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Effectiveness of vectors of pollen and longevity of capitula for four species of Asteraceae in central Mexico.

Breeding systems of plants are highly variable. For example, plants within the family Asteraceae predominantly are self-incompatible; however, the family contains both outcrossing and selfing species (e.g., Lawrence, 1985; Lane, 1996; Nielsen et al., 2003; Heenan et al., 2005; Ortiz et al., 2006). self-incompatible, outcrossing species within Asteraceae are pollinated by a diversity of vectors of pollen, including insects and wind (e.g., Grashoff and Beaman, 1970; Sullivan, 1975; Schmitt, 1980, 1983; Berry and calvo, 1989; Lane, 1996). conversely, self-compatible species may experience outcrossing via pollinators as well as spontaneous and pollinator-assisted self-fertilization (Grashoff and Beaman, 1970; Faegri and van der Pijl, 1971; Meeuse, 1978; stelleman, 1978). Although Asteraceae is among the largest families of plants, there is a lack of information on breeding systems of species and on effectiveness of different vectors of pollen on reproductive success.

Reproductive success is determined by availability of vectors of pollen, degree of self-compatibility, or both. in addition, other factors including life span of flowers and environmental conditions are crucial for reproductive success. Longevity of flowers, as well as longevity of buds and fruits, may have a strong influence on reproductive success because greater longevity increases potential exposure to adverse factors that may prevent maturation of fruits and seeds (i.e., risks of predation, unfavorable weather conditions, and asynchrony between maturation of seeds and dispersers of seeds; primack, 1987). some factors affecting longevity of mature flowers might also determine duration of other stages (i.e., buds and fruits); thus, influencing availability of flowers to pollinators and having direct consequences on reproductive success. Longevity of flowers has been studied in many families of plants. However, little attention has been paid to factors affecting longevity of other developmental stages, such as buds or fruits (Primack, 1987). Moreover, there is a lack of studies on longevity of capitula and its relationship to reproductive success.

Longevity of flowers may be influenced by timing of pollination, mating system, and growth form (Devlin and Stephenson, 1984; primack, 1985; stratton, 1989; schoen and Ashman, 1995; clayton and Aizen, 1996). in many species, senescence of flowers occurs immediately after fertilization of the ovule; the sooner that transfer of pollen and fertilization occur, the faster the flower senesces (Devlin and stephenson, 1984; proctor and Harder, 1995; schoen and Ashman, 1995; clayton and Aizen, 1996). in self-incompatible species (i.e., dependent upon vectors of pollen), longevity of flower is longer than in self-compatible ones that are able to self-fertilize early after anthesis of flowers (primack, 1985; schoen and Ashman, 1995). in general, annual herbaceous plants show shorter floral longevities than perennial plants (stratton, 1989).

in addition, longevity of flowers and reproductive success may be affected by environmental factors; e.g., shade will limit availability of sunlight for photosynthesis and availability of resources for production of flowers (Rathcke and Lacey, 1985). Hence, display of flowers and their attractiveness to pollinators will be affected (stanton and preston, 1988; Young and stanton, 1990; eckhart, 1991); thus, causing greater longevity of flowers (Young and stanton, 1990; eckhart, 1991). All of these factors combined (timing of pollination, mating system, growth form, and environment) will influence reproductive success.

At Reserva ecologica el pedregal de san Angel in central Mexico, Asteraceae is the best represented family of plants (valiente-Banuet and De Luna, 1990), contributing a high percentage of total biomass (Cano-Santana, 1994) and the greatest number of species. Thus, Asteraceae is an important resource for folivores, florivores, nectarivores, and pollinivores (Cano-Santana, 1994). Because species of Asteraceae are dominant flowering plants and because of the lack of information regarding breeding systems and factors that can affect reproductive success, it is important to study modes of pollination and how life span of capitula and environmental conditions influence reproductive success. The main goals of our study were to determine the breeding system of four species (Eupatorium petiolare, Dahlia coccinea, Tagetes lunulata, and Verbesina virgata) and to investigate the influence that shade has on effectiveness of vectors of pollen and longevity of capitula. specific goals were to determine: presence of spontaneous self-fertilization (i.e., breakdown of self-incompatibility) in three species, D. coccinea, T. lunulata, and V. virgata; effectiveness of different vectors of pollen on production of fruits of these species as well as E. petiolare; longevity of reproductive phenophases in the four species and how longevity is related to mating system and growth form; and effect of shade on production of fruits by V. virgata and on longevity of reproductive phenophases of D. coccinea and V. virgata.

MATERIALS AND METHODS--This research was conducted at Reserva ecologica el pedregal de san Angel on the main campus of universidad Nacional Autonoma de Mexico in Mexico City (19[degrees]20'N, 99[degrees]08'W, 2,300 m above sea level). Mean annual temperature is 15.5[degrees]C and mean annual rainfall is 879 mm with two distinctive seasons; rainy season is June-October and dry season is November-May (Rzedowski, 1954; Valiente-Banuet and De Luna, 1990; Cesar-Garcia, 2002). The ecosystem originated with the eruption of Xitle Volcano ca. 2,000 years ago (Carrillo, 1995). Processes of cooling and solidification of lava produced an irregular topography, which includes large flat rocks, deep holes, and cracks. in shaded sites, there is arboreal vegetation (>40% coverage) and sunny sites have <15% arboreal coverage (Cano-Santana, 1994). Photosynthetically active solar radiation in shaded sites (mean = 328.8 [+ or -] SD = 90.6 [micro]M/s [m.sup.2]) is only 32.8% of that available in sunny sites (1,006.7 [+ or -] 68.4 [micro]M/s [m.sup.2]).

On the reserve, Asteraceae has the greatest species richness (20%) of flowering plants (Valiente-Banuet and De Luna, 1990) and above-ground net primary productivity of the ecosystem (>32.6%; Cano-Santana, 1994). species we studied were chosen based on their contribution to the above-ground net primary productivity: V. virgata 15.1%, D. coccinea 9.6%, and E. petiolare 2.5% (Cano-Santana, 1994). Tagetes lunulata is an herbaceous plant that contributes significantly to above-ground phytomass of the ecosystem. Collectively, flowers of these four species are visited by [greater than or equal to] 117 species of insects (Figueroa-Castro and Cano-Santana, 2004). Morphological and ecological characteristics of the four species are presented elsewhere (Rzedowski and Rzedowski, 1985; Figueroa-Castro, 1997; Martinez, 1997; Figueroa-Castro et al., 1998; Figueroa-Castro and Cano-Santana, 2004).

To determine effect of different guilds of vectors of pollen on production of achenes, pollination treatments were applied during the flowering season of each of the four species in 1996: control, with access to all possible mechanisms of pollination (insects, wind, and autonomous self-fertilization); diurnal pollination, with access to diurnal insects (from dawn to sunset), wind, and autonomous self-fertilization; nocturnal pollination, with access to nocturnal insects (from sunset to dawn), wind, and autonomous self-fertilization; wind pollination, preventing access by insects but allowing autonomous self-fertilization; and, autonomous self-fertilization, prohibiting access by both insects and wind. in typical sites for each species, 20-35 healthy plants of each species were randomly chosen. Five capitula per plant, each one corresponding to one of the five experimental treatments were randomly chosen, except for E. petiolare, in which 1-5 capitula were used for each treatment per plant. Experimental capitula were chosen before anthesis and bagged using 1-mm-aperture mesh bags, which allowed passage of airborne pollen but excluded most insects (Berry and Calvo, 1989; Bernardello et al., 1999; Goodwillie, 1999). Filter-paper bags were used instead of mesh bags in self-fertilization treatments. Bags in self-fertilization and wind treatments remained on capitula for the entire experimental period. in other treatments, buds remained bagged until the flowering-stage when capitula were bagged and unbagged according to each treatment. we did not control for possible self-pollinations caused by bagging or unbagging capitula for diurnal and nocturnal pollination treatments, and we did not detect a significant difference in production of achenes in these treatments compared to wind and control treatments, as would be expected if manipulation of capitula had increased self-pollination.

Pollination treatments for each species took place over 5 days and 4 nights, except for E. petiolare, in which treatments were during 5 days and 5 nights (11-15 March). All five treatments were applied to each experimental individual of each species during the peak of its flowering season. However, only the first four treatments were applied to E. petiolare. Treatments were applied to T. lunulata on 21-25 october. Because V. virgata was distributed in both sunny and shaded sites, all treatments were applied under both conditions to quantify the effect of shade on production of fruits (18-22 November). Although D. coccinea was in both sunny and shaded sites, treatments were applied only in sunny sites (12-15 August) because of the low production of reproductive structures in shaded sites. At the end of the experimental period, all capitula were bagged, preventing access by insects and, at the end of the reproductive season, fruits were collected and number of achenes per capitulum was recorded as a measure of reproductive success.

Because in the wind treatment, autonomous self-fertilization and, in the diurnal and nocturnal treatments, both wind and autonomous self-fertilization were not prevented, we calculated net production of achenes for each vector of pollen (diurnal visitors, nocturnal visitors, wind, and autonomous self-fertilization) in the following way (Table 1): net production of achenes due to wind ([A.sub.w]) was calculated as [A.sub.w] = [A.sub.w+s] - [A.sub.s], where [A.sub.w+s] = mean number of achenes produced under treatment with wind, which also includes the effect of autonomous self-fertilization, and [A.sub.s] = mean number of achenes produced by autonomous self-fertilization. in the same way, net production of achenes due to pollination by insects ([A.sub.i]) was calculated as [A.sub.i] = [A.sub.i+w+s] - [A.sub.w+s], where [A.sub.i+w+s] = mean number of achenes produced by treatments of diurnal or nocturnal pollinators and i = either diurnal or nocturnal pollinators.

To quantify longevity of each reproductive stage (number of days for each stage of development), 10-15 capitula at the early stage of budding were marked on [greater than or equal to] 5 individuals/site/species. Capitula were individually marked with a colored 1-mm-diameter wire. Longevity of reproductive structures was recorded at those sites in which each species was distributed, i.e., shaded sites for E. petiolare, sunny sites for T. lunulata, and both shaded and sunny sites for D. coccinea and V. virgata. Stage of development for each marked reproductive structure was recorded every other day for one reproductive season.

Six stages of development of capitula were categorized according to occurrence of the following morphological characteristics: development of reproductive structures (young bud); opening of capitula (mature bud); development of ligulate florets and, development by E. petiolare of a white coloration on the apical side of buds (young flower); anthesis of at least one disc floret (mature flower); senescence of florets in anthesis together with beginning of abscission of ligules (young fruit); and overall abscission of ligules and dryness of fruits (mature fruit). This final stage ended with dispersal of the last fruit in the infructescence. To determine duration (in days) of each floral stage, any damaged capitulum was replaced by another healthy reproductive structure at about the same stage of development, so that further stages could be followed.

A one-way ANOVA with pollination treatment as a fixed effect was applied to data for production of achenes per capitulum for E. petiolare, T. lunulata, and D. coccinea. Because pollination treatments were applied to > 1 capitulum/individual (range = 1-5) of E. petiolare, average number of achenes per capitulum per plant produced under each treatment was used for statistical analysis. Data for V. virgata were analyzed with a two-way ANOVA (pollination treatment and site). To fit assumptions of the test, production of achenes per capitulum was transformed as [(x + 0.5).sup.0.5] (Zar, 1999). Post-hoc Scheffe tests were conducted on those cases where ANOVA was significant. All statistical analyses were conducted on Statistica (Statistica for Windows, version 5.1., Tulsa, Oklahoma). To compare duration of each phenophase for capitula of V. virgata and D. coccinea between sites (sun versus shade), t-tests for independent samples were applied (Zar, 1999).

RESULTS--Pollination treatment did not have a significant effect on number of achenes per capitulum for E. petiolare ([F.sub.3,61] = 0.06, P > 0.05) and T. lunulata ([F.sub.4,146] = 1.05, P > 0.05). Eupatorium petiolare had an average of 43.2 [+ or -] 0.7 achenes/capitulum. Tagetes lunulata had a mean of 22.8 [+ or -] 0.7 achenes/capitulum. In contrast, there was a significant effect of treatment on production of achenes per capitulum for D. coccinea ([F.sub.4, 143] = 181.12, P < 0.001). The largest number of achenes per capitulum was produced under the control-pollination treatment (59.7 [+ or -] 3.7 achenes/capitulum), which did not differ significantly from results obtained with the diurnal-pollination treatment (52.8 6 5.1 achenes/ capitulum; Fig. 1a). Number of achenes per capitulum was significantly lower under nocturnal pollination (4.0 [+ or -] 0.9 achenes/capitulum). Dahlia coccinea produced few achenes per capitulum under both wind-pollination and autonomous-self-fertilization treatments (1.3 [+ or -] 0.5 and 0.1 [+ or -] 0.1 achenes/capitulum, respectively).

For V. virgata, there was a significant effect of sun and shade treatments ([F.sub.1,246] = 34.49; P < 0.05) but not for pollination-vector treatments ([F.sub.4,246] 5 0.62, P > 0.05) or the interaction of sun and shade treatments by pollination-vector treatments ([F.sub.4,246] = 0.81, P > 0.05) on number of achenes per capitulum. Production of achenes per capitulum on average was 24% greater in sunny sites than in shaded ones (Fig. 1b).

Results for net production of achenes indicated a low contribution of diurnal and nocturnal visitors, as well as wind on production of achenes of T. lunulata and V. virgata (in both sun and shade; Table 1). In contrast, for D. coccinea, diurnal visitors had the greatest contribution to production of achenes, but other vectors of pollen were not so efficient. For E. petiolare, net production of achenes showed that wind plus autonomous self-fertilization were the main contributors to production of achenes.

Significant differences were detected between sun and shade treatments in stage of mature fruit and overall longevity for D. coccinea (Table 2). Longevity was significantly longer in shaded environments (mature fruit: [t.sub.16] = 3.039, P < 0.05; overall longevity: [t.sub.14] = 2.372, P < 0.05). For V. virgata, longevity of mature flowers and young fruits was significantly longer at shaded sites than at sunny ones (mature flowers: [t.sub.24] = 2.074, P < 0.05; young fruits: [t.sub.25] = 6.176, P < 0.001). This might determine a longer total longevity of capitula in shaded environments. unfortunately, at sunny sites, we were only able to observe one capitulum across its entire development, preventing any statistical analysis of longevity.

Ranking of overall longevity of reproductive structures were (Table 2): V. virgata > D. coccinea in shaded environments > T. lunulata > D. coccinea in sunny environments > E. petiolare. The mature-fruit stage had greatest longevity, except in E. petiolare, whose young-fruit stage lasted longer. The mature-fruit stage of E. petiolare was the shortest stage. In contrast, the young-fruit stage was the shortest in all other species. Longevity of buds (young bud plus mature bud) varied among species as follows: V. virgata (36.8 days) > D. coccinea (23.0 days) > T. lunulata (15.2 days) = E. petiolare (13.8 days). For phenophases previous to mature flower (bud plus young flower), the following was observed: V. virgata (40.8 days) > D. coccinea (25.0 days) > E. petiolare (20.4 days) > T. lunulata (17.6 days). Average longevity of mature flowers also had differences among species: V. virgata in shade (15.0 days) > V. virgata in sun (10.4 days) > T. lunulata (8.7 days) > E. petiolare (6.4 days) > D. coccinea (4.2 days). Duration of mature fruit varied among species: V. virgata = D. coccinea in shade > T. lunulata > D. coccinea in sun > E. petiolare. The fruit stage (young fruit plus mature fruit) varied among species: V. virgata in shade (163.4 days) > D. coccinea in shade (139.4 days) = V. virgata in sun (129.8 days) > T. lunulata (99.2 days) > D. coccinea in sun (74.9 days) > E. petiolare (19.6 days).

DISCUSSION--Species of Asteraceae have been considered to be predominantly self-incompatible; thus, they require vectors for their pollination (Proctor and Yeo, 1972; Burtt, 1977; Richards, 1986; de Nettancourt, 2001). As in other studies (Lawrence, 1985; Lane, 1996; Nielsen et al., 2003; Heenan et al., 2005; Ortiz et al., 2006), our results demonstrated that this is not always true. From the four species studied here, only D. coccinea was self-incompatible and completely dependent upon diurnal visitors for pollination.

Several floral traits of D. coccinea seem to favor cross-fertilization through visitation by insects. For example, the large size of its ligules may be used as a landing platform for floral visitors with a range of sizes (Leppik, 1977). Size of ligule has a direct effect on number of floral visitors arriving to floral capitula of this species (Figueroa-Castro, 2001). Moreover, being polymorphic for color of ligule (from yellow to orange) can attract a diversity of potential pollinators (Figueroa-Castro and Cano-Santana, 2004); thus, increasing chances for outcross fertilization. Ability of ligules to close over disc florets at night might prevent loss of pollen that would not be delivered effectively by nocturnal visitors (Figueroa-Castro, 1997).

Although T. lunulata and V. virgata were independent from vectors of pollen for production of fruits, we cannot discard the possibility that action of vectors might produce outcross-pollinations and that offspring produced this way might have greater fitness than those produced by self-pollination. Spontaneous self-pollination was proven for T. lunulata and V. virgata, but it was not tested for E. petiolare. Eupatorium petiolare does not rely upon any particular vector of pollen for its reproduction; however, wind and spontaneous self-fertilization could be acting as its main vectors. Although its flowers present typical characteristics of nocturnal pollination (white color and sweet fragrance produced at night), other traits, such as growing in large patches of plants close to each other and low diversity of flowering species and pollinators during its flowering season, might favor wind pollination (Whitehead, 1969; Faegri and van der Pijl, 1971; Richards, 1986; Berry and Calvo, 1989). Thus, it is not surprising to find that wind is an important vector of pollen for E. petiolare. Grashoff and Beaman (1970) and Sullivan (1975) suggested that wind is the main vector of pollen for four other species of Eupatorium.

It is possible that the importance of abiotic mechanisms of pollination (i.e., wind pollination and self-fertilization) in E. petiolare, T. lunulata, and V. virgata might be the result of disappearance of their original pollinators (Levin and Anderson, 1970; Berry and Calvo, 1989). Loss of local populations of insects caused by disturbances of habitats has been recorded elsewhere (Pyle et al., 1981). The Reserva Ecologica el Pedregal de San Angel has suffered several intense disturbances associated with the continuous population growth of Mexico City, i.e., electric lights, air pollution, inversions in the air temperature gradient, and introduction of the European honeybee (Apis mellifera; Cano-Santana, 1987; Rojo, 1994). Beutelspacher (1972), e.g., recorded a decrease in >50% of the sphingid fauna during 1939-1969. Therefore, it is possible that low abundance of pollinators, local extinctions of pollinators, or both, have been common here.

In our study, effect of different vectors of pollen on reproductive success of species of Asteraceae was estimated in terms of production of achenes per capitulum. However, production of achenes alone is not a good measure of reproductive success of Asteraceae, especially when flowers are self-pollinated, because a high percentage of achenes produced by self-pollination do not contain an embryo (Nielsen et al., 2003). Therefore, to account for production of achenes, further analysis such as X-ray photos of achenes are necessary (Nielsen et al., 2003). Because of this, our results might be overestimating importance of self-pollination in T. lunulata and V. virgata. Conclusions stated for D. coccinea are not affected by overestimation of production of achenes through spontaneous self-fertilization. Although this mechanism of pollination was overestimated in our experiment, production of achenes obtained through self-pollination in D. coccinea was significantly lower than production of achenes obtained via diurnal insects. Thus, it does not change our conclusion about dependence of D. coccinea on diurnal insects for its pollination.

Our results did not show the relationship between growth form of plant and longevity of flowers described by Stratton (1989) or the relationship between breeding system and longevity of flowers predicted by Primack (1985) and Schoen and Ashman (1995). Stratton (1989) suggested that annual plants have shorter floral longevities than trees and shrubs. Primack (1985) and Schoen and Ashman (1995) suggested that species capable of self-pollination have shorter longevity of flowers than outcrossing species. in contrast to these predictions, D. coccinea was the only species depending upon vectors for pollination (Fig. 1a), it had the shortest longevity of capitula (4.2-4.3 days; Table 2), and it did not show autonomous self-pollination. These results might indicate that transfer of pollen and fertilization of ovule in D. coccinea occur soon after anthesis, whereas the greater longevity of capitula recorded for the other species may be associated with a sporadic frequency of visits and delayed fertilization, such as suggested for other systems (Devlin and Stephenson, 1984; Richardson and Stephenson, 1989; Aizen, 1993; Ashman and Schoen, 1994; Proctor and Harder, 1995; Clayton and Aizen, 1996).

Flowering time and mechanism of dispersal of seeds might have an effect on total reproductive period (from buds to dispersal of seeds) of these Asteraceae. Species that flower during the rainy season (D. coccinea, T. lunulata, and V. virgata) had a longer total reproductive period than E. petiolare, which flowers during the dry season. it is likely that species flowering during the rainy season have a longer total reproductive period because seeds are dispersed in the following dry season, when strong winds and lack of vegetation allow for maximal dispersal of seeds for all of these wind-dispersed species (Cesar-Garcia, 2002). For E. petiolare, its total reproductive period may be relatively short because flowering and dispersal of seeds occur in a single dry season. These patterns suggest that plants flowering during the rainy season show a longer fructification than flowering period, such as Cesar-Garcia (2002) recorded for other species in our study area.

As with production of seeds, longevity of reproductive structures might be influenced by other selective pressures, e.g., availability of resources needed to achieve maturation of flowers and fruits, escape from seed predators and herbivores, and synchrony between time of dispersal of seeds and optimal factors for them to fulfill a successful germination (Primack, 1987). Such pressures might be in conflict with each other; therefore, it is expected that the total reproductive period would be a balanced result among all of these selective forces, resulting in the greatest possible fitness of plants.

Individuals of V. virgata growing in shade had lower production of achenes than individuals growing in sunny sites. This reduction in production of achenes can be related to availability of solar radiation, which increases energy available to produce flowers, gametes, and fruits (Stone, 1983). Floral density is determined directly by availability of resources to produce reproductive structures. Floral density has a strong influence on frequency of floral visitors and, thus, also on frequency of successful pollinations (e.g., Willson and Bertin, 1979; Wolfe, 1987; Campbell, 1989; Eckhart, 1991). Floral density of V. virgata in sunny sites is 20% greater than in shaded sites (Figueroa-Castro et al., 1998). Therefore, it is possible that pollination occurs more frequently in sunny sites than in shaded ones, directly affecting production of achenes.

Mature flowers and young fruits of V. virgata, as well as mature flowers and fruits of D. coccinea, lasted longer (in days) in shaded sites than in sunny sites. Two factors might be causing these patterns. First, at sunny sites, there is a high density of capitula and coverage of foliage by other plants is low (Whitehead, 1969; Rathcke, 1983; Burquez et al., 1994). Dense patches of flowers in sunny sites might be highly attractive to pollinators that might forage longer in these sites and, thus, might influence time of fertilization. Then it is possible that pollination occurred in a shorter period of time at sunny sites. Second, at sunny sites, plants have a high availability of resources that can be allocated to development of reproductive structures (Stone, 1983). In addition, greater longevity of the mature-fruit stage in D. coccinea at shaded sites might be caused by difficulties associated with dispersal by wind in these sites where there is a high coverage of vegetation preventing action of wind for dispersal of seeds (Pianka, 1994).

CONCLUSIONS--In our study, we confirmed variability in effectiveness of pollinators and longevity of capitula within Asteraceae. Tagetes lunulata and V. virgata showed autonomous self-fertilization, whereas D. coccinea was recorded as the only self-incompatible species, depending upon diurnal pollinators for its reproduction. The mechanism of pollination for E. petiolare is not completely clear, but our results suggest that either wind or self-fertilization might be the mechanism acting in this species. Longevity of various phenophases of reproductive structures also was variable among species. Species that self-fertilize autonomously last longer in anthesis; perhaps, to give the opportunity for outcrossing. Species flowering in the dry season showed a shorter reproductive period than species flowering during the rainy season. Plants growing in shaded habitats showed a decrease in production of achenes per capitulum (V. virgata) and an increase in longevity of capitula (D. coccinea and V. virgata) compared to those patterns for the same species in sunny sites. Future studies of reproductive biology of Asteraceae should address the relative importance of direct and indirect effects produced by shade and consequences of selfing on fitness.

We thank E. Camacho, C. Gonzalez, C. Anaya, R. Leon, O. Nunez, and C. Maravilla for assistance in the field. L. Dudley, S. Ellberg, R. Kaczorowski, J. Ketner, A. Dona, M. Brock, and two anonymous reviewers made valuable suggestions that helped to improve the manuscript. M. A. Romero-Romero and S. Mendoza provided technical assistance. This research was supported by a grant from Consejo Nacional de Ciencia y Tecnologia (0202P-N9506) provided to ZC-S. DMF-C was funded with a scholarship from universidad Nacional Autonoma de Mexico.

Submitted 1 April 2009. Accepted 15 October 2010. Associate Editor was Janis K. Bush.


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Departamento de Ecologia y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, 04510 Mexico, Distrito Federal, Mexico

Present address of DMF-C: Laboratorio de Biologia Vegetal, Escuela de Biologia, Benemerita Universidad Autonoma de Puebla, Boulevard Valsequillo y Avenida San Claudio, Edificio 112A, Ciudad Universitaria, Colonia Jardines de San Manuel, C.P. 72570, Puebla, Mexico

* Correspondent:
Table 1--Net production of achenes per capitulum obtained through
different vectors of pollen in four species of Asteraceae at the
Universidad Nacional Autonoma de Mexico, Reserva Ecologica el
Pedregal de San Angel in Mexico City. Autonomous self-fertilization
was not applied for E. petiolare; thus, wind includes both
autonomous self-fertilization and effects of wind.

                                    Eupatorium     Dalea     Tagetes
Experimental treatment               petiolare    coccinea   lunulata

[A.sub.A] = all vectors of pollen      44.1         59.7       24.8
[A.sub.D] = diurnal pollinators         0.0         51.5        2.8
[A.sub.N] = nocturnal pollinators       0.5          2.7        2.2
[A.sub.W] = wind pollination           43.4          1.2        0.0
[A.sub.S] = autonomous
  self-pollination                  not applied      0.1       23.5

                                    Verbesina virgata

Experimental treatment               Sun    Shade

[A.sub.A] = all vectors of pollen   85.3     77.3
[A.sub.D] = diurnal pollinators      0.0      2.3
[A.sub.N] = nocturnal pollinators    1.2      5.0
[A.sub.W] = wind pollination         5.8      0.0
[A.sub.S] = autonomous
  self-pollination                  84.9     67.6

Table 2--Longevity in days [+ or -] SE (n; range in days) for
each developmental stage of capitulum, from young bud to
dispersal of mature fruits for four species of Asteraceae
distributed in two light environments (sun and shade) at the
Universidad Nacional Autonoma de Mexico, Reserva Ecologica el
Pedregal de San Angel in Mexico City. Different letters within
the same species and stage indicate significant differences
between treatments (t-test; P < 0.05).

                              Eupatorium              Tagetes
                               petiolare              lunulata

         Stage                   Shade                  Sun

Young bud                  8.5 [+ or -] 1.0      13.0 [+ or -] 0.8
                              (10; 4-14)             (11; 9-19)
Mature bud                 5.3 [+ or -] 0.6       2.2 [+ or -] 0.1
                               (10; 3-9)             (11; 2-3)
Young flower               6.6 [+ or -] 0.6       2.4 [+ or -] 0.3
                              (10; 4-10)             (11; 1-5)
Mature flower              6.4 [+ or -] 0.4       8.7 [+ or -] 0.5
                               (10; 5-9)             (10; 7-12)
Young fruit                16.4 [+ or -] 1.3     22.4 [+ or -] 10.7
                              (10; 6-21)             (8; 1-95 )
Mature fruit               3.2 [+ or -] 0.6      76.8 [+ or -] 20.1
                               (10; 1-8)            (9; 15-147)
Mean overall longevity     46.4 [+ or -] 1.1    138.5 [+ or -] 26.6
                              (10; 39-52)           (4; 91-187)

                                              Dahlia coccinea

         Stage                    Sun                   Shade

Young bud                  19.6 [+ or -] 6.5      17.8 [+ or -] 0.9
                              (9; 13-34)a            (13; 11-22)a
Mature bud                  4.5 [+ or -] 0.6       4.0 [+ or -] 0.5
                               (9; 3-7)a              (13; 1-8)a
Young flower                2.0 [+ or -] 0.4       2.1 [+ or -] 0.3
                               (9; 1-4)a              (13; 1-5)a
Mature flower               4.2 [+ or -] 0.3       4.3 [+ or -] 0.4
                               (8; 3-5)a              (13; 2-7)a
Young fruit                32.2 [+ or -] 1.3      26.7 [+ or -] 2.2
                              (6; 26-35)a            (13; 6-38)a
Mature fruit               42.7 [+ or -] 9.3     112.7 [+ or -] 23.1
                             (10; 14-116)b           (8; 29-213)a
Mean overall longevity    108.0 [+ or -] 13.3    170.6 [+ or -] 22.8
                              (8; 67-192)b           (8; 92-271)a

                                              Verbesina virgata

         Stage                    Sun                   Shade

Young bud                  19.5 [+ or -] 4.3      17.5 [+ or -] 3.8
                              (8; 14-49)a            (14; 5-61)a
Mature bud                       18 (1)           18.5 [+ or -] 1.5
                                                     (12; 10-28)
Young flower                4.8 [+ or -] 1.0       3.2 [+ or -] 0.3
                               (6; 2-8)a              (12; 2-5)a
Mature flower              10.4 [+ or -] 1.4      15.0 [+ or -] 1.7
                              (14; 4-20)b            (12; 9-30)a
Young fruit                25.6 [+ or -] 2.3      45.4 [+ or -] 2.1
                              (15; 14-42)b           (12; 30-53)a
Mature fruit               104.2 [+ or -] 8.8     118.0 [+ or -] 8.5
                              (9; 73-141)a          (12; 34-147)a
Mean overall longevity          187 (1)           215.1 [+ or -] 8.2
                                                    (12; 136-238)
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