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Paulina Anna Zigelski

Paulina Anna Zigelski's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at Hamburg University in the year 2016.

Title of awarded thesis

"Molecular biogeography of the Syzygium guineense complex: How environment and genetics push suffrutication in Africas Miombo region"

For the first time the origins of „underground trees“ in southern Africa were investigated in detail using a model species: an interaction of environmental and genetic factors play a crucial role in their evolution.

The woodland-grassland mosaic of the Miombo region in southern Africa is home to a curious phenomenon: Many woody species of different plant families grow as regular trees in these woodlands but have closely related taxa in the open plains, growing as dwarf shrubs with huge underground woody biomass, as “underground trees” or so called geoxylic suffrutex.

The model species Syzygium guineense (Willd.) DC s.l. was chosen to clarify the degree of relatedness between tree and suffrutex. The roles of environment and genetics upon the growth forms and the suffrutex evolution of were furthermore investigated and assessed. Seven different phenotypes of S. guineense were identified, sampled and ecologically and genetically via sequence- and SSR- analysis characterized.

All phenotypes were genetically very close, whereas nonetheless three distinct genotypes were identified that correspond to broader ecotypes: a water-dependent tree-ecotype growing alongside rivers, a stress tolerant shrub-/tree-ecotype growing on ferralitic soils of Miombo woodlands and finally the suffrutex-ecotype of open sandy plains. The genetic patterns and their similarity in contrast to their strong ecological distinction point to a common ancestor from humid tropical regions which speciated in several directions due to changing environmental conditions. A climate change approx. 2.5 mya led to increased precipitation seasonality with marked wet and dry seasons and accordingly habitat loss for tropical humid biota. Evolutive adaptation had been facilitated for S. guineense by ist polyploidy, a genetic preadaptation that enhances responsiveness to environmental factors. Of these, frost and fire are probable initiators of the suffrutex lifeform as both events became more frequent with marked dry seasons. Therefore the combination of genetic preadaptation and filtering environmental factors were probable drivers of the S. guineense suffrutex evolution, yet not enough time has passed to call it a separate species. 

more information about the project: http://www.biodiversity-plants.de/theses_bee.php?lang=en

Her thesis is published: http://www.biodiversity-plants.de/publications_bee.php?pers_publ=108

Paulina Anna Zigelski conducted this work at the Biozentrum Klein Flottbek of Hamburg University in the working group of Prof. Dr. Norbert Jürgens.

Phenotypic varieties of Syzygium guineense s.l., S. benguellense (middle left) and S. cordatum (upper right). This morphological diversity is a response to adaptation to different habitats of southern Africa like rivers, flood plains, open grasslands, more or less open woodlands and mountainous areas.Photos: Paulina Zigelski
Three Syzygium-phenotypes had been distinguished ecologically as well as genetically. Both sequence analysis and microsatellite analysis showed genetic differentiation as can be seen in the figure of the STRUCTURE analysis above. Therein three genetic groups had been identified of which one corresponds to the “underground trees” of sandy soils, another to the shrub/tree form of ferralitic, open woodland sites and the last to trees of wet sites. Photos: Paulina Zigelski