Havran, J. Christopher , Ballard, H. E. .
Evolutionary mechanisms of pre-zygotic isolation in two replicate sublineages of Hawaiian Violet (Viola, Violaceae).
On the Hawaiian Islands, two sublineages of Violets, containing montane bog and swamp forest ecomorphs, are distributed on the islands of Kauai (Viola wailenalenae and V. kauaensis) and Molokai (V. robusta and V. maviensis). The two sublineages represent evolutionary replicates, separated by approximately 3 million years, and offer a unique opportunity to study the evolution of pre-zygotic isolation. During the summers of 2005 and 2006, the potential temporal, ethological and mechanical isolation mechanisms maintaining species integrity and limiting gene flow between intra-island taxa were investigated. On Kauai, observations of flowering phenology during July and August revealed that V. kauaensis produces cleistogamous flowers throughout most or all of this time period while V. wailenalenae produces only chasmogamous flowers. On Molokai, V. robusta and V. maviensis produce chasmogamous flowers concurrently. On both Kauai and Molokai, no Violet species were visited by insect pollinators. Pollinator exclusion experiments indicated that each species is capable of producing fruit in the absence of insect pollinators. Anatomical investigations of flowers that developed inside pollinator exclusion bags showed that the Hawaiian Violets are capable of producing fruit autogamously, perhaps by the delayed selfing mechanism characterized in eastern North American V. pubescens. On Molokai, the hybrid V. x luciae (V. maviensis x V. robusta) is confined to the bog-swamp forest ecotone. The hybrid has 37% pollen stainability, indicating that it has substantially depressed fertility, and produces malformed carpels and seeds (and is probably an F1). The presence of the hybrid, and lack of temporal isolation on Molokai, indicate that pre-zygotic isolation on this island are not as fully developed as on Kauai. Because no differences were observed to confirm other pre-zygotic isolation mechanisms (ethological and mechanical), temporal isolation may represent the last step in the establishment of complete pre-zygotic isolation among co-occurring sister species of Hawaiian Violets.
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1 - Ohio University, Department of Environmental and Plant Biology, Porter 315, Athens, OH, 45701, U.S.A.
2 - Ohio University, Department of Environmental & Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Lake Ontario/Hilton
Date: Tuesday, July 10th, 2007
Time: 8:45 AM