From Phylogenetics To Host Plants: Molecular And Ecological Investigations Into The Native Urticaceae Of Hawai‘i

Abstract

The following study investigated the native Hawaiian Urticaceae in both an evolutionary and ecological context. First, the phylogenetic relationships of the native Urticaceae were determined using molecular DNA techniques. Second, the relationships between the native Urticaceae and an endemic Hawaiian specialist herbivore, Vanessa tameamea (Lepidoptera, Nymphalidae), were explored in order to assess variation among urticaceous species as host plants. The family Urticaceae has undergone several taxonomic revisions in the past two decades as a result of molecular phylogenetic studies, although little phylogenetic attention has been paid to the Urticaceae taxa native to Hawai‘i despite four species being federally endangered and the presence of two endemic genera. Overall, results from the phylogenetic analysis using Bayesian inference presented here revealed that taxonomic revisions to five of the seven nativerepresented genera are necessary based on polyphyletic and paraphyletic relationships to other genera. Further DNA analysis is suggested to elucidate species-level relationships for the native species of Pipturus and several species of Neraudia. The analysis produced a well-supported, monophyletic Hawaiian Urera/Touchardia clade, and it can be inferred that a single colonization event, as opposed to the previously hypothesized two colonization events, led to the current three extant species in this clade. Results from a no-choice bioassay experiment revealed that V. tameamea performed best on two native, but distantly related species, Urera glabra (tribe Urticeae) and Pipturus albidus (tribe Boehmerieae). Additionally, caterpillars from both O‘ahu populations recognized and readily ate the non-native C. obtusifolia, although caterpillars from Hawai‘i Island reared on this plant diet did not recognize C. obtusifolia as a food source and subsequently died within their first instar. No significant correlations were found between putative defense or nutritive leaf traits and the metrics of performance. Thus, it remains unclear what factors underlie variation among plant species in suitability as host plants for V. tameamea. The bioassay experiment highlights the complex relationships between a herbivore and its host plants.