Sexual behaviour in Loxosceles gaucho Gertsch (Araneae, Sicariidae)

5 Pages·1998·0.63 MB·English

by  Rinaldi, I M P

Bull.Br.arachnol.Soc.(1998)11(2),57–61 57
Sexual behaviour in Loxosceles gaucho Gertsch Thespiderlingswerefed,firstwithDrosophilasp.,and
(Araneae, Sicariidae) then Musca domestica, Gryllus sp. and other insects
collected by sweeping.
Isabela M. P. Rinaldi and André A. Stropa Random pairs of adult females and males of L.
InstitutodeBiociênciasdaUniversidadeEstadualPaulista, gaucho, from different mothers, were used in trials. In
DepartamentodeZoologia,UNESP/Botucatu, each case, the male was placed on the female’s web,
18618-000RubiãoJunior,Botucatu,SP,Brazil always keeping a certain distance from her. Two
experiments were developed: (1) 28 trials, by placing
the male on the female’s web, and recording 41 copu-
Summary
lationsoncassettetapes.Thebehavioursweregrouped
Sexualbehaviourinthebrownspider,Loxoscelesgaucho, and quantified by analysing the playback of each
is described by a flow diagram on the basis of laboratory copulation and transforming them into percentages
observationsof28monogamouscouplesperformingatotal
(Fig.5).Thisallowedustoassessthereceptivityofthe
of 41 copulations. In courtship, both males and females
pairs for copulation, since they were left to mate until
showedforelegvibration,palpaldrummingandabdominal
pulsation,inaccordancewiththegeneralpatterninhaplo- receptiveness ceased. (2) To quantify the time spent in
gynespiders.However,theyusedthewebinthecopulatory each sexual behaviour phase and analyse their more
processandhadasimilarmatingposturetothatshownby conspicuous behaviours, we used a VHS video re-
someotherweb-spinningspiders.Thesexualbehavioursof
corder during 19 copulations carried out by 19 virgin
another 19 virgin pairs in 19 copulations were quantified,
pairs, different from those used in the first test. Males
andshowedthatthefemaleswereasactiveasthemales.The
frequenciesofthesebehavioursincourtshipandprecopula- and females were separated just after the first copula-
tion were estimated, revealing a remarkable increase in tion.Toquantifythesexualphases,itwasnecessaryto
sexualbehavioursduringprecopulation.Thesexualbehav- define the limits of each phase. Courtship was defined
iourinL.gauchofollowsthesamegeneralpatternasthat
as beginning when the male emitted its first sexual
describedforLoxosceleslaetaandL.reclusa,butwithsome
differences in both courtship and copulation, suggesting signal, e.g. palpal drumming or foreleg vibration. The
thatreproductiveisolationinthesespeciesdependsonthe end of courtship and start of precopulation was when
vibratory pattern of palpal drumming and abdominal the male palps became hidden under the female’s
pulsation. cephalothorax.Similarly,thestartofthemale’spalpal
insertion into the female’s genital pores was set as the
limit between the precopulation and copulation
Introduction
phases. Palpal drumming could not be recorded in the
Little is known about the biology, ecology and precopulation phase.
behaviour of Loxosceles spp. The spiders of this genus In order to compare behavioural patterns between
constitute an important group in veterinary and human males and females and between both phases (courtship
medicine, therefore the study of their reproductive and precopulation) we used the t-test for dependent
behaviour contributes to the understanding of the samples on the square roots of data.
factors that may influence their population growth.
Comparison with other species is relevant to discover
the behaviour mechanisms which are general to all the
Results
group. Galiano (1967) described courtship and mating
behaviour for L. laeta (Nicolet) using five phases: Preliminary observations indicated that both male
precourtship, courtship, precopulation, copulation and and female L. gaucho perform three main sexual behav-
postcopulation. iours: foreleg vibration (Fig. 1), palpal drumming (Fig.
Despite being abundant in south-eastern Brazil, L. 2)andabdominalpulsation(Fig.3).Forelegvibrationis
gauchoGertschisoneoftheleaststudiedspecies.Itcan the simultaneous vertical movement of the forelegs,
be found in house yards, being sedentary in irregular whose tarsi touch the female’s web. Rhythmical vi-
webs which cover the substrate like a sheet (Gertsch, bration of the male’s forelegs is very impulsive, while in
1967). the female it is more constant and slower. In palpal
In the current study, the frequency of the sexual drumming, the spiders move their palpi alternately and
behaviours of pairs of L. gaucho was recorded and vertically, this being most frequent in males and rare in
described in a flow diagram, and its sexual behaviour females. The abdominal pulsation is a quick vertical
iscomparedwiththatofL.laetaandL.reclusaGertsch and horizontal abdominal movement in the male,
& Mulaik, according to the data available in the whereas in females it is a slower vertical movement.
literature. In the copulation, the L. gaucho male, in a single
quick striking movement, lifts the female upside-down
in relation to the substrate while the palps are inserted
Methods
(Fig. 4).
Pairs of L. gaucho were reared individually in the Duringcourtship,themales,whentheyfirstcontacted
laboratory from the moment of hatching onwards. The the female’s web, always vibrated their forelegs (Fig. 5).
spiderswerekeptindiettubesuntiltheirsubadultphase On dense webs, the males often cut some of the threads
(4th instar), and then transferred to acrylic boxes with their chelicerae while they approached the females.
(17(cid:1)8(cid:1)7cm). The females, which were beside or behind the males,
58 SexualbehaviourinLoxoscelesgaucho
movedslowlyintoaface-to-facepositioninresponseto spiders that mated successfully had an average of
the male’s foreleg vibration. For palpal drumming, the 2.41(cid:3)1.42 copulations per couple.
malesverticallytwistedtheirleftpalpsclockwiseandthe The sequence and frequency of the sexual behaviours
rightpalpsintheoppositedirection,makinga90(cid:2)angle performed in 41 copulations by the 17 receptive pairs,
in relation to the substrate. In the precopulation phase, and by the other 11 non-receptive pairs, are shown in
when the males advanced under the female’s cephalo- Fig. 5. The observed frequency of their behaviours is
thorax, their palps gradually came to rest (horizontal, represented by the thickness of the arrows. The palpal
parallel to the substrate). In the copulation, at the drumming of females did not reach the minimum
momentofpalpalinsertion,themalestwistedtheirpalps frequency needed to include it in Fig. 5.
in an inverse direction from the courtship, reaching an
angle of 180(cid:2).
Duration of the sexual behaviour phases
Inthecopulation,L.gauchobehavesliketheprimitive
spiders: the male faces towards the female, the female In the total period of courtship and mating, 19 pairs
lifts her own cephalothorax and the male inserts his spent an average of 17.35(cid:3)8.35min. The courtship
palps into the female’s gonopores. However, the male phase lasted for 9.85(cid:3)6.38min, the precopulation
occupies a parallel position, like other web-spinners phase occupied 5.02(cid:3)3.02min, and the copulation
(Fig. 4). During the male’s strike, the weight of the phase 2.48(cid:3)2.55min.
femaleandthemaleissupportedonlybythemale’s4th
legs and abdomen (Fig. 4). The male’s striking move-
Total numbers of sexual behaviours in males and females
ment was always quick, followed by palpal insertion.
Therewasnoinsertionwithoutthestrike.Sometimesthe There was a significant difference between the sexes
femalesappearednon-receptive(Fig.5),i.e.theyresisted concerning their total numbers of sexual behaviours
the male’s stroking. During courtship, the females (Table 2). During courtship, the total number of palpal
stretched their legs sideways (Fig. 5), ceasing their body drummings was higher in males than in females.
movements. On the other hand, foreleg vibration and abdominal
pulsation occurred more frequently in females than in
males during both courtship and precopulation (Table
Receptivity of the pairs for mating
2). Without taking into consideration the duration of
In 28 trials with 28 males and 28 females, 17 pairs each phase, for both sexes, the number of foreleg
(60.7%) copulated at least once, while 11 pairs (39.3%) and abdominal movements was slightly higher in the
did not perform any copulation. Table 1 shows the courtship than in the precopulation phase, but not
distributionofnumbersofcopulationsbythepairs.The significantly different (Table 2).
Figs.1–4: SexualbehaviourofL.gaucho.1Forelegvibration(simultaneousverticalmovementofthepairsoflegswhosetarsitouchthefemale’s
web); 2 Male palpal drumming (alternate vertical palp movements); 3 Abdominal pulsation (vertical and horizontal abdomen
movements);4Pairinmatingposition(maleshaded).
IsabelaM.P.Rinaldi&A.A.Stropa 59
Fig.5. FlowdiagramofsexualbehaviourinL.gauchobasedon41copulationsby17pairsandon11otherpairswhichdidnotcopulate.Arrows
a,bandcindicatefrequencybetween8.3–35.3%,35.4–43.8%,and93.8–100%.Dashedlinesdelimitsexualbehaviour.
60 SexualbehaviourinLoxoscelesgaucho
Copulations Number Palpaldrummingwasmorefrequentinmales,butthis
percouple ofcouples maysimplybebecausemalesarebetterequippedforthis
1 4
behaviour.Theforelegvibration,palpaldrumming,and
2 8
abdominalpulsationshownbythemaleweresequential,
3 2
never simultaneous, and usually led to the female’s
4 1
5 1 response and, finally, copulation. However, these three
6 1 behaviours are not all essential for a successful copu-
Total 41 17 lation, suggesting that they may occur according to the
degree of acceptance by the female. With less receptive
Table 1: Distribution of numbers of copulations by pairs of L. females, the males may have to use all three. Horner &
gaucho. Stewart (1967) described in L. reclusa two of the same
behavioursthatweobservedinL.gaucho,i.e.‘‘rhythmic
pulsation of the male’s or female’s abdomen’’ and
‘‘intermittent palpal vibration’’ which was more
Frequency of male and female sexual behaviours in each
intensive in males than females.
phase
When the available data for L. laeta, according to
Theaveragefrequencyofforelegvibrationwassignifi- Galiano (1967), are compared with L. gaucho, both
cantly higher in the precopulation phase than during follow the same general pattern, differing specifically
courtship, in both males and females (Fig. 6). For the in the courtship phase, the receptive L. gaucho
females, t=(cid:4)2.02 (p<0.059) and for males, t=(cid:4)5.48; males being provoked into courtship by the web of
(p<0.0001). the female and not only by direct contact between the
In females, the average frequency of abdominal pairs as in L. laeta (Platnick, 1971). In the copulation
pulsation was significantly higher in precopulation than of L. laeta and L. reclusa, the single, quick strike
during courtship (t=(cid:4)3.22; p<0.001), but in males was not observed. We agree with Starr (1988), who
there was no significant difference in frequency between interpreted that the stroking serves to overcome the
courtship and precopulation (t=(cid:4)1.08; p<0.30) female’s resistance and is therefore another good
(Fig. 7). indication of mate choice. In the copulation, the
performance of L. gaucho differed from that of L.
reclusa, where the female was tilted backwards by a
thrust, until the tip of her abdomen touched the floor
Discussion (Horner & Stewart, 1967).
Sperm transference, in all these species, involves the
In two of the three sexual behaviours studied, the simultaneousinsertionofbothpalps,asdescribedinthe
females exceeded the males in number and frequency of haplogynes by Foelix (1982). The act of stretching their
foreleg vibration and abdominal pulsation, indicating legssideways,whileceasingbodymovements,asseenin
her active participation in mating. The cautious move- L. gaucho females, has also been observed in other
ments of the male towards the female and his frequent haplogynes, as in Pholcus phalangioides (Fuesslin) by
retreats (running, jumping) showed a tension, which is Uhl et al. (1995).
probablyrelatedtoself-protection.However,aggressive In L. laeta, palpal insertion is very quick, taking not
acts by the females occurred infrequently and the pairs morethanacoupleofseconds,whereasinL.gauchoitis
tendedtobetolerant,remainingclosetoeachothereven much more variable, from a couple of seconds up to 11
when not in copulation. Only in a minority of trials did minutes. The number of copulations may reach four in
the female attack the male. Our interpretation of the L. laeta and up to six in L. gaucho.
results agrees with several studies (e.g. Jackson, 1979; The frequency of foreleg vibration increased in pre-
Robinson&Robinson,1980;Starr,1988)whichsupport copulation in both males and females (Fig. 6). The
the view that courtship is mainly a matter of female frequency of abdominal pulsation, which increased in
choice rather than derived from a need to inhibit precopulationinfemales(Fig.7),maysignifythatother
predation. non-sexual behaviours were inhibited. Maybe the
Behaviour Matingphases
Courtship Precopulation
(cid:5) (cid:6) t (cid:5) (cid:6) t
Palpaldrumming 6.07 1.80 6.18 – – –
(cid:3)0.60 (cid:3)0.36 p<0.0001 – – –
Forelegvibration 8.00 11.17 (cid:4)3.28 7.20 9.38 (cid:4)2.58
(cid:3)0.64 (cid:3)1.16 p<0.005 (cid:3)0.35 (cid:3)0.96 p<0.019
Abdominalpulsation 3.99 9.09 (cid:4)5.94 2.58 8.85 (cid:4)6.86
(cid:3)0.58 (cid:3)0.79 p<0.0001 (cid:3)0.25 (cid:3)0.83 p<0.0001
Table 2: Total numbers of sexual behaviours performed by males and females of L. gaucho during courtship and
precopulation(means(cid:3)SDandt-tests).
IsabelaM.P.Rinaldi&A.A.Stropa 61
male is allowed to explore the web, his first act is to
communicatehispresencebyvibratinghislegs,thesame
probably occurring in natural conditions. As both
species followed the same general behaviour pattern in
courtship and copulation, we suspect that the mech-
anisms of reproductive isolation between them depend
onthevariationsinpalpaland/orabdomenmovements,
i.e. intensity, frequency, and duration.
Acknowledgements
WeshouldliketothankNedyA.S.AndrésandPedro
R. Evangelista for field and laboratory assistance,
Dra Luzia Aparecida Trinca for statistical assistance,
Dr Gilson Luiz Volpato for his valuable suggestions,
and José Mario Pisani for the illustrations. This study
was supported by a fellowship to A. A. S. from the
Fundação de Amparo à Pesquisa do Estado de São
Paulo (FAPESP No. 96/09389-0).
References
FOELIX,R.F.1982:Biologyofspiders.1-306.Cambridge,Harvard
UniversityPress.
GALIANO, M. E. 1967: Ciclo biológico y desarrollo de Loxosceles
laeta(Nicolet,1849)(Araneae,Scytodidae).Actazool.lilloana
23:431–464.
GERTSCH, W. J. 1967: The spider genus Loxosceles in South
America(Araneae,Scytodidae).Bull.Am.Mus.nat.Hist.136
(3):117–174.
HORNER, N. V. & STEWART, K. W. 1967: Life history of the
Figs. 6–7: Average frequency (acts per second) of female and male
brownspider,LoxoscelesreclusaGertschandMulaik.Tex.J.
sexual behaviours during the courtship and precopulation Sci.19(4):333–347.
phases in L. gaucho. 6 Foreleg vibration; 7 Abdominal
JACKSON,R.R.1979:ComparativestudiesofDictynaandMallos
pulsation.
(Araneae,Dictynidae).II.Therelationshipbetweencourtship,
mating, aggression and cannibalism in species with differing
typesofsocialorganization.Revuearachnol.2:103–132.
increase in these behaviours is related to the vulner-
PLATNICK, N. I. 1971: The evolution of courtship behaviour in
abilityofthepairsintheprecopulationphase,sincethey
spiders.Bull.Br.arachnol.Soc.2(3):40–47.
are so close together, prompting their self-protection.
ROBINSON,M.H.&ROBINSON,B.1980:Comparativestudiesof
The slight reduction in the male’s abdominal pulsation thecourtshipandmatingbehavioroftropicalaraneidspiders.
during precopulation (Fig. 7) may be related to the Pacif.InsectsMonogr.36:1–218.
positionofhisbody,incontactwiththesubstrate,while STARR,C.K.1988:SexualbehaviorinDictynavolucripes(Araneae,
Dictynidae).J.Arachnol.16:321–330.
under the female.
These differences between the species may have been UHL, G., HUBER, B. A. & ROSE, W. 1995: Male pedipalp mor-
phology and copulatory mechanism in Pholcus phalangioides
partly influenced by the manner in which the pairs were
(Fuesslin,1775)(Araneae,Pholcidae).Bull.Br.arachnol.Soc.
introduced in the experiments. Obviously, when the 10(1):1–9.