Breeding vocalizations of the piping plover (Charadrius melodus): structure, diversity, and repertoire organization

We studied breeding vocalizations and the vocal repertoire of the endangered piping plover (Charadrius melodus Ord, 1824) to describe diversity of the species' non-learned vocalizations, provide a basis for comparative studies, and enable standardization of terminology and interpretation of vocal classes for management purposes. Adults have 14 call types and newly hatched chicks have three; these are underestimates of repertoire size because they represent breeding vocalizations only and are biased toward loud, easily recorded sounds. Vocalizations are structurally diverse: duration, ~10 ms to 1.5 s; peak frequency (adults), <900 to >3000 Hz; tonal to pulsed or noisy; narrow- to broad-band; and nonharmonic to harmonic. Vocalizations are higher in frequency in females than in males. High vocal diversity results from differential combination and sequencing of fairly simple acoustic attributes such as pulsing and frequency modulation, and from quantitative variation in such attributes. Homologies with other species of Charadriidae in acoustic traits of calls, call types, and organization (syntax) within calls and across call types are suggested. Acoustic characters at different organizational levels are highly conserved evolutionarily; hence, they seem to hold promise for phylogenetic analyses within the family.

Effects of pharmacological treatment and photoinactivation on the directional responses of an insect neuron

Soma-ipsilateral branches of the large segmental omega neuron of the phaneropterid bush cricket Ancistrura nigrovittata have smooth endings, which extend through most of the auditory neuropile. Correspondingly, it shows a broad frequency tuning. Large excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) are observed when recording from soma-ipsilateral branches. Stimulation from the soma-ipsilateral side leads to a strong excitation. Soma-contralateral branches have a strong, beaded appearance. IPSPs, which seem to be of soma-contralateral origin, can be recorded from these branches. Stimulation from the soma-contralateral side leads to a strong inhibition of the omega neuron. Soma-contralateral stimulation must be 30-40 dB more intense than soma-ipsilateral stimulation to evoke similar spike numbers in the omega neuron. The side-to-side difference is reduced to 10-15 dB after cutting the input from the soma-contralateral leg (tympanic nerve). The thresholds for eliciting IPSPs by soma-contralateral stimulation correspond roughly to excitatory thresholds of the mirror-image omega with the same stimuli. Pharmacological treatment with picrotoxin (PTX) or photoinactivation of the Lucifer Yellow filled mirror-image omega neuron reduces contralateral inhibition considerably and eliminates all visible IPSPs. Nevertheless, an additional contralateral inhibition survives both procedures and is only eliminated after cutting the soma-contralateral tympanic nerve. These results demonstrate that the mirror-image partners of the omega neuron mutually inhibit each other in bush crickets--as in crickets. This mutual inhibition is PTX-sensitive. At least one additional element exerts contralateral PTX-insensitive inhibition on the omega neuron.

Acoustic evolution in crickets: need for phylogenetic study and a reappraisal of signal effectiveness

Cricket stridulums and calls are highly stereotyped, except those with greatly modified tegmina and/or venation, or "unusual" frequency, duration and/or intensity. This acoustic diversity remained unsuspected until recently, and current models of acoustic evolution in crickets erroneously consider this clade homogeneous for acoustic features. The few phylogenetic studies analyzing acoustic evolution in crickets demonstrated that acoustic behavior could be particularly labile in some clades. The ensuing pattern for cricket evolution is consequently extremely complex. We argue that: (1) phylogeny should always be considered when analyzing acoustic evolution, whatever characters are considered (signals, stridulums or behaviors). Consequently, future studies should be devoted to entire clades, and not consider isolated taxa; character and character state definitions should allow significant reconstructions of character evolutionary transformations; and homologies should be carefully defined for all characters, including behavior. (2) The factors responsible for song effectiveness should be reconsidered and hypotheses on their potential influence on signal evolution tested jointly by phylogenies (for example, to assess correlated transformations of acoustic and ecological features), and population studies (for example, to correlate call range and population structure, or test the predation risk associated with a signal structure). Better understanding these points should help clarifying acoustic evolution in crickets.