Macroevolutionary analyses provide new evidence of phasmid wings evolution as a reversible process

The concept that complex ancestral traits can never be re-acquired after
their loss is still widely accepted, despite phylogenetic and molecular
approaches suggesting instances where phenotypes may have been lost
throughout the evolutionary history of a clade and subsequently reverted
back in derived lineages. One of the first and most notable examples of
such a process is wing evolution in phasmids; this polyneopteran order of
insects, which comprises stick and leaf insects, has played a central role
in initiating a long-standing debate on the topic. In this study, a novel
and comprehensive time tree including over 300 Phasmatodea species is used
as a framework for investigating wing evolutionary patterns in the clade.
Despite accounting for several possible biases and sources of uncertainty,
macroevolutionary analyses consistently revealed multiple reversals to
winged states taking place after their loss, and reversibility is coupled
with higher species diversification rates. Our findings support a loss of
or reduction in wings that occurred in the lineage leading to the extant
phasmid most recent common ancestor, and brachyptery is inferred to be an
unstable state unless co-opted for nonaerodynamic adaptations. We also
explored how different assumptions of wing reversals probability could
impact their inference: we found that until reversals are assumed to be
over 30 times more unlikely than losses, they are consistently inferred
despite uncertainty in tree and model parameters. Our findings demonstrate
that wing evolution is a reversible and dynamic process in phasmids and
contribute to our understanding of complex trait evolution.