Table Of Content2006. The Journal of Arachnology 34:51-61
ROLE OF THE ANTERIOR LATERAL EYES OF THE WOLF
SPIDER LYCOSA TARENTULA (ARANEAE, LYCOSIDAE)
DURING PATH INTEGRATION
Joaquin Ortega-Escobar: Department of Biological Psychology, Faculty of
Psychology, University Autonoma of Madrid, 28049“Madrid, Spain. E-mail: joaquin.
[email protected]
ABSTRACT. Spiders ofthe speciesLycosa tarentula (Linnaeus 1758) (Araneae, Lycosidae) useavector
navigation system while homing under natural conditions. Under laboratory conditions, in the absence of
information relative to the sun’s position or any pattern of polarized light, L. tarentula uses a path inte-
gration system which consists of turning at a fixed angle similar to one that could carry it to its burrow.
In the absence of light, the angle is random. In this study we ask whether the spiders acquire the infor-
mation about the angle turned during the outwardjourney through the anterior lateral eyes (ALEs), whose
visual fields are directed towards the ground. To answerthis question, two groups ofanimals were studied:
one group with only the ALEs covered and another group with all eyes except ALEs covered. Ourresults
show that ALE information alone is adequate to obtain the angle at which the animal should turn when
homing.
Keywords: Direction estimation, spiders, optical flow
Animals that are central foragers move enced during the flight and that this measure-
from a central point (nest, burrow) to find ment is independent of image structure (Si et
food or mates. After this displacement, these al. 2003). In another experiment, Ugolini
animals must be able to reach that central (1987) displaced wasps from their nests to
point. Path integration (PI) is one of the most various sites, released them, and observed
frequently used mechanisms to get it (Papi their homing trajectories. He found that they
1992). While moving, the animal measures headed accurately towards their nests if they
and integrates the angles (rotations) as well as had been displaced in a transparent container
distances travelled to obtain a vector whose but not when they had been displaced in an
orientation indicates home direction and opaque container.
whose length indicates the distance, so that it In spiders, homing has been thoroughly
can always take a direct path back to its start- studied in the funnel web spider Agelena la-
ing point. That means that the animal does not byrinthica (Clerck 1757), which can use vi-
retrace its outwardjourney. tsiuvaelocnueess (toCgoertnheerr&witChlataascti1l9e85a)n.dHporompirnigocheaps-
Information about changes of direction can
also been studied in the nocturnal ctenid spi-
be obtained in arthropods through exoskeletal
der Cupiennius salei (Keyserling 1877) (Sey-
sense organs (Seyfar&th et al. 1982; Mitte&L farth & Barth 1972; Seyfarth et al. 1982;
staedt 1983; Corner Claas 1985; Durier
Barth 2002). It was demonstrated that C. salei
Rivault 1999) orby the use ofbiological com- needs proprioceptive information for homing
passes based on the sun or the pattern of ce- because animals that have been surgically al-
l2e0s0t4ia;l pMoalpapriezsed&ligHhotm(bWeerhgner200149)9.7;IHnosmebveerragl toerrgeadns(e.ogf.,tshpeidfeermsuwritahndthteibliyaridfeosrtmroslyietdsemnes-e
insects, it has been shown that they use trans- chanically) returned with less success to the
lational image motion (optic flow) to estimate site from which they had been chased. In C.
flight- or running distances (review: Sriniva- salei, Schmid (1997) noted differences in the
san & Zhang 2004) In particular, several stud- kind of locomotion depending upon whether
ies made with honeybees (Srinivasan et al. they were in bright light (normal walking
1997) demonstrated that honeybees integrate movements with eight legs) or complete dark-
over time the image velocity that is experi- ness (first pair of legs used as antennae).
51
52 THE JOURNAL OF ARACHNOLOGY
In Lycosidae, the first studies about homing a 90° angle between legs; at the end of the
were realized in the European species Arctosa outbound path, the spider was lifted and
&
perita (Latreille 1799) (Papi 1955; Papi placed in an arena with its body axis oriented
Tongiorgi 1963). This species displays so- at random. When this procedure was carried
called “zonal orientation” or “orientation to out under illumination, the spiders showed PI
Y axis,” which means that after an active or by turning a constant angle and walking in
passive displacement away from the shore, search ofthe burrow, while in darkness (really
they orient and move perpendicular to the under red light to which they are insensitive)
shore until they reach it. Papi (1955) demon- they also showed PI but in this case they
strated thatA. perita could find the shore from turned a random angle. Thus, it is possible
which it had been displaced only if the sky that L. tarantula needs visual information
was not heavily overcast. Later, the contribu- about their movement (optic flow) and given
tions of innate and learned components to as- the visual fields oftheir eyes (Land 1985), the
tronomical orientation were analyzed by Papi eyes that could give more precise information
& Tongiorgi (1963). Magni et al. (1964) about optic flow would be the anterior lateral
showed that the anterior median eyes (AMEs) eyes (ALEs) which look towards the ground.
were primarily responsible for homing behav- The aim of the present study was to check
ior by using celestial polarized light inA. var- what eyes provide to L. tarentula the most
iana Koch 1847. However, the structural basis reliable information about directional changes
for polarization sensitivity in AMEs was not in PI in the laboratory in the absence of ce-
found (Bacetti & Bedini 1964). The first study lestial cues. In a first approach, I have ana-
that discovered the structural basis for polar- lyzed the contributions of anterior lateral eyes
ization sensitivity in Lycosidae was by Me- (ALEs) versus the rest of the eyes.
lamed & Trujillo-Cenoz (1966) in Lycosa er- METHODS
ythrognatha Lucas 1836 (= L. raptoria
Walckenaer 1837) followed by the research on Experimental animals.—Twelve lab-
L. tarentula (Linnaeus 1758) (Kovoor et al. reared adult females ofL. tarentula wereused.
1993). Recently, Dacke et al. (2001) have They were maintained in individual containers
found the same structural basis in Lycosa god- measuring 17 X 13 X 8 cm, big enough for
ejfroyi L. Koch 1865 and other lycosids. them to move around to dig burrows. They
Lycosa tarentula is a circum-Mediterranean were fed blow flies (Calliphora vomitoria)
wolf spider that typically lives in a burrow in and given water twice a week. These animals
which the superior part is delimited by little had been captured from a wild popWulation in
twigs held together by silk (Ortega-Escobar Madrid (central Spain; N 40° 32' 3° 42')
1986). The depth and diameter of the burrow and went through the final 2-3 molts in the
is correlated with the spider’s size (Ortega-Es- laboratory; all were close to the same age and
cobar 1986). The prosoma of L. tarentula fe- all trials were conducted after—maturation.
males is variable in size: it can measure from Experimental procedure. To begin the
mm
6.0-9.5 in width (unpub. data). study of homing orientation, animals were
The visual system of the lycosid spider Ly- placed in a terrarium measuring 60 X 30 X
cosa tarentula has been studied both from the 35 cm. This terrarium had a 15 cm deep sub-
behavioral (orientation to nest: Ortega-Esco- stratum of soil similar to the natural substrate
bar & Munoz-Cuevas 1999; Ortega-Escobar (Fig. 1 right); in the middle of one long side
2002a; locomotor activity rhythms: Ortega- ofthe terrarium, an artificial burrow was built,
Escobar 2002b; Ortega-Escobar et al. 1992) similar to that which the spider digs in the
and structural aspects (Kovoor et al. 1992, field. After 5 days of habituation to the ter-
1993, 1999, 2005a, b). In the study by Ortega- rarium, the experiment began. During these 5
Escobar & Munoz-Cuevas (1999), when spi- days, spiders were mostly in the burrow dur-
ders were under an overcast sky, they did not ing the daytime and moved about during some
orient homewards; instead, they turned an al- hours at night. To displace the spiders, they
most constant angle for PI or path integration. were gently removed from the burrow and
In an indoor study (Ortega-Escobar 2002a), pushed along the edge of the terrarium on a
individuals of L. tarentula were displaced by path traversing half the length and the full
moving them along a two-leg trajectory with width of the terrarium. When the spider ar-
—
ORTEGA-ESCOBAR—ANTERIOR LATERAL EYES AND PATH INTEGRATION 53
Figure 1. Left: Setup used to study homing in L. tarentula. Right, top view ofterrarium in which the
animal lived during the study; arrows indicate the outward path. Left, dorsal view of the arena in which
the animal was left after being taken from the right corner opposite to the burrow. Burrow direction was
at 350°. The big arrow indicates the transfer ofthe animal to the center ofthe arena (shown at halfofits
actual size in relation to the terrarium). To go to the burrow, the spider must turn an angle of 135° in its
terrarium. Right: Aspect of the substratum of the terrarium.
rived at the end ofthe path, it was placed into two groups: “uncovered ALEs group” and
a transparent open glass container and trans- “covered ALEs group” that were observed
ferred to the center of an arena 90 cm in di- without eye covering (control test) and with
ameter (wall height, 48 cm; visual angle, 47°) eye covering (experimental test). To cover the
(Fig. 1 left). There, if the animal turned at an eyes, the animals were anesthetized with ether,
angle of 135° towards the left, it would be their legs restrained with adhesive plaster and
oriented to its burrow. Both the terrarium and their eyes covered by first applying a layer of
the arena were in a roomwithoutnatural light- collodion over the anterior region of the pro-
ing. The room was lit in the daytime (0800- soma; then by applying two layers of water-
2000 h) with white light by two SYLVA- soluble black paint (Van Gogh); and, finally,
NIA® Standard F36W fluorescent tubes by applying another layer of collodion. Eye
producing 200 lux at the floor level ofthe are- occlusion was checked in each case after the
na. Each animal was used in 8 trials (eight completion ofruns using a stere—o microscope.
control trials and eight experimental trials; see Automated video tracking. The image
below) and placed in one of the following ofthe arena was captured by an Ikegami ICD-
compass directions at random: 0°, 45°, 90°, 42B BAV CCD video camera and displayed
135°, 180°, 225°, 270°, 315°. The spider’s ori- on a Sony® Trinitron color video monitor. Si-
entation was recorded when it was at a dis- multaneously, the video signal was digitized
tance of 20 cm from the center of the arena. by aTarga 1 frame grabberthat was interfaced
Ifthe spiderhad not moved during 20 minutes with a personal computer supporting an object
it was returned to the terrarium. The floor of video-tracking system (Etho-Vision, Noldus
the arena was thoroughly cleaned with ethanol Information Technology, Wageningen, The
before each test. All the trials were run be- Netherlands). The paths supplied by Etho-
tween 11 and 18 h with lights on. Vision were later digitized. The best-fitting
All spiders (ji = 12) were observed first line to a trajectory was computedby the meth-
&
with all eyes uncovered (control test; eighttri- od of principal axes (Sokal Rolf 1995).
als for each animal). Afterwards, spiders were The following parameters were determined
assigned at random to one oftwo groups. One in both conditions (covered or experimental
set of spiders {n — 6) had all eyes but the and uncovered orcontrol eyes) in both groups:
ALEs covered (uncovered ALEs group, ex- (1) topographic bearing ofthe digitized home-
perimental test), while the other set {n = 6) ward path when the spider crossed a virtual
had only the ALEs covered (covered ALEs circle 20 cm in diameter from the starting
group, experimental test). Therefore, we had point of the return; (2) angle (a angle) of the
54 THE JOURNAL OF ARACHNOLOGY
two X two repeated measure analysis of var-
iance with the type of eyes (PMEs/PLEs/
AMEs, and ALEs) and covering (control -
without eye covering-, and experimental -with
eye covering-) as factors.
Voucher specimens have been deposited in
the Museo Nacional de Ciencias Naturales
(Madrid, Spain).
RESULTS
Homing—in uncovered ALEs group (con-
trol test). Homing paths followed by the
spiders in the arena were either roughly
straight, finishing with a sudden turn either to
the right or to the left, followed by a turn in
the opposite direction, as described previously
(Ortega-Escobar 2002a) or they walked until
they touched the arena wall. This series of
— turns has also been observed when the animal
Figure 2. Example of a homeward path in the
arena. The black square in the center represents the is taken from the burrow without having been
point where the spider is placed, and its orientation displaced and transferred to the center of the
is indicated by the arrow; theblackcirclerepresents arena. This type of behavior, called “system-
the burrow compass direction; a is the angle be- atic search” (Wehner & Wehner 1986), was
tween the initial orientation and final bearing not analyzed in this study.
(where homing path crosses the circle). Topographic bearings: None ofthe six spi-
ders oriented themselves towards the burrow
position or towards another point of the room
body axis when the spider crossed the virtual in a constant way in the eight trials (Fig. 3
circle with respect to the starting position of top, left).
the body axis; as the animal could turn either a angle: a was non-randomly oriented in
clockwise or counterclockwise, the a angle all six animals (Table 1 and Fig. 4 top, left).
was always taken counterclockwise, which The mean vectors of the six animals were not
was the expected direction for the animal to randomly distributed (Moore’s test: D =
turn in the terrarium (Fig. 2); (3) turning di- 1.277, P < 0.05). Table 1 shows the mean
rection (clockwise or co—unterclockwise). angle and length ofthe vector foreach animal.
Statistical analyses. The directions fol- In two animals the turn that the spider should
lowed by the animals were analyzed as cir- have made to go to the burrow in the terrarium
cular variables according to Batschelet (1981). (135°) was included in the confidence interval
For first-order statistics, the Rayleigh test was of the mean, but their mean vectors were sta-
used to determine whether the observed hom- tistically significant (Fig. 4 top, left).
ing directions from particular individuals were Homing in un—covered ALEs group (ex-
significantly oriented. To see if the deviation perimental test). The homing paths in the
between individual significant vectors and the experimental test were similar to those shown
angle of home direction (Fig. 2) was signifi- by animals when all eyes were uncovered.
cant we used the confidence interval for the Topographic bearings: Only one of the six
mean angle (P < 0.05; Batschelet 1981). On spiders oriented itselftowards one point ofthe
the second-order level, Moore’s and Mardia- room in a consistent way in the eight trials.
Watson-Wheeler’s tests (Batschelet 1981) (Fig, 3 bottom, left). The other five animals
were used to test directionality significance oriented themselves at random.
and differences in the orientation of the sub- OL angle: a was non-randomly oriented in
jects between control and experimental tests all six animals (Table 1 and Fig. 4 bottom,
respectively. left). The mean vectors of the six animals
The percentage of turning in the correct di- were not randomly distributed (Moore’s test:
rection (counterclockwise) was analyzed by a D = 1.353, P < 0.05), Table 1 shows the
ORTEGA-ESCOBAR—ANTERIOR LATERAL EYES AND PATH INTEGRATION 55
ALEs uncoveredgroup ALEs covered group
Experimental test Experimental test
—
Figure 3. Top left: Mean vectors (control test) oftopographicalbearings oftheuncoveredALEsgroup.
The dashed circle indicates the critical r-value of E = 0.05. 0° indicates the magnetic North. Top right:
Mean vectors (control test) of topographical bearings of the covered ALEs group. Bottom left: Mean
vectors (experimental test) of topographical bearings of the uncovered ALEs group. Bottom right: Mean
vectors (experimental test) of topographic bearings ofthe covered ALEs group.
mean angle and length of the vector for each these animals were very similar to those ob-
animal. In four animals, the turn that the spi- served for the other group (ALEs uncovered
der had to make to go to the burrow in the group).
terrarium (135°) was included in the confi- Topographic bearings: None of the six spi-
dence interval of the mean. ders oriented itselftowards the burrow position
Ho—ming in covered ALEs group (control or towards another point ofthe room in a con-
test). As expected, the homeward paths of sistent way in the eight trials (Fig. 3 top, right).
a
56 THE JOURNAL OF ARACHNOLOGY
—
Table 1. angle (mean a angle (6) and vector length (r)) in the controls and tests of both groups.
Asterisks indicate the degree of significance of the first and second order data; *, R < 0.05.
Covered ALEs group Uncovered ALEs group
All eyes uncovered ALEs covered All eyes uncovered ALEs uncovered
Individual 0 r 0 r Individual 0 r 0 r
1 159° 0.87* 61° 0.39 1 154° 0.81* 146° 0.80*
2 38 0.71* 42 0.56 2 164 0.83* 172 0.80*
3 134 0.65* 318 0.14 3 169 0.74* 158 0.91*
4 165 0.66* 51 0.27 4 165 0.95* 154 0.93*
5 161 0.87* 204 0.69* 5 195 0.91* 187 0.75*
6 60 0.68* 55 0.55 6 122 0.94* 137 0.96*
Group means 126 0.64 42 0.51 162 0.93* 159 0.96*
Mardia test Rd = 14.91, P < 0.05 Rd = 0.27, NS
a angle: The a angle (Fig. 4 top, right) was Percentage ofturnin—g in the expected di-
non-randomly oriented in all the animals of rection (see Methods), Turning in the ex-
this group. The mean vectors of the six ani- pected direction by the six animals of the un-
mals were randomly distributed (Moore’s test: covered ALEs group (control test) was 70.8
D = 0.923, P > 0.05). Table 1 shows the ± 6.5 % (mean ± SD), while among the six
mean angle and length of the vector for each in the covered ALEs group (control test) it
animal. In four animals the turn that the spider was 87.5 ± 19.4 % (Fig. 6).
had to make to go to the burrow in the ter- In experimental tests, 75 ± 22.4% of the
rarium (135°) was included in the confidence animals with only the ALEs uncovered turned
interval ofthe mean. In the othertwo animals, in the expected direction while 50 ± 22.4%
the 135° value was not included in the confi- of those animals with only ALEs covered
dence interval of the mean, but their mean turned in the expected direction.
vectors were statistically significant (Fig. 4 The ANOVA of the percentage of turning
top, right). in the expected direction showed no effects
Homing in—covered ALEs group (experi- for the two factors and significant effects for
mental test). The homeward paths of the the interaction (Fi lo — 15.625, P = 0.003).
animals with covered ALEs were very similar
DISCUSSION
to those observed when no eye was covered.
However, in several animals, circular path- As in a previous study (Ortega-Escobar
ways were observed (Fig. 5). These circular 2002a), the present results show that during
pathways were not used for the analysis. the day L. tarentula does not orient itself to-
Topographic bearings: Only one of the six wards the topographic burrow position in the
spiders oriented itself towards a point of the absence oftacto-chemical information and the
room in a consistent way in the eight trials presence of distant visual landmarks of the
(Fig. 3 bottom, right). laboratory. The results agree with what has
a angle: The a angle (Fig. 4 bottom, right) been observed when the animals could use
was randomly oriented in all but one of the neither the sun nor the polarized light pattern
animals of this group. In this animal, this an- for homing (Ortega-Escobar & Mufioz-Cue-
gle (Table 1) has a value of 204°, very differ- vas 1999).
ent from 135°; this value was not included in With all the eyes uncovered, this study
its confidence interval. shows that L. tarentula tries to return home
Comparison of ol —angle in control tests by turning a fixed angle, a, near to 135°. The
between both groups. To test ifboth groups turn near to 135° would let the animal walk
have the same mean orientation in control to a point near the burrow if its orientation
tests we have used the Mardia-Watson-Wheel- had not been changed in the arena.
er test. In this case, Rf = 1, NS, therefore If L. tarentula used only proprioceptive in-
there is no difference in the a angle between formation forhoming, it should be able to turn
both groups. an a angle near to 135° when it was displaced
ORTEGA-ESCOBAR—ANTERIOR LATERAL EYES AND PATH INTEGRATION 57
ALEs uncovered group ALEs covered group
Control test Control test
Experimental test Experimental test
—
Figure 4. Top left: Mean vectors (control test) of a of the uncovered ALEs group. The dashed circle
indicates the critical revalue ofF = 0.05. 0° indicates that the animal walks in the same direction that it
has beenplacedin the arena. The external arrow represents the anglethe spiderhas to turn intheterrarium
to go back to the burrow (a= 135°). Top right: Mean vectors (control test) of a of the covered ALEs
group. Bottom left: Mean vectors (experimental test) of a of the uncovered ALEs group. Bottom right:
Mean vectors (experimental test) of a of the covered ALEs group.
in the darkness. The previous study (Ortega- There is anotherpossibility to estimate the an-
Escobar 2002a) had shown that this is not the gle a: the use of the self-induced optic flow
case. Therefore, there must be some kind of through some eyes. The visual field of ALEs
visual information that the spider must use for is disposed in such a way that optic flow
homing. The present results exclude the pos- through them is more constant than optic flow
sibility of using distant visual landmarks giv- through the other eyes (Fig. 7). As the animal
en that topographic bearings are not constant. walks, the distance to the ground is rathercon-
—
58 THE JOURNAL OF ARACHNOLOGY
p<Q.m
UncoveredALEsgroup CoveredALEsgroup
—
Figure 6. Percentage ofturning in the expected
direction (mean ± SD) in the control and experi-
mental tests of both groups.
—
Figure 5. Two examples ofhomeward paths of
two different spiders with only ALEs covered.
Black square represents the initial position of the
spider; arrow represents the initial body direction;
black circle represents burrow direction.
stant and they mainly image the ground on
which the animal walks. On the other hand,
the other eyes image different objects and the
optic flow is more complex in relation to the
distance to the eyes. It is proposed that L. tar-
entula is able to perceive the optic flow ofthe
natural soil of the terrarium where it is dis-
placed, and afterwards it uses this information
to turn in the correct direction and angle even
if it is placed over an unstructured substrate
such as the white substratum ofthe arena. Are
the ALEs able to discriminate the small peb-
bles ofthe terrarium soil? One measure ofthe
resolution capacity ofa simple eye is the sam-
&
pling frequency, Ug (Land Nilsson 2002)
such thatUg — 1/ (2AT>) where A# is the inter-
Figure 7. Top: Frontolateral picture of L. tar-
receptor angle. Using the values obtained by
tKaorveontourla&feMmuaflieo,z-foCruetvheasAL(1E9s96/19“970).3f0orcyL.- ePteonrstituoelrrailosatrheorlawalitenerygael;theAeyeMp;oEs:PitMiAEonn:tserPoiofosrtthemereieodyrieasm.neAdeyiLeaE;n:PeLAyEne:-.
cles/degree which means that a grating con- Bottom: Schema showing the visual fields of the
sisting of two stripes, one black and one differenteyes ofLycosa tarentula (taken fromLand
white, will occupy 3.33° of the visual field. 1985).
ORTEGA-ESCOBAR—ANTERIOR LATERAL EYES AND PATH INTEGRATION 59
Supposing that the distance between the ALEs with the visual information generated by the
and the soil is 1 cm, the sampling frequency ALEs. Besides, the rhabdoms of the ALEs
of these eyes is high enough to distinguish have been shown (Kovoor et al. 1995) to be
between the small pebbles that the spiderfinds capable of functioning well between 12 and
while she walks about in the terrarium. Ad^ 19 h, the time when these experiments were
ditional experiments will be needed in which carried out. In the PMEs and PLEs, membrane
the animal is trained to walk in an artificial synthesis takes place at this time, and they are
structured environment (e.g., a grating of not in a good functional state. However, they
black and white stripes with a certain fre^ probably could function well under a light in-
quency) and thee tested in an unstructured en- tensity higher than that used in this experi-
vironment (white substratum) or a differently ment.
structured one (e.g., a grating perpendicularto It seems that there is a specialization in the
the training one). functioning ofL. tarentula eyes as it has been
The main results presented in this study proposed for anotherlycosid, Rabidosa rabida
(Figs. 4 & 6) clearly demonstrate that visual (Walckenaer 1837) (Roveer 1993) and for the
input gathered through ALEs influences the ctenid Cupiennius salei (Schmid 1998). ALEs
spider's estimate ofthe turning angle to reach are specialized for navigation when sun/polar-
home. The mean vectors ofanimals with only ized-light pattern compasses are not available
ALEs uncovered do not differ statistically and to setthe locomotor activity rhythmto LD
from the mean vectors of these animals when cycles (Ortega-Escobar 2002a, b), AMEs are
they could use visual information gathered specialized for navigation with the sun or the
&
through all eyes. pattern of polarized light (Ortega-Escobar
However, the results obtained when all the Mufioz-Cuevas 1999). PMEs do not seem to
othereyes (PMEs, PLEs, and AMEs) wereun- function in homing (this study; Ortega-Esco-
covered and only ALEs covered show that the bar & Munoz-Cuevas 1999) but other studies
visual information gathered through the for- (Roveer 1993) suggest that they are involved
mer eyes is not usable for homing. In fact, in recognizing form.
results under this condition are not different In the other two well-studied spiders, Cu-
from, those obtained when animals walked in piennius salei and Agelena labyrinthica, the
darkness during the outward and homeward possible differential role of the eyes in path
paths (Ortega-Escobar 2002a). Anteriorlateral integration has not been studied in the former,
eyes seem to transfer information about the but it has been well documented in the latter
&
direction of turning and the angle turned be- (Corner Claas 1985). Cupiennius (Seyfarth
cause when they are not functional, the animal et al. 1982) was studied in a situation in which
turns clockwise or counterclockwise at ran- it could be shown that the spider did not need
dom and at a random angle. to retrace its outward journey; but animals
In the wild in the daytime, female L. tar- with specific eye coverings were not studied.
entula walk out of their burrows only when In A. labyrinthica, “the experiments to date
there is prey or another member ofthe species have not revealed whether the different types
present, while at eight they walk out sponta- of eye have separate functions with respect to
neously. This behavior must also be based on optical navigation by a light source" (Corner
some differences between the states of the & Claas 1985: p. 281). Consequently, thekind
eyes in the day and at night and between the ofvisual navigation studied inA. labyrinthica
visual fields of the different eyes. Lycosa tar- was quite different from the present study of
entula would achieve PI by using propriocep- L. tarantula, and no comparison is possible.
tive and visual information gathered through ACKNOWLEDGMENTS
the anterior lateral eyes (ALEs), which have
ventral visual fields whose images change I thank Miguel Ruiz and Ignacio Montero
very little when the animal walks in compar- for statistical expertise and assistance. Dr. A.
ison with the images through the anterior me- Kovoor reviewed the English version of the
dian (AMEs), posterior mediae (PMEs) or manuscript. Thanks are also due to J. Rovner
posterior lateral eyes (PLEs), which move and an anonymous reviewer as well as to the
quickly, given their visual fields. This is the editor Dr. G. Stratton for their help in im-
easiest way to associate the proprioceptive proving the manuscript. I also thank “Canal
60 THE JOURNAL OF ARACHNOLOGY
de Isabel 11” for the permission to re-collect Kovoor, J., A. Munoz-Cuevas & J. Ortega-Escobar.
the animals in one of its installations. 2005b. The visual system of Lycosa tarentula
(Araneae, Lycosidae): Microscopic anatomy of
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97-122.
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