The best of both worlds: cicada males change costly signals to achieve mates while females choose a mate based on both calling and courtship songs.

Cicadas usually sing and mate in the higher parts of trees. Studies addressing the effects of different acoustic signals on mate choice in Cicadidae are very limited. We investigated the effects of both acoustical features and morphological traits on mate choice in an East Asian cicada Platypleura kaempferi. Males produce high-rate calling songs that attract females, then produce low-rate courtship songs to secure mating when a female is attracted. Higher calling song rate (CR), shorter single-pulse duration, and shorter pulse period of the calling song, together with lower courtship song rate and longer echeme period of the courtship song, are the most desirable traits used by females to choose a mate. These traits indicate that the more a male can raise the rate of song production, the higher the probability he is sexually selected by the female. No correlation was found between morphological traits and mating success. After mating, a minority of males started emitting calling songs again, but the CR was significantly lower than before mating and none of them attracted a new mate later. This promotes females mating with unmated males. We hypothesize that P. kaempferi may have the best of both worlds due to the unique song modulation and the mechanism of female mate choice: males change energetically, costly acoustic signals to achieve mates, while females choose a mate based on males' acoustic properties. Our results contribute to better understanding the diversity of mating preference and enrich the mechanism of mate choice in acoustic insects.

Females prefer males producing a high-rate song with shorter timbal-stridulatory sound intervals in a cicada species.

Uncovering mate choice and factors that lead to the choice are very important to understanding sexual selection in evolutionary change. Cicadas are known for their loud sounds produced by males using the timbals. However, males in certain cicada species emit 2 kinds of sounds using respectively timbals and stridulatory organs, and females may produce their own sounds to respond to males. What has never been considered is the mate choice in such cicada species. Here, we investigate the sexual selection and potential impact of predation pressure on mate choice in the cicada Subpsaltria yangi Chen. It possesses stridulatory sound-producing organs in both sexes in addition to the timbals in males. Results show that males producing calling songs with shorter timbal-stridulatory sound intervals and a higher call rate achieved greater mating success. No morphological traits were found to be correlated with mating success in both sexes, suggesting neither males nor females display mate preference for the opposite sex based on morphological traits. Males do not discriminate among responding females during mate searching, which may be due to the high energy costs associated with their unusual mate-seeking activity and the male-biased predation pressure. Females generally mate once but a minority of them re-mated after oviposition which, combined with the desirable acoustic traits of males, suggest females may maximize their reproductive success by choosing a high-quality male in the first place. This study contributes to our understanding mechanisms of sexual selection in cicadas and other insects suffering selective pressure from predators.

Identification of candidate olfactory genes in cicada Subpsaltria yangi by antennal transcriptome analysis.

Olfaction in antennae is essential for regulating insect behaviors such as host preference and oviposition site selection. To better understand the olfactory mechanisms in the cicada Subpsaltria yangi that has a very narrow host range far fewer than diets of most other cicadas, an antennal transcriptome was constructed in this study. We identified 10 unigenes encoding putative odorant-binding proteins (OBPs), 10 chemosensory proteins (CSPs), 8 sensory neuron membrane proteins (SNMPs), 7 gustatory receptors (GRs), 29 odorant receptors (ORs) and 13 ionotropic receptors (IRs). We found that the OBPs were separated into two groups, Classic OBPs and Plus-C OBPs, according to their motifs. Based on sequence alignment and phylogenetic analysis, we found five Orcos in OR family. However, no pheromone receptor was identified, which may be related to that cicadas are sound-producing insects and acoustic signals other than pheromones play most important role in sexual communication. We used qRT-PCR to examine the expression profile of ten OBPs genes in various organs, and found that they were mainly expressed in olfactory organs such as antennae and mouthparts. Our results make it possible for future research of the olfactory system of S. yangi at the molecular level, and provide important bases for elucidation of the molecular mechanisms and evolution of chemosensation in sap-sucking insects.