Estereotipia e plasticidade na seqüência predatória de Theridion evexum keyserling 1884 (Araneae: Theridiidae)

Abstract

Web-spiders' foraging behaviour starts with the selection of a suitable site for web construction. The predatory sequence is initiated following spider contact with or receipt of some stimulus from a potential prey. The sequence continues with an approach or pursuit followed by attack and capture of the prey item; spider predatory behaviour shows varying degrees of plasticity. The present study describes the web of Theridion evexum (Theridiidae), and its predatory sequence upon the ant Atta sp. and Tenebrio molitor beetle larvae. The level of stereotypy present in the predatory sequences of T. evexum was evaluated and compared with other three theridiid species. The predatory sequences of T. evexum were taperecorded, transferred from the camera to a computer and analyzed with the assistance of EthoSeq, resulting in an ethogram for each of the prey types, and in a list of behavioural routines. The web of T. evexum has viscid elements all around. The selection of microhabitat with high humidity levels could be adaptive in this species, since the humidity conserves the viscid thread properties for a longer period of time, and thus reduces energy expenditures due to thread reposition. Preying upon ants requires more bites and partial transports than preying upon tenebrio larvae. This suggests that the immobilization of the ant is more difficult than the beetle larvae immobilization. The predatory behaviour is equally stereotyped to both prey types. This is probably related to dietary and web structure changes in the evolution from orbweavers to theridiids, which lead to a reduction in prey capture repertoire size in this family. Among the theridiids, T. evexum has the most stereotyped predatory sequence, and this seems to be associated with the low density of threads present in its web.Key words: Theridion evexum, predatory sequence, stereotypy, natural history, evolution. ResumoPara as aranhas de teia, o forrageamento inicia-se com a seleção de um local conveniente à construção da teia, sendo a seqüência predatória iniciada no momento em que a aranha entra em contato com ou recebe algum estímulo de uma presa. Aproximação, perseguição e captura da presa dão continuidade à seqüência predatória, a qual pode apresentar diferentes graus de estereotipia e plasticidade. O presente trabalho descreve a teia de Theridion evexum (Theridiidae), bem como sua seqüência predatória frente a formiga Atta sp. e a larva do besouro Tenebrio molitor. O grau de estereotipia presente no comportamento predatório de T. evexum é avaliado e comparado ao de outras três espécies de teridídeos. As seqüências predatórias dos indivíduos de T. evexum foram filmadas, transcritas ao computador e analisadas com o auxílio do programa EthoSeq, resultando em um etograma para cada presa em questão e em uma lista de rotinas comportamentais. A teia de T. evexum possui viscosidade em toda a sua extensão. A seleção de locais com alta umidade poderia ser adaptativa nesta espécie, pois a umidade conserva as propriedades dos fios viscosos por um maior p...

On the sticky cobwebs of two theridiid spiders (Araneae: Theridiidae)

“…This species, however, also forages as a kleptoparasite in webs of Eriophora pustulosa (Walckenaer, 1842) (Araneidae) and its solitary web may be just a temporary structure, where juveniles spend the winter (Whitehouse 1986(Whitehouse , 1997. Argyrodes flavipes Rainbow, 1916 (Whitehouse andJackson 1998) and Theridion evexum Keyserling, 1884 (Garcia and Japyassú 2005), on the other hand, were observed constructing webs with the same characteristics as those built by H. longicauda and C. intervales: an irregular structure of threads positioned on the inferior surface of a leaf, with some lines reaching the upper surface of another leaf located directly below, and viscid droplets on all the threads. An interesting similarity among these theridiids with webs entirely composed of viscid silk is that they seem to occur associated with water bodies.…”

“…Whitehouse and Jackson (1998) found webs of A. flavipes in places stationed away from sunlight, close to a stream in a rain forest near Cairns, Queensland, Australia. Garcia and Japyassú (2005) collected T. evexum in two areas in southeastern Brazil, at vegetation around a lake at Ibiú na, State of São Paulo, and close to waterfalls in Parque Nacional de Itatiaia, State of Rio de Janeiro. We could not find H. longicauda and C. intervales at sites located away from the rivers, while these species were abundant at the relatively humid sites.…”

Revision of the wolf spider genusDiahognaRoewer, 1960 (Araneae, Lycosidae)

“…This species, however, also forages as a kleptoparasite in webs of Eriophora pustulosa (Walckenaer, 1842) (Araneidae) and its solitary web may be just a temporary structure, where juveniles spend the winter (Whitehouse 1986(Whitehouse , 1997. Argyrodes flavipes Rainbow, 1916 (Whitehouse andJackson 1998) and Theridion evexum Keyserling, 1884 (Garcia and Japyassú 2005), on the other hand, were observed constructing webs with the same characteristics as those built by H. longicauda and C. intervales: an irregular structure of threads positioned on the inferior surface of a leaf, with some lines reaching the upper surface of another leaf located directly below, and viscid droplets on all the threads. An interesting similarity among these theridiids with webs entirely composed of viscid silk is that they seem to occur associated with water bodies.…”

“…Whitehouse and Jackson (1998) found webs of A. flavipes in places stationed away from sunlight, close to a stream in a rain forest near Cairns, Queensland, Australia. Garcia and Japyassú (2005) collected T. evexum in two areas in southeastern Brazil, at vegetation around a lake at Ibiú na, State of São Paulo, and close to waterfalls in Parque Nacional de Itatiaia, State of Rio de Janeiro. We could not find H. longicauda and C. intervales at sites located away from the rivers, while these species were abundant at the relatively humid sites.…”

Extended spider cognition

“…Web tensing is not a rare behaviour in spiders. It is used for prey detection among groups as diverse as Pholcidae (Japyassú and Macagnan 2004), Scytodidae (Japyassu and Machado 2010), Araneidae (Lubin 1980), Theridiidae (Japyassú and Jotta 2005; Garcia and Japyassú 2005), Tetragnathidae (Yoshida 1990), Nephilidae (Japyassú and Viera 2002), or Mygalomorphae (Coyle 1986) and occurs even among web-less spiders that invade other spiders’ webs (Whitehouse 1986). One of the primary, and basal, functions of spider silk is prey detection, a widespread function present in all major spider groups, from Mesothelae, through Mygalomorphae to Araneomorphae, including Haplogynae and Entelegynae (Coddington and Levi 1991; Blackledge et al 2009).…”