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Abstract Detail

Annonaceae evolution: integrating molecules, biogeography and ecology


Evolution and phylogenetic significance of pollen morphology in Annonaceae.

The remarkable diversity of pollen morphology in Annonaceae has attracted systematic and evolutionary attention since the light microscopic, SEM, and TEM studies of Walker and Le Thomas in the 1970s and 80s.  Morphological cladistic analyses led to some general inferences that have held up, but increasingly detailed molecular phylogenetic analyses of the family have provided an unprecedentedly robust and well-resolved framework for analysis of pollen evolution and the systematic value of pollen characters.  Optimization of pollen characters on molecular phylogenetic trees confirms that the ancestral pollen type was monosulcate and had granular infratectal structure, as in the basal genus Anaxagorea, the near-basal subfamily Ambavioideae, and the closest magnolialean outgroups.  However, granular structure is derived from columellar in the context of angiosperms as a whole.  Both infratectal structure and other pollen characters are more homoplastic within Annonaceae than initially thought, but they do have considerable systematic value in parts of the tree.  Because columellar taxa (Annickia, Bocageeae) diverged earlier than previously thought in the two sister clades that make up most of the family, Malmeoideae (MPM clade, SBC) and Annonoideae (inaperturate clade, LBC), reticulate-columellar structure may have reoriginated in the common ancestor of these clades, but several reversals to granular structure occurred within both.  In Malmeoideae, several lines retain reticulate-columellar monosulcate pollen, but Miliuseae are united by loss of the sulcus and a shift to a verrucate tectum and show an uncertain number of origins of disulculate pollen.  Permanent tetrads arose several times in Annonoideae, as well as in isolated lines elsewhere, but they reverted to globose inaperturate monads in Isolona and probably Uvarieae, where one clade evolved small echinate pollen.  Lines that reverted to granular structure include not only Uvarieae but also Xylopia and Duguetieae.  Loss of the sulcus has been considered a synapomorphy of Annonoideae, but recognition by Tsou and Fu that microspores undergo rotation in tetrads of Annona and polyads of Cymbopetalum (Bocageeae) suggests that the proximal thin area in these taxa is a modified distal sulcus, implying that an aperture persisted some way into Annonoideae.  However, rotation does not occur in all groups with tetrads, and a broader developmental survey is needed to evaluate the significance of this phenomenon.

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1 - University Of California Davis, DEPT OF EVOL & ECOLOGY, One Shields Avenue, Davis, CA, 95616-8537, USA


Presentation Type: Symposium or Colloquium Presentation
Session: SY04
Location: Pines South/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 10:30 AM
Number: SY04006
Abstract ID:154
Candidate for Awards:None

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