Is there a trade-off between the melanin allocated to the immune system and to camouflage on larvae of the dragonfly Micrathyria catenata Calvert,1909 (Odonata: Libellulidae)?

Abstract

In insects, the immune system responds to the presence of antigens involving them in melanin. However, the melanin is also allocated into the exoskeleton’s pigmentation, used to camouflage. We aimed to test the existence of a trade-off between the allocation of melanin to the immune system and to camouflage on the larvae of Micrathyria catenata. We conducted the study in the “Reserva do km 41” (41 km’ Reserve), 80 km distant from Manaus, Amazonas, Brazil. We implanted a nylon line into the abdomen of 30 larvae and observed if had or not deposition of melanin in the line. We counted the number of individuals who responded to implant depositing melanin and, later, we took photos of the larvae’s heads and calculate gray intensity. We used a t-test for independent samples. 76% of larvae responded to treatment depositing melanin on the implants. There were no significant differences in the intensity of gray between the larvae that responded to the implants and those who did not responded. There is no trade-off to allocation of melanin for camouflage and for the immune system. This should happen because the immune system is not limited by the acquisition of resources or the camouflage’s demand for melanin is not enough to influence the immune system.

Key words: dragonfl y, camouflage, immune system, Micrathyria catenata, trade-off.