The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant

The location and timing of domestication of the olive tree, a key crop in Early Mediterranean societies, remain hotly debated. Here, we unravel the history of wild olives (oleasters), and then infer the primary origins of the domesticated olive. Phylogeography and Bayesian molecular dating analyses based on plastid genome profiling of 1263 oleasters and 534 cultivated genotypes reveal three main lineages of pre-Quaternary origin. Regional hotspots of plastid diversity, species distribution modelling and macrofossils support the existence of three long-term refugia; namely the Near East (including Cyprus), the Aegean area and the Strait of Gibraltar. These ancestral wild gene pools have provided the essential foundations for cultivated olive breeding. Comparison of the geographical pattern of plastid diversity between wild and cultivated olives indicates the cradle of first domestication in the northern Levant followed by dispersals across the Mediterranean basin in parallel with the expansion of civilizations and human exchanges in this part of the world.     

Convergent evolution of floral signals underlies the success of Neotropical orchids

The great majority of plant species in the tropics require animals to achieve pollination, but the exact role of floral signals in attraction of animal pollinators is often debated. Many plants provide a floral reward to attract a guild of pollinators, and it has been proposed that floral signals of non-rewarding species may converge on those of rewarding species to exploit the relationship of the latter with their pollinators. In the orchid family (Orchidaceae), pollination is almost universally animal-mediated, but a third of species provide no floral reward, which suggests that deceptive pollination mechanisms are prevalent. Here, we examine floral colour and shape convergence in Neotropical plant communities, focusing on certain food-deceptive Oncidiinae orchids (e.g. Trichocentrum ascendens and Oncidium nebulosum) and rewarding species of Malpighiaceae. We show that the species from these two distantly related families are often more similar in floral colour and shape than expected by chance and propose that a system of multifarious floral mimicry—a form of Batesian mimicry that involves multiple models and is more complex than a simple one model–one mimic system—operates in these orchids. The same mimetic pollination system has evolved at least 14 times within the species-rich Oncidiinae throughout the Neotropics. These results help explain the extraordinary diversification of Neotropical orchids and highlight the complexity of plant–animal interactions.     

Molecular phylogenetic investigations of Bulinus (Gastropoda: Planorbidae) in Lake Malawi with comments on the topological incongruence between DNA loci

Freshwater snails of the genus Bulinus, subfamily Bulininae, are widespread in Africa and the Middle East. Several species are intermediate hosts for schistosomes, mammalian blood flukes that cause schistosomiasis. The genus is split into four species groups and without recourse to further molecular DNA studies, phylogenetic relationships within and between species‐groups remain obscure. For example, the Bulinus truncatus/tropicus species complex, which cannot be adequately defined with morphological characters, appears to be monophyletic but increased taxon sampling is warranted for confirmation when this group appears to contain species with limited sequence divergence in either mitochondrial 16S rRNA or Cytochome Oxidase subunit I (COI) loci. In the present study, taxonomic sampling is increased through addition of several taxa, including B. nyassanus and B. succinoides both endemic to Lake Malawi. From DNA analyses, these two species appear basal within the B. truncatus/tropicus species complex which provides an interesting evolutionary insight into its origins. The relationship of the B. truncatus/tropicus species complex with the three other groups, however, is more problematic as incongruence between loci and computational methodologies exist. This phenomenon is likely due to mutational saturation of the COI as evidenced by the transition : transversion ratio which also results in placement of the discoidal Indoplanorbis exustus, a member of the Bulininae, within the ingroup. To resolve these more basal incongruencies between species groups inspection of more evolutionary conserved molecular loci is needed, for example, the nuclear histone H3 gene, and 18S and 28S rDNA. Louise V. Gersdorff Jørgensen, Thomas K. Kristensen and Henry Madsen, The Mandahl‐Barth Research Centre for Biodiversity and Health, DBL — Centre for Health Research and Development, Department of Veterinary Pathobiology, Faculty of Life Sciences, University of Copenhagen, Jægersborg Allé 1D, DK‐2920 Charlottenlund, Denmark. E‐mails: lgj@life.ku.dk , tkk@life.ku.dk , hmad@life.ku.dk J. Russell Stothard, Biomedical Parasitology Division, Department of Zoology, Natural History Museum, Cromwell Road, London SW7 5BD, UK. E‐mail: R.Stothard@nhm.ac.uk     

DNA barcoding as a heuristic tool for classifying undescribed Nearctic Myrmica ants (Hymenoptera: Formicidae)

The Palearctic species of the ant genus Myrmica are well studied. In contrast, the taxonomy of the Nearctic species is outdated, making identification impossible. We collected Myrmica samples in the Holarctic and investigated their diversity using mtDNA data. We analysed a barcode sequence of the Cytochrome Oxidase I gene for 57 Palearctic and 293 Nearctic Myrmica samples. We used sequences of known Palearctic species to search for Myrmica barcode patterns. All but one Palearctic species groups were recovered. The Nearctic diversity was much higher than known. We retrieved the punctiventris, crassirugis and incompleta groups, and established nine additional tentative species groups. Genetic distance analysis revealed a large overlap of intra- and inter-specific distances in Palearctic species and species groups. We could not find a variation gap to separate Nearctic sequences into species with COI data only. Variation in scape morphology divided two genetic groups further. Scape morphology correlated with most molecular groups, except three specimens. Our results illustrate that barcoding, using only a limited amount of genetic information, cannot serve as a universal proxy for taxonomy and species demarcation. It should be considered a first step in understanding the taxonomic diversity of an unknown group of organisms.     

Natural variation in MAM within and between populations of Arabidopsis lyrata determines glucosinolate phenotype

The genetic variation that underlies the glucosinolate phenotype of Arabidopsis lyrata ssp. petraea was investigated between and within populations. A candidate glucosinolate biosynthetic locus (MAM, containing methylthioalkylmalate synthase genes) was mapped in A. lyrata to a location on linkage group 6 corresponding to the homologous location for MAM in A. thaliana. In A. thaliana MAM is responsible for side chain elongation in aliphatic glucosinolates, and the MAM phenotype can be characterized by the ratios of long- to short-chain glucosinolates. A quantitative trait loci (QTL) analysis of glucosinolate ratios in an A. lyrata interpopulation cross found one QTL at MAM. Additional QTL were identified for total indolic glucosinolates and for the ratio of aliphatic to indolic glucosinolates. MAM was then used as the candidate gene for a within-population cosegregation analysis in a natural A. lyrata population from Germany. Extensive variation in microsatellite markers at MAM was found and this variation cosegregated with the same glucosinolate ratios as in the QTL study. The combined results indicate that both between- and within-population genetic variation in the MAM region determines phenotypic variation in glucosinolate side chains in A. lyrata.     

Neutral theory, phylogenies, and the relationship between phenotypic change and evolutionary rates

The neutral theory of molecular evolution predicts that rates of phenotypic change are largely independent from genotypic change. A recent study by Bromham et al. (2002) confirmed this expectation, finding no evidence for correlated phenotypic and molecular evolutionary rates in animals. We reevaluate this hypothesis, sampling at different taxonomic levels in plants and animals, using Bayesian inference to reconstruct phylogenetic trees and estimate rates of molecular evolution. We use independent contrasts in branch lengths to maximize the information extracted from each of the trees and nodal posterior probabilities to assess the influence of phylogenetic error. Our results indicate that in vascular plants between 2% and 11% of the variation in phenotypic rates of change can be explained by the rate of genotypic change. These results may be explained by the idea that processes that affect general evolutionary rates, such as body size, may also be expected to influence rates of morphological change.     

Note on a possible proarrhythmic property of antiarrhythmic drugs aimed at improving gap-junction coupling

Reduced conduction velocity (CV) in the myocardium is well known to increase the probability of arrhythmia and can be caused by structural changes, reduced excitability of individual myocytes, or decreased electrical coupling in the tissue. Recently, investigators have developed antiarrhythmic drugs that target the connections between individual myocytes with the goal of restoring tissue CV, specifically through increasing gap-junction coupling. In a simple but qualitatively relevant mathematical model, we show here that the introduction of a drug that improves intercellular conductance will indeed increase the CV. However, conditions that would require such a drug, such as fibrotic remodeling, may also increase the load of fibroblasts. Fibroblasts may couple to myocytes in much the same way as myocytes couple to each other, and therefore the use of such an agent may also improve coupling between myocytes and fibroblasts. We present numerical examples illustrating that when the load of coupled fibroblasts on myocytes is low or nonexistent, the drug works as expected, i.e., the drug increases CV. On the other hand, when the fibroblast load is high, changes in CV are nonmonotonic, i.e., the CV first increases and then decreases with an increase in dosage. The existence of coupled fibroblasts may therefore impair the effect of the drug, and under unfortunate conditions may be proarrhythmic.     

Towards decoding the conifer giga-genome

Several new initiatives have been launched recently to sequence conifer genomes including pines, spruces and Douglas-fir. Owing to the very large genome sizes ranging from 18 to 35 gigabases, sequencing even a single conifer genome had been considered unattainable until the recent throughput increases and cost reductions afforded by next generation sequencers. The purpose of this review is to describe the context for these new initiatives. A knowledge foundation has been acquired in several conifers of commercial and ecological interest through large-scale cDNA analyses, construction of genetic maps and gene mapping studies aiming to link phenotype and genotype. Exploratory sequencing in pines and spruces have pointed out some of the unique properties of these giga-genomes and suggested strategies that may be needed to extract value from their sequencing. The hope is that recent and pending developments in sequencing technology will contribute to rapidly filling the knowledge vacuum surrounding their structure, contents and evolution. Researchers are also making plans to use comparative analyses that will help to turn the data into a valuable resource for enhancing and protecting the world??s conifer forests.     

Flower colours along an alpine altitude gradient, seen through the eyes of fly and bee pollinators

Alpine flowers face multiple challenges in terms of abiotic and biotic factors, some of which may result in selection for certain colours at increasing altitude, in particular the changing pollinator species composition, which tends to move from bee-dominated at lower elevations to fly-dominated in high-alpine regions. To evaluate whether growing at altitude—and the associated change in the dominant pollinator groups present—has an effect on the colour of flowers, we analysed data collected from the Dovrefjell National Park in Norway. Unlike previous studies, however, we considered the flower colours according to ecologically relevant models of bee and fly colour vision and also their physical spectral properties independently of any colour vision system, rather than merely looking at human colour categories. The shift from bee to fly pollination with elevation might, according to the pollination syndrome hypothesis, lead to the prediction that flower colours should shift from more bee-blue and UV-blue flowers (blue/violet to humans, i.e. colours traditionally associated with large bee pollinators) at low elevations to more bee-blue-green and green (yellow and white to humans—colours often linked to fly pollination) flowers at higher altitude. However, although there was a slight increase in bee-blue-green flowers and a decrease in bee-blue flowers with increasing elevation, there were no statistically significant effects of altitude on flower colour as seen either by bees or by flies. Although flower colour is known to be constrained by evolutionary history, in this sample we also did not find evidence that phylogeny and elevation interact to determine flower colours in alpine areas. Handling editor: Neal Williams     

Local adaptation in European populations of Arabidopsis lyrata (Brassicaceae)

We studied local adaptation to contrasting environments using an organism that is emerging as a model for evolutionary plant biology-the outcrossing, perennial herb Arabidopsis lyrata subsp. petraea (Brassicaceae). With reciprocal transplant experiments, we found variation in cumulative fitness, indicating adaptive differentiation among populations. Nonlocal populations did not have significantly higher fitness than the local population. Experimental sites were located in Norway (alpine), Sweden (coastal), and Germany (continental). At all sites after one year, the local population had higher cumulative fitness, as quantified by survival combined with rosette area, than at least one of the nonlocal populations. At the Norwegian site, measurements were done for two additional years, and fitness differences persisted. The fitness components that contributed most to differences in cumulative fitness varied among sites. Relatively small rosette area combined with a large number of inflorescences produced by German plants may reflect differentiation in life history. The results of the current study demonstrate adaptive population differentiation in A. lyrata along a climatic gradient in Europe. The studied populations harbor considerable variation in several characters contributing to adaptive population differentiation. The wealth of genetic information available makes A. lyrata a highly attractive system also for examining the functional and genetic basis of local adaptation in plants.