Behavioral ecology of Neochlamisus leaf beetles: the role of fecal cases and associated traits
Brown, Christopher Glen
This dissertation examines the natural history, potential adaptations, and tradeoffs of fecal cases of Neochlamisus leaf beetles. Fecal cases begin as wrappings around eggs. Each larva maintains and expands its case throughout the juvenile stadia, eventually sealing it for pupation. Once an adult, it cuts a circular cap to escape. In the field, fecal cases are required for larval survival and lab studies showed that fecal material, plant hairs embedded in the external wall of the case, and plant hairs embedded in an internal chamber (i.e., trichome attic) individually reduce predation risk. Normally these plant hairs, or trichomes, are considered adaptations by plants to prevent herbivory. N. platani larvae, which incorporate trichomes into their cases to an extensive degree, can feed on pubescent, denuded, and naturally glabrous leaves equally. Unusually, they also seek out and spend more time on pubescent leaves when given a choice, perhaps co-opting the host's defense for their own protection. I found no evidence that fecal cases moderate the effects of or increase survival in low humidity. Rather, individuals that pupated in low humidity were incapable of escaping the case. This mortality appears to be due to the strengthening of case material when relative humidity was low, becoming too strong for adults to cut and emerge. Strong cases, however, also decrease the ability of predators to penetrate the case. Therefore, an ecological abiotic factor (i.e., relative humidity) causes a plastic response in the animal architecture that imparts a trade-off between normal adult emergence and preventing predation. In addition, I found evidence that fecal cases and larvae may be adapted to prevent overheating. Fecal cases slow the rise in internal temperatures and larvae move to the undersides of leaves and lift the case above the leaf surface when ambient temperatures are high. I also include an observation of a rare 'predation event' of a casebearer, i.e., eggs were incorporated into the bags of the evergreen bagworm. This is by far the most detailed study of this amazing example of animal architecture.