Evolutionary Developmental Biology (Evo-Devo)
Hearn, David , McDade, Lucinda A. .
Major evolutionary transitions in plant form are coupled across the eudicots: Revisiting convergent evolution of succulent lineages.
Stem succulence (SS) is a major evolutionary innovation that permits some plants to live in dry and hot habitats. Despite multiple centuries of interest in succulent plants, relatively few studies have examined the evolutionary consequences of SS in an explicit phylogenetic context. Prior phylogenetic work focused on Adenia (Passifloraceae) suggested that both SS and tubers evolved on multiple occasions, that transitions in abundance of succulent tissue between close relatives can be dramatic, and that the time scale of transition can be on the order of hundreds of thousands of years. What can account for frequent and rapid transitions from non-succulent ancestors to succulent descendants? Are there commonalities among separate origins? The approach to investigate these questions was double-edged. First, anatomy of young and mature stems and tubers of 58 species of Adenia (Passifloraceae) was studied in an explicit phylogenetic context. The diversity of cambial variants (CVs) in Adenia is found to be high, so Carlquist’s innervation hypothesis is tested. The innervation hypothesis predicts that evolutionary gains of SS will be associated with gains of CVs that facilitate transport through water storage tissue. Felsenstein’s method of independent contrasts revealed that gains of CVs are statistically associated with gains of SS in corroboration of the innervation hypothesis. Moreover, it was observed that tubers share the relatively uncommon CVs observed in succulent stems. Second, a novel comparative method, the ancestral distance test, investigated the generality of these patterns. Across eudicots, tuberous plants are found to be more closely related to stem succulents than expected by chance, and both tubers and succulent stems evolved on multiple occasions within several groups. These observations are discussed in light of evolutionary-developmental models.
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1 - University of Arizona, Plant Sciences, Forbes Room 303, Tucson, CA, 85721, USA
2 - Rancho Santa Ana Botanic Garden, 1500 N. College Ave., Claremont, CA, 91711, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Astoria Room/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:30 AM