Genus

About: Genus is a research topic. Over the lifetime, 68921 publications have been published within this topic receiving 590966 citations. The topic is also known as: monospecies genus & genus (zoology).

Genetic determination of castes in the genus melipona

Abstract: IFFERENT mechanisms of caste determination are encountered in difD ferent genera of stingless bees (KERR 1946,1947, 1948). In Trigona and in Lestrimelitta a phenotypic caste determination, long known in Apis, is observed: a larva develops into a queen or into a worker depending upon the food it receives. In Melipona, on the other hand, caste determination is genotypic. Fertile females (queens) are heterozygous in some species for two, and in other species for three, pairs of genes, homozygosis for any one of which makes the individual develop into a worker. A review of the previously published evidence, as well as new data, relevant to the problem of caste determination in Melipona are reported in the present article. It should be noted that males of stingless bees, like those of other Hymenoptera, differ from females in having a haploid, instead of diploid, chromosome complement. Females of several species of Melipona are known to have 18, while drones have only 9 chromosomes. Spermatogenesis in Melipona follows the well-known Apis scheme. The first meiotic division is abortive, and results in expulsion of a cytoplasmic bud; the second division is equational, and a bud of cytoplasm containing a nucleus is produced which subsequently degenerates, while the remaining cell develops into a spermatid and a spermatozoon. Cytological abnormalities in spermatogenesis occur in Melipona, as they do in Apis, in testes of pupae exposed to temperature variations. The oogenesis in Melipona has not been studied owing to technical difficulties. The chromosome counts were made in cells of nerve tissue and in those of the ovarial wall.

DNA barcoding of Cuban freshwater fishes: evidence for cryptic species and taxonomic conflicts

Abstract: Despite ongoing efforts to protect species and ecosystems in Cuba, habitat degradation, overuse and introduction of alien species have posed serious challenges to native freshwater fish species. In spite of the accumulated knowledge on the systematics of this freshwater ichthyofauna, recent results suggested that we are far from having a complete picture of the Cuban freshwater fish diversity. It is estimated that 40% of freshwater Cuban fish are endemic; however, this number may be even higher. Partial sequences (652 bp) of the mitochondrial gene COI (cytochrome c oxidase subunit I) were used to barcode 126 individuals, representing 27 taxonomically recognized species in 17 genera and 10 families. Analysis was based on Kimura 2-parameter genetic distances, and for four genera a character-based analysis (population aggregation analysis) was also used. The mean conspecific, congeneric and confamiliar genetic distances were 0.6%, 9.1% and 20.2% respectively. Molecular species identification was in concordance with current taxonomical classification in 96.4% of cases, and based on the neighbour-joining trees, in all but one instance, members of a given genera clustered within the same clade. Within the genus Gambusia, genetic divergence analysis suggests that there may be at least four cryptic species. In contrast, low genetic divergence and a lack of diagnostic sites suggest that Rivulus insulaepinorum may be conspecific with Rivulus cylindraceus. Distance and character-based analysis were completely concordant, suggesting that they complement species identification. Overall, the results evidenced the usefulness of the DNA barcodes for cataloguing Cuban freshwater fish species and for identifying those groups that deserve further taxonomic attention.

Checklist of the Anostraca

Abstract: In this checklist, we number the named anostracan fauna of the world at 258 species and seven subspecies organized in 21 genera. The list contains all species described through 31 December 1993, and those new species names made available in previous pages of this volume. The most species rich genus is Streptocephalus with 58 described species level taxa. Chirocephalus with 43, Branchinecta 35, and Branchinella 33 occupy the next three places. With the exception of Branchipodopsis and Eubranchipus each having 16 species, all the other genera include less than 10 species each. The need for zoogeographic study of these animals is demonstrated by the fact that almost 25% of the named taxa are known only from their type localities.

Waipatia maerewhenua, new genus and new species (Waipatiidae, new family), an archaic Late Oligocene dolphin (Cetacea: Odontoceti: Platanistoidea) from New Zealand

Abstract: is probably a waipatiid close to W. maerewhenua. These taxa reveal an early radiation of the Platanistoidea by the late Institu- tion. Washington, D.C.

Phylogenetic basis for a taxonomic dissection of the genus Clostridium.

Abstract: The 16S rDNA-based phylogenetic analysis of the genus Clostridium has been completed by determination of the phylogenetic position of the type strains of 15 species and two non-validated species. These strains are members of phylogenetic clusters I, III, IV, V, IX, XIVa and XVIII as defined previously by Collins et al. [Int. J. Syst. Bacteriol. 44 (1994) 812-826]. Members of the genus Clostridium span a large evolutionary distance and the genus is not a phylogenetically coherent taxon but is intermixed with members of different genera, exhibiting a combination of Clostridium- and non-Clostridium-type properties. Anaerobacter polyendosporus, Syntrophococcus sucromutans and Acetivibrio multivorans also cluster within the radiation of Clostridium species. Although several taxa have been described for former Clostridium species with distinct phenotypic properties, the majority of Clostridium species, which are not members of the core cluster I, can at present not be reclassified as long as taxon-specific, phenotypic properties are not available.