Turtles, like other amphibious animals, face a trade-off between terrestrial and aquatic hearing. We used laser vibrometry and auditory brainstem responses to measure their sensitivity to vibration stimuli and to airborne versus underwater sound. Turtles are most sensitive to sound underwater, and their sensitivity depends on the large middle ear, which has a compliant tympanic disc attached to the columella. Behind the disc, the middle ear is a large air-filled cavity with a volume of approximately 0.5 ml and a resonance frequency of approximately 500 Hz underwater. Laser vibrometry measurements underwater showed peak vibrations at 500-600 Hz with a maximum of 300 mm s 21 Pa 21 , approximately 100 times more than the surrounding water. In air, the auditory brainstem response audiogram showed a best sensitivity to sound of 300-500 Hz. Audiograms before and after removing the skin covering reveal that the cartilaginous tympanic disc shows unchanged sensitivity, indicating that the tympanic disc, and not the overlying skin, is the key sound receiver. If air and water thresholds are compared in terms of sound intensity, thresholds in water are approximately 20-30 dB lower than in air. Therefore, this tympanic ear is specialized for underwater hearing, most probably because sound-induced pulsations of the air in the middle ear cavity drive the tympanic disc.

Physiological and anatomical studies have suggested that alligators have unique adaptations for spatial hearing. Sound localization cues are primarily generated by the filtering of sound waves by the head. Different vertebrate lineages have evolved external and/or internal anatomical adaptations to enhance these cues, such as pinnae and interaural canals. It has been hypothesized that in alligators, directionality may be enhanced via the acoustic coupling of middle ear cavities, resulting in a pressure difference receiver (PDR) mechanism. The experiments reported here support a role for a PDR mechanism in alligator sound localization by demonstrating that (1) acoustic space cues generated by the external morphology of the animal are not sufficient to generate location cues that match physiological sensitivity, (2) continuous pathways between the middle ears are present to provide an anatomical basis for coupling, (3) the auditory brainstem response shows some directionality, and (4) eardrum movement is directionally sensitive. Together, these data support the role of a PDR mechanism in crocodilians and further suggest this mechanism is a shared archosaur trait, most likely found also in the extinct dinosaurs.

This paper presents a model that simulates the size distribution and erosivity of raindrops and throughfall drops. It utilizes existing models of rainfall drop size distribution and fall velocity and combines them with newly collated evidence of throughfall drop size distributions. A sensitivity analysis reveals that the model is sensitive to parameters that are easily measured or estimated: rainfall intensity, the mean volume drop diameter of the intercepted throughfall, canopy cover, and canopy height.The results of the model may be used at two levels. Firstly, to calculate specifically the size and fall velocity of individual drops, parameters that are needed in studies examining the response of soil surfaces to forces applied by rainfall. Secondly, to produce erosivity indices, based on rainfall intensity but which take account of the effects of a

Neuropeptide Pigment-Dispersing Factor (PDF)-secreting large ventrolateral neurons (lLNvs) in the Drosophila brain regulate daily patterns of rest and arousal. These bilateral wake-promoting neurons are light-responsive and integrate information from the circadian system, sleep circuits, and light environment. In order to begin to dissect the synaptic circuitry of the circadian neural network, we performed simultaneous dual whole-cell patch clamp recordings of pairs of lLNvs. Both ipsilateral and contralateral pairs of lLNvs exhibit synchronous rhythmic membrane activity with a periodicity of about 5 to 10 seconds. This rhythmic lLNv activity is blocked by tetrodotoxin (TTX) voltage-gated sodium blocker, or α-bungarotoxin (α-BuTX) nicotinic acetylcholine receptor antagonist, indicating that action potential-dependent cholinergic synaptic connections are required for rhythmic lLNv activity. Since injecting current into one neuron of the pair had no effect on the membrane activity of the other neuron of the pair, this suggests that the synchrony is due to bilateral inputs and not coupling between the pairs of lLNvs. To further elucidate the nature of these synaptic inputs to lLNvs, we blocked or activated a variety of neurotransmitter receptors and measured effects on network activity and ionic conductances. These measurements indicate the lLNvs possess excitatory nicotinic ACh receptors, inhibitory ionotropic GABAA receptors, and inhibitory ionotropic glutamate-gated chloride (GluCl) receptors. We demonstrate that cholinergic input, but not GABAergic input, is required for synchronous membrane activity, while GABA can modulate firing patterns. We conclude that neuropeptidergic lLNvs that control rest and arousal receive synchronous synaptic inputs mediated by ACh.

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