RESUMEN
This study confirms the presence of two species of the non-native mosquitofish Gambusia in Argentina. The risks that they represent to native biota, their potential dispersal in the region, and their effectiveness in mosquito larvae control are discussed.
Asunto(s)
Agentes de Control Biológico , Culicidae , Ciprinodontiformes/fisiología , Especies Introducidas , Animales , Argentina , Análisis Costo-Beneficio , Ciprinodontiformes/anatomía & histología , Ciprinodontiformes/clasificación , Conducta Alimentaria , Larva , Caracteres SexualesRESUMEN
Closely related species are key models to investigate mechanisms leading to reproductive isolation and early stages of diversification, also at the genomic level. The brittle star cryptic species complex Ophioderma longicauda encompasses the sympatric broadcast-spawning species C3 and the internal brooding species C5. Here, we used de novo transcriptome sequencing and assembly in two closely related species displaying contrasting reproductive modes to compare their genetic diversity and to investigate the role of natural selection in reproductive isolation. We reconstructed 20 146 and 22 123 genes for C3 and C5, respectively, and characterized a set of 12 229 orthologs. Genetic diversity was 1.5-2 times higher in C3 compared to C5, confirming that species with low parental investment display higher levels of genetic diversity. Forty-eight genes were the targets of positive diversifying selection during the evolution of the two species. Notably, two genes (NHE and TetraKCNG) are sperm-specific ion channels involved in sperm motility. Ancestral sequence reconstructions show that natural selection targeted the two genes in the brooding species. This may result from an adaptation to the novel environmental conditions surrounding sperm in the brooding species, either directly affecting sperm or via an increase in male/female conflict. This phenomenon could have promoted prezygotic reproductive isolation between C3 and C5. Finally, the sperm receptors to egg chemoattractants differed between C3 and C5 in the ligand-binding region. We propose that mechanisms of species-specific gamete recognition in brittle stars occur during sperm chemotaxis (sperm attraction towards the eggs), contrary to other marine invertebrates where prezygotic barriers to interspecific hybridization typically occur before sperm-egg fusion.
Asunto(s)
Equinodermos/genética , Canales Iónicos/genética , Aislamiento Reproductivo , Selección Genética , Espermatozoides/metabolismo , Animales , Femenino , Fertilización , Variación Genética , Masculino , SimpatríaRESUMEN
Tropical South America possesses the largest ichthyofauna of any continental region. To test whether palaeohydrological changes may have been the causes of such diversification, the 'hydrogeological' hypothesis, the phylogenetic relationships of 51 representatives of the catfish genus Hypostomus (Siluriformes: Loricariidae) were inferred using mitochondrial D-loop haplotype sequences. Specimens were collected in all main tropical South American rivers systems east to the Andes. The major interrelationships found with the D-loop data were confirmed with a subset of 21 species using complete internal transcribed spacer (ITS) region sequences. The phylogenetic analysis indicate that the genus Hypostomus can be divided into four monophyletic clades. The historical biogeographical analysis of each of these clades allows the identification of seven major cladogenetic events. Using calibrated D-loop and ITS molecular clocks, date estimations were attributed to each of these cladogenetic events allowing a linkage between four of them with documented hydrogeological changes. Comparisons with published distribution patterns of unrelated fish groups indicate that several of the reconstructed and dated hydrogeological-cladogenetic events may have acted at a large scale on the diversification of Neotropical freshwater fish fauna during late Tertiary.
Asunto(s)
Bagres/genética , Evolución Molecular , Geografía , Filogenia , Ríos , Animales , Secuencia de Bases , Bagres/fisiología , Cartilla de ADN , ADN Mitocondrial/genética , Fenómenos Geológicos , Geología , Funciones de Verosimilitud , Modelos Genéticos , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , América del SurRESUMEN
A novel mycobacterial species is described in this study. The strain was isolated from the cerebrospinal fluid of a severely immunocompromised AIDS patient. It was scotochromogenic and slow-growing. Characteristic features for its differentiation from other mycobacteria are its lipid pattern and the unique gene sequences within the hypervariable regions of the 16S rDNA. The strain shows susceptibility to current antimycobacterial drugs. The pathogenicity of the novel mycobacterium and its clinical significance are not certain, as the neurological symptoms of the patient could also be due to concomitant infection with Cryptococcus neoformans. The name Mycobacterium doricum sp. nov. is proposed for the novel mycobacterium; the type strain is strain FI-13295T (= DSM 44339T = CIP 106867T).
Asunto(s)
Infecciones Oportunistas Relacionadas con el SIDA/microbiología , Líquido Cefalorraquídeo/microbiología , Infecciones por Mycobacterium/microbiología , Mycobacterium/clasificación , Mycobacterium/genética , Secuencia de Bases , ADN Ribosómico/genética , Ácidos Grasos/análisis , Humanos , Masculino , Persona de Mediana Edad , Datos de Secuencia Molecular , Mycobacterium/química , Mycobacterium/aislamiento & purificación , Ácidos Micólicos/análisis , Filogenia , ARN Ribosómico 16S/genética , Análisis de Secuencia de ADNRESUMEN
The phylum Mesozoa comprises small, simply organized wormlike parasites of marine invertebrates and is composed of two classes, the Rhombozoa and the Orthonectida. The origin of Mesozoa is uncertain; they are classically considered either as degenerate turbellarians or as primitive multicellular animals related to ciliated protists. In order to precisely determine the phylogenetic position of this group we sequenced the complete 18S rRNA gene of one rhombozoid, Dicyema sp., and one orthonectid, Rhopalura ophiocomae. The sequence analysis shows that the Mesozoa branch early in the animal evolution, closely to nematodes and myxozoans. Our data indicate probably separate origins of rhombozoids and orthonectids, suggesting that their placement in the same phylum needs to be revised.