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Visual Brightness Discrimination of the Jumpin G Spider Menemerus Bivittatus ( Araneae , Salticidae )
| Content Provider | Semantic Scholar |
|---|---|
| Author | Tiedemann, Klaus Bruno |
| Copyright Year | 2004 |
| Abstract | It was observed that the jumping spider Menemerus bivittatus lives on light surfaces as well as on dark surfaces, hunting prey which is lighter or darker than the surface the spider is on . From these observation s arises the question about the brightness or contrast discrimination abilities of this spider. The orientation response was recorded for 14 spiders to a moving circular prey-stimulus varying from white, through grey, to black, against a white, grey or black background . When the stimulus was darker than the background, there was a rapi d increase in response as the stimulus gets darker . This rapid change in response with stimulus brightness did no t occur when the stimulus was lighter than the background . These results reveal a high contrast discriminatio n ability and also a dependence of the response on the overall stimulation conditions . The visual system of jumping spiders (Salticidae) is highly developed when compared to other families of spiders. Like most spiders , jumping spiders have four pairs of eyes . The mos t specialized are the anterior median eyes (AM) , that are used in prey pursuit (Land 1971) . It ha s been suggested by Land that the AM are capable of color vision. The other eyes function primaril y to detect prey movement and to elicit orientatio n toward prey (bringing the prey into the visua l field of the AM eyes). The jumping spider Menemerus bivittatus (Dufour) is common in Southern Brazil and ca n be found throughout the year in almost all home s of Sao Paulo . Retreats are generally located in the highest part of doors or window frames or under an outside overhang . Preliminary observations of the habitat preferences ofM. bivittatus revealed that (1) spiders hunted on either a dark surface (e .g., black painted poles) or a light surface (e .g ., wall of buildings) and (2) on both of these surfaces both light colored prey (e .g., small Diptera) and darkly colored prey (e.g ., Musca) were taken. There appeared to be no difference in prey catching efficiency between the different backgrounds . Since M. bivittatus has a light appearance (greyish brown with black stripes) the spider is very conspicuou s on a black ground and almost invisible on ligh t colored walls . These observations raised the question of whether jumping spiders are capable of discriminating differences in contrast between stimulus and background . Since single visual receptor cells are known to react with graded potentials to light intensity, the physiological capability for contrast discrimination appears available . The most likely mechanism is a neural circuit that enhances brightness differences and contrast in th e same way as is known for many vertebrates and invertebrates . However, the question remains on how contrast discrimination is integrated int o specific behaviors, such as prey catching and mate recognition . The reflexive behavior of jumping spiders to orient themselves and the AM eye s toward the prey after its detection by the secondary eyes (Land 1972) is a very simple behavioral response that can be easily observed an d recorded in the laboratory. The purpose of this experiment was to establish the psychophysical brightness discrimination function measured by this orientation response for different levels of ground brightness . Another question was to find if the function fo r the discrimination of a light stimulus against a dark background is symmetrical to a dark stimulus against a light background. Lack of symmetry between the functions would indicate an increased ability at prey detection in one of the situations and might suggest that the spider woul d have a preference for one of the hunting conditions. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.americanarachnology.org/JoA_free/JoA_v21_n1/JoA_v21_p1.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
