Zoology 106 (2003): 223–231 © by Urban & Fischer Verlag http://www.urbanfischer.de/journals/zoology Spinning activity of the spider Trogloneta granulum (Araneae, Mysmenidae): web, cocoon, cocoon handling behaviour, draglines and attachment discs Jaromír Hajer* and Dana Rˇ eháková Department of Biology, University J.E. Purkinje, Ústí nad Labem, Czech Republic Received March 14, 2003 · Revised version received July 09, 2003 · Accepted July 13, 2003 Summary The spider species Trogloneta granulum, which in the wild lives inside scree slopes, builds three-dimensional orb webs. During egg-laying and egg sac building, the females stay with their dorsa down at the central part of the web. In this process, the hub is used as a platform. The threads of the hub are not incorporated into the silk cover of the egg sac. The silk wall of the egg sac is very thin, with all the silken threads constituting it having a uniform ultrastructure. The silk wall of the egg sac and the spin- nerets are permanently linked by a dragline. Draglines produced by T. granulum affect the direction of movements of the fe- male carrying its cocoon. Egg sacs are handled using draglines. The low number of piriform glands leads to the formation of very simple attachment discs, which fix the individual threads to the substratum. Thread bundles are attached to the substratum by means of accumulated attachment discs. Key words: spiders, Mysmenidae, silk, cocoon, draglines, attachment discs Introduction sensu lato. The family of Mysmeidae includes 24 gen- era with 96 known species (Platnick, 2003). Griswold Trogloneta granulum Simon, 1922 is a rare European et al. (1998) consider the Mysmenidae to be a poorly species with an extramediterranean distribution (Ru˚zˇicˇka, understood family. Little is known about the behaviour 1994; Buchar and Ru˚zˇicˇka, 2002). These spiders live on of these tiny spiders (Schütt, 2003). Eberhard (1987) the bottom side of stones in damp areas of scree slopes described webs and web building behaviour of several and in scree forests (Buchar and Ru˚zˇicˇka, 2002). With a symphytognathoid spiders, including two mysmenids total body length of up to 1.1mm in adult females and (Mysmena sp. and Maymena sp.). Kropf (1990) de- 0.9mm in adult males (Thaler, 1975), T. granulum is scribed web construction in the species Comaroma si- among the small spiders of Central Europe. moni Bertkau, 1889 which belongs to the Anapidae. The species belongs to the Mysmenidae, which, along Symphytognathoid families include small to minute with the Anapidae, Symphytognathidae and Theridio- species, which build three-dimensional orb webs (Gris- somatidae, forms the group of symphytognathoid fami- wold et al., 1998; Schütt, 2003). The symphytognathoid lies (Coddington, 1990; Griswold et al., 1998), “sym- orb web is most probably a synapomorphy of the group phytognathoids” being part of the superfamily Arane- (Schütt, 2003). Egg sacs (“cocoons”) have never before oidea. Schütt (2003) regards Mysmenidae along with been studied in detail in any other species of the Mys- Anapidae, Micropholcommatidae and Symphytog- menidae and very little is known about the construction nathidae sensu strictu as part of the Symphytognathidae of cocoons by other symphytognathoids. Kropf (1997) *Corresponding author: Jaromír Hajer, Department of Biology, University J.E. Purkinje, Cˇ eské mládezˇe 8, 400 96 Ústí nad Labem, Czech Republic; phone: ++420-475-601 309; fax: ++420-475-601 589; e-mail: [email protected] 0944-2006/03/106/03-223 $ 15.00/0 J. Hajer and D. Rˇ eháková gives a description of the egg sac structure in the of the spiders (Hajer, 2000). A high relative humidity species Comaroma simoni. (97–100%), also corresponding to the natural environ- Dragline silk is an extracellular fibrous protein called ment, was maintained by wrapping damp filter paper spidroin (Warner et al., 1999). Used by spiders to build around the outside of the Petri dishes. The dishes with web frames and to drop in controlled fashion from high spiders under observation were changed every 24 hours. places, it exhibits a unique combination of strength and This observation method was chosen, inter alia, due to toughness (Tirell, 1996). Anchored to the substratum Trogloneta granulum being not only a psychrophilic but by attachment discs, the “silk track” allows the spider also a photophobic species. Therefore, for the observa- to return safely to the starting point after a thrust at prey tion of living spiders it was necessary to use “cold light” or following a free fall; it also allows spiderlings to (circular fibre illuminator KVO). Video sequences of maintain contact with the parental web. The dragline the activity were copied on CD, and relevant pictures material is produced by a pair of major ampullate were printed on photographic paper. The photographs glands, while the material of attachment discs is se- showing movement of the spiders in detail during their creted by piriform glands (Foelix, 1996). Both types of spinning activity (and, therefore, not always perfectly glands are located at the surface of anterior lateral spin- focussed) were processed using an ACC (Adaptive nerets and have jet-like outlets called spigots. Contrast Control) Image Structure and Object Analyser. The research described in the present paper primarily This software was used to process Figs. 1–3 and 9. To focuses on the basic products of spinning activity, egg study the microstructure and ultrastructure of spidroin sacs and draglines, which, along with snares, are of crit- threads, we used an Eclipse E600 Nikon light micro- ical importance for the life of the studied spiders. Fol- scope equipped with a camera and a phase contrast fa- lowing up the latest study of the species (Hajer, 2000), cility, as well as a Tesla BS-340 scanning electron mi- we also researched the webs used for laying eggs. Be- croscope (Figs. 5, 7 and 8). Sections of a cocoon (Fig. 4) haviours associated with weaving the egg sac and using with embryos of Trogloneta granulum were made on draglines to handle the cocoon during development of day 5 of their embryonic development. For the process the eggs were observed. The results expand our knowl- of cutting with a microtome, the cocoon was inserted in edge of the family of Mysmenidae and may also be a piece of mouse liver. Sections (7 µ) were stained with used in analyses of phylogenes of the Araneoidea. hematoxylin and eosin. To study the ultrastructure of the threads forming the wall of the cocoon (Fig. 6), we em- ployed an AFM (Contact Atomic Force Microscope) Materials and methods METRIS 2001 (Burleigh Instruments Inc.). All material studied was from the Vysoká Beˇta area in the Blansky´ Les protected landscape area (South Bo- Results hemia, Czech Rep.). A total of 32 cocoons were ob- tained in the course of the research undertaken between Webs 1998 and 2002. Seven of these 32 egg sacs were col- lected at the above locality, while the other 25 were pro- Specimens of all nympho-imaginal stages of the onto- duced by 19 females kept under laboratory conditions. genetic cycle (except adult males) weave three-dimen- Most ethological observations were made from May 4, sional webs, resembling (if viewed from above) the 2001 to August 12, 2001. A video microscope equipped small orbs built by orb-weavers of the Araneidae. with a CCD camera was used during the study. The ma- Around the hub there are inner transverse threads which terial studied in this case consisted of 3 groups of 4 fer- connect all the radii and are continuously laid in the tilised females each, kept inside three Petri dishes form of concentric circles (Fig. 1). In completed webs, 100 mm in diameter and 15 mm high. Another 4 fe- more transverse peripheral threads are found distally males were kept separately in cubic glass boxes, made (Fig. 2B); however, these usually connect only two by glueing together the edges of four microscope glass (rarely three) neighbouring radii. With the exception of cover slips with dimensions of 22 × 22 mm. All contain- the hub, all components of the web are covered with ers were lined with black paper shaped so as to simulate droplets of a viscous secretion (Hajer, 2000). In gen- the uneven surface of stones. This arrangement gave the eral, the central part is oriented horizontally: so far, no spiders a place to hide and to spin their webs and co- web with a vertical hub has been observed. In the coons. At all times, one of the three Petri dishes was in- course of this study, the diameter of hubs woven by stalled under the video microscope, while the other two adult females varied from 0.5 to 1.0 mm (n = 27). In the were stored in a refrigerator at a temperature of centre of the web, spiders wait for prey. At the time of 9–11 °C. This temperature had been repeatedly mea- egg incubation, the same part of the web accommodates sured at the above-mentioned locality during collection egg sacs (Fig. 2 A–B). 224 Zoology 106 (2003) 3 Spinning activity of Trogloneta Egg sacs 3–5 eggs covered with viscous secretion on the ventral side of the spider’s opistosoma (i.e. immediately after During this study, the complete process of egg-laying leaving the gonopore); they did not continue with the and silk egg sac production (Fig. 3) was observed only construction of the cocoon. Having fled from the cen- five times. In the other three cases observed, the tral part the web, the female will shed the eggs, leaving females were interrupted by lightwhile there were them scattered throughout the web, and not revisit them. During egg laying, the female rests suspended on the threads of the central part of the web, with its dorsum downwards, as if waiting for prey (Fig.