Systematics/Phytogeography / Taxonomie/ Section
Fishbein, Mark , Agrawal, Anurag .
Are Milkweeds Getting Hairier? An Evaluation of Herbivore-Driven Escalation of Trichome Density in Asclepias (Apocynaceae).
A long-standing theory of the coevolution of plants and their herbivores predicts an escalation of plant defenses in response to increasing ability of herbivores to circumvent defenses. Many studies have demonstrated the selective advantage within populations of mechanical defenses, such as trichomes, but only rarely has the prediction of escalation been tested. Recently, we demonstrated the correlated evolution of dense trichomes and copious latex, which together form one of three alternative defense strategies in milkweeds (Asclepias, Apocynaceae). More recently, we showed, paradoxically, that over the evolutionary history of milkweeds, there has not been an escalation of investment in trichomes and latex, as measured in greenhouse-grown representatives of 37 species. Here, we further test the escalation hypothesis using trichome density measurements from herbarium specimens of 90 of the 130 species of Asclepias. Escalation of trichome density is evaluated against the null hypothesis of random evolution in a likelihood framework under gradualistic and speciational models of evolution.
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1 - Portland State University, Biology Department, Po Box 751, Portland, Oregon, 97207-0751, USA
2 - Cornell University, Department of Ecology & Evolutionary Biology, Corson Hall, Ithaca, New York, 14853, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, July 30th, 2008
Time: 8:30 AM