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Explaining patterns of deformity in freshwater turtles using MacCulloch’s hypothesis

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A growing body of literature details the effects of teratogenic chemicals on embryonic development in freshwater turtles. However, other factors affecting developmental deformities have not been recently considered and evaluation of the significance of deformities in adults is lacking. We collected 193 wild Midland Painted Turtles (Chrysemys picta marginata Agassiz, 1857) and 39 Common Snapping Turtles (Chelydra serpentina (L., 1758)) from an uncontaminated site in Ontario and recorded incidence of deformity of the shell, limbs, face, and tail. We tested MacCulloch’s hypothesis (that incidence of deformity increases along a latitudinal gradient) by comparing our data with previously published deformity records from both uncontaminated and heavily polluted sites at varying latitudes. Incidence of nonembryonic deformity varied among wild populations and was not correlated with pollution levels. Thus adult deformity cannot be used as an indicator of site quality. Frequency of deformity increased with latitude in C. picta, supporting MacCulloch’s hypothesis, whereas deformities in C. serpentina did not. We refer to essential differences in the biology of the two species to explain this disparity and recommend that latitudinal variation be included as a covariate in the future when developmental trends are compared among distant sites.

Une littérature de plus en plus abondante décrit les effets des produits chimiques tératogènes sur le développement embryonnaire des tortues d’eau douce. Cependant, on n’a pas considéré récemment les autres facteurs qui affectent les déformations du développement, ni évalué la signification des déformations chez les adultes. Nous avons récolté 193 tortues peintes (Chrysemys picta marginata Agassiz, 1857) et 39 tortues serpentines communes (Chelydra serpentina (L., 1758)) sauvages dans un site non contaminé en Ontario et avons noté la fréquence des déformations de la carapace, des membres, de la face et de la queue. Nous avons testé l’hypothèse de MacCullough (selon laquelle la fréquence des déformations augmente en fonction d’un gradient latitudinal) en comparant nos données à celles de la littérature, tant de sites non contaminés que fortement pollués, à diverses latitudes. La fréquence des déformations non embryonnaires varie d’une population sauvage à une autre et n’est pas en corrélation avec les niveaux de pollution. Les déformations des adultes ne peuvent donc pas servir d’indicateurs de la qualité d’un site. La fréquence des déformations augmente avec la latitude chez C. picta, ce qui appuie l’hypothèse de MacCulloch, mais non chez C. serpentina. Nous invoquons les différences fondamentales dans la biologie de ces deux espèces pour expliquer cette disparité; nous recommandons d’inclure dorénavant la variation longitudinale comme covariable dans la comparaison des tendances du développement entre des sites éloignés.

Document Type: Research Article

Publication date: 2009-05-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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