[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 .
Full-text · Article · May 2001 · Journal of Molluscan Studies
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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).
[Show abstract][Hide abstract] ABSTRACT: We investigated genetic differentiation among 8 populations of the protected damselfly Lestes viridis (Vander Linden, 1825) in permanent ponds in northern Belgium by means of allozyme electrophoresis and isoelectric focusing, and estimated levels of gene flow using F-statistics. In addition, we did a capture-mark-recapture experiment to estimate direct levels of gene flow. Our aim was to test whether populations of L. viridis represented a single, large panmictic population or formed a series of demographically isolated populations, which may be defined as appropriate management units (MU). None of the marked individuals moved among the ponds, indicating a strong fidelity for adults to their breeding pond. Only 1 population was genetically strongly differentiated, whereas little or no differentiation was observed among the 7 other ponds. Absence of adult dispersal but genetic homogeneity between ponds thus suggested substantial teneral dispersal. We observed large heterozygote deficiencies at 2 loci (Fdh and Est). Significant differences in allele frequencies among ponds suggests that populations of L,. viridis in northern Belgium may consist of >1 MU. Management plans for conservation should therefore take into consideration the presence of several MUs in this species.
No preview · Article · Jun 2000 · Journal of the North American Benthological Society