Can’t you find me? Female sexual response in Grammostola schulzei (Schmidt 1994), an Argentinean tarantula.

FERRETTI, N., S. COPPERI, G. POMPOZZI, F. PÉREZ-MILES

Siedlce, Polonia

Congreso; 18th International Congress of Arachnology; 2010

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Studies of mating behavior are limited to few species. Vibratory sexual signals (acoustic and seismic) are frequently used in spider courtship, especially in tarantulas (Uetz & Stratton 1982; Prentice 1992; Quirici & Costa 2005, 2007). Seismic signals generated by male spiders can reach 1 m in ctenids (Barth et al. 1988) and 1.30 m in theraphosids (Quirici & Costa 2007). The usual indicator of effective male signals is the behavioral change of the receptive female. The most unambiguous receptive response usually is leg waving, leg tapping or body vibrations (Ferretti & Ferrero 2008; Prentice 1992; Quirici & Costa 2005, 2007). Grammostola schulzei (Schmidt 1994) is a tarantula from Argentina that lives in burrows under stones in rocky hills (Ferretti & Ferrero 2008). G. schulzei is the unique species of the genus where females showed sexual response to courting males, but the context and possible function of this response was not elucidated (Ferretti & Ferrero 2008). In captivity, female sexual response could be observed allowing females to build and occupy a retreat as in natural conditions but not in open arena (Bertani et al. 2008). The main objective of this work is to elucidate under what context females responded to male’s courtships and to determine the possible function of these behaviors.   MATERIAL AND METHODS   Eight males and eleven females were collected in Sierra de la Ventana (38º 07’63” S 61º 47’ 30” W), Buenos Aires, Argentina during October – January 2008 – 2009. For all experiments, females of known reproductive history were used. They were housed in glass jars of 13 cm diameter and 15 cm height, with 5 cm of soil as substrate and water provision. They were fed ad libitum with Zophobas sp. larvae. We carried out three series of 20 experiments each with different situations for the encounters male-female. In series “A”, males were placed free in terrarium but with no access to female due to the heavy stone covering the burrow. In series “B”, males were placed far off from the female burrow (30 cm) and confined into a glass cup. In series “C”, males were placed over the heavy stone that closed the burrow of female and confined into a glass cup. The courtship of males was elicited by abundant silk of females inside the glass cup. For the encounters we used glass terraria measuring 30 x 35 and 30 cm high containing a 10 cm thick layer of soil as substrate. In each terrarium, a burrow was constructed against the glass wall, allowing visual observations of female behavior inside burrow. Each terrarium was placed in different tables in order to minimize ground vibrations and to prevent seismic signals from passing between terraria. Females were placed in terraria and trials were carried out for > 5 days, allowing each female to adapt to the burrow. The entrance of each burrow was closed with a heavy stone (collected from their natural habitat) so females couldn’t leave the burrow and had no access to males. We considered active each male which showed intense courtship of >30 min. The encounters were videotaped with a Handycam Panasonic SDR-S7 and video records were analyzed with a PC program.     RESULTS   We observed two types of responses of females to male courtships: leg tapping and body movements. In series A, three different females made their sexual display tapping vigorously with palps and first pair of legs or only with palps. In video analyses, females made leg flexing, lifting and lowering against the substrate. The mean number of leg movements during leg tapping was 16.44 ± 15.26 SD and the mean number of bouts was 20.5 ± 12 SD. The mean duration of leg tapping was 1.63s ± 0.90 SD and the mean duration between bouts of female leg tapping was 48.20s ± 37.49 SD. All responses were after the palpal drumming of males and long courtships (approximately 1 hour). Moreover, females that responded with leg tapping scraped vigorously the stone with first pair of legs. One male obtained responses from two different females. After female tapping, males frequently oriented to the female burrow and stayed courting nears her. Females responded with body movement in series A and C, where males were confined. These displays consisted in high frequency downward and upward movement of the entire body. In video analysis, we observed a contraction of the third pair of legs during movements. These responses were observed after male palpal drumming and the number of the movements was highly variable, ranging from 2 to 61 (mean = 16.6 ± 24.96 SD). One female made body movements with two different males in series A and C. Two more females performed this behavior in series C and even one of them made body movements with two different males. During series C one female that performed body movements made three attempts of abrupt emergence inside the burrow and the male quickly retreated.     DISCUSSION               Our results suggest the presence of seismic communication by substrate during courtship in G. schulzei in agreement with findings of Quirici & Costa (2005) in other theraphosids. Female leg tapping as response to some male courtship seems to indicate her receptive condition and her attractiveness, as was found for Acanthoscurria suina and Eupalaestrus weijenberghi (Pérez-Miles et al., 2007; Quirici & Costa, 2005). However, female leg tapping response was only observed in series A in which males freely walked in the terrarium and after extremely long courtships. We suggested that additionally female response could orient male towards her location. This orientation could serve at long distance because when males were very near the burrow, females did not respond (series C). Considering that female response is obtained after an insistent long male courtship, we interpret that such response could act in extreme cases where males could not find her burrow or if is difficult for the female to exit from the burrow. Also insistence of males could be a positive honest signal of males with good condition to mate, and consequently selected by females. These females responded with leg tapping to males which present long courtships together with active searching (walking) for female’s location (series A). This was not the case in series B and C with males confined. Although these males confined courted, they did not receive female tapping response. Summarizing females respond with leg tapping only to males which court and walk. The female body movements are interpreted here as a rejection considering male retreated after this female behavior in series C.  Body movements seems to be different from the piston behavior observed for E. weijenberghi (Pérez-Miles et al., 2007), because in G. schulzei this behavior consisted in downward and upward body movements, have higher frequency, and are probably originated by third pair of legs. Piston behavior was proposed as a ritualized rejection response, considering that after that male immediately escaped (Pérez-Miles et al., 2007). Female body movements are a signal that could help the male to save time and energy spent in courtship and also to reduce the risk of attracting predators. For the female this rejection of male contributes avoiding her distraction from other biological activities (Pérez-Miles et al., 2007). We observed body movements of females predominated in series C, where males were confined in the nearest possible location to female burrow.       BIBLIOGRAPHY     Barth, F.G., H. Bleckmann, J. Bohnenberger & Seyfarth, E.A. 1988. Spiders of the genus Cupiennius Simon 1891 (Araneae, Ctenidae). II. On the vibratory environment of a wandering spider. Oecologia. 77:194–201.   Bertani, R., C. S. Fukushima & Silva Júnior, P. I. 2008. Mating behavior of Sickius longibulbi (Araneae, Theraphosidae, Ischnocolinae), a spider that lacks spermathecae. Journal of Arachnology. 36:331–335.   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.   Pérez-Miles, F., Postiglioni, R., Montes de Oca, L., Baruffaldi, L. & Costa, F.G. 2007. Mating system in the tarantula spider Eupalaestrus weijenberghi (Thorell, 1894): Evidences of monandry and polygyny. 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