Communication about predation risk between parents and offspring groups in treehoppers

Abstract

False alarms should be common and costly for group-living animals, but to limit false alarms, animals must evade a tradeoff between response sensitivity and accuracy. I investigated this topic in two closely-related species of treehoppers, Umbonia crassicornis and Platycotis vittata, in which mothers defend their group-living offspring from invertebrate predators. Umbonia offspring groups produce synchronous signals to alert their mothers of predator attacks, and U. crassicornis offspring groups are known to produce false alarms. I examined a) the function of vibrational signals by U. crassicornis mothers after predator attacks, b) the functions of P. vittata offspring and maternal signals during predator encounters, and c) the response of a vibrationally-sensitive insect predator to P. vittata familial vibrational signals. Results showed that U. crassicornis maternal signals function as negative feedback, dampening the collective signaling of their offspring after predator attacks. This likely reduces false alarms by offspring without reducing the sensitivity of predator detection. Platycotis vittata mothers and offspring also partition communicative roles, with offspring signaling predator presence and maternal signals dampening offspring signaling response. However, false alarms are unlikely in this species and thus benefits of negative feedback are unlikely to be the same as for U. crassicornis. Finally, P. vittata offspring signals attract a species of generalist insect predator, whereas P. vittata maternal signals had no effect on the same predator. Predator eavesdropping may favor maternal suppression of unnecessary offspring signaling.