Abstracts

Genitalic stridulation during copulation in a species of crane fly,Tipula (Bellardina) sp.

Ciudad Universitaria, Costa Rica; william.eberhard@gmail.com

2. Department of Entomology, The Academy of Natural Sciences, 1900 Ben Franklin Parkway Philadelphia, PA,

gelhaus@ansp.org

Correspondence.

Tipula (Bellarina) from San José Province, Costa Rica. A male crane fly stridulated (produced vibrations) during copulation using sustained and stereotyped movements of file and scraper structures on his genitalia.

Key words: copulatory courtship, genitalic evolution, sexual selection, cryptic female choice, Costa Rica.

Chartergellus (Richards 1978). No behavioral observations of genitalic stridulation have ever been made, however, and stridulation prior to copulation, as occurs in the pyralid moth Syntonarcha iriastis using the male genitalia (Gwynne & Edwards 1986),was not ruled out in these groups.

Tipula (Bellardina) sp. It describes file and scraper structures in this and related species, and presents the first direct observations of the behavior of such a genital structure, confirming that the file and scraper are used to stridulate during copulation.

2006 a copulating pair of T. (Bellardina) sp. was found by one of us (WGE) at about 11 AM clinging to the outer wall of a house near San Antonio de Escazú, 1 325m, San José Province, Costa Rica, with the male hanging below the female. The female was induced to climb onto a plant stem, and the stem was placed under a dissecting microscope, where the pair’s genitalia were observed. Behavior was taped at 30 frames/sec through the microscope at room temperature using a SONY DCR TRV50 digital video camera. The flies gave little sign of being disturbed by this treatment, and their large size permitted detailed observations. “Dorsal” and “ventral” in the descriptions below are determined with respect to the male. The specimens are deposited in the collection of the Academy of Natural Sciences, Philadelphia.

^{Fig. 1}). For about 10-15min the pair was nearly completely immobile, except for one brief 2-3second burst  of rhythmic genital movements. Then, however, the male abruptly began to vibrate his genitalia in bursts, and continued to do so nearly continually for more than 10min (just over 8.5min were taped). Each vibration consisted of two movements: movements of his ninth sternite apical lobes (and thus of the female’s cerci which they held) (two curved arrows at left of ^{Fig. 1A}); and a smaller, simultaneous movement of the outer gonostylus in approximately the opposite direction (arrow at right in ^{Fig. 1A}). The female cerci shifted little if at all in the grip of the male ninth sternite apical lobes during these movements.

During each movement the tip of the strong, dark-tipped, flattened extension of the outer gonostylus (“scraper” in ^{Fig. 1A}, ^2B) scraped across a striated region at the lateral base of the male apical lobes of the ninth sternite (“file” in ^{Figs. 1A}, ^2C). The scraper typically  moved across about four ridges of the file with each stroke (^{Fig. 1A}). The scraper was probably in contact with the file during these movements, as the setae on the more basal portion of the outer gonostyluswere sometimes deflected by contact with the file during a scraping movement.

The rate of scrapes during a single burst of vibration was on the order of 15-30cycles/sec. The rhythm of bursts of scraping and pauses between them was very regular, except during one 33.9sec burst of scraping (^{Fig. 3}). During the regular phase, the duration of a burst averaged 2.02+0.39sec (N=83), and bursts were separated by pauses that averaged 2.91+0.90sec (N=79). During the exceptional 33.9sec interval, both the rhythm of bursts of scraping and the movements themselves changed. Stridulatory movements were nearly continuous, but an additional movement was imposed, in which the male’s ninth sternite apical lobes periodically slid distally along the female cerci and also moved slightly dorsally (^{Fig. 1B}), and then returned to the previous position. This movement was also very rhythmic, occurring on average once every 1.34+0.36sec.

Tipula (Bellardina) is an entirely New World group of 15 species distributed from the Central and Southwestern USA to the central Andes (Oosterbroek 2006); the aquatic larval stage is described in Gelhaus (1986) and biogeographic distribution is discussed by Contreras Ramos & Gelhaus (2002). Although identification to subgenus can be made by keys (Alexander & Byers 1981 for North America; Gelhaus, 2009, for Central America), the group is otherwise poorly known, with no keys or comprehensive reviews of species, and the identity of several described species is still uncertain. Gelhaus (2009), provides a summary of knowledge for this group in Central America; there are no described species recorded for Costa Rica.

Costa Rica, with none clearly matching any identified species in the material from the Smithsonian or Academy collections. Based on scraper and

T. rupicola species group including at least T. cydippe (Guatemala, Venezuela), T. fuscolimbata (Mexico), T. larga (Mexico), T. rupicola (Arizona, USA) and two undescribed species from Costa Rica, including the Costa Rican specimens whose behavior is described here. The male genitalia of these species all show the following traits. The apical lobe of the outer gonostylus (scraper) in flat, of variable length, with a slightly expanded, darkened truncate to spatulate apex (^{Fig. 2b}). The mesal aspect of the outer gonostylus is expanded into a ridge near the base covered with a distinct brush of strong setae. The apical lobes of the ninth sternite show distinct ridges on their outer surfaces at the base (^{Fig. 2c}); the number and height of the ridges is variable among the species. The species which is the subject of this paper is closest to T. rupicola, differing in minor details such as the lobe of the outer gonostylus.

T. schizomera species group including at least T. flinti (Mexico), T. praeluta (Southwest USA), T. pura (Southern Rockies, USA), T. schizomera (Southwest USA to Mexico) and two undescribed species from Costa Rica. In the male genitalia of these species, the apical lobe of the outer gonostylus (scraper) forms a strong, black, apical spine, often separated from an equally long fleshy lobe. The mesal aspect of the outer gonostylus is not expanded into a ridge and lacks strong setae, although scattered hairs are sometimes present. The apical lobes of the ninth sternite lack distinct strong striae or ridges at the base, but have a roughened surface of fine bumps extending from midlength to near the apex, sometimes set in a depressed region.

T. theobromina species group includes only this single species (distributed in the Central to Northern Andes). The male genitalia of this species are intermediate with respect to the above two groups. The apical lobe of the outer gonostylus (scraper) is flat, with a rounded, not expanded, darkened apex. The mesal aspect of the outer gonostylus is slightly expanded into a ridge, but has only scattered setae that are not concentrated in a distinct brush. The apical lobes of the ninth sternite lack distinct strong striae at the base, but show a set of very fine lines at midlength which are seen at high magnifications (400X) to be a roughened surface of fine bumps.

T. (Bellardina) sp. is the brush of robust pointed setae projecting medially from the male’s outer gonostylus (^{Fig. 2B}). These setae probably press on the female’s 10th segment pleural membranous area, just basal to her cerci during copulation, and the setae may scrape against the female during male stridulatory movements. These setae may thus constitute

T. (Bellardina). In addition, in six other species of T. (Bellardina), there is a spine-like “scraper” structure, and there is no “file” structure but instead a roughened or bumpy surface at midlength of the ninth sternite apical lobes, indicating either a lack of stridulation, or possibly a different mechanism. These species also lack a brush of setae on the mesal aspect of the outer gonostylus.

et al. 2003, Arnqvist & Rowe 2005.) There is no female “lock” with which the stridulatory structures mesh; and stridulation by the male exerts no appreciable coercive force on the female.

We thank STRI and UCR for financial support to WGE. We thank Wayne Mathis, curator, and Holly Williams, collection manager, for the loan of specimens from the Alexander Collection of Crane Flies at the Smithsonian Institution.

Tipula (Bellardina) sp. estriduló (produjo vibraciones) por medio de movimientos estereotipados de estructuras de sus órganos genitales durante varios minutos de la cópula. Los machos de algunas especies relacionadas poseen estructuras similares, lo cual sugiere que también estridulan durante la cópula.

Palabras clave: cortejo copulatorio, evolución órganos sexuales, selección sexual, selección críptica en hembras, Costa Rica.

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