Flight performance during hunting excursions in Eleonora's falcon Falco eleonorae.
(9/1367)
Among birds, falcons are high-performance flyers, in many cases adapted for aerial hunting and hence suitable targets for investigating limits to flight performance. Using an optical range finder, we measured flight tracks of Eleonora's falcon (Falco eleonorae), a species breeding in the Mediterranean region and specialised for hunting autumn passage bird migrants, when commuting between their nesting colony and offshore hunting areas (straight transportation flight) and when searching for prey (transecting and searching flight). Airspeed during searching flight was significantly slower than during straight transportation and transecting flight, but there was no significant difference in airspeed between the latter two flight modes. Straight transportation flight was significantly faster than predicted minimum power speed. Also, during straight transportation flight, the falcons responded to head- and tailwinds by increasing their airspeed when flying into the wind. However, they did not show any significant airspeed adjustments with respect to the angle between the track and the heading, as would be expected in birds trying to maintain a constant track direction. Mean sustainable climb rate (during (greater than or equal to) 240 s) was 1.4+/-0.31 m s-1 (mean +/- s.d., N=13), which is rather a high rate for a bird the size of an Eleonora's falcon. The climb rate was used to calculate maximum load-carrying capacity and maximum sustained horizontal flapping flight speed. The mean wingbeat frequency during powered climbing flight was 4.68 Hz, which was used to estimate the mass-specific muscle work. When falcons were leaving the colony for offshore hunting, they gained altitude by slope-soaring when there was an onshore wind. We formulated a simple criterion for the required gliding-flight rate of climb during an initial slope-soaring episode when minimizing the energy cost of reaching a certain altitude far out over the sea (which is where the prey is to be found). This climb rate was 0.36 m s-1, and our observations indicated that the falcons experienced climb rates above this value when soaring in slope-lift. (+info)
Association of visual objects and olfactory cues in Drosophila.
(10/1367)
Context-dependent preferences in a choice between an upper and a lower visual object of otherwise identical appearance were recorded during stationary flight of the fruitfly, Drosophila melanogaster, in a flight simulator. The test animal was held in a fixed orientation at the center of a wing-beat processor that converts attempted turns into counter-rotations of a surrounding cylindrical panorama. This allowed the fly to maneuver the preferred object into the actual direction of flight. Single flies were trained to avoid a course toward the visual object that had been associated with the aversive odor benzaldehyde (BAL). Conditioned object avoidance was investigated in different treatment groups by collective evaluation of the scores from 80 long-lasting flights (> 1 hr). In addition to a significant cross-modal association, we found a striking long-term effect of transient exposure to BAL both in the embryonic and larval states. The preimaginal experience significantly increased the indifference to BAL in the adult flies. Disturbed vision does not account for this effect: Neither the perception nor the discrimination of the visual objects was significantly impaired in the investigated flies. Disturbed olfaction could explain the present results. Recently, however, preimaginal BAL uptake has been found to interfere directly with the retention of heat-shock-conditioned object avoidance. (+info)
Conditioned visual flight orientation in Drosophila: dependence on age, practice, and diet.
(11/1367)
Orientation preferences for visual patterns can be conditioned in tethered flies (Drosophila melanogaster) at the flight simulator. In a reversal conditioning procedure using heat as reinforcement, flies can be trained to successively prefer different flight orientations with respect to the patterns. As in many learning paradigms, conditioned responses are highly variable. Although during training most flies reliably avoid the heat and the corresponding flight orientations, in subsequent learning tests without heat some show no consistent preference for the permissive orientations. We have started to investigate the interindividual differences in learning performance and describe here three significant variables: the age of the animals, their experience in the flight simulator prior to the experiment, and the composition of the fly food. Flies learn more reliably at 3-4 days than at 1-2 days of age but learning indices do not increase further in even older flies. Learning is improved if flies are allowed to become familiar with the flight simulator before the start of the conditioning procedure. Most important, poor nutrition causes complete amnesia within three or four generations. The reverse shift from poor to nutritious food restores learning ability with an even longer delay. (+info)
Behavioral analysis of Drosophila landmark learning in the flight simulator.
(12/1367)
Drosophila flies can be trained in the flight simulator to operantly avoid heat by choosing certain orientations relative to landmarks. Flies primarily store pattern orientations associated with the absence of heat. They readily escape from heat-associated orientations under the direct influence of the reinforcer but not in the subsequent memory tests. The flies tend to keep the largest possible distance from the "hot" or potentially "hot" regions, that is, they head toward the center of the "cold" sector. The results are discussed in the light of the retinotopic matching model explaining visual memory in flies by the superposition of a retinotopically stored template with the actual retinal image. Window experiments confining visual feedback to two 90 degrees sectors indicate that the memory template covers most of the visible space. (+info)
A direct screen identifies new flight muscle mutants on the Drosophila second chromosome.
(13/1367)
An ethyl methanesulfonate mutagenesis of Drosophila melanogaster was undertaken, and >3000 mutagenized second chromosomes were generated. More than 800 homozygous viable lines were established, and adults were screened directly under polarized light for muscle defects. A total of 16 mutant strains in which the indirect flight muscles were reduced in volume or disorganized or were otherwise abnormal were identified. These fell into seven recessive and one semidominant complementation groups. Five of these eight complementation groups, including the semidominant mutation, have been mapped using chromosomal deficiencies and meiotic recombination. Two complementation groups mapped close to the Myosin heavy chain gene, but they are shown to be in different loci. Developmental analysis of three mutations showed that two of these are involved in the early stages of adult myogenesis while the other showed late defects. This is the first report of results from a systematic and direct screen for recessive flight muscle defects. This mutant screen identifies genes affecting the flight muscles, which are distinct from those identified when screening for flightlessness. (+info)
Motion detection in insect orientation and navigation.
(14/1367)
The visual systems of insects are exquisitely sensitive to motion. Over the past 40 years or so, motion processing in insects has been studied and characterised primarily through the optomotor response. This response, which is a turning response evoked by the apparent movement of the visual environment, serves to stabilise the insect's orientation with respect to the environment. Research over the past decade, however, is beginning to reveal the existence of a variety of other behavioural responses in insects, that use motion information in different ways. Here we review some of the recently characterised behaviours, describe the inferred properties of the underlying movement-detecting processes, and propose modified or new models to account for them. (+info)
Mosquito hearing: sound-induced antennal vibrations in male and female Aedes aegypti.
(15/1367)
Male mosquitoes are attracted by the flight sounds of conspecific females. In males only, the antennal flagellum bears a large number of long hairs and is therefore said to be plumose. As early as 1855, it was proposed that this remarkable antennal anatomy served as a sound-receiving structure. In the present study, the sound-induced vibrations of the antennal flagellum in male and female Aedes aegypti were compared, and the functional significance of the flagellar hairs for audition was examined. In both males and females, the antennae are resonantly tuned mechanical systems that move as simple forced damped harmonic oscillators when acoustically stimulated. The best frequency of the female antenna is around 230 Hz; that of the male is around 380 Hz, which corresponds approximately to the fundamental frequency of female flight sounds. The antennal hairs of males are resonantly tuned to frequencies between approximately 2600 and 3100 Hz and are therefore stiffly coupled to, and move together with, the flagellar shaft when stimulated at biologically relevant frequencies around 380 Hz. Because of this stiff coupling, forces acting on the hairs can be transmitted to the shaft and thus to the auditory sensory organ at the base of the flagellum, a process that is proposed to improve acoustic sensitivity. Indeed, the mechanical sensitivity of the male antenna not only exceeds the sensitivity of the female antenna but also those of all other arthropod movement receivers studied so far. (+info)
Substitution of flight muscle-specific actin by human (beta)-cytoplasmic actin in the indirect flight muscle of Drosophila.
(16/1367)
The human (beta)-cytoplasmic actin differs by only 15 amino acids from Act88F actin which is the only actin expressed in the indirect flight muscle (IFM) of Drosophila melanogaster. To test the structural and functional significance of this difference, we ectopically expressed (beta)-cytoplasmic actin in the IFM of Drosophila that lack endogenous Act88F. When expression of the heterologous actin was regulated by approximately 1.5 kb of the 5' promoter region of the Act88F gene, little (beta)-cytoplasmic actin accumulated in the IFM of the flightless transformants. Including Act88F-specific 5' and 3' untranslated regions (UTRs) yielded transformants that expressed wild-type amounts of (beta)-cytoplasmic actin. Despite the assembly of (beta)-cytoplasmic actin containing thin filaments to which endogenous myosin crossbridges attached, sarcomere organization was deficient, leaving the transformants flightless. Rather than affecting primarily actin-myosin interactions, our findings suggest that the (beta)-cytoplasmic actin isoform is not competent to interact with other actin-binding proteins in the IFM that are involved in the organization of functional myofibrils. (+info)