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Phylogenetic Uncertainty and Fossil Calibration of Asteraceae Chronograms LETTER Jose L

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Phylogenetic Uncertainty and Fossil Calibration of Asteraceae Chronograms LETTER Jose L LETTER Phylogenetic uncertainty and fossil calibration of Asteraceae chronograms LETTER Jose L. Panero1 Barreda et al. (1) claim a Cretaceous fossil pollen type is an opposed to other Barnadesioideae. Encoding “columel- extinct Asteraceae. Concluding this pollen type is “nested late layer visibility under light microscopy” (character 19) within Dasyphyllum (crown representative),” they calibrate results in unintentional character weighting. Exine thick- a Dasyphyllum + Barnadesia crown node (Dasyphyllum ness (character 22) is much smaller in Dasyphyllum crown absent) and estimate an 85.9-Ma Asteraceae crown inerme and Dasyphyllum velutinum than in other Dasy- age that potentially compresses asterid evolution by tens phyllum spp. (3) that would be scored as other Barnade- of millions of years. However, the bootstrap majority con- sioideae and different from the fossil had they been sensus topology reported could not be reproduced from sampled. Characters 19, 21, and 22 clearly contribute the data; instead, the fossil resolved in a trichotomy with to place the fossil with Dasyphyllum. Character 17 as- Calyceraceae and Asteraceae. Thus, unambiguous assign- sumes that concavities distributed asymmetrically ment of these pollen grains to Asteraceae is premature. (sometimes absent) along the intercolpal region in the Paleocene, not Cretaceous, mean ages of Asteraceae fossil are homologous with symmetrically distributed result from calibration placement consistent with the intercolpal concavities in extant taxa and not the result fossil’s phylogenetic position in the reproduced bootstrap of compression forces during fossilization (figure 4 in tree. Calibration at the Asteraceae + Calyceraceae crown ref. 1). This character is scored as “present” in the fossil node (second calibration scenario; figure S5A and table (table S1 in ref. 1) but described as “present or absent” S2 of ref. 1) is not consistent with the bootstrap, because [supporting information (p. 2) in ref. 1]. The authors did it excludes the possibility that the fossil is a stem member not explore the robustness of phylogenetic results to of the Asteraceae + Calyceraceae clade. The third sce- alternative scoring, encoding, or Dasyphyllum sampling. nario placement is consistent with the fossil + Asteraceae + Readers should not construe finding Paleocene- Calyceraceae trichotomy supported by 69% bootstrap Eocene hothouse climate coincident with diversification proportion. The study’s six calibration scenarios illustrate of South American lineages as primarily due to the Dasy- the ambiguous phylogenetic position (identity) of Tubuliflor- phyllum + Barnadesia calibration. Ages for these diver- idites lilliei type A pollen that hinders unequivocal placement gences result chiefly from the placement here of the in chronogram construction. Mutisiapollis telleriae + Raiguenrayun constraint as ra- Furthermore, we should be cautious of sensational tionalized by Panero et al. (4), not at the Asteraceae conclusions underpinned by an inferred phylogenetic crown node shown by Barreda et al. (5). These two cal- relationship supported by few characters. Crucial char- ibrations placed in Asteraceae result in contrasting early acter scoring and encoding are particularly difficult from evolutionary patterns in Barnadesioideae vs. the sister taxa of the dispersed pollen fossil record (2). Extant clade (stem lengths in figure 5 in ref. 1). The authors Dasyphyllum, Chuquiraga,andDoniophyton have an do not comment on this interesting consequence of exine bilayer (3), but when the same character observed their calibration placement, an effect that shrinks when under light microscopy is scored (character 21), Dasy- the T. lilliei type A calibration is placed outside Asteraceae phyllum spp. share a single layer state with the fossil as (figure S5 in ref. 1). 1 Barreda VD, et al. (2015) Early evolution of the angiosperm clade Asteraceae in the Cretaceous of Antarctica. Proc Natl Acad Sci USA 112(35):10989–10994. 2 Crepet WL, Nixon KC, Gandolfo MA (2004) Fossil evidence and phylogeny: The age of major angiosperm clades based on mesofossil and macrofossil evidence from Cretaceous deposits. Am J Bot 91(10):1666–1682. 3 Tellería MC, Palazzesi L, Barreda VC (2015) Evolutionary significance of exine ultrastructure in the subfamily Barnadesioideae (Asteraceae) in the light of molecular phylogenetics. Rev Palaeobot Palynol 221:32–46. 4 Panero JL, et al. (2014) Resolution of deep nodes yields an improved backbone phylogeny and a new basal lineage to study early evolution of Asteraceae. Mol Phylogenet Evol 80:43–53. 5 Barreda VD, et al. (2012) An extinct Eocene taxon of the daisy family (Asteraceae): Evolutionary, ecological and biogeographical implications. Ann Bot (Lond) 109(1):127–134. Department of Integrative Biology, The University of Texas, Austin, TX 78712 Author contributions: J.L.P. wrote the paper. The author declares no conflict of interest. 1Email: [email protected]. www.pnas.org/cgi/doi/10.1073/pnas.1517649113 PNAS | January 26, 2016 | vol. 113 | no. 4 | E411 Downloaded by guest on September 28, 2021.
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