fernando ibarra - Profile on Academia.edu (original) (raw)

Papers by fernando ibarra

Digestive Diseases and Sciences, 1988

Previous studies of blood volume (BV) in cirrhosis have either not adjusted BV properly for body ... more Previous studies of blood volume (BV) in cirrhosis have either not adjusted BV properly for body size; determined plasma volume from the dilution of labeled albumin 10–20 min postinjection, when some extravascular redistribution has already occurred; and/or not used the correct whole body-peripheral hematocrit ratio (0.82) in calculating whole BV from plasma volume and the peripheral hematocrit. We measured BV with attention to these considerations in 19 patients with cirrhosis and reexamined the determinants of vascular volume and the relationship between vascular volume and sodium retention. BV was calculated as plasma volume (determined from extrapolated plasma activity of intravenously injected [131I]+albumin at time 0) divided by (peripheral hematocrit × 0.82). The result was expressed per kilogram “dry” body weight, determined by subtracting the mass of ascites (measured by isotope dilution; 1 liter=1 kg) from the actual body weight of nonedematous patients. Measured and expressed in this way, BV correlated strongly with esophageal variceal size (r=0.87, P

Proceedings of The National Academy of Sciences, 2009

Orchids employing sexual deceit attract males of their pollinator species through specific volati... more Orchids employing sexual deceit attract males of their pollinator species through specific volatile signals that mimic female-released sex pheromones. One of these signals proved to be 2-ethyl-5propylcyclohexan-1,3-dione (chiloglottone1), a new natural product that was shown to be most important in the relations between orchids of the genus Chiloglottis, native to Australia, and corresponding pollinator species. Systematic investigations on the mass spectrometric fragmentation pattern of 2,5-dialkylcyclohexan-1,3diones identified key ions providing information about the structures of the substituents at positions 2 and 5. Results enabled us to identify 2-ethyl-5-pentylcyclohexan-1,3-dione (chiloglottone2) and 2-butyl-5-methylcyclohexan-1,3-dione (chiloglottone3) as new natural products that play a decisive role in the pollination syndrome of some Chiloglottis species. During field bioassays, pure synthetic samples of chiloglottone1-3 or mixtures thereof proved to be attractive to the corresponding orchid pollinators. Because of their likely biogenesis from ubiquitous fatty acid precursors, 2,5dialkylcyclohexan-1,3-diones may represent a hitherto overlooked, widespread class of natural products.

Chemoecology, 2000

The dulotic queen ant, Polyergus rufescens, must first penetrate a host colony and kill the resid... more The dulotic queen ant, Polyergus rufescens, must first penetrate a host colony and kill the resident queen in order to successfully founding a new colony. Successful usurpation by a newly mated queen predictably depends on a dual strategy. Although, it can sneak in by being ''chemically insignificant'' with respect to cuticular hydrocarbons, it may also need to deter prospective host-worker aggressors. Chemical analysis of Dufour's gland secretion of P. rufescens queens and workers by GS/MS revealed that queen secretion is typified by esters of butanoic acid and acetic acid, of which decyl butanoate comprises over 80%. Butanoates and acetates are also present in the workers' secretion, but these are of higher molecular weight, and octadecyl butanoate represents the major compound. Using synthetic mixtures of queen and worker Dufour's gland, we tested the hypothesis that these secretions modify the aggressive behavior of the host species Formica cunicularia. The queen-like synthetic mixture significantly reduced aggression of the host workers towards alien conspecifics, but neither pentane nor the worker-like synthetic mixture showed this effect. Although Dufour's gland content of Polyergus queens was suggested to function as an appeasement pheromone , we hypothesized that it may in fact act as a repellent. In order to test this hypothesis we exposed starved F. cunicularia workers to a droplet of honey on a glass slide applied with one of the following compounds: decyl butanoate (queen major compound), octadecyl butanoate (worker main compound), limonene (a reported ant repellent), and pentane (solvent control). Of these, the workers were repelled only by the decyl butanoate and did not approach the honey. We conclude that during usurpation the queen actively repels aggressive workers by emitting Dufour's gland repellent, comprising the alternative tactic in the usurpation dual strategy. This represents another chemical weapon in the diverse arsenal used by parasites to overcome the host's resistance.

Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2003

The bumblebee Bombus (Psithyrus) norvegicus Sp.-Schn. is an obligate social parasite of B. (Pyrob... more The bumblebee Bombus (Psithyrus) norvegicus Sp.-Schn. is an obligate social parasite of B. (Pyrobombus) hypnorum L. Behavioural observations indicated that nest-invading B. norvegicus females may use allomones to defend themselves against attacking host workers. However, so far no defensive chemicals used by social parasitic bumblebee females have been identified. We analysed volatile constituents of the cuticular lipid profile of B. norvegicus females. Furthermore, we performed electrophysiological studies and behavioural experiments in order to identify possible chemical weapons. Coupled gas chromatography-electroantennography showed 15 compounds to trigger responses in antennae of the host workers. Using gas chromatography–mass spectrometry, the main compound among the cuticular volatiles of B. norvegicus females was found to be dodecyl acetate. A corresponding mixture of synthetic volatiles as well as pure dodecyl acetate showed a strong repellent effect on starved host workers. B. norvegicus females use dodecyl acetate to repel attacking B. hypnorum workers during nest usurpation and subsequently during colony development. Dodecyl acetate is the first repellent allomone identified in bumblebees.

Behavioral Ecology and Sociobiology, 2001

The role of Dufour's gland secretion as an egg discriminator pheromone was reevaluated by simulta... more The role of Dufour's gland secretion as an egg discriminator pheromone was reevaluated by simultaneously exposing workers to two combs, one containing queen- or worker-laid eggs and the second containing treated or untreated worker-laid eggs. Treatments included extracts of Dufour's gland secretion as well as the synthetic esters that were identified in the secretion. Policing was clearly detected both in queenright and queenless colonies by the swift removal of worker, but not of queen eggs. However, neither the glandular secretion nor its synthetic ester constituents were able to protect worker-born eggs from policing. Treated worker eggs were removed significantly faster than queen eggs, and at the same rate as non-treated worker eggs. These results are not consistent with the hypothesis that the secretion serves as an egg-marking pheromone. Chemical analyses of the queen abdominal tips revealed the presence of Dufour's esters, indicating that the glandular secretion oozes out and spreads over the cuticle around the genital chamber. However, contamination while ovipositing may also explain the minute amounts of these esters that were detected on the egg surface. Dufour's gland caste-specific composition suggests that in queens it may constitute a signal that plays a role in queen-worker interactions. Attraction bioassays revealed that the queen secretion, but not that of workers, is very attractive to workers. When applied either on a glass slide or on another worker, a retinue formed around the "surrogate queen". We conclude that Dufour's gland secretion constitutes part of a complex queen signal that is the basis for the social integrity of the honeybee colony.

Identification of Queen Sex Pheromone Components of the Bumblebee Bombus terrestris

Journal of Chemical Ecology, 2006

We investigated the origin and chemical composition of the queen sex pheromone of the primitively... more We investigated the origin and chemical composition of the queen sex pheromone of the primitively eusocial bumblebee, Bombus terrestris (Apidae). Physiologically and behaviorally active compounds were identified by coupled gas chromatography electroantennography (GC-EAD), gas chromatography-mass spectrometry (GC-MS), and laboratory behavioral tests. In the behavioral assays, virgin queens frozen previously at −20°C were highly attractive to males. Dummies impregnated with surface and cephalic extracts obtained from virgin queens that had been frozen at −50°C were more attractive to males than odorless dummies. Male mating behavior was stimulated by components of cephalic secretions that are smeared onto the cuticle surface by the queen. Overall, 21 compounds present in surface and cephalic extracts evoked electroantennographic responses in male antennae. These included saturated and unsaturated fatty acids, ethyl- and methyl esters of the fatty acids, heptacosene, 2-nonanone, and geranyl geraniol. A blend of synthetic versions of these compounds elicited typical male mating behavior. Since solvent-impregnated dummies were approached by the males, but did not release copulatory behavior, visual cues may be important in the initial step of stimulating male mating behavior. Close-range olfactory signals are more important for releasing male mating behavior as well as for species recognition. In further behavioral assays, the attractiveness of a frozen virgin queen decreased as the storage time at −20°C increased from 2 hr to 1 d. Therefore, the chemical composition of the sex pheromone may change during freezing as behaviorally active compounds may decompose.

Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2000

We investigated the female-produced sex pheromone of the solitary bee Andrena nigroaenea and comp... more We investigated the female-produced sex pheromone of the solitary bee Andrena nigroaenea and compared it with floral scent of the sexually deceptive orchid Ophrys sphegodes which is pollinated by Andrena nigroaenea males. We identified physiologically and behaviorally active compounds by gas chromatography with electroantennographic detection, gas chromatography-mass spectrometry, and behavioral tests in the field. Dummies scented with cuticle extracts of virgin females or of O.sphegodes labellum extracts elicited significantly more male reactions than odorless dummies. Therefore, copulation behavior eliciting semiochemicals are located on the surface of the females' cuticle and the surface of the flowers. Within bee and orchid samples, n-alkanes and n-alkenes, aldehydes, esters, all-trans-farnesol and all-trans-farnesyl hexanoate triggered electroantennographic responses in male antennae. Most of the alkanes and alkenes occurred in similar patterns both in the bees and orchids. O. sphegodes leaf extracts contained mostly the same compounds but in different proportions. In behavioral tests with synthetic compounds, blends of alkenes triggered significantly more approaches and pounces of the males whereas alkanes were not more attractive than odorless dummies. Since alkanes and alkenes together were most attractive, we conclude they constitute the bees' sex pheromone as well as the pseudocopulation-behavior releasing orchid-odor bouquet.

Oikos, 2002

fstedt, C. 2002. Odour-mediated nectar foraging in the silver Y moth, Autographa gamma (Lepidopte... more fstedt, C. 2002. Odour-mediated nectar foraging in the silver Y moth, Autographa gamma (Lepidoptera: Noctuidae): behavioural and electrophysiological responses to floral volatiles. -Oikos 99: 75 -82.

Evolution, 2000

The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee An... more The orchid Ophrys sphegodes Miller is pollinated by sexually excited males of the solitary bee Andrena nigroaenea, which are lured to the flowers by visual cues and volatile semiochemicals. In O. sphegodes, visits by pollinators are rare. Because of this low frequency of pollination, one would expect the evolution of strategies that increase the chance that males will visit more than one flower on the same plant; this would increase the number of pollination events on a plant and therefore the number of seeds produced. Using gas chromatography-mass spectrometry (GC-MS) analyses, we identified more than 100 compounds in the odor bouquets of labellum extracts from O. sphegodes; 24 compounds were found to be biologically active in male olfactory receptors based on gas chromatography with electroantennographic detection (GC-EAD). Gas chromatography (GC) analyses of odors from individual flowers showed less intraspecific variation in the odor bouquets of the biologically active compounds as compared to nonactive compounds. This can be explained by a higher selective pressure on the pollinator-attracting communication signal. Furthermore, we found a characteristic variation in the GC-EAD active esters and aldehydes among flowers of different stem positions within an inflorescence and in the n-alkanes and n-alkenes among plants from different populations. In our behavioral field tests, we showed that male bees learn the odor bouquets of individual flowers during mating attempts and recognize them in later encounters. Bees thereby avoid trying to mate with flowers they have visited previously, but do not avoid other flowers either of a different or the same plant. By varying the relative proportions of saturated esters and aldehydes between flowers of different stem positions, we demonstrated that a plant may take advantage of the learning abilities of the pollinators and influence flower visitation behavior. Sixty-seven percent of the males that visited one flower in an inflorescence returned to visit a second flower of the same inflorescence. However, geitonogamy is prevented and the likelihood of cross-fertilization is enhanced by the time required for the pollinium deposited on the pollinator to complete its bending movement, which is necessary for pollination to occur. Cross-fertilization is furthermore enhanced by the high degree of odor variation between plants. This variation minimizes learned avoidance of the flowers and increases the likelihood that a given pollinator would visit several to many different plants within a population.

Proceedings of The Royal Society B: Biological Sciences, 2003

Ophrys flowers mimic virgin females of their pollinators, and thereby attract males for pollinati... more Ophrys flowers mimic virgin females of their pollinators, and thereby attract males for pollination. Stimulated by scent, the males attempt to copulate with flower labella and thereby ensure pollination. Here, we show for the first time, to our knowledge, that pollinator attraction in sexually deceptive orchids may be based on a few specific chemical compounds. Ophrys speculum flowers produce many volatiles, including trace amounts of (w -1)-hydroxy and (w -1)-oxo acids, especially 9-hydroxydecanoic acid. These compounds, which are novel in plants, prove to be the major components of the female sex pheromone in the scoliid wasp Campsoscolia ciliata, and stimulate male copulatory behaviour in this pollinator species. The specificity of the signal depends primarily on the structure and enantiomeric composition of the oxygenated acids, which is the same in wasps and in the orchids. The overall composition of the blend differs significantly between the orchid and its pollinator and is of secondary importance. 9-Hydroxydecanoic acid is a rarely occurring compound that until now has been identified only in honeybees. Contrary to the standard hypothesis that Ophrys flowers produce only 'second-class attractivity compounds' and are neglected once the pollinator females are present, we show that flowers are more attractive to the males than are their own females.