1,721,024 research outputs found
Chromosome evolution in treehole breeding Anopheles (Diptera, Culicidae)
No full textThe cytogenetic profile of two Nearctic and one Paleartic treehole mosquitoes belonging to the Coelodiazesis group, Anopheles barberi, Anopheles judithae, and Anopheles plumbeus, was outlined by means of standard banding techniques and in situ hybridization. Results indicate that, during the evolution of this species group, several rearrangements have occurred including inversions, translocations, and loss of heterochromatic material and rRNA genes copy number. The karyotype of A. barberi is markedly different from the other two species, in spite of morphological similarities with the other North American species, A. judithae. This latter species has retained part of a more ancestral karyotype still shared with the Paleartic A. plumbeus. Chromosomal repatterning in A. barberi has probably facilitated isolation and divergence of the two Nearctic species, impairing introgressive hybridization with A. judithae
RIBOSOMAL RNA GENES IN MOSQUITOES: LOCALIZATION BY FLUORESCENCE IN SITU HYBRIDIZATION (FISH)
No full text
Genetic structure and population dynamics of Culicoides obsoletus and Culicoides scoticus (Diptera: Ceratopogonidae): implications for the transmission and maintenance of bluetongue
No full textAbstract. Culicoides species belonging to the Obsoletus complex (Diptera: Ceratopogonidae)
have been indicated as primary bluetongue (BT) vectors in many European
countries and their possible involvement in the maintenance and overwintering of BT
viruses has been suggested, even in regions where Culicoides imicola Keiffer is the
main vector. The Obsoletus complex includes two predominant taxa, Culicoides obsoletus
(Meigen) and Culicoides scoticus Downes & Kettle. However, the role played
by each species in the epidemiology of BT is still unknown. Taxonomic identification
is mainly based on the morphology of male genitalia and the lack of other reliable
diagnostic features makes the screening of trap-collected vector populations, mainly
females, particularly difficult. Although molecular markers have facilitated species
identification, little information is yet available on the biology, abundance and population
dynamics of the two taxa. The aim of this work was to investigate the genetic
profile and temporal distribution of C. obsoletus and C. scoticus by using isozyme
electrophoresis applied to adult midges, collected weekly at two selected farms in
southern Sardinia. A total of nine enzyme loci were analysed and five of them provided
diagnostic allozyme markers (Hk, Mdh, Pgi, Idh-1 and Idh-2 ). Nei’s genetic distance
between the two taxa was in the range of other well-separated taxa (D = 1.792),
supporting their status as true species. Culicoides scoticus represented almost 61%
of the 562 specimens analysed; its genetic structure was characterized by a very
low level of intra-population variation (mean heterozygosity He = 0.019) and higher
genetic divergence between populations (FST = 0.0016) than in C. obsoletus. The latter
species had significantly more heterozygotes (He = 0.123), a higher percentage
of polymorphic loci, and no inter-population differentiation (FST
∼=
0). We suggest
that different biological and ecological constraints, such as breeding habitat requirements,
may contribute to shaping the genetic profiles of C. scoticus and C. obsoletus.
However, enough gene flow was maintained between populations of each species as
no spatial and temporal structuring was sustained by Fisher’s exact probability test
(P > 0.5). The seasonal distributions of C. scoticus and C. obsoletus only partially
overlapped: both species were mainly found early in the year, when the main vector,
C. imicola, was present in low numbers, and peaked in abundance in April and May.Culicoides scoticus was predominant until May, decreased rapidly in the following
months and increased again in winter, whereas C. obsoletus decreased more slowly
and was still present in early summer. Consequently, C. scoticus may be a good candidate
for playing a role in the transmission and maintenance of BT virus in Sardinia,as well as in other Mediterranean countries, during the months of late winter and early
spring when the seroconversion of sentinel animals is still occurring in the absence of the main vector
Reappearance of Aedes albopictus in Sardinia
No full textAedes (Stegomyia) albopictus is a vector of major human diseases. From 1979 established populations were found in the Mediterranean Region. The first record of Ae. albopictus in Italy goes back to 1990 and at present it is permanently established in several provinces of central and northern Italy. Ae. albopictus was detected for the first time in Sardinia in 1995, and a new record was reported in 1997. After these two isolated episodes, the "tiger-mosquito" was considered apparently eradicated. At the end of September 2006, two natural breeding populations including adults of Ae. albopictus were recorded in two different localities of South-Sardinia: in the botanical garden of downtown Cagliari and in a private garden of a small village, Teulada, on the south-western coast of Sardinia. The origin of this new introduction of Ae. albopictus in Sardinia is still unclear. In both cases the species has been found in artificial containers in densely populated areas
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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