First notes on reproductive biology, burrows and eggsacs of the tiny mygalomorph spider Xenonemesia platensis (Araneae, Microstigmatidae)

NELSON FERRETTI; GABRIEL POMPOZZI; SOFÍA COPPERI; FERNANDO PÉREZ-MILES; ALDA GONZÁLEZ

Siedlce, Polonia

Congreso; 18th International Congress of Arachnology; 2010

University of Podlasie & International Society of Arachnology

INTRODUCTION The Microstigmatidae are characterized by the rounded book-lungs openings, in conjunction with extremely shortened posterior lateral spinnerets (Goloboff, 1995). This family comprises 15 species, nine of them distributed in the New World (Platnick, 2010). Microstigmatidae are ground-dwelling and free-living spiders that appear to make minimal use of silk and could readily attack and fed upon small insects (Griswold, 1985). Some studies were done on reproductive biology of Mygalomorphae (Coyle 1985; Coyle & O´Shields 1990; Costa & Pérez-Miles 2002; Ferretti & Ferrero 2008; Yañez et al. 1999) but sexual behavior of Microstigmatidae is up to now unknown. Few records of natural history and ecology were reported for the Old World microstigmatids (Griswold, 1985) and for a Brazilian species (Indicatti et al., 2008). Xenonemesia platensis is the only microstigmatid species present in Argentina and only some comments on their habitat have been provided (Goloboff, 1988). In the present study we describe the mating behavior of X. platensis based on three successful matings under laboratory conditions and give some notes on their burrows and eggsacs.   MATERIAL AND METHODS Two males and six females were collected during August 2009 on the Martín García Island (34º 11’ 25’’S; 58º 15’ 38’’W). The individuals were mantained in plastic Petri dishes (9 cm diameter), with soil as substratum and a wet cotton wool. All individuals were fed weekly with cockroaches (Blattela germanica). We carried on five sexual encounters. The female dish was placed in the center of a larger glass cylindrical container (19 cm diameter and 10 cm high) with a layer of soil of approximately 6 cm. Then, the male was gently placed far off from the female position. The room temperature during the experiments was 26.7° ± 1.52° C. The encounters were videotaped and analyzed with a PC program (Sony Vegas 9.0). RESULTS Males initiated courtship when contacted with the female body. Females remain passive. The courtship started with body vibrations originated by contractions of the first and second pair of legs followed by fast upward and downward movements of palps in a simultaneous phase. The frequency was 33.5 ± 3.8 SD bouts/min and the mean duration was 0.54s ± 0.06 SD (n = 25). Also males made palpal boxing that consisted in alternating movements of the pedipalp touching the genital zone of the female. The males performed 6.66 ± 4.04 SD bouts/min with a mean duration of 1.92s ± 0.95 SD (n = 6). After contact, males vigorously hit the first and second pair of legs of females with his second pair of legs extended. This behavior consisted in tapping at high frequency in an alternating or synchronous phase; male tarsi contacted with the metatarsi of female. Males performed 6 ± 1.73 SD bouts/min with a mean duration of 0.96s ± 0.38 SD (n = 7). After tapping, the males clasped with first pair of legs between palps and chelicerae of the female. The distal portion of each male tibia without tibial apophyses or megaspines was against the prolateral surface of each female pedipalp base and then begins palpal insertion attempts. The mean number of insertions was 8 ± 6.2 SD and their mean duration was 17.61s ± 18.11 SD (range = 3 – 37.88). During insertions, males continued courting the female by tapping with legs II and body vibrations. Males then added a new courtship behavior; they raised the second pair of legs with an angle of 90° between femur and patella, and quickly moved legs upward and downward.  Male tibia, metatarsi and tarsi remain extended and the tarsi beat and scrape the second and third coxae of female. This behavior had a mean duration of 8.62s ± 5.85 SD and the velocity was 14 beats per second. During the palpal insertion attempts the second pair of legs was pushing the first pair of legs of female and the female’s pedicel was flexed upwards so that the cephalothorax-abdomen angle was 30-50°. The mean duration of copulation was 4.04min ± 1.13 SD. After copulation females retreated into the burrows. In one case, the male followed courting her in contact making body vibrations. We observed one female rejection that consisted in vigorous lateral abdominal oscillations with body elevated. After that male escaped. All individuals were found in a shore forest occupying short burrows with little silk covering the walls and the entrance closed with silk and debris. In nature, the silk tube entrance ranged from 0.8 to 9.5 mm diameter and its length 16.15 mm ± 7.7 SD; the short burrow measured approximately 12 mm. The temperature inside the burrows was 15°C and the environment temperature was 14°C. In laboratory they constructed the same shelters as in nature but with more silk covering the walls. Two egg-clutches were observed in the laboratory. One female made the eggsac on 23 November 2009 and the other on 16 December 2009. The eggs were agglomerated in a sphere without a well developed silk cover. They measured 5 mm width x 8.6 mm length containing 17 eggs and 6.7 mm width x 8.4 mm length. Both females abandoned their eggsacs between 7 January 2010 and 25 January 2010.        DISCUSSION As far as we know, these are the first reports on sexual behavior of a Microstigmatidae. Some uncommon behaviors are remarkable. Differing from most known mygalomorphs the male did not started courtship when contact female silk but only after contact with female. Early studies proposed that mygalomorph spiders lacked chemical cues in sexual communication (Baerg, 1958; Platnick 1971); however, more recent studies reported the presence of pheromone associated with silk threads of females (Costa & Pérez-Miles 2002, Ferretti & Ferrero 2008). Our findings in X. platensis could reveal the absence of pheromone associated to silk. The body vibrations observed in the courtship of X. platensis could be similar to those observed in some theraphosids (Costa & Pérez-Miles 2002, Ferretti & Ferrero 2008) but in X. platensis the vibration is generated by first and second pair of legs instead of pair III involved in theraphosids. Others remarkable behaviors in X. platensis were the brusque movements of the palp and the scraping with legs II during courtship that were not reported in any other mygalomorph spider. The brusque movements of palps could be similar to the “twitching” observed in a diplurid (Coyle & O´Shields, 1990) which consisted in separate sudden flexions or extensions of one or more legs or palps. The male courtship in copula observed in X. platensis was not reported in mygalomorphs (Costa & Pérez-Miles, 1998; Costa & Pérez-Miles 2002; Ferretti & Ferrero, 2008; Jackson & Pollard, 1990). It is possible that the female may be testing male’s copulatory ability, monitoring his performance not only in genital stimulation, as suggested by Eberhard (1985). This male behavior could additionally inform the female about his good quality and consequently could be interpretable as other mechanism for seduction.          BIBLIOGRAPHY   Baerg, W.J. 1958. The Tarantula. University of Kansas Press, Lawerence, Kansas. 88 pp.   Costa, F.G. & F. Pérez-Miles. 1998. Behavior, life cycle and webs of Mecicobothrium thorelli (Araneae, Mygalomorphae, Mecicobothriidae). Journal of Arachnology, 26: 317–329.   Costa, F.G. & F. Pérez-Miles. 2002. Reproductive biology of Uruguayan theraphosids (Araneae, Theraphosidae). Journal of Arachnology, 30: 571–587.   Coyle, F.A. 1985. Observations on the mating behaviour of the tiny migalomorph spider, Microhexura montivaga Crosby & Bishop (Araneae, Dipluridae). Bulletin of the British Arachnological Society 6(8):328-330.   Coyle, F.A. & T.C. O’Shields. 1990. Courtship and mating behavior of Telochoris karschi (Araneae, Dipluridae), an African funnel web spider. Journal of Arachnology, 18: 281–296.   Eberhard, W.E . 1985. Sexual selection and animal genitalia. Harvard Univ. Press, Harvard, Massachusetts.   Ferretti, N. & Ferrero, A. 2008. Short Communication: Courtship and mating behavior of Grammostola schulzei (Schmidt 1994) a burrowing tarantula from Argentina. Journal of Arachnology, 36: 480-483.