R. Ramousse.
Body, Web-building and Feeding Characteristics of Males of the Spider Araneus diadematus (Araneae: Araneidae).
Psyche 80:23-47, 1973.

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BODY, WEB-BUILDING AND FEEDING
CHARACTERISTICS OF MALES OF
THE SPIDER ARANEUS DIADEMATUS
(ARANEAE : ARANEIDAE)
BY RAYMOND RAMOUSSE*
Division of Research
North Carolina Department of Mental Health P. 0. BOX 7532
Raleigh, North Carolina 2761 I
INTRODUCTION
Many investigators have observed female orb-web spiders in their natural habitats (Enders, 1972 ; Eberhard, 1971 ) , but there have been relatively few scientific observations of males outdoors. A major reason for this is because after maturation males discontinue web building and they seek mates and are difficult to follow in an un- confined setting. Males have also attracted less attention in labora- -
tory situations since they have shorter life spans than females and because they stop building webs after reaching maturity. The activity of spiders in laboratories has been observed primarily in relation to their web-building behavior (LeGuelte, I 966, Witt, 1g63a,b), making the female a more frequent subject of study. Thus, with the exception of maturation on web-building (Witt et al., 1972), only females have been comprehensively studied. The focus of this research is to explore the activities of the males of Araneus diadematus Clerck and their role in the female-male relationship which ultimately determines the continuity of the species. Two characteristics related to the females have already been identi- fied .as possibly playing a part in the survival of the species. These include cocoon hatching and differential maturing. Cocoons have been observed hatching at two different times for a single species of spider - presumably providing an advantageous distribution of egg- production over a period of time (Potzsch, 1963). Also, within a set1 of spiderlings, different rates of maturation have been observed. Some females grow rapidly and die early while others grow slowly "Present address of author: Laboratoire d'Ethologie experimentale, 1 rue Raulin, 69 Lyon 7e, France
Manuscript received by the editor March 26,1973 'To avoid confusion with the designation of "family" used in nomencla- ture, offsprings from a single cocoon will be called a "set." Pu&e 80:23-48 (1973). hup Ytpsychu einclub orgtSWaO-023 html



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19731 Ramousse - Araneus diadematus
23
and live at least four months longer (Reed & Witt, 1972). The related differential maturing rates may provide an advantageous distribution of spiderlings over a period of time. Together, these mechanisms would seem to help a species survive drastic or poten- tially destructive changes in environmental conditions. This research seeks to explore the male's role in these phenomena. At what rate is he growing, maturing and dying during the female's life cycle? This leads to the question of inbreeding. An observation of the
maturation rates of spiderlings of the same set was conducted in an effort to determine if inbreeding is possible. Also, if the rate of growth is a factor in the rate of maturation (and spiders of the same set are known to present a considerable variation in size even under apparently optimal conditions), (Witt et al., 1968)) is growth prenatally or genetically d,etermined or a function of external factors?
The effects of an even diet independent of manifest behavior (Witt et al., 1972) and differential force-feeding on various schedules (Benforado & Kistler, 1972) have already been studied. What, however, would happen to the growth rate of male and female spiders if they could choose their foo'd quantity through web-building frequency ?
The answers to some of these questions about the growth and maturation of male spiders should provide clues about their role in the reproductive cycle and, more generally, about their role in the continuity of the species.
METHODS
Two Araneus diadematus cocoons collected in the field, were placed in two different rearing boxes in the laboratory, where they hatched (February 23, 1972, one cocoon and 14 days later, March 6, 1972, the other). The offspring from the first cocoon will be called set I, and the offspring from the second cocoon, set 11. The laboratory
provided a cycle of long warm days and short cool nights throughout the lifespan of the animals.
As the animals left the communal web to build individual webs, they were put in glass tubes. Five weeks after hatching for set I and three weeks after hatching for set I1 the spiderlings were caged in individual labeled frames (w X 50 X 10 cm) where they could build webs without apparent limitation in size. All observations began at this moment; however, some molts were noticed inside the cocoon, and the spiderlings molted one or two times in the glass tubes.



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24 Psyche [March-June
In the rearing boxes as well as in the glass tubes they were pro- vided water and gnats ad libitum. In the frames the spiderlings were fed with de-winged houseflies. A weighed fly was given one time every three days only when a web had been built, thus rewarding the spiders for high frequency of building.
The individual weights of the spiders (accuracy 0.1 mg) were recorded every week and web-building was recorded every day. Each web was photographed then collapsed by the experimenter, and ana- lyzed for size, shape, fine structure and regularity (Reed et al.,
1965). The dates of the molts of each spiderling were recorded and the length of the first leg was measured on the molted limb (ac- curacy in mm. ) .
In the following pages the initials FG and SG are used in place of fast growing males and slow growing males. Statistical com- parison between the two groups (SG & FG) where not specifically mentioned was made with the Wilcoxon test, adapted by White for unpaired measurements (White, I 952) .
RESULTS
Of 31 spiderlings that reached maturity in set I, twelve were identified as males. There were 14 males out of a total of 29 animals in set 11. The number of males in each set is significantly repre- sentative of the expected 50% probability of males in a population (Binomial test, p = 0.01 in each case) . Some characteristics of the male
The adult males of Araneus diadematus have enlarged black palps, relatively narrow elongated abdomens, and weigh about a fifth of the adult females. Adult females are characterized by long yellow palps and a globulous abdomen (Figure I ) . Other characteristics of the males include banding of the legs that is generally darker, a lack osf humps on the abdomen, and a modified second tibia that is stronger than in females and has short spines (Levi, 1971). The enlarged palps appear at the end of the next-to-the-last molt, whitish instead of black, and blacken between the two last molts. One animal exhibited enlarged palps prematurely two molts before the last one and four other animals after the last molt, but these were exceptions.
After the last molt, when they reached sexual maturity and maxi- mum weight, the males stopped building webs. Sekiguchi ( 1955) reported that a male of Araneus ventricosus, in the laboratory, did



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19731 Ramwsse - Araneus diadematus
Figure 1. Outline of a male (left) and a female (right). Note the difference of size (female front leg: 16 TOTO, male front leg: 12 mm), of weight
(female: 144.1 mg, male: 47.0 teg) and the difference of form of the palps (short and enlarged for the male, long and thin for the female). not spin a web after its last molt, and that the aggregate glands become vestigial in the adult males. Prior to this point the involve- ment of the aggregate glands in the formation of the catching area of a web was clearly shown (Peakall, 1964). We may suppose that adult males are unable to spin webs because their aggregate glands are no longer functional.
The males ate scarcely, even when we attempted to induce prey catching by placing the flies in front of their mouths. While an immature male transformed a fly into a small compact ball through eating; the different parts of the body of a fly abandoned after eating by a mature male were easily recognizable. Even when they ate, the mature males used only a small amount of the food available. Males of Linyphia triangularis CIerck did not require food in the adult stage, and were still able to mate with females that later produced fertile eggs. When these males were provided with food, the rate of prey capture and the rate of food consumption dropped sharply



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Figure 2. Body weight of four FG and seven SG littermate males in set I of Araneus diadematus, hatched in the laboratory from one cocoon on February 23, 1972. Dashed line: weekly mean body weights of the FG males. Dotted line: weekly mean body weights of the SG malel%. Numerals followed by an arrow indicate the number of animals molting for the last time during a week. Numerals surmounted on black circles indicate the number of animals dying during a week. The FG males reached their maximum weight the 13th week of post-hatching, the SG males reached their maximum the 29th week of post-hatching. Note that the SG animals need twice as much time to mature as the FG. (Turnbull, I 962). We may assume that the adult males, no longer able to build a web, do not neeed food to fulfill their mating role. Four males in this study continued to spin webs until they died; they built webs for a few days after the last molt was recorded, then stopped building for three or four weeks and generally built a final web six or seven days before death. These facts suggest that these four males were not able to go through an additional molt to com- plete their development. Also, these males presented enlarged palps only after the last molt recorded which is another confirmation of thir inability to complete their development. During the web building period the males are distinct from the females only between the two last molts
(about 3 weeks). This
explains why few studies have been made of the males either outdoors or in the laboratory.




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19731 Ramsse - Aruneus diadematus
Weight increase
In each set, the individual weight curves follow two distinct pat- terns and no in between: a group with an early maximum (FG) and a group with a late maximum (SG). In set I the course of the growth of four males with early maxima (between 10th and 15th week post hatching) was compared to seven males with late maxima (between 22nd and 33rd week post hatching) (Figure 2). In the second set the growth of I I males which reached their maximum weight between the 8th and 16th week post hatching was compared to three males reaching their maximum weight between the 19th and 23rd week post hatching (Figure 4). In both sets the SG animals needed approximately twice as much time to complete the last molt and to attain sexual maturity as did the FG animals. In each set the females could be divided into fast and slow growth groups in the same way as males. Figure 6 shows the body weight of the FG and SG males and females. The data from the two sets were combined forming four groups: FG and SG males and females. The weight gain per day until maturation, in both sets, was sig- nificantly higher for the FG males than for the SG males (set I: T = 6,P = 0.05 ; set 11: T = 7, P = 0.05). The mean weight gain per day between the two last molts for each group was :
set I set I1
In each set, every animal showed a weight gain per day significantly higher between the two last molts than during the preceding period of observation (Wilcoxon matched-pairs signed ranks test : set I : N = 9, T = 3, P = 0.02; set 11: N = 13,T=o, P=o.oI). Frequency of building
The mean of webs built per day to reach the last molt were: set I
set I1




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28 Psyche [March- June
The FG males had a higher rate of building while they grew than did the SG males (set I: T = 6, P = 0.05; set 11: T = 6, P = 0.01). The differences in the rate of building appear clearly on the graphs (Figs. 3 and 5) obtained by plotting the mean fre- quency of building per week for each group in each set. The frequency of building is strongly correlated with the amount of food eaten per day (Kendall rank coefficient; set I: 7 = 0.59, P = 0.004; set 11: y = 0.52, P = 0.005). This is the necessary consequence of the feeding schedule. We might suppose that this relation occurs in nature. A fresh snare probably increases the chances of capturing prey.
----
FG males
set I
......
FG males
I .
8 12 16 20 2 4
weeks post hatching
Figure 3. Frequency of building of the FG and SG males of set I. Dashed line: weekly mean of frequency of building for the four FG m,ales. Dotted line: weekly mean of frequency of building for the seven SG males̀ Note the similarity in the pattern between weight increase and web building frequency. (Compare with Fig. 2.)




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FG males
set II
SG males
4 8 12 16 20 24
weeks post hatching
Figure 4. Body weight of 14 male littermates in set I1 of Araneus diadematus hatched in the laboratory on March 6, 1972. Dashed line: weekly mean body weight for the 11 FG males. Dotted line: weekly mean body weight for the three SG males. Numerals followed by an arrow indicate the number of animals molting for the last time during a week. The FG animals reached their maximum weight the 12th week post-ha,tch- ing, the SG males reached their maximum the 27th week post-hatching, when the FG males are dead. (Compare with Fig. 2.) The rate of building:
set I set I1
between the two last molts was significantly higher than the rate of building during the previous stages of growth in both sets (set I: N = 9, T = 2, P = 0.01; set 11: N = 12, T = 1.5, P = 0.01 Wilcoxon test) .
What explanations are there for differences in frequency of build- ing? A multiplicity of factors have been found to have some in- fluences on web-building: a change from dark to light, a steep rise



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- FG males
set I1
- * S G males
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0) 0
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4 8 12 16 20 24
weeks post hatching
Figure 5. Frequency of building of the FG and SG males of set 11. Dashed line: weekly mean frequency of building for the 11 FG males. Dotted line: weekly mean frequency of building for the three SG males.
Note similarity to Fig. 3.
in temperature following a temperature minimum, weather condi- tions, barometric pressure, a full silk supply, hunger (Witt, et al., 1968). In the laboratory, all the spiders were subjected to the same environmental conditions, therefore the differences in rate of building should be due to an internal state, such as hunger. There is a gen- eral agreement in the literature that hunger is a strong drive for web-building. Heavy feeding is followed by several days without web-building (Koenig, I 95 I ; Wolf & Hempel, 195 I ; Wiehle, I 927 ; Peters, 1932). The interpretation is that the hunger drive is too low for releasers like temperature and light to operate. On the other hand, spiders deprived of food built almost every day (Peters, 1939) and built webs even at the expense of other body constituents (Witt, 1963b). We may assume that the FG males have a higher level of hunger than the SG males, which induces a higher rate of building. Rood consumption
Each time a spider was fed, the fly was weighed before eating. Since only one or two percent of a fly was rejected by a spider after



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19731 Ramousse - Araneus diadematus 31
eating, we assume that a fly was eaten entirely. The mean quantity
of f,ood consumed per day was :
set I set I1
rhe FG spiders a,te a significantly higher quantity of food per day than the SG ones (set I: T = 6, P = 0.05 ; set 11: T = 8, P = 0.05). There was a significant difference in the amount of food consumed per day between FG males of the two sets (T = 8.5, p = 0.05).
The mean quantity of food eaten between the last two molts was: set I set I1
In each set the mean quantity of food consumed per day between the last two molts was significantly highmer than the mean amount of food eaten per day during the preceding observation period, (Wil- coxon test: set 1 : N = 10, T = 0, P = 0.01 ; set 11: N = 13, T = I, P = 0.01).
A relationship exists between the amount of food eaten per day and the growth rate in both sets, indicating that the growth rate is a function of the amount of food consunled (Kendall rank coefficient; set I: y = 0.55, P = 0.01 ; set 11: y = 0.60, P = 0.001). The foot eaten was used to sustain the 'basal metabolism, to make silk, and to build the body of the spiders. A rough estimate of the per- centage of food transformed into spider tissues was obtained by dividing the gain of body-weight per day by the quantity of food consumed per day: the FG males used about 57 % (set I) and 47% (set 11) of the food they ate, while the SG males transformed only 33% (set I) or 32% (set 11) of their food into spider tissues. The FG groups transformed a greater amount of food consumed into spider tissues than did the SG groups (set I: T = 6, P = 0.05;



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FG females
SG females
- SG males
I I I I I
1 3 5 7 9
months post hatching
Figure 6.
Body weight and number of molts of 25 males (15 FG, 10 SG), and 25 females (15 FG, 10 SG) from the two sets cocoons of Araneus diadematus studied. Each line connects mean body weights at one, two, five, seven and nine months post-hatching. Large black circles: FG females, large dashed line: early life of SG females; small black circles: FG males, small dashed line: SG males.
Arrows indicate the number of molts to the time. Note the different growth rates and the related different speed of maturation in FG and SG males and females, and the similarities for both sets.
set 11: T =
14, P = 0.05). As a result of having more food available for metabolism, an FG male was able to utilize more energy for other metabolic processes than basal metabolism, such as synthesis of silk, synthesis of body constituents, etc. This would assure a larger supply of silk for the FG spiders than for the SG, which could be an important drive for web-building (Peakall, 1967). The increased frequency of building in the FG spiders leads to a greater amount of food consumed which in time results in the rapid weight gain and growth.




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Ramousse - Araneus diadematus
Maturation
Between the start of the observations and the time of sexual ma- turity (last molt) the mean number of molts recorded for each group was :
set I set I1
1 SG 1 4.50 molts 1 3.66 molts
The SG males in set I went through a significantly higher number of molts than did the FG males (T = 12, P = 0.05) and reached a higher weight (see below). In set 11, we had only three SG males and one of them did not complete its development, this explains the difficulty to obtain a significant difference between SG and FG ani- mals in this set.
For set I the mean time of maturation was 81.6 days for the FG spiders and 202.5 days for the SG spiders. In set I1 maturation was reached in a mean time of 78.0 days for the FG males and 163.0 days for the SG ones. The time of maturation was significantly longer for the SG animals (set I: T = 6, P = 0.05 ; set I1 : T = 6, P = 0.01). In addition the time of maturation was sig- nificantly longer for the SG in the first set than in the second set (T = 6, P = 0.05).
The rate of maturation, number of molts divided by the number of days necessary to complete these transformations, was significantly higher for the FG males than for the SG males (set I: T = 6, P = 0.01; set 11: T = 6, P = 0.05).
The Kendall rank coefficient between the gain of weight per day and the number of molts per day was 0.61 for set I and 0.66 for set I1 (in both P = 0.001). A relationship exists between the rate of growth and the rate of maturation which is in agreement with the findings of Deevey (1949) with Latrodectus mactans (Fabri- cius) and of Benforado and Kistler (1973) with Araneus diadema- tus. We may assume that the maturation rate is correlated with the growth rate. The mean length of time in days between two con- secutive molts was determined. In 3 out of 4 groups, the last inter- molt was longer than the other intermolts (table I) ; for the FG males, this last intermolt was significantly longer than the earlier (N = 10, T = 1.5, P = 0.01).




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Table I
I 2 3 4
set I FG 20.6 14.0
SG 63.3 37.5 46. I 29.6
set I1 FG 22.7 12.0
SG 26.5 54.0 55.0 I 7.0
Mean length of time in days separating two consecutive molts. The numerals designate each intermolt and its order in rela,tion to the final one, I being the last.
Increase in leg-lengt h
The mean length of the first leg as measured on the last molt was: set I set I1
S'G males, which were also heavier, had significantly longer first legs