Speciation in sexually deceptive orchids: pollinator-driven selection maintains discrete odour phenotypes in hybridizing species

Ophrys orchids mimic the female sex pheromones of their pollinator species to attract males for pollination. Reproductive isolation in Ophrys is based on the selective attraction of only a single pollinator species. A change of floral odour can result in the attraction of a new pollinator species that acts as an isolation barrier towards other sympatrically occurring Ophrys species. Ophrys lupercalis, Ophrys bilunulata, and Ophrys fabrella grow sympatrically and bloom consecutively on Majorca and are pollinated by three species of Andrena. We investigated variation of phenotypic and genotypic flower traits, aiming to study the role of the floral odour for reproductive isolation and speciation. Using chemical and electrophysiology (gas chromatography coupled with an electroantennographic detector) methods, we show that the three Ophrys species use the same odour compounds for pollinator attraction, but in different proportions. A comparison of the floral odour bouquets in a multivariate analysis revealed a clear grouping of plants from the same species, although with an overlap between species. A comparison of the same plants using molecular markers gave a contrasting result. Although O. lupercalis and O. fabrella were genetically well separated, plants of O. bilunulata did not form a distinct group but were similar to either O. lupercalis or O. fabrella. Our data indicate gene flow and hybridization to occur between O. bilunulata and O. lupercalis as well as between O. bilunulata and O. fabrella. All plants of O. bilunulata, despite having different genotypes, showed a very similar floral odour. This reflects a strong selective pressure by the pollinating males. The overlap of genotypes of O. bilunulata and O. fabrella supports our hypothesis that O. fabrella diverged from O. bilunulata by scent variation and the attraction of a new pollinator species, Andrena fabrella. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 439–451.     

The Arabidopsis Xylem Peptidase XCP1 Is a Tracheary Element Vacuolar Protein That May Be a Papain Ortholog

XCP1 is a xylem-specific papain-like cysteine peptidase in Arabidopsis. To determine whether XCP1 could be involved in tracheary element autolysis, promoter activity and localization of XCP1 were investigated using XCP1 promoter-beta-glucuronidase fusions and immunofluorescence confocal microscopy. A tracheary element expression pattern was detected for XCP1. Results from confocal microscopy and biochemical subcellular fractionation indicated that XCP1 was localized in the vacuole. Ectopic expression of XCP1 resulted in a reduction in plant size in some lines and early leaf senescence, as indicated by early loss of leaf chlorophyll. Reduced plant size was correlated with higher levels of XCP1, as shown by immunoblot and peptidase activity gel analyses. The XCP1 prodomain exhibits exceptionally high similarity (greater than 80%) to the prodomains of papain and other papain-like enzymes isolated from papaya (Carica papaya) laticifers when compared with all other reported papain-like enzymes. The potential for XCP1 and papain to perform common functions as catalysts of autolytic processing following cell death due to programmed suicide or to wounding is discussed.     

A theory of follicle selection: II. Computer simulation of estradiol administration in the primate

A theory of follicle selection (Lacker, 1981) is tested in the primate by simulating the effects of estradiol administration at different times, strengths, and durations during the follicular phase of the menstrual cycle (Clark et al., 1981; Zeleznik, 1981; Dierschke et al., 1985). The theory can account for the observed atretogenic effects of circulating estradiol on follicle development including full, partial, and delayed atresia of the dominant follicle (Dierschke et al., 1985) and can explain why similar estradiol doses achieve different qualitative effects when given at different times during the cycle. The theory predicts that recovery from early atresia may be possible, and it can also account for the loss of control in the number of maturing follicles that has been observed when estradiol antibodies are given in the midfollicular phase (Zeleznik et al., 1985). These results support the hypothesis that the selection mechanism in the primate is a consequence of feedback involving an essentially equipotent follicle population interacting through circulating estradiol and pituitary gonadotropins. A quantitative test of the theory awaits experimental identification of the maturation surfaces that are predicted by it. An experimental design for this purpose is proposed.     

Bioactive compounds produced by cyanobacteria

Cyanobacteria produce a large number of compounds with varying bioactivities. Prominent among these are toxins: hepatotoxins such as microcystins and nodularins and neurotoxins such as anatoxins and saxitoxins. Cytotoxicity to tumor cells has been demonstrated for other cyanobacterial products, including 9-deazaadenosine, dolastatin 13 and analogs. A number of compounds in cyanobacteria are inhibitors of proteases — micropeptins, cyanopeptolins, oscillapeptin, microviridin, aeruginosins- and other enzymes, while still other compounds have no recognized biological activities. In general cyclic peptides and depsipeptides are the most common structural types, but a wide variety of other types are also found: linear peptides, guanidines, phosphonates, purines and macrolides. The close similarity or identity in structures between cyanobacterial products and compounds isolated from sponges, tunicates and other marine invertebrates suggests the latter compounds may be derived from dietary or symbiotic blue-green algae.