Tag Archives: frenchguyane

Modeling on Giant African Snail invasion

An Argentinan group of colleagues has elaborated the potential areas where the Giant African Snail (GAS) might occur or invade (Vogler et al., 2013). Using the same methodology as Borrero et al. (2009), they have detailed now the potential distribution areas for all South American countries. The abstract reads:

The best way to reduce problems related to invasive species is by preventing introductions into potentially susceptible areas. The purpose of this study was to create distribution models for the invasive gastropod Achatina fulica Bowdich, 1822 in South America in order to evaluate its potential geographic distribution and identify areas at potential risk. This mollusc, considered one of the 100 world’s worst invasive alien species, is the focus of intense concern due to its impact on agriculture, human health, and native fauna. We tested two commonly used ecological niche modeling methods: Genetic Algorithm for Rule-Set Prediction (GARP) and Maximum Entropy (MaxEnt). Models were run with occurrence points obtained from several sources, including the scientific literature, international databases, governmental reports and newspapers, WorldClim bioclimatic variables, and altitude. Models were evaluated with the threshold-independent Receiver Operating Characteristic (ROC) and Area Under the Curve (AUC). Both models had consistent performances with similar areas predicted as susceptible, including areas already affected and new potentially susceptible areas in both tropical and temperate regions of South America.

This new study is more detailed and much more elaborated than Borrero et al. (2009), and uses two modeling methods, (A) GARP and (B) Maxent, of which the latter is generally performing best in comparative studies. The relevance of presenting country maps for potential distribution of this species in each South American country is clear: the responsible authorities now have a handle to focus their attention to areas most under threat. Generally, the Amazon basin is most infected or theathened, but certain areas in Ecuador, Colombia and Venezuela are across the Andes but have already been invaded. The following table shows that none of the South American countries can escape to the threat of GAS, although there are gradual differences.

References:
Borrero F.J. et al., 2009. Into the Andes. Three new introductions of Lissachatina fulica (Gastropoda, Achatinidae) and its potential distribution in South America. – Tentacle 17: 6-8.
Vogler, R.E., Beltramino, A.A., Sede, M.M., Gutiérrez Gregoric, D.E., Nuñez, V. & Rumi, A., 2013. The Giant African Snail, Achatina fulica (Gastropoda: Achatinidae): using bioclimatic models to identify South American areas suspectible to invasion. – American Malacological Bulletin 31: 39-50.

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New land snails from French Guiana

Published just before the end of the year, Gargominy & Muratov described three new land snails from French Guiana; one of these species is placed in a new genus.

This is the first paper on the malacofauna of this country after the recent revision of Massemin et al. (2009), in which the first author covered the land snails. Material obtained from sieved leaf litter and soil collected during 1997 and 1999 yielded three new species so far; however, many of the micromolluscs then collected prove to be new to science but still await description. More papers are thus to be expected.

The abstract of the paper is:
Three new species and a new genus of terrestrial gastropods are described from the Reserve naturelle des Nouragues in French Guiana. Cyclopedus anselini n. gen., n. sp. (forming new monotypical genus in the family Neocyclotidae Kobelt & M??llendorff, 1897) seems to be the smallest known cyclophoroid in the western hemisphere. The descriptions of the other two new species, Pseudosubulina theoripkeni n. sp. and P. nouraguensis n. sp., from the family Spiraxidae Baker, 1939, extend not only our knowledge of the geographical distribution of Pseudosubulina Strebel & Pfeffer, 1882 (previously known with certainty from Mexico only) but also the diagnosis of this genus, which now includes species with large penial stimulator and apertural dentition.

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Cyclopedus anselini n. gen., n. sp.

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Pseudosubulina theoripkeni n. sp.

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Pseudosubulina nouraguensis n. sp.

Reference:
Gargominy, O. & Muratov, I., 2012. New taxa of land snails from French Guiana. – Zoosystema 34: 783-792. 

Taxonomic position of Bulimus demerarensis

In the Guianas two species of Leiostracus occur, L. demerarensis (Pfeiffer, 1861) and L. ruthveni (H.B. Baker, 1926). Recently Muratov & Gargominy (2011) have studied both species and proposed a new taxonomic placement.

In their paper, Muratov & Gargominy have studied the type material of both taxa, respectively in the London and Philadelphia museums. Moreover, they have studied the anatomy of a single specimen from French Giuana; unfortunately the specimen was dried in and had to be re-hydrated. 
The protoconch sculpture, an important characteristic in the orthalicoids, consists of fine spiral lines. The authors state this sculpture has only been observed in three genera: Discoleus Breure, 1978, Bostryx Troschel, 1847, and Leiostracus Albers, 1850. There is, however, a fourth genus with a similar protoconch scultpture, viz. Lopesianus Weyrauch, 1958, represented with a single species from Brazil. Discoleus seems improbable, as it only occurs in southern Argentina, so the choice is between Bostryx and Leiostracus.

Study of the genitalia reveals that the spermoviduct is simple. In the known Leiostracus species this duct is swollen in its distal part, becoming very slender towards the spermatheca after a sudden transition. Bostryx species have a slender spermathecal duct throughout and a distal penis sheath. “Unfortunately we were unable to observe the penial sheath clearly on our re-hydrated specimen but we strongly suspect its presence since it was quite difficult to trace the vas deferens on the surface of the distal part of the penis”. The shell morphology is quite similar to some species of Leiostracus in having a peripheral angle on the body whorl, but “does not resemble any known species of Bostryx” (o.c.: 613-614). From the genitalia they notwithstanding concluded that the species belongs to Bostryx.

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From the rehydrated specimen also the radula and mandibula could be extracted; only the mandibula was illustrated . The radula is said to be “with monocuspid central, bicuspid lateral and weakly tricuspid marginal teeth”.  The radula formula for Bostryx is C/1 + LM/2, or C/1 + L/1 + M/2; for Leiostracus C/1 + L/2 + M/3 (Breure 1978 Zool. Verhand. 164: 239-240). This points more to the latter than to the former genus. Unfortunately, the radula has not been illustrated by Muratov & Gargominy.

In conclusion, Muratov & Gargominy re-classified Bulimus demerarensis Pfeiffer, 1861 with Bostryx, at the same time considering Drymaeus (Leiostracus) ruthveni H.B. Baker 1926 as a junior subjective synonym of Pfeiffer’s taxon. 
Although I can agree with the synonymization, I find the evidence presented for the generic transfer insufficient. The more so since Leiostracus is grouped in a different family (Simpulopsidae). In my humble opinion more evidence, e.g. also molecular, is needed for such a re-classification. 
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Reference:
Muratov, I.M. & Gargominy, O., 2011. Taxonomic position of the land snail Bulimus demerarensis L. Pfeiffer 1861 (Gastropoda, Pulmonata, Bulimulidae). – Journal of Conchology 40: 611-615.

Snails from French Guyane

The malacofauna of French Guyane is now well-known since the book of Massemin et al., published in 2009. In the latest issue of Folia Conchyliologica (#8, http://www.cernuelle.com/download.php?lng=fr) a paper was published that also gives an overview of the land and freshwater snails of that country. It appears to be a revised manuscript, originally drafted in 2003. 

As part of the revision to update the manuscript, a table has been prepared comparing the taxonomy from the earlier work of Tillier in 1980 and the recent  overview by Massemin et al. Besides eight colour plates (figuring many species in an old-fashioned way upside-down), there are many text figures on living snails.
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Reference:
Thouvenot, M., 2011. Escargot et limaces de Guyane. – Folia Conchyliologica 8: 4-30.  

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