Social recognition in the arachnida

Abstract

More than 99 % of arachnid species are solitary, aggressive and often cannibalistic predators. A few species are social and cooperative, but they do not reach the level of eusociality found in some insects. Kin recognition is suggested to be a key feature for the evolution of cooperation and sociality and thus found predominantly in those few species. While kin recognition and social interactions are well investigated in spiders, these behaviours are understudied in other arachnid taxa. Nevertheless, social species are also known in the Acari, Pseudoscorpiones, Scorpiones, Opiliones and Amblypygi. Still, we have limited information on the adaptive value of social recognition in arachnids, how it is facilitated and maintained. While this field of research is still young, it has produced some encouraging results. This chapter reviews the knowns and the unknowns of social recognition mechanisms with respect to their importance for the evolution of arachnid sociality. We will particularly focus on kin recognition and kin discrimination. First, we shortly introduce the evolution of sociality in arachnids which provides the background for the understanding of the different recognition and discrimination mechanisms explained subsequently. Further, we illustrate the interspecific discrimination abilities of arachnids, and present the state of the art on intraspecific recognition and kin recognition in spiders and other arachnids. This chapter illustrates that various social recognition abilities and especially kin recognition exist in social but also non-social arachnids. These mechanisms allow different species to distinguish between familiar and foreign, or related and unrelated individuals, to either support or discriminate against them. In contrast to eusocial insects, the necessity of maintaining kin recognition abilities often appears to be obscure and highly context-dependent. Thus, a generalisation of its adaptive value in arachnids is not possible. There is some evidence for the concept of kin recognition facilitating the evolutionary transition from subsocial to permanently social living. However, kin recognition has not yet been demonstrated in permanently social species and is thus subject of ongoing research. It might have been lost during evolution due to the lack of encounters with unrelated individuals in permanent arachnid societies or replaced by direct benefits of cooperation. Finally, we discuss some research gaps and new approaches to improve the knowledge of the adaptive significance of kin recognition in arachnids.