Table Of Content2001. The Journal of Arachnology 29:244-248
EGG SAC RECOGNITION BY FEMALE
MIAGRAMMOPES ANIMOTUS (ARANEAE, ULOBORIDAE)
Brent D. Opell: Department of Biology, Virginia Polytechnic Institute and State
University, Blacksburg, Virginia 24061 USA
ABSTRACT. After producing a cylindrical egg sac, a female Miagrammopes animotus holds it until
spiderlings emerge and disperse. When sacs were taken from females, these females exhibited a putative
searching behavior and, upon contacting either their sacs or those of conspecifics, exhibited a putative
recognition behavior. These responses would cause a female to search for and reclaim her sac if it were
temporarily abandoned during feeding or web construction. Females with sacs did not respond positively
to sacs from which spiderlings had emerged. Females that did not have sacs did not respond positively
to viable sacs. Females separated from their sacs for increasing time periods exhibited adeclinein positive
responses to their sacs. Thus, contact with the sac appears necessary to maintain an affinity for the sac
during the development of spiderlings.
Keywords: Maternal care, spider
Females of the simple-web species Mia- disperse and begin constructing capture webs.
grammopes animotus Chickering 1968 pro- Females continue to tend their egg sacs until
duce cylindrical egg sacs consisting of two spiderlings leave (Fig. 3).
columns of eggs surrounded by two thin lay- While collecting M. animotus in conjunc-
ers of silk (Lubin et al. 1978; Opell 1984). tion with studies of their cribellar threads and
During the day, a female attaches her egg sac cribella, I routinely collected females withegg
along one of the web’s non-sticky lines and sacs. When I attempted to remove a female’s
aligns herself with the egg sac, her abdomen egg sac so that I could weigh and measure her,
touching the egg sac, her legs I and II extend- she held tenaciously to her egg sac. Unless all
ing directly anteriorly, and her legs III and IV of her legs were removed from the egg sac,
extending directly posteriorly (Fig. 1; Lubin she quickly regained her firm grasp. After I
et al. 1978; Opell 1989a). This posture en- separated a female from her egg sac and
hances the twig-like appearance of both the placed her on a horizontal surface, she walked
female and her egg sac. Miagrammopes ani- rapidly and made broad, rapid sweeping
motus females range in color from light tan to movements with her first legs. When she con-
dark, reddish-brown and produce egg sacs tacted her egg sac, she held it tightly with her
whose wrapping silk is similar in colorto their first two pairs of legs, immediately pressed
bodies (Opell 1989a). This makes it even her chelicerae to its surface for a few seconds
more difficult to distinguish a spider and her (although I could not determine if she bit the
egg sac and further enhances the cryptic ap- egg sac’s silk covering), and then immediately
pearance of each. firmly grasped the egg sac with her first and
At dusk a female detaches her egg sac from second legs. When a female with an egg sac
the line and holds the sac with her first leg as was placed on a horizontal surface, she often
she monitors her web (Fig. 2; Lubin et al. attached a dragline to her egg sac and walked
1978; Opell unpubl. obs.). This suggests that away, possibly searching for a secure site to
her linear, day-time posture is a defense climb. When either the egg sac or dragline
against visually hunting predators like insects was touched, the female ran quickly to heregg
and birds. When spiderlings emerge from an sac, pressed her chelicerae to its surface and
egg sac as second instars, they lack functional then grasped the egg sac.
cribella and cling to the egg sac for several I interpreted this rapid walking and leg
days until they molt to the third instar (Lubin waving behavior as searching behavior, the
et al. 1978; Opell 1989b), at which time they cheliceral contact as egg sac evaluation be-
244
OFELL^MIAGRAMMOPES EGG SAC RECOGNITION 245
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Figures 1“3. Miagrammopes animotus females tending egg sacs during the day (1), at night (2), and
after spiderlings have emerged (3).
havior, and the subsequent grasping ofthe egg search’s El Verde, Puerto Rico field station.
sac as positive egg sac recognition. To better Voucher specimens are deposited in Harvard
understand this behavior, I evaluated the re- University’s Museum of Comparative Zoolo-
sponses of females that had no egg sacs, in- gy. All observations were made in a window-
vestigated the specificity of egg sac recogni- less laboratory that was illuminated by fluo-
tion, and determined if this behavior was rescent lights and had a temperature of20-24
expressed after a female had been separated °C and a relative humidity of 60-63%.
from her egg sac for different lengths oftime. After removing a female’s egg sac, I placed
METHODS each in a separate, clean glass vial stoppered
A
with a cotton plug. small piece of moist
Spiders and egg sacs were collected at the cotton was placed with each spider. Vials were
Center for Energy and Environment Re- numbered so that I could identify each spi-
246 THE JOURNAL OF ARACHNOLOGY
der’s egg sac, though only by referring to a mosus (Walckenaer 1841) from Blacksburg,
record book. Observations were conducted by Virginia. Another five females that responded
mm
placing a female in a clean, 40 diameter positively to egg sacs that contained eggs re-
aluminum weighing pan and observing herre- sponded negatively to egg sacs from which
sponse to an object or an egg sac. I define a spiderlings had emerged, walking over these
positive response to an object or an egg sac egg sacs and continuing to exhibit searching
as the female clinging tightly to the object af- behavior.
ter contacting it with herchelicerae so that she Figure 4 shows the percentages of females
could not be easily dislodged by repeated that responded positively to their egg sacs af-
prodding with a small artist’s brush. Occa- ter times of increasing separation. In each of
sionally, a female rested momentarily on an the first six time intervals, the responses of
egg sac or object, but did not bring her che- females used in a second trial did not differ
licerae to its surface. In these cases a light from that of females that were used in only
prod with a brush caused her to leave the ob- one trial (x" < 0.425, I df, P > 0.50). How-
ject and continue walking and I scored this as ever, in the last interval (23-25 h) five of the
a negative response. six females used in a second trial responded
I examined the duration of egg sac recog- positively to their egg sacs, a greater number
nition in 82 females that were collected with than predicted by the responses of females
egg sacs. After removing theiregg sacs, I kept used in only one trial (x^ = 16.000, I df, P <
these spiders for periods of5-25 h. At the end 0.001). The median time of these seven peri-
of each of these 21 periods the responses of ods regresses against the percent positive re-
2-10 females to their own egg sacs were ob- sponse (Y = -2.06X + 92.92; F = 8.20, P
= =
served. Thirty-four of the females that re- 0.035, 0.62), indicating that a female’s
sponded positively to their egg sacs were used ability to identify and respond to her egg sac
for a second trial after each was kept in a vial decays with increasing separation. Additional
with her egg sac for 12-24 h to permit pro- support for this decay comes from a compar-
longed contact with her sac. ison ofthe responses when grouped into short,
intermediate, and long periods ofegg sac sep-
RESULTS aration (5-9 h, n = 35; 10-20 h, n = 48; and
Eleven mature females that had no egg 21-25 h, n = 33; respectively). For this com-
sacs, including five whose abdomens were parison, I determined the mean positive re-
clearly swollen with eggs, did not cling to egg sponse for each of the 21 hourly trials and
sacs or press their chelicerae to their surfaces then compared the grand means of responses
when each was presented with 7-10 egg sacs in the three periods. A Kruskal-Wallis test
of conspecifics, nor did they cling tightly to showed that the values of these periods (X ±
pieces of grass or cotton that I placed in their 1 SD: 78.7% ± 19.7, 66.0% ± 27.4, and
collecting vials. In contrast, 26 of 32 females 38.9% ± 7.9, respectively) differed (x^ =
whose egg sacs were removed 5-6 h earlier 6.47, P = 0.039).
responded positively to their reintroduced egg
DISCUSSION
sacs. The response of each group differed
from a null model in which 50% of the indi- These observations indicate that sensory
—
viduals responded positively to egg sacs (x^ stimuli from one or several sources unique to
11.0 and 12.5, respectively, P < 0.001). oviposition or egg sac construction cause per-
Two females that responded positively to sistent but reversible changes in a spider’s
their own egg sacs also responded positively physiology that alter its response to egg sacs.
to egg sacs produced by nine other females. Possible sources of these stimuli include the
Seven females that responded positively to pressure exerted on the oviducts as eggs pass
their own egg sacs also responded positively through them and the activation oftubuliform
to an egg sac ofthe closely related species M. silk glands and spigots that, in uloborids, ap-
pinopus Chickering 1968 from St. John, U.S. pear to be used only for egg sac production
Virgin Islands. However, they did not respond (Kovoor 1977; Foelix 1996; Opell 1984).
positively to a piece of cotton, a section of Copulation is an unlikely source ofstimuli, as
wooden applicator stick similar in size to an females store sperm and mating may occur
egg sac, or to an egg sac of Uloborus glo- long before eggs are fertilized and deposited.
OmUL—MIAGRAMMOPES EGG SAC RECOGNITION 247
Hours of Egg Sac Separation
—
Figure 4. Positive egg sac recognition following periods ofincreasing separation of a female and her
egg sac. Bars represent the means of the three-hour periods. The sample size is given within each bar.
The number offemales used in a second trial is given in parentheses.
Once a positive response to an egg sac has lings to emerge from the egg sac (Opell 1979,
&
been established it appears to be general and 1982; Peaslee Peck 1983).
does not permit a female to distinguish her Unlike members of other uloborid genera,
egg sac from those of conspecifics. However, Miagrammopes females have no permanent
unlike wolf and fishing spiders, M. animotus attachment site for their egg sacs. At night fe-
females can not be tricked into accepting sub- males probably temporarily attach the egg sac
stitute objects (Gertsch 1979; Foelix 1996). to a line while renewing their capture webs
Egg sac recognition persists for varying pe- and feeding. This behavior has not been ob-
riods of time, but lasts long enough to cause served in M. animotus; but Lubie et al. (1978)
a female to search thoroughly for her egg sac report that females of an unidentified Mia-
if she left it. The regression formula for the grammopes species hung their egg sacs from
decay of positive responses to egg sacs sug- threads at night and resumed prey capture ac-
gests that egg sac recognition disappears in all tivity until dawn, at which time they again
females afterthey are separated fromtheiregg tended their egg sacs. Egg sac recognition
sacs forabout45 h. Continual orfrequentcon- would cause a female to search for her egg
tact with an egg sac appears to be necessary sac ifshe were forced to abandon it during the
to maintain a female's positive response to her day or to anchor it while building or repairing
egg sac during the approximately 20 days re- her capture web at night.
quired for the eggs to develop and the spider- I did not investigate cues that might permit
248 THE JOURNAL OF ARACHNOLOGY
females to distinguish viable egg sacs from LITERATURE CITED
those that the young have abandoned. The Foelix, R.G. 1996. Biology ofSpiders. 2^^ ed. Ox-
masses of viable and empty egg sacs differ; ford Univ. Press, New York.
but, in my laboratory observations, females Gertsch, WJ. 1979. American Spiders. Van Nos-
did not appear to lift egg sacs to assess their trand Company, Inc., New York.
masses. Second instar spiderlings may deposit Kovoor. J. 1977. Lappareil sericignene dans le
silk on the egg sac’s outer surface and this genera Uloborus Latr. (Araneae, Uloboridae). I.
Anatomic Revue Arachnologique 1:89-102.
may mask the egg sac silk that allows a fe- Lubin, Y.D., W.G. Eberhard & G.G. Montgomery.
male to identify an egg sac. Alternatively, the 1978. Webs of Miagrammopes (Araneae: Ulo-
female may identify andrespond negatively to boridae) in the Neotropics. Psyche 85:1-23,
the silk of these spiderlings. Opell, B.D, 1979. Revision ofthe genera and trop-
The loss of egg sac recognition has advan- ical American species of the spider family Ulo-
tages for M. animotus females that appear to boridae. Bulletin ofthe Museum ofComparative
produce several egg sacs during a lifetime and Zoology 148:433-549.
A Opell, B.D. 1982, Post-hatching development and
often reach high densities. female’s nega-
web production of Hyptiotes cavatus (Hentz)
tive response to an egg sac from which spi-
(Araneae, Uloboridae). Journal of Arachnology
derlings have emerged and dispersed allows 10:185-191,
her to shift her activity from egg sac tending Opell, B.D. 1984, Eggsac differences in the spider
to web building and foraging so that another family Uloboridae (Arachnida: Araneae). Trans-
egg sac can be produced. This negative re- actions of the American Microscopical Society
sponse may also reduce intraspecific conflict. 103:122-129.
At El Verde, I often observed 3-5 mature fe- Opell, B.D. 1989a. Do female Miagrammopes an-
imotus (Araneae: Uloboridae) spin color-coordi-
males on a single under-story plant or cluster
nated egg sacs. Journal ofArachnology 17:108-
of vegetation occupying a space of about 1 111
m^. Under these high densities, the loss ofegg Opell,. B.D. 1989b. Functional associations be-
sac recognition would eliminate contests be- tween the cribellum spinning plate and prey cap-
tween females that were tending egg sacs and ture threads of Miagrammopes animotus (Ara-
those from whose egg sacs spiderlings had re- neida, Uloboridae). Zoomorphology 108:263-
cently dispersed. In the absence ofindividual- 261,
specific egg sac recognition, the failure of fe- Peaslee, J.E. & W.B, Peck. 1983, The biology of
Octonoba octonaria (Muma) (Araneae, Ulobor-
males to respond to old egg sacs also assures
idae). Journal of Arachnology 11:51-67,
that they will not mistakenly abandon viable
egg sacs for these discarded egg sacs that Manuscript received 20 June 2000, revised 28No-
sometimes remain suspended from vegetation. vember 2000.
