03010nas a2200181 4500008004100000245009100041210006900132520234200201653002902543653001202572653002402584653004202608653003302650653002302683100002202706700001902728856008102747 2013 eng d00aDiversity of acoustic tracheal system and its role for directional hearing in crickets0 aDiversity of acoustic tracheal system and its role for direction3 a

Background: Sound localization in small insects can be a challenging task due to physical constraints in deriving sufficiently large interaural intensity differences (IIDs) between both ears. In crickets, sound source localization is achieved by a complex type of pressure difference receiver consisting of four potential sound inputs. Sound acts on the external side of two tympana but additionally reaches the internal tympanal surface via two external sound entrances. Conduction of internal sound is realized by the anatomical arrangement of connecting trachea. A key structure is a trachea coupling both ears which is characterized by an enlarged part in its midline (i.e., the acoustic vesicle) accompanied with a thin membrane (septum). This facilitates directional sensitivity despite an unfavorable relationship between wavelength of sound and body size. Here we studied the morphological differences of the acoustic tracheal system in 40 cricket species (Gryllidae, Mogoplistidae) and species of outgroup taxa (Gryllotalpidae, Rhaphidophoridae, Gryllacrididae) of the suborder Ensifera comprising hearing and non hearing species.

Results: We found a surprisingly high variation of acoustic tracheal systems and almost all investigated species using intraspecific acoustic communication were characterized by an acoustic vesicle associated with a medial septum. The relative size of the acoustic vesicle - a structure most crucial for deriving high IIDs - implies an important role for sound localization. Most remarkable in this respect was the size difference of the acoustic vesicle between species; those with a more unfavorable ratio of body size to sound wavelength tend to exhibit a larger acoustic vesicle. On the other hand, secondary loss of acoustic signaling was nearly exclusively associated with the absence of both acoustic vesicle and septum.

Conclusion: The high diversity of acoustic tracheal morphology observed between species might reflect different steps in the evolution of the pressure difference receiver; with a precursor structure already present in ancestral non-hearing species. In addition, morphological transitions of the acoustic vesicle suggest a possible adaptive role for the generation of binaural directional cues.

10aAcoustic tracheal system10acricket10adirectional hearing10aInteraural intensity difference (IID)10aPressure difference receiver10aSound localization1 aSchmidt, Arne, KD1 aRömer, Heiner uhttp://frontiersinzoology.biomedcentral.com/articles/10.1186/1742-9994-10-6102397nas a2200181 4500008004100000022001300041245008400054210006900138260001600207300001600223490000700239520181000246100002902056700002302085700002002108700002102128856006602149 2015 eng d a0960982200aEvolution of a Communication System by Sensory Exploitation of Startle Behavior0 aEvolution of a Communication System by Sensory Exploitation of S cJan-12-2015 a3245 - 32520 v253 a

New communication signals can evolve by sensory exploitation if signaling taps into preexisting sensory biases in receivers [1 ;  2]. For mate attraction, signals are typically similar to attractive environmental cues like food [3; 4; 5 ;  6], which amplifies their attractiveness to mates, as opposed to aversive stimuli like predator cues. Female field crickets approach the low-frequency calling song of males, whereas they avoid high-frequency sounds like predatory bat calls [7]. In one group of crickets (Eneopterinae: Lebinthini), however, males produce exceptionally high-frequency calling songs in the range of bat calls [8], a surprising signal in the context of mate attraction. We found that female lebinthines, instead of approaching singing males, produce vibrational responses after male calls, and males track the source of vibrations to find females. We also demonstrate that field cricket species closely related to the Lebinthini show an acoustic startle response to high-frequency sounds that generates substrate vibrations similar to those produced by female lebinthine crickets. Therefore, the startle response is the most likely evolutionary origin of the female lebinthine vibrational signal. In field crickets, the brain receives activity from two auditory interneurons; AN1 tuned to male calling song controls positive phonotaxis, and AN2 tuned to high-frequency bat calls triggers negative phonotaxis [9 ;  10]. In lebinthine crickets, however, we found that auditory ascending neurons are only tuned to high-frequency sounds, and their tuning matches the thresholds for female vibrational signals. Our results demonstrate how sensory exploitation of anti-predator behavior can evolve into a communication system that benefits both senders and receivers.

1 aHofstede, Hannah, M. ter1 aSchöneich, Stefan1 aRobillard, Tony1 aHedwig, Berthold uhttp://linkinghub.elsevier.com/retrieve/pii/S0960982215013585