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El sexo, el tamao y el comportamiento de las araas lobo (Araneae, Lycosidea)
Sex, size and behavior in wolf spiders (Araneae, Lycosidea)
Lycosids, or Wolf spiders, are widespread in many habitats and are important predators on leaf litter arthropods. They are highly territorial yet roam to forage. When they encounter another wolf spider they may fight, flee or court them. To determine whether Wolf spider size or sex determined agonistic or courting behavior, thirty spiders were captured and placed in pairs of male-male, female-female, and male-female for a short period of time. Size was not found to be a determining factor. However, female-female
interactions elicited significantly more aggression than either male-female or male-male encounters. Additionally, avoidance was seen as the primary response of the spiders across all pairs. A close second was aggression. This study concluded that same sex spider pairs were more likely to avoid one another than fight and different sex pairs were either more likely to be aggressive or display courting behavior.
Los licsidos o araas lobo estn ampliamente distribuidas en muchos hbitats y son depredadores importantes de los artrpodos de mantillo. Son altamente territoriales, sin embargo, forrajean. Cuando se encuentran con otra araa lobo, pueden pelear, huir o cortejarla. Para saber si el tamao y el sexo de las araas lobo determinan si el comportamiento es agonstico o de cortejo; treinta araas fueron capturadas y colocadas en pares de macho-macho, hembra-hembra y macho-hembra por un periodo corto de tiempo. No se encontr que el tamao sea un factor determinante. Sin embargo, las interacciones de hembra-hembra provocaron de forma significativa ms agresin que en los encuentros de macho-hembra o de macho-macho. Adicionalmente, la evasin fue la primera respuesta entre las araas en todos los pares. Esto fue seguido por la agresin. Este estudio concluye que las parejas de araas del mismo sexo son ms propensas a evitarse que a agredirse y las parejas de araas de diferente sexos son ms propensas a ser tanto agresivas como a demostrar comportamientos de cortejo.
Text in English.
Monteverde Biological Station (Costa Rica)
Estacin Biolgica de Monteverde (Costa Rica)
Tropical Ecology Spring 2011
Ecologa Tropical Primavera 2011
t Monteverde Institute : Tropical Ecology
Sex, Size and Behavior in Wolf Spiders (Araneae, Lycosidea) Nina Kor o ma Department of Zoology, University of Wisconsin Madison ABSTRACT Lycosids, or Wolf spiders, are widespread in many habitats and are important predators on leaf litter arthropods. They are highly territorial yet roam to forage. When they encounter another wolf spider they may fight, flee or court them. To determine whether Wolf spider size or sex determined agonistic or courting behavior, thirty spiders were captured and placed in pairs of male male, female female, and male female for a short period of time. Size was not found to be a determining factor. However female female interactions elicited significant ly more aggression th an either male female or male male encounters Additionally avoidance was seen as the primary response of the spiders across all pairs. A close second was aggression. This study concluded that same sex spider pairs were more likely to av oid one another th a n fight and different sex pairs were either more likely to be aggressive or display courting behavior. RESUMEN Los licsidos o araas lobo estn ampliamente distribuidas en muchos habitats y son depredadores importantes de artrpodos de mantillo. Son altamente territoriales, sin embargo, forrajean. Cuando se encuentran con otra araa lobo, pueden pelear, huir o cortejarla. Para saber si el tamao y el sexo de las araas lobo determinan si el comportamiento es agonstico o de cortejo; treinta araas fue ron capturadas y colocadas en pares de macho macho, hembra hembra y macho hembra por un periodo corto de tiempo. No se encontr que el tamao sea un factor determinante. Sin embargo, interacciones hembra hembra provocaron de forma significativa ms agresi n que encuentros macho hembra o macho macho. Adicionalmente, la evasin fue la primera respuesta entre las araas en todos los pares. Esto fue seguido por la agresin. Este estudio concluye que las parejas de araas del mismo sexo son ms propensas a evita rse que agredirse y las parejas de araas de diferente sexo son ms propensas a ser tanto agresivas como a demostrar comportamientos de cortejo. INTRODUCTION As one of the main leaf litter predators for arthropods t he family Lycosidae is one of the largest spider families having almost 2200 species worldwide (Coddington and Levi 1991 ) Wolf spiders are characterized by their extremely large eyes and ground foraging habits As a result of their large eyes they have great vision and are not only good hunters but also effective at avoid ing predation. Like most spiders they are solitary highly territorial and can be found in a wide range of habitats ( Coddington and Levi 1991 ) Being active during the day and at night make them a great family to investigate behaviors ( Coddington and Levi 1991 ) Due to the fact that they are roamers they tend to have encounter s with other lycosids. The reactions to such encounters are to fight, flee or court. Different factors such as sex or si ze can influence wh ich behavior they respond with. T he behavior elicited
also depends on the situation and for most Lycosidea, conspecifics are more likely seen as their competitor as opposed to potential prey or predators, therefore they usually use communication rather than fighting ( Nossek and Rovner 1984). Regardless aggressive behavior involves risks; even to the attacker therefore avoidance is typical during interactions (Nos sek and Rovner 1984). Because spiders are venomous even to conspecifics their degree of threat to each other is fairly high. On the other hand when coming across a conspecific of the opposite sex males tend to display multiple courting behaviors that femal es either accept or reject by acting aggressively ( Jiao et al. 201 1) Wolf spiders tend to signal in multiple modalities (visual, seismic, chemical) to communicate during encounters Just like most animals Wolf Spiders use their senses and good eyesight to gage risk and act accordingly depending on the perceived risk (Lima & Dill 1990) Though behavior s differ between species (Gordon and Uetz 201 1 ) previous studies have found avoidance is the most common behavior displayed in wolf spiders However some spiders do act aggressively but it is more common for the lycosid adult females to eat adult male or female conspecifics, but this rarely occurs with adult males observed under similar conditions (Nossek and Rovner 1984). Antagonistic behavior in wolf spiders typically includes withdrawal as well as threat and attack (Nossek and Rovner 1984). Such behaviors in similar studies have observed and described the m as le g waving displays or v ibrations ( Nossek and Rovner 1984) Although visual communication and avoidance are primary responses in wolf spiders, killing does occur occasionally but this is typically an act of hunger and the kill is generally followed by cannibalism (No ssek and Rovner 1984) In addition to antagonistic behavior courting behavior is seen. Some studies have found that upon contact with females, males engage in intense courtship consisting of two distinct behaviors, body shaking and foreleg raising (Jiao et al. 201 1 ). F emale wolf spiders also show greater receptivity to males that court more vigorously since it reflects the condition ( Gordon and Uetz 201 1 ) However courtship behavior is still very unknown in the whole Lycosidea family and though some specific behavior patterns have been noticed a lot is still uncertain with the factors that influence a choice. Although the Lycosidae family is fairly s tudied more can be learned about their conspecific interactions and what factors influence their actions A lot of studies have focused on same sex interactions but there are still many inconsistencies. Additionally there are almost no studies that have d etailed findings on mating and courtship behaviors. Given these uncertainties b y placing individuals of a given species in male : male female : female and male : female pairs I will be able to observe the frequency of different reactions as well as the specific behaviors associated with each Further, I can add to our understanding of how size and sex impact intra species interactions within the Lycosidae family. METHODS Spiders were collected in a field next to the Monteverde Butterfly garden at 1400 meters in elevation Trials were conducted indoors at the Estaci n Biol gica de Monteverde Monteverde, Puntarenas, Costa Rica at 1550 meters The spiders were housed in small, 15X15X5cm plastic containers and protected from direct sun by blanket placed over nearby windows. Thirty four spiders were captured and housed in this way.
Spiders were fed crickets or houseflies t o control for hunger ; spiders were fed at least a couple hours before trials. Water was provided as a wet cotton ball. In order to observe their behavior s, spiders were placed in a 24x12x9.5cm clear, square plastic container with no top. Before placing pairs together spiders were weighed T he spiders were also sexed ( males have swollen p edi pa lps ; Nossek and Rovner 1984) The small est spiders those smaller than .10 g ra ms, were categorized as juveniles and not used. In all, there were 30 adult spiders for use d in trials T rials All trial s were done between the afternoon and 5pm. Both spiders were placed into a plastic container Once one spider was placed into the container an index card was put to keep them separated until the other spider was fully in container. When they both were in the container the index card was removed; the timer began and ran for five minutes. Behavior was put into three categories: aggressive avoidant and ignore These were based off of the outcome of the interaction, with special attention to specific behaviors that might characterize them The onl y time the c l ock was stopped before the five minute is if a fight occurred and one was trying to eat the other. If this occurred, I would try to separate them either by shaking the container or using tweezers. This was in order to make sure all of my spide rs survived. Once a trial was complete d both spiders were placed into separate containers. The same procedure was done for all trials For the male: female trials courtship was added to the o bserved behavio r categories. A total of 81 trials were done in total, 27 trials each for the different sex interactions. RESULTS Based off of the different types of behavior observed w hen the spiders were in pairs categorize were developed and behavior s associated with each one. Aggressive behavior 1. Leg lifts one of the spiders would raise one or both of their front two legs 2. Chasing a spider would charge the other or run after it 3. Attacking the spiders would collide and have their legs connected Avoidance Behavior 1. Running away one of the spiders would run in the opposite direction of the other 2. R unning over the other s ometimes in order to get to the opposite side a spider would run over the top of the other spider 3. Staying away from the other being in a different area than the other spider at all times Ignore 1. Focusing more on escape the spiders would just try to climb the sides of the container and not pay attention to the other 2. Showing no signs of hostility when both would be near each other yet not aggressive behavior was displayed
3. Not avoiding but no interest in the other both spiders would be close but one would just go about whatever they were doing, one example of t his was when one spider began eating a maggot Courting 1. Slow approach seen in the males where they would flatten their body then slowly inch towards the female 2. Long leg extension occurred once the male was by the female where he would slowly extend one o f his legs and place it on her and wait for her reaction. Sometime if he got no reaction he would move the leg further up her leg until she reacted. 3. Vibrations seen in females where they would vibrate their abdomen and walk towards the male. Trials The number of times that each behavior occurred ( aggression, avoidance, and ignoring) did not differ for male: male interaction s ( Figure 1 a ; C hi square = 3.32, df = 2 p>0.05 ) Avoidance (18) and aggression ( 17) we re fairly common havin g similar observed behavior for the male spiders. Both of these behaviors were seen about twice as much as ignoring ( 7). For female: female intra specific interactions reactions differed significantly ( Figure 1b; C hi square= 8.75, df=2, p<0.05) Avoidan ce in females was most frequent ( n = 20). They were four times more likely to avo id then ignore one another. Aggression was also common in females ( n = 15). Male: female interactions ( figure 1 c ) had no significant difference ( C hi square= 4.09, df= 3, p> 0.05) between the four different observed behaviors observed: avoidance, aggressive, ignoring, and courting
FIGURE 1. Outcome of lycosid intraspecific interactions when there were two males, two females or a male and female. Each interaction had just one outcome: aggression, avoidance, and ignoring There was no significan t difference between outcomes with male : male pairs (n=27 ; C hi square= 3.32, df= 2, p>0.05). Male : female intraspecific interactions differed significantly behaviorally ( C hi square= 8.75, df=2, p<0.05) Male : female intra specific interactions had no significant difference ( C hi square= 4.09, df= 3, p>0.05) For both male: male interactions and female: female interactions avoidance was observed the most. Male: female intera c tio ns courting and aggression were obse r ved the same amount. (Chi square= 4.09, df= 3, p>0.05). Courting (n=16) and aggression (n=16) were the most abundant behaviors that occurred. In male intraspecific interactions spider size had no significant effect on whether a spider avoided or not ( Figure 2, C hi square=3.95, df=2, p>0.05). Despite this, s maller spiders ( n = 21 trials ) tended to avoid large spiders, while the larger spiders ( n= 10 trials ) were less likely to avoid small ones Size also had no signif icant affect on aggressive behavior of ma l e spiders ( C hi square= 1.26, df=2, p>0.05). However when the spiders n = 2 trials ). (figure 2) the other spider ( C hi square=3.48, df=2, p>0.05) FIGURE 2. Result of when male pairs of the same size or different sizes were placed together. M ale inter specific interactions size (n=27) had no significant influence in whether a spider was avoidant or not ( C hi square=3.95, df=2, p>0.05). Size also had no significant affect on aggressive behavior of male spiders ( C hi square= 1.26, df=2, p>0.05). S ize had no significant influence on ignoring either ( C hi square=3.48, df=2, p>0.05).
Though larger males (10) were twice as likely to ignore the smaller (5) males than the smaller spiders A f effect on determining whether a female would avoid ( C hi squared=1.91, df=2, p>0.05) be aggressive ( C hi square=1.45, df 2, p>0.05), or ignore ( C hi squared= 67 df=2, p>0.05) the other female (Figure 3) Larger female were most often more aggressive ( 11) and smalle r females avoided ( 14) the larger females more. FIGURE 3. The outcome of when female pairs of different and same sizes were placed together. Female (n=27) had no significant differences on determining whether a female would be avo idant ( C hi squared=1.91, df=2, p>0.05), aggressive ( C hi square=1.45, df 2, p>0.05), or ignore ( C hi squared= 67 df=2, p>0.05)
In male female interactions size had no significant impact one the frequency of avoidan ce ( C hi square= 3.01, df=3, p>0.05 ), a ggressi on ( C hi square= 2.02, df=3, p>0.05 ), ignor ing ( C hi square = 3.67, df=3, p>0.05 ), or court ship ( C hi square = .05, df=3, p>0.05 ) see F igure 4 Still, smaller individuals tended to avoid, larger tended to be aggressive and few ignored. Courtship was seen about equally for large and small spiders FIGURE 4. When male and female pairs of the same and different sizes were placed together (n=27) size had no significant different in whether one was avoidant ( chi square=3.01, df=3, p>0.05), a ggressive ( C hi square=2.02, df=3, p>0.05), ignored ( C hi square=3.67, df=3, p>0.05), or courted ( C hi square= .05, df=3, p>0.05). When [ same sex and o pposite sex interactions (figure 5) were taken into account the occurrence of each behavior was significantly different from one another ( C hi square= 14.32, df=2, p<0.05) Ignoring and aggressive behavior were fairly similar the avoidance was the most common ( n= 52) more than twice as likely to occur then a one ignoring the other ( 21).
FIGURE 5. When the interaction s were observed over all pairs strictly looking only a behavior displayed, The spiders choice in which behavior presented was significa nt ( C hi square= 14.32, df=2, p<0.05) Avoidance was the behavior seen the most (n=52) and aggression was a close second (n= 48). Ignoring was seen half as much as the other behaviors (n=21). ADDITIONAL OBSERVATION Though most of the spiders displayed normal behavior two of the females were extremely aggressive and when they were put into a container with another spider they would try to kill it. They ate two spiders in preliminary trials Additionally some of the sp iders acquired parasites from flies that were in the container and it caused the death of two male spiders Both of these influenced the trials because they made the sample size smaller and the two females were only used once more until it was apparent tha t they were extremely aggressive. DISCUSSION Overall, spiders tended to avoid each other or were aggressive. Few spiders ignored the other spider. For male: male interactions, individuals were equally likely to avoid or act aggressively, which is also the case for males and female encounters, although these also included about an equal frequency of courtship. Female s generally avoided other females, though there were still many aggressive encounters Although size had no significance in determining which behavior was displayed the general trend was
that smaller spiders were more likely to avoid and larger spiders were more likely to be aggressive. Size is typically a reflection of fitness and health. Despite the fact that all the spiders were given the same conditions larger spiders were more fit and more likely to be stronger therefore they were able to establish their dominance over the smaller spiders in most cases. For male: female interactions aggression and courting behavior were equally as likely to be seen. This could be because reproduction is a choice and females tend to cho o se male s that try hard showing off their fitness. T hough most of the males di s played a c ourting behavior none of the females showed any interest instead they would respond aggressively. That is why both behaviors were seen equally as much. A voidance was the behavior that was seen the most. This is most like due to the fact that it is the safest way to survive an encounter However aggression was a close second Aggression is unlikely to result from hunger because spiders were fed regularly and shortly before trials. Also, s piders are well adapted to long periods of food deprivation (And erson 1974). After observing the spider for long periods of time what became apparent was that dominance and submissiveness was usually established fairly quick and though it not necessarily always had to due with size, larger individuals were usually the dominant one. To establish this order one spider was usually aggressive until the other backed off or fought back and lost. However most encounters were usually short lived and the spiders typically after establishing rank avoided one an other. This was see n in almost all the male: male interaction and female: female interactions. All these behavior seen are consistent with previous studi e s and just further proof that spiders similar to most animals, like to gauge their risk and proceed with caution. Although most did end up acting aggressively this just goes along with their territorial nature. Despite this most of the spiders still tried to survive and the best way for them to do that was to avoid potential threa ts. My study brought a little more insight in intraspecific interactions but a lot more could be found out. Courting behavior though little was observed in my study, would be an interesting topic to research more ; specifically the factors that determine w hether a spider will mate or not. Furthermore for wolf spiders in intraspecific interactions though they were territorial and displayed a lot of aggression, avoidance was their typical response to one another and size was no real contributor AKNOWLED GMENTS I would like to thank Danis and Licho for helping me with emotional support, Alan Masters for helpi ng advise me and for not giving up on me Timothy Curry for helping me hand le the spiders When I needed extra help Cody Will for helping me catch spiders, Jose Carlos Calderon for helping me with my statistics, and Gisela Fernandez always being willing to answer my questions.
LITERATURE CITED Coddington J. and Levi W.1991. Systematics and Evolution of Spiders (Araneae) Annual Review of Ecolo gy and Systematics. 22: 565 592 Gordon, S. D. and Uetz, G.W. 2011. Multidudinal Communication of Wolf Spiders on different Substrates Evidence for Behavior Plasticity. Animal Behaviour. 81: 367 375 Habets E., Stratton, Gail. Miller Garry. 1996. Habitat and Courtship Behavior of the Wolf Spider Schizocosa Retrorsa (Araneae, Lycosidae) The Journal of Arachnology 24: 141 147 Jiao. X. Chen Z., Wu, J., Du, F., Chen, J. and Li, D. 201 1 Male Remating and Female Fitness in the Wolf Spider Pard osa astrigera : the Role of Male Mating History. Behavior Ecology Social Biology 65: 325 332. Lima, S. L. and Dill, L. M. 1990. Behavioral decisions made under the risk of predation: a review and prospectus. Canadian Journal of Zoology 68 : 619 640. Nossek, M. E. and Rovner, J. S. 1984. Agonistic Behavior in Female Wolf Spiders (Araneae, Lycosidae) Journal of Arachnol. 11: 407 422. Persons, M.H, Walker, S.E., Rypstrat, A.L., and Marshall, S.D. 2001. Wolf Spider Predator Avoidance Tactics and Su rvival in the Presence of Diet associated Predator Cues (Araneae: Lycosidae). Animal Behaviour.61: 43 51.