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Abstract Detail



Developmental and Structural Section

Lens, Frederic [1], Davin, Nicolas [2], Smets, Erik [2].

Secondary woodiness within angiosperms. A case study on the Canary Islands.

Charles Darwin's ingenious ideas on the theory of evolution by natural selection originated when he visited islands, which are still considered to be natural laboratories of evolution. Gigantism in small animals or flightlessness in birds are examples of insular animal evolution, but also insular floras typically include species with a remarkable degree of woodiness. This so-called insular woodiness - or more broadly circumscribed as secondary woodiness - was described and interpreted correctly by Darwin, who stated in his famous work On the origin of species that natural selection would increase wood development in herbaceous plants when growing on an island. Darwin's hypothesis that at least some woody island endemics have continental herbaceous ancestors is supported by recent results, but his idea received many criticisms because it was - and still is -  generally accepted that the opposite shift from (primary) woodiness towards herbaceousness is much more common in flowering plants. We are working on the first world-wide secondary woodiness review within flowering plants at the genus level, in which all available information on molecular phylogenies, revisions, floras and wood anatomical papers is assembled and interpreted. It is clear that secondarily woody genera are more abundant in the later diverging lineages of angiosperms (mainly asterids), and are mostly restricted to islands or confined to island-like regions such as tropical mountain peaks. Surprisingly, a considerable proportion of the secondarily woody angiosperms only grow in markedly dry continental regions such as savannas or (semi-)deserts, suggesting that an increased wood development in these groups might help plants to achieve a stronger embolism resistance by avoiding too much air bubble formation inside its vessels at a certain negative pressure. In this paper we present the results of our investigation on the presence of secondary woodiness on the Canary Islands. The Canary Islands flora is characterized by at least 38 independent shifts towards insular woodiness, representing an important part of the endemic angiosperms on the archipelago. These parallel evolutionary events emphasize the remarkable plasticity in growth forms between herbaceous and woody lineages, but it remains puzzling which environmental variables trigger these shifts and how these independent shifts are regulated genetically. However, the majority of the insular woody taxa on the Canaries typically grow in the dry coastal regions, supporting the possible causal link between increased embolism resistance and the increase of woodiness.

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1 - Naturalis Biodiversity Center, Leiden University, P.O. Box 9514, Leiden, N/A, 2300RA, Netherlands
2 - Naturalis Biodiversity Center, PO Box 9517, Leiden, 2300RA, Netherlands

Keywords:
Insular woodiness
Secondary woodiness
Angiosperms
Canary Islands
Embolism
parallel evolution
Anatomy.

Presentation Type: Oral Paper:Papers for Sections
Session: 15
Location: Jasperwood/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 8:45 AM
Number: 15004
Abstract ID:380
Candidate for Awards:None


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