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The wasp spider Argiope bruennichi (Arachnida, Araneidae): ballooning is not an obligate life history phase.


ABSTRACT. Aerial dispersal ("ballooning") involving Argiopebruennichi spiderlings may be claimed being an obligate life historytrait and a prerequisite with regard to spinning prey-capture webs. If this weretrue, any ballooning phase will be crucial for just about any laboratory rearingof A. bruennichi creating rearing protocols especially elaborate. Wetested your significance regarding ballooning regarding second-instar spiderlings inthe laboratory as well as demonstrated that the ballooning behavior is not essentialfor building prey-capture orb webs. Our outcomes also give simply no evidencefor your hypothesis which latest all-natural choice has evolved ballooningbehavior throughout newly founded field populations.

Keywords: Araneae, ballooning experiment, laboratory rearing, web-building behavior.

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Ballooning can end up being a widespread dispersal mechanism for a lot of modern spiders (Coyle 1983; Dean & Sterling 1985; Weyman 1993), which behavior is specially essential for sustaining genetic cohesion amongst Argiope populations (Ramirez & Haakonsen 1999). The Actual lifestyle reputation Argiope is seen as a ballooning, your aerial transport on wind-blown silk threads. The good illustration for the significance involving ballooning for range expansion may always be the Palearctic wasp spider Argiope bruennichi (Scopoli 1772). the spider is an r-strategist (Guttmann 1979), characterized by high aerial dispersal capability as well as an ongoing postglacial expansion of its geographical range in Europe (van Helsdingen 1982). Females of A. bruennichi create as a lot as five cocoons within the field, usually containing several hundred eggs (Crome & Crome 1961; Kohler & Schaller 1987). the expansion with the species provides accelerated within the second half of the final century most likely credited to end up being able to factors favoring dispersal by ballooning (Guttmann 1979; Levi 1983; Sacher & Bliss 1990; Scharff & Langemark 1997; Jonsson & Wilander 1999; Smithers 2000). The wasp spider prefers grassy or perhaps herbaceous vegetation inside open, ephemeral or shrubby websites (Wiehle 1931; Pasquet 1984; Malt 1996) in coarse-grained (patchy) landscapes (Gillandt & Martens 1980; Sacher & Bliss 1989) and has regionally benefited through extra time of farming production and urbanization (Lohmeyer & Pretscher 1979; Arnold 1986; Nyffeler & Benz 1987). River valleys have got been identified as favored dispersal corridors further supporting the importance of ballooning with regard to dispersion (Gauckler 1967; Puts 1988).

Follner & Klarenberg (1995) claimed ballooning being an obligate stage within the development of A. bruennichi. These authors monitored the pre-ballooning and ballooning behavior regarding spiderlings throughout a grassland study website close to Munich (Germany). Since that they never found aggregations involving orb webs in the neighborhood with the cocoons from which the over-wintering 2nd instar spiderlings eclosed plus they only observed the constructing of very first prey-capture orb webs following a ballooning trip, they concluded "that aeronautic behaviour in Bavarian populations regarding A. bruennichi is actually obligatory". Moreover, these authors suggested in which spiderlings, which have hatched coming from the cocoon, will starve in order to death, unless that they carry out the ballooning trip. Ballooning should thus end up being an obligate cycle in order to swap through a non-predatory, passive phase to one of active predation simply by spinning prey-capture orbs. Follner & Klarenberg (1995) argued in which the obligatory aerial dispersal might be the consequence of current natural selection and stay the reason powering the actual swift expansion of the species. New populations which usually are throughout place during a period of expansion are always founded by individuals, which have ballooned.

If ballooning were any truly obligate phase, it might not merely be important with regard to natural choice yet be also important for practically terraria cheat codes any rearing protocol with regard to A. bruennichi. Permitting for ballooning in the rearing procedure might effortlessly render laboratory breeding unfeasible because it could prove to be as well time-consuming and laborious. However, an obligate ballooning stage hasn't been observed before, neither in other Argiope nor within the usually well studied A. bruennichi. Tolbert (1976, 1977) studied ballooning behavioral elements associated with A. trifasciata (Forska[degrees]l 1775) and also A. aurantia Lucas 1833. He concluded from field along with laboratory observations that will "it will be unnecessary for spiderlings associated with possibly Argiope species in order to engage in aerial dispersal before creating an orb web" (Tolbert 1977), which is an obvious discrepancy to always be able to Follner's along with Klarenberg's (1995) claims. We here test the actual significance associated with ballooning for the construction of the first preycapture web inside the laboratory simply by looking at spiderlings reared under a pair of experimental conditions, 1 together with and one without ballooning.

We collected cocoons regarding A. bruennichi (n = 6) throughout dry along with semi-dry grasslands northeast of Halle (Saale) within late April 2002 (Germany, 160 m a.s.l., 51[degrees]33'31" N, 011[degrees]52'49" E). They had been maintained inside the lab in individual glass vials (9 cm diameter, 13 cm height, coated with fine gauze) with 23 [+ or -] 2 [degrees]C and also mist-sprayed together with h2o each a couple of days for you to avoid desiccation. The Particular vial bottom ended up being covered using initially wet cellulose wadding (1 cm). Second-instar spiderlings hatched in the cocoons in early May.

One day following hatching we simulated individual ballooning with regard to 60spiderlings (10 through each as well as every cocoon) by simply exposing the particular spiderling about aspatula for an air stream generated with a heat supply along with a fan (see Figs.1-4 pertaining to details of the experimental design). We observed behavioralelements inside the pre-ballooning cycle at length as well as noticed its mode.When your spiderling became airborne, we tracked it and retrieved it atthe "landing strip" (Figs. 3, 4). The Particular ballooning experimentwas repeated instantly (re-ballooning) pertaining to every individual to always be able to satisfya achievable "ballooning drive" (see Tolbert 1977). Thespiderlings had to actively participate in this experiment by showingthe entire sequence involving pre-ballooning along with ballooning behavior (Figs.1-4).

[FIGURES 1-4 OMITTED]

Following your experiments, the particular "ballooners" were kept in the exact same unheated indoor room using windows admitting indirect natural light. These People had been housed in groups (n = 20) within three gauze covered glass terraria (50 x 30 x 31 cm; 25 [+ as well as -] three [degrees]C; 65 [+ as well as -] 10% RH) and fed advert libitum 45-50 live Drosophila melanogaster when the day. Every two times we sprinkled the interior surfaces of the terraria using water. This prevented desiccation along with allowed for normal drinking behavior of the spiderlings. The Actual bottoms of the terraria had been covered using a layer of commercial, pasteurized potting soil (3 cm) along with grass tufts, some dry twigs and wooden skewers for you to enhance your quantity of potential attachment points for web building.

A manage team of spiderlings (n = 60) had been treated in the same way, however with out the actual ballooning procedure ("non-ballooners"). In both teams (ballooners vs. non-ballooners) spiderlings as well as orb webs were noted 3 x day-to-day from six a.m., 12 p.m. and six p.m. in order to ensure individual based information sets. The Actual rearing period has been cut off following 19 days when all the surviving people had spun their own first preycapture orb-webs.

Voucher specimens are generally deposited inside the Entomological Collection of the Martin-Luther-University Halle-Wittenberg (Zoological Institute), Germany (identification quantity 2568).

The web-building exercise of the spiderlings elevated within both the ballooners as well as the non-ballooners with time and reached 90 [+ or perhaps -] 5% for ballooners (n = 54, 3 terraria) along with 95 [+ or even -] 5% for non-ballooners (n = 57, three terraria) inside a new time period associated with 19d (Fig. 5). The distinctions within the web-building activity (Fig. 5) were not statistically significant among both sets of spiderlings (Kruskal-Wallis test, P = 0.7515; tested pertaining to every day built-first webs). The imply latency time with regard to web-building (time coming from hatching via the cocoon towards the construction regarding the extremely first prey-capture web) has been 8.61 [+ or -] 4.28 times and also 8.18 [+ or even -] 3.60 days regarding ballooners (n = 54) and non-ballooners (n = 57) respectively. This kind of distinction was not statistically significant (t-test, P = 0.56).

[FIGURE 5 OMITTED]

Although mortality increased inside the 2nd 1 / two of the actual observation period (Fig. 6), it didn't exceed 22% after the actual experiment (ballooners: 21.7 [+ or -] 2.89%, n = 13, non-ballooners: 20.0 [+ as well as -] 8.66%, n = 12, distinction not really significant, t-test, P = 0.77). The surviving animals caught prey in their orb webs as well as showed normal development using approximately four molts inside the particular experimental time.

[FIGURE 6 OMITTED]

Using our protocol, we might initiate the particular complete sequence of ballooning behavior promptly in each as well as every experiment. Your A. bruennichi spiderlings often confirmed an identical sequence associated with pre-ballooning and ballooning behavior (Fig. 1-4). Whenever exposed to the heat from your lamp, they displayed your "ballooning drive" behavior. Individuals walked to the margin with the spatula, spooled out a new dragline and also dropped down hanging from the line. Whilst suspended along with holding on for the drag line, they will discrete one more collection regarding 50-100 cm ballooning silk (Fig. 1). Any time it was lifted by the breeze generated through the fan and the heat source, the actual spiderlings cut the actual dragline and also became airborne (Figs. 2, 3). after landing (Fig. 4) they hauled within the ballooning line, formed it with the particular legs right directly into a silk blob and lastly ate the actual silk, bringing the ballooning behavioral sequence to become able to completion.

Tolbert (1977) observed a pair of modes associated with preparation regarding ballooning in sympatric area populations of A. trifasciata and A. aurantia. A spiderling attempting in order to become airborne climbed for the top of some blade involving grass or another structures along with adopted the typical "tiptoe" posture through depressing the particular cephalothorax and also elevating the opisthosoma. Multiple silk lines were then exuded through the spinnerets. When moving air generated sufficient silk, your spiderling became the "ballooner" (Nielsen 1932; Richter 1970; Eberhard 1987). Alternatively, the particular spiderling could grow to be airborne through dropping and hanging from a dragline, spinning a ballooning thread, which in turn then gradually lifted and lengthened in the breeze. The Particular ballooner then cut the dragline and floated off in in order to the air (Nielsen 1932; Bristowe 1939).

Argiope bruennichi can display both pre-ballooning modes. However, the drop as well as dragline mediated ballooning seems to be more frequent (Follner & Klarenberg 1995). Inside the particular field, second-instar spiderlings usually attach your draglines to guidelines involving grass blades as well as they will use silk threads which usually connect the ideas involving grass haulms as attaching points (Follner & Klarenberg 1995). in our experiments, we offered individual spiderlings optimal beginning conditions, and that we never observed your tip-toe ballooning mode. Follner (1994) suggested that "tip-toe" could be any tactical alternative pertaining to individuals in unfavorable beginning points (e.g., overcrowded ideas of grass blades).

Our results show that it isn't essential for spiderlings associated with A. bruennichi to engage in aerial dispersal before building a new prey-capture web. while ballooning can be frequent within the area (Follner & Klarenberg 1995), it is clearly not necessarily an obligate part inside the growth and also development of this species. Inside spite in the rapid expansion of the species more than the past decades as well as the prospective importance of aerial dispersal pertaining to colonizing new habitats, the particular role regarding ballooning in A. bruennichi will not differ from A. trifasciata and also A. aurantia where this cycle in your own life history is also not necessarily obligate (Tolbert 1977).



The mortality regarding concerning 20% following 19 times in each experimental groups (difference statistically not necessarily significant) points too rearing of A. bruennichi spiderlings to adulthood might become challenging. Our rearing approach according to an consuming plan together with Drosophila melanogaster, comparable to Mu"ller & Westheide (1993), worked well for our purpose, where we just tested the actual outcomes of ballooning throughout second-instar spiderlings on their capacity to produce their particular first web.

On average, much more then eight days elapsed just before A. bruennichi spiderlings began to build his or her very first prey-capture web. This particular appears to be any surprisingly long period, because the animals are only in the position to feed once the 1st web can be built. We can not exclude that is a laboratory artifact, regarding example due for you to unattractive web sites regarding web construction. However, the actual extended latency didn't interfere with almost all the rearing regime. The animals appeared being well adapted to always be able to temporary starvation since the mortality was lower in this phase (Fig. 6). Additionally in the field, the spiderlings do not really right away start along with prey-capture web construction (Follner & Klarenberg 1995) along with endure extended durations of starvation. Argiope spiderlings effortlessly survive several days nearby their cocoons, sometimes with communal meshworks regarding interlocking dragline threads ("communal tangles") (Tolbert 1976, 1977; Follner & Klarenberg 1995) exactly where that they find shelter until favorable weather or microclimate conditions enable ballooning (Tolbert 1977; Follner & Klarenberg 1995; notice in addition Suter 1999 regarding physics associated with ballooning).

Argiope spiderlings actively select suitable sites by ballooning, re-ballooning or walking (Enders 1973; Tolbert 1977; Follner & Klarenberg 1995). also on this nonpredatory stage the spiderlings must avoid starvation. Tolbert (1976) held A. aurantia spiderlings in the laboratory with out food along with water. Mortality remained reasonable in these experiments pertaining to a couple associated with days and just elevated distinctly about two weeks right after hatching.



The behavioral ballooning sequence could possibly be simply triggered under artificial conditions in our study, suggesting which it's likely to also occur in the area whenever environmental conditions allow. Therefore dispersal and also population structure will be primarily driven by microclimatic conditions inside the neighborhood habitats. The Actual neighborhood persistence of non-emigrants (non-ballooners and also short-distance ballooners) within A. bruennichi populations may well facilitate aggregated dispersion patterns, just such as weather phases which are unfavorable regarding aerial dispersal. Given ballooning is really a less effective means of long distance dispersal than formerly thought (Roff 1981; Decae 1987; Sensible 1993; Bonte et al. 2003), this could additionally explain the genetic differentiation amongst habitat patches within various other Argiope species (Ramirez & Haakonsen 1999).

The role of natural variety in range expansion features recently been discussed regarding insects inside the context involving global warming (e.g., Pimm 2001; Thomas et al. 2001). However, improving environmental circumstances at range margins may initiate range extensions purely around the foundation of ecological, physiological as well as population-dynamic processes certainly not requiring any evolutionary adjust (Thomas et al. 2001; notice also Coope 1995; Williamson 1996). Our results are in range with one associated with these views and also reject the hypothesis associated with Follner & Klarenberg (1995) which evolutionary processes have changed ballooning behavior within recently founded populations.

ACKNOWLEDGMENTS

We are grateful for you to Peter Neumann, Gail E. Stratton and two anonymous reviewers with regard to useful remarks upon previous drafts regarding the manuscript. We thank Christian W.W. Pirk pertaining to statistical advice, Vlastimil Ruzicka along with Theo Blick pertaining to providing literature. This study was supported by means of a analysis fellowship to A.W. in the State of Saxony-Anhalt along with from the Deutsche Forschungsgemeinschaft (DFG) grant to P.B. (BL 776/1-1).

Manuscript received 17 September 2004, revised ten August 2005.

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Andre Walter, Peter Bliss (1) and also Robin F.A. Moritz: Institut fur Zoologie, Martin-Luther-Universitat Halle-Wittenberg, Hoher Weg 4, D-06120 Halle (Saale), Germany. E-mail: bliss@zoologie.uni-halle.de

(1) Corresponding author.

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