Notes on a sinistral specimen of Nesopupa bisulcata (Jickeli) (Gastropoda Pulmonata: Vertiginidae) from Kenya

3 Pages·1993·0.4 MB·English

by  Van Bruggen, A C

BASTERIA, 57: 103-105, 1993
Notes onasinistral specimen ofNesopupa bisulcata (Jickeli) (Gastropoda
Pulmonata:Vertiginidae) fromKenya
A.C. van Bruggen
SystematicZoologySection, InstituteofEvolutionaryand EcologicalSciences, LeidenUniversity,
c/oNational MuseumofNaturalHistory, P.O. Box 9517, 2300 RALeiden, theNetherlands
& B. Verdcourt
c/o The Herbarium,Royal BotanicGardens, Kew, Richmond, SurreyTW9 3AB,England,U.K.
AsinistralshellofNesopupabisulcatafromnearHomaBay on theeasternshoresofLake Victoria
inKenyais thefirstsuchabnormalityrecordedforthespecies.Itrepresents thecommontypeof
shellwithfiveaperturaldenticles.The shellisoneofalotofsix, sothatitobviouslyrepresentsa
populationwithsinistral shells.The taxonomic implicationsofthis arebriefly discussed.
Key words: GastropodaPulmonata,Vertiginidae,Nesopupa,sinistrality,isolatingmechanisms,
Kenya.
Among the papers left by Dr.WilliamAdam(1909-1988), late curator ofmolluscs of
the Institut Royal des Sciences Naturelles de Belgique (IRSNB), Brussels (Belgium),
there is a fine drawing madein 1984 by his professional artist, Mrs. Jacqueline van
Melderen-Sergysels, ofa sinistral specimen ofNesopupa bisulcata (Jickeli, 1873) (fig. 1).
Thankstothecooperation ofDr.J.L.van Goethem,thesuccessor toDr. Adam, theshell
in question was easily traced in the Brussels Museum. It is labelled as having been
collectedby M. Pickford at Bala, HomaBay, ontheeastern shoresofLake Victoriain
western Kenya, on 17May 1983,andwas identifiedasN.bisulcataby Dr.Adamin 1984.
The history ofthe specimen is asfollows. The secondauthorreceived asample ofsix
Nesopupa shells, allsinistral, from theabove locality from Mr. M. Pickford. Oneofthese
was sent to Dr. Adam, who replied (in litt., 18.X.1984) "I should like to know ifyou
allow meto describe it as a new species." Verdcourtwrote on26.X.1984and sent the
other five specimens, which were acknowledged by Dr. Adam in a letter dated
6.XI.1984; however, the specimens in question have not been traced in the Brussels
Museum. The letter shows that Dr. Adam changed his mind and considered the
specimens sinistral shells ofN. bisulcata.
Theperfect specimen (fig. 1) measures 1.59 x0.94 mm, ratio length/major diameter
1.70, length last whorl 0.94 mm, aperture height x width 0.62 x 0.56 mm, and has
slightly less than43A whorls. Theaperture hasfive denticles. Seenin mirrorimage (fig.
2), the shell seems perfectly normal and compares well to e.g. the seriesoffigures in
Adam(1954, figs. 12D-J). As farasknown, thisis thefirstrecordedsinistralspecimen of
the species underdiscussion.
Sinistralspecimens ofspecies withdextralshells amongNesopupa arerare.Nomention
is madeofsuch shells in Dautzenberg (1914), orPilsbry (1918-1920, 1922-1926), for
which reasonthe specimen under discussion is put on record.
104 BASTERIA, Vol. 57,No. 4-6, 1993
Figs. 1-2.SinistralshellofNesopupabisulcata(Jickeli)fromBala, HomaBay,Kenya(IRSNB),actuallength 1.59mm
(fig.2 printedin mirror image).Drawing by Mrs. J.van Melderen-Sergysels,photographby A. ‘tHooft,Leiden
University.
Normal sinistral chirality doesoccurwidely in the family Vertiginidae, mostly onthe
species level, but sometimesalso on the (sub)generic level (Zilch, 1959: Truncatellina,
Vertigo, Lyropupa, Cylindrovertilla, Nesopupa). It is also fairly common among the closely
alliedfamiliesOrculidae, Chondrinidaeand Pupillidae. Pilsbry (1920: 298, 333; 1926:
227) enumerates only two sinistral species inthegenusNesopupa, viz. N.infrequens Cooke
& Pilsbry, 1920 (Hawaii) and N. norfolkensis (Sykes, 1900) (Norfolk I.),both products of
remote islandradiations.The latterspecies is the monotypeofthe subgenus Nesopuparia
Pilsbry, 1926,which, incidentally, is not based onthe sinistrality ofthe shell.
Abnormalsinistrality hasbeen shown to occuroccasionally amongothervertiginids,
e.g. Vertigo substriata (Jeffreys, 1833) (Standen, 1905). Obviously itis arare phenomenon
as e.g. Pokryszko (1990: 139) who studied aprofuse materialof vertiginids inPoland,
didnotcome across any reversed specimen.
It is evidentthat the specimen discussed here represents a population with sinistral
shells, as shown by the presence of five more reversed specimens. Among the accom-
panying comparatively diverse malacofaunano dextral specimens ofN. bisulcata were
found.Thisposes the question whetherthispopulation representsa species ofits own; if
this is indeed the case, then it would have nomenclatorialimplications. Sinistrality
might imply instantaneous reproductive isolation because ofthe virtual mechanical
impossibility ofbreeding withdextral specimens. Referenceshouldbe madeto Gitten-
berger (1988), who has elaborated onthe possibilities ofsympatric speciation in such
cases.
VanBruggen & Verdcourt: Sinistral specimenofNesopupa bisulcatafrom Kenya 105
The similarity to normal, dextral shells ofN. bisulcata as regards size and shape,
sculpture andapertural dentition(fig. 2), issuch that, forthetimebeing, the singleshell
examinedis considereda reversed specimen ofthis species.
Publishedrecords ofN. bisulcata in Kenya are scarce. Adam(1957: 7) simply reports
"Kenya", while Verdcourt (1983: 208) gives Shimoni (s.n. “N. cf. bisulcata”) and
"Rumurutito Mt. Kenya" [s.n. “N. iota”(Preston, 1911), a synonym ofN. bisulcata)].
The Homa Bay record extends the Kenya range westward for some considerable
distance.
REFERENCES
ADAM,W., 1954. fitudes surles mollusques del'Afrique centrale etdes regions voisinesI. Vertiginidaeet
Valloniidae.—Vol.Jub.Victor van Straelen2:725-817. Brussels.
,Va1l9lo57n.iidfiatued(easddseunrdleusm)m.o—lluBsquulle.sIndset.lR'Aofyr.iqSucei.cNeantt.raBleelge.t3d3es(3r8e):gio1n-2s6.voisines.2. — Vertiginidaeet
DAUTZENBERG,P.,1914. [Presidentialaddressof"presidentd'honneur"onabnormallysinistral and dextral
gastropods].—Bull.Soc. Zool.France 39: 50-60.
GITTENBERGER, E., 1988. Sympatric speciationin snails; a largely neglectedmodel. — Evolution 42:
826-828.
PILSBRY, H.A., 1918-1920. Pupillidae(Gastrocoptinae, Vertigininae).— Man. Conch. (2)25: i-ix, 1-401.
Philadelphia.
, 1922-1926.Pupillidae(Orculinae,Pagodulinae,Acanthinulinae,etc.). —Man. Conch.(2)27:i-v, 1-369.
Philadelphia.
POKRYSKZO, B., 1990. The VertiginidaeofPoland(Gastropoda:Pulmonata: Pupilloidea)— asystematic
monograph.— Ann.Zool.Warszawa 43: 133-257.
STANDEN,R., 1905. Vertigosubstriata (Jeff.)m. sinistrorsum. —J. Conch. London 11: 200.
VERDCOURT, B., 1983. A list ofthe non-marine Mollusca ofEast Africa (Kenya, Uganda, Tanzania,
excludingLake Malawi).— Achatina 11: 200-239.
ZILCH,A., 1959-1960.Euthyneura.In: O.H. SCHINDEYVOLF,ed.,Handbuch der Palaozoologie6(2):I-XII,
1-834.Berlin-Nikolassee.