Scouler's catchfly (Silene scouleri ssp. grandis): COSEWIC assessment and status report: chapter 6
Biology
General
Silene scouleri ssp. grandis is a tap-rooted perennial species with a shallowly buried caudex that gives rise to multiple stems that form compact genets. Large clumps may die off in segments as in Silene douglasii var. oraria (Kephart and Paladino 1997). This could produce gaps creating several weakly separated clumps from a single genet. Silene scouleri ssp. grandis does not possess rhizomes or any other means of vegetative reproduction. No information is available on its biology and ecology in British Columbia.
Reproduction
Little is known about pollination and reproduction in Silene scouleri ssp. grandis. Several species of Silene are self-compatible (Kephart and Nebenzahl 1983, Lesica 1993, Menges 1995). Jürgens et al. (1996) noted that the stigmas of some Silene are receptive in the bud and flowers may be capable of selfing. Lesica (1993) concluded that flowers of S. spaldingii rarely self-pollinate because the anthers shed their pollen before styles expand, although he observed limited fruit development in flowers denied access to pollinators.
Sticky-glandular hairs on the foliage and calyx tube capture small insects that try to steal nectar without pollinating the flowers hence the common name, catchfly.
Seed production in some species of Silene decreases greatly when pollinators are excluded (Lesica 1993, Menges 1995) and juvenile plants from selfed seed may be substantially smaller than those from open-pollinated seed (Lesica 1993). Many species of Silene are pollinated by insects including bumblebees, moths and mosquitoes (Brantjes and Leemans 1976, Kay et al. 1984, Kephart and Nebenzahl 1983, Lesica 1993, Pettersson 1991). They typically possess nectaries at the base of their stamens (Jürgens et al. 1996). The larger and more colourful Silene regia is pollinated by hummingbirds rather than insects (Menges 1995) but this appears to be an exception.
Silene scouleri ssp. grandis at Trial Island matured slowly in 2001 and 2002. A few of the earliest flowers produced abundant mature seed as early as September while others still had pale, small seeds or no seeds at all by late October.
Survival
Silene scouleriseeds typically germinate best at about 20ºC when sown in a pot of stone mulch such as grani-grit, placed in polyethylene bag. Germination occurs over 2-5 weeks (Deno 1994; Jane Grushow, professional gardener, pers. com. February 2002; Tom Clothier, native seed supplier, http://users.anet.com/~manytimes/page62.htm). Seeds of Silene douglasii and S. spaldingii, two closely related species, appear to require cold stratification as germination occurs mainly in spring (Lesica 1988, Kephart and Paladino 1997).
There is no documentation of factors affecting the establishment of Silene scouleri ssp. grandis seedlings. Seedlings of Silene douglasii var. oraria had higher survival rates in burned areas compared to unburned plots, which may be attributable to higher seedling mortality in areas of thick litter (Kephart and Paladino 1997). Silene spaldingii produces rosettes in the first summer and flowers during or after the second season (Lesica 1993).
Perennial species of Silene may survive for several to many years under natural conditions (Marsden-Jones and Turrill 1957).
Field observations of the Trial Island population during the summers of 2000, 2001 and 2002 did not reveal any significant cases of adult mortality. There was no evidence of leaf or flower herbivory in either population, aside from a light infestation of spittlebugs on one Trial Island plant in 2001.
The small population that once occurred on Mount Tzuhalem gradually declined in vigour during the 1990s, first failing to flower and finally failing to overwinter. This atypical site is approximately 250 m above sea level and climatic limitations may have led to the population’s demise.
Individuals of both Silene spaldingii and S. douglasii var. oraria may reappear after a year of dormancy, as desiccated stems produce new plants (Kephart and Paladino 1997, Lesica and Steele 1994).
Physiology
The physiology of Silene scouleri ssp. grandis has not been studied.
Movements/dispersal
There is no information on gene dispersal by Silene scouleri ssp. grandis. Insects are presumably capable of dispersing pollen over short distances but between-population dispersal in Canada is unlikely given the distances involved. It is possible that some gene exchange may occur between Trial Island and Little Trial Island, which are only 500 m apart.
Seeds of Silene scouleri ssp. grandis lack any strong adaptations for long-distance dispersal and most seeds are probably gravity-dispersed, although the pimply surface texture may aid in short-distance wind dispersal as with other species in the genus (Marsden-Jones and Turrill 1957). During a 10-year study, Silene douglasii var. oraria, another rare species of coastal grasslands, was not able to colonize a network of vacant quadrats within an established population (Kephart and Paladino 1997).
The localized distribution and well-documented history of populations in British Columbia suggest that dispersal and establishment of new populations is rare.
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