The genus Tibicina Kolenati, 1857 in Morocco (Hemiptera: Cicadidae: Tibicininae): taxonomic assessment from integrative research

A new subspecies, Tibicina quadrisignata pilleti Puissant ssp. nov. is described from Morocco. This cicada is similar to Tibicina quadrisignata (Hagen, 1855) but differs mainly in the body color of the males and some acoustic parameters, notably in the courtship song. A complete pipeline is developed for detailed analysis of the morphology and acoustic behavior of the two Tibicina taxa currently known in Morocco, i.e. Tibicinaquadrisignata (Hagen, 1855) pilleti Puissant ssp. nov. and Tibicina maldesi Boulard, 1981. Biology, ecology and distribution are presented for the first time for both taxa. Tibicinamaldesi emits an abnormally high carrier frequency relative to its size. It could be an adaptation to avoid acoustic interference with a sympatric Tibicina species yet to be discovered or extinct.

Wing movements underlying sound production in calling, rivalry, and courtship songs of the cricket Gryllus bimaculatus (DeGeer)

We recorded the wing movements and sound signals during the production of calling, rivalry, and courtship song in the bispotted field cricket Gryllus bimaculatus. Recordings confirm that salient sound pulses during calling and rivalry song are generated during the closing movements of the wings. Wing movements for calling and rivalry song start from an elevated wing position and are performed with a very similar opening-closing movement, indicating that both types of songs may be generated by the same neuronal network. Wing movements for courtship song start from a low wing position; rapid closing movements generate high-frequency ticks and low-amplitude wing oscillations lead to low-amplitude pulses, generated during the opening and closing movements with a carrier frequency corresponding to the calling song. The two types of wing movements underlying courtship song indicate a different motor control as compared to calling song and may represent an early evolutionary phenotype.

Anthropogenic noise disrupts mate choice behaviors in female Gryllus bimaculatus

By assessing the sexual signals produced by conspecifics, individuals can make informed decisions on the best choice of mate, which can lead to reproductive fitness benefits. However, these communication systems are often vulnerable to disruption by conflicting with stimuli present in the environment. Anthropogenic noise may act as one such disruptive stimulus, leading to inefficient mate choice decisions and, thus, reductions to an animal’s fitness. In this study, the mate choice behaviors of female Gryllus bimaculatus were tested when presented with artificial male courtship songs of differing “quality” under different acoustic conditions. In ambient noise conditions, females significantly preferred mates paired with higher-quality songs, indicated by increased mating rates and reduced latency to mate. However, this mate selection pattern was disrupted in both traffic and white noise conditions. Additionally, “high-quality” courtship songs had an increased mounting latency in traffic and white noise conditions, when compared to ambient noise conditions. Making nonoptimal mating decisions, such as the ones seen here, can lead to deleterious fitness consequences, alter population dynamics, and weaken sexual selection, unless individuals adapt to cope with anthropogenic interference.

Induced expression of a vestigial sexual signal

Vestigial morphological traits are common and well known in a variety of taxa. Identification of vestigial genes has illustrated the potential for evolutionary reversals and the re-expression of atavistic traits. Here we induce expression of a behavioural sexual signal, male calling song, in a cricket species, Gryllus ovisopis, which lacks a functional calling song. We successfully used acetylcholine injections in the frontal space of the head of male crickets to activate cerebral command neurons for cricket calling, and we recorded calling songs with a temporal chirp pattern similar to that of G. ovisopis' close evolutionary relatives, G. firmus and G. pennsylvanicus, implying that the neural pattern generators that underlie cricket calling behaviour persist in a vestigial state in G. ovisopis To our knowledge, this is the first demonstration of the induced expression of a vestigial behaviour in any organism. The retention of latent neural capacity to express sexual behaviours could have important implications for rapid evolution, trait re-emergence and reproductive isolation.

What is the password? Female bark beetles (Scolytinae) grant males access to their galleries based on courtship song

Acoustic signals are commonly used by insects in the context of mating, and signals can vary depending on the stage of interaction between a male and female. While calling songs have been studied extensively, particularly in the Orthoptera, much less is known about courtship songs. One outstanding question is how potential mates are differentiated by their courtship signal characteristics. We examined acoustic courtship signals in a new system, bark beetles (Scolytinae). In the red turpentine beetle (Dendroctonus valens) males produce chirp trains upon approaching the entrance of a female's gallery. We tested the hypotheses that acoustic signals are honest indicators of male condition and that females choose males based on signal characteristics. Males generated two distinct chirp types (simple and interrupted), and variability in their prevalence correlated with an indicator of male quality, body size, with larger males producing significantly more interrupted chirps. Females showed a significant preference for males who produced interrupted chirps, suggesting that females distinguish between males on the basis of their chirp performances. We suggest that interrupted chirps during courtship advertise a male's size and/or motor skills, and function as the proverbial 'passwords' that allow him entry to a female's gallery.

Barriers to gene exchange in hybridizing field crickets: the role of male courtship effort and cuticular hydrocarbons

Background

Pre-zygotic barriers often involve some form of sexual selection, usually interpreted as female choice, as females are typically the choosier sex. However, males typically show some mate preferences, which are increasingly reported. Here we document previously uncharacterized male courtship behavior (effort and song) and cuticular hydrocarbon (CHC) profiles in the hybridizing crickets Gryllus firmus and G. pennsylvanicus. These two species exhibit multiple barriers to gene exchange that act throughout their life history, including a behavioral barrier that results in increased time to mate in heterospecific pairs.

Results

We demonstrated that male mate choice (as courtship effort allocation) plays a more important role in the prezygotic behavioral barrier than previously recognized. In gryllids females ultimately decide whether or not to mate, yet we found males were selective by regulating courtship effort intensity toward the preferred (conspecific) females. Females were also selective by mating with more intensely courting males, which happened to be conspecifics. We report no differences in courtship song between the two species and suggest that the mechanism that allows males to act differentially towards conspecific and heterospecific females is the cuticular hydrocarbon (CHC) composition. CHC profiles differed between males and females of both species, and there were clear differences in CHC composition between female G. firmus and G. pennsylvanicus but not between the males of each species.

Conclusion

Although many barriers to gene exchange are known in this system, the mechanism behind the mate recognition leading to reduced heterospecific mating remains unknown. The CHC profiles might be the phenotypic cue that allow males to identify conspecifics and thus to adjust their courtship intensity accordingly, leading to differential mating between species.

Recognition of variable courtship song in the field cricket Gryllus assimilis

We analyzed the courtship song of the field cricket Gryllus assimilis. The song comprises two elements: groups of ca. 10 pulses (chirps) with low fundamental frequency (3.5-3.7 kHz) alternating with high-frequency (15-17 kHz) pulses (ticks) that usually occur as doublets. Some elements of courtship song are quite variable (high coefficient of variation) both within and between males, whereas others are more stereotypical. In experiments with playback of synthesized courtship songs, we studied the importance of several song parameters for mating success, which we evaluated as the probability with which females mounted muted, courting males. Altering some features that show little variability, such as chirp-pulse rate or carrier frequency of ticks, resulted in significant decreases in mounting frequency, consistent with the notion that trait values showing little variability are constrained by stabilizing selection exerted by females. However, alteration of one invariant trait, the occurrence of both song components, by omitting either component from test songs only slightly affected female responsiveness. Alteration of a variable song trait, the number of ticks per song phrase, had no effect on female response rate, thus failing to provide support for the idea that variable traits provide a substrate for sexual selection. An unusual characteristic feature of the song of G. assimilis is that chirp pulses often contain substantial high-frequency power, and indeed may entirely lack power at the fundamental frequency. Playback experiments showed that such songs are, nevertheless, behaviorally effective. To understand the neural basis for this, we recorded the responses of the two principal ascending auditory interneurons of crickets, AN1 and AN2. Our results suggest that the frequency selectivity of the neurons is sufficiently broad to tolerate the spectral variability of courtship chirps.

Deciphering information encoded in birdsong: male songbirds with fertile mates respond most strongly to complex, low-amplitude songs used in courtship

Research on the function of acoustic signals has focused on high-amplitude long-range songs (LRS) and largely ignored low-amplitude songs produced by many species during close-proximity, conspecific interactions. Low-amplitude songs can be structurally identical to LRS (soft LRS), or they can be widely divergent, sharing few spectral and temporal attributes with LRS (short-range song [SRS]). SRS is often more complex than LRS and is frequently sung by males during courtship. To assess function, we performed two playback experiments on males of a socially monogamous songbird. We compared responses of males whose mates were fertile or nonfertile with differences in song structure (SRS vs. LRS and soft LRS), amplitude (SRS and soft LRS vs. LRS), and tempo (slow SRS vs. fast SRS). Males responded more strongly to SRS than to LRS or soft LRS, indicating that song structure had a greater effect on response than song amplitude. SRS tempo did not detectably affect male response. Importantly, males responded more strongly to SRS when their mates were fertile, presumably because hearing SRS can indicate that a male's mate is being courted by an intruding male and a strong response can deter extrapair competitors. We conclude that low-amplitude songs can function in both inter- and intrasexual communication and should receive greater attention in future studies of mate choice and male-male competition.

Speciation, Divergence, and the Origin of Gryllus rubens: Behavior, Morphology, and Molecules

The last 25 years or so has seen a huge resurgence of interest in speciation research. This has coincided with the development and widespread use of new tools in molecular genetics, especially DNA sequencing, to inform ecological and evolutionary questions. Here I review about a decade of work on the sister species of field crickets Gryllus texensis and G. rubens. This work has included analysis of morphology, behavior, and the mitochondrial DNA molecule. The molecular work in particular has dramatically re-shaped my interpretation of the speciational history of these taxa, suggesting that rather than ‘sister’ species we should consider these taxa as ‘mother-daughter’ species with G. rubens derived from within a subset of ancestral G. texensis.