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 distribution of micro-organisms through a bunded lagoon in Rutland Water

The distribution of micro-organisms entering a bunded lagoon in Rutland Water from a sewage effluent outflow was assayed. The majority of micro-organisms were found to settle out in the immediate vicinity of the effluent outflow. In this area micro-organisms, especially spore formers, were present in numbers exceeding 1 × 10⁶ organisms per gram of sediment. The lagoon lies within a nature reserve and a reduction in the reservoir water level could lead to contact between shore feeding waterfowl and pathogenic microorganisms in the freshly exposed sediment.     

Structure of sensilla trichodea of female Aedes aegypti with comments on innervation of antennal sensilla

On each antenna of female Aedes aegypti four types of sensilla trichodea are distinguishable: long and short, pointed-tipped ones and blunt-tipped types I and II. All types are innervated by two neurones, except the short, pointed-tipped trichodea with which only one neurone is associated. Both pointed-tipped types have unbranched dendrites and relatively thicker hair walls perforated by fewer pores than the blunt-tipped types. The long, pointed-tipped trichodea are 50–60 μm in length and the short ones 20 μm. In both blunt-tipped types the dendrites divide and the hair walls are perforated by numerous pores. Blunt-tipped type I trichodea are 20–40 μm in length and taper somewhat whereas the type II hairs are 11–13 μm in length, do not taper appreciably, and have exceedingly thin walls. All types of sensilla trichodea are olfactory receptors and the blunt-tipped type I are known to respond to repellents.An investigation of the possibility of axon fusion in the flagellar nerve gave negative results.Each flagellar nerve is composed of an estimated 2058 neurones. A majority of these, namely 93%, are involved in the recognition and discrimination of olfactory cues. Approximately 65% of the neurones respond to repellents, 5% to mechanical stimuli, and 2% to heat transferred by convection.     

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.