Cunha Islands Research Articles

Observational effect for the lunar gravity on meteor streams

Meteoroids always posed a great hazard to spacecraft security. A meteoroids stream assembled by a large massive body will further enhance the hazard severalfold. For example, the radiant of Northern Taurids (NTA) will be occulted by the Moon on Nov. 12, 2011. Since the gravitational lensing effect of massive bodies can gather together the orbits of meteoroids, the observable flux of meteoroids will increase. In this paper a set of numerical methods was built to discuss the observational effect of this kind of phenomena. The ZHR of NTA is generally small. But it can be local strong on the Earth by the lunar gravitational assembling. The calculated result suggests that a ten times stronger than normal NTA will appear in the sea area of Tristan da Cunha islands during 00h45m UT to 02h00m UT on Nov. 12, 2011.

Freshwater invertebrate fauna of the Tristan da Cunha islands (South Atlantic Ocean), with new records for Inaccessible and Nightingale Islands

As part of a multidisciplinary floristic-faunistic study, a three week survey of the invertebrate fauna of Inaccessible Island (South Atlantic Ocean) was carried out in October/November 1989. In addition, one day of collecting was done on Nightingale Island. This paper deals only with the fauna associated with freshwater ecosystems from these islands, some of which are usually associated with marine or brackish conditions. On Inaccessible Island, five distinct types of freshwater body were identified—pH neutral streams, acidic streams (pH 5), an open pool of standing water (pH 6), areas of acidic bog, and seepages down rock faces. The survey, the most comprehensive for Inaccessible Island to date, has resulted in the discovery of 19 aquatic invertebrate species previously unrecorded on Inaccessible Island, two new to Nightingale Island, and 14 of which are new to the Tristan da Cunha archipelago. Many of the species are known from other parts of the world, indicating a low degree of endemicity within the freshwater invertebrate community. Recolonisation from the source populations, preventing an isolated gene pool, may account for the low endemicity. Several of the species have a degree of salinity tolerance, enabling them to withstand transportation across tracts of ocean, and others have marine origins.

Ten microsatellite loci for evolutionary research on Nesospiza buntings

AbstractWe tested 19 loci originally developed for Vidua and Geospiza, of which six Vidua loci were polymorphic and furthermore, developed four microsatellite loci for Nesospiza buntings. Allelic variation ranged from two to 13 alleles, with heterozygosity from 0 to 0.82. Ascertainment bias was evident as increased allelic diversity of loci developed for Nesospiza, versus those developed for Vidua. Two loci showed linkage, and several, deviation from Hardy–Weinberg equilibrium. We suggest such deviations are through introduction of new alleles by introgression, or of the Wahlund effect. These loci will contribute to the understanding of speciation in Nesospiza buntings of the Tristan da Cunha islands.

Karyotypes of basal lineages in notothenioid fishes: the genus Bovichtus

Using comparative cytogenetic techniques, we characterized the chromosomes of fishes from the family Bovichtidae, the basal lineage of the largely Antarctic suborder Notothenioidei. We focused on three Sub-Antarctic species of the genus Bovichtus that differ greatly in their circumpolar distributions: B. diacanthus (Tristan da Cunha Island Group), B. variegatus (New Zealand) and B. angustifrons (Tasmania). Chromosomes were analyzed both by conventional karyotyping and by cytogenetic mapping of ribosomal genes using fluorescence in situ hybridization. The three species displayed a strongly conserved karyotype consisting entirely of telocentric chromosomes (diploid number = 48; Fundamental Number = 48), in agreement with our previously published hypothesis that the bovichtid karyotype is the basal state for notothenioid fishes. The chromosomal distribution of ribosomal genes differed from those of most notothenioid species studied to date, with the 45S and 5S genes separated on two different chromosome pairs. Separation of two classes of ribosomal genes is the most widespread condition in teleosts, including the bovichtids. Most notothenioid lineages on the other hand exhibit a derived consolidation of these genes.

Speciation: Marathon mollusc migrations

Speciation: Marathon mollusc migrations

Molecular trails from hitch-hiking snails

Darwin was fascinated by the transportation of land snails across great swathes of open ocean by birds--he even immersed snails in sea water to see how long they would survive. Here we follow a molecular phylogenetic trail that reveals the incredible transequatorial dispersal of the land snail Balea from Europe to the Azores and the Tristan da Cunha islands, and back again. This long-distance dispersal is unexpected for what are proverbially considered the most pedestrian of creatures.

The triple T allergy hypothesis.

The early induction of allergy is a complex process involving protective and destructive gene variants, environmental and nutritional co-factors as well as allergen exposure. Although critical doses, interactions and susceptible time frames have not been identified so far, late gestation and early childhood seem to be important time periods for allergic sensitization. At least three risk factors can be distinguished based on altered early Th1 lymphocyte development. First, the number of children with an inborn maturation defect may have increased since the beginning of the last century, when this condition would otherwise have had a lethal outcome without antibiotics and other modern health care (survival hypothesis). Second, another group of children in industrialized countries may have a deficit of environmental Th1 triggers during early life (hygiene hypothesis). A third factor may also be found predominantly in western societies. The prophylaxis of rickets with vitamin D has the apparent side effect of suppressing Th1 development (vitamin hypothesis). Experimental as well as epidemiological studies now provide evidence for the vitamin hypothesis, which is examined in this paper by a time-course analysis of vitamin D application in Germany. Also paper studies in Swedish anthroposophic school children, the Tristan da Cunha islanders, and Swiss, Austrian and Bavarian farmers may be linked to either excessive or absent early vitamin D exposure.

The free‐living pterygote insects of Gough Island, South Atlantic Ocean

Gough Island, the furthest outlier of the Tristan da Cunha Island group, is a remote land mass in the South Atlantic Ocean. Pterygote insect species representing nine orders have been recorded on the island, the Psocoptera (booklice), Hemiptera (leafhoppers, aphids etc.), Thysanoptera (thrips), Coleoptera (beetles), Diptera (flies), Lepidoptera (moths), Hymenoptera (wasps etc.), and parasites of vertebrates in the Phthiraptera (lice) and Siphonaptera (fleas). Excluding parasites of vertebrates, 99 species have been recorded, 54 of which are recorded here for the first time. In total, 24 species occurring on Gough Island are thought to be endemic to the Tristan da Cunha Island group, four species are naturally occurring but found elsewhere, and 71 species are accidental introductions. The indigenous species have predominantly Neotropical associations, whilst the introduced ones are almost all globally widespread, the majority being of Holarctic origin. Approximately 28% of the introduced species are known to exhibit parthenogenesis compared with 7% of the indigenous species. In this paper we present keys and descriptions of all 99 species of pterygote insects, with notes on ecology, biology and conservation issues.

The tropical Atlantic meridional SST gradient index and its relationships with the SOI, NAO and Southern Ocean

The tropical Atlantic meridional SST gradient (TAMG) is a mode of climatic variability known to be largely associated with abnormal rainfall regimes in South America and West Africa. A TAMG index is defined by the difference between area indices of sea surface temperature anomaly north (TN index) and south (TS index) of the meteorological equator (∼5°N). We investigate, for the 1964–1998 period, the decadal variability of the TAMG index and the relationship of its TN and TS components with the Southern Oscillation Index (SOI), the North Atlantic Oscillation (NAO), sea level pressure (SLP) signals in South Atlantic islands, the global NCEP-NCAR SLP field, and sea-ice extent data in the Southern Ocean. We explore the relationship between the SOI and the TN and TS signals, after estimating their fluctuating lags with the cross-wavelet transform technique. The SOI always leads TN with an average time lead of 5.4 months. On the contrary, TS leads the SOI by ∼4 months after 1984. When exploring the origin of such a precursory event of the SOI, observed in TS, it is found that the highest correlation between TS, the global SLP field, and the sea-ice extent around Antarctica is located in the Ross sea, where the ice signal leads the SOI. High correlation between TS and the SLP field is also observed in the western tropical Pacific. The continuous wavelet transform is then used to extract the low-frequency components of the TN and TS signals. These components are strong well-defined oscillations with mean periods at 9.6 years for TN and 14 years for TS. Given this asynchronous non-dipole nature of the TN and TS decadal components, we can anticipate that the TAMG undergoes decadal oscillations that are variable on a longer multi-decadal timescale. These components are also very similar to the low-frequency components of the NAO index, for TN (with the NAO leading TN by 14 months) and SLP anomaly signals at St. Helena and Tristan da Cunha islands, for TS. These results indicate that the TN or TS decadal component is each related to the larger climatic milieu in the same hemisphere, but that the climatic milieu of the South Atlantic is distinct from that of the North Atlantic.

Cryptic species of rockfishes (Sebastes: Scorpaenidae) in the southern hemisphere inferred from mitochondrial lineages.

We used mitochondrial DNA sequence variation of Sebastes from the southeastern Pacific and three localities in the South Atlantic to address long-standing systematic and evolutionary issues regarding the number of species in the Southern Hemisphere. Sequences of the hypervariable mitochondrial control region were obtained from 10 specimens of S. capensis from South Africa (n = 5) and from Tristan da Cunha Island (n = 5) and 27 of S. oculatus from Valparaiso, Chile (n = 10), and the Falkland Islands (n = 17). Results of the study include (1) significant levels of genetic differentiation among the sampled populations (phi ST = 0.225, P < .000001), thus indicating limited gene flow; (2) corroboration of the existence of two different lineages of austral Sebastes corresponding to S. capensis and S. oculatus; (3) finding that S. capensis is not restricted to Tristan da Cunha and South Africa, but is widespread across the South Atlantic; (4) the position of S. capensis as the ancestral lineage of the austral Sebastes; (5) the existence of a third evolutionary lineage with high levels of genetic divergence, particularly abundant in the south-western Atlantic, which may be recognized as a third austral species of Sebastes.

The founding mitochondrial DNA lineages of Tristan da Cunha Islanders.

Genealogical histories show that the inhabitants of Tristan da Cunha are derived from a known number of founders. Using the transmission of mitochondrial DNA (mtDNA) from mother to offspring pairs, we traced the mtDNA types found in 161 extant individuals to five female founders. Although the historical data claimed that two pairs of sisters were among the founding females, mtDNA data showed support for only one pair of sisters. We also studied the fidelity of mtDNA transmission in conjunction with the genealogical data. We did not detect any mutations from 698 base pairs of sequence data from 75 individuals, which together accounted for 108 independent transmissions of mtDNA from mother to offspring. Based on this observation, we estimate that the mtDNA mutation rate is no more than one new mutation every 36 transmissions. These results indicate a high fidelity of maternal mtDNA transmission and support the utility of mtDNA in evolutionary and forensic studies.

Bottom pressure correlations in the South Atlantic

Bottom pressure in the Fine Resolution Antarctic Model (FRAM) shows regions where fluctuations are dominated by small‐scale internal variability of the currents, and are not directly related to the wind. There are often very sharp boundaries between these regions and regions of large scale coherence. Bearing this in mind, the measured coherence of BPR measurements near Tristan da Cunha island in the South Atlantic is taken as evidence that mesoscale variability associated with the Antarctic Circumpolar Current (ACC) reaches further north in the model than in reality. There are many possible reasons for this, but the significant result is that the BPR measurements can provide useful information about the dynamical regime of the deep ocean, which can not be discovered by surface measurements.

BIOLOGY OF THE TRISTAN THRUSH NESOCICHLA EREMITA

Summary M.W. Fraser, P.G. Ryan, W.R.J. Dean, D.J. Briggs, & C.L. Moloney 1994. The biology of the Tristan Thrush Nesocichla eremita. Ostrich 65:14-25. The Tristan Thrush Nesocichla eremita is a little known species restricted to the Tristan da Cunha Islands, South Atlantic Ocean. We describe several aspects of the species' biology, based primarily on observations made at Inaccessible Island. Tristan Thrushes are monomorphic, assuming adult plumage after a partial juvenile moult. There is little sex-related size dimorphism within island populations, which may reflect limited genetic variation. Tristan Thrushes are generalist foragers, using a variety of techniques to consume both animal and plant matter. Breeding occurs during the austral spring, with a single brood raised from clutches of two eggs at Inaccessible and Tristan. Three-egg clutches have only been recorded at Nightingale Island, where they comprise about half of all clutches. Adults perform a very soft, melodic warbling song, which is most frequently uttered immediately prior to the spring breeding season. Typical calls are simple, high-pitched whistles. Adults moult after the breeding season, and primary moult is completed within 80 das. Moult commences at least one week earlier at tie coast than on the plateau (elevation 250–500 m) at Inaccessible Island. We provide a revised population estimate for Inaccessible Island, and make recommendations for the species' conservation.

The impact of the commercial lobster fishery on seabirds at the tristan da Cunha Islands, South Atlantic Ocean

Observations were made on the effect of the commercial rock-lobster Jasus tristani fishery on seabird populations at the Tristan da Cunha Islands, central South Atlantic Ocean. The most serious impact of the fishery is the large number of seabirds killed when dazzled by the ships' lights at night. These night-strikes affect thousands of individuals of eight or more species annually. Recommendations are made to reduce this largely avoidable mortality. The killing of rockhopper penguins Eudyptes chrysocome for baiting lobster traps has ceased. Indirect effects on seabird prey populations resulting from rock-lobster exploitation are likely to be negligible, because there are no inshore-feeding birds that feed extensively on benthic organisms. Dietary supplementation also is unimportant because few seabirds scavenge from the fishery relative to the large breeding populations occurring at the islands. Dumping of refuse and broken gear should be discontinued; it entangles marine birds and mammals, and is aesthetically unacceptable. Continuous vigilance is essential to keep the ships rodent-free, because their accidental introduction to the uninhabited islands poses the greatest threat to the island faunas.

Human Biology in Britain

Human Biology in Britain

The rock-lobster Jasus tristani on Vema Seamount: Drifting buoys suggest a possible recruiting mechanism

The recruitment mechanism for rock-lobster larvae to the isolated location of Vema Seamount in the South Atlantic Ocean could occur by the drift of larvae from the distant Tristan da Cunha Islands. An analysis of the drifts of free-floating weather bouys in the area presents the first support for this long-standing hypothesis by showing that the drift directions, the travel times, and the sea-surface temperatures experienced on route are those required for successful recruitment.

Ca-enrichment in olivines from volcanic rocks

Data are presented on the Ca-content of olivines in a range of volcanic rocks from a variety of suites. These include olivine basalts through to trachytes from Gough, St. Helena and Tristan da Cunha Islands; trachytes from central Victoria, Australia, and a leucitite and phonclitic-tephrite series from Bufumbira, Uganda. In olivine crystals from basaltic lavas the Ca- and Mn-contents are low and Fe shows the most significant zoning from core to rim. In Fe-rich olivines from trachytic differentiates Ca and Mn frequently show more significant variation than Fe. While the Mn-content is proportional to the Fe-content of these olivines, Ca-zoning, in many cases, is unrelated to Fe-content. The marked Ca-enrichment in olivines occurs with the absence of plagioclase in the host lavas. The Ca(Al  Na  K) ratio is shown to be related not only to the Ca-content of the olivines in the lava, but may be used to predict olivine stability in evolved compositions.

Reviews &amp; Notices - Man and Nature in the Tristan da Cunha Islands, by N. M. Wace &amp; M. W. Holdgate. (IUCN Monograph 6, Published with the support of the World Wildlife Fund.) International Union for Conservation of Nature and Natural Resources, Morges, Switzerland: 114 pp., illustr., 23.5 × 16 × 0.5 cm, paper covers, US $5, 1976.

Reviews &amp; Notices - Man and Nature in the Tristan da Cunha Islands, by N. M. Wace &amp; M. W. Holdgate. (IUCN Monograph 6, Published with the support of the World Wildlife Fund.) International Union for Conservation of Nature and Natural Resources, Morges, Switzerland: 114 pp., illustr., 23.5 × 16 × 0.5 cm, paper covers, US $5, 1976. - Volume 4 Issue 1

RECENT ORNITHOLOGICAL PUBLICATIONS

RECENT ORNITHOLOGICAL PUBLICATIONS

Asthma amongst Tristan da Cunha islanders.

SummaryThe incidence of asthma amongst Tristan da Cunha islanders was recorded over a period of 16 months. Thirty‐two per cent of the islanders gave a history of asthma, and 22% had one or more attacks during the survey period. Three‐quarters of the affected islanders had mild asthma. Both the incidence and severity of asthma on Tristan have declined since 1944.Over half the asthmatics were allergic to house dust extracts on skin testing; so was a large proportion of non‐asthmatic islanders. Large numbers of house dust mites are present in Tristan dust, but airborne allergens are scarce. Total TgE levels were greater than normal in the serum of twenty‐three of sixty‐seven islanders investigated. Allergy was thought to be the main cause of asthma in about a third of the active asthmatics.The high incidence of asthma on Tristan derives from two or three asthmatics amongst the fifteen ancestors of this highly inbred community. Nevertheless, asthma on Tristan, as elsewhere, seems to have a multifactorial aetiology.