THE WASP SPIDER ARGIOPE BRUENNICHI (ARACHNIDA, ARANEIDAE): BALLOONING IS NOT AN OBLIGATE LIFE HISTORY PHASE

2005·7.6 MB·English

by  André Walter

2005. The Journal of Arachnology 33:516-522
THE WASP SPIDER ARGIOPE BRUENNICHI
(ARACHNIDA, ARANEIDAE): BALLOONING NOT AN
IS
OBLIGATE LIFE HISTORY PHASE
Andre Walter, Peter Bliss^and Robin F.A. Moritz: Institut fur Zoologie, Martin-
Luther-Universitat Halle-Wittenberg, Hoher Weg 4, D-06120 Halle (Saale), Germany.
E-mail: [email protected]
ABSTRACT. Aerial dispersal (“ballooning”) ofArgiope bruennichi spiderlings has been claimedtobe
an obligate life history trait and a prerequisite for spinning prey-capture webs. If this were true, a bal-
looning phase would be essential for any laboratory rearing of A. bruennichi making rearing protocols
particularly elaborate. We tested the significance of ballooning for second-instar spiderlings in the labo-
ratory and showed that the ballooning behavior is not essential for building prey-capture orb webs. Our
results also give no evidence for the hypothesis that recent natural selection has changed ballooning
behavior in newly founded field populations.
Keywords: Araneae, ballooning experiment, laboratory rearing, web-building behavior.
Ballooning is a common dispersal mecha- & Martens 1980; Sacher & Bliss 1989) and
nism for many modern spiders (Coyle 1983; has regionally benefited from an extension of
Dean & Sterling 1985; Weyman 1993), and farming production and urbanization (Loh-
this behavior is particularly important for meyer & Pretscher 1979; Arnold 1986 Nyf-
maintaining genetic cohesion among Argiope feler & Benz 1987). River valleys have; been
populations (Ramirez & Haakonsen 1999). identified as favored dispersal corridors fur-
The life history ofArgiope is characterizedby ther supporting the importance of ballooning
ballooning, the aerial transport on wind-blown for dispersion (Gauckler 1967; Puts 1988).
silk threads. A good example for the impor- Follner & Klarenberg 1995 claimed bal-
( )
tance ofballooning for range expansion is the looning to be an obligate phase in the devel-
Palearctic wasp spider Argiope bruennichi opment ofA. bruennichi. These authors mon-
(Scopoli 1772). The spider is an r-strategist itored the pre-ballooning and ballooning
(Guttmann 1979), characterized by high aerial behavior of spiderlings in a grassland study
dispersal capability and an ongoing postgla- site near Munich (Germany). Since they never
cial expansion ofits geographical range in Eu- found aggregations of orb webs in the neigh-
rope (van Helsdingen 1982). Females of A. borhood of the cocoons from which the over-
bruennichi produce up to five cocoons in the wintering second instar spiderlings eclosed
field, often containing several hundred eggs and they only observed the construction of
(Crome Si Crome 1961; Kohler & Schaller first prey-capture orb webs after a ballooning
1987). The expansion of the species has ac- trip, they concluded “that aeronautic behav-
celerated in the second halfofthe last century iour in Bavarian populations ofA. bruennichi
probably due to factors favoring dispersal by is obligatory”. Moreover, these authors sug-
ballooning (Guttmann 1979; Levi 1983; Sach- gested that spiderlings, which have hatched
Jeron&ssBolnis&s 1W9i9l0a;nSdcehrarf1f99&9 LSamnigtehmearrsk21090907; from the cocoon, will starve to death, unless
; ). they perform a ballooning trip. Ballooning
The wasp spider prefers grassy or herbaceous should thus be an obligate phase to switch
vegetation in open, ephemeral or shrubby sites from a non-predatory, passive phase to one of
(Wiehle 1931; Pasquet 1984; Malt 1996) in active predation by spinning prey-capture
coarse-grained (patchy) landscapes (Gillandt &
orbs. Follner Klarenberg 1995 argued that
( )
the obligatory aerial dispersal might be a re-
' Corresponding author. sult ofrecent natural selection and be the rea-
516
T
WALTER ET AL.—BALLOONING IN Ai?G/OP£ 317
j
1
—
Figures 1-4, Design andcourseoftheballooningexperiment. The spiderlings wereplacedon aspatula
(sp) and exposed to a light air current by a fan (ve) and heat source (hs), which were placed at the left
edge of a lab bench (240 cm). After cutting the drag line the spiderlings became airborne to land on the
lab bench, which served as a landing strip (Is), 1. Pre-ballooning behavior: sp = spatula; ve = ventilator
(light breeze); hs == heat source (25 Watt lamp, distance to spatula = 20 cm); sh = spiderling hanging
from a dragline; bt = ballooning thread. 2. Initial ballooning phase. 3. Airborne spiderling: Is = “landing
strip” (lab bench of 240 cm length). 4. Landing phase.
son behind the swift expansion ofthe species. vidual glass vials (9 cm diameter, 13 cm
New populations v/hich are established during height, coated with fine gauze) at 23 ± 2 °C
a period of expansion are always founded by and mist-sprayed with water every two days
individuals, which have ballooned. to avoid desiccation. The vial bottom was
Ifballooning were a truly obligate phase, it covered with initially wet cellulose wadding
would not only be important for natural selec™ (1 cm). Second-instar spiderlings hatched
tion but also be important for any rearing pro^ from the cocoons in early May.
tocol forA. bruennichi. Allowing for balloon- One day after hatching we simulated indi-
ing in a rearing procedure might easily render vidual ballooning for 60 spiderlings (10 from
laboratory breeding unfeasible as it could each cocoon) by exposing the spiderling on a
;
proveto be too time-consuming and laborious. spatula to an air stream generated by a heat
:
However, an obligate ballooning phase has source and a fan (see Figs. 1-4 for details of
I never been observed before, neither in other the experimental design). We observed behav-
i
Argiope nor in the generally well studied A. ioral elements in the pre-ballooning phase in
I! bruennichi. Tolbert (1976, 1977) studied baL detail and noticed its mode. When the spider-
loonieg behavioral elements of A. trifasciata ling became airborne, we tracked it and re-
I
(ForskM 1775) and A. aurantia Lucas 1833. trieved it at the “landing strip” (Figs, 3, 4).
i He concluded from field and laboratory ob- The ballooning experiment was repeated im-
servations that “it is unnecessary for spider- mediately (re-ballooning) for each individual
lings of either Argiope species to engage in to satisfy a possible “ballooning drive” (see
aerial dispersal before building an orb web” Tolbert 1977). The spiderlings had to actively
(Tolbert 1977), which is an obvious discrep- participate in this experiment by showing the
ancy to Folleer’s and Klareeberg’s (1995) entire sequence of pre-ballooning and bal-
claims. We here test the significance of bal- looning behavior (Figs. 1-4).
^I looning for the construction of the first prey- Following the experiments, the “balloon-
capture web in the laboratory by comparing ers” were kept in the same unheated indoor
S
spiderlings reared under two experimental room with windows admitting indirect natural
i conditions, one with and one without balloon- light. They were housed in groups {n “ 20)
(
ing. in three gauze covered glass terraria (50 X 30
j We collected cocoons of A. bruennichi {n X 31 cm; 25 ± 3 °C; 65 ± 10% RH) and fed
I = 6) in dry and semi-dry grasslands north- ad libitum 45-50 live Drosophila melanogas-
east of Halle (Saale) in late April 2002 (Ger- ter once a day. Every two days we sprinkled
many, 160 m a.s.L, 5r3331" N, 0ir52'49" the inside surfaces of the terraria with water.
E). They were maintained in the lab in indi- This prevented desiccation and allowed for
518 THE JOURNAL OF ARACHNOLOGY
Web-building activity
Days
——— Ballooner — — Non-Ballooner
—
Figure 5. Web-building activity of the A. bruennichi spiderlings during laboratory rearing for both
ballooners and non-ballooners.
normal drinking behavior of the spiderlings. ences in the web-building activity (Fig. 5)
The bottoms of the terraria were covered with were not statistically significant between the
I
a layer ofcommerciak pasteurized potting soil two groups ofspiderlings (Kruskal-Wallistest,
(3 cm) with grass tufts, some dry twigs and P = 0.7515; tested for daily built-first webs). |
i
wooden skewers to enhance the numberofpo- The mean latency time for web-building (time
tential attachment points for web building. from hatching from the cocoon to the con- |'
A control group ofspiderlings (n = 60) was struction of the first prey-capture web) was
!
treated in the same way, but without the bal- 8.61 ± 4.28 days and 8.18 ± 3.60 days for
looning procedure (“non-ballooners’'). In ballooners (n = 54) and non-ballooners (n =
I
both groups (ballooners vs. non-ballooners) 57) respectively. This difference was not sta-
spiderlings and orb webs were noted three tistically significant (t-test, P = 0.56).
times daily at 6 a.m., 12 p.m. and 6 p.m. to Although mortality increased in the second
ensure individual based data sets. The rearing half of the observation period (Fig. 6), it did ^
period was cut off after 19 days when all the not exceed 22% at the end of the experiment
surviving individuals had spun their firstprey- (ballooners: 21.7 ± 2.89%, n = 13, non-bal-
capture orb-webs. looners: 20.0 ± 8.66%, « == 12, difference not
Voucher specimens are deposited in the En- significant, t-test, P = 0.77). The surviving i
tomological Collection of the Martin-Luther- animals caught prey in their orb webs and
University Halle-Wittenberg (Zoological In- showed normal development with up to four
stitute), Germany (identification number molts within the experimental time.
2568). Using our protocol, we could initiate the
The web-building activity ofthe spiderlings full sequence ofballooning behaviorpromptly j
increased in both the ballooners and the non- in every experiment. The A. bruennichi spi-
ballooners over time and reached 90 ± 5% for derlings always showed an identical sequence
ballooners (n = 54, three terraria) and 95 ± of pre-ballooning and ballooning behavior ;
5% for non-ballooners (n = 57, three terraria) (Fig. 1-4). When exposed to the heat fromthe
within a period of 19d (Fig. 5). The differ- lamp, they displayed the “ballooning drive” ij
WALTER ET AL.—BALLOONING IN ARGIOPE BRUENNICHI 519
Mortality
— Days
“ “ “
^Ballooner Non-Balfooner
—
Figure 6. Mortality ofthe A. bruennichi spiderlings during laboratory rearing.
behavior. Individuals walked to the margin of ually lifted and lengthened in the breeze. The
I
the spatula, spooled out a dragline and ballooner then cut the dragline and floated off
dropped down hanging from the line. While into the air (Nielsen 1932; Bristowe 1939).
' suspended and holding on to the drag line, Argiope bruennichi can display both pre-
they let out an additional line of 50-100 cm ballooning modes. However, the drop and
: bbaylltohoenibnrgeeszielkg(eFnige.ra1t)e.dWbhyenthethifsanwaasndlifttheed mdroargelinfereqmueednitat(eFodllbnaerll&oonKilnagreseebeemrsg 1t9o95b)e.
I
heat source, the spiderlings cut the dragline In the field, second-instar spiderlings usually
I and became airborne (Figs. 2, 3). After land- attach the draglines to tips of grass blades or
I
ing (Fig. 4) they hauled in the ballooning line, they use silk threads which connect the tips
I &
formed it with the legs into a silk blob and ofgrass haulms as attaching points (Follner
j finally ate the silk, bringing the ballooning be- Klarenberg 1995). In our experiments, we of-
havioral sequence to completion. fered individual spiderlings optimal starting
Tolbert (1977) observed two modes of conditions, and we never observed the tip-toe
preparation for ballooning in sympatric field ballooning mode. Follner (1994) suggested
populations ofA. trifasciata and A. aurantia. that “tip-toe” might be a tactical alternative
A spiderling attempting to become airborne for individuals in unfavorable starting points
I
climbed to the top of some blade of grass or (e.g., overcrowded tips of grass blades).
:
other structures and adopted the typical “tip- Our results show that it is not necessary for
I toe” posture by depressing the cephalothorax spiderlings ofA. bruennichi to engage in ae-
and elevating the opisthosoma. Multiple silk rial dispersal before building a prey-capture
1
lines were thee exuded from the spinnerets. web. While ballooning is frequent in the field
! When moving air generated sufficient silk, the (Follner & Klareeberg 1995), it is clearly not
I spiderling became a “ballooner” (Nielsen an obligate part in the development of this
I
1932; Richter 1970; Eberhard 1987). Alter- species. In spite of the rapid expansion of the
I natively, the spiderling could become airborne species over the past decades and the potential
j by dropping and hanging from a dragline, importance of aerial dispersal for colonizing
spinning aballooning thread, whichthen grad- new habitats, the role of ballooning in A.
520 THE JOURNAL OF ARACHNOLOGY
bruennichi does not differ from A. trifasciata croclimatic conditions in the local habitats.
and A. aurantia where this phase in life his- The local persistence of non-emigrants (non-
tory is also not obligate (Tolbert 1977). ballooners and short-distance ballooners) inA.
The mortality of about 20% after 19 days bruennichi populations might facilitate aggre-
in both experimental groups (difference statis- gated dispersion patterns, just as in weather
tically not significant) suggests that rearing of phases which are unfavorable for aerial dis-
A. bruennichi spiderlings to adulthood may be persal. Given ballooning is a less effective
challenging. Our rearing method based on a means of long distance dispersal than previ-
diet with Drosophila melanogaster, similar to ously thought (Roff 1981; Decae 1987; Wise
Muller & Westheide (1993), worked well for 1993; Bonte et al. 2003), this could also ex-
our purpose, where we only tested the effects plain the genetic differentiation among habitat
of ballooning in second-instar spiderlings on patches in other Argiope species (Ramirez &
their ability to make their first web. Haakonsen 1999).
On average, more then eight days elapsed The role of natural selection in range ex-
before A. bruennichi spiderlings began to pansion has recently been discussed for in-
build their first prey-capture web. This ap- sects in the context of global warming (e.g.,
pears to be a surprisingly long period, because Pimm 2001; Thomas et al. 2001). However,
the animals can only feed once the first web improving environmental conditions at range
is built. We cannot exclude that this is a lab- margins can initiate range extensions purely
oratory artifact, for example due to unattrac- on the basis of ecological, physiological and
tive sites for web construction. However, the population-dynamic processes not requiring
long latency did not interfere with the rearing any evolutionary change (Thomas et al. 2001;
regime. The animals appeared to be well see also Coope 1995; Williamson 1996). Our
adapted to temporary starvation because the results are in line with these views and reject
mortality was low in this phase (Fig. 6). Also the hypothesis ofFollner & Klarenberg (1995)
in the field, the spiderlings do not immediately that evolutionary processes have changed bal-
start with prey-capture web construction (Foll- looning behavior in newly founded popula-
&
ner Klarenberg 1995) and endure extended tions.
periods of starvation. Argiope spiderlings eas-
ACKNOWLEDGMENTS
ily survive several days nearby their cocoons,
sometimes with communal meshworks of in- We are grateful to Peter Neumann, Gail E.
terlocking dragline threads (“communal tan- Stratton and two anonymous reviewers for
&
gles”) (Tolbert 1976, 1977; Follner Klar- helpful comments on previous drafts of the
enberg 1995) where they find shelter until manuscript. We thank Christian WW. Pirk for
favorable weather or microclimate conditions statistical advice, Vlastimil Ruzicka and Theo
&
allow for ballooning (Tolbert 1977; Follner Blick for providing literature. This study was
Klarenberg 1995; see also Suter 1999 for supported by a research fellowship to A.W.
physics of ballooning). from the State of Saxony-Anhalt and by the
Argiope spiderlings actively select suitable Deutsche Eorschungsgemeinschaft (DFG)
web sites by ballooning, re-ballooning or grant to P.B. (BL 776/1-1).
walking (Enders 1973; Tolbert 1977; Follner
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