95 research outputs found
Two matched filters and the evolution of mating signals in four species of cricket
<p>Abstract</p> <p>Background</p> <p>Male field crickets produce pure-tone calling songs to attract females. Receivers are expected to have evolved a "matched filter" in the form of a tuned sensitivity for this frequency. In addition, the peripheral directionality of field crickets is sharply tuned as a result of a pressure difference receiver. We studied both forms of tuning in the same individuals of four species of cricket, where <it>Gryllus bimaculatus </it>and <it>G. campestris </it>are largely allopatric, whereas <it>Teleogryllus oceanicus </it>and <it>T. commodus </it>occur also sympatrically.</p> <p>Results</p> <p>The sharpness of the sensitivity filter is highest for <it>T. commodus</it>, which also exhibits low interindividual variability. Individual receivers may also vary strongly in the best frequency for directional hearing. In <it>G. campestris</it>, such best frequencies occur even at frequencies outside the range of carrier frequencies of males. Contrary to the predictions from the "matched filter hypothesis", in three of the four species the frequency optima of the two involved filters are not matched to each other, and the mismatch can amount to 1.2 kHz. The mean carrier frequency of the male population is between the frequency optima of both filters in three species. Only in <it>T. commodus </it>we found a match between both filters and the male carrier frequency.</p> <p>Conclusion</p> <p>Our results show that a mismatch between the sensitivity and directionality tuning is not uncommon in crickets, and an observed match (<it>T. commodus</it>) appears to be the exception rather than the rule. The data suggests that independent variation of both filters is possible. During evolution each sensory task may have been driven by independent constraints, and may have evolved towards its own respective optimum.</p
Critical Song Features for Auditory Pattern Recognition in Crickets
Many different invertebrate and vertebrate species use acoustic communication
for pair formation. In the cricket Gryllus bimaculatus, females recognize
their species-specific calling song and localize singing males by positive
phonotaxis. The song pattern of males has a clear structure consisting of
brief and regular pulses that are grouped into repetitive chirps. Information
is thus present on a short and a long time scale. Here, we ask which
structural features of the song critically determine the phonotactic
performance. To this end we employed artificial neural networks to analyze a
large body of behavioral data that measured females’ phonotactic behavior
under systematic variation of artificially generated song patterns. In a first
step we used four non-redundant descriptive temporal features to predict the
female response. The model prediction showed a high correlation with the
experimental results. We used this behavioral model to explore the integration
of the two different time scales. Our result suggested that only an attractive
pulse structure in combination with an attractive chirp structure reliably
induced phonotactic behavior to signals. In a further step we investigated all
feature sets, each one consisting of a different combination of eight proposed
temporal features. We identified feature sets of size two, three, and four
that achieve highest prediction power by using the pulse period from the short
time scale plus additional information from the long time scale
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A small, computationally flexible network produces the phenotypic diversity of song recognition in crickets.
How neural networks evolved to generate the diversity of species-specific communication signals is unknown. For receivers of the signals, one hypothesis is that novel recognition phenotypes arise from parameter variation in computationally flexible feature detection networks. We test this hypothesis in crickets, where males generate and females recognize the mating songs with a species-specific pulse pattern, by investigating whether the song recognition network in the cricket brain has the computational flexibility to recognize different temporal features. Using electrophysiological recordings from the network that recognizes crucial properties of the pulse pattern on the short timescale in the cricket Gryllus bimaculatus, we built a computational model that reproduces the neuronal and behavioral tuning of that species. An analysis of the model's parameter space reveals that the network can provide all recognition phenotypes for pulse duration and pause known in crickets and even other insects. Phenotypic diversity in the model is consistent with known preference types in crickets and other insects, and arises from computations that likely evolved to increase energy efficiency and robustness of pattern recognition. The model's parameter to phenotype mapping is degenerate - different network parameters can create similar changes in the phenotype - which likely supports evolutionary plasticity. Our study suggests that computationally flexible networks underlie the diverse pattern recognition phenotypes, and we reveal network properties that constrain and support behavioral diversity
Divergent mechanisms of acoustic mate recognition between closely related field cricket species (Teleogryllus spp.)
Funding support to N.W.B. from the Natural Environment Research Council (NE/G014906/1, NE/L011255/1, NE/I027800/1)Effective recognition of conspecific mating signals reduces the risk of maladaptive hybridization. Dissecting the signal recognition algorithms that underlie preferences is a useful approach for testing whether closely related taxa evaluate the same or different signal features to achieve mate recognition. Such data provide information about potential constraints and targets of selection during evolutionary divergence. Using a series of mate choice trials, we tested whether closely related, but genetically and phenotypically divergent, field cricket species (Teleogryllus oceanicus and Teleogryllus commodus) use shared or distinct recognition algorithms when evaluating acoustic male calling songs. These species overlap in sympatry, show premating isolation based on female discrimination of male calling songs, yet are capable of producing hybrid offspring. Unexpectedly, female selectivity for features of male song differed between the two species. We found that the two species use a combination of shared and unique signal filtering mechanisms, and we characterized how information about male carrier frequency, pulse rate and temporal patterning is integrated to achieve song recognition in each species. These results illustrate how comparatively few, simple modifications in key components of signal recognition algorithms can lead to striking interspecific discrimination between closely related taxa, despite apparent signal complexity. The finding that some steps during signal recognition and filtering are shared between the species, while others differ, can help to identify behavioural traits targeted by selection during evolutionary divergence.PostprintPeer reviewe
On the nature of long-range contributions to pair interactions between charged colloids in two dimensions
We perform a detailed analysis of solutions of the inverse problem applied to
experimentally measured two-dimensional radial distribution functions for
highly charged latex dispersions. The experiments are carried out at high
colloidal densities and under low-salt conditions. At the highest studied
densities, the extracted effective pair potentials contain long-range
attractive part. At the same time, we find that for the best distribution
functions available the range of stability of the solutions is limited by the
nearest neighbour distance between the colloidal particles. Moreover, the
measured pair distribution functions can be explained by purely repulsive pair
potentials contained in the stable part of the solution.Comment: 6 pages, 5 figure
Direct measurement of three-body interactions
Three-body interactions have been measured among three charged colloidal
particles in deionized solvent. Two of the particles have been confined to an
optical line-trap while the third one was approached by means of a focused
laser beam. The experimentally determined three-body interactions are
attractive and roughly of the same magnitude and range as the
pair-interactions. In addition, numerical calculations have been performed,
which show good agreement with the experimental results
Ultrahigh-Field MRI in Human Ischemic Stroke – a 7 Tesla Study
INTRODUCTION: Magnetic resonance imaging (MRI) using field strengths up to 3 Tesla (T) has proven to be a powerful tool for stroke diagnosis. Recently, ultrahigh-field (UHF) MRI at 7 T has shown relevant diagnostic benefits in imaging of neurological diseases, but its value for stroke imaging has not been investigated yet. We present the first evaluation of a clinically feasible stroke imaging protocol at 7 T. For comparison an established stroke imaging protocol was applied at 3 T. METHODS: In a prospective imaging study seven patients with subacute and chronic stroke were included. Imaging at 3 T was immediately followed by 7 T imaging. Both protocols included T1-weighted 3D Magnetization-Prepared Rapid-Acquired Gradient-Echo (3D-MPRAGE), T2-weighted 2D Fluid Attenuated Inversion Recovery (2D-FLAIR), T2-weighted 2D Fluid Attenuated Inversion Recovery (2D-T2-TSE), T2* weighted 2D Fast Low Angle Shot Gradient Echo (2D-HemoFLASH) and 3D Time-of-Flight angiography (3D-TOF). RESULTS: The diagnostic information relevant for clinical stroke imaging obtained at 3 T was equally available at 7 T. Higher spatial resolution at 7 T revealed more anatomical details precisely depicting ischemic lesions and periinfarct alterations. A clear benefit in anatomical resolution was also demonstrated for vessel imaging at 7 T. RF power deposition constraints induced scan time prolongation and reduced brain coverage for 2D-FLAIR, 2D-T2-TSE and 3D-TOF at 7 T versus 3 T. CONCLUSIONS: The potential of 7 T MRI for human stroke imaging is shown. Our pilot study encourages a further evaluation of the diagnostic benefit of stroke imaging at 7 T in a larger study
P-TEFb Activation by RBM7 Shapes a Pro-survival Transcriptional Response to Genotoxic Stress
DNA damage response (DDR) involves dramatic transcriptional alterations, the mechanisms of which remain ill defined. Here, we show that following genotoxic stress, the RNA-binding motif protein 7 (RBM7) stimulates RNA polymerase II (Pol II) transcription and promotes cell viability by activating the positive transcription elongation factor b (P-TEFb) via its release from the inhibitory 7SK small nuclear ribonucleoprotein (7SK snRNP). This is mediated by activation of p38MAPK, which triggers enhanced binding of RBM7 with core subunits of 7SK snRNP. In turn, P-TEFb relocates to chromatin to induce transcription of short units, including key DDR genes and multiple classes of non-coding RNAs. Critically, interfering with the axis of RBM7 and P-TEFb provokes cellular hypersensitivity to DNA-damage-inducing agents due to activation of apoptosis. Our work uncovers the importance of stress-dependent stimulation of Pol II pause release, which enables a pro-survival transcriptional response that is crucial for cell fate upon genotoxic insult.Peer reviewe
Adaptation and Selective Information Transmission in the Cricket Auditory Neuron AN2
Sensory systems adapt their neural code to changes in the sensory environment, often on multiple time scales. Here, we report a new form of adaptation in a first-order auditory interneuron (AN2) of crickets. We characterize the response of the AN2 neuron to amplitude-modulated sound stimuli and find that adaptation shifts the stimulus–response curves toward higher stimulus intensities, with a time constant of 1.5 s for adaptation and recovery. The spike responses were thus reduced for low-intensity sounds. We then address the question whether adaptation leads to an improvement of the signal's representation and compare the experimental results with the predictions of two competing hypotheses: infomax, which predicts that information conveyed about the entire signal range should be maximized, and selective coding, which predicts that “foreground” signals should be enhanced while “background” signals should be selectively suppressed. We test how adaptation changes the input–response curve when presenting signals with two or three peaks in their amplitude distributions, for which selective coding and infomax predict conflicting changes. By means of Bayesian data analysis, we quantify the shifts of the measured response curves and also find a slight reduction of their slopes. These decreases in slopes are smaller, and the absolute response thresholds are higher than those predicted by infomax. Most remarkably, and in contrast to the infomax principle, adaptation actually reduces the amount of encoded information when considering the whole range of input signals. The response curve changes are also not consistent with the selective coding hypothesis, because the amount of information conveyed about the loudest part of the signal does not increase as predicted but remains nearly constant. Less information is transmitted about signals with lower intensity
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