Abstract
In Maghreb, the land snail Helix aspersa consists of two anatomically and biochemically divergent groups of populations between which the separation occurs roughly to the east of the Lesser Kabylia. To document the patterns of migration across the suspected contact zone between these two geographical entities, we have analysed changes in allele frequencies at 13 polymorphic allozyme loci in five intermediate Algerian populations ranging from Azeffoun (Great Kabylia) to El Hedaick (Skikda), thus including three western and two eastern colonies. Multivariate analyses and exact tests for population differentiation were used to show the genetic divergence between samples; deviations from panmixia were calculated to account for the effect of migration. Whereas some loci showed abrupt changes in allelic composition across the hybrid zone, some others were introgressed, especially into eastern populations in the central colony of Djemila. It is tempting to ascribe this allelic distribution to gene exchanges between populations on the east and west. However, the large number of private alleles found in adjoining populations apparently does not support this explanation, although such an increase in rare alleles has been observed in other hybrid zone surveys. In addition, it may be that this discrepancy between the patterns of common and private allele variation may result from the time since contact occurred. Whatever the explanation of this finding, the genetic structure in Djemila, and particularly the large linkage disequilibria observed, indicates population mixing. Although not ruling out the possibilities of tectonic events and of human transport, the most likely hypothesis for contacts between eastern and western populations are that these result from climatic phenomena during the Quaternary.
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References
Addad. 1992. Logiciel de traitement, version micro 92. Association pour le Développement et la Diffusion de l'Analyse des Données, Paris.
Arntzen, J W, and Wallis, G P. 1991. Restricted gene flow in a moving hybrid zone of the newts Triturus cristatus and T. marmoratus in western France. Evolution, 45, 805–826.
Barton, N H, and Hewitt, G M. 1985. Analyses of hybrid zones. Ann Rev Ecol Syst, 16, 113–148.
Barton, N H, and Slatkin, M. 1986. A quasi-equilibrium theory of the distribution of rare alleles in a subdivided population. Heredity, 56, 409–415.
Barton, N H, Halliday, R B, and Hewitt, G M. 1983. Rare electrophoretic variants in a hybrid zone. Heredity, 50, 139–149.
Benzecri, J P. 1973. L'Analyse des Données. Dunod, Paris.
Cain, A J, and Currey, J D. 1963. Area effects in Cepaea. Phil Trans R Soc B, 246, 1–83.
Clarke, B. 1968. Balanced polymorphism and regional differentiation in land snails. In: Drake, E. T. (ed.) Evolution and Environment, pp. 351–368. Yale University Press, New Haven, CT.
Escofier, B, and Pages, J. 1990. Analyses Factorielles Simples et Multiples - Objectif, Méthodes et Interprétation, 2nd edn. Dunod, Paris.
Gould, S J, and Woodruff, D S. 1978. Natural history of Cerion, VIII: Little Bahama Bank - a revision based on genetics, morphometries, and geographic distribution. Bull Mus Comp Zool Harvard Univ, 148, 371–415.
Guiller, A, and Madec, L. 1991. Variabilité enzymatique dans quelques populations naturelles de Cepaea nemoralis et Cepaea hortensis en France. C r Acad Sci Paris, 313, 299–306.
Guiller, A, and Madec, L. 1993. A contribution to the study of morphological and biochemical differentiation in French and Iberian populations of Cepaea nemoralis. Biochem Syst Ecol, 3, 323–339.
Guiller, A, Madec, L, and Daguzan, J. 1994. Geographical patterns of differentiation in the landsnail Helix aspersa Müller (Gastropoda: Pulmonata). J Moll Stud, 60, 205–221.
Guo, S W, and Thompson, E A. 1992. Performing the exact test of Hardy–Weinberg proportion for multiple alleles. Biometrics 48, 361–372.
Harrison, R G (ed.) 1993. Hybrid Zones and the Evolutionary Process. Oxford University Press, New York.
Hartl, D L, and Clark, A G. 1989. Principles of Population Genetics. Sinauer Associates, Sunderland, MA.
Johnson, M S. 1976. Allozymes and area effects in Cepaea nemoralis on the western Berkshire Downs. Heredity, 36, 105–121.
Johnson, M S, Murray, J, and Clarke, B. 1993. The ecological genetics and adaptative radiation of Partula on Moorea. Oxf Surv Evol Biol, 9, 167–238.
Jones, J S, Selander, R K, and Schnell, G D. 1980. Patterns of morphological and molecular polymorphism in the land snail Cepaea nemoralis. Biol J Linn Soc, 14, 359–357.
Lazaridou-Dimitriadou, M, Karakousis, Y, and Staikou, A. 1993. Geographic variation in shell morphology and isoenzymes of Helix aspersa Müller, 1774 (Gastropoda, Pulmonata), the edible land snail, from Greece and Cyprus. Heredity, 71, 434–447.
Louis, E J, and Dempster, E R. 1987. An exact test for Hardy-Weinberg and multiple alleles. Biometrics, 43, 805–811.
Madec, L. 1989. Etude de la Differenciation de Quelques Populations Géographiquement Isolées de l'Espèce Helix Aspersa Müller (Mollusque Gastéropode Pulmoné): Aspects Morphologiques, écophysiologiques et Biochimiques. Ph.D. Thesis, University of Rennes.
Madec, L. 1991. Variabilité enzymatique dans quelques populations naturelles de l'espèce Helix aspersa Müller. C r Acad Sci Paris, 313, 339–344.
Madec, L, and Guiller, A. 1994. Geographic variation of distal genitalia in the landsnail Helix aspersa Müller. J Zool, 233, 215–231.
Nei, M, and Li, W H. 1973. Linkage disequilibrium in subdivided populations. Genetics, 75, 213–219.
Ohta, T. 1982a. Linkage disequilibrium due to random genetic drift in finite subdivided populations. Proc Natl Acad Sci USA, 79, 1940–1944.
Ohta, T. 1982b. Linkage disequilibrium with the island model. Genetics, 101, 139–155.
Raymond, M, and Rousset, F. 1994. GENEPOP Version 1.0. University des Sciences et Techniques du Languedoc, Montpellier.
Raymond, M, and Rousset, F. 1995a. GENEPOP (Version 1.2): a population genetics software for exact tests and ecumenicism. J Hered, 86, 248–249.
Raymond, M, and Rousset, F. 1995b. An exact test for population differentiation. Evolution, 49, 1280–1283.
Rousset, F, and Raymond, M. 1995. Testing heterozygote excess and deficiency. Genetics, 140, 1413–1419.
Rice, W R. 1989. Analyzing tables of statistical tests. Evolution, 43, 223–225.
Selander, R K, and Foltz, D W. 1981. Gametic disequilibrium between esterase loci in populations of Cepaea nemoralis in western New York. Evolution, 35, 190–192.
She, J X, Autem, M, Kotulas, G, Pasteur, N, and Bonhomme, F. 1987. Multivariate analysis of genetic exchanges between Solea aegyptiaca and Solea senegalensis (Teleosts, Soleidae). Biol J Linn Soc, 32, 357–371.
Slatkin, M. 1985. Rare alleles as indicators of gene flow. Evolution, 39, 53–65.
Swofford, D L, and Selander, R B. 1989. BIOSYS-1. A computer program for the analysis of allelic variation in population genetics and biochemical systematics. Release 1.7. In: Swofford, D. L. (ed.) Illinois Natural History Survey, pp. 1–43. Champaign, IL.
Szymura, J M, and Barton, N H. 1991. The genetic structure of the hybrid zone between the fire-bellied toads Bombina bombina and B. variegata: comparisons between transects and between loci. Evolution, 45, 237–261.
Taylor, J W. 1913. Monograph of the Land and Freshwater Mollusca of the British Isles, pp. 236–273. Taylor Brothers, Leeds.
Weir, B S, and Cockerham, C C. 1984. Estimating F-statistics for the analysis of population structure. Evolution, 38, 1358–1370.
Woodruff, D S. 1989. Genetic anomalies associated with Cerion hybrid zones: the origin and maintenance of new electrophoretic variants called hybrizymes. Biol J Linn Soc, 36, 281–294.
Woodruff, D S, and Gould, S J. 1987. Fifty years of interspecific hybridization: genetics and morphometries of a controlled experiment on the landsnail Cerion in Florida Keys. Evolution, 41, 1022–1045.
Wright, S. 1965. The interpretation of population structure by F-statistics with special regard to systems of mating. Evolution, 19, 395–420.
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Guiller, A., Coutellec-Vreto, MA. & Madec, L. Genetic relationships among suspected contact zone populations of Helix aspersa (Gastropoda: Pulmonata) in Algeria. Heredity 77, 113–129 (1996). https://doi.org/10.1038/hdy.1996.116
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DOI: https://doi.org/10.1038/hdy.1996.116
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