Sofie Geenen

Royal Belgian Institute of Natural Sciences, Bruxelles, Brussels Capital Region, Belgium

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Publications (7)15.19 Total impact

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    ABSTRACT: The original description of the slugs Arion (Carinarion) fasciatus, Arion (Carinarion) silvaticus and Arion (Carinarion) circumscriptus was based on subtle differences in body pigmentation and genital anatomy. However, body pigmentation in these slugs may be influenced by their diet, whereas the genital differences between the species could not be confirmed by subsequent multivariate morphometric analyses. Hence, the status of the three nominal morphospecies remains controversial, with electrophoretic studies based on albumen gland proteins and allozymes also providing conflicting results. These studies suggested that Carinarion species are difficult to reconcile with the biological species concept because there is evidence of interspecific hybridization in places where these predominantly self-fertilizing slugs apparently outcross. Therefore, in the present study, the three Carinarion species are evaluated under a phylogenetic species concept, using nucleotide sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS-1) and the mitochondrial 16S rDNA. ITS-1 showed no species specific variation. However, 16S rDNA yielded five haplotype groups. Three of these grouped haplotypes by species, whereas the two others joined haplotypes of different species and included all haplotypes that were shared by species (22% of all haplotypes). Hence, the three nominal Carinarion species appear to be inconsistent with a phylogenetic species concept. The present data also confirmed that North American Carinarion populations are genetically impoverished and may be not sufficiently representative with respect to the taxonomy of Carinarion. In conclusion, we currently regard Carinarion as a single species-level taxon, whose taxonomically deceiving, correlated phenotypic and genetic intraspecific variation is caused by sustained self-fertilization. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89, 589–604.
    Biological Journal of the Linnean Society 11/2006; 89(4):589 - 604. · 2.41 Impact Factor
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    ABSTRACT: Several insect species seem to persist not only in permanent but also in temporary ponds where they face particularly harsh conditions and frequent extinctions. Under such conditions, gene flow may prevent local adaptation to temporary ponds and may promote phenotypic plasticity, or maintain apparent population persistence. The few empirical studies on insects suggest the latter mechanism, but no studies so far quantified gene flow including both pond types. We investigated the effects of pond type and temporal variation on population genetic differentiation and gene flow in the damselfly Lestes viridis in northern Belgium. We report a survey of two allozyme loci (Gpi, Pgm) with polyacrylamide gel electrophoresis in 14 populations from permanent and temporary ponds, and compared these results with similar data from the same permanent populations one year before. The data suggested that neither pond-drying regime, nor temporal variation have a substantial effect on population genetic structuring and did not provide evidence for stable population differentiation in L. viridis in northern Belgium. Gene flow estimates were high within permanent and temporary ponds, and between pond types. Our data are consistent with a source-sink metapopulation system where temporary ponds act as sinks in dry years, and are quickly recolonized after local population extinction. This may create a pattern of apparent population persistence of this species in permanent and temporary ponds without clear local adaptation.
    Genetica 08/2005; 124(2-3):137-44. · 1.68 Impact Factor
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    ABSTRACT: The predominantly selfing slug species Arion (Carinarion) fasciatus, A. (C.) silvaticus and A. (C.) circumscriptus are native in Europe and have been introduced into North America, where each species consists of a single, homozygous multilocus genotype (strain), as defined by starch gel electrophoresis (SGE) of allozymes. In Europe, the "one strain per species" hypothesis does not hold since polyacrylamide gel electrophoresis (PAGE) of allozymes uncovered 46 strains divided over the three species. However, electrophoretic techniques may differ in their ability to detect allozyme variation. Therefore, several Carinarion populations from both continents were screened by applying the two techniques simultaneously on the same individual slugs and enzyme loci. SGE and PAGE yielded exactly the same results, so that the different degree of variation in North American and European populations cannot be attributed to differences in resolving power between SGE and PAGE. We found four A. (C.) silvaticus strains in North America indicating that in this region the "one strain per species" hypothesis also cannot be maintained. Hence, the discrepancies between previous electrophoretic studies on Carinarion are most likely due to sampling artefacts and possible founder effects.
    Electrophoresis 03/2003; 24(4):622-7. · 3.26 Impact Factor
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    ABSTRACT: Ten flexible characters for two collections of a pulmonate land slug that differed in their method of preservation (ethanol or freezer/ethanol), were measured four times – twice with calipers and twice with a stage micrometer – by two different people. Repeated measurements were used to estimate the measurement error (ME) associated with the ten characters. ME ranged from 2% to 90% and differed significantly between the characters. Characters with low mean values and a high flexibility showed the largest ME. With the stage micrometer, one measurer obtained significantly higher ME, but both measurers obtained the same ME with calipers. There was no detectable effect of preservation method on the size and shape of characters, yet, results differed when characters were measured with either calipers or a stage micrometer. One measurer obtained significantly larger mean values for three characters with calipers. Additionally, presumed species differences between three Carinarion species (Arion fasciatus, A. silvaticus and A circumscriptus; subgenus Carinarion Hesse 1926) were tested using principal component analysis and canonical discriminant analysis. Despite possible measurer biases and high ME, the different datasets yielded highly similar results, indicating that biometrical data of soft, flexible structures may yield valuable and reliable data which can be examined statistically. Our results indicate that A. fasciatus is larger than the other two species, but it is hard to distinguish from both of the other species when size is not considered. Arion silvaticus and A. circumscriptus can be separated only when colour characters are used. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 533–542.
    Biological Journal of the Linnean Society 01/2002; 75(4):533-542. · 2.41 Impact Factor
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    ABSTRACT: Body pigmentation is a popular taxonomic marker in slugs to discriminate closely related species. However, the genetic background of body pigmentation is known only for a few species, while in many others body pigmentation is influenced by age, food and/or climate. In this study, we investigated the effects of different food items on body pigmentation expression in two selfing pulmonate gastropods, Arion (Carinarion) silvaticus and Arion (Carinarion) fasciatus . Both species mainly differ in the distribution of yellow-orange granules on the body, which in A. fasciatus are concentrated in lateral bands, and in A. silvaticus are evenly scattered. Animals were raised individually under the same conditions, while they laid eggs as a consequence of selfing. This F 1 generation was afterwards divided into two groups, which were fed with different food items. A diet of carrot, lettuce or paper had no effect on the distribution of the yellow-orange granules in A. silvaticus , but provoked a loss of the yellow-orange lateral bands in A. fasciatus so that externally these F 1 specimens became similar to A. silvaticus . In both species, a diet of nettle resulted in a strong yellow-orange pigmentation, which often formed yellow-orange lateral bands. These results indicate that food can probably influence the 'species-specific' body pigmentation in Carinarion, and thus question the reliability of colour traits to distinguish A. silvaticus and A. fasciatus .
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    ABSTRACT: Allozyme analyses of the hermaphroditic slugs Arion (Carinarion) fasciatus, A. (C.) circumscriptus and A. (C.) silvaticus have suggested that the three species in North America and north-west Europe predominantly reproduce uniparentally, most probably by selfing. We used allozyme electrophoresis to investigate the population genetic structure of these species throughout a larger part of their native European distribution. Our results show that the previously reported "species" specific allozyme markers are no longer valid if populations from central Europe are investigated, and A. fasciatus and A. silvaticus appear to be "paraphyletic" taxa. In contrast to the general belief that selfing organisms show low gene diversities, the high selfing rates in N-NE European Carinarion do not necessarily result in low gene diversities. Moreover, our data suggest a geographical pattern in the prevalence of outcrossing, at least in A. fasciatus, with selfing in N-NE Europe and a mixed breeding system (i.e. selfing and outcrossing) in central Europe. Possible scenarios for the disjunct distribution of breeding systems in Carinarion are discussed.
    Heredity 01/2001; · 4.11 Impact Factor
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    ABSTRACT: The phenetic analysis of non-nodulatingAcacia species by Harrier et al. (1997) was repeated to illustrate how different computer programs may generate alternative UPGMA trees for the very same data, even in the absence of data input order effects (ties). For example, all Harrier et al.'s UPGMA dendrograms produced by software from the Scottish Agricultural Statistics Service differed from those obtained by the packages NTSYS and MVSP87. Particularly, the positions ofA. albida, A. rovumae, andA. pentagona, as well as the relationships betweenDiacanthae andTriacanthae were affected by this phenomenon. Hence, whenever clustering techniques are used, care should be taken to consider possible software-dependent caveats and artefacts. Nevertheless, all programs provided clusterings that largely coincided with the subgeneric and sectional groupings proposed by Vassal (1972) although the positions of some species varied depending on whether morphological or molecular data were considered (e.g.A. albida andA. rovumae).
    Plant Systematics and Evolution 01/2000; 220(3):139-146. · 1.31 Impact Factor