Sexual selection on bushcricket genitalia operates in a mosaic pattern

In most species with internal fertilization, male genitalia evolve faster than other morphological structures. This holds true for genital titillators, which are used exclusively during mating in several bushcricket subfamilies. Several theories have been proposed for the sexual selection forces driving the evolution of internal genitalia, especially sperm competition, sexually antagonistic coevolution (SAC), and cryptic female choice (CFC). However, it is unclear whether the evolution of genitalia can be described with a single hypothesis or a combination of them. The study of species-specific genitalia action could contribute to the controversial debate about the underlying selective evolutionary forces. We studied female mating behaviors in response to experimentally modified titillators in a phylogenetically nested set of four bushcricket species: Roeseliana roeselii, Pholidoptera littoralis littoralis, Tettigonia viridissima (of the subfamily Tettigoniinae), and Letana inflata (Phaneropterinae). Bushcricket titillators have several potential functions; they stimulate females and suppress female resistance, ensure proper ampulla or spermatophore attachment, and facilitate male fixation. In R. roeselii, titillators stimulate females to accept copulations, supporting sexual selection by CFC. Conversely, titillator modification had no observable effect on the female's behavior in T. viridissima. The titillators of Ph. l. littoralis mechanically support the mating position and the spermatophore transfer, pointing to sexual selection by SAC. Mixed support was found in L. inflata, where manipulation resulted in increased female resistance (evidence for CFC) and mating failures by reduced spermatophore transfer success (evidence for SAC). Sexual selection is highly species-specific with a mosaic support for either cryptic female choice or sexually antagonistic coevolution or a combination of both in the four species

Correlated sexual selection on male genitalia, copulatory performance and nuptial gifts in a bushcricket (Orthoptera: Tettigoniidae) indicated by allometric scaling

We adopt an allometric framework of scaling relationships for comparison between mating-related traits in the middle European bushcricket Roeseliana roeselii (Hagenbach, 1822). Eight characters, covering ontogenetic fitness (size traits; fixed at final moult), male condition (mass traits) and mating motivation (reproductive behaviours), were analysed in unrestricted matings and in matings involving genital manipulation. Shortening the male titillators had no effect on mating-related traits in males. However, titillators, known to be under sexual selection, scale hyperallometrically, with larger males possessing proportionally longer titillators, performing more titillator movements and exhibiting a reduced duration of copulation. Scaling was also hyperallometric for spermatophore mass, with larger males being heavier and transferring heavier nuptial gifts. Both titillator length and spermatophore mass might be condition-dependent indicators, because their variances were nearly twice as large those of body size or body mass. Mass traits were also dynamic, increasing by 11% for male body mass and 17% for spermatophore mass between the first and second matings. Sexual selection by female choice seems to favour larger trait size in the bushcricket R. roeselii, acting in concert on titillator length, intensity of titillator movements and spermatophore mass.Peer Reviewe

Male genital titillators and the intensity of post-copulatory sexual selection across bushcrickets

Animal genitalia are diverse and a growing body of evidence suggests that they evolve rapidly under post-copulatory sexual selection. This process is predicted to be more intense in polyandrous species, although there have been very few comparative studies of the relationship between the complexity of genital structures in males and measures of the degree of polyandry. In some bushcricket families, males possess sclerotised copulatory structures known as titillators, which are inserted into the female’s genital chamber and moved rhythmically. Like other genital structures, bushcricket titillators are widely used as important taxonomic characters and show considerable variation across species in structure, shape and the extent to which they are spined. Here, we examine relationships between the presence/absence of titillators, titillator complexity and both mating frequency and the degree of polyandry in bushcrickets, using phylogenetic comparative analyses. Using published sources combined with original observations, data were obtained for the mean level of polyandry, the duration of the male and female sexual refractory periods and the level of complexity of titillators. To analyse data, we fitted phylogenetic generalised least squares models. No significant relationships were found between titillator presence or complexity and either the level of polyandry, duration of the male’s sexual refractory period or the ratio of the female and male sexual refractory periods. The duration of the female’s refractory period, however, was positively associated with titillator presence and negatively associated with titillator complexity. The data therefore partially support the hypothesis that post-copulatory sexual selection drives genital evolution in this taxon

Two species? - Limits of the species concepts in the pygmy grasshoppers of the Tetrix bipunctata complex (Orthoptera, Tetrigidae)

Today, integrative taxonomy is often considered the gold standard when it comes to species recognition and delimitation. Using the Tetrix bipunctata complex, we here present a case where even integrative taxonomy may reach its limits. The Tetrix bipunctata complex consists of two morphs, bipunctata and kraussi, which are easily distinguished by a single character, the length of the hind wing. Both morphs are widely distributed in Europe and reported to occur over a large area in sympatry, where they occasionally may live also in syntopy. The pattern has led to disparate classifications, as on the one extreme, the morphs were treated merely as forms or subspecies of a single species, on the other, as separate species. For this paper, we re-visited the morphology by using multivariate ratio analysis (MRA) of 17 distance measurements, checked the distributional data based on verified specimens and examined micro-habitat use. We were able to confirm that hind wing length is, indeed, the only morphological difference between bipunctata and kraussi. We were also able to exclude a mere allometric scaling. The morphs are, furthermore, largely sympatrically distributed, with syntopy occurring regularly. However, a microhabitat niche difference can be observed. Ecological measurements in a shared habitat confirm that kraussi prefers a drier and hotter microhabitat, which possibly also explains the generally lower altitudinal distribution. Based on these results, we can exclude classification as subspecies, but the taxonomic classification as species remains unclear. Even with different approaches to classify the Tetrix bipunctata complex, this case is, therefore, not settled. We recommend continuing to record kraussi and bipunctata separately

Development, reproductive capacity and diet of the Mediterranean grasshopper Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Caelifera: Acrididae: Gomphocerinae)

Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Acrididae) is a rare grasshopper native to Mediterranean grassland habitats in the Languedoc-Roussillon region of southern France. Changes in land-use have modified these unique habitats, thus threatening the survival of A. b. vicheti populations. To improve the conservation of this species this study aimed to describe important aspects of its biology and ecology. Development of nymphs passed through five instars after hatching and was closely associated with the Mediterranean spring season. A prominent sexual size dimorphism is highlighted, but the larger females developed in the same number of instars as males. Hind femur length and number of antenna segments were useful characters when distinguishing between nymphal instars. All individuals were brachypterous, indicating that A. b. vicheti is unable to fly. Adult females laid 15 eggs on average and deposited no more than two egg pods in their lifetime. Grass debris made up 93% of faecal content of both sexes. Our results provide valuable information for the conservation of this highly endangered grasshopper species.Peer reviewe

Development, reproductive capacity and diet of the Mediterranean grasshopper Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Caelifera: Acrididae: Gomphocerinae)

Arcyptera brevipennis vicheti Harz 1975 (Orthoptera: Acrididae) is a rare grasshopper native to Mediterranean grassland habitats in the Languedoc-Roussillon region of southern France. Changes in land-use have modified these unique habitats, thus threatening the survival of A. b. vicheti populations. To improve the conservation of this species this study aimed to describe important aspects of its biology and ecology. Development of nymphs passed through five instars after hatching and was closely associated with the Mediterranean spring season. A prominent sexual size dimorphism is highlighted, but the larger females developed in the same number of instars as males. Hind femur length and number of antenna segments were useful characters when distinguishing between nymphal instars. All individuals were brachypterous, indicating that A. b. vicheti is unable to fly. Adult females laid 15 eggs on average and deposited no more than two egg pods in their lifetime. Grass debris made up 93% of faecal content of both sexes. Our results provide valuable information for the conservation of this highly endangered grasshopper species.Peer reviewe

Unravelling the Stability of Nightingale Song Over Time and Space Using Open, Citizen Science and Shared Data

Open science approaches enable and facilitate the investigation of many scientific questions in bioacoustics, such as studies on the temporal and spatial evolution of song, as in vocal dialects. In contrast to previous dialect studies, which mostly focused on songbird species with a small repertoire, here we studied the common nightingale (Luscinia megarhynchos), a bird species with a complex and large repertoire. To study dialects on the population level in this species, we used recordings from four datasets: an open museum archive, a citizen science platform, a citizen science project, and shared recordings from academic researchers. We conducted the to date largest temporal and geographic dialect study of birdsong including recordings from 1930 to 2019 and from 13 European countries, with a geographical coverage of 2,652 km of linear distance. To examine temporal stability and spatial dialects, a catalog of 1,868 song types of common nightingales was created. Instead of dialects, we found a high degree of stability over time and space in both, the sub-categories of song and in the occurrence of song types. For example, the second most common song type in our datasets occurred over nine decades and across Europe. In our case study, open and citizen science data proved to be equivalent, and in some cases even better, than data shared by an academic research group. Based on our results, we conclude that the combination of diverse and open datasets was particularly useful to study the evolution of song in a bird species with a large repertoire.Peer Reviewe

Unravelling the Stability of Nightingale Song Over Time and Space Using Open, Citizen Science and Shared Data

Open science approaches enable and facilitate the investigation of many scientific questions in bioacoustics, such as studies on the temporal and spatial evolution of song, as in vocal dialects. In contrast to previous dialect studies, which mostly focused on songbird species with a small repertoire, here we studied the common nightingale (Luscinia megarhynchos), a bird species with a complex and large repertoire. To study dialects on the population level in this species, we used recordings from four datasets: an open museum archive, a citizen science platform, a citizen science project, and shared recordings from academic researchers. We conducted the to date largest temporal and geographic dialect study of birdsong including recordings from 1930 to 2019 and from 13 European countries, with a geographical coverage of 2,652 km of linear distance. To examine temporal stability and spatial dialects, a catalog of 1,868 song types of common nightingales was created. Instead of dialects, we found a high degree of stability over time and space in both, the sub-categories of song and in the occurrence of song types. For example, the second most common song type in our datasets occurred over nine decades and across Europe. In our case study, open and citizen science data proved to be equivalent, and in some cases even better, than data shared by an academic research group. Based on our results, we conclude that the combination of diverse and open datasets was particularly useful to study the evolution of song in a bird species with a large repertoire

Copulatory courtship by internal genitalia in bushcrickets

Male genital organs are among the fastest evolving morphological structures. However, large parts of the male’s genitalia are often hidden inside the female during mating. In several bushcricket species, males bear a pair of sclerotized genital appendices called titillators. By employing synchrotron-based in vivo X-ray cineradiography on mating couples, we were able to visualize titillator movement and spermatophore attachment inside the female. Titillators are inserted and retracted rhythmically. During insertion the titillator processes tap the soft and sensillae-covered dorsal side of the female’s flap-like genital fold, which covers the opening of the female’s genitalia, without tissue penetration. Titillators thus appear to be initially used for stimulation; later they may apply pressure that forces the female’s genital fold to stay open, thereby aiding mechanically in spermatophore transfer

Community engagement and data quality: best practices and lessons learned from a citizen science project on birdsong

Citizen Science (CS) is a research approach that has become popular in recent years and offers innovative potential for dialect research in ornithology. As the scepticism about CS data is still widespread, we analysed the development of a 3-year CS project based on the song of the Common Nightingale (Luscinia megarhynchos) to share best practices and lessons learned. We focused on the data scope, individual engagement, spatial distribution and species misidentifications from recordings generated before (2018, 2019) and during the COVID-19 outbreak (2020) with a smartphone using the ‘Naturblick’ app. The number of nightingale song recordings and individual engagement increased steadily and peaked in the season during the pandemic. 13,991 nightingale song recordings were generated by anonymous (64%) and non-anonymous participants (36%). As the project developed, the spatial distribution of recordings expanded (from Berlin based to nationwide). The rates of species misidentifications were low, decreased in the course of the project (10–1%) and were mainly affected by vocal similarities with other bird species. This study further showed that community engagement and data quality were not directly affected by dissemination activities, but that the former was influenced by external factors and the latter benefited from the app. We conclude that CS projects using smartphone apps with an integrated pattern recognition algorithm are well suited to support bioacoustic research in ornithology. Based on our findings, we recommend setting up CS projects over the long term to build an engaged community which generates high data quality for robust scientific conclusions.Gesellschaftliches Engagement und Datenqualität: Bewährte Praktiken und Erfahrungen aus einem bürgerwissenschaftlichen Projekt zum Vogelgesang Citizen Science (CS) ist eine Forschungsmethode, die in den letzten Jahren an Bedeutung gewonnen hat und innovatives Potenzial für die Dialektforschung in der Ornithologie bietet. Da die Vorbehalte gegenüber CS-Daten immer noch weit verbreitet sind, haben wir die Entwicklung eines dreijährigen CS-Projekts zum Gesang der Nachtigall (Luscinia megarhynchos) analysiert, um bewährte Praktiken und gewonnene Erfahrungen darzustellen. Wir fokussierten uns auf den Datenumfang, das individuelle Engagement von Teilnehmenden, die räumliche Verteilung und die Fehlbestimmungen von Arten aus Aufnahmen, die vor (2018, 2019) und während des COVID-19-Ausbruchs (2020) mit einem Smartphone unter Verwendung der "Naturblick" App erstellt wurden. Die Anzahl der Aufnahmen von Nachtigallgesängen und das individuelle Engagement stiegen stetig an und erreichten ihren Höhepunkt in der Saison während der Pandemie. 13.991 Aufnahmen von Nachtigallgesängen wurden von anonymen (64%) und nicht-anonymen Teilnehmenden (36%) erstellt. Im Laufe des Projekts weitete sich die räumliche Verteilung der Aufnahmen aus (von Berlin auf bundesweit). Die Rate der Fehlbestimmungen war gering, ging im Laufe des Projekts zurück (von 10% auf 1%) und wurde hauptsächlich von gesanglichen Ähnlichkeiten mit anderen Vogelarten beeinflusst. Unsere Studie zeigte außerdem, dass das gesellschaftliche Engagement und die Datenqualität nicht direkt von den durchgeführten Disseminationsaktivitäten beeinflusst wurden, sondern dass erstere von externen Faktoren abhingen und letztere von der App profitierte. Wir schließen daraus, dass CS-Projekte, die Smartphone-Apps mit einem integrierten Mustererkennungsalgorithmus verwenden, gut geeignet sind, um die bioakustische Forschung in der Ornithologie zu unterstützen. Auf der Grundlage unserer Ergebnisse empfehlen wir, CS-Projekte langfristig zu etablieren, um eine aktive Teilnehmergemeinschaft (Community) aufzubauen, die qualitativ hochwertige Daten für fundierte wissenschaftliche Schlussfolgerungen generiert