1. Centro de Estudios Parasitológicos y de Vectores CEPAVE (CCT-CONICET-La Plata) (UNLP), Calle 2 Nº 584, (1900) La Plata, Argentina; nferretti@conicet.gov.ar 2. Facultad de Ciencias, Sección Entomología, Iguá 4225, (11400) Montevideo, Uruguay; myga@fcien.com.uy
Intraspecific interactions of araneomorph spiders have received considerable attention, but there are few detailed studies on intraspecific interactions of mygalomorph spiders. Moreover, a thorough understanding of theraphosid biology and ecology is necessary from a conservation standpoint because natural populations may be threatened by habitat disturbances and captures for ]]>
Grammostola schulzei during non-sexual interactions, under laboratory conditions. Pairs of individuals involving adult males, adult females and juveniles were confronted and observed in resident and intruder conditions, totalizing 115 trials. When confronted two adult females, they retreated or grappled, and performed gaping display with bite attempts, usually resulted in severe injury of the intruder spiders. When confronted females with large juveniles, we frequently observed cannibalism on juveniles. Juveniles exposed to females or to other ]]>
Hay pocos estudios ]]>
Grammostola schulzei durante interacciones nosexuales en condiciones de laboratorio. Se confrontaron y observaron pares de individuos involucrando machos adultos, hembras adultas y juveniles en condiciones de locatarios y visitantes, totalizando 115 encuentros. Cuando dos hembras adultas se enfrentaron, retrocedieron o lucharon adoptando elevaciones anteriores e intentos de mordeduras que ]]>
Palabras clave: tarántulas argentinas, interacciones coespecíficas, comportamiento, territorialismo.
Mygalomorphs spiders (theraphosids spider lineages in particular) possess life-history traits that differ markedly from other spiders. For example, some species live for 15-30 years and require 5-6 years to reach reproductive maturity (Main 1978, Vincent 1993). Most species are habitat specialists and are extraordinarily sedentary (Main 1987, Vincent 1993, Coyle & Icenogle 1994). These life-history traits promote geographic fragmentation over space and time, resulting in a large number of taxa that have small geographic distributions. This combination of ]]>
et al. 2000). Moreover, a thorough understanding of theraphosid biology and ecology is necessary from a conservation standpoint because natural populations may be threatened by habitat disturbances and captures for pet commerce (Costa & Pérez-Miles 2002). ]]>
Intraspecific interactions of araneomorph spiders have received considerable attention, but there are few detailed studies on intraspecific interactions of mygalomorph spiders (Paz 1988, Jackson & Pollard 1990, Pérez-Miles & Costa 1992). This gap should be filled because, as Raven (1980) pointed out, mygalomorphs have many features that are plesiomorphic for spiders and this suggests that research on these spiders will provide important perspectives on evolutionary hypotheses. An increasing number of ]]>
et al. 1999, Costa & Pérez-Miles 2002, Quirici & Costa 2005). Theraphosids
may be especially useful models on which to base evolutionary interpretations in biological studies (Costa & Pérez-Miles 2002) and their phylogenetic systematics is reasonably wellknown (Pérez-Miles et al. 1996, Bertani 2000).
Theraphosids male courtship mainly ]]>
aggregated distribution is expected (Stradling 1994, Shilington & McEwen 2006). Moreover, in diplurid ]]>
Grammostola schulzei (Schmidt 1994) ]]>
the egg sac for two ]]>
The aim of this study was to describe the non-sexual interactions among males, females and large juveniles of G. schulzei ]]>
Materials and methods
Spiders: All the ]]>
ad libitum with cockroaches (Blattela germanica) and
Tenebrio sp. larvae (Coleoptera). For the trials we initially used five adult males, five adult females and five juveniles of G. schulzei. When spiders were injured or dead in the trials, new spiders of the same category were used. “Male” and “female” refer only to adult animals while “juveniles” refer to large immature individuals of unknown sex. All the females ]]>
averaged 21mm±3.1SD (n=5) and weighed 8.95g±0.75SD (n=5); male carapace length averaged 15.4mm±1.6SD (n=5) and weight showed average 4.72g±0.82SD ]]>
Experimental design: All the ]]>
- Female (R) (25 trials), Female (I) – Juvenile (R) (25 trials), Female - Female (20 trials) and Juvenile - Juvenile (20 trials), totalizing 115 trials. The pairs Male - Female were not used because the sexual behavior of this species was already described (Ferretti & Ferrero 2008). In the Male - Juvenile pairs, males were only intruders due to the wandering characteristics of adult males. Male - Male pairs were not carried out due the same reason. On each experimental group, one individual was exposed to the other spiders (five spiders in the first three experimental groups and ]]>
Encounters were directly observed ]]>
tests to compare frequencies of occurrences and no-occurrence of each behavior between two samples. The Pearson (when variables where non parametric) and Spearman (with ]]>
Results ]]>
Behaviors performed by females, juveniles and males in each experimental group are shown in Table 1, expressed as occurrence frequencies.
Female-female ]]>
: In three cases, intruder females made very rapid attacks “charges” by walking towards the other spider (mean speed 16.6cm per second). In these cases, we observed an initial fast motion along the first 15.0cm that then turned slower near the other spider (1.08cm/s). A single resident female made a “charge”. After contact, we observed two types of responses. One of them was “retreat” of one or both individuals, separating each other by retreating walking slowly or turning away. There were no significant differences between retreats of residents and intruders spiders (χ2=25.33, p=0.06). The other response was “gaping ]]>
Fig. 1). We found no significant differences in the occurrence frequencies of gaping between residents and intruders (χ2=13.56, p=0.19). We found statistically significant differences between correlations of weight and carapace length with “gaping display” of resident females and with “retreats” of intruder females (Table 2).
Other observed behavior was “grappling”, in which both spiders positioned face-to-face, interlacing the extended first and second pair of legs, and moving them quickly and irregularly. Palps were maintained raised and fangs extended (Fig. 2). Four intruders were injured on forelegs and one was killed. Six females retreated safely. Females that did not retreat displayed gaping during ]]>
observed 13 bouts swinging performed by resident females and five by intruder females during all encounters. The “release of draglines” by intruder females was frequent before retreating or confronting (16 bouts in all interactions). Each female oscillated side to side the abdomen, laying silken threads on the substrate while often walked slowly.
Female-juvenile interactions: Eight resident females performed “charge” towards the juveniles, while two females performed it as intruders. Occurrences frequencies of retreat were greater in intruder females than resident females (χ2=14.5, p<0.001). Eight resident females killed juveniles by biting the abdomen and carapace. The intruder females did not display “gaping” but ]]>
substrate. These behaviors were considered as a single behavior “tapping/drumming”, showing a mean duration of 5.20seconds (±1.93, n=10). We found statistically significant differences between correlations of weight and carapace ]]>
Table 2). Female “retreats” after contact were determined by the weight and size of both individuals and the smaller females did not “grapple” with juveniles of similar size.
Juveniles did not perform “charge” ]]>
Table 2). Only juveniles displayed “gaping” and “bite attempt” in response to female attacks. Intruder juveniles showed higher occurrence frequencies of “tapping/drumming” (17 bouts) when compared to resident juveniles (only one bout) using ]]>
Juvenile-juvenile interactions: Juvenile intruders made 21 bouts of “tapping/drumming” and only one juvenile resident performed it. We found significant differences in the occurrence frequencies of “tapping/drumming” between resident and ]]>
Table 2).
Male-juvenile interactions: Males made “charge” eight times towards juveniles and retreated in six cases. Before contacting, males performed “palpal drumming” far away from the juvenile location, as well as “leg tapping” and “body vibrations” caused by contractions of the third pair of legs. After contacting, five males made “spasmodic beats” on the body of juveniles with the second pair of legs, alternated or synchronously. These males “clasped” the juvenile’s fangs with the tibial apophyses of forelegs, and raised the juvenile carapace by extending forelegs and pushing it. One male ]]>
Table 1). Juveniles performed 27 retreats, nine gaping displays and one bout of “tapping/drumming”. No cases of biting or cannibalism were observed. ]]>
Discussion
Usually, intraspecific interactions of mygalomorph spiders in captivity (mainly during mating behavior) probably do not differ from the behaviors observed in the wild (Jackson 1988, Jackson & Pollard 1990, Bertani
et al. 2008, Ferretti & Ferrerro 2008) and it seems likely that our observations in captivity are representative of G. schulzei behavior. The agonistic behavior including offensive and defensive ones predominated during this study, as expected in predatory and cannibalistic animals as the spiders. Moreover, these behaviors could be acting as ritualized ones, thus determining the spatial distribution and protecting their burrows and shelters on nature.
]]>
Female-female interactions: Before the “grapples”, small intruder females tend to make “retreat” than large ones. Unexpectedly, intruder females made more “charges” than residents. Contrarily, Paz (1988) observed that intruder spiders of the diplurid Linothele sp. always retreated. These “charges” from intruder females could be a tactic to displace resident spiders and occupy limited shelters open areas. As expected, once in contact the ]]>
females. Pérez-Miles & Costa (1992) observed in Grammostola mollicoma (Ausserer 1875) that weight determined the predominance and that mutual estimation of ]]>
G. mollicoma, the grapple pattern, scarcity of injuries and the inhibition of attacks in non-frontal position suggest that this species is territorial but can live in an aggregated distribution (Pérez-Miles & Costa 1992). ]]>
In nature the encounters between females of G. schulzei could be more frequent than expected; for example, in the territorial boundaries because these Theraphosids are sedentary and also when some spiders abandon sites with scarce resources. In Brachypelma vegans Ausserer 1875, females were attracted for the cues left by other conspecific females, leading to aggressive ]]>
et al. 2008). Resident G. schulzei spiders also were very aggressive towards the intruders, in agreement to the observations of Paz (1988) in Linothele sp. (Dipluridae), as a clear tactic for both protecting burrows and foraging opportunities. The “gaping display” could be a threatening display, persuading conspecific spiders against dangerous ]]>
Porrothele antipodiana (Walckenaer 1837). This behavior could be also displayed towards any large animal perceived as a potential predator. “Gaping display” is widespread in Theraphosidae, and is performed when tarantulas are disturbed in open areas where burrows and refuges are scarce (Pérez-Miles et al. ]]>
G. schulzei spiders perform forward and backward movements with the first and second pair of legs, is described here for the first time for therpaphosid spiders. Acanthoscurria suina Pocock, 1903 also makes vigorous forward and backward movements, but involving only the first pair of legs (Pérez-Miles et al. 2005). ]]>
Female-juvenile interactions: Female “retreats” after contact were determined by the weight and size ]]>
Porrothele antipodiana. Juveniles also ]]>
Female-juvenile encounters maybe frequent during juvenile dispersion, allowing cannibalism. The ]]>
Brachypelma klaasi are capable of travelling not more than 3 or 5m away from their burrow searching for food or shelters (Yañez & Floater 2000). In Hadronyche sp. (Hexathelidae) individuals can travel exceptionally distances of 23m while searching for unoccupied shelters (Woodman et al. 2006). Juveniles also would contact with other juveniles and females when they establish their refuges and emerge for prey capture.
Juvenile-juvenile and male-juvenile interactions: The behavioral units of courtship of males observed during this study were similar to that reported by Ferretti & Ferrero (2008) in sexual interactions for this species. The juveniles “clasped” by males remained active and tried to escape or bite, as was ]]>
P. antipodiana. These facts suggest a connection between sexual and agonistic behavior (Pérez- Miles & Costa 1992). The clasping and mating attempts from males to conspecific other than adult females had already been reported by Pérez-Miles & Costa (1992) for G. mollicoma in male-male encounters.
Most mygalomorph ]]>
G. schulzei comprises hilly zones where they build the burrows, but burrow dimensions are always limited by the heavy stony substrate (N.E. Ferretti, pers. observ.). Juveniles and females need to find new shelters according to their ]]>
behaviors observed in this study during intraspecific interactions could play an important role by limiting density due to the scarcity of adequate sites for refuge construction. This intense competition could be less intense in species that dig and inhabit burrows in meadows, where females and juveniles dispose of many adequate sites (Main 1987).
Acknowledgments
Thanks to Anita Aisenberg for the valuable comments on this manuscript and to improve English. Thanks also to the anonymous reviewers for improving the manuscript. Daniela ]]>
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Correspondencia a: Nelson E. Ferretti. Centro de Estudios Parasitológicos y de Vectores CEPAVE (CCT-CONICET-La Plata) (UNLP), Calle 2 Nº 584, (1900) La Plata, Argentina; nferretti@conicet.gov.ar Fernando Pérez-Miles.Facultad de Ciencias, Sección Entomología, Iguá 4225, (11400) Montevideo, Uruguay; myga@fcien.com.uy
Received 13-IX-2010. Corrected 20-I-2011. Accepted 15-II-2011.