic Relationship among Some Species of Oryzomyini and Akodontini Tribes (Rodentia: Sigmodontinae)

Sigmodontinae rodents represent one of the most diverse and complex components of the mammalian fauna of South America. Among them most species belongs to Oryzomyini and Akodontini tribes. The highly specific diversification observed in both tribes is characterized by diploid complements, which vary from 2n = 10 to 86. Given this diversity, a consistent hypothesis about the origin and evolution of chromosomes depends on the correct establishment of synteny analyzed in a suitable phylogenetic framework. The chromosome painting technique has been particularly useful for identifying chromosomal synteny. In order to extend our knowledge of the homeological relationships between Akodontini and Oryzomyini species, we analyzed the species Akodon montensis (2n = 24) and Thaptomys nigrita (2n = 52) both from the tribe Akodontini, with chromosome probes of Hylaeamys megacephalus (2n = 54) of the tribe Oryzomyini. The results indicate that at least 12 of the 26 autosomes of H. megacephalus show conserved synteny in A. montensis and 14 in T. nigrita. The karyotype of Akodon montensis, as well as some species of the Akodon cursor species group, results from many chromosomal fusions and therefore the syntenic associations observed probably represent synapomorphies. Our finding of a set of such associations revealed by H. megacephalus chromosome probes (6/21; 3/25; 11/16/17; and, 14/19) provides phylogenetic information for both tribes. An extension of these observations to other members of Akodontini and Oryzomyini tribes should improve our knowledge about chromosome evolution in both these groups.     

Chromosomal characterization of two species of genus <Emphasis Type="Italic">Steatogenys</Emphasis> (Gymnotiformes: Rhamphichthyoidea: Steatogenini) from the Amazon basin: sex chromosomes and correlations with Gymnotiformes phylogeny

Gymnotiformes are an important component of the Neotropical ichthyofauna and they are known for their ability to generate and detect electrical discharges. Phylogenetic relationships of Gymnotiformes are still not well understood. However, the monophyly of the superfamily Rhamphichthyoidea is well accepted, despite the position of tribe Steatogenini (Steatogenys, Hypopygus and Stegostenopos) within this superfamily is unclear. The genus Steatogenys includes three species that, together with Hypopygus and Stegostenopos, form tribe Steatogenini. Cytogenetic information is currently only available for Hypopygus lepturus. Here, we describe the karyotypes of Steatogenys elegans from four localities and S. duidae from two localities. S. elegans was found to have 2n = 50, ZZ/ZW (12m-sm/38st-a), while S. duidae had 2n = 50 (50m-sm). In S. elegans, constitutive heterochromatin (CH) was observed in the centromeric regions of all chromosomes, in the interstitial region of 1q, and in two blocks of Wq. In S. duidae, CH was observed in the centromeric and pericentromeric regions of all chromosomes, and in the interstitial regions of 2q, 3q, 5q, and 7q. Nucleolar organizer regions (NORs) were identified in the distal regions of one chromosome pair in each species. The CMA₃ fluorochrome (specific to G-C rich regions) coincided with the NORs in both species, and with the HC of S. elegans except on chromosome pair 5 and the W. The DAPI fluorochrome (specific to A-T rich regions) coincided with the CH of both species, and was very intense for chromosome pair 5 and the W of S. elegans. Our observations suggest that the ZZ/ZW system observed in S. elegans likely evolved through CH addition followed by a paracentric inversion. The chromosomal data described herein are consistent with the phylogenetic hypothesis that tribe Steatogenini should be positioned within family Ramphychthyidae.     

Chromosomal diversity in three species of electric fish (Apteronotidae,Gymnotiformes) from the Amazon Basin

Cytogenetic studies were carried out on samples of Parapteronotus hasemani, Sternarchogiton preto and Sternarchorhamphus muelleri (Apteronotidae, Gymnotiformes) from the Amazon basin. The first two species exhibited both a 2n = 52 karyotype, but differed in their karyotypic formulae, distribution of constitutive heterochromatin, and chromosomal location of the NOR. The third species, Sternarchorhamphus muelleri, was found to have a 2n = 32 karyotype. In all three species the DAPI and chromomycin A3 staining results were consistent with the C-banding results and nucleolar organizer region (NOR) localization. The 18S rDNA probe confirmed that there was only one pair of ribosomal DNA cistron bearers per species. The telomeric probe did not reveal interstitial telomeric sequences (ITS). The karyotypic differences among these species can be used for taxonomic identification. These data will be useful in future studies of these fishes and help understanding the phylogenetic relationships and chromosomal evolution of the Apteronotidae.