Notodiscus (Charopidae) on South Georgia: some implications of shell size, shell shape, and site isolation in a singular sub-Antarctic land snail

2011 ◽  
Vol 23 (5) ◽  
pp. 442-448 ◽  
Author(s):  
P.J.A. Pugh ◽  
R.I. Lewis Smith
Keyword(s):  
East Coast ◽  
Land Snail ◽  
Shell Shape ◽  
Shell Size ◽  
Site Isolation ◽  
South Georgia ◽  
North East ◽  
Larus Dominicanus ◽  
Close Proximity ◽  
Georgia Population

AbstractMultivariate analysis shows that shells of Notodiscus sp. (Charopidae: Pulmonata) reported from South Georgia are smaller and proportionately taller than, but otherwise similar to, populations of Notodiscus hookeri (Reeve) from Iles Crozet and Iles Kerguelen. The origin of this solitary, and spatially limited, South Georgia population is enigmatic. It is confined to a remarkably small coastal lowland site which was glaciated at Last Glacial Maximum, precluding a Tertiary relict origin, and on the leeward north-east coast, ruling out post-glacial ocean rafting. The site is close to the King Edward Point settlement, yet the absence of any logistics connections with the Iles Crozet or Iles Kerguelen mitigates against anthropogenic introduction. The close proximity of the population to nests of blue-eyed shag (Phalacrocorax atriceps), Dominican gull (Larus dominicanus) and light-mantled sooty albatross (Phoebetria palpebrata) could imply the snail was originally introduced to South Georgia via these ocean transiting seabirds.

II.—Further Notes on the Petrography of South Georgia

1916 ◽  
Vol 3 (10) ◽  
pp. 435-441 ◽  
Author(s):  
G. W. Tyrrell
Keyword(s):  
East Coast ◽  
The South ◽  
South Georgia ◽  
South Eastern ◽  
North East ◽  
The North ◽  
New Material ◽  
Rock Specimens

The new material on which this paper is based has lately been received through Mr. D. Ferguson, who recently investigated the geology of the island, and collected the rocks described in an earlier paper. It consists of twenty-seven rock specimens from the south-eastern end of the island, between Cape Disappointment and Cooper Island, and nine specimens from Gold Harbour on the north-east coast between Cooper Island and Royal Bay. All these were collected by the staff of the South Georgia Co., Ltd., under the instructions of Mr. Th. E. Salvesen, managing director, of Leith.

HMS Owen's hydrographic surveys in South Georgia, 1960–61

Polar Record ◽  
1963 ◽  
Vol 11 (73) ◽  
pp. 423-430
Author(s):  
G. P. D. Hall
Keyword(s):  
East Coast ◽  
Summer Season ◽  
The West ◽  
South Georgia ◽  
North East ◽  
The North ◽  
Coastal Shipping ◽  
General Improvement ◽  
Colonial Office

In response to pressure from the Colonial Office and whaling interests for improvement of the Admiralty charts of South Georgia, the Hydrographer of the Navy despatched a surveying ship to operate there during the 1960–61 summer season. Priority was given to a thorough survey of the waters surrounding the western extremities of the island in order to facilitate the shortest passage between the whaling grounds in the west and the whaling stations on the north-east coast. Other commitments were the landing of scientists in co-operation with the Administration and, as opportunity offered, general improvement of the existing charts with particular reference to the coastal shipping routes.

scholarly journals Glacier retreat on South Georgia and implications for the spread of rats

2010 ◽  
Vol 22 (3) ◽  
pp. 255-263 ◽  
Author(s):  
A.J. Cook ◽  
S. Poncet ◽  
A.P.R. Cooper ◽  
D.J. Herbert ◽  
D. Christie
Keyword(s):  
East Coast ◽  
Average Rate ◽  
South Georgia ◽  
North East ◽  
The North ◽  
Breeding Populations ◽  
Increased Risk ◽  
South West Coast ◽  
Present Distribution ◽  
The 1950S

AbstractUsing archival photography and satellite imagery, we have analysed the rates of advance or retreat of 103 coastal glaciers on South Georgia from the 1950s to the present. Ninety-seven percent of these glaciers have retreated over the period for which observations are available. The average rate of retreat has increased from 8 Ma-1 in the 1950s to 35 Ma-1 at present. The largest retreats have all taken place along the north-east coast, where retreat rates have increased to an average of 60 Ma-1 at present, but those on the south-west coast have also been steadily retreating since the 1950s. These data, along with environmental information about South Georgia, are included in a new Geographic Information System (GIS) of the island. By combining glacier change data with the present distribution of both endemic and invasive species we have identified areas where there is an increased risk of rat invasion to unoccupied coastal regions that are currently protected by glacial barriers. This risk has significant implications for the surrounding ecosystem, in particular depletion in numbers of important breeding populations of ground-nesting birds on the island.

scholarly journals An ontogenetic perspective on the evolution of shell size and shell shape in the land snail genus Plectostoma

2014 ◽  
Author(s):  
Thor-Seng Liew ◽  
Menno Schilthuizen
Keyword(s):  
Parallel Evolution ◽  
Land Snail ◽  
Character Evolution ◽  
Growth Trajectory ◽  
Shell Shape ◽  
Shell Size ◽  
General Issue ◽  
Shell Form ◽  
Developmental Program

The rampant convergent and parallel evolution in shell form in the Gastropoda is well known. Many studies focus on the functional drivers which have been regarded as a major force in shell evolution. There is, however, a scarcity in studies that aim at understanding shell form evolution with respect to their ontogeny. Hence, we investigated the evolution of shell form in the micro-landsnail genus Plectostoma (Diplommatinidae) from the viewpoint of shell ontogeny. We examined the aperture ontogeny profiles that describe how aperture form and growth trajectory change along the shell ontogeny, and how the aperture ontogeny profiles relate to the observed shell forms. We also estimated the phylogeny of Plectostoma species, and examined patterns of character evolution for shell form. Our study revealed a general issue in the characterisation of shell shape and demonstrated how shell shape differences can be expressed as differences in the ontogeny of morphospace. It is clear that in Plectostoma the phylogenetic history does not prevent the course of shell ontogeny, and the resultant form. Finally, each species has a unique aperture ontogeny profile that determines its shell shape while retaining a conserved developmental program that maintains shell size.

scholarly journals An ontogenetic perspective on the evolution of shell size and shell shape in the land snail genus Plectostoma

2014 ◽  
Author(s):  
Thor-Seng Liew ◽  
Menno Schilthuizen
Keyword(s):  
Parallel Evolution ◽  
Land Snail ◽  
Character Evolution ◽  
Growth Trajectory ◽  
Shell Shape ◽  
Shell Size ◽  
General Issue ◽  
Shell Form ◽  
Developmental Program

The rampant convergent and parallel evolution in shell form in the Gastropoda is well known. Many studies focus on the functional drivers which have been regarded as a major force in shell evolution. There is, however, a scarcity in studies that aim at understanding shell form evolution with respect to their ontogeny. Hence, we investigated the evolution of shell form in the micro-landsnail genus Plectostoma (Diplommatinidae) from the viewpoint of shell ontogeny. We examined the aperture ontogeny profiles that describe how aperture form and growth trajectory change along the shell ontogeny, and how the aperture ontogeny profiles relate to the observed shell forms. We also estimated the phylogeny of Plectostoma species, and examined patterns of character evolution for shell form. Our study revealed a general issue in the characterisation of shell shape and demonstrated how shell shape differences can be expressed as differences in the ontogeny of morphospace. It is clear that in Plectostoma the phylogenetic history does not prevent the course of shell ontogeny, and the resultant form. Finally, each species has a unique aperture ontogeny profile that determines its shell shape while retaining a conserved developmental program that maintains shell size.

scholarly journals Intrapopulation variation in shell morphological traits and banding polymorphism of the land snail Cepaea vindobonensis (Gastropoda; Pulmonata; Helicidae)

2020 ◽  
Vol 10 (5) ◽  
pp. 114-121
Author(s):  
A.S. Kramarenko ◽  
Zh.V. Ignatenko ◽  
O.I. Yulevich
Keyword(s):  
Morphological Traits ◽  
Shell Height ◽  
Spatial Differentiation ◽  
Spatial Arrangement ◽  
Land Snail ◽  
Shell Shape ◽  
Shell Size ◽  
Intrapopulation Variation ◽  
Phenetic Diversity ◽  
High Level

The main goal of this paper was to analyze intrapopulation variation of both morphological traits and shell banding polymorphism using the example of a continuous population (a metapopulation) of the land snail Cepaea vindobonensis (Férussac, 1821). A total of 14 samples of the land snail C. vindobonensis from a population located in the “Dubki” Park (Ukraine, Mykolayiv) were collected in May-July 2007. The land snail collection sites are divided into three areas by buildings and asphalt roads, indicated by the Latin letters A, B and C. The major diameter of shell (MJD), the minor diameter of shell (MID) and the shell height (SH) were measured with a digital calliper to the nearest 0.05 mm. Two shell shape indices (SF1 and SF2) were also computed. A high level of the intrapopulation variation of the land snail C. vindobonensis was found in our study. Significant differences between sample means were found for all shell traits and indices used (except for SF1), however, maximum difference was noted for SH and SF2 (in both cases: P ≤ 0.001). About 80% of the total variation of the variance-covariance matrix was explained by the 1st and 2nd Principal Components (PC1 and PC2). The PC1 was characterized by high positive factor loadings of MJD, MID and SH and thus can be interpreted as “shell size dimension” and the PC2 had a high correlation with SF2 and thus it can be interpreted as “shell globularity”. The PC1 and PC2 determined a high level of spatial differentiation of intrapopulation morphological variation of the land snail C. vindobonensis. Samples with small (area A) and large (areas B and C) shells were separated from each other according to the PC1. Areas B and C were characterized by individuals with flatness and globularity shells, respectively. The areas A, B and C differed significantly in the total number of morphs, average number of morphs and frequency of rare morphs (Kruskal-Wallis H-test; in all cases P ≤ 0.010). At the same time, the highest value of phenetic diversity was noted for samples collected within A and C areas. In general all phenetic diversity estimators showed a positive correlation with sample size (Spearman's correlation coefficient; in all cases P ≤ 0.05). It was found that the type of biotope did not likely affect the frequency of individual morphs with respect to the shell banding polymorphism pattern. With regard to the most common morphs two patterns of the spatial arrangement of the intrapopulation variation were found – clinal pattern was for the frequency of pallescens morph and chaotic pattern was for frequency of “12345” morph.

The problematic fossil Triplicatella from the Early Cambrian of Greenland, Canada, and Siberia

2004 ◽  
Vol 41 (11) ◽  
pp. 1273-1283 ◽  
Author(s):  
Christian B Skovsted ◽  
John S Peel ◽  
Christian J Atkins
Keyword(s):  
New Species ◽  
Functional Morphology ◽  
Lower Cambrian ◽  
Early Cambrian ◽  
Taxonomic Affinity ◽  
East Greenland ◽  
North East ◽  
Close Proximity ◽  
Two New Species

The cap-shaped Early Cambrian fossil Triplicatella, previously known only from Australia, is reported from the upper Lower Cambrian of North and North-East Greenland, western Newfoundland, and Siberia. The occurrence of Triplicatella in Laurentia strengthens faunal ties between Laurentia and the Australian margin of Gondwana in late Early Cambrian times and supports hypotheses advocating the close proximity for the two palaeocontinents. Two new species, Triplicatella sinuosa n. sp., and T. peltata n. sp. are described, morphological details of which help elucidate the functional morphology and taxonomic affinity of the group. Three opercular types attributable to Triplicatella are left in open taxonomy. The postulated affinity of Triplicatella to hyoliths is confirmed, although the genus can not be placed within either of the two orders of hyoliths currently recognized.

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