Plant Syst. Evol. 232: 63–71 (2002)

Self-pollination in Euphrasia willkommii Freyn (Scrophulariaceae), an endemic species from the alpine of the Sierra Nevada (Spain)

J. M. Go´ mez

Departamento de Biologı´ a Animal y Ecologı´ a, Facultad de Ciencias, Universidad de Granada, Granada, Spain

Received May 2, 2001 Accepted December 6, 2001

Abstract. The reproductive ecology of Euphrasia selfing has evolved to allow reproduction when willkommii (Scrophulariaceae), an endemic species conditions for outcrossing are unfavourable, from the Mediterranean alpine environments of this phenomenon known as reproductive the SE Spain, has been experimentally studied assurance (Barrett 1998, Holsinger 2000, Aars- during two reproductive seasons. The flowers of sen 2000). According to the reproductive this plant species were visited by very few insects assurance hypothesis, the fitness advantage of belonging only to two generalist taxa, thrips and selfing comes from increased success with ants. Nevertheless, reproduction is not pollen limited in E. willkommii. Hand-pollinations dem- respect to outcrossing (Aarssen 2000). A main onstrated that this plant species is capable of ecological factor that can decrease outcrossing selfing, reproductive success being similar in auto- advantage and thereby promote selfing in many gamous and allogamous crosses. Moreover, poll- plant species is the shortage of pollinators inator-exclusion experiments also showed that, (Erhardt and Ja¨ ggi 1995, Kampny 1995, under natural conditions, this plant relies predom- Navarro and Guitia´ n 2001, Fausto et al. 2001). inantly on selfing, seed production being similar in In Scrophulariaceae, many species have a presence or absence of pollinators. Selfing in mixed mating system in which selfing is E. willkommii is presumably an ecological mecha- assumed to provide a reproductive assurance nism to ensure successful reproduction in a harsh when pollinators are scarce (Dole 1990, 1992; environment where pollinator availability is Ortega Olivencia and Devesa 1993a; Kalisz extremely low. et al. 1999). For example, long-tubed flowers Key words: Euphrasia willkommii, Scrophulariaceae, of Ourisia spp. (Scrophulariaceae) self sponta- Mediterranean high-mountains, pollinator abun- neously when pollinators are unavailable dance, reproductive assurance, self-fertilization. (Arroyo and Pen˜ azola 1990). Similarly, delayed selfing occurs in Collinsia verna when there is a limitation of pollinators (Kalisz et al. 1999). The type of environment in which the Introduction plant inhabits, by determining predictability Self-pollination is a common trend in angio- and abundance of pollinators, can indirectly sperm evolution (Holsinger 1992, Schoen et al. affect the frequency of selfing. In fact, several 1997, Barrett 1998). In some plant species, alpine and subalpine Scrophulariaceae, where 64 J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae pollinators are scarce, are predominantly auto- gamous (Kampny 1995). Euphrasia willkommii Freyn (Scrophularia- ceae) is an alpine species endemic to the Sierra Nevada high-mountains (Spain). Here, as in most alpine environments, conditions are es- pecially harsh for plant life, the vegetative period being very short, since the area is covered by snow many months of the year. In addition, because the zone also has a Fig. 1. Schematic view of a flower of Euphrasia Mediterranean climate, strong summer willkommii Freyn. a corolla width, b central petal droughts constrain the growth and reproduc- length, c lateral petal length, d corolla depth tion period of the plants while limiting the diversity and abundance of the floral visitors Sedum anglicum Hudson subsp. melanantherum (Go´ mez and Zamora 1992, 1996). In this (DC.) Maire, and Lotus glareosus Boiss. & Reuter. study, I experimentally explore the reproduc- In this habitat, E. willkommii is very abundant, tive ecology of E. willkommii in this severe forming populations with hundreds of individuals environment. Specifically, I (1) quantify the growing very closely. abundance and composition of the floral Reproductive traits. The reproductive traits of visitor assemblage, (2) experimentally deter- E. willkommii were studied by tagging 20 plants in mine the breeding system of the plant, (3) test each of the two years of study, and recording the number of flowers, fruits and seeds produced by whether pollinators are necessary for seed each plant. The parameters used to estimate production, and (4) test whether reproduction reproductive success were number of fruits pro- in this plant is pollen-limited. duced per plant (fruits/plant), percentage of flowers ripening to fruit (fruit set), percentage of ovules Methods ripening to seeds in each ripe fruit (SO ratio), and overall number of seeds produced per plant (seeds/ The plant species and the study site. E. willkommii is plant). a tiny (up to 6 cm high) perennial herb inhabiting The floral morphology was quantified from 60 wet as well as dry high-mountain meadows (above arbitrarily selected individuals in 1996. Measure- 2500 m a.s.l., Molero Mesa et al. 1992). It flowers ments (in mm), taken in one flower of each plant, during the summer, between June and July in the were corolla width (from the apex of the two outer study area. Flowers are pink-purple with some lateral petals), length of the central petal, length of yellow spots in the bottom petals. The corolla tube one lateral petal and depth of the corolla (from the is short and the flower is open with lobes spreading tip of the upper petals to the calyx, see Fig. 1). To weakly actinomorphically (Fig. 1). Fruits are cap- quantify nectar production, I covered all the sules containing from 4 to 10 seeds. flowers produced by 30 plants in 1995 and 40 The study was performed during 1995 and plants in 1996 (350 flowers in total), and tried to 1996 in a 2-ha plot located at 2600 m a.s.l. in the extract the nectar with capillary micropipettes. Sierra Nevada National Park (Granada, SE Spain). Floral visitor censuses. I determined the com- The study area is a dry Mediterranean alpine position and abundance of the floral visitor assem- habitat inhabited by scattered stunted shrubs and blage during 1995 and 1996 by counting all insects cushion plants belonging to the species Thymus visiting flowers of E. willkommii individuals arbi- serpylloides Bory, Hormathophylla spinosa Ku¨ pfer, trarily chosen in the study plot during 1-min Alyssum purpureum Lag. & Rodr. or Arenaria periods. I made a total of 5385 1-min censuses tetraquetra L., and by many species of perennial (aprox. 90 hours of observations) evenly distribut- herbs, notably, Mucizonia sedoides (DC.) D.A. ed from sunrise to sunset, with 85% of the censuses Webb, Dianthus subacaulis Vill, Sempervivum min- made during the diurnal period (before 20.00 pm utum (Kunze ex Willk.) Nyman ex Pau in Bol., GMT) and the remaining 15% made during the J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae 65 nocturnal period (between 20.00 pm and 01.00 am pollination (N ¼ 15 plants). (2) ‘‘Only Ants treat- GMT) using moon nights to avoid the use of lights, ment’’, in which flowers were excluded from all which could attract insects and thus alter the results visitors but ants (n ¼ 15 plants). To achieve this, I of the censuses. During the censuses, I stayed about loosely covered plants with mosquito netting that 1 m from the flowering plant, to monitor all the screened out all winged insects while allowing ants floral visitors but not disturb their foraging beha- to crawl up the stems. In this treatment, the viour. Any insect seen on the flowers that could development of the inflorescences revealed no make contact with the anthers and/or stigma was abnormalities. (3) ‘‘Only Winged treatment’’, in sampled. Pollinator abundance is expressed as the which flowers were visited only by winged insects number of insects per plant and per 10 min. I (n ¼ 15 plants). Ants were excluded by the applica- visually determined the type of food collected by tion of glue (Tanglefoot) surrounding the plants the floral visitors (pollen vs. nectar). (see Go´ mez et al. 1996 for a detailed description of Experimental study of the breeding system. In the methodology). (4) ‘‘No Pollinator treatment’’ in 1996 60 plants were tagged and then covered with which flowers were not visited by insects (n ¼ 15 mosquito netting which was attached to the soil plants). Total exclusion of all flower visitors was surface using Tanglefoot to impede both winged ensured by using the two previous techniques and wingless insect access to the flowers. All the simultaneously. The plants used in the exclusion flowers produced by 20 plants randomly selected experiments were not the same that those used in were pollinated once using pollen from the same the censuses of floral visitors. The initial number of flower (obligate autogamy). The flowers from flowers produced per plant did not vary among another 20 randomly-selected plants were emascu- treatments (F3,56 ¼ 0.002, P ¼ 0.96). lated and hand-pollinated once using pollen from The experiments were checked every two-three another individuals growing at least 2m from the days until flower senescence to ensure that the recipient plant (xenogamy). Finally, the remaining exclusions did not affect the normal foraging of 20 plants were left netted and not hand-pollinated flower visitors. I recorded no wingless insects (spontaneous autogamy). Flowers were pollinated visiting the flowers of the ‘‘Only Winged’’ or ‘‘No only once to decrease the number of manipulations Pollinators’’ treatments. During fruiting period, which might affect to the effectiveness of pollinator fruits were counted and collected to quantify exclusions. The experiment was checked every day reproductive estimate as above mentioned. until flower senescence to ensure that the exclusions Experimental determination of pollen limita- successfully eliminated insect visits. tion. In 1996 I tagged 40 plants, leaving 20 At the beginning of the experiments, I counted randomly selected plants exposed to the natural the number of flowers per plant, which was level of pollination as the control group. The other statistically similar between treatments 20 plants were also exposed to natural pollinators, (F2,57 ¼ 0.72, P ¼ 0.49, being 3.8 ± 0.5 for plants but I supplemented the number of pollen grains with spontaneous autogamy, 4.6 ± 0.3 in obligat- arriving to the stigmas by hand-pollinating all ed autogamy and 3.8 ± 0.7 in xenogamy), and at flowers of each plant with pollen from at least 5 the end of ripening I counted the proportion of donor plants (Pollen-supplementation treatment). these that set fruits, in order to calculate the Artificial pollination was repeated in each flower at fruiting success for each treatment. For each least twice to ensure successful pollination. The treatment, all fruits from each plant were collected initial number of flowers per plant did not vary at the end of the ripening period before seed between treatments (F1,38=0.002, P=0.96), being dispersal, and a laboratory count was made of the 5.8±0.9 for control plants and 5.7±0.6 for pollen- number of mature seeds, aborted seeds and unfer- supplemented plants. During the fruiting period, tilized ovules within each fruit. fruits were counted and collected to quantify Role of pollinators in plant reproductive suc- reproductive estimate as mentioned above. cess. I studied the role of pollinators of Statistical analysis. All experiments were anal- E. willkommii by selectively excluding flowers from ysed by one-way ANOVAs (GLM procedure, SAS ants and winged insects. The basic design of the 1997), introducing each estimate of the plant experiments had four treatments: (1) ‘‘Control reproductive success as a dependent variable, the treatment’’, in which flowers were left to open treatments as fixed factors and the plant as the 66 J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae individual units. When departure from normality, I with a very short corolla tube, since corolla arcsin-transformed ratios and log-transformed the depth was just 4.32±0.2 mm (Table 2). As remaining variables. Since I repeated the same shown in Table 2, there was a strong correla- model for each reproductive success estimate, I tion between most floral traits (p<0.0001 all used the sequential Bonferroni correction to avoid pairwise Pearson correlations, after Bonferroni experiment-wise type I error, adjusting the p values correlation), the only trait not correlating with of the statistical test to a<0.05. the others being the depth of the corolla. Although observations suggest that the flowers Results produce nectar, the quantities produced are so Plants reproductive traits and flower mor- small that they cannot be realiably measured. phology. On average, plants in the study site Pollinators. The abundance of the insects produced 6.4±0.6 flowers [range: 1–21, n ¼ 40] visiting the flowers of E. willkommii was per year. Fruit set and the SO ratio of extremely low. During the diurnal period, no successful fruit (both in percentage) were insect was observed at all visiting the flowers of 75.5±5.0 [0–100] and 79.5±2.1 [10–100], E. willkommii during 1995. In 1996 I observed respectively. Consequently, the average only two species of flower visitors, an ant number of seeds produced per plant every species (Proformica longiseta, Formicidae), year was 37.7±6.2[0–210].The only repro- and an unknown thrip species (Thysanoptera), ductive parameter varying between years was with only 3 and 1 plant visited, respectively. In fruit set, which was significantly higher in 1996 addition, no insect at all was observed visiting than in 1995 (Table 1). the flowers of E. willkommii during the The flower of E. willkommii had a wide nocturnal censuses. For this reason, only 3% corolla, 4.79±0.14 mm in width and of the 128 plants I monitored received an insect 3.49±0.09 mm in length of the central petal, visit during the study period.

Table 1. Between-years comparisons of reproductive parameters of Euphrasia willkommii 1995 1996 F# Flowers/plant 7.3 ± 0.8 5.8 ± 0.9 1.34 ns Fruits/plant 3.9 ± 0.4 5.3 ± 0.8 1.54 ns Seeds/plant 25.3 ± 2.7 46.9 ± 10.3 3.16 Fruit set (%) 58.4 ± 5.9 88.4 ± 6.211.71*** SO ratio (%) 79.9 ± 3.4 79.5 ± 2.5 0.01 ns # df = 1, 38, ns = non-significant, p = 0.08, *** p < 0.002. All p-values adjusted to a = 0.05 after Bonferroni correction

Table 2. Descriptive statistics of each floral trait considered. Also shown is the variance-covariance matrix among floral traits. Figures above diagonal are covariances, in diagonal are variances, and below diagonal are correlations. Correlations statistically significants after Bonferroni correction appear in bold face Floral traits Mean ± 1 Range Variance-covariance matrix SE (mm) Corolla Central petal Lateral petal Corolla width length length depth

Corolla width 4.8±0.1 2.1–6.6 1.115 0.665 0.593 )0.080 Central petal length 3.5±0.1 1.3–4.8 0.860 0.537 0.410 )0.552 Lateral petal length 2.5±0.1 1.1–3.8 0.803 0.799 0.490 )0.359 Corolla depth 4.3±0.23.5–6.2 )0.021 )0.142 )0.126 0.574 J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae 67

Both species of flower visitors apparently P=0.56) and seeds/plants (F2,57=0.15, visited the flower for nectar. The thrip spent P=0.86, see Fig. 2). considerable time visiting the same flower Role of pollinators in plant reproductive (about five minutes), whereas the ants usually success. Whereas fruit set was statistically spent little time at each flower (less than 30 s), similar among treatments, SO ratio was visiting only one or two flowers per plant. significantly lower in plants excluded from Nevertheless, the ants observed were appar- winged insects (Table 3). Furthermore, the ently visiting E. willkommii flowers only number of seeds produced per plant was incidentally, since they spent much more time similar in plants excluded from winged insects, visiting flowers of co-occurring plant species wingless insects or from all pollinators than in as Sedum anglicum, Thymus serpylloides, Hor- flowers left open to all pollinators (Table 3). mathophylla spinosa, Alyssum purpureum or Experimental determination of pollen limi- Arenaria tetraquetra, the flowers of which tation. The experiment showed that the plants were aboundantly visited by these apterous are not pollen limited, since there were no insects. differences between control and pollen-supple- By using magnifying glasses, I searched for mented plants in fruit set (F1,38=2.18, P= E. willkommii pollen grains on the body of the 0.15), SO ratio (F1,38=0.58, P=0.41), fruits/ ants. However, due to the low number of plant (F1,38=0.084, P=0.77) and seeds/plants flower visitor specimens collected, I could not (F1,38=0.001, P=0.98, see Fig. 3). determine whether they actually are a pollen vector of E. willkommii. Nevertheless, I Discussion observed ants touching the anthers and stigma of the flowers during foraging bouts. I could The several experiments conducted during not gather information on thrips. 1995 and 1996 strongly imply that Experimental study of the breeding E. willkommii has the capacity for a high system. No difference was found between degree of autofertility and relies mainly on treatments in any of the components of selfing, since the fruit set and seed set were reproductive success examined, such as fruit similar between autogamously- and alloga- set (F2,57=1.43, P=0.25), SO ratio (F2,37= mously hand-pollinated plants, and spontane- 0.08, P=0.92), fruits/plant (F2,57=0.58, ously selfed flowers produced the same amount

Fig. 2. Differences between treat- ments in reproductive parameters of Euphrasia willkommii; SA Spontane- ous Autogamy, OA Obligated Autog- amy, and X Xenogamy 68 J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae

Table 3. Results of the experimental exclusion of floral visitors. Within a column, values with different superscripts differ significantly after Bonferroni correction Treatments Fruit set (%) SO ratio (%) Seeds/plant Control 58.4 ± 05.9 79.9 ± 3.4a 18.1 ± 1.7 Only ants 49.8 ± 11.3 55.7 ± 3.8b 10.4 ± 0.8 Only winged 53.7 ± 05.5 71.8 ± 5.4a,b 15.0 ± 2.1 No pollinator 47.6 ± 07.9 71.0 ± 6.8a,b 17.5 ± 2.8 F-value# 0.88 ns 4.53** 3.53 ns # df = 3, 56, ns = non significant, ** p < 0.01. All p-values adjusted to a ¼ 0:05 after Bonferroni cor- rection

Fig. 3. Effect of experimental pollen supplementation on the reproductive success of Euphrasia willkommii of fruits and seeds as did hand-pollinated isons. Nevertheless, this species bears flowers flowers and open-pollinated flowers. Several significantly smaller that those borne by other additional traits of E. willkommii suggest that co-occurring Scrophulariaceae, as Digitalis this plant species is primarily autogamous. purpurea L. Linaria glacialis Boiss. or Chae- Thus, nectar production is extremely low, if norrhinum glareosum (Boiss.) Willk. (Molero not absent in most flowers. In addition, its Mesa et al. 1992). flowers are very small, only 5 mm in width and Selfing in Euphrasia species has long been 4 mm in length. A decrease in flower size has reported (see e.g. Mu¨ ller 1883). No information been repeatedly associated with the evolution exists about the mechanisms promoting selfing toward selfing (e.g. Herrera 1992). Indeed, in E. willkommii. A main mechanism favouring Ortega Olivencia and Devesa (1993a) have selfing in many Euphrasia species, like in other shown that the autogamous species of iberian Scrophulariaceae (Dole 1990, 1992; Donnelly Scrophularia have flowers significantly smaller et al. 1998; Kalisz et al. 1999), is delayed self- than the outcrossers. Unfortunately, there is pollination. Selfing is prevented during the first no other Euphrasia species, whether outcros- day of the flower life by a pronounced herkog- sers or selfers, in the alpine of the Sierra amy, when the stigma projects beyond the tip Nevada to make accurate flower-size compar- of the corolla. However, the corolla later J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae 69 elongates, moving the adnate stamens, whereas et al. 1996). The limitation of pollinators is so the style does not increase in length. Conse- extreme in these habitats that some typical quently, during the last days of the lifetime of a entomophilous plant species (for example, the flower, anthers and stigma become closer, crucifer Hormathophylla spinosa) have even leading to self-pollination (Faegri and van der evolved the ability of using wind as a pollen Pijl 1979). Delayed self-pollination occurs if vector in their highest populations (Go´ mez and flowers have not previously been pollinated Zamora 1996). The presence of the few ants and (Dole 1990, Navarro 1997, Kalisz et al. 1999). thrips found in the flowers of E. willkommii is Nevertheless, Leclerc-Potvin and Ritland made possible by the fact that the small and low- (1994) did not found delayed selfing in Mimulus reward flowers are wide, short and tubular, guttatus. For this reason, it is necessary to allowing access to almost any type of insect. In study whether selfing in E. willkommii is addition, since the entire plant is very low (<5 promoted by delayed self-pollination or by cm in height), the flowers are normally very close any other mechanism, as for example incom- to the ground, discouraging discovery by and plete dichogamy or close proximity of anthers accessibility for large flying insects and thus and stigmas during dehiscence. favouring access by non-flying insects such as The ecological scenario where E. willkommii ants. inhabits, the Mediterranean high-mountains of Selfing may explain why, despite the SE Spain, presumably favour the evolution of absence of floral visitors, E. willkommii proved selfing, since stressful abiotic conditions usually not to be pollen-limited in natural conditions. make pollinators a limiting resource – either This contrasts with many other alpine plants, scarce and unpredictable or lacking synchrony in which reproduction is highly limited by between insect life cycles and flowering (Go´ mez pollen availability (Galen 1985, Berry and and Zamora 1996). Indeed, the pollinator Calvo 1991, Campbell 1991, Stentro¨ m and censuses during two reproductive seasons, Molau 1992). Furthermore, selfing could also with almost 90 hours of observations, have explain why the percentage of flowers ripening shown that, in fact, the abundance of insects at to fruit and the percentage of ovules ripening E. willkommii flowers is quite low in these alpine to seed is very high in E. willkommii (>80% for environments. I observed many flowers wilted both parameters). Empirical and theoretical without receiving a single insect visit. In addi- studies have shown that these two ratio- tion, the species of insects visiting the flowers of oriented estimates of the reproductive success E. willkommii, ants and thrips, were tiny and are usually low in allogamous but high in considered as generalist and low-efficient pol- autogamous plant species (e.g. Lee 1988). All linators. This observation contrasts with the of these data suggest the benefit that selfing abundant literature on the pollination ecology can confer on E. willkommii reproduction, of many other species of plants belonging to the although it may be necessary to explore the Scrophulariaceae, which have shown that the effect of selfing on other, postdispersal stages floral visitors are usually efficient pollinators, of the recruitment process, as for example seed such as hummingbirds, moths, butterflies, bum- germination or seedling survival. blebees, long-tongued bees, etc. (e.g. Dieringer In brief, according to the data of this study, 1992, Vickery 1992, Ortega Olivencia and E. willkommii is predominantly autogamous. Devesa 1993b, Sutherland and Vickery 1993, In this case, selfing appears to be an ecological Kampny 1995, Kampny and Dengler 1997, mechanism to ensure successful reproduction Jones and Reithel 2001). Ants, and other gen- in a harsh environment where pollinator eralist floral visitors such as mosquitoes or availability and predictability is extremely low. Muscid flies, are important pollinators of other plant species in the Sierra Nevada high moun- Adela Gonza´ lez Megı´ as helped during the field tains (Go´ mez and Zamora 1992, 1999; Go´ mez work. I thank very much the comments of Dr. Luı´ s 70 J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae

Navarro which have substancially improved an Galen C. (1985) Regulation of seed-set in Polemo- early version of the manuscript. David Nesbitt nium viscosum: floral scents, pollination, and improved the English. This work was partially resource. Ecology 66: 792–797. supported by DGICYT grants PB900852y Go´ mez J. M., Zamora R. (1992) Pollination by AMB95-0479. ants: consequences of the quantitative effects on a mutualistic system. Oecologia 91: 410–418. Go´ mez J. M., Zamora R. (1996) Wind pollination References in high-mountain populations of Hormathophy- lla spinosa (Cruciferae). Amer. J. Bot. 83: 580– Aarssen L. W. (2000) Why are most selfers annu- 585. als? A new hypothesis for the fitness benefit of Go´ mez J. M., Zamora R. (1999) Generalization vs. selfing. Oikos 89: 606–612. specialization in the pollination system of Hor- Arroyo M. K. T., Pen˜ azola A. (1990) Genetic self- mathophylla spinosa (Cruciferae). Ecology 80: incompatibility in a South American species of 796–805. Ourisia (Scrophulariaceae). New Zeal. J. Bot. 28: Go´ mez J. M., Zamora R., Ho´ dar J. A., Garcı´ aD. 467–476. (1996) Experimental determination of pollina- Barrett S. C. H. (1998) The evolution of mating tion by ants in Mediterranean high mountain strategies in flowering plants. Trends in Plant and arid habitats. Oecologia 105: 236–242. Science 3: 335–341. Herrera J. (1992) Flower variation and breeding Berry P. E., Calvo R. N. (1991) Pollinator limita- system in the Cistaceae. Plant Syst. Evol. 179: tion and position dependent fruit set in the high 245–255. Andean orchid Myrosmodes cochlerare (Orchid- Holsinger K. E. (1992) Ecological models of plant aceae). Plant Syst. Evol. 174: 93–101. mating systems and the evolutionary stability of Campbell D. R. (1991) Effects of floral traits on mixed mating systems. In: Wyatt R. (ed.) Ecol- sequential components of fitness in Ipomopsis ogy and evolution of plant reproduction. Chap- aggregata. Amer. Nat. 137: 713–737. man and Hall, New York, NY, pp. 169–191. Dieringer G. (1992) Pollinator effectiveness and Holsinger K. E. (2000) Reproductive systems and seed set in populations of Agalinis strictifolia evolution in vascular plants. Proc. Natl. Acad. (Scrophulariaceae). Amer. J. Bot. 79: 1018–1023. Sci. 97: 7037–7042. Dole J. A. (1990) Role of corolla abscission in Jones K. N., Reithel J. S. (2001) Pollinator-medi- delayed self-pollination of Mimulus guttatus ated selection on a flower color polymorphism in (Scrophulariaceae). Amer. J. Bot. 77: 1505–1507. experimental populations of Antirrhinum Dole J. A. (1992) Reproductive assurance mecha- (Scrophulariaceae). Amer. J. Bot. 88: 447–454. nisms in three taxa of the Mimulus guttatus Kalisz S., Vogler D., Fails B., Finer M., Shepard complex (Scrophulariaceae). Amer. J. Bot. 79: E., Herman T., Gonzales R. (1999) The mech- 650—659. anism of delayed selfing in Collinsia verna Donnelly S. E., Lortie C. J., Aarssen L. W. (1998) (Scrophulariaceae). Amer. J. Bot. 86: 1239–1247. Pollination in Verbascum thapsus (Scrophularia- Kampny C. M. (1995) Pollination and flower ceae): the advantage of being tall. Amer. J. Bot. diversity in Scrophulariaceae. The Botanical 85: 1618–1625. Review 61: 350–366. Erhardt A., Jaggi B. (1995) From pollination by Kampny C. M., Dengler N. G. (1997) Evolution of Lepidoptera to selfing: the case of Dianthus flower shape in Veroniceae (Scrophulariaceae). glacialis (Caryophyllaceae). Plant Syst. Evol. Plant Syst. Evol. 205: 1–25. 195: 67–76. Lee T. D. (1988) Patterns of fruit and seed Faegri K., van der Pijl L. (1979) The principles of production. In: Lovett Doust J., Lovett Doust pollination ecology, 3rd edn. Pergamon Press. L. (eds.) Plant reproductive ecology, patterns Fausto J. A., Eckhart V. M., Geber M. A. (2001) and strategies. Oxford University Press, New Reproductive assurance and the evolutionary York, USA, pp. 179–202. ecology of self-pollination in Clarkia xantiana Leclerc-Potvin C., Ritland K. (1994) Modes of (Onagraceae). Amer. J. Bot. 88: 1794–1800. self-fertilization in Mimulus guttatus (Scrophu- J. M. Go´ mez: Self-pollination as reproductive assurance in an alpine Scrophulariaceae 71

lariaceae): a field experiment. Amer. J. Bot. 81: Schoen D. J., Morgan M. T., Bataillon T. (1997) 199–205. How does self-pollination evolve? Inferences Molero Mesa J., Perez Raya F., Valle F. (1992) from floral ecology and molecular genetic vari- Parque Natural de Sierra Nevada: Paisaje, ation. In: Silvertown J., Franco M., Harper J. L. fauna, flora, itinerarios. Editorial Rueda, Alco- (eds.) Plant life history. Cambridge University rco´ n, Madrid, Spain. Press, Cambridge, UK, pp. 77–101. Mu¨ ller H. (1883) The fertilization of flowers. Stenstro¨ m M., Molau U. (1992) Reproductive Macmillan and Co, London, UK. ecology of Saxifraga oppositifolia: Phenology, Navarro L. (1997) Is the dichogamy of Salvia mating system, and reproductive success. Artic verbenaca (Lamiaceae) an effective barrier to and Alpine Research 24: 337–343. self-fertilization? Plant Syst. Evol. 207: 111–117. Sutherland S. D., Vickery R. K. (1993) On the Navarro L., Guitian J. (2001) The role of floral relative importance of floral color, shape, and biology and breeding system on the reproductive nectar reward in attracting pollinators to Mimu- success of the narrow endemic Petrocoptis visco- lus. Great Basin Naturalist 53: 107–117. sa Rothm. (Caryophyllaceae). Biol. Conserv. Vickery R. K. (1992) Pollinator preferences for 103: 125–132. yellow, orange, and red flowers of Mimulus Ortega Olivencia A., Devesa J. A. (1993a) Sexual verbenaceous and M. cardinalis. Great Basin reproduction in some Scrophularia species Naturalist 52: 145–148. (Scrophulariaceae) from the Iberian Peninsula and the Balearic Islands. Plant Syst. Evol. 184: 159–174. Address of the author: Jose´ M. Go´ mez, Ortega Olivencia A., Devesa J. A. (1993b) Floral Departamento de Biologı´ a Animal y Ecologı´ a, rewards in some Scrophularia species (Scrophu- Fac. de Ciencias, Universidad de Granada, lariaceae) from the Iberian Peninsula and the E-18071 Granada, Spain (e-mail: jmgreyes@goli- Balearic Islands. Plant Syst. Evol. 184: 139–158. at.ugr.es).