Maternal care is a valuable resource for offspring and one expects competition amongst offspring to gain maximal maternal protection. In the subsocial treehopper Umbonia crassicornis, the nymphs form a cylindrical aggregation around stems of their host plants and are vulnerable to attack by many predators. The mother sits below nymphal aggregations and protects them against predators. Synchronized nymph signaling transmitted in the form of substrate-borne vibrations is required to elicit the mother's protection. Even with maternal protection some nymphs get preyed upon; the risk is highest for those farthest away from mother, and on the edges of the aggregation. Given the asymmetry in predation risks we investigated the factors that influence the propensity of a nymph to signal. We simulated predation using a paintbrush and making repeated contacts to a nymph on the end of an aggregation. We performed the experiment at both ends of the aggregation, and in the presence and absence of the mother for eleven families. Nymphs closer to the predator signaled more than the nymphs farther away. Likelihood of signaling also increased for nymphs on the edges and when the predator was at the top of the aggregation. These results indicate that nymphs perceive certain risks and vary their signaling accordingly. The motivation of the nymphs to signal depends on their position in the aggregation and the consequent levels of risk they face.
Species 1: Homoptera Membracidae Crassicornis umbonia (treehopper)
Keywords: nymph signaling, predation
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