Thorn-like prickles and heterophylly in Cyanea: adaptations to extinct avian browsers on Hawaii?

The evolution of thorn-like structures in plants on oceanic islands that lack mammalian and reptilian herbivores is puzzling, as is their tendency toward juvenile-adult leaf dimorphism. We propose that these traits arose in Cyanea (Campanulaceae) on Hawaii as mechanical and visual defenses against h...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1994-03, Vol.91 (7), p.2810-2814
Main Authors: Givnish, T.J, Sytsma, K.J, Smith, J.F, Hahn, W.J
Format: Article
Language:English
Subjects:
ADAPTACION
ADAPTATION
ANATOMIA DE LA PLANTA
ANATOMIE VEGETALE
ANSERIFORMES
Archipelagos
Biological and medical sciences
Biological evolution
Biological taxonomies
Botany
Browsing
CAMPANULACEAE
Cyanea
Endemic species
EVOLUCION
EVOLUTION
Extinct species
FEUILLE
Fundamental and applied biological sciences. Psychology
Genetics of eukaryotes. Biological and molecular evolution
HAWAI
HAWAII
HERBIVORE
Herbivores
HERBIVOROS
HOJAS
Islands
Leaves
PATURAGE AERIEN
Plant spines
RAMONEO
Young animals
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Summary:The evolution of thorn-like structures in plants on oceanic islands that lack mammalian and reptilian herbivores is puzzling, as is their tendency toward juvenile-adult leaf dimorphism. We propose that these traits arose in Cyanea (Campanulaceae) on Hawaii as mechanical and visual defenses against herbivory by flightless geese and goose-like ducks that were extirpated by Polynesians within the last 1600 years. A chloroplast DNA phylogeny indicates that thorn-like prickles evolved at least four times and leaf dimorphism at least three times during the last 3.7 million years. The incidence of both traits increases from Oahu eastward toward younger islands, paralleling the distribution of avian species apparently adapted for browsing. The effectiveness of visual defenses against avian browsers (once dominant on many oceanic islands, based on the vagility of their ancestors) may provide a general explanation for insular heterophylly: the other islands on which this previously unexplained phenomenon is marked (New Zealand, New Caledonia, Madagascar, Mascarene Islands) are exactly those on which one or more large flightless avian browsers evolved.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.91.7.2810