The Ancestral Conifer Cone: What Did It Look Like? A Modern Trait-Evolution Approach

• Published in: International journal of plant sciences Vol. 181; no. 9; pp. 871 - 886
• Main Authors: Herting, Julian, Stützel, Thomas, Klaus, Kristina V.
• Format: Journal Article
• Language: English
• Published: Chicago The University of Chicago Press 01.11.2020; University of Chicago, acting through its Press
• Subjects: Bayesian analysis; Cones; Conifers; Evolution; Fossils; Mesozoic; Ontogeny; Paleozoic; Phylogeny; Pollination; Reconstruction; Seed dispersal; Statistical inference; Supports; trait evolution; seed cone; conifers; ancestral state reconstruction; BayesTraits
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/710489

Premise of research. Seed conifer cones and their fossil record have been the subject of intensive study over the past century. In those studies, however, the interpretation of fossil cones differs substantially. Additionally, despite the rich fossil record, the last common ancestor of modern conifers remains enigmatic. In this study, we endeavor to reconstruct the original and ancestral character traits of the seed conifer cone. Methodology. We reconstructed the phylogeny of conifers by using Bayesian inference and a large-scale molecular data set of four marker regions (18S, matK, phyP, rbcL). We also reconstructed the ancestral character states of seed cones using a broad set of morphological data and a model-based approach. In addition, we compared the cone traits with fossil ovulate cones from the late Paleozoic and early Mesozoic. Pivotal results. According to our reconstruction, the micropyle of the last common ancestor of modern conifers points toward the cone axis during pollination and seed dispersal. Furthermore, the ancestral cone features an axillar structure that supports the ovule, and it develops before the ontogenetic phase. The presence of a predeveloped structure coincides with a change of orientation of the ovule during development. Comparison with fossil cones shows that a micropyle facing toward the cone axis is a common character trait of late Paleozoic conifers. Conclusions. Analyzing conifers by means of ancestral state reconstruction sheds novel light on the trait evolution of this group. For the first time, we could infer characters of ancient conifers that are usually unobtainable from fossils, for example, developmental characters. From them, we conclude that the original purpose of the predeveloped structure was to turn the ovule during development. Ultimately, we advocate for a wider use of ancestral state reconstructions among conifers.