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

January 4, 2016
ABSTRACT. Aerial dispersal ("ballooning") regarding Argiopebruennichi spiderlings continues to always be able to be claimed to become an obligate lifestyle historytrait along using a prerequisite regarding spinning prey-capture webs. When this weretrue, the ballooning cycle would be essential for nearly any laboratory rearingof A. bruennichi making rearing protocols specially elaborate. Wetested the particular significance of ballooning regarding second-instar spiderlings inthe laboratory and showed that the actual ballooning behavior just isn't essentialfor creating prey-capture orb webs. Our results in addition give simply no evidencefor the hypothesis that will recent all-natural choice has evolved ballooningbehavior inside freshly founded field populations.

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

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Ballooning can end up being a typical dispersal mechanism for a whole lot of modern spiders (Coyle 1983; Dean & Sterling 1985; Weyman 1993), and in addition this behavior is especially essential for maintaining genetic cohesion amongst Argiope populations (Ramirez & Haakonsen 1999). The Actual lifestyle reputation Argiope is seen as an ballooning, the particular aerial transport upon wind-blown silk threads. A New great instance for that significance associated with ballooning for range expansion will always be the Palearctic wasp spider Argiope bruennichi (Scopoli 1772). Your spider is surely an r-strategist (Guttmann 1979), characterized by high aerial dispersal capability and an ongoing postglacial expansion of its geographical range in Europe (van Helsdingen 1982). Females of A. bruennichi produce approximately five cocoons in the field, frequently containing several hundred eggs (Crome & Crome 1961; Kohler & Schaller 1987). the expansion in the species has accelerated within the 2nd half of the past century probably thanks to end up being able to elements favoring dispersal by ballooning (Guttmann 1979; Levi 1983; Sacher & Bliss 1990; Scharff & Langemark 1997; Jonsson & Wilander 1999; Smithers 2000). The wasp spider prefers grassy as well as herbaceous vegetation within open, ephemeral or shrubby sites (Wiehle 1931; Pasquet 1984; Malt 1996) in coarse-grained (patchy) landscapes (Gillandt & Martens 1980; Sacher & Bliss 1989) and it has regionally benefited coming from 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 pertaining to dispersion (Gauckler 1967; Puts 1988).

Follner & Klarenberg (1995) claimed ballooning to become an obligate phase in the growth and also development of A. bruennichi. These kind of authors monitored the actual pre-ballooning as well as ballooning behavior of spiderlings throughout a grassland research website near Munich (Germany). Since they by absolutely no means found aggregations involving orb webs in the neighborhood of the cocoons coming from which the over-wintering second instar spiderlings eclosed and therefore they only observed the construction of initial terraria hack world prey-capture orb webs right after a ballooning trip, they concluded "that aeronautic behaviour in Bavarian populations regarding A. bruennichi is actually obligatory". Moreover, these authors suggested which spiderlings, which could have hatched via the cocoon, will starve to death, unless these people carry out a ballooning trip. Ballooning must thus become an obligate phase for you to switch coming from a non-predatory, passive cycle for you to among active predation by spinning prey-capture orbs. Follner & Klarenberg (1995) argued that the obligatory aerial dispersal could be the result of current natural selection and be the reason behind the swift expansion in the species. New populations which in turn have set up yourself throughout a time period involving expansion are always founded by simply individuals, which might have ballooned.

If ballooning were the really obligate phase, it would not merely be important pertaining to organic variety nevertheless even be important for just regarding any rearing protocol regarding A. bruennichi. allowing for ballooning in the rearing procedure might simply render laboratory breeding unfeasible because it could prove to become as well time-consuming as well as laborious. However, an obligate ballooning phase has never been observed before, neither inside other Argiope nor inside the generally well studied A. bruennichi. Tolbert (1976, 1977) studied ballooning behavioral elements of A. trifasciata (Forska[degrees]l 1775) along with A. aurantia Lucas 1833. He concluded from field and also laboratory observations which "it is actually unnecessary for spiderlings regarding either Argiope species to engage in aerial dispersal before constructing an orb web" (Tolbert 1977), which is an obvious discrepancy to end up being able to Follner's and also Klarenberg's (1995) claims. We here test your significance regarding ballooning for your construction regarding the first preycapture web inside the laboratory simply by comparing spiderlings reared under 2 experimental conditions, one along with and something without ballooning.

We collected cocoons of A. bruennichi (n = 6) within dry as well as 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 within the lab inside individual glass vials (9 cm diameter, 13 cm height, coated together with fine gauze) from 23 [+ as well as -] 2 [degrees]C and also mist-sprayed along with h2o each and also every two days to avoid desiccation. Your vial bottom was covered together with initially wet cellulose wadding (1 cm). Second-instar spiderlings hatched from your cocoons in early May.

One day right after hatching we simulated individual ballooning regarding 60spiderlings (10 through each cocoon) by simply exposing your spiderling on aspatula to an air stream generated by a heat supply along with a fan (see Figs.1-4 with regard to information on the experimental design). We observed behavioralelements in the pre-ballooning phase in much more detail along with noticed its mode.When the spiderling became airborne, we tracked it along with retrieved it atthe "landing strip" (Figs. 3, 4). the ballooning experimentwas repeated instantly (re-ballooning) pertaining to every individual for you to satisfya possible "ballooning drive" (see Tolbert 1977). Thespiderlings had to actively participate on this experiment through showingthe entire sequence involving pre-ballooning along with ballooning behavior (Figs.1-4).

[FIGURES 1-4 OMITTED]

Following the particular experiments, the actual "ballooners" were held in the identical unheated indoor room along with windows admitting indirect natural light. These People had been housed within groups (n = 20) in 3 gauze covered glass terraria (50 x 30 x 31 cm; 25 [+ or even -] three [degrees]C; 65 [+ as well as -] 10% RH) and fed advertisement libitum 45-50 are living Drosophila melanogaster once a new day. Every two times we sprinkled the within surfaces with the terraria using water. This prevented desiccation as well as permitted regarding typical drinking behavior of the spiderlings. Your bottoms in the terraria were covered with a layer of commercial, pasteurized potting soil (3 cm) together with grass tufts, some dry twigs and wooden skewers for you to enhance the actual quantity of potential attachment factors pertaining to web building.

A manage team regarding spiderlings (n = 60) had been treated within the same way, nevertheless with out your ballooning procedure ("non-ballooners"). In both groups (ballooners vs. non-ballooners) spiderlings and also orb webs were noted 3 x daily from 6 a.m., 12 p.m. and 6 p.m. for you to ensure individual based information sets. The Actual rearing period had been cut off after 19 days when every 1 involving the surviving people had spun his or her very first preycapture orb-webs.

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

The web-building exercise with the spiderlings increased inside both the ballooners and the non-ballooners with time as well as reached 90 [+ or even -] 5% for ballooners (n = 54, 3 terraria) and also 95 [+ or even -] 5% for non-ballooners (n = 57, 3 terraria) within any time period involving 19d (Fig. 5). The variances inside the web-building exercise (Fig. 5) had been not statistically significant in between the 2 categories of spiderlings (Kruskal-Wallis test, P = 0.7515; tested regarding every day built-first webs). The suggest latency period with regard to web-building (time via hatching through the cocoon for the construction involving the initial prey-capture web) ended up being 8.61 [+ or -] 4.28 days as well as 8.18 [+ or -] 3.60 times pertaining to ballooners (n = 54) and non-ballooners (n = 57) respectively. This particular difference was not statistically significant (t-test, P = 0.56).

[FIGURE 5 OMITTED]

Although mortality elevated in the 2nd half of the actual observation period (Fig. 6), it didn't exceed 22% following the particular experiment (ballooners: 21.7 [+ or perhaps -] 2.89%, n = 13, non-ballooners: 20.0 [+ or even -] 8.66%, n = 12, difference certainly not significant, t-test, P = 0.77). The surviving animals caught prey inside their orb webs and showed normal development together with up to 4 molts inside the particular experimental time.

[FIGURE 6 OMITTED]

Using our protocol, we could initiate the actual total sequence of ballooning behavior promptly in every experiment. The Actual A. bruennichi spiderlings always confirmed an identical sequence involving pre-ballooning and ballooning behavior (Fig. 1-4). When exposed towards the heat from your lamp, they displayed the particular "ballooning drive" behavior. Individuals walked for the margin of the spatula, spooled out a dragline along with dropped down hanging from your line. Whilst suspended and holding about towards the drag line, these people let out one more range associated with 50-100 cm ballooning silk (Fig. 1). Whenever it was lifted by the breeze generated from the fan and additionally the heat source, the actual spiderlings cut the particular dragline and also became airborne (Figs. 2, 3). Following landing (Fig. 4) that they hauled in the ballooning line, formed it with the actual legs in to a silk blob and finally ate your silk, bringing the ballooning behavioral sequence in order to completion.

Tolbert (1977) observed 2 modes associated with preparation pertaining to ballooning in sympatric area populations involving A. trifasciata as well as A. aurantia. A spiderling attempting for you to turn out to become able to be airborne climbed for the surface of some blade involving grass or other structures and also adopted the typical "tiptoe" posture by depressing your cephalothorax and elevating the opisthosoma. Multiple silk lines had been then exuded from the spinnerets. While moving air generated sufficient silk, the actual spiderling became a new "ballooner" (Nielsen 1932; Richter 1970; Eberhard 1987). Alternatively, the actual spiderling could grow for you to be airborne simply by dropping and hanging from a dragline, spinning a new ballooning thread, that then gradually lifted and also lengthened within the breeze. Your ballooner then cut the dragline and also floated off into the air (Nielsen 1932; Bristowe 1939).

Argiope bruennichi can display each pre-ballooning modes. However, the drop and dragline mediated ballooning seems to become more frequent (Follner & Klarenberg 1995). Within the particular field, second-instar spiderlings usually attach the actual draglines to always be able to suggestions of grass blades or they use silk threads that connect your suggestions associated with grass haulms as attaching points (Follner & Klarenberg 1995). Inside our experiments, we offered individual spiderlings optimal starting conditions, and that will we never observed the tip-toe ballooning mode. Follner (1994) suggested that "tip-toe" may be the tactical alternative regarding individuals in unfavorable beginning factors (e.g., overcrowded ideas involving grass blades).

Our outcomes reveal that it is not essential for spiderlings involving A. bruennichi for you to engage in aerial dispersal prior to creating the prey-capture web. Whilst ballooning will be frequent within the area (Follner & Klarenberg 1995), it truly is clearly not an obligate part inside the progression of this species. in spite in the rapid expansion of the species more than the particular past decades and in addition the potential significance associated with aerial dispersal pertaining to colonizing new habitats, the role regarding ballooning inside A. bruennichi doesn't differ from A. trifasciata and also A. aurantia exactly where this cycle in everyday life history is also not necessarily obligate (Tolbert 1977).

The mortality regarding regarding 20% after 19 days within both experimental groups (difference statistically not really significant) shows that rearing of A. bruennichi spiderlings in order to adulthood could be challenging. Our rearing method according to a diet plan plan using Drosophila melanogaster, comparable to Mu"ller & Westheide (1993), did wonders pertaining to our purpose, where we just tested the actual results of ballooning in second-instar spiderlings on their ability to make their very first web.



On average, a lot more then eight times elapsed before A. bruennichi spiderlings began to create his or her initial prey-capture web. This particular appears to be the surprisingly extended period, as the animals can only feed once the first web is actually built. We cannot exclude that is a laboratory artifact, regarding instance because of for you to unattractive websites for web construction. However, the actual long latency did not interfere with the rearing regime. The animals appeared to become well adapted in order to temporary starvation simply because the mortality has been lower on this stage (Fig. 6). In Addition within the field, the spiderlings do not immediately begin along with prey-capture web construction (Follner & Klarenberg 1995) and endure extended periods of starvation. Argiope spiderlings effortlessly survive several days neighborhood their cocoons, sometimes using communal meshworks involving interlocking dragline threads ("communal tangles") (Tolbert 1976, 1977; Follner & Klarenberg 1995) where they locate shelter until favorable weather or microclimate circumstances permit ballooning (Tolbert 1977; Follner & Klarenberg 1995; see additionally Suter 1999 regarding physics regarding ballooning).

Argiope spiderlings actively select suitable web sites by ballooning, re-ballooning or walking (Enders 1973; Tolbert 1977; Follner & Klarenberg 1995). In Addition on this nonpredatory phase the actual spiderlings must stay away from starvation. Tolbert (1976) stored A. aurantia spiderlings in the laboratory with out meals along with water. Mortality remained reasonable in these experiments for a few days and just increased distinctly about two weeks following hatching.

The behavioral ballooning sequence might be effortlessly triggered under artificial conditions within our study, suggesting that it's going to furthermore occur in your area whenever environmental circumstances allow. Therefore dispersal and population construction will probably be primarily driven by microclimatic conditions inside the local habitats. The Actual nearby persistence of non-emigrants (non-ballooners and short-distance ballooners) within A. bruennichi populations may facilitate aggregated dispersion patterns, just as with weather phases that are unfavorable for aerial dispersal. Given ballooning is actually a less effective way of cross country dispersal than previously believed (Roff 1981; Decae 1987; Sensible 1993; Bonte et al. 2003), this could furthermore explain the particular genetic differentiation amongst habitat patches inside additional Argiope species (Ramirez & Haakonsen 1999).

The role associated with all-natural variety in range expansion has just lately been discussed with regard to insects inside the context involving climate change (e.g., Pimm 2001; Thomas et al. 2001). However, improving environmental conditions at range margins can initiate range extensions purely around the schedule of ecological, physiological as well as population-dynamic processes not requiring any evolutionary adjust (Thomas et al. 2001; see also Coope 1995; Williamson 1996). Our results have been in line with these views and also reject the hypothesis involving Follner & Klarenberg (1995) in which evolutionary processes possess changed ballooning behavior in newly founded populations.

ACKNOWLEDGMENTS

We are grateful to Peter Neumann, Gail E. Stratton and two anonymous reviewers pertaining to beneficial remarks in prior drafts involving the manuscript. We thank Christian W.W. Pirk pertaining to statistical advice, Vlastimil Ruzicka along with Theo Blick regarding providing literature. This study was supported with a analysis fellowship to be able to A.W. from your State of Saxony-Anhalt and also 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 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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