Notes on Dipoena melanogaster

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Acrobatic Copulation in the Theridiid Spider Dipoena melanogaster (C. L. Koch, 1837) by Barbara Knoflach

From The Newsletter No. 89 November 2000

Theridiidae exhibit considerable diversity in mating behaviour (Gerhardt, 1927; Bristowe, 1958; Braun, 1963; Knoflach, 1998). Copulation involves only two insertions in Crustulina scabripes Simon, 1881, but up to 350 in Theridion varians Hahn, 1831. It may last for a few seconds, as in Achaeamnea tepidariorum (C. L. Koch, 1841), or for several hours, as in Crustulina and Theridion. A mating plug, which prevents a female from remating, may be present. On the basis of the moment sperm uptake two groups exist. In the T. varians group, copulation starts with a preinsemination phase without sperm transfer, named pseudocopulation, and is interrupted serveral times by construction of sperm web and sperm induction. In this group the male approaches the female at her retreat. In contrast, the Steatoda type sperm induction takes place independently and copulation is without pseudocopulation. Most males of this type court on a mating thread and induce the females to approach them. For some of the 45 species studied by the author, observations were rather casual. Here, preliminary notes on the copulatory behaviour of Dipoena melanogaster (C. L. Koch, 1837) and D. tristis (Hahn, 1831) are given, with information about the acrobatic copulation of D. melanogaster.

Although Dipoena melanogaster and D. tristis are common in Middle Europe, their biology is poorly known (Wiehle, 1937; Miller, 1967; Knoflach & Thaler, 1998). As typical Dipoena they feed on ants. D. melanogaster occurs on bushes, deciduous trees and conifers, D. tristis mainly on pines. Both species have there reproductive period in May and June. In N. Tyrol (Austria) all females collected in July were gravid. The cocoon is woolly, much larger than the female, contains about 20 eggs, and is bright white in D. melanogaster, yellow in D. tristis. There is no brood care. Females remain near the egg-sac for a few days only.

All copulations (n=10) took place on a mating thread and involved 2-5 brief insertions only. Sperm induction occurs first some time after the final moult and again after copulation. Why may the copulatory behaviour be called 'acrobatic' in this species?—because D. melanogaster exceeds all comb-footed spiders hitherto studied in the extreme rapidity of its movements. The pair seems to perform a high-wire act.

Courtship is rather inconspicuous. The male approaches the female at the hub, sometimes plucking with his forelegs, attaches the mating thread and draws this thread horizontally for a distance of 3-4 cm. When receptive, the female immediately follows him along this thread. While doing so, her position lowers because of lengthening of this thread. When the male returns from the attachment point, she hangs almost cataleptic in a horizontal position, which is the mating posture, at the lowest point of the strongly inflexed mating thread. Insertion may take place at once. Usually the male descends several times from the attachment point (maximum observed 18 times), each time releasing a separate strand of silk. He stops just in front of the female, instals a new thread there and ascends once more along his safety thread, cutting the old mating thread. The new mating thread changes her position again. More details of this procedure cannot be given, as they were not clearly discernible even on the videotape. Thread replacement is sometimes combined with an unsuccessful insertion attempt. He always approaches her from above. After successful insertion the female returns hastily to the hub. For each insertion a new mating thread is spun and this acrobatic interplay is repeated. Insertions are brief, 6.5 seconds on average (n = 18; SD 2.9). I observed six copulations with two insertions, two with three, and even one with five insertions. Nevertheless, the entire insertion time was rather similar in six copulations (number of insertions in brackets): 13.3 (5), 14.0 (2), 15.8 (3), 16.5 (2), 17.3 (2), 18.6 (2) seconds. Afterwards the male remained close to the female, cleaning his palps and legs. He did not make a further attempt to mate within the next three hours. Then I separated them.

About 20 minutes after copulation (mean; n=7) the male starts construction of the sperm web. The whole procedure of sperm induction lasts on average 6.5 minutes. The large, white sperm droplet is absorbed by only 10-15 dipping movements of the palps, the contact of palp and droplet being rather long (c. 20 seconds). One male built two sperm webs in succession, another even three, but one without a droplet. Therefore sperm induction actually occupies more time than copulation. Females may remate: two refused, and two accepted a second copulation.

Description is based on five observations. Copulation differs from D. melanogaster as follows. No mating thread is constructed. The male approaches the female directly and starts with insertions, when the female is receptive. Then 60-110 brief insertions follow, each of only 1-3 seconds. Left and right palp are applied alternately, haematodochal swelling is rapid, but comparatively small. The entire copulatory sequence takes 3-10 minutes. Copulatory posture is typically theridiid. Movements are less rapid than in D. melanogaster. Some 13-20 minutes after copulation, the male spins the sperm web; two males even spun a second web 35 minutes after the first. Sperm induction lasts on average 6.3 minutes (n=5). The absorption of the sperm droplet involves 26-31 dipping movements.

Discussion
D. melanogaster, type species of the genus, clearly fits the Steatoda type, as copulation takes place outside the hub on a mating thread, and the sperm web is built independent of copulation. As in other species which do not charge their palps with sperm during copulation, sperm induction lasts rather a long time. Unlike Steatoda, the female of D. melanogaster is not lured to the mating thread by plucking movements and vibrations, but follows the male immediately. The male brings the female into the mating position by lengthening of the thread. The unusually rapid tempo of copulation is reminiscent of that in the Araneidae. Courtship via a mating thread is present in many araneid spiders and is considered as derived, as it represents an additional construction (Robinson & Robinson, 1980). 'Derived' Theridiidae (in the sense of Levi & Levi, 1962) court at the hub (e.g. Coleosoma, Neottiura, Rugathodes, Theridion), whereas more 'primitive' ones construct mating threads (e.g. Steatoda, Enoplognatha).

Timing and duration of sperm uptake place D. tristis also in the Steatoda type. Nevertheless, approach behaviour and high number of insertions are similar to those of the Theridion uarians group. Apparently high numbers of insertions occur independently in different lineages of theridiid spiders. These observations furthermore A. Male at the female hub B. Female following male along mating thread strengthen the splitting of Dipoena Thorell, 1869, suggested by Wunderlich (1988). However, the separation of Lasaeola Simon, 1881 and Dipoenata Wunderlich, 1988 still has to be investigated more closely. D. tristis, type species of Lasaeola (see Bonnet, 1957), apparently shows the features listed for Dipoenata (see Wunderlich, 1988).

References
Bonnet, P. (1957) Bibliographia Araneorum, 2 (3). Douladoure, Toulouse.
Braun, R. (1963) Zur Sexualbiologie der Theridion sisyp/iium-Gruppe (Arach., Aran., Theridiidae). Zoo/. Anz. 170: 91-107.
Bristowe, W. S. (1958) The World of Spiders. Collins, London.
Gerhardt, U. (1927) Neue biologische Untersuchungen an einheimischen und auslandischen Spinnen. Z. Morph. Okol. Tiere, 8: 96-186.
Knoflach, B. (1998) Mating in Theridion varians Hahn and related species (Araneae: Theridiidae). J. not. Hist. 32: 545-604.
Knoflach, B. & Thaler, K. (1998) Kugelspinnen und verwandte Familien von Osterreich. Okofaunistische Ubersicht (Araneae: Theridiidae, Anapidae, Mysmenidae, Nesticidae). Stapfia (Linz), 53: 667-712.
Levi, H. W. & Levi, L. R. (1962) The genera of the spider family Theridiidae. Bull. Mus. comp. Zoo/. Harv. 127: 1-71. figs 1-334.
Miller, F. (1967) Studien uber die Kopulationsorgane der Spinnengattung Zelotes, Micaria, Robertus und Dipoena nebst Beschreibung einiger neuer oder unvollkommen bekannten Spinnenarten. Pfirodov. Pr. Cesk. Akad. Ved., N.S.I: 251-298.
Robinson, M. H. & Robinson, B. (1980) Comparative studies of the courtship and mating behavior of tropical araneid spiders. Pacif. Insects Monogr. 36: 1-218.
Wiehle, H. (1937) 26. Familie: Theridiidae oder Haubennetzspinnen (Kugelspinnen). Tierwelt Dtl. 33: 119-222. Wunderlich, J. (1988) Die fossilen Spinnen im Dominikanischen Bernstein. Beitr. Araneol. 2: 1-378.
 
Added by John Partridge at 12:16 on Thu 9th Feb 2012. Return to Summary for Dipoena melanogaster