title: Incompatible Ages for Clearwing Butterflies Based on Alternative Secondary Calibrations.
abstract: The recent publication of a time-tree for the plant family Solanaceae (nightshades) provides the opportunity to use independent calibrations to test divergence times previously inferred for the diverse Neotropical butterfly tribe Ithomiini. Ithomiini includes clades that are obligate herbivores of Solanaceae, with some genera feeding on only one genus. We used 8 calibrations extracted from the plant tree in a new relaxed molecular-clock analysis to produce an alternative temporal framework for the diversification of ithomiines. We compared the resulting age estimates to: (i) a time-tree obtained using 7 secondary calibrations from the Nymphalidae tree of Wahlberg et al. (2009), and (ii) Wahlberg et al.'s (2009) original age estimates for the same clades. We found that Bayesian clock estimates were rather sensitive to a variety of analytical parameters, including taxon sampling. Regardless of this sensitivity however, ithomiine divergence times calibrated with the ages of nightshades were always on average half the age of previous estimates. Younger dates for ithomiine clades appear to fit better with factors long suggested to have promoted diversification of the group such as the uplifting of the Andes, in the case of montane genera. Alternatively, if ithomiines are as old as previous estimates suggest, the recent ages inferred for the diversification of Solanaceae seem likely to be seriously underestimated. Our study exemplifies the difficulty of testing hypotheses of divergence times and of choosing between alternative dating scenarios, and shows that age estimates based on seemingly plausible calibrations may be grossly incongruent.
authors.affiliation: Evolution and Ecology Group, Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132, USA; ivonne.garzon@gmail.com.
authors.forename: Ivonne J
authors.initials: IJ
authors.lastname: Garzón-Orduña
authors.affiliation: Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Piracicaba, São Paulo, Brazil;
authors.forename: Karina L
authors.initials: KL
authors.lastname: Silva-Brandão
authors.affiliation: McGuire Center for Lepidoptera and Biodiversity, Florida Museum of Natural History, University of Florida, Gainesville, FL 32611, USA; and.
authors.forename: Keith R
authors.initials: KR
authors.lastname: Willmott
authors.affiliation: Departamento de Biologia Animal and Museu de Zoologia Instituto de Biologia, Universidade Estadual de Campinas, Campinas, São Paulo, Brazil.
authors.forename: André V L
authors.initials: AV
authors.lastname: Freitas
authors.affiliation: Evolution and Ecology Group, Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132, USA;
authors.forename: Andrew V Z
authors.initials: AV
authors.lastname: Brower
mesh_terms: D000818:Animals; D002080:Butterflies / Q000145:classification*; D002965:Classification / Q000379:methods*; D005580:Fossils; D010802:Phylogeny; D019657:Solanaceae / Q000145:classification; D013995:Time
keywords: Danainae; Ithomiini; Nymphalidae; Solanaceae; asynchronous association; crown ages; dating; herbivory; hostplant; molecular clock; secondary calibrations