Natural allelic variation at seed size loci in relation to other life history traits of Arabidopsis thaliana.
We have analyzed two Arabidopsis strains differing in the mean seed size and seed number they produced. The accession Cape Verde Islands (Cvi) yielded on average about 40% fewer seeds than the laboratory strain Landsberg erecta (Ler), but Cvi seeds were almost twice as heavy. Maternal and nonmaternal genetic factors were involved in the seed size variation, and interactions between both types of factors presumably occurred. The Ler/Cvi seed size difference increased through seed development from ovule maturation until seed desiccation, suggesting that multiple processes of seed development were affected. In addition, it involved changes in the final cell number and cell size of the seed coat and the embryo. Cell number variation was controlled mainly by maternal factors, whereas nonmaternal allelic variation mostly affected cell size. By using a recombinant inbred line population derived from Ler and Cvi, we mapped quantitative trait loci (QTLs) affecting 12 life history traits related to seed size, fruit size, seed number, and plant resources. Five of the seed size QTLs colocated with QTLs for other traits, suggesting that they control seed size via maternal components affecting ovule number and/or carpel development, ovule development, or reproductive resource allocation in the mother plant. The six remaining putative seed size QTLs did not show a significant effect on any other trait, suggesting that this allelic variation may be involved specifically in seed development processes. (+info)
Molecular evidence for multiple origins of woodiness and a new world biogeographic connection of the Macaronesian island endemic Pericallis (Asteraceae: senecioneae).
The prevalence of woody species in oceanic islands has attracted the attention of evolutionary biologists for more than a century. We used a phylogeny based on sequences of the internal-transcribed spacer region of nuclear ribosomal DNA to trace the evolution of woodiness in Pericallis (Asteraceae: Senecioneae), a genus endemic to the Macaronesian archipelagos of the Azores, Madeira, and Canaries. Our results show that woodiness in Pericallis originated independently at least twice in these islands, further weakening some previous hypotheses concerning the value of this character for tracing the continental ancestry of island endemics. The same data suggest that the origin of woodiness is correlated with ecological shifts from open to species-rich habitats and that the ancestor of Pericallis was an herbaceous species adapted to marginal habitats of the laurel forest. Our results also support Pericallis as closely related to New World genera of the tribe Senecioneae. (+info)
Evolutionary novelties in islands: Drosophila santomea, a new melanogaster sister species from Sao Tome.
The finding of new melanogaster sister species may help us in understanding more about how the emergence of genetic novelties, particularly in insular habitats, can result in speciation. Here we report on the discovery of Drosophila santomea, which is the first melanogaster sibling found off West-equatorial Africa, on Sao Tome, one of the Gulf of Guinea islands. Although the eight other melanogaster sister species are remarkably conservative in their morphology except for their terminalia, the new find has a morphological trait distinguishing it from all of these: a pure yellow body coloration of both sexes without the normal black abdominal banding. Evidence from the terminalia, polytene and mitotic chromosomes, period gene and allozymes are provided indicating that it is nonetheless the nearest relative of Drosophila yakuba with which it coexists on the island. The new find is a clear-cut taxon as shown by the production of sterile male hybrids, eventually with developmental defects, in both directions of cross with yakuba and by the existence of an altitudinal divide accompanied by a hybrid zone at mid-elevation on the island. Molecular and karyotypic data further support this conclusion. In contrast to the significant divergence of their nuclear DNAs, an intriguing similarity in their cytochrome b sequences was observed indicating a recent coalescence common to santomea, yakuba and also teissieri cytoplasms. These were shown to harbour the same Wolbachia endosymbiotic bacteria which could possibly be responsible for mitochondrial DNA hitchhiking across the species barrier. (+info)
Open-sea migration of magnetically disturbed sea turtles.
Green turtles (Chelonia mydas) that shuttle between their Brazilian feeding grounds and nesting beaches at Ascension Island in the middle of the Atlantic Ocean are a paradigmatic case of long-distance oceanic migrants. It has been suggested that they calculate their position and the direction of their target areas by using the inclination and intensity of the earth's magnetic field. To test this hypothesis, we tracked, by satellite, green turtles during their postnesting migration from Ascension Island to the Brazilian coast more than 2000 km away. Seven turtles were each fitted with six powerful static magnets attached in such a way as to produce variable artificial fields around the turtle that made reliance on a geomagnetic map impossible. The reconstructed courses were very similar to those of eight turtles without magnets that were tracked over the same period and in the previous year, and no differences between magnetically disrupted and untreated turtles were found as regards navigational performance and course straightness. These findings show that magnetic cues are not essential to turtles making the return trip to the Brazilian coast. The navigational mechanisms used by these turtles remain enigmatic. (+info)
mtDna and the islands of the North Atlantic: estimating the proportions of Norse and Gaelic ancestry.
A total of 1,664 new mtDNA control-region sequences were analyzed in order to estimate Gaelic and Scandinavian matrilineal ancestry in the populations of Iceland, Orkney, the Western Isles, and the Isle of Skye and to investigate other aspects of their genetic history. A relative excess of private lineages in the Icelanders is indicative of isolation, whereas the scarcity of private lineages in Scottish island populations may be explained by recent gene flow and population decline. Differences in the frequencies of lineage clusters are observed between the Scandinavian and the Gaelic source mtDNA pools, and, on a continent-wide basis, such differences between populations seem to be associated with geography. A multidimensional scaling analysis of genetic distances, based on mtDNA lineage-cluster frequencies, groups the North Atlantic islanders with the Gaelic and the Scandinavian populations, whereas populations from the central, southern, and Baltic regions of Europe are arranged in clusters in broad agreement with their geographic locations. This pattern is highly significant, according to a Mantel correlation between genetic and geographic distances (r=.716). Admixture analyses indicate that the ancestral contributions of mtDNA lineages from Scandinavia to the populations of Iceland, Orkney, the Western Isles, and the Isle of Skye are 37.5%, 35.5%, 11.5%, and 12.5%, respectively. (+info)
Mannose-binding lectin polymorphisms in a Canary Islands (Spain) population.
We have compared the structural and promoter variants of the mannose-binding lectin (MBL) gene in a population from Gran Canaria with that from other populations previously reported. The observed frequencies of the seven alleles of the MBL gene in our population were: HYPA, 0.24; LYQA, 0.22; LYPA, 0.08; LXPA, 0.19; LYPB, 0.17; LYQC, 0.03 and HYPD, 0.07. The frequency of non-producer alleles and of MBL-deficient individuals in our population is higher than in other European and Asian population. (+info)
Genetic diversity of the Macaronesian leafy liverwort Porella canariensis inferred from RAPD markers.
Plant colonization of the North Atlantic raises the intriguing question of the relationships between extant island species with their continental counterparts (European, African, and American), which may provide clues to past geographic distribution and colonization history. It has been suggested that during past glaciations, many plant species with typical Mediterranean distributions survived in the Atlantic islands that belong to what is today known as Macronesia. We used random amplified polymorphic DNA (RAPD) markers to study 12 populations of the liverwort Porella canariensis partly covering its present-day distribution (Azores, Madeira, Canary and Cape Verde Islands, and Iberian Peninsula). Unweighted pair-group (UPGMA) and principal component (PCO) analyses showed a similar geographical pattern that suggested a close relationship between Iberian populations and those from the Canaries and Cape Verde Islands. Populations from Madeira had more genetic variation than those from the Azores, a result from either a richer diversity of habitats in Madeira, which prompted more population diversification, successive colonization waves from different origins, or an older colonization of Madeira. The data show that continuous patches of liverworts are often comprised of more than one individual. Finally, RAPDs can be used to investigate intraspecific diversity within a comparatively large geographic area and, with utmost care, can be used to infer a historic context to explain the patterns observed. (+info)
Linkage disequilibrium and demographic history of the isolated population of the Faroe Islands.
The isolated population of the Faroe Islands has a history of recent expansion after being limited to a small size for centuries. Such an isolated population may be ideal for linkage disequilibrium mapping of disease genes if linkage disequilibrium (LD) extends over large regions. Analyses of 18 markers on 12q24.3, spanning a region of 4.3 Mb (16 cM), revealed extensive LD in the Faroese population. Maximum LD was found between marker pairs separated by more than 3.8 Mb. The same region had a maximum LD of only 1.2 and 1.4 Mb respectively in two outbred Danish and British populations analysed here for comparison. The analyses of gene diversity excess at 15 unlinked microsatellite markers did not reveal any sign of a severe bottleneck to have occurred within approximately 1200 years' history of the Faroese population. The extensive LD in this population may, therefore, have arisen primarily by random genetic drift. The implications for future gene mapping studies are discussed. (+info)