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In this report, I have taken the journal, "Route selection by a jumping spider (Portia labiata) during the locomotory phase of a detour" written by Michael Tarsitano, in the year 2006 and I will summarise the findings. Tarsitano has background information on both this spider and a similar type of method due to previously having done an in-depth study in 1998 on the same spider but just focusing on whether scanning and detour behaviour was evident. This more recent piece extends this by investigating the processes in further detail and breaking down the locomotory phase.
Detour behaviour is that which is used by certain animals to reach a goal within their environment, usually this being their prey which they can't necessarily see but have the ability to create a route in which allows them to get to their goal. It is this adaptive behaviour which puts the jumping spider Portia libiata at an advantage in its environment. Originally the author investigated what effect it had on detour behaviour in an open area, in this paper the experiment has shown the effect of being confined to an elevated platform. When confined to this elevated platform, they have shown detour behaviour, scanning and a type of decision making to make their selection of route. This experimental approach in which is frequently used to investigate animals behavior with which the animal has to make a choice between different options and these being significant in their findings.
This paper sets out to investigate the detour behaviour shown in route selection of the female jumping spider; Portia labiata. The main investigation involves testing which direction the spider will go when given different options. It sets out to prove that the spider will go in a different direction to its goal, this being the lure which is most case is the longer route in order to reach it. For example, you would expect if detour behaviour wasn't present and it was just trial and error, that the spider would go directly towards the prey pole and then have to try and figure out how to get to it. The experiment ultimately sets out to investigate into some of the behavioural features of this animal. When there is a lure placed directly in front of it but with no alternate route, the spider would have headed straight towards it yet when there is not a ramp to the lure; it needs to use scanning and detouring behaviour to take an alternative route. Therefore, this spider needs to be also involved in deciding whether it is a direct or indirect route. The journal which I have read looks to investigate further into this principle and prove that this detour route selection is evident in this species of spider.
Firstly, it is important to take into account that with the chosen method is measuring trial and error detour performance which involves single trials rather than observing if any detour learning is taking place. If this was the case, there would be repeated trials testing whether the spiders can recall from the learning process. The method Tarsitano has used for the experiment is a laboratory based test using only laboratory reared female Portia labiata spiders, with the apparatus as shown below in figure 1.
This involves a still table with four plain walls attached securely to it with the purpose of it being to minimise any external motion and remove any other possible distractions which may affect the validity of the results. The spiders were deprived of food prior to this experiment for approximately four days which would ensure that all the spiders were equally hungry. Referring to figure 1 again, the lure was made to look like an Ariadnea spider which is Portia's common prey. This lure is then attached to the top of a prey pole which has a connected ramp way providing a route to the access pole. The principle of this apparatus and experiment is that if they choose to go via the correct route, they will go up the access pole, this would lead them along the ramp way and reach the prey pole but if they selected the incorrect way, they would be expected to either go underneath the prey pole, up the dead end pole or in the gap between these. All spiders were put on the same starting hole which was centrally placed 15cm away from the prey pole.
The second part of the experiment is shown in figure 2. Fisher's exact test of independence for two by two tables makes it easier for us to understand what the figure is presenting which can then be used efficiently to make initial comparisons (Sokal & Rohlf 1981). This figure is showing the choices made throughout the sequences of the spiders when choosing which direction to go at each of the segments. The table shows the spiders change in direction whilst in motion in the initial general direction of forwards towards the lure. From these findings, I can conclude that the majority (13 out of 19) already heading towards the correct side will continue in the same correct direction. There are thirteen spiders that go to the wrong side and of these seven go to the different side which would mean at the end of the spiders in this analysis there were only 6 that went to the wrong side and another one which could not be caterorgised. Taking this into account, the results agree with the author's hypothesis in that there is a form of decision making as part of the overall process of hunting their prey as for the seven that were originally heading for the wrong route; as they got nearer they changed their detour. An important factor to note is that the spider has to go a longer route in order to get to its prey otherwise it would go straight to underneath the prey which would be a shorter distance. From the results and from observation, it has been found that this is evidence that the spider is using decision making as it uses the cues in the environment to logically plan a route which would be successful.
Results also show that the spider has the mental ability to trace back previous motions up to the present segment in the experiment to trace to see if it is a straight track to the lure or if there is a connecting pole which ultimately would result in a detour route to that which it had originally planned to go.
The spiders were scored as either solving, this being eventually choosing to go up the access pole or failing, this being the dead end pole, towards the gap or placing themselves underneath the prey. I agree with what the author says about their data but for a clearer way of presenting these findings I would use a different format as well as the ones they have already used. They collected data of which spiders solved the 'task' and which spiders failed yet they haven't presented this. Therefore, it would have been more suitable I believe if the author had shown these results in one table and possibly in a graph showing the percentage of successful against unsuccessful spiders. This isn't stated directly in the text, it gives a table showing the number for those at different segments but missing these simple figures makes it harder to understand the rest of the data.
The major findings were similiar to previous experiments in that these spiders in the open arena, which had been initially confined to an elevated platform, used the process of scanning movements using their exceptional visual ability and decision making. From this additional research, it has been found that the spiders used the scanning process not only at the start but stopped at various stages and repeated it, and using a form of decision making throughout the route of the detour. Ultimately, the spider did not have one smooth movement to reach its goal; it would pause for about a second and break down the route to avoid choosing the wrong path.
From the data we are given, I can gather that 70% of the spiders went in the correct direction or either the ramp way or the access pole; of these 40% chose the access pole and the remaining 30% chose the ramp way or were catergorised as solving the problem if they were within 2.5cm of the access pole. It was found that eleven out of the twenty seven spiders stopped during their approach to scan their surroundings. The initial direction after the first scanning had been completed, the spiders were split equally between choosing to go to the access pole or the ramp way. Only one spider was found to go towards the gap in order to get to the lure. This is significant because this rules out that when a detour is available the spider will always choose a direct route over the detour route. As proven by the results this is not the case. Few spiders changed their mind to go from the correct direction to the incorrect direction towards the dead end pole but it was found in the final segment that most the spiders realigned themselves or finalised that they were going in the correct direction. The final choice in the part of apparatus to finish at was developed gradually as the spider approached the main part of the apparatus.
Also observed in the experiment, which from my point of view was an unusual finding; that some of the spiders would stop, scan their surroundings having selected the direction in which they will go and then not give any hint or indication as to which route they had selected. I find this unusual as I would have expected them to give some visual clue by looking in the direction they have planned to go but this is not the case, they don't give signals until they have started their movement which is a quick movement until the next stage of which they stop and repeat this process.
The first indication of further research could be to investigate whether the choice between the correct pole (ramp way) or the incorrect pole (dead-end pole) was to what extent decision making, the psychological processes or scanning; the physiological visual ability. For example, is one of these components more dominant than the other or do they both play as important part in the hunting process of the Portia labiata spiders.
It is also suggested that the Portia spiders scanning and detouring behaviour in these cases is actual rather than vicarious, with suggestion that the spiders undergo a type of trial and error, using scanning as a method to look back and forth at the possible options available for the route selection to get to their goal before making a final decision (Tolman 1939). An idea which is hinted here for future research is to do with both the scanning and the detour idea. When the spiders stop briefly for about a second, they scan their surroundings. The experiment would be investigating when this scanning has stopped, whether the detouring then takes place or do the two behaviours intermingle at the same time.
The Portia's field of view, fixation and turning behaviour makes it possible for us to analyse how this spider uses their ability to scan its surroundings and back track from its goal before setting off in locomotion (Tarsitano & Andrew 1999). Research which could extend and develop this particular investigation further could be to add additional features and apparatus to make the 'environment' more visually stimulating to see what effect this has on the spiders detour performance rather than the current plain walls of this experiment which isolates the spider from any distractions.
- Check references
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- Sokal, R & Rohlg F. 1981. Biometry. San Francisco: W. H. Freeman
- Tarsitano, M. S. 2006. Route selection by a jumping spider (Portia labiata) during the locomotory phase of a detour. Animal Behaviour, 72, 1437-1442
- Tarsitano, M. S. & Andrew, R. 1999. Scanning and route selection in the jumping spider Portia labiata. Animal Behaviour, 58, 255-265
- Tolman, E. C. 1939. Prediction of vicarious trial and error by means of the schematic sowbug. Psychological Review, 46,