Reproductive ecology of Trillium recurvatum (trilliaceae) in Wisconsin.
Pollen limitation due to low or variable frequencies of pollinators or pollination can be an important factor contributing to reduced population vitality and the survival capacity of a species (Bierzychudek, 1981; Johnston, 1991; Anderson, 1995; Bernadello et al., 1999; Holsinger, 1999; Karrenberg and Jensen, 2000; Cane and Tepedino, 2001; Wilcox and Neiland, 2002; Ashman et al., 2004; Knight et al., 2005). This is especially evident in fragmented habitats that are strongly influenced by human activities (Wilcox and Murphy, 1985; McNeeley et al., 1990; Brown and Kephart, 1999; Cunningham, 2000; Kery et al., 2000). Habitat fragmentation disrupts effective metapopulation structure, creating small isolated populations that are prone to extinction (Holsinger and Gottlieb, 1991; Menges, 1991a; With and Crist, 1995). Fragmentation also interferes with plant-pollinator interactions essential for effective reproduction (Janzen, 1974; Howe, 1984). The consequences of reduced pollinator visitation as a result of fragmentation and consequent pollen limitation can be severe, greatly increasing extinction probabilities (Harris and Johnson, 2004). Effects include a reduction in gene flow and maintenance of selfing rates (Morgan and Wilson, 2005), a smaller effective population size (Bawa, 1990; Menges, 1991b; Aizen and Feinsinger, 1994), loss of genetic variability within isolated populations and reduced progeny fitness due to inbreeding depression (Lloyd, 1965; Frankel and Soule, 1981; Karron, 1989; Templeton et al., 1990; Barrett and Kohn, 1991; Menges, 1991b), a loss of incompatibility alleles in obligate self incompatible species (Mauro, 1989; Les et al., 1991; Reinartz and Les, 1994) or absolute reproductive failure (Jennersten, 1988; Bawa, 1990).
The Endangered Species Act of 1973 (16 U.S.C. 1531-1544: USFWS, 2002) mandates the development and implementation of recovery plans for endangered and threatened species. Among the significant factors influencing the abundance of plant species is their reproductive system (Holsinger, 1991; Schemske et al., 1994; Weller, 1994). Effective reproduction in flowering plants often may depend upon insect pollinators (Macior, 1974; Buchmann and Nabhan, 1996; Levin, 2006; Losey and Vaughan, 2006). It is estimated that 67% of all flowering plants rely on insects for pollination and, hence, fruit and seed production (Tepedino, 1979). A comprehensive knowledge of the breeding system of rare entomophilous plant species currently listed as Special Concern (SC) will provide conservationists with an understanding of why species are rare, and aid in developing and implementing their recovery plans should they become threatened or endangered.
Although recognized as vital to the reproductive fitness of plants, surprisingly few studies of the reproductive biology of rare entomophilous species (Kevan, 1975; Buchmann and Nabhan, 1996; Kearns and Inouye, 1997; Spira, 2001) and even fewer comparative studies involving pollen limitation as a cause of rarity have been conducted (Sutherland, 1986; Burd, 1994; Larson and Barrett, 2000). The dearth of studies in basic pollination biology is so apparent that Kearns et al. (1998) called for a redoubling of "... efforts to study basic aspects of plant-pollinator interactions in natural and agricultural systems." The lack of studies is evident regardless of the size of the area considered. For example, from among the 89 rare, entomophilous, flowering plant species with congeners in Wisconsin and currently ranked as SC by the Wisconsin Department of Natural Resources (Jan. 2007), the pollination biology of only seven (7.9%) have been studied. Only one of these studies was undertaken in Wisconsin (Iltis, 1963).
Trillium recurvatum is a long lived perennial found in the southern part of the state, its northernmost distributional range and an area subject to considerable habitat fragmentation. It has perhaps the seventh greatest distributional range of the trilliums (Case, 2002). It is ranked as S3 with a status of SC (species of which an abundance or distribution problem is suspected but not proven; the category focuses attention on species before becoming threatened or endangered) by the Wisconsin Department of Natural Resources. The S3 ranking means the species is rare or uncommon with 21 to 100 occurrences. There are 87 collections in the Wisconsin State Herbarium, 26 (29.8%) from Green County, 55 (63.4%) from Green, Racine and Milwaukee Counties. Of the more recent collections (1975 to present), 14 of 44 (31.8%) are noted as being common or abundant at non-overlapping sites. If these comments remain accurate, it implies that only 14 well populated sites persist in Wisconsin. This is a sufficiently small number to either place this species on threatened status or SC with an S2 ranking (6 to 20 occurrences). Its imperilment is likely due to forest fragmentation, development and loss of habitat to agriculture, but pollen limitation also may contribute significantly.
This species may reproduce sexually or vegetatively via rhizomes. Ohara and Utech (1986) found that a single rhizome of Trillium lancifolium Raf., perhaps the closest relative of T. recurvatum (Gates, 1917; Kawano and Kato, 1995; Farmer and Schilling, 2002; Farmer, 2006), produces two or three flowering offshoots, the eldest of which eventually disassociates from the parent and establishes itself independently. The breeding system of T. lancifolium and most other sessile flowered trilliums has yet to be investigated. Little is known about asexual reproduction, the breeding system or the reproductive ecology of T. recurvatum in Wisconsin.
To determine if consistent differences existed in the breeding systems and pollen availability between common and rare species of sessile flowered Trillium, the author determined that aspects of the reproductive ecology of common and rare closely related congeners should be compared and discussed (Kunin and Gaston, 1997; Young and Brown, 1998; Hegde and Ellstrand, 1999; Lloyd et al., 2002; Rymer, 2006; Farnsworth, 2007) where data was available. Special interest was focused on T. sessile that likely possesses a mixed breeding system (Ihara, 1973; Whitkus et al., 1987) and is pollinated by flies and beetles in Tennessee (Robertson, 1896; Patrick, 1975; see Table 1 for differences). Both trilliums are in subgenus Phyllantherum and are closely related (Freeman, 1975; Kawano and Kato, 1995; Farmer and Schilling, 2002; Farmer, 2006). These comparisons should give an idea of how T. recurvatum contrasts with other sessile flowered species and it was hoped that the reasons for the rarity of T. recurvatum due to pollen limitation, if present, might become clearer.
This study tests the hypothesis that either lack of pollinators or lack of pollen distribution contributes to the rarity of Trillium recurvatum in Wisconsin. To this end, the breeding system and reproductive ecology of T. recurvatum were investigated. Its reproductive ecology was compared to published results for other sessile flowered Trillium species where available.
To test the hypothesis that Trillium recurvatum is pollen limited, field studies were conducted among wild plants in three forested sites in southern Wisconsin (Green, Jefferson and Waukesha Counties) during the spring months of 2002, 2003 and 2004. In addition to forested areas, the Jefferson County site also contained plants that were in an unshaded, extended, roadside ditch. Populations were mapped; estimates of population sizes were made by counting plants within a site or by laying out ten, randomized, 10 x 10 meter quadrats and extrapolating total estimates for plant counts. Plant densities were determined for each site. Because 7: recurvatum reproduces vegetatively by rhizomes, several plants were excavated and replanted; the number of flowering ramets (mean = 2.3 [+ or -] 0.21; n = 10) projected from these observations was divided into the number of flowering stalks to estimate the number of genets in a site. Overall integrity of habitats was assessed by determining overall presence/absence of invasive species establishment within a site.
To obtain a quantitative estimate of pollinator activity and thereby an estimate of outcrossing frequency in wild populations, 288 individual plants (30 in Green, 96 in Jefferson and 162 in Waukesha Counties) from eight areas were observed and assessed during 10 min intervals for the frequency of insect visitation and patterns of insect movement. Forty-two plants in a 1 ac forested area in Green Co., 56 plants in a 1 ac forested area and 30 plants in a 1/2 ac open ditch area in Jefferson Co. and 32 plants each in five 10 x 10 m forested areas in Waukesha Co. were observed for a total of 144 total hs. Each plant was observed for three 10 min intervals. Observations were performed in 2003 and 2004 at anthesis during early morning, midday and late afternoon just before dusk for each plant. Because the flowers are deep reddish-purple, it was not believed that night pollination was a viable option. Several drops of Tauglefoot[R] also were applied to the base of 36 flowers in the Waukesha site via toothpicks to trap insect visitors. Insects considered to be effective pollinators were those that visited many flowers on different plants and that did not spend a great deal of time on any one plant (Faegri and van der Pijl, 1979). Insect visitors and pollen from flowers of Trillium recurvatum were collected via killing jars containing ethyl acetate the covers of which were quickly closed over flowers when visitors were detected. Insect visitors were later surveyed for the presence or absence of T. recurvatum pollen grains via light microscopy. Pollen traces were removed and compared with those collected from T. recurvatum anthers. Pollen of T. recurvatum was quite distinct and easy to detect (Takahashi, 1982). Later in 2008 4 h of observations during 10 min intervals were conducted on 84 plants at the Jefferson County site and collection of insects was once again undertaken; pollen from collected insects was again compared with pollen from T. recurvatum anthers. Insect specimens were vouchered.
Pollen and seeds taken from fruit of wild plants were used to estimate pollen and seed viability. Seed viability was estimated among 100 randomly collected seeds pooled from among 100 plants from all three populations following the procedures of Moore (1962) using tetrazolium red. Pollen viability was estimated using pollen from single anthers collected from 17 randomly selected plants at the Waukesha site using in vitro pollen germination in a 10% sucrose solution (Kearns and Inouye, 1993). Pollen to ovule ratios were calculated to obtain an estimate of breeding system dynamics (Cruden, 1977). Pollen was removed from unopened anthers on 17 randomly selected flowers and preserved in 70% alcohol. Pollen grains were counted using a haemocytometer following Lloyd (1965). Ovules (and seeds) were collected from ripened fruits later in the season from the same 17 flowers to determine the number of ovules per flower. The number of ovules per flower was divided into the estimated number of pollen grains per flower to determine pollen to ovule ratios.
To determine the breeding system, i.e., if plants were self-compatible or self-incompatible, and whether plants were pollen limited, crossing studies were conducted in the field at each of the sites. Plants used in crossing studies were at least 2 m apart to insure that genets were being sampled. Unbagged control (open pollinated) groups (n = 20 plants at each site) were designated and left unbagged. A group of plants (n = 20 plants at each site) were crossed with pollen from the same flower (autogamous hand pollinations) to determine if plants were self-compatible. These plants also acted as bagged controls, excluding pollinators. Pollen was taken from the anthers of these plants and deposited on receptive stigmatic surfaces of the same plants. These plants were bagged before and after crosses were performed to exclude pollinators. A group of plants (n = 20 plants at the Green County site, n = 40 plants at the Jefferson County site, n = 59 plants at the Waukesha County site) were crossed (xenogamous hand pollinations). Crosses were conducted to determine if outcrossing via hand pollination could improve fruit or seed set over that in open pollinated controls, thus demonstrating pollen limitation. Among these xenogamous crosses flowers were bagged before and after crosses were performed to exclude pollinators that might confound the results. Anthers of plants receiving pollen were removed before they opened to prevent the possibility of selfing and pollen from a distant plant was deposited on receptive stigmas. Pollen from the closest neighbor of these plants (presumed to be a ramet) was removed and deposited on the closest neighbor of the distant pollen donor from which anthers had been removed. Fruits were removed from among 20 xenogamous hand and 20 open pollinated plants and preserved in 70% alcohol (three from Green, five from Jefferson and 12 from Waukesha Counties). Fruit and seed set were calculated for each type of cross and for open pollinated controls later in the season. Fruit set was calculated by dividing the number of fruits produced into the number of plants crossed. Seed set was calculated by dividing the number of seeds produced into the total possible ovule number per fruit. Plants were not tested for the possibility of apomictic fruit production. ANOVAs on log transformed data were performed to compare fruit and seed set data among xenogamous hand pollinated and open pollinated crosses using OpenEpi Statistics program version 2.2.1 (Dean et al., 2007). Fruit and seed set in the wild populations were calculated among randomly sampled early flowering (first flowering before May first) and late flowering (first flowering after May 22) plants.
Potential number of ovules was calculated from 24 randomly selected fruits, three from Green Co., seven from Jefferson Co. and 14 from Waukesha Co. in 2004 to calculate ovule numbers and mean seed numbers and weights. Fruits were stored in 70% alcohol. Seeds were counted, extracted and air dried for 48 h. Of these, 100 pooled seeds were randomly selected and weighed on a Denver APX-60 balance (Denver, Colorado, USA) for comparison with other Trillium species (Ohara and Utech, 1986). Seed counts were compared to those for other sessile flowered trilliums using a G-test. Seed weights between Trillium recurvatum and T. lancifolium also were compared using paired t-tests.
In summary, populations were mapped and population densities estimated. Frequency of insect visitation and patterns of insect movement were assessed. Insect visitors were surveyed for presence/absence of Trillium recurvatum pollen grains. Pollen and seed viabilities were estimated. To determine the breeding system of T. recurvatum, fruit and seed set in autogamous and xenogamous hand pollinations were compared with that in open pollinated controls using ANOVAs. Number of ovules, number of seeds, seeds per ovule and seed weights were calculated and compared with other sessile flowered trilliums.
In southern Wisconsin where soils are limestone derived (Curtis, 1971), Trillium recurvatum does well in rich, mesic, southern hardwood forested sites as well as in more open mesic sites. Genets were exponentially greater in density from site to site (Table 2). Flowering stalks projected from the tips of rhizomes that reached lengths of up to about 6.5 cm. Bloom times extended from the last week in Apr. to the last week in May. Petals on plants growing in open areas faded from purple to yellow in age, however a morph yellow throughout anthesis was present in open areas of the Jefferson County site. Stigmas became receptive slightly after most of the anthers within a population became receptive and remained receptive throughout anthesis. Anthers were incurved and likely came into contact with mature stigmas at anthesis.
During the many hours of observations among plants neither insect visitors nor potential pollinators initially were observed. The application of Tanglefoot[R] to the base of flowers also proved ineffective at trapping insect visitors. Two visitors eventually were found. Both carried pollen of Trillium recurvatum. One was one of six possible brightly-colored species of Collops Say (subfamily Malachiinae, family Melyridae) found in Wisconsin. These are predacious softwinged flower beetles. Only two specimens were found during the 3 y of observations. They were sedentary within flowers and were never seen to move or visit neighboring flowers. A voucher specimen of this species was unavailable because both intact specimens were inadvertently destroyed after identification. In 2008 at the Jefferson County site large numbers of Coleomegilla maculata, family Coccinellidae, were observed visiting greater than 80% of observed flowers of T. recurvatum. These native ladybeetles were continually on the move visiting many flowers for short to long durations often mating within flowers and eating pollen. Several specimens were collected, vouchered and inspected for the presence of T. recurvatum pollen. All specimens carried T. recurvatum pollen (Fig. 1).
Pollen viability (n = 17 flowers) was estimated to be 93.7%. Mean pollen grains per flower (n = 17 flowers) was 187,254 [+ or -] 12,208 (range = 100,000-388,900) and mean ovules per flower (n = 17 flowers) was 61.2 [+ or -] 5.0 (range = 36-107; Table 3). The estimated pollen to ovule ratio was 3255 to 1 and was highly variable among the 17 flowers investigated (Table 4). The mean number of ovules per fruit was intermediate among the six sessile flowered species investigated by Ohara and Utech (1986; Table 3).
Autogamous crosses (n = 58) produced less than 2% fruit set overall. In open pollinated controls (n = 59), mean fruit set was 31.7 [+ or -] 3.4%, less than most species of Trillium for which this variable has been measured (Broyles et al., 1997; Griffin and Barrett, 2002; Table 2). An ANOVA on log transformed data showed this to be significantly less than in xenogamous hand pollinations (n = 97; Table 5). Fruits producing no seeds did not develop. Mean seed set in open pollinated controls (n = 14 fruits) was 77.1 [+ or -] 4.2%, much higher than that for other sessile flowered Trillium for which these data have been collected (Ohara and Utech, 1986). An ANOVA on log transformed data showed this to be significantly greater than for xenogamous hand pollinations (n = 21 fruits; Table 6).
Seed viability (n = 100) was estimated to be 85.7 [+ or -] 3.1%. In wild populations plants produced 28.7 [+ or -] 15.3 seeds per fruit (n = 24; range = 5-64; Table 3). This was 157% greater than the average number of seeds (18.3 [+ or -] 6.1; range = 2-65) produced by the six sessile flowered species investigated by Ohara and Utech (1986; Table 3). Seed numbers were significantly different among the seven species of Trillium evaluated (G = 14.0; df = 6; P = 0.0245). Seed weight (n = 100) was very low (range = 1.1-6.3 mg), the lowest of any sessile flowered Trillium measured to date including its closest relative T. lancifolium (Table 3). A t-test with unequal variance showed seed weight between these two species to be significantly different (t statistic = 11.41; df = 67; P = <<0.00001).
Because fruit set was significantly greater in outcrossed hand pollinations than in open pollinated controls, it is inferred that this species is likely pollen, not resource, limited. The high seed set in open pollinated controls implies that, although plants have insufficient pollen delivery to provide substantial fruit set, pollinators are delivering sufficient pollen from selected flowers to fertilize a large percentage of ovules. A lack of fruit found in nearly all autogamously hand pollinated plants and the high pollen to ovule ratio (Cruden, 1977) strongly suggest that this species, unlike Trillium sessile, is self-incompatible. The relatively low fruit set in hand pollinations and the proximity of pollen bearing anthers to receptive stigmas indicates a self-incompatibility mechanism. This was not investigated in this study.
In this study, pollen limitation was demonstrated for Trillium recurvatum. Pollen limitation may result from the establishment of adaptive traits in a given environment, enhancing fitness in that environment (Givnish, 2003) or from inadequate pollen delivery resulting from the stochasticity of the pollination system in ecological situations that restrict pollinator activity (Burd, 1995). Adaptive traits possessed by T. recurvatum in its forest environment include its polycarpic, perennial, rhizomatous habit; its self-incompatibility [vs. mixed mating system in its close relative T. sessile (Whitkus et al., 1987)]; production of large quantities of ovules and seeds in wild populations [average of 61 ovules and 47 seeds/plant vs. 32.6 ovules and 9.7 seeds/plant in its closest relative T. lancifolium (Ohara and Utech, 1986); Table 3] and its occurrence as a spring ephemeral, allowing it to take advantage of available light before canopy cover occurs later in the season. None of these traits serve to directly explain the reasons for pollen limitation. There are likely two major reasons for pollen limitation in this species. First, pollination patterns are observably stochastic. What is now considered to be the primary effective pollinator of this species, Coleomegilla maculata, exhibits swarming patterns in the spring (late May and early Jun.; Nault and Kennedy, 1999) and visits plants on an irregular basis. Although an effective pollinator known to include pollen in up to 50% of its diet (Atallah and Newsom, 1966) and likely often present, they were not observed over the initial 3 y period of this study. They may have been overlooked or may have emerged early or late during those years. Extensive habitat fragmentation in southern Wisconsin also may influence the frequency of these insects. The presence of a single effective pollinator in a fragmented habitat makes T. recurvatum, a self-incompatible species, especially susceptible to pollen limitation (Bond, 1994; Larson and Barrett, 2000; Knight et al., 2005). The only other observed visitors Collops are not effective pollinators. Collops are predacious species that do not rapidly move from flower to flower, spending a great deal of time within a single flower presumably awaiting the arrival of prey. Second, the primary pollinator may be threatened by population decline (Hodek and Michaud, 2008). Conversely, T. recurvatum is a long-lived perennial, giving it an advantage and allowing it to overcome over time the obstacles imposed by pollen limitation. Likewise C. maculata tends to be more prevalent in areas with high densities of corn production (Andow and Risch, 1985; Day and Tatman, 2006; Hoheisel and Fleischer, 2007) as are found in southern Wisconsin.
Some 38 species of North American Trillium are recognized according to the Flora of North America (Case and Case, 1997; Case, 2002). Given the large number of native species, few studies have been conducted addressing their reproductive biology. Trillium grandiflorum (Michx.) Salisb. and T. erectum L. are the only species that have been thoroughly investigated, probably due to their high frequencies (Blain, 1946; Bound, 1980; Davis, 1981; Broyles et al., 1997; Kalisz et al., 1999; Irwin, 2000; Sage et al., 2001; Griffin and Barrett, 2002; Steven et al., 2003). Trillium ovatum Pursh (Levkovitz, 1984) and T. reliquum Freeman (Heckel and Leege, 2007) also have been studied. None of these studies compared the reproductive biology between rare and common congeners. Ohara and Utech (1986) looked at various reproductive aspects of six sessile flowered trilliums (Table 3). Patrick (1975) looked at pollinator activity in five sessile flowered species in Tennessee, including T. cuneatum Raf., T. flexipes Raf., T. recurvatum, T. sessile L. and T. stamineum Harbison. He found that in the one site where T. recurvatum was found, plants were visited by five species of beetles, namely Cantharis sp., one species of Alticinae (Glyptina spuria LeConte?), Chalepus scapularis Olivier, Cymatadora bicolor Say and Homeotarsus pallipes Gravenhourst. Cantharis and Cymatadora were observed eating pollen. This same contingent of effective pollinators was not found in Wisconsin. Although an effective pollinator known to include pollen in up to 50% of its diet (Atallah and Newsom, 1966) and likely often present, C. maculata were not observed over the initial 3 y period of this study.
[FIGURE 1 OMITTED]
Flowering genets of Trillium recurvatum were found to be pollen limited in terms of fruit production, but not in terms of seed production. Ovules likely were being fertilized differentially by pollen loads carried by pollinators from a limited number of randomly selected plants. This suggests that inadequate pollen delivery to a large number of plants may contribute to pollen limitation.
Results of this study fit for the most part with most (five of eight) of the predictions of Larson and Barrett (2000). Their analyses predicted that self-incompatible, xenogamous, polycarpic, non-nectiferous species of forested habitats should be pollen limited. These are characteristics of Trillium recurvatum. The pollen limitation index (L = 1 - [[P.sub.o]/[P.sub.s]], where [P.sub.o] is percent fruit set for open-pollinated controls and Ps is percent fruit set for plants receiving supplemental cross pollen; the higher the value of L, the greater the pollen limitation) for T. recurvatum as calculated by Larson and Barrett (2000) was 0.32, somewhat less than the average for most angiosperms (0.40), but greater than that for the Liliaceae (<0.20). It is not known whether T. lancifolium is self-incompatible or whether close relatives T. lancifolium, T. maculatum or T. sessile are pollen limited.
Seeds produced from selfing are likely at a selective disadvantage during germination, establishment and juvenile stages (Davis, 1981; Kawano et al., 1986; Ohara, 1989; Kawano et al., 1992; Hanzawa and Kalisz, 1993), and hence a selective advantage of self-incompatibility in this species. Trillium recurvatum produces the smallest sized seeds of any other Trillium including its closest relative T. lancifolium (Ohara and Utech, 1986; Table 3). Although pollen limitation is present and fruit set is limited, pollinators apparently are effective at providing sufficient pollen for high levels of seed set. However, high seed set may be somewhat offset by relatively low seed viability. Despite this impediment, seed set in this species was found to be greater than for other trilliums for which this data has been collected, regardless of whether or not species possess a mixed-mating system. The large number of very small seeds in T. recurvatum is likely an adaptive compensatory mechanism with the advantage that greater dispersal may be accomplished at a similar cost as producing fewer larger seeds.
This study has shown that, unlike Trillium sessile, T. recurvatum is self-incompatible, produces many, extremely small seeds (unlike all other trilliums), is pollinated primarily by a single pollinator in Wisconsin, Coleomegilla maculata, and is pollen limited. Even though pollen limitation has been demonstrated here, and is considered to be contributory to the rarity of this species, loss of habitat due to development, habitat fragmentation due primarily to agricultural expansion and effects of distributional range limitation may not be discounted as forces influencing rarity of this species.
Acknowledgments.--I thank the WIS herbarium and website for informational data. I especially thank David Gennrich for allowing permission to study on the Waukesha Land Conservancy property. I also thank the undergraduate students who participated in this project without whose help the project would not have been completed. They include Kimberly Budenz, Terri Peters, Stephanie Schapveld and Christine Sibigtroth. I thank Kerry Katovich of the University of Wisconsin-Whitewater for his willingness to identify insect visitors. Lastly, I thank Susan Farmer of the University of Tennessee and Donald Les of the University of Connecticut for their informative advice concerning this and other Trillium species.
SUBMITTED 8 OCTOBER 2008 ACCEPTED 20 MARCH 2009
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NEIL W. SAWYER
Department of Biological Sciences, University of Wisconsin-Whitewater, Whitewater 53190
TABLE 1.--Comparison of distribution and reproductive aspects between Trillium recurvatum and T. sessile Trillium spp. Distribution Corolla odor Anthers recurvatum Lacking Incurved; dark purple (Alexander, 1955 sessile Greater & Pungent, Straight; more spicy light northerly (Robertson, purple 1896; Weed, 1900 Pollinators in Trillium spp. Sepals Morphs Tennessee recurvatum Reflexed Purple, yellow 5 beetles (Patrick, (Steyermark, 1975 1959; Freeman and Heineke, 1987 sessile Spreading Purple, 6 beetles, 2 or yellow, Diptera, 1 ascending greenish- Hymenopteran light purple wasp, 3 thrips (Whitkus (Patrick, 1975) et al., 1987) TABLE 2.--Results of site analysis and pollination experiments for Trillium recurvatum Population size (no. of Autogamous hand genets); site density and pollinations--% Site degree of disturbance fruit set Green County ~1 acre; 42 genets 0 (42/acre); highly disturbed Jefferson County ~2 acres; -870 genets 0 (435/acre); minor disturbance Waukesha County ~32 acres;~130,400 ~2 genets (4,075/acre); pristine Mean ~2 Xenogamous hand Open pollinated pollinations % fruit controls %o fruit Site set--%seed set set--%seed set Green County 35.0 [+ or -] 2.7 25.0 [+ or -] 1.4 -25 [+ or -] 4.4 -82.7 [+ or -] 3.7 Jefferson County 53.0 [+ or -] 3.2 40.0 [+ or -] 2.1 -60.8 [+ or -] 4.6 -70.4 [+ or -] 6.5 Waukesha County 46.7 [+ or -] 11.1 20.5 [+ or -] 1.7 -54.6 [+ or -] 5.7 -75 [+ or -] 25.5 Mean 44.5 [+ or -] 2.2 31.8 [+ or -] 1.6 -4.9 [+ or -] 5.5 -77.0 [+ or -] 4.2 TABLE 3.--Comparison of ovule and seed attributes among seven sessile flowered trilliums, modified from Ohara and Utech (1986) No. ovules / No. seeds / Trillium species plant plant T. lancifolium 32.6 [+ or -] 4.1 9.7 [+ or -] 6.4 T. ludovicianum 57.3 [+ or -] 18.9 25.3 [+ or -] 9.8 T. maculatum 155.0 [+ or -] 6.9 24.2 [+ or -] 15.0 T. reliquum 41.7 [+ or -] 7.4 15.4 [+ or -] 8.4 T. recuruatum 61.2 [+ or -] 5.0 28.7 [+ or -] 15.4 T. stramineum 48.7 [+ or -] 4.3 14.3 [+ or -] 12.6 T. underuioodii 75.8 [+ or -] 15.7 20.7 [+ or -] 13.6 Mean 68.5 [+ or -] 41.0 34.0 [+ or -] 6.8 No. seeds / Seed weight Trillium species No. ovules (%) (mg) T. lancifolium 29.7 4.89 [+ or -] 0.58 T. ludovicianum 44.1 10.75 [+ or -] 1.07 T. maculatum 15.6 8.17 [+ or -] 1.47 T. reliquum 36.9 10.07 [+ or -] 0.88 T. recuruatum 46.9 2.84 [+ or -] 1.27 T. stramineum 29.4 7.41 [+ or -] 1.73 T. underuioodii 27.3 10.28 [+ or -] 1.50 Mean 32.8 [+ or -] 10.7 7.77 [+ or -] 3.0 TABLE 4.--Variability in sorted pollen to ovule ratios for Trillium recuruatum among three sites in Wisconsin Ratio Ratio 1466 to 1 3556 to 1 1661 to 1 3623 to 1 2222 to 1 3704 to 1 2448 to 1 3831 to 1 2632 to 1 3922 to 1 2748 to 1 4040 to 1 3150 to 1 4248 to 1 3333 to 1 5247 to 1 3509 to 1 Mean = 3255 to 1 [+ or -] 966.9 TABLE 5.--Results of ANOVA on log transformed data for fruit set in pooled open pollinated controls (A) and xenogamous hand pollinations (B) Mean (%) SE SS df F P A. 31.8 1.65 6010.6 1 16.641 <0.001 B. 44.5 2.23 55624 154 6163.7 155 TABLE 6.--Results of ANOVA on log transformed data for seed set in pooled open pollinated controls (A) and xenogamous hand pollinations (B) Mean (%) SE SS df F P A. 77.0 4.16 4139.9 1 8.64191 0.006 B. 54.9 5.49 15808.5 33 19948.3 34
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|Author:||Sawyer, Neil W.|
|Publication:||The American Midland Naturalist|
|Date:||Jan 1, 2010|
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