Cochlostoma nouleti ( Dupuy, 1851 )

Gofas, Serge, 2001, The systematics of Pyrenean and Cantabrian Cochlostoma (Gastropoda, Cyclophoroidea) revisited, Journal of Natural History 35 (9), pp. 1277-1369 : 1319-1326

Cochlostoma nouleti ( Dupuy, 1851)

(®gures 35±38)

Pomatias nouleti Dupuy, 1851: 513 , pl. 26, ®gure 12. Type locality: Axiat (ArieÁge, CH 9838).

Pomatias arriensis Saint-Simon, 1867a: 10 ±11; 1867b: 5,11,15. Type locality: at the foot of Montagne d’Arri, between St BeÂat and Marignac; Cierp, near the left bank of river Pique. Syntype (MNHN), coll. A. Dollfus ex Saint-Simon, collected ii.1867. Pomatias arriacus Mabille, 1875: 158 (unjusti®ed emendation). Pomatias marquetianus Saint-Simon, 1876: 142 (unneeded replacement name for P. arriensis ).

Cyclostoma nouleti Matheron, 1862 (5 Pomatias cieuracense Noulet, 1868 ) is a junior homonym.

Description

Shell up to 11.8 Ö 4.8 mm with 7.5 to 8.5 quite rounded whorls. Early whorls with a peripheral angle which is concealed by the suture or slightly apparent next to it; body whorl slightly constricted, with a quite apparent discontinuity of pro®le circling the peri-umbilical area. Sculpture of weak wrinkles on the ®rst embryonic half whorl, then grading to crowded (20±25/mm) ribs on the second whorl. Spire whorls with alternating strong ribs (3±4 major ribs/mm) between which 0±3 ®ner or inconspicuous one are intercalated; ribs not thickened at their termination along the suture.

Aperture only slightly thickened even in well grown specimens, and expanded into a narrow collar, with a very distinct rim inside the outer lip. Peristome hardly auriculated, gradually narrowing at the columellar insertion.

Shell colour of a pale brown to tan background, with irregular darker axial ¯ames, and two dark spiral bands on the peri-umbilical area of the body whorl. Peristome white.

Female genital system as in general description. Male with a characteristic keyshaped penis, compressed and lobed on one side, and curled up. Testis rather large, occupying three spire whorls.

Remarks

Cochlostoma nouleti super®cially resembles some heavily ribbed morphs of C. crassilabrum , but is distinguished by the alternating strong and weak ribs on spire whorls, the ¯ame-like colour pattern, and the outer lip which is less calci®ed although with an inner rim.

Cochlostoma nouleti most resembles a fossil from the Pliocene of Burgundy (®gure 35d), which Schlickum (1975) and PuisseÂgur (1976) referred to Cochlostoma lugdunense (Delafond and DepeÂret, 1893) . The shared characters are the alternate ribbing, the inner rim of aperture (stronger on the fossil), the colour pattern of ¯ames (persistent on the fossil shells). Cochlostoma lugdunense is smaller (maximum 8.5 Ö 2.4 mm) and more variabl e regarding the height/diameter ratio.

Habitat

Where sympatric with C. crassilabrum , C. nouleti is restricted to mounds of limestone blocks, and occupies clean surfaces concealed in these. In the eastern part of its area, it is more ubiquitous and was found in large quantities in May 1989 creeping on beech trunks at altitude 800±1200 m.

Distribution Endemic to the French deÂpartements of Haute-Garonne, ArieÁge and Aude.

Key to the Pyrenean and Cantabrian species of Cochlostoma

Sculpture of spire whorls (5th±7th) with alternating strong and weak ribs... 1 Sculpture of spire whorls (5th±7th) with sculpture of subequal ribs..... 2 1 Colour pattern more or less plain [Cantabrian].... C. bicostulatum p. 1317 ± Colour pattern with brown ¯ames [Pyrenean]....... C. nouleti p. 1319

2 Colour pattern more or less plain.............. 3 ± Colour pattern with spiral series of brown/white patches........ 5

3 Outer lip narrowing abruptly at the columellar insertion (ex. ®gure 18).....

................... C. martorelli p. 1299 ± Outer lip narrowing gradually at the columellar insertion (ex. ®gure 24)....

4 Ribs strong and de®nitely ¯exuose, aperture with rusty hue.. C. asturicum p. 1313 ± Ribs hardly ¯exuose, outer lip white........ C. hidalgoi p. 1310

5 Shell stout, height less than twice greatest diameter.... C. oscitans p. 1315 ± Shell slender, height more than twice greatest diameter........ 7

7 Aperture without a de®nite inner rim; brown peri-umbilical bands de®nite... 8 ± Aperture with a de®nite inner rim.............. 10 8 Ribs more spaced on the spire whorls (4th±7th) than on body whorl..... 9 ± Ribs not more spaced on the spire whorls (4th±7th) than on body whorl....

................... C. partioti p. 1294

9 Aperture with slightly thickened outer lip [lowlands].... C. obscurum p. 1288 ± Aperture with well calci®ed, thick outer lip..... C. crassilabrum p. 1292

10 Colour pattern of brown ¯ames, shell large> 15 mm ..... C. gigas p. 1307 ± Colour pattern formed by coordinate white segments on ribs.. C. martorelli p. 1299

Genetic distances between conspeci W c populations and between species

Between allopatric populations which have been considered conspeci®c on the basis of morphology, characteristic alleles and distribution, Nei’s genetic distance is generally lower than 0.4 (®gure 39). The only exception is found between the populations of C. martorelli from Berga and from the upper Llobregat, which will be discussed later. The high values are found between populations of the widely distributed species, namely C. martorelli , C. hidalgoi and C. crassilabrum . but in every such case, there are also populations with very low distances and there is a continuum of values in the material examined here.

Distances between non-conspeci®c populations of the Cantabrian species, where other evidence shows that reproductive isolation is achieved, can be surprisingly low. The distance between C. hidalgoi and C. asturicum can be as low as 0.08, and FIG. 35. Shells of Cochlostoma nouleti and C. lugdunense . a,b: C. nouleti , female (11.2 mm) and male (9.2 mm) from Axiat (Aude). c: Syntype of Pomatias arriensis from Montagne d’Arri (ArieÁge). d. shell (8.4 mm) of C. lugdunense , fossil fron the Pliocene of Cessey s/Tille (Burgundy). e,f,g: C. nouleti , apical part showing embryonic whorls, specimens from Etang de Lers (ArieÁge) (scale bars are 1 mm).

is respectively 0.18 and 0.22 at the two sites where sympatry tests the reproductive isolation. Distances are also very low between C. bicostulatum and C. hidalgoi , or between C. bicostulatum and C. asturicum , despite the very clearcut morphological diOEerence in sympatric populations.

The phenetic clustering of populations by UPGMA and the two distance methods applied yield similar topologies of the dendrograms. Populations of the widespread species remain togethe r and this is consistent with predictions from the morphological data. The species cluster in two major groups, one including the Pyrenean species except C. nouleti , the other one C. nouleti and the ®ve Cantabrian species. Cochlostoma nouleti and C. oscitans appear as very diOEerentiated species from their overall genetic distances, and may cluster together (distance-Wagner tree) because of their dissimilarity from others rather than because of real a nity.

The UPGMA reconstruction diOEers in that C. gigas is not included in the branch containing all C. martorelli populations, a result which is not supported by all other allozymic and morphological evidence.

Parsimony reconstruction

The heuristic search under PAUP, using the matrix of multistate locus characters, ®nds a large number of equiparsimonious trees, which were arbitrarily limited to 100. These trees have a length of 149 steps, with a consistency index of 0.87. A 50% majority rule consensus, which retains any grouping found in more than 50 of these, is presented on ®gure 43 as an unrooted tree; groupings with a 100% majority are those also retained in a strict consensus.

The alternative matrix, where the data are scored as present/absent independent alleles, also ®nds a large number of equiparsimonious trees, with a lower (0.35) consistency index. The majority-rule consensus of these trees has a quite similar topology; the main diOEerence lies in the placement of the branch including all C. crassilabrum , which clusters as a sister-group of the branch including C. partioti , C. obscurum , C. martorelli and C. gigas .

Cochlostoma septemspirale was scored as a potential outgroup, but this was found to diOEer from all species of the ingroup at all loci. Thus, it was of no help for character polarization within the Pyrenean group and was not included in the ®nal analysis. The only informationÐbut not minorÐfrom this outgroup comparison is that it demonstrates that the species studied belong to a single monophyletic group.

The main outcome of the parsimony analysis is that populations cluster in two major groups, with a topology that is consistent with the results from the distance methods. These two groups can be characterized by alternative alleles of the most conservative loci, always monomorphic within a given population:

group (1) group (2)

MPI A, B or C E

SOD A or null B

MDH2 null B or C

This result, which is found in 100% of the equiparsimonious trees in the reconstruction using all characters, is repeated in 63% of 100 bootstrap replicates for the matrix of multistate locus characters, performed under PAUP with the same settings as before. Of the alternate groupings, 36% are due to the placement of C. nouleti in group 1. This means that the contribution of any single locus is important to the outcome of the reconstruction. The recognition of group 1 vs. group 2 is more robust (91% of 100 replicates) if the bootstrap is performed with the characters scored as present/absent independent alleles.