The endocarp evolution of Cissampelideae (Menispermaceae): integrating extant and fossil species

The integration of extant and extinct species is essential to understand the character evolution of organisms. However, the effect of incorporating fossil information on inferring evolutionary patterns of morphological characters is still poorly understood. Here, we used Cissampelideae, a tribe of pantropical lianas with rich fossil records, to provide new insights into the role of fossils in the inference of character evolution.

Based on seven DNA regions and 24 endocarp characters, we reconstructed a dated phylogeny for 39 extant and 11 fossil species of Cissampelideae. For comparison, we also reconstructed a dated phylogeny for only extant species. Within the dated phylogenetic frameworks, we then reconstructed the evolutionary patterns of endocarp characters in the tribe.

Ancestral-state inferences of 6 of the 24 endocarp characters are changed when fossils are integrated. The endocarp of the most recent common ancestor of Cissampelideae had unbroken short raised transverse ridges lower than the unspiny dorsal crest. Within Cissampelideae, the broken transverse ridge is derived from the unbroken transverse ridge, the columnar protuberance is derived from the long raised transverse ridge, and the long raised transverse ridge is derived from the short raised transverse ridge.

Endocarp transverse ridges of Cissampelideae show evolutionary trends of becoming fragmented and more elevated, which may be related to adaptation to limestone karst environments. This study highlights that fossil species have played important roles in recording morphological character evolution and showcases the necessity of integrating fossil and extant taxa to improve the inference of character evolution.