Spatial variation of shell morphometrics in the subantarctic land snail Notodiscus hookeri from Crozet and Kerguelen Islands
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The land snail Notodiscus hookeri, widely distributed in subantarctic islands, shows a large intraspecific variation in shell morphology. In the present work, shell size and form of individuals from populations located in Crozet and Kerguelen archipelagos were investigated by means of multivariate statistics. Variation in shell morphometrics was analysed after the partitioning of the overall variation into size and shape components by means of a principal component-based approach. Shell size shows a significant spatial heterogeneity, which seems essentially related to environmental pressures. Previous works pointed to a greater conchological variation between populations from Kerguelen but present observations show that intra-island variances are not significantly different in the two islands studied. Variation in shell shape splits the populations into two main entities because of different allometric relationships between two shell height components and all other measurements. However, using geographical affinities of populations as instrumental variables shows that more complex environmental features interfered in population clustering.
KeywordsInstrumental Variable Land Snail Shell Size Shell Shape Shape Component
This research was supported by the Institut Polaire Français P.E.Victor (IPEV; programme 136). We are grateful to Y. Le Gallic, E. de Oliveira and to their supervisor Y. Frenot for their work on the field and in the laboratory. P. Vernon, M. Lebouvier and two anonymous referees are acknowledged for their useful suggestions on the manuscript.
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