Stonefly duets: vibrational sexual mimicry can explain complex patterns

What do molecular data and vibrational communication tell us about the taxonomy of the genus Tyrrhenoleuctra Consiglio, 1957 (Plecoptera: Leuctridae) in Spain?

In this paper we present the results of a study of different populations of the genus Tyrrhenoleuctra, which includes morphologically cryptic species, in the Iberian Peninsula. A total of six populations were analysed from a molecular point of view and a behavioural study was conducted on three of them. Two phylogenetic trees, maximum likelihood (ML) and neighbour joining (NJ), were constructed using both new COI sequences and COI sequences already available in GenBank. Furthermore, intra- and interspecific p-distances were calculated within and between sequences of the different populations. As regards behavioural analyses, the male call of individuals from three of the studied populations was recorded, analysed and described. Both phylogenetic approaches used, ML and NJ, were congruent in discriminating five well-defined clusters, representing the four known Iberian Tyrrhenoleuctra species and a previously unknown taxon. The sequences from the six studied populations produced in this study fell within two clades: T. lusohispanica (four populations) and the new taxon (two populations). These results were supported also by the behavioral study, in which the drumming calls of individuals belonging to the two clades differed in some important parameters such as the number of sequences, intersequence interval and interbeat interval. The obtained results expand the previously known distribution of T. lusohispanica and show the existence of a new species (Tyrrhenoleuctra hynesi sp. n.) within this genus from a more restricted area, that will be described in this paper.

Biotremology: Vibrational communication of Psylloidea

Psyllids perform duetting via vibrational signals between genders that are important in pre-copulation species specific recognition. To date, vibrational behavior has been recorded in more than 100 species of psyllid, which is still only a small fraction of the ∼4000 described species. In this overview, we categorize the duet behavior into (1) reciprocal duets, (2) engaged duets, (3) three-way duets and (4) loose duets. In species with notable signal differences between genders, typically the male possesses a longer, more complex signal, which is emitted at a higher frequency compared to those of the females. Vibrational signals exhibit species specific characteristics that are taxonomically informative in some cases. Despite only a limited number of vibrational communication studies incorporating phylogenetic analyses, these reveal that signals can have reliable systematic information, but also that evolutionary and/or environmental factors may influence signal characteristics in ways that confound phylogenetic signal. Other possible strategies employed in mate finding in psyllids are chemical and visual signals. The most likely mechanism of vibrational signal production in psyllids involves stridulation between forewing and thorax. In some applied approaches, methods exploiting vibrational signals to disrupt mating may be effective to control psyllid pests in the field.

Female answer specificity to male drumming calls in three closely related species of the stonefly genus Zwicknia (Plecoptera: Capniidae)

This study examines the rate of female answers to conspecific versus heterospecific male vibratory calls in three, closely related stonefly species: Zwicknia bifrons, Z. acuta, and Z. rupprechti. In a previous study those three species were recognized on the basis of their distinct male drumming calls along with differences in genital morphology and genetic divergence. During this study no-choice playback experiments using original male call samples from each species were performed, and the answer rate of females to conspecific and heterospecific signal variants was measured. Mixed effect logistic regression models were used to test if male call species identity had a statistically significant effect on female answer probability. Females answered conspecific male calls with significantly higher probability than heterospecific calls in all the three examined species, suggesting that the divergence of vibrational communication can be an important component of the prezygotic isolation between them. Low, but well detectable responsiveness to heterospecific calls was observable between Z. bifrons and Z. acuta, the two species closest to each other regarding mitochondrial genetic divergence and male call pattern similarity. Thus, our results are most congruent with a tight, gradual coevolution of male calls and female preferences.

Pea leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) uses vibrational duets for efficient sexual communication

The pea leafminer (Liriomyza huidobrensis) is a notorious pest of vegetables and ornamental plants worldwide. Despite a large number of studies on its biology and ecology, the courtship behavior and sexual communication of this species remain unclear. Here, we studied vibrational communication in the sexual interaction of the pea leafminer. On host plant leaves, females and males behaviorally displayed the bobbing-quivering alternation, which finally led to copulation. Moreover, records of laser vibrometry revealed three-signal duets underlying the behavioral alternation. Sexually mature males spontaneously emitted calls (MCs) to initiate the duets. The females rapidly responded to MCs by emitting replies (FRs) that are longer in duration. The FRs further triggered male replies (MRs) in their search for potential partners. Leafminer-produced vibrational signals convey efficient information to partners and generate pair formation on stretched substrates, such as plant leaves and nylon mesh, but cannot elicit responses on dense substrates, such as glass and plastic. Vibrational playbacks of both MCs and FRs can elicit replies in females and males, respectively. This study completely characterizes substrate-borne vibrational duets in a dipteran insect. The discovery of vibrational sex signals in the pea leafminer provides new insights for the development of novel approaches to control the pest and its relative species.

Ecological speciation by temporal isolation in a population of the stonefly Leuctra hippopus (Plecoptera, Leuctridae)

Stream dwelling invertebrates are ideal candidates for the study of ecological speciation as they are often adapted to particular environmental conditions within a stream and inhabit only certain reaches of a drainage basin, separated by unsuitable habitat. We studied an atypical population of the stonefly Leuctra hippopus at a site in central Norway, the Isterfoss rapids, in relation to three nearby and two remote conspecific populations. Adults of this population emerge about a month earlier than those of nearby populations, live on large boulders emerging from the rapids, and are short-lived. This population also has distinct morphological features and was studied earlier during the period 1975-1990. We reassessed morphological distinctness with new measurements and added several analyses of genetic distinctness based on mitochondrial and nuclear sequence markers, as well as AFLP fingerprinting and SNPs mined from RAD sequences. The Isterfoss population is shown to be most closely related to its geographical neighbors, yet clearly morphologically and genetically distinct and homogeneous. We conclude that this population is in the process of sympatric speciation, with temporal isolation being the most important direct barrier to gene flow. The shift in reproductive season results from the particular temperature and water level regime in the Isterfoss rapids. The distinct adult body shape and loss of flight are hypothesized to be an adaptation to the unusual habitat. Ecological diversification on small spatial and temporal scales is one of the likely causes of the high diversity of aquatic insects.

The Effect of Timing of Female Vibrational Reply on Male Signalling and Searching Behaviour in the Leafhopper Aphrodes makarovi

Sexual communication in animals often involves duetting characterized by a coordinated reciprocal exchange of acoustic signals. We used playback experiments to study the role of timing of a female reply in the species-specific duet structure in the leafhopper Aphrodes makarovi (Hemiptera: Cicadellidae). In leafhoppers, mate recognition and location is mediated exclusively by species- and sex-specific substrate-borne vibrational signals and a female signal emitted in reply to male advertisement calls is essential for recognition and successful location of the female. In A. makarovi, males have to initiate each exchange of vibrational signals between partners, and in a duet the beginning of a female reply overlaps the end of the male advertisement call. Results of playback treatments in which female replies were delayed and did not overlap with the male call revealed that in order to trigger an appropriate behavioural response of the male, female reply has to appear in a period less than 400 ms after the end of the initiating male call. Results also suggest that males are not able to detect a female reply while calling, since female reply that did not continue after the end of male call triggered male behaviour similar to behaviour observed in the absence of female reply. Together, our results show that vibrational duets are tightly coordinated and that the species-specific duet structure plays an important role in mate recognition in location processes.