Stridulation can suppress cannibalism in a specialised araneophagous predator
Acoustic signalling is widespread in arthropods and appears to be common in spiders, but the function is still unknown in many species. Acoustic signals have several functions and can be used both in interspecific (e.g., to threaten potential predators) and intraspecific (during courtship) communication. In our study, we investigated the intraspecific role of stridulation in the araneophagous Palpimanus spider (Araneae: Palpimanidae). These spiders are specialised in hunting other spiders at all ontogenetic stages. We hypothesised that stridulation is used to avoid cannibalism. We investigated the morphology of the stridulatory apparatus, analysed the acoustic signals that various stages produce, and found two types of stridulation, low- and high-intensity stridulation. Then, we investigated the presence of cannibalism between individuals of variable body size and the use of stridulation during interactions. We found that cannibalism occurred only when the prosoma size difference between the two opponents was more than 200%. Then, we paired conspecific large control Palpimanus with smaller control individual or with individual whose stridulatory organs were impaired and found that impaired spiders suffered significantly higher cannibalism than the control spiders. Our study reveals a novel role of acoustic communication in the conspecific recognition of araneophagous spiders.
Cannibalism is widespread among predatory animals. However, cannibalism might not be an optimal strategy for several reasons and should be a less preferred option for predators. Palpimanus spiders are prey specialised predators preying primarily on other spiders thus the risk of cannibalism is even higher than in generalist predators. These spiders possess stridulatory apparatus and they often stridulate following a contact with conspecifics. We found that cannibalism occasionally occurred during contact with conspecifics and that the probability of cannibalism increased with the size difference between the interacting individuals. When the spiders were not able to stridulate during contact, the probability of cannibalism increased significantly. Our results thus show that Palpimanus spiders use stridulation to reduce cannibalism among unequally sized individuals.
KeywordsAcoustic signal Araneophagy Defence Intraspecific interaction Predation Spider
We would like to thank Ladislav Ilkovics from the Department of Histology and Embryology at the Medical Faculty of Masaryk University, for help in taking SEM pictures. We thank Stanislav Korenko for help in collecting spider specimens. We also thank to three anonymous reviewers for their comments.
SP conceived the study, acquired and analyse data on morphology and stridulation and conducted comparative analysis; EL acquired and analyse behavioural data; LS acquired behavioural data; EL, LS, SP and FŠ collected tested specimens. EL and SP interpreted data and wrote the manuscript. LS and FŠ helped to draft the manuscript. All the authors gave final approval for publication.
Compliance with ethical standards
Data availability statement
The datasets generated and analysed during the current study are available in the Terrestrial invertebrate research group repository, http://www.sci.muni.cz/zoolecol/inverteb/?page_id=18.
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