Unusual Karyotype in the Malagasy Colubrid Snake Mimophis Mahfalensis

Short Notes 215

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Received: June6, 2002. Accepted: July 8,2002.

Unusual karyotype intheMalagasy colubrid snake Mimophis mahfalensis

GennaroAprea 1,GaetanoOdierna 1,FrancoAndreone 2, Frank Glaw3,MiguelV ences 4

1 Dipartimentodi BiologiaEvolutiva e Comparata,Università di Napoli“ FedericoII” , Via Mezzocannone8, 80134Napoli, Italy e-mail: [email protected] 2 MuseoRegionale di Scienze Naturali,Via G.Giolitti36, 10123 Torino, Italy e-mail: [email protected] 3 ZoologischeStaatssammlung, Mü nchhausenstr. 21, 81247 Mü nchen, Germany e-mail: [email protected] 4 Institutefor Biodiversity and Ecosystem Dynamics,Zoological Museum, Mauritskade 61, 1090 GT Amsterdam, TheNetherlands e-mail: [email protected]

Theextant reptile fauna of Madagascarhas in great parts been shaped by dispersalevents from Africa (e.g.,Mausfeld et al., 2000; V enceset al., 2001a, b), but no conclusive hypothesisis availableat present for thebiogeographic origin of the18 endemicMalagasy colubridgenera. One especially enigmatic genus is Mimophis whichhas been classi ed in severaldifferent subfamilies, e.g. in theBoodontinae and Psammophiinae (Meirte, 1992;

Zaher,2000). A numberof charactersfrom hemipenialand generalmorphology and natural historyindicate close relationships of Mimophis tothe largely African psammophiines (Brygoo,1982), and it currently is included in this subfamily (Zaher, 2000). Mimophis containsa singlespecies, i.e., M.mahfalensis .Thestatus of asecondform from central Madagascar,treated as subspecies M.mahfalensismadagascariensis (see Glaw and Vences,1994), is currentlyuncertain. In this paper we presentthe rst dataon theunusual karyotypein Mimophismahfalensis ,whichin the future may become relevant to assessits phylogeneticrelationships. Ourdata were obtainedfrom a singlefemale specimen whichis currently preserved at theMuseo Regionale diScienze Naturali,Torino (MRSN R1833, from Ambovombe, Tulé ar Faritany,leg. F. Andreone and G. Aprea 27.XII.1997).Following the method of Baker et al.(1971), the specimen was injectedtwice (interval24 h) with aphytohaemagglutininsolution (dilution 1 :15of stock solution; 0.01 ml/ gofbody weight). 48 hafter the rst injectionthe specimen was injectedwith a 0.5mg/ lcolchicinesolution (0.01 ml/ gofbody weight). Two hours later, 0.5-1ml ofbloodwas extracted fromthe caudal vein using a heparinizedsyringe. The collected blood was centrifugedat 500rpm for 3 min,and the supernatant white cells washed in5 ml ofa salt balancedsolution (Hank’s solution).Cells were transferred toa 0.7%sodium citrate solutionfor 30 min and subsequently xed inacetic methanol(1 part of acetic acid,3 partsof methanol).Finally they were droppedon clean slidesand air dried.Chromosomes were stainedfor 5 minin a 5%Giemsa solution.Karyotypes were assembled from vemetaphase plates andtheir relative lengthsand centromeric indicesmeasured. Additionallywe performed C-banding(Sumner, 1972) and sequential C CMA DAPI staining(Odierna et al.,2000). C 3 C Theexamined specimen had a karyotypeof 2n 44elements. Of these,24 were D macrochromosomesand 20 were microchromosomes.All macrochromosomes were acrocentric(uniarmed) except one metacentric element ( g. 1).This biarmed element, together withan uniarmed element formed the fourth pair in length. W econsiderthis heteromorphic pairas sex chromosomes, the biarmed chromosome corresponding to the Z elementand theuniarmedchromosome to theWelement( g. 1A). Relativechromosome lengths, given as mean standarddeviation (chromosome pair number in parentheses,was 9 :7 0:9 (1), § § 8:2 0:7 (2), 7:2 0:8 (3), 3:3 0:9 (4Z), 3:6 0:8 (4W), 6:5 0:7 (5), 6:4 0:6 (6), § § § § § § 6:3 0:6 (7), 5:9 0:7 (8), 5:7 0:8 (9), 5:5 0:7 (10), 4:5 0:8 (11), 4:3 0:7 (12), § § § § § § 23:6 2:5(13-22).The centromeric index was 43 :9 3:5for chromosome4W ,0for all § § theother (acrocentric) chromosomes. Pericentromericheterochromatin was presenton the Z chromosome,while the W-elementwas completelyheterochromatic except for aninterstitialeuchromatic region. Theother macrochromosomes showed centromeric heterochromatin, while the microchro- mosomeswere variable:some pairs being euchromatic, some completely or partiallyhet- erochromatic( g. 1B). After combinedC-banding and uorochrome-staining,allhete- rochromaticregions resulted to be CMA 3 andDAPI negative( g. 1C-D). Thepresence of sexchromosomes on the4 th chromosomepair agrees with the state in mostsnakes, in which usually the Z elementis biarmed(metacentric or submetacentric), andthe W elementdisplays a largeinterspeci c variationin shape,length and heterochro- matindistribution (Singh, 1972; Mengden and Stock, 1980; Olmo, 1986). In contrast, the chromosomenumber of Mimophis differs from themost common situation in colubrids (2n 36).Also the acrocentric condition of almost all macrochromosomes is unusual. D