Genetic differentiation in natural populations of Drosophila ananassae

Inversion polymorphism has been studied in three natural populations of Drosophila ananassae. The three cosmopolitan inversions have been detected in all the three populations analysed. Some quantitative variations in the inversion frequencies seem to exist and the level of inversion heterozygosity varies between the different populations.     

Genetic distance in inversion polymorphism among natural populations of Drosophila ananassae

Based on the differences in the gene arrangement frequencies average genetic distance has been estimated among natural populations of Drosophila ananassae. Genetic distance obtained by pairwise comparison ranges from 0.002 to 0.371. The most differentiated populations are those from the Andaman and Nicobar Islands. Although the populations from localities separated by a small geographic distance show less genetic distance, the relation between genetic distance and geographic distance does not seem to be positive.     

Post Bleaching Assessment of Corals in Andaman and Nicobar Islands

Reefs of Andaman and Nicobar Islands harbour 418 species of scleractinian corals spread over an area of 2,000 km². In April to May, 2010, due to the delayed onset of the southwest monsoon the sea surface temperature of the coastal and oceanic region increased to 31.7 °C in respect to the earlier record of maximum 29.0 °C during the said period. This resulted in mass bleaching of hermatypic corals during May, 2010. Rapid under water surveys have been conducted in reefs of Andaman and Nicobar Islands to assess the health of corals between May 2010 and August 2011. It is estimated that 76.62 ± (SD) 10.83 % of coral species are bleached up to a water depth of 10–15 m. Species from the genus Acropora appeared more susceptible to bleaching than those belong to the genus Porites. During the month of June 2010 the sea surface temperature was reduced to 29 °C perhaps due to the rainfall which stimulated rebuilding of zooxanthellae population in bleached corals. Recovery of 85.54 ± (SD) 6.33 % of bleached corals was seen during the study period of 11 months after the bleaching event. Porites spp. showed a high recovery rate, while Acropora spp. had the highest mortality rate. Coral mortality can have profound ecological and socio-economical implications and highlights the need for sustained monitoring for coral reef conservation in India. Hence, steps must be taken to improve management tools to protect these resources of global significance.     

Joint effects of natural selection and recombination on gene flow between Drosophila ananassae populations

We estimated DNA sequence variation in a 5.7-kb fragment of the furrowed (fw) gene region within and between four populations of Drosophila ananassae; fw is located in a chromosomal region of very low recombination. We analyzed gene flow between these four populations along a latitudinal transect on the Indian subcontinent: two populations from southern, subtropical areas (Hyderabad, India, and Sri Lanka) and two from more temperate zones in the north (Nepal and Burma). Furthermore, we compared the pattern of differentiation at fw with published data from Om(1D), a gene located in a region of normal recombination. While differentiation at Om(1D) shows an isolation-by-distance effect, at fw the pattern of differentiation is quite different such that the frequencies of single nucleotide polymorphisms are homogenized over extended geographic regions (i.e., among the two populations of the northern species range from Burma and Nepal as well as among the two southern populations from India and Sri Lanka), but strongly differentiated between the northern and southern populations. To examine these differences in the patterns of variation and differentiation between the Om(1D) and fw gene regions, we determine the critical values of our previously proposed test of the background selection hypothesis (henceforth called F(ST) test). Using these results, we show that the pattern of differentiation at fw may be inconsistent with the background selection model. The data depart from this model in a direction that is compatible with the occurrence of recent selective sweeps in the northern as well as southern populations.     

Impact of tsunami on the forest and biodiversity richness in Nicobar Islands (Andaman and Nicobar Islands), India

Occurrences of extreme events are likely to cause major decline in global biodiversity. In one such event, on December 26, 2004 tsunami caused extensive damage and irreparable losses to the ecology and biodiversity of low-lying areas of the countries located around the Indian Ocean region. Archipelago of Andaman and Nicobar Islands, one of the richest centre of endemism and biodiversity in the Indo-Malayan region, suffered great loss of forests and coastal biodiversity owing to its closeness to the epicenter of tsunami, i.e. just off the coast of Indonesia. There is little insight into the resilience and rate of recovery pattern of tropical coastal habitats consequent to catastrophic impacts of tsunami. It’s important to study the impacts of tsunami on the forest and biodiversity in order to suggest mitigation, restoration measures and long-term conservation planning. Here we have assessed the immediate after-effects of December 26, 2004 tsunami on the forests and areas prioritized for biodiversity conservation analyzing pre and post tsunami satellite imageries. The effect of topographic patterns of Island’s coastal areas and their distance from the epicenter of tsunami with respect to changes in the forests and different levels of biologically rich areas modeled for prioritization for different groups of Islands in Nicobar has been studied. Great Nicobar accounted for higher proportion of total forest area damaged and submerged in Nicobar, followed by Central Nicobar and Car Nicobar. Mangroves, littoral forest, beach forest and low land swamps and Syzygium swamps were most affected. Study brings out spatially explicit scenario of damaged, submerged and lost forest areas and corresponding area statistics, vital for understanding and mitigating medium and long term effects of tsunami an extreme event.     

Evolution of mating isolation between populations of Drosophila ananassae

Prezygotic mating isolation has been a major interest of evolutionary biologists during the past several decades because it is likely to represent one of the first stages in the transition from populations to species. Mate discrimination is one of the most commonly measured forms of prezygotic isolation and appears to be relatively common among closely related species. In some cases, it has been used as a measure to distinguish populations from subspecies, races, and sister species, yet the influences of various evolutionary mechanisms that may generate mate discrimination are largely unknown. In this study, we measured the level and pattern of mate discrimination among 18 populations of a cosmopolitan drosophilid species, Drosophila ananassae , from throughout its geographical range and its sister species, Drosophila pallidosa, which has a restricted geographical distribution in the South Pacific Islands. In addition, we measured genetic differentiation between all 18 populations using mitochondrial DNA polymorphism data. Mate discrimination varies considerably throughout the species range, being higher among populations outside the ancestral Indonesian range, and highest in the South Pacific. Our results suggest that colonization and genetic differentiation may have an influence on the evolutionary origin of mate discrimination. Our phylogeographical approach clarifies the ancestral relationships of several populations from the South Pacific that show particularly strong mate discrimination and suggests that they may be in the early stages of speciation. Furthermore, both the genetic and behavioral results cast doubt on the status of D. pallidosa as a good species.     

Cycas dharmrajii sp. nov. (Cyadaceae) from Andaman and Nicobar Islands,India

Cycas dharmrajii L.J.Singh (Cycadaceae), a new species from the Andaman Islands, India is described and illustrated, and its conservation status is assessed. An abnormal branching habit of the giant trunk, its swollen base, often branched, polymorphic aerial roots, medium‐sized leaves, megasporophylls with well‐defined 10–28 paired lateral hook‐like structures and 1–3 pairs of ovules, 2‐schizo‐lysigenous mucilage canals in leaflet, and characteristic pitting on the periclinal walls of the epidermal cells of the leaflets distinguishes it from all previously known species. A key to the species of Cycas from the Andaman and Nicobar Islands is also provided.     

Musa paramjitiana sp. nov. (Musaceae) from Andaman and Nicobar Islands,India

A new species of wild banana, Musa paramjitiana L. J. Singh, from the Andaman Islands, India is described and illustrated, and its conservation status is assessed. A key to the species of Musa L. from Andaman and Nicobar Islands is also provided.     

Centotheca ganeshaiahiana sp. nov. (Poaceae) from Andaman and Nicobar Islands,India

Centotheca ganeshaiahiana M. V. Ramana, Alok Chorghe, Prasanna & Sanjappa, a new species from Saddle Peak National Park, north Andaman, Andaman and Nicobar Islands, India is described and illustrated. It is closely allied to C. uniflora Swallen, a Vietnamese species, but differs mainly in shorter culms, leaf blades and inflorescences, longer pedicels, spikelets with 2 fertile florets and lemmas with bulbous based hairs.     

Zingiber pseudosquarrosum sp. nov. (Zingiberaceae) from Andaman and Nicobar Islands,India

Zingiber pseudosquarrosum L. J. Singh & P. Singh sp. nov. (Zingiberaceae) from Andaman and Nicobar Islands, India is described and illustrated and its conservation status is evaluated. This new species seems related to Z. squarrosum Roxb. but can be distinguished by the presence of a small pseudostem, long ligule and petiole, broadly lanceolate leaves with cuneate base, caudate apex and paxillate venation, urceolate or prolate inflorescences, very long underground peduncle, long calyx, very long corolla tube, labellum deep purple red (claret) at centre, orange red (vermillion) at lateral sides with ivory (off white) spots, tip truncate and slightly notched, margin folded back, stamen with short filament, yellow orange anther, light brown ovary, blood red (cinnabar) seeds covered by a white aromatic aril. A key to the species of Zingiber Mill. from the Andaman and Nicobar Islands is also provided.     

The role of natural selection in genetic differentiation of worldwide populations of Drosophila ananassae

The main evolutionary forces leading to genetic differentiation between populations are generally considered to be natural selection, random genetic drift, and limited migration. However, little empirical evidence exists to help explain the extent, mechanism, and relative role of these forces. In this study, we make use of the differential migration behavior of genes located in regions of low and high recombination to infer the role and demographic distribution of natural selection in Drosophila ananassae. Sequence data were obtained from 13 populations, representing almost the entire range of cosmopolitan D. ananassae. The pattern of variation at a 5.1-kb fragment of the furrowed gene, located in a region of very low recombination, appears strikingly different from that of 10 noncoding DNA fragments (introns) in regions of normal to high recombination. Most interestingly, two main haplotypes are present at furrowed, one being fixed in northern populations and the other being fixed or in high frequency in more southern populations. A cline in the frequency of one of these haplotypes occurs in parallel latitudinal transects. Taken together, significant clinal variation and a test against alternative models of natural selection provide evidence of two independent selective sweeps restricted to specific regions of the species range.     

Tsunami and tropical island ecosystems: a meta-analysis of studies in Andaman and Nicobar Islands

Tropical islands are special and sensitive ecosystems which are subjected to various disturbances imposed by human activities and natural disasters. A detailed study about the changing landscape scenarios of these fragile island systems induced by various driving factors could be used for setting up measurements in support of conservation and sustainable development projects. The current research is a meta-analysis of the studies carried out in Andaman and Nicobar islands which analyzed the impact of tsunami of 2004 using geospatial tools. Based on the analysis, it was observed that the Nicobar islands were more affected compared to the Andaman islands. The majority of the researchers used pre- and post-tsunami satellite imagery and adopted visual interpretation method to delineate the changed classes. The study infers uplift of land in Andaman (exposing) and subsidence in Nicobar islands (inundation) with severe damage to the coastal elements like mangroves, coral reefs, plantations and in few cases interior forest. The analysis showed there were no records of the damage for some small islands. Finally, it is concluded that utility of microwave satellite data for change analysis will prove better in regions like Andaman and Nicobar where it is difficult to get cloud free optical data because of the high monsoon periods in these islands. It is also suggested that future work utilizing suitable temporal satellite imagery should focus on the extent of recovery of vegetation and other coastal elements which suffer the impact of disaster.     

Potential gene flow in natural populations of the Drosophila ananassae species cluster inferred from a nuclear mitochondrial pseudogene

A pseudogene with 94% similarity to mitochondrial cytochrome c oxidase subunit I (COI) was identified and localized to chromosome 4 of Drosophila ananassae. Because this chromosome is believed to have reduced recombination, its history can be traced using the pseudo-COI sequence. Pseudo-COI sequences were obtained from 27 iso-female lines of six taxa belonging to the D. ananassae species cluster in which reproductive isolation is incomplete. The phylogenetic network constructed from seven recognized haplotypes (#0-#6) indicated that different taxa inhabiting the same geographic area share the haplotypes: #1 from Papua New Guinean populations of D. ananassae and pallidosa-like-Wau; #2 from Papua New Guinean populations of D. ananassae, pallidosa-like, and papuensis-like; and #4 from South Pacific populations of D. ananassae and D. pallidosa. Taxon-K has a unique haplotype (#6), and 18 mutation steps separate it from the closest haplotype, #2. We discuss the possibility of chromosome 4 introgression beyond taxon boundaries.     

The genetic structure of Drosophila ananassae populations from Asia, Australia and Samoa

Information about genetic structure and historical demography of natural populations is central to understanding how natural selection changes genomes. Drosophila ananassae is a widespread species occurring in geographically isolated or partially isolated populations and provides a unique opportunity to investigate population structure and molecular variation. We assayed microsatellite repeat-length variation among 13 populations of D. ananassae to assess the level of structure among the populations and to make inferences about their ancestry and historic biogeography. High levels of genetic structure are apparent among all populations, particularly in Australasia and the South Pacific, and patterns are consistent with the hypothesis that the ancestral populations are from Southeast Asia. Analysis of population structure and use of F-statistics and Bayesian analysis suggest that the range expansion of the species into the Pacific is complex, with multiple colonization events evident in some populations represented by lineages that show no evidence of recent admixture. The demographic patterns show isolation by distance among populations and population expansion within all populations. A morphologically distinct sister species, D. pallidosa, collected in Malololelei, Samoa, appears to be more closely related to some of the D. ananassae populations than many of the D. ananassae populations are to one another. The patterns of genotypic diversity suggest that many of the individuals that we sampled may be morphologically indistinguishable nascent species.     

Ethnobotanical studies of the tribes of Andaman and Nicobar Islands,India. I. Onge

This paper deals with the ethnobotany of the Onge tribe. Brief accounts of the geography of the island, ethnology, and history of ethnobotanical studies in addition to the methodology of the present work are given. Plants used in everyday life, such as for bows and arrows, dugouts and canoes, fibers, food, medicines, and shelter, are described and discussed. The 40 species dealt with in the paper have 52 uses. The present study indicates that the Onge tribe shows certain similarities with other southeastern Asian Negrito races.