High amounts of genetic differentiation between populations of the malaria vector Anopheles arabiensis from West Africa and eastern outer islands.
Polymorphism at nine microsatellite loci was examined to assess the level of genetic differentiation between four Anopheles arabiensis populations from Senegal, the high plateau of Madagascar, and Reunion and Mauritius islands. Eight of nine loci showed great polymorphism (2-16 alleles/locus) and significant genetic differentiation was revealed between all four populations by F- and R-statistics, with Fst estimates ranging from 0.080 to 0.215 and equivalent Rst values ranging between 0.022 and 0.300. These high amounts of genetic differentiation are discussed in relation to geographic distance including large bodies of water, and history of mosquito settlement, and insecticide use on the islands. The results suggest that historical events of drift rather than mutation are probably the forces generating genetic divergence between these populations, with homogenization of the gene pool by migration being drastically restricted across the ocean. (+info)
The rise and fall of the Aldabran giant tortoise population.
At the end of the 19th century, after prolonged and extensive harvesting, indigenous giant tortoises had been eliminated from all islands in the Indian Ocean, except Aldabra atoll, where only a few survived. With greatly reduced levels of exploitation during the 20th century, the population recovered to a revised estimated total of 129,000 in 1973-1974, when the first sample census was conducted. A repeat census in 1997 revealed a highly significant reduction in numbers over the past 24 years to an estimated total of 100,000. The great majority of tortoises are still found at relatively high density in south-eastern Grande Terre, where the number of animals has declined by more than one-third. In contrast, low-density subpopulations on Malabar and Picard have almost doubled in size, but they represent less than 5% of the total population. Corroborative evidence for the crash in the Grande Terre subpopulation comes from two independent observations: a significant increase in tortoise mortality; and a significant decline in tortoise counts on long-term population monitoring transects. These population changes are attributed to natural population regulatory mechanisms, exacerbated by low rainfall years in the period 1980-1997, including two consecutive years of below average rainfall in 1995-1996 and 1996-1997. (+info)
Ancient mitochondrial DNA and morphology elucidate an extinct island radiation of Indian Ocean giant tortoises (Cylindraspis).
Ancient mitochondrial DNA sequences were used for investigating the evolution of an entire clade of extinct vertebrates, the endemic tortoises (Cylindraspis) of the Mascarene Islands in the Indian Ocean. Mitochondrial DNA corroborates morphological evidence that there were five species of tortoise with the following relationships: Cylindraspis triserrata ((Cylindraspis vosmaeri and Cylindraspis peltastes) (Cylindraspis inepta and Cylindraspis indica)). Phylogeny indicates that the ancestor of the group first colonized Mauritius where speciation produced C. triserrata and the ancestor of the other species including a second sympatric Mauritian form, C. inepta. A propagule derived from this lineage colonized Rodrigues 590 km to the east, where a second within-island speciation took place producing the sympatric C. vosmaeri and C. peltastes. A recent colonization of Reunion 150 km to the southwest produced C. indica. In the virtual absence of predators, the defensive features of the shells of Mascarene tortoises were largely dismantled, apparently in two stages. 'Saddlebacked' shells with high fronts evolved independently on all three islands. This and other features, such as a derived jaw structure and small body size, may be associated with niche differentiation in sympatric species and may represent a striking example of parallel differentiation in a large terrestrial vertebrate. The history of Mascarene tortoises contrasts with that of the Galapagos, where only a single species is present and surviving populations are genetically much more similar. However, they too show some reduction in anti-predator mechanisms and multiple development of populations with saddlebacked shells. (+info)
Field application of Lepto lateral flow for rapid diagnosis of leptospirosis.
The Lepto lateral flow assay for leptospirosis was evaluated at a primary health centre in the Andaman Islands, where leptospirosis is endemic. One hundred and seventeen suspected patients were included in the study; acute serum samples were collected from all of them and convalescent samples from 104. The standard criteria for diagnosis of leptospirosis were: (i) isolation of leptospires from blood, (ii) seroconversion in microscopic agglutination test (MAT) with a minimum titre of 100, (iii) a fourfold rise in titre in MAT or (iv) a MAT titre of 400 or more if only a single sample was available. The results of the lateral flow test were compared with these criteria. Lepto lateral flow had sensitivity of 52.9 % (37/70) in the first week of illness and 86 % (49/57) during weeks 2-4. The corresponding specificities were respectively 93.6 % (44/47) and 89.4 % (42/47). The sensitivity was 34.3 % (12/35) on days 2-3 of the illness, 63.3 % (14/22) on days 4-5 and 84.6 % (11/13) at the end of the first week. The test had a positive predictive value of 92.5 % (37/40) during the first week and 90.7 % (49/54) subsequently. Corresponding negative predictive values were respectively 57.1 % (44/77) and 84 % (42/50). Agreement of the results with the standard criteria was low during the first week, but high during weeks 2-4, with a kappa value of 0.7491. The positivity rates of the tests showed a logarithmic relationship with the MAT titres of samples (r(2) = 0.9271). All indices of validity and utility of lateral flow were similar to those of IgM ELISA and Lepto dipstick. The test can be performed at the bedside of the patient, as whole blood can also be used for testing. (+info)
Antigenic and genetic relatedness of Leptospira strains isolated from the Andaman Islands in 1929 and 2001.
Leptospirosis is a major public health problem in Andaman Islands. Several strains of Leptospira have been isolated from the Andamans over the years. Leptospires isolated recently from human cases were compared with one of the earliest available isolates from these islands, dating back to 1929, to study their serological and genetic relatedness. Randomly amplified polymorphic DNA (RAPD) fingerprints of the isolates, generated with a primer used previously to differentiate between Leptospira species and serovars, revealed that some of the recent isolates were genetically identical to the 1929 isolate. The antigenic properties of these strains, as revealed by microscopic agglutination tests with group-specific rabbit antisera and mAbs, were also similar. These findings suggest that a Leptospira strain originally isolated in 1929 has possibly persisted in these islands for over 70 years and continues to cause acute leptospirosis in humans. (+info)
Leptospira interrogans serovar Valbuzzi: a cause of severe pulmonary haemorrhages in the Andaman Islands.
Outbreaks of leptospirosis that present with predominant pulmonary signs and symptoms have been occurring in the Andaman Islands since the late 1980s. Before this, pulmonary haemorrhage had not been observed as a common complication of leptospirosis in India. During an outbreak on North Andaman in 1997, four leptospire isolates were obtained from blood of a fatal case and three other patients who recovered. These isolates were characterized using serological and molecular techniques. Cross-agglutination absorption tests and microscopic agglutination tests using mAbs were used for serological characterization. Genetic typing was done using DNA sequencing of PCR products. Serologically, the isolates were closely related to strain Valbuzzi serovar Valbuzzi of serogroup Grippotyphosa. The sequences of PCR products from these isolates were compared with those of 45 strains belonging to seven species. The isolates showed 97.5-100 % sequence similarity to reference strains belonging to Leptospira interrogans, indicating that the isolates belong to L. interrogans. Serogroups Icterohaemorrhagiae and Australis have been incriminated as the cause of pulmonary haemorrhage in China, Korea and Australia. The four isolates characterized in the present study were obtained from patients with similar symptoms. However, they belonged to serovar Valbuzzi of serogroup Grippotyphosa, indicating that serogroups other than Icterohaemorrhagiae and Australis can also cause pulmonary haemorrhage. (+info)
"SALTWATER ANOPHELES GAMBIAE" ON MAURITIUS.
In this paper the author reports the results of three months' study of the saltwater-breeding member of the Anopheles gambiae complex of sibling species on Mauritius.There is evidence for the views that this form's distribution on the island is limited by the availability of suitable breeding areas, that it does not usually disperse far from the breeding grounds or coast, and that it is probably not an important vector except, perhaps, in the near vicinity of its breeding places.Some new evidence is presented in support of the view that this form (and forms A and B) are distinct species. This turns on the observed close coexistence of these three forms on Mauritius, supported by a theoretical consideration of what would be expected to happen in such circumstances if a system of random mating prevailed.Evidence is given that the Mauritian saltwater-breeding form of the A. gambiae complex is conspecific with the form occurring on the east coast of Africa.The practical importance of reaching general agreement on the evolutionary status of the members of the A. gambiae complex is emphasized. (+info)
Geographic origin and taxonomic status of the invasive Privet, Ligustrum robustum (Oleaceae), in the Mascarene Islands, determined by chloroplast DNA and RAPDs.
Information concerning the area of origin, genetic diversity and possible acquisition of germplasm through hybridisation is fundamental to understanding the evolution, ecology and possible control measures for an introduced invasive plant species. Among the most damaging of alien plants that are invading and degrading native vegetation in the Mascarene Islands of the Indian Ocean is the Tree Privet, Ligustrum robustum. Exact information about the geographic source of introduced material of this species is lacking, in part because Ligustrum is a taxonomically difficult genus. Native material of L. robustum ssp. walkeri from Sri Lanka, L. robustum ssp. robustum from northeastern India, and the closely related L. perrottetii from southern India was compared with introduced material from La Reunion and Mauritius using chloroplast DNA RFLP markers and random amplified polymorphic DNA (RAPDs). Sri Lankan and introduced material was monomorphic for the same cpDNA haplotype that was absent from south and northeast Indian Ligustrum. Sri Lankan and introduced material was also clearly distinguished from Indian Ligustrum by RAPDs. It was concluded that material introduced and established in the Mascarene Islands is derived from the Sri Lankan subspecies L. robustum ssp. walkeri. No geographic structuring of genetic variation within Sri Lanka was detected for this taxon, so the location(s) within Sri Lanka from which introduced material is derived could not be pinpointed. RAPDs indicate that L. robustum ssp. walkeri in Sri Lanka is more similar to south Indian L. perrottetii than to northeast Indian L. robustum ssp. robustum. Moreover, RAPDs showed that introduced material in La Reunion has undergone little or no loss of genetic diversity since introduction. However, there was no evidence that it is introgressed with germplasm from two other alien Ligustrum species present on La Reunion. (+info)