SHORT COMMUNICATION DIFFERENCES IN THE ACTIVITY OF JUVENILES, FEMALES AND MALES OF TWO HUNTING SPIDERS OF THE GENUS CTENUS (ARANEAE, CTENIDAE): ACTIVE MALES OR INACTIVE FEMALES?

3 Pages·2001·2.4 MB·English

by  Fabiola M D Salvestrini

2001. The Journal of Arachnology 29:276-278
SHORT COMMUNICATION
DIFFERENCES IN THE ACTIVITY OF JUVENILES,
FEMALES AND MALES OF TWO HUNTING SPIDERS OF
THE GENUS CTENUS (ARANEAE, CTENIDAE):
ACTIVE MALES OR INACTIVE FEMALES?
Fabiola M.D. Salvestrini and Thierry R. Gasnier: Depto. de Biologia/ICB,
Fundagao Universidade do Amazonas, Av. Gal. R.O.J. Ramos 3000, CEP 69067-000,
Manaus, AM, Brazil
ABSTRACT. The difference in activity levels between adult male andfemale spiders hasbeenattributed
to a more sexually motivated searching behavior by males, but the possibility that females reduce their
activity when they reach maturity has not been considered, which may be evaluated by comparing adults
and late instarjuveniles behavior. We recorded the displacements during 15 min periods for 137 males,
females andjuveniles ofCtenus amphora and C. crulsi, two similar-sized syntopic hunting spiders species
which search for prey on the leaf litter in central Amazonian tropical rainforests. For both species, males
were significantly more active than females andjuveniles. Ctenus amphora females were less active than
juveniles, but the C. crulsi female activity did not differ from thejuvenile activity. There were no signif-
icant differences in activity between these species for males and females, but thejuveniles ofC. amphora
where more active than thejuveniles of C. crulsi. Therefore, differences in activity between sexes are not
always restricted to changes in male behavior, and the degree of decrease in female activity may depend
on how activejuveniles are.
Keywords: Amazonia, behavior, movements, foraging mode
Hunting spiders actively move about in The observations were made in Adolfo
search of prey (Uetz et al. 1999). However, Ducke Forest Reserve, a 10,000 ha “terra-fir-
activity levels may differ between adult males me” primary forest reserve 25 km north of
and females (e.g., Schmitt et al. 1990). This the city of Manaus, Brazil, where the ecology
difference has been attributed to a more sex- of this genus has been intensively studied
u(aRlolvynemroti&vatBeadrthsea1r9c8h1i)n;g bbueth,avaisorfaorfamsalwees H(H5offeerr2e0t01al). a1n9d94o;nGtahsenicearmp1u9s96;ofGtahseniUenriv&-
know, the possibility that females reduce their ersidade do Amazonas, a forest fragment in
activity when they reach maturity has notbeen Manaus. Using head lamps, we observed the
considered. To test this hypothesis it is nec- spiders during their nocturnal activity, in the
essary to compare the behavior of adults with
dry (2 nights in June and 3 nights in October
that of late instar juveniles. The objective of
of 1998) and wet seasons (6 nights in January
the present paper is to evaluate whether the and 3 nights in April of 1999). We memorized
differences in activity between sexes in two
species of hunting spiders {Ctenus amphora the trajectory ofthe movements for 15 min of
Mello-Leitao 1930 and C. crulsi Mello-Leitao activity and recorded the total displacement
1930) may be attributed to a more active be- (including curves) with a tape measure. This
havior of adult males, a less active behavior was possible because ofthe low activity levels
of adult females, or both. Both species forage and the tendency of the spiders to move in
on the leaf litter, do not have fixed retreats, straight lines. We tried to minimize the effect
have similar size (both with prosoma length of our presence on the behavior of the spider
of 5.5-1 1 mm) and are sympatric in the study by using a red filter on the lamp and by avoid-
areas. ing movements. Voucher specimens for these
276
SALVESTRINI & GASNIER—ACTIVITY IN CTENUS 211
studies are deposited in the arachnological 150
collection of the Institute Nacional de Pes- Juveniles
quisas da Amazonia underthe numbers INPA- §100
001 to INPA=023. We used non-parametric I
statistics (Mann Whitney U-test and Kruskal- SOn 50 ••
Wallis //“test), for all comparisons. Our sig- Q
nificance level was a — 0.05; however, we
adjusted a when multiple comparisons were 0
performed following Rice (1989). When we C. amphora C. crulsi
compared juveniles, males and females, we
had three pairs ofcomparisons per species: in
these cases, we used the significance levels of 700
^600_ • Males
0.017, 0.025 and 0.05 from the greatest to
smallest P value. |500-
We observed 137 Ctenus crulsi individuals «400 ••
|300
(28$, 19(3 and 37 juveniles) and C. amphora •
•5200 ik
(15$, IAS and 24 juveniles). There were no •
100- •
significant differences between the species in
t0h.e91d)is(pFilga.ce1m)enotrsfoefmamlaelses (f/1419=— 118366,,PP =- 0 C. amphora C. crulsi
0.44). However, C. amphora juveniles were
significantly more active than C. crulsi juve-
niles (C/ = 579, P = 0.03). 120
There24.w37ere significant differences in dis- dOi 100“ Females
placement among males, females and juve- BV 80
niles within each species (C. amphora: H = 56 60-
14.45, P < 0.001; C. crulsi: H = 19.71, P < .S 40
® —
0.001). For both species, the males were sig- 20
nificantly more active than females (C. am- ...* I
phora: C/i415 = 176, P < 0.001 and C. crulsi: C. amphora C. crulsi
^ ~ 436, P < 0.001) and significantly —
19.28 Figure 1. Displacement (cm) of juveniles and
more active thanjuveniles (C. amphora: C/24.14 adults of Ctenus amphora and Ctenus crulsi during
” 94.50, P = 0.02 and C. crulsi: C/3719 = 143, a 15 minute period.
P < 0.001). However, the species differed
when we compared the activity offemales and
juveniles. Ctenus amphora females were sig- suit from differences in the species’ diets and
nificantly less active than juveniles (C/24.14 “ the resources available. It will be necessary to
267, P = 0.01), and C. crulsi female activity study diet and resource availability to deter-
did not differ from juvenile activity (C/3728 = mine whether these factors affect the activity
564.50, P = 0.48). of males, females and juveniles of these spe-
Our results support the hypothesis that cies, and why some females become less ac-
males become more active when they reach tive and others maintain the same level ofac-
maturity. However, at least for C. amphora, tivity as juveniles.
females activity does decline. The reason for We thank William Magnusson for sugges-
this, andforthe absence ofadecline in Ctenus tions that improved the manuscript. Financial
crulsi, is not clear, Gasnier (1996) found no support came from a fellowship grant from
evidence that these species differed in repro- CAPES (PET program) for the first author,
ductive cycle and apparently they reproduce and from CNPq (Project 400023/98) for field
continuously throughout the year, so males work.
probably seek females in all seasons. Extreme
sedentary behavior appears to be the foraging LITERATURE CITED
strategy adopted by adult females of this ge- Gasnier, TR. 1996. Ecologia comparada de quatro
nus. However, juveniles of these species have especies de aranhas errantes do genero Ctenus
different foraging strategies and this may re- (Walckenaer) (Araneae, Ctenidae) em uma flo-
278 THE JOURNAL OF ARACHNOLOGY
resta na Amazonia Central: Bases para um mo- Rovner, J.S. & EG. Barth. 1981. Vibratory com-
delo integrado de coexistencia. Dr. Thesis, munication through living plants by a tropical
CAPES/INPA/FUA, Manaus, Brasil. 77 pp. wandering spider. Science 214:464-466.
Gasnier, TR. & H. Hofer. 2001. Patterns of abun- Schmitt, A., M. Schuster& EG. Barth. 1990. Daily
dance of four species of wandering spiders locomotor activity patterns in three species of
(Ctenidae, Ctenus) in a forest in central Ama- Cupiennius (Araneae, Ctenidae): The males are
zonia. Journal of Arachnology 29:95-103. the wandering spiders. Journal of Arachnology
Hofer, H., A.D. Brescovit & T. Gasnier. 1994. The 18:249-255.
wandering spiders species of the genus Ctenus Uetz, G.W., J. Halaj & A.B. Cady. 1999. Guild
(Ctenidae, Araneae) of Reserva Ducke, a rain- structure of spiders in major crops. Journal of
forest reserve in central Amazonia. Andrias 13: Arachnology 27:270-280.
81-98.
Rice, W.R. 1989. Analysing tables of statistical Manuscript received 21 July 2000, revised 8 Jan-
tests. Evolution 43:223-225. uary 2001.