Behavioral Ecology and Evolution of Hawaii's Endemic Carnivorous Caterpillars (Lepidoptera: Cosmopterigidae Hyposmocoma spp.)

Abstract

The endemic Hawaiian moth genus Hyposmocoma includes hundreds of species, providing dramatic examples of explosive radiation and ecological specialization. Many of these species exhibit typical caterpillar feeding ecology, consuming plant material, including aquatic algae-grazing and fern stem-boring. However, one clade deviates from this norm and has developed carnivorous behavior, an extremely rare trait in Lepidoptera worldwide. These species demonstrate behavior ranging from simple scavenging to molluscivorous prey capture, and their behavioral ecology and morphology reflects this. Here I investigate the degree of specialization and variation in behavior and morphology of several species of carnivorous Hyposmocoma, including both described and undescribed species. Observations and analyses are focused on prey preference of the carnivorous, "cigar" case clade, and mandible morphology within this and other Hyposmocoma groups. My results demonstrate that prey preference varies among species within the carnivorous clade, and ranges from arthropod scavenging to specialized snail capture behavior. The genus Hyposmocoma exhibits extraordinary diversity in terms of: number of species, caterpillar case morphology, feeding behavior (from algae eaters in streams to obligate snail eaters in native forests) and preferred habitat (from dry lowland forests to upper elevation cloud forest, to streams). This study set out to investigate whether similar levels of polymorphism exist in mandible microstructure. My hypothesis was that with so many vastly different natural history traits, a feature with critical adaptive function such as mandible morphology will reflect this dramatic level of variation. However, an unexpectedly low level of variation was observed. Mandible microstructure was found to be highly conserved, whether preferred feeding type included wood boring or snail feeding. Possible reasons for mandible structure conservation include recent speciation events, and the possibility that the structure observed across the genus is versatile enough such that it is functionally effective in diverse settings. Continued analyses of Hyposmocoma ecology, behavior, and morphology will prove useful in phylogenetic inference, and warrants continued study alongside ongoing molecular research.