A conserved domain of alkaline phosphatase expression in the Malpighian tubules of dipteran insects.
(17/97)
Malpighian (renal) tubules are key components of the insect osmoregulatory system and show correspondingly great diversity in both number and length. Recently, the organisation of the Drosophila melanogaster tubule has been elucidated by enhancer trapping, and an array for functional properties has been shown to align with the functional domains. In Drosophila, there is a lower tubule domain, which coincides with expression of alkaline phosphatase and delineates the absorptive region of the tubule. Here, these observations are extended to three dipteran vectors of disease (Aedes aegypti, Anopheles stephensii and Glossina morsitans) and a non-dipteran out-group, Schistocerca gregaria (Orthoptera). Despite a huge range in cell number and size, alkaline phosphatase was found on the apical surface of the lower 10% of each of the dipteran tubules but nowhere within the orthopteran tubule. An alkaline phosphatase lower tubule domain is thus conserved among Diptera. Cell counts are also provided for each species. As in Drosophila, stellate cells are not found in the lower tubule domain of Anopheles or Aedes tubules, confirming the unique genetic identity of this domain. As previously reported, we failed to find stellate cells in Schistocerca but, remarkably, also failed to find them in Glossina, the dipteran most closely related to Drosophila. The orthodoxy that stellate cells are unique to, and general among, Diptera may thus require revision. (+info)
Karyotype, C- and G-band patterns and DNA content of Callimenus (=Bradyporus) macrogaster macrogaster.
(18/97)
Chromosomes and detailed karyotype information (the number, shape, relative length, arm ratio, centromeric index) of Callimenus (=Bradyporus) macrogaster macrogaster Lef. (Orthoptera: Tettigonioidea, Bradyporini) of Turkey belonging to the subfamily Bradyporinae are described. The diploid number of chromosomes was found to be 2n male symbol = 23, with 2 metacentric pairs, 2 submetacentric pairs, 6 acrocentric pairs. The X chromosome is metacentric. This species has a XX female symbol / X0 male symbol sex determining mechanism. The basic karyotype is complemented by a description of C- and G-banding patterns. The C-banding pattern in spermatogonial metaphase was characterized by the presence of paracentromeric C-bands in all chromosomes, and a distal C-band in chromosome 5. The G-banding pattern was complex. The 2C nuclear DNA content was found to be 10.26 +/- 0.16 picograms by microspectrophotometry. (+info)
The mechanics of sound production in Panacanthus pallicornis (Orthoptera: Tettigoniidae: Conocephalinae): the stridulatory motor patterns.
(19/97)
To examine whether sound production in katydids relies on an escapement mechanism similar to that of crickets we investigated the functional anatomy and mechanical properties of the stridulatory apparatus in the katydid Panacanthus pallicornis. Males of this species produce sustained pulses with a sharp low frequency peak of approximately approximately 5 kHz and a broad band spectrum between 15 and 25 kHz. Simultaneous recordings of movement and sound indicate that the entire stridulatory file is used for sound production and there is nearly a 1:1 correspondence between the number of cycles in a song and the number of teeth on the file. There is an overall tendency for both the spacing of teeth to increase along the file and the velocity of wing closure to increase as the scraper traverses the file. There is considerable variation, however, in the evenness of tooth spacing and in the instantaneous velocity of wing closure during sound production. The production of sustained pulses appears to depend on resonance in the right tegmen, with the left tegmen acting primarily as a damping element. This resonance is not strongly coupled to the scraper and, unlike crickets, the timing of file-scraper interactions, and therefore the phasing of energy input to wing oscillations, is variable. Similarly, the quality of the sound spectrum varies over the course of a single stridulatory wing-stroke. Based on measurements of tooth spacing on the stridulatory file and cycle-by-cycle frequency of sound output, we predicted the velocity of wing movement that would provide consistent phasing of file-scraper interactions with respect to sound-radiating wing oscillations and compared this with measurements of wing velocity. Acceleration of wing velocity during stridulation results in a closer match to the velocity required for optimal phasing during a portion of the call, and this corresponds with higher amplitudes of radiated sound and the excitation of higher order modes of vibration (evident as distinct harmonic peaks in spectrograms). Our results suggest that in katydid stridulation, the movement of the scraper along the file is not regulated by an escapement mechanism as it is in crickets. Instead, katydids that produce pure-tone songs sweep their wings over a range of velocities, within which some portion matches file tooth spacing to give optimal phasing of energy input to excite a resonance in the right tegmen. (+info)
Are solitary and gregarious Mormon crickets (Anabrus simplex, Orthoptera, Tettigoniidae) genetically distinct?
(20/97)
Phase polyphenisms are usually thought to reflect plastic responses of species, independent of genetic differences; however, phase differences could correlate with genetic differentiation for various reasons. Mormon crickets appear to occur in two phases that differ in morphology and behaviour. Solitary individuals are cryptic and sedentary whereas gregarious individuals form bands, migrate, and are aposematically coloured. These traits have been thought to be phenotypically plastic and induced by environmental conditions. However, there has been no previous investigation of the extent of genetic differences between solitary and gregarious populations of this widespread North American species. We sequenced two mitochondrial genes, COII and COIII, in samples of Mormon crickets from gregarious populations west of the continental divide and solitary mountain populations primarily east of the divide. Sequencing revealed two genetically distinct clades that broadly correspond with the solitary eastern populations and the mainly gregarious western populations. We used coalescent modelling to test the hypothesis that the species consists of two deep genetic clades, as opposed to a series of equally distinct populations. Results allowed us to reject the null hypothesis that a radiation independent of phase produced these clades, and molecular clock estimates indicate the time of divergence to be approximately 2 million years ago. This work establishes that the solitary populations found in the mountains on the eastern slope are part of a clade that is genetically distinct from the western populations, which are primarily gregarious, and the implications of this apparent correlation between phase and genetic differentiation are discussed. (+info)
Aggregation, defence and warning signals: the evolutionary relationship.
(21/97)
In a seminal contribution, Fisher argued how distastefulness could incrementally evolve in a prey species that was distributed in family groups. Many defended prey species occur in aggregations, but did aggregation facilitate the evolution of defence as Fisher proposed or did the possession of a defence allow individuals to enjoy the benefits of group living? Contemporary theory suggests that it can work both ways: pre-existing defences can make the evolution of gregariousness easier, but gregariousness can also aid the evolution of defence and warning signals. Unfortunately, the key phylogenetic analyses to elucidate the ordering of events have been hampered by the relative rarity of gregarious species, which in itself indicates that aggregation is not a pre-requisite for defence. Like the underlying theory, experimental studies have not given a definitive answer to the relative timing of the evolution of defence and aggregation, except to demonstrate that both orderings are possible. Conspicuous signals are unlikely to have evolved in the absence of a defence and aggregated undefended prey are likely to be vulnerable to predation in the absence of satiation effects. It therefore seems most likely that defence generally preceded the evolution of both aggregation and signalling, but alternative routes may well be possible. (+info)
Generation of extreme ultrasonics in rainforest katydids.
(22/97)
The calling song of an undescribed Meconematinae katydid (Tettigoniidae) from South America consists of trains of short, separated pure-tone sound pulses at 129 kHz (the highest calling note produced by an Arthropod). Paradoxically, these extremely high-frequency sound waves are produced by a low-velocity movement of the stridulatory forewings. Sound production during a wing stroke is pulsed, but the wings do not pause in their closing, requiring that the scraper, in its travel along the file, must do so to create the pulses. We hypothesize that during scraper pauses, the cuticle behind the scraper is bent by the ongoing relative displacement of the wings, storing deformation energy. When the scraper slips free it unbends while being carried along the file and its deformation energy contributes to a more powerful, higher-rate, one-tooth one-wave sound pulse, lasting no more than a few waves at 129 000 Hz. Some other katydid species make pure-tone ultrasonic pulses. Wing velocities and carriers among these pure-tone species fall into two groups: (1) species with ultrasonic carriers below 40 kHz that have higher calling frequencies correlated with higher wing-closing velocities and higher tooth densities: for these katydids the relationship between average tooth strike rate and song frequency approaches 1:1, as in cricket escapement mechanisms; (2) a group of species with ultrasonic carriers above 40 kHz (that includes the Meconematinae): for these katydids closing wing velocities are dramatically lower and they make short trains of pulses, with intervening periods of silence greater than the duration of the pulses they separate. This signal form may be the signature of scraper-stored elastic energy. (+info)
Neuroethology of female preference in the synchronously singing bushcricket Mecopoda elongata (Tettigoniidae; Orthoptera): why do followers call at all?
(23/97)
Imperfect synchrony between male calls occurs in the acoustically interacting bushcricket Mecopoda elongata, and males establishing the temporal leadership attract more females in choice experiments. An asymmetrical representation of leader and follower signals in pairs of direction-selective neurons of the auditory pathway was suggested to represent the neural basis for the preference of females. We investigated the time-intensity trading effect, which occurs when the temporal advantage of the leader signal is compensated, and can be reversed, by an additional sound pressure level of the follower. In behavioural arena trials the intensity trading of the preference of females for leader signals depends on the playback level; a higher sound pressure level (SPL) is needed for compensation at higher playback levels. We studied the simultaneous neuronal representation of leader and follower signals, and the time-intensity trading function in the pair of omega-neurons in the CNS. Consistent with the behavioural data, the representation of leader and follower signals can be reversed with an additional loudness of the follower, and the steepness of the trading function depends on the playback level. We also implemented data on the neuronal representation of synchronized signals in individual receivers into computer-based agents, which performed phonotaxis in a virtual sound field. Results of these simulations closely resemble those obtained from real females with respect to the overall preference under the various time-intensity trading conditions. Furthermore, in combination with the observed trading functions these simulations demonstrate, that under more realistic field conditions the ultimate success of followers in attracting females is much higher than suggested from arena trials. We discuss the evolutionary consequences for male calling strategies in synchronously calling Orthoptera. (+info)
Intersegmental coordination: influence of a single walking leg on the neighboring segments in the stick insect walking system.
(24/97)
A key element of walking is the coordinated interplay of multiple limbs to achieve a stable locomotor pattern that is adapted to the environment. We investigated intersegmental coordination of walking in the stick insect, Carausius morosus by examining the influence a single stepping leg has on the motoneural activity of the other hemiganglia, and whether this influence changes with the walking direction. We used a reduced single leg walking preparation with only one intact front, middle, or hind leg. The intact leg performed stepping movements on a treadmill, thus providing intersegmental signals about its stepping to the other hemiganglia. The activity of coxal motoneurons was simultaneously recorded extracellularly in all other segments. Stepping sequences of any given single leg in either walking direction were accompanied by an increase in coxal motoneuron (MN) activity of all other segments, which was mostly modulated and slightly in phase with stance of the walking leg. In addition, forward stepping of the front leg and, to a lesser extent, backward stepping of the hind leg elicited alternating activity in mesothoracic coxal MNs. Forward and backward stepping of the middle leg did not elicit alternating activity in coxal MNs in any other hemiganglia, indicating that the influence of middle leg stepping is qualitatively different from that of forward front and backward hind leg stepping. Our results indicate that in an insect walking system individual segments differ with respect to their intersegmental influences and thus cannot be treated as similar within the chain of segmental walking pattern generators. Consequences for the current concepts on intersegmental coordination are discussed. (+info)