| BEN |
| BOTANICAL ELECTRONIC NEWS |
|---|
| ISSN 1188-603X |
| No. 215 February 21, 1999 | aceska@victoria.tc.ca | Victoria, B.C. |
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This Symposium is organized by the School of Environmental Studies and Restoration of Natural Systems Program, University of Victoria, in Partnership with The Pacific Wildlife Research Centre of The Canadian Wildlife Service and The Garry Oak Meadow Preservation Society.
The Garry Oak Meadow constitutes a major distinctive ecosystem complex in North America. Today these ecosystems are under serious threat from urban growth, land management practices and invasion by exotic species. The threats to these biologically diverse ecosystems are particularly acute in the only area of Garry Oak Meadow in Canada, on southern Vancouver Island and the Gulf Islands. Interest and concern about this special ecosystem complex in Canada and adjacent United States has grown dramatically. We invite you to join us in a Symposium and Community event to learn about and celebrate our Garry Oak Meadow ecosystems.
We will be addressing issues concerning biology, ecology, ethnobotany, management, restoration, conservation, protection and education of Garry Oak Meadow ecosystems. In celebration, there will be art exhibits, music, festivals, story telling, dancing and children's activities and much, much more focusing on Garry Oak ecosystems.
We will have special speakers representing of the Garry Oak ecosystems from California to British Columbia and from other Oak ecosystems too. If you are interested in participating, or for further information, please contact UVic Conference Management or consult our WEB page:
You are welcome to present a Poster (to be mounted on a 4' x 4' board) on any topic related to Garry Oak ecosystems, please see the following WEB site for details:
For more information contact:
Henderson's checker-mallow, Sidalcea hendersonii Wats. (Malvaceae) is a perennial herb inhabiting low elevation wet meadows and tidal marshes from southwestern British Columbia to Oregon. In British Columbia, Sidalcea hendersonii is listed as "blue" - vulnerable (Douglas et al. 1998). This designation is used for indigenous species of special concern because of characteristics that make the species particularly sensitive to human activities and natural events. Several factors contribute to the plant's rarity including human encroachment into wetland habitats, displacement by aggressive invasive species such as Lythrum salicaria, and insect seed predation.
Sidalcea hendersonii is gynodioecious. This is a mating system whereby populations consist of separate coexisting hermaphroditic individuals and female individuals. Hermaphroditic Sidalcea hendersonii flowers contain both functional anthers and ovaries, are self-compatible but protandrous. Female flowers have functional ovaries but nonfunctional stamens. In gynodioecious species, female plants would seem to have a reproductive disadvantage relative to hermaphrodites since they do not contribute genes through pollen (Lewis, 1941). Females must produce significantly more seeds than hermaphrodites for male sterility mutations to be maintained in gynodioecious populations (Charlesworth and Ganders, 1979).
We investigated the genetic and ecological factors contributing to the maintenance of females in British Columbian populations of Sidalcea hendersonii - see Marshall 1998. Crossing experiments indicated that male sterility is controlled by a dominant
nuclear allele. High frequencies of female plants in the majority of populations surveyed, in combination with the nuclear determination of sex, elevates the theoretical requirements for female fitness in this species. Females did have higher fitness, producing more surviving offspring than hermaphrodite plants in an experimental population. However, no inherent fitness advantages were evident in natural populations where females and hermaphrodites did not differ in viable seed production.
Two species of Curculionid beetles (weevils), Macrorhoptus sidalcea Sleeper and Anthonomus melancholicus Dietz, parasitize the flowers of Sidalcea hendersonii in British Columbia. Anthonomus melancholicus is restricted to populations of Sidalcea hendersonii located on Vancouver Island, where the frequency of females was unusually high. In populations where female plants were abundant, weevil larvae destroyed significantly more seeds from hermaphrodite plants, substantially reducing hermaphrodite seed production overall. The extent and mode of seed predation was dependent upon which weevil species was present in the population. In populations where Macrorhoptus sidalcea was present, the seed was only partially consumed. While M. sidalcea larvae feed on the interior of the seed, creating small tunnels in the seed coat, Anthonomus melancholicus larvae appear to consume the entire fruit. Sex-related predation was evident only in populations where Anthonomus melancholicus occurred (on Vancouver Island) and was correlated with the more destructive feeding pattern of this weevil.
The basis for discrimination between flower types was not investigated, but adult A. melancholicus weevils are likely attracted to hermaphrodite flowers because hermaphrodite flowers also contain pollen, a known food source. Extensive predation of hermaphrodite seed could provide the necessary advantage to females of Sidalcea hendersonii. To our knowledge, this study provides the first evidence that sex-related predation may be responsible for high female frequencies in natural populations of a gynodioecious species.
References
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