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Senin, 26 Januari 2009

The Defense Methods of Spiders

In the world, there is one type of creature that most people are afraid of, Spiders. Ever since I was younger, I have always enjoyed keeping and watching spiders. If more people would study spiders, they would find out there is lots about spiders that is very interesting. There are species of spiders that are prey - specific prey - catching. The types of species are known as araneophagic salticids. Another thing about spiders that people don't realize is that spider have defense maginisms to protect them from predators, such as, flicking their hairs off their abdomen. Reproduction for spiders can be very dangerous and challenging for the male. When males are ready to mate, they have to be careful so that they don't either get cannibalized or chased either by the female or another male.
Spiders have prey preference
All spiders are predators and have prey - catching behaviors which are different. In spiders, there are two different types of predators. One is the stenophagous and the other is euryphagous. The stenophagous predators behavior may or may not be specialized being prey - specific prey - catching. The euryphagous predators behavior is not as specialized as what their diet is. This type of predator may be specialized in prey - catching but not specialized in their diet. There is two types of jumping spiders which have stenophagous behavior, one is ant - eating species and the other is spider - eating species. Both have certain ways they catch their prey. When the ant - eating species catch their prey they must be careful so that they don't get killed in the process. An ant is an insect which most species of spiders will not choose for prey. The spider - eating species uses the web of the prey to catch their prey. First thing for them to do is to get on the web without making the web move, instead of walking across the whole web to catch the prey they stay in one place and jiggle the web so the prey thinks it is prey for them. The species of spiders that use their prey's web to catch them are known as araneophagic salticids which are Brettus adonis, Brettus cingulatus, and Gelotia lanka from Sri Lanka; Cyrba algerina from Southern Europe; Cyrba ocellata from Australia, Kenya, Sri Lanka, and thailand; and five species of Portia which are P. africana and P. schultzi from Kenya, P. albimana from Sri Lanka, P. labiata from Malaysia and Sri Lanka and P. fimbriata from Australia, Malaysia, and Sri Lanka. These types of spiders also catches prey which are outside of the webs, then invades another spiders web which it uses aggressive mimicry and catches the resident spider and takes insects and resident spider eggs also.

One species of spiders uses a cryptic stalking motion to catch the salticids. This spider is in Queensland, Australia known as Portia fimbriata. When P. fimbriata moves in a web, it moves very slowly and when detected it is too late for the salticid to escape. Salticids have secondary eyes which are good movement detectors and if it sees the P. fimbriata it moves around a lot to figure out what is behind it. If this happens, the P. fimbriata totally stands still until the salticid turns away again. P. fimbriata may have to be concerned with the size and type of prey to eat because a salticid which is large maybe able to either injure or kill the P. fimbriata. The size of the meal is more important to females then males. Females are normally bigger then males and have a greater need for large food and are more ready to take a risk getting their prey.
There were tests done on the feeding habits of the P. fimbriata. In the tests, the female P. fimbriata ate web building spiders and salticids more often then eating insects, but they preferred to eat salticids over web building spiders. There was a test done to see if the P. fimbriata female would take a web building spider over an insect. Most of them would drop the insect and take the web building spider. Another test done was to find if the P. fimbriata female would take an insect over an salticid. The P. fimbriata female would drop the insect for the salticid. Another test done was with size of prey they would eat. Sizes were very small, small, and large web building and salticids. The P. fimbriata females ate small species more often then very small species. Also they ate large species more often then small species. With males they resembled females by attacking spiders first more often then attacking insects. With both male and female P. fimbriata, they ate salticids more often then web building spiders. Males ate small spiders more often then very small spiders like female, but males are different in eating small spiders more often then large spiders. In all tests done with insects, the P. fimbriata also took spiders over insects. Portia is a genus of salticids which studied in nature feed mostly on web building spiders. The behavior of Portia salticids are prey - specific prey - catching against web building spiders. These types of predators have an unusual diet and evolved prey - specific prey - catching behavior for certain types of prey. Species of spiders that eat prey which can be dangerous to them have prey - specific prey - catching behavior and have distinctive preferences for unusual and dangerous prey. Studying males in nature, they often feed on the same types of web building spiders as females do and also use same behaviors as females, prey - specific prey - catching. Both male and female P. fimbriata prefer web building spiders over insects but often prey on cursorial salticids. They both use cryptic stalking to catch the cursorial salticids. When catching prey, females are more effective then males. When P. fimbriata catches prey it first touches the prey with its forelegs, and slowly moves over the prey and bites it. Most all species of Portia studied seldom leaps on any kind of prey.
Defense Behaviors
There are species of spiders that use their urticating hair on their dorsum of the abdomens for defense. When they use hair for defense, they release their hairs by using their hind legs. Then they rub their abdomen with their hind legs and the hairs fly off their abdomen and hit what they are protecting them selves from. The main species of spiders that use this defense are the Mygalomorph. These hairs are found in different places on different spiders. The hairs on the genus Ephebopus are found on a distinctive pad on the distal prolateral surface of the pedipalpal femur. One genus of Mygalomorph which has hairs on the abdomen has never been recorded with hair flicking, this is the genus Aviculariinae. According to the Bertani and Marques 1995/1996 article, the mechanism which releases the hairs are still not known very well. Aviculariinae have five species which they insert urticating hairs by direct contact with the predator, reported by Bertani and Marques. There were tests done on certain spiders, these were Avicularia avicularia, Avicularia walckenaeri, Avicularia sp., Pachistopelma rufonigrum, Theraphosinae, Acanthoscurria atrox, Vitalius sorocabae, Lasiodora klugi, Grammostola actaeon, and Theraphosa blondi. These species were studied in the Laboratorio de Artropodos of the Instituto Butantan, Sao Paulo. To test this defense behavior in the laboratory, they were touched with forceps or tip of a finger which caused them to respond. All tests were recorded to study the defense method in greater detail. The main species that showed the hair flicking defense was the Theraphosinae spiders. To flick their hairs, they lifted either one or both hind legs on the dorsum of the abdomen and kicked the hair off them. With the Aviculariinae species, they have well developed claw tufts at ends of legs to help them hold on to the object and directed their abdomen toward the object. The Aviculariinae turned its abdomen toward the object and rubbed it against the object. After hairs hit the skin, they penetrate into the skin slowly and embeds completely after one to two days. This species would only use the rubbing method for defense if they were in their silk webs but if out of the web, they would take a flight and run across the cage floor or climb the walls. Theraphosicae have many spines on their legs which help to comb the hairs to flick them off the abdomen. Theraphosicae are the only group that can flick and shed their hairs. Many hairs still remain attached while others are combed off the abdomen. The Aviculariinae do not have spines on their legs like the Theraphosidae, but a few have apical spines. There is a difference in size and types of hairs between Theraphosidae and Aviculariinae. The Theraphosidae have type I, type III, and type IV. Type I hairs are 0.2 to 0.6 mm in length, type III hairs are 0.3 to 1.2 mm in length , and type IV hairs are 0.06 to 0.2 mm in length. Most of the hair are thin, short, and flow by air. Aviculariinae spiders have two types of hair, type II and type V. Type II are only found in the abdomen of the genera Avicularia, Pachistopelma, and Iridopelma. Type II are 0.5 mm in length which are longer than the other hairs. They are also stout and have many small, scale-like barbs. When this type are scraped off the spider, they do not get carried by air but fall to the ground instead. The penetrating tip of the hair in type II are directed downwards which in type I, type III, and type IV are directed upward. The type II hairs are only released when the abdomen of the spider is touched and the penetrating tip rises up to come in contact with the object that touched it. The next type of hair are type V which are short and stout, with many barbs and are easily blown thru the air. The types of hair have different structures and release in different ways. These urticating hairs are the same size as cactus thorns and when they touch the skin, you can't see them but sure can fill them.
Reproduction in Spiders
Female spiders can have multiple mating. Males have to be concerned about this because they have to make sure that their sperm fertilizes the eggs and not by another male. To prevent this from happening, the male has to ejaculate lots of sperm and prevent the female from attracting other males. To stop the female from attracting other males, males can physically repell them by placing obstructions over her genital opening, or by transferring chemical compounds that induce refractory period which female will not be sexually receptive anymore. There is a period where mate guarding is used until onset of refractory period begins. Male spiders using mechanisms that enable the female to mate with other males have been reported by Austad 1984, Christenson et al. 1985, Suter 1990, Watson 1991, Dodson and Beck 1993, Eberhard et al. 1993, Masumoto 1993, Uhl 1993, and Prenteret al. 1994. Watson 1986 found a species of spider that used a sex attracting pheromone that destroyed the web of the female, which was the male Linyphia litigiosa. Another type of male spider studied by Masumoto 1993, used a copulatory plug during mating which inhibits the transfer of sperm by other male spiders, this species are known as the Agelena limbata. Many male species stay around the female after mating to repell off other males. Andrade 1996 found that male redback spiders sexually cannibalize to reduce the proportion of eggs that were fertilized by subsequently mating.
Many females after mating go into the refractory period and are not sexually receptive to other males that are around her, this is common in most insects also. This type of period has not totally been widely documented for spiders. The multiple mating by females are more likely to be in gregarious spiders then solitary spiders. More males are attracted by female gregarious because of the aggregation which males can move easily among these females. A gregarious spider which form aggregation of orb webs share structural threads like other females, this spider is known as Gasteracantha minax which is the Australian jewel spider. A female G. minax spiders can be surrounded by several courting males which wait at edge of her web for her to react for mating. Without leaving the aggregation, the males can count several females. Before mating, court male G. minax locates the female web and constructs a mating thread from the vegetation of the edge of the female web. Then the male goes halfway up the thread with his first and second pair of legs. The female eventually moves out onto the thread toward the male. The male and female touches legs before the male grabs her tightly and clasps her ventral surface of her abdomen with his legs. The male then places one of his palps adjacent to the females epigyne, inserts his embolus, and transfers sperm. Then they take less then a minute interval which the female returns to central hub while male is still attached. Eventually male leaps away from female by the thread attached to the web. The male then courts the female a second time and inserts the embolus from his other palp. For more details on the mating and courtship behavior among these spiders refer to Mascord 1970 and Robinson and Robinson 1980. Different species of orb weaving maybe different in sexual dimorphism. In some species, females maybe larger in the order of magnitude then males. Usually females are at least one and a half times bigger in size then males and court of a mating thread is less pronounced in different species. During mating the female G. minax are three times the weight size of the male G. minax which is surprising for the courtship behavior. Elgar and Bathgate did some experiments to investigate the way male G. minax reduce the females to remate. To do this Elgar and Bathgate introduced males at different times during the courtship and mating sequence. They also did another experiment study on the influence of male-male competition and sexual cannibalism on sexual dimorphism.
The amount of G. minax spiders were counted in late December 1992 and early January 1993 on the coastal salt marsh fringe of Port Philip Bay at Williamstown, Victoria. Then Elgar and Bathgate counted the number of males and females on solitary or aggregated webs that were bisected by the transect lines. They also collected immature males and females from this group. Elgar and Bathgate put the immature males and females in individual containers in the laboratory for them to mature. These spiders were feed bush flies known as Lucilia cuprina. The mature females were weighed on an electronic balance and transferred into a enclosed perspex mating frame with the measurements of 70 x 50 x 10 cm.Within a few days, the females built a complete orb web. Most females used in the study weighed 38.3 mg. The males were weighed on the days that they were used for mating. The average weight was 13.7 mg for males. For Elgar and Bathgate to test the relationship between female receptivity and male mate-guarding behavior then introduced the males either while mating was going on or the following day after mating. One test was to add one male only to a virgin female and he was either removed after successfully doing both pedipalp insertions or left in mating frame overnight with the female. The next test was to release one male into the mating frame with a virgin female then releasing the second male in the same mating frame either during first or second pedipalp insertion of the first male or male released into the mating frame with solitary female the next day after mating occured. These types of testing were done to see what happens with courtship, copulation, and aggressive behavior of males and females at different times of mating. When putting males in with females, they were put on the base of the mating frame which then the males would find the female orb webs themselves by walking up the side of the frame. Elgar and Bathgate would record the time the male got to the orb web. Copulation was initiated and ended when female would chase the male and the males would chase the rival males. For Elgar and Bathgate to tell what male was whom, they would either tell by size or natural markings.
The results of Elgar and Bathgates experiments, the adult and immature G. minax female spiders per aggregation at Williamstown was 3.1 and for male adult G. minax per aggregation was 1.6. There were nine females and four males that were the largest aggregation. Between number of females and number of males there were positve correlation found within aggregations. When Elgar and Bathgate did these experiments, they found out it was hard to estimate the number of adult males per female for each aggregation because they could not always tell which females the males congregated. The mean of adult males per solitary females were 1.45. The solitary females had at least one male and one of these females had three males on the periphery of her web. It took about 20.2 minutes for the male G. minax to locate the orb web of the female G. minax and then the female would capture and cannibalize the male before he could embrace her, this happened in three of thirty trials. The males that were cannibalized by females did not have a different weight from those males that avoided being cannibalized. The females that were cannibalistic did not have a weight difference from females that were noncannibalistic. There was also no differences in behavior in the males that were either cannibalized or noncannibalized. Elgar and Bathgate defined the duration of copulation as the time when the male first embraced the female to when he leapt away from her. The duration copulation had a positive correlation with that of the second compulation when female encountered a single male. The duration of either first or second copulation was not significantly correlated with either male or female size. There were also no difference in duration of first copulation with either virgin females or mated females with mating males.
Studing in the field, males that were already on the female orb web would pluck or pull silk threads to get rid of intruding males. These aggressive interactions would work when one male would retreat and go to the edge of the orb web. This also happenend in the laboratory when other males were introduced to the orb web. In the lab, the males that were already there would chase the other males off the web. The time between first and second copulation was 22.7 minutes when there was no other males in the web. When other males were present, the time was shorter. The duration of the second copulation was influenced when other males were present. When no other males were present, the duration of the second copulation were longer then the first copulation but if another male was present, it was not much different.
Female G. minax would mate several times if she was not mated the day before. For male to mate with a female after she mated before, the courtship must be within an hour after previous mating. Females would chase the males off more frequently if they were mated a day before compared to within the hour. Males reacted to other males more often it they would be in the web the same time they were copulating then if the male entered the web the following day. The male left overnight with the female would move off the orb web by the next morning. When male spiders mate, there are things they have to be careful so that they don't get cannbalized by the female or chased off by either another male or the female. For spiders to survive, they must have different methods to defend themselves. Spiders all are very defensive when it comes to catching prey, protecting themselves from predators, and when they are ready to reproduce.

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