MATING IN THE ABSENCE OF VISUAL CUES BY SCHIZOCOSA OCREATA (HENTZ 1844) WOLF SPIDERS (ARANEAE, LYCOSIDAE)

2006·5.3 MB·English

by  Phillip W Taylor

2006 (2007). The Journal of Arachnology 34:501-505
MATING IN THE ABSENCE OF VISUAL CUES BY
SCHIZOCOSA OCREATA (HENTZ WOLF
1844)
SPIDERS (ARANEAE, LYCOSIDAE)
Phillip W. Taylor,* J. Andrew Roberts^ and George W. Uetz^: 'Centre for the
Integrative Study of Animal Behaviour, Macquarie University, New South Wales
2109, Australia. E-mail: [email protected]; ^Department of Evolution,
Ecology and Organismal Biology, The Ohio State University, Ohio 43055, USA;
^Department of Biological Sciences, University of Cincinnati, Ohio 45221, USA.
ABSTRACT. Male Schizocosa ocreata (Hentz 1844) wolf spiders court females with multi-modal dis-
plays that include both seismic and visual components. The seismic components arethoughtto beancestral
whereas the visual components are thought to have been more recently derived. We here present evidence
that, despite the evolution ofelaborate visual display components in males, female S. ocreata remain able
to derive sufficient information about males through the seismic display components alone. We compared
the mating tendency offemales courted by males in the light (seismic and visual components present) and
in the dark (only seismic components present). With a sample of 79 pairs in each condition, pairs were
not significantly less likely to mate when in the dark (62%) than when in the light (73%). While all males
performed courtship, and latency from the release ofmales until the onset ofcourtship was similar in the
light and in the dark, latency until mounting tended to be much longer in the dark. This may mean that
it takes longer for females to gather the information required to accept a male in the absence of visual
cues or may instead simply reflect the challenge of locating mates and orienting for mounting. Lighting
conditions did not influence how long the male remained mounted, indicating that these wolfspiders lack
the condition-dependent flexibility in copula duration that is found in somejumping spiders.
Keywords; Multimodal signalling, vision, Lycosidae
Spiders have provided valuable models for One of the key questions in studies ofmul-
recent studies into the function and evolution ti-modal communication is of the extent to
of “multi-modal communication” (sensu Par- which each modal component contributes to
&
tan Marler 1999). In particular, the wolfspi- receiver responses. Recently, Hebets (2005)
der genus Schizocosa Chamberlin 1904 (Ly- investigated the extent to which the male vi-
cosidae) has been widely adopted as a sual and seismic courtship components are re-
productive model system. Schizocosa vary in quired for female acceptance in S. uetzi Strat-
their use of seismic and visual displays in ton 1997, a species with only rudimentary
courtship communication, ranging from sta- visual displays. During courtship, male S. uet-
tionary palpal stridulation with little detect- zi stand stationary while stridulating with their
able movement through to combinations of pedipalps. Their forelegs have darkened mid-
stridulation and percussion along with extrav- tibiae and, while stridulating, they intermit-
agant raising and waving of ornamented legs tently raise their forelegs in a slow arch (Strat-
(Uetz 2000; Stratton 2005). Seismic signalling ton 1997). Hebets (2005) found that pairs
appears to be ancestral, and is used by all were similarly likely to mate in the dark (vi-
Schizocosa species regardless ofwhether they sual components occluded) as in the light (vi-
also have visual display components (Stratton sual components present), as long as the seis-
2005). On the other hand, dynamic and mor- mic components were present. That is, the
phological visual signalling components are evolution ofvisual display components in this
observed in only a subset of Schizocosa spe- species appears not to have extinguished their
cies and appear to have evolved more recently ability to interact and make mating decisions
(McClintock & Uetz 1996; Hebets & Uetz when limited to the ancestral seismic com-
1999; Uetz 2000; Stratton 2005). ponents alone. Is this also the case in Schi-
501
502 THE JOURNAL OF ARACHNOLOGY
zocosa species with more developed visual fed 2-3 crickets twice weekly and had contin-
display components? ual access to water by way ofa soaked cotton
Compared with S. uetzi, S. ocreata (Hentz wick inserted through a hole in the cage floor
1844) has much more elaborate dynamic vi- into a reservoir below. Spiders matured in the
sual elements in its courtship and more elab- laboratory and were used in experiments be-
orate morphological modifications that are tween 7 and 50 days after maturing. All spi-
thought to enhance detection of signals (Uetz ders were virgins when tested.
& Denterlein 1979; Stratton & Uetz 1981, Mating trials were carried out in open plas-
1983, 1986; Uetz 2000; Taylor et al. 2005). tic boxes (150 X 100 X 50 mm, Iwh) during
Two quite different seismic components are the laboratory light phase (which correspond-
produced along with visual displays; percus- ed closely with daylight), excluding the first
sion is produced by rapidly “jerking’’ the and last two hours. In nature, we have often
body downward to strike the substrate, and seen S. ocreata courtship taking place in dark
strong bursts of stridulation are produced by places (e.g., in dense leaf litter under forest
specialized organs in the pedipalps as the spi- canopy) during the day. Since all trials were
ders display visually by moving their forelegs run at the same period of the day, we con-
up and down. Males have dark forelegs bear- trolled forpossible biorhythms in the behavior
ing large tufts and in several studies females of the spiders. A clean piece of 5 mm thick
have shown greater receptivity toward males foam-core board covered the floor. This ma-
&
with large tufts (McClintock Uetz 1996; terial allows excellent transmission of vibra-
Scheffer et al. 1996; Uetz 2000; Persons & tions. A thin film ofVaseline® petroleumjelly
Uetz 2005). prevented spiders from climbing out of the
In this study, we investigate how often the box. A new piece of foam-core board was
seismic courtship component alone provides used in each trial, and the plastic box was
sufficient information for S. ocreata females washed with warm soapy water and 70% eth-
to accept males as mates. From an evolution- anol between trials to remove any silk and
ary perspective, we are hence asking aboutthe chemical cues. All trials were carried out in a
extent to which these spiders have come to photographic darkroom. For trials in the light,
W
depend on the secondarily added visual dis- illumination was provided by two 25 fluo-
m
play components. If females are usually able rescent lights suspended 0.5 above the are-
to obtain all the information they need to ac- na (mean 87.8 ± SE 1.3 lx). For trials in the
cept males as mates even when the visual sig- dark (no detectable visible light), illumination
nalling component is altogether absent, we was provided by an Infra-Red (IR) light
should find similar mating tendency in the source (Sony HVL-IRC). Wolfspider eyes are
light and in the dark. On the other hand, ifthe not sensitive to IR light (DeVoe 1972, sum-
visual mode provides necessary information, marized in Yamashita 1985) and so this set-
we should find a marked reduction in mating up is equivalent to total darkness for the spi-
tendency of pairs in the dark. In addition to ders. All trials were video-recorded using an
considering the female’s decision of whether IR-sensitive camera (Watec WAT-902C) po-
to accept the male as a mate, we also consider sitioned above the testing arena, which was
other measures of male sexual success, in- connected to the video input of a VHS VCR
cluding latency until mounting from the start (Sony DA Pro 4 head).
of trials and from the onset of courtship, and Virgin females were released into the arena
how long the male remained mounted. 1 h before males. During this hour, males were
Sub-adult males and females of 5. ocreata kept in the light conditions under which the
were collected from dense leaf litter at Cin- trial was to be carried out. Males were then
cinnati Nature Center, Rowe Woods (Cler- transferred into the testing arena from main-
mont County, Ohio, USA: 39°07.556'N, 84° tenance cages by the use of a 10 ml plastic
15.()59'W), during March, April, May and vial. Pairs were left to interact for two hours
September 2001. We kept spiders visually iso- after which un-mounted pairs were returned to
lated from each other in white cylindrical their home cages. Mounted pairs were video-
plastic cages (11 cm diameter, 8.5 cm high) recorded until they separated naturally. There
under laboratory conditions of 13:1 1 L:D pho- were no incidences of sexual cannibalism ei-
toperiod, —23 °C and —65% RH. Spiders were ther in the light or in the dark.
TAYLOR ET AI..—SCHIZOCOSA OCREATA MATING IN THE DARK 503
Effects oflight regime on the probability of
mating were investigated by log-likelihood ra-
tio (G). Effects of light regime on latency
from male release until onset ofcourtship, la-
tency from male release until mounting, laten-
cy from onset ofcourtship until mounting, and
how long the male was mounted (“mount du-
ration”) were analyzed by Wilcoxon two-sam-
ple tests, using approximation to the normal
distribution z (none of these data sets were
normally distributed or ofequal variance). All
analyses were carried out using IMP v5 (SAS
Institute).
With a sample size of79 trials in each con-
dition, pairs of S. ocreata wolf spiders were —
not significantly less likely to mate when in mouFingtuerdeov1e.r tCiummeulafatteirvtehepornospeotrotfiocnourotfshispp.idTehres
the dark (seismic display component only) last spider to mount in the light was at 1378 s after
than when in the light (visual + seismic dis- the male began courting (1407 s after the male was
play components available). Mounting and released); the last in the dark was at 1857 s after
copulation was recorded within the 2-h testing the male began courting (1898 s after the male was
period in 58 (73%) trials in the light and 49 released).
(62%) trials in the dark (« = 158, G, = 2.354,
P = 0.125). In previous studies, female S.
ocreata have given “receptivity displays” to
ested primarily in male display rate, then they
unseen courting males in adjacent chambers may gain sufficient information regardless of
that occlude visual contact but allow trans-
whether the visual display components are
mission of seismic signals (Scheffer et al.
present.
1996; Uetz 2000). Results of this study of di-
All tested males performed the majorcourt-
rect interactions are consistent with results of &
ship element of “jerky tapping” (Stratton
these previous studies of female responses to
males in adjacent chambers, indicating thatfe- Uetz 1981, 1983, 1986) during trials, regard-
male S. ocreata are usually able to obtain less of whether they succeeded in mounting
the female. Latency from release of the male
whatever information they need about a male
through the seismic components of multi- until the onset of courtship did not vary be-
modal signals alone. Ourresults forS. ocreata tween the dark (median = 22 s, range = 1-
Hareebeatlsso(2v0e0r5y),siwmhiloarfotountdhonsoeefvoirdSe.ncueetozfi rbey- 5=512-s4)1a5nds)i{nnth=e 1li5g8h,tz(m=ed0i.a0n30,—P28=s,0.r9a7n6g)e.
duced mating tendency when trials were run However, latency from the onset of courtship
in darkness. until mounting was greater in the dark (me-
While choice ofminordisplay elements and dian = 230 s, range 38-1857 s) than in the
non-display behavior may vary slightly de- light (median = 74.5 s, range 9-1378 s) {n =
pending on whether S. ocreata males are 107, z = 5.431, P < 0.001; Fig 1). Similarly,
courting in the dark or in the light, major dis- latency from release of the male until mount-
play elements are performed similarly and the ing was greater in the dark (median = 308 s,
visual and seismic components of each dis- range 42-1898 s) than in the light (median =
play element are both retained regardless of Ills, range 31-1407 s) {n = 107, z = 5.271,
lighting conditions (Taylor et al. 2005). The P < 0.001). One potential explanation for this
close synchrony of visual and seismic signal- is that females take longer over decisions to
ling components in S. ocreata means that dis- accept males when in the dark, needing more
play rates in these modes are tightly linked. time to acquire critical information about their
In some wolf spiders, display rate is a key suitors. Alternatively, these differences in
male attribute on which females base mating mounting latency may simply reflect the rel-
decisions (Kotiaho et al. 1996; Parri et al. ative ease with which males can locate fe-
1997). If females of S. ocreata are also inter- males, orient and mount or with which fe-
504 THE JOURNAL OF ARACHNOLOGY
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181.
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ACKNOWLEDGMENTS
Behaviour 53:305-312.
This research was supported by a U.S. Na- Partan, S. & P. Marler. 1999. Communication goes
tional Science Foundation grant (IBN9906446) multimodal. Science 283:1272-1273.
to GWU and a Macquarie University Re- Persons, M.H. & G.W. Uetz. 2005. Sexual canni-
search Development Grant to PWT. We are balism and mate choice decisions in wolf spi-
ders: influence ofmale size and secondary sexual
grateful to Cincinnati Nature Center for per-
characters. Animal Behaviour 69:83-94.
mission to collect spiders on their property. Roberts, J.A., P.W. Taylor & G.W Uetz. 2003. Kin-
Voucher specimens from this population ofS. ship and food availability influence cannibalism
ocreata are deposited in the collections ofthe tendency in early-instar wolf spiders (Araneae:
U.S. National Museum of Natural History, Lycosidae). Behavioral Ecology and Sociobiol-
Smithsonian Institution and the Cincinnati ogy 54:416-422.
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