Evolution of pharmacophagy in tiger moths (Lepidoptera: Erebidae: Arctiinae)

The focus of this study was to reconstruct a phylogenetic hypothesis for the moth subfamily Arctiinae (tiger moths, woolly bears) to investigate the evolution of larval and adult pharmacophagy of pyrrolizidine alkaloids (PAs) and the pathway to PA chemical specialization in Arctiinae. Pharmacophagy, collection of chemicals for non-nutritive purposes, is well documented in many species, including the model species Utetheisa ornatrix L. A total of 85 exemplar ingroup species representing tiger moth tribes and subtribes (63 genera) and seven outgroup species were selected. Ingroup species included the most species-rich generic groups to represent the diversity of host plant associations and pharmacophagous behaviors found throughout Arctiinae. Five genetic markers were sequenced: one mitochondrial (COI barcode region), one nuclear rRNA (D2 region, 28S rRNA), and three nuclear protein coding gene fragments (elongation factor 1-a protein, wingless and ribosomal protein subunit S5). These data were analyzed using model-based phylogenetic methods: maximum likelihood (ML) and Bayesian inference (BI). Ancestral pharmacophagous behaviors and obligate PA associations were reconstructed using the resulting Bayes topology and Reconstructing Ancestral States in Phylogenies (RASP) software. Our results corroborate earlier studies on the evolution of adult pharmacophagous behaviors, suggesting that this behavior arose multiple times and is concentrated in the phaegopterine-euchromiine-ctenuchine clade (PEC). Results refute the earlier scenario that generalist, PA-pharmacophagous larvae was the ancestral condition and then these gave rise to specialist PA larvae. Rather, results support the conclusion that PA specialization arose early in the phylogeny of the subfamily and that facultative pharmacophagous behaviors are the derived condition.