Incompatible Ages for Clearwing Butterflies Based on Alternative Secondary Calibrations

Area of Science:

• Evolutionary Biology
• Molecular Phylogenetics
• Insect Ecology

Background:

• The plant family Solanaceae (nightshades) and the butterfly tribe Ithomiini exhibit close co-evolutionary relationships, with Ithomiini genera often specializing on specific Solanaceae genera.
• Previous divergence time estimates for Ithomiini relied on secondary calibrations, leading to questions about their accuracy.

Purpose of the Study:

• To establish an alternative temporal framework for Ithomiini diversification using independent calibrations from a new Solanaceae time-tree.
• To compare new Ithomiini divergence estimates with previous studies and assess the impact of calibration choices.

Main Methods:

• A relaxed molecular-clock analysis was performed using 8 calibrations derived from the Solanaceae time-tree.
• Bayesian phylogenetic methods were employed to estimate divergence times.
• Results were compared against a time-tree using Nymphalidae calibrations and original estimates from Wahlberg et al. (2009).

Main Results:

• Divergence time estimates for Ithomiini were consistently younger, approximately half the age of previous estimates, when calibrated with Solanaceae ages.
• Bayesian clock estimates demonstrated sensitivity to analytical parameters like taxon sampling.
• Younger dates for Ithomiini align better with hypotheses linking diversification to Andean orogeny.

Conclusions:

• Calibrations derived from closely related plant families can significantly alter butterfly divergence time estimates.
• The study highlights the challenges in testing divergence time hypotheses and the potential for incongruence with different calibration strategies.
• Discrepancies suggest either Ithomiini diversification is more recent or Solanaceae diversification is older than previously estimated.