Specialised use of working memory by Portia africana, a spider-eating salticid
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Using expectancy–violation methods, we investigated the role of working memory in the predatory strategy of Portia africana, a salticid spider from Kenya that preys by preference on other spiders. One of this predator’s tactics is to launch opportunistic leaping attacks on to other spiders in their webs. Focussing on this particular tactic, our experiments began with a test spider on a ramp facing a lure (dead prey spider mounted on a cork disc) that could be reached by leaping. After the test spider faced the lure for 30 s, we blocked the test spider’s view of the lure by lowering an opaque shutter before the spider leapt. When the shutter was raised 90 s later, either the same lure came into view again (control) or a different lure came into view (experimental: different prey type in same orientation or same prey type in different orientation). We recorded attack frequency (number of test spiders that leapt at the lure) and attack latency (time elapsing between shutter being raised and spiders initiating a leap). Attack latencies in control trials were not significantly different from attack latencies in experimental trials, regardless of whether it was prey type or prey orientation that changed in the experimental trials. However, compared with test spiders in the no-change control trials, significantly fewer test spiders leapt when prey type changed. There was no significant effect on attack frequency when prey orientation changed. These findings suggest that this predator represents prey type independently of prey orientation.
KeywordsExpectancy–violation Predatory versatility Prey classification Categorisation Mental rotation Representation
We thank Stephene Abok Aluoch, Godfrey Otieno Sune and Jane Atieno Obonyo for their assistance at ICIPE. We are grateful to G. B. Edwards (Florida State Collection of Arthropods, Gainsville, Florida), Ansie Dippenaar-Schoeman (ARC–Plant Protection Research Institute, Pretoria) and Charles Warui (National Museums of Kenya) for their help with spider taxonomy. We also gratefully acknowledge support of grants from the Foundation for Research, Science and Technology (UOCX0903), the Royal Society of New Zealand (Marsden Fund (M1096, M1079) and James Cook Fellowship (E5097)), the National Geographic Society (8676–09, 6705–00) and the US National Institutes of Health (R01-AI077722).
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