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South African Journal of Botany 73 (2007) 657–660 www.elsevier.com/locate/sajb

Short communication Investigation of the breeding systems of four species in Namaqualand, ⁎ C. Mayer a, , G. Pufal b

a Biocentre Klein Flottbek and Botanical Garden, University of Hamburg, Ohnhorststrasse 18, 22609 Hamburg, Germany b Institute for Biodiversity Research and Botanical Institute, University of Rostock, Germany Received 7 November 2006; received in revised form 4 June 2007; accepted 7 June 2007

Abstract

We investigated the breeding systems of four different Aizoaceae species in Namaqualand, South Africa. Results showed that all four species are xenogamous with negligible amounts of seeds produced when flowers are left to spontaneous self-pollination (autogamy) or self-pollinated. Experiments allowing single visits of pollinators resulted in significantly higher seed numbers in relation to bagged unmanipulated flowers for two species. Pollen–ovule ratios were extremely high and supported the notion that the investigated Aizoaceae species are obligate outcrossers depending on insects as pollen vectors. © 2007 SAAB. Published by Elsevier B.V. All rights reserved.

Keywords: Cheiridopsis; Leipoldtia; Pollen–ovule ratio; Pollination experiments; Ruschia

1. Introduction 2. Material and methods

Aizoaceae and Asteraceae are the two most dominant During the main flowering season (August to October) of families of the Succulent Karoo Biome in South Africa 2003 and 2004 field experiments were conducted on two (Cowling and Hilton-Taylor, 1994). The prevailing life forms standardized 1 km2 Biodiversity Observatories in the area of in this winter rainfall area are succulent dwarf shrubs. Plant Leliefontein. Annual precipitation in this arid winter rainfall species belonging to the Aizoaceae have been considered to be region ranges from 150 to 250 mm with a coefficient of variance self-incompatible (Jacobson 1960 in Milton et al., 1997) and of 33% (Todd and Hoffman, 1999). Struck (1994) reports entomophilous pollination syndromes for The breeding systems of (Haw.) most of the species in the Goegap Nature Reserve. Only clonal, N.E.Br., Cheiridopsis imitans L.Bolus, Ruschia goodiae invasive Carpobrotus species have been reported to be self- L.Bolus, and Leipoldtia schultzei (Schltr. and Diels) Friedrich compatible (Vilà et al., 1998; Suehs et al., 2004). However, very were investigated. For pollination experiments, between 42 and few field studies on the breeding systems of Aizoaceae have 74 buds on as many (i.e. only one bud per plant individual) been conducted (but see Peter et al., 2004) and so far, pollen– of each species were bagged individually with gauze to prevent ovule ratios (i.e. pollen grains per flower divided by ovules per access of pollinators. Of these, after anthesis, 35 to 41 flowers per flower) have only been reported for Carpobrotus (Suehs et al., species were left for spontaneous self-pollination (autogamy). To 2006). Cruden (1977) proposed that this ratio is a good indicator test for self-compatibility, another 15 individuals of C. imitans for plant breeding systems. With the investigation of four (with 93 flowers in total) and L. schlutzei (with 26 flowers in total) Aizoaceae species growing in Namaqualand, the north-western were completely covered with gauze. When all flowers had part of the Succulent Karoo (Rutherford and Westfall, 1986), we opened they were self-pollinated with flowers from the same aimed to contribute to the knowledge about this huge and plant. Due to practicability (much bigger plant individuals) and diverse family. time limitation this experiment was not applied to C. denticulata and R. goodiae. ⁎ Corresponding author. The remaining individually bagged flowers were emascu- E-mail address: [email protected] (C. Mayer). lated to avoid autogamy and single visits of pollinators were

0254-6299/$ - see front matter © 2007 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2007.06.001 658 C. Mayer, G. Pufal / South African Journal of Botany 73 (2007) 657–660 simulated. For that purpose, pollinators (Apoidea — bees, (Zeiss Axiovert 10) following a modified method used by Bombyliidae — bee flies, Hopliini — monkey beetles) were Jürgens et al. (2002). caught from flowers of the same species and put on the bagged After testing for normal distribution (with the Kolmogorov– flowers. Unfortunately, this method was not applicable for Smirnoff test) pair wise comparisons between independent L. schultzei since its flowers are very small and insects got groups were conducted with student's t-test (pollen–ovule caught in the gauze bags before reaching the stigma. A more ratios) or Mann–Whitney-U test (number of seeds), according subtle method would have been to remove the bags for the to the distribution of the data. For repeated comparisons, critical single visit of a pollinator and close the flowers again. However, levels of significance were adjusted according to the Bonferroni the mean visitation rate on the study sites was 1.5 visits per method (Dytham, 2003). flower per hour (unpublished data) definitely exceeding the limits of the experiment. 3. Results After fruiting, capsules were collected, dried at 80 °C for 24 h to kill potential seed predators, and mature seeds counted. All flowers that were excluded from insect pollination Additionally, 60 to 90 fruits from each species were collected (“autogamy”) and that had been self-pollinated with pollen from randomly from the study sites as control to measure natural the same plant developed extremely few seeds (Fig. 1A–D). A pollination in the field. All fruits that had been damaged by seed single visit by a pollinator, however, resulted in significantly predators were excluded from analyses. more seeds per capsule compared to those fruits that had been To determine pollen–ovule ratios, ten buds of each species left to spontaneous self-fertilization (Fig. 1A–C) and those were collected and conserved in 70% alcohol. Anthers, pollen resulting from self-pollination (Fig. 1A). Capsules without and ovules were counted with the help of an inverse microscope treatment (“control”)ofC. imitans and R. goodiae contained

Fig. 1. A–D. Number of seeds per fruit capsule resulting from different treatments for the examined species (Boxes followed by the same letter are not significantly different at minimum pb0.0167, multiple Mann–Whitney-U tests, Bonferroni adjusted p-levels). C. Mayer, G. Pufal / South African Journal of Botany 73 (2007) 657–660 659

Table 1 Thus, the high ratios determined for the investigated Aizoaceae Mean (±SD) number of anthers, pollen grains and ovules per bud and the species substantiate the suggestion that they are xenogamous resulting pollen–ovule ratios (p/o) of investigated species (Lines that share the same letter are not significantly different at minimum pb0.0167, multiple and depend on insects as pollen vectors. On the other hand, student's t-tests, Bonferroni adjusted p-levels) Carpobrotus affine acinaciformis and Carpobrotus edulis have comparable proportions of pollen to ovules (3000 to 3500), but N Anthers Pollen total Ovules p/o are partially and fully self-compatible (Suehs et al., 2006). It C. denticulata 10 594 a 3 047 657 a 1 484 a 2 146 a seems that the capability to self-pollinate in these species is (±152) (±1 020 139) (±296) (±879) C. imitans 10 918 b 4 185 728 a 474 b 10 641 b rather an exception and supports their invasive character. (±448) (±2 161 233) (±220) (±7 987) Pollination experiments further demonstrated that a single R. goodiae 9 127 c 489 462 b 78 c 6 402 b visit of a pollinator can lead to full pollination success for species (±17) (±123 591) (±11) (±1 859) that have low ovule numbers (e.g. Ruschia). Other species like L. schultzei 10 98 d 422 932 b 131 d 3 366 c C. denticulata also received considerable amounts of pollen (±16) (±84 927) (±30) (±907) from single visits. It is concluded that one pollinator visit alone is sufficient for ample pollination. relatively low numbers of seeds (mean: 45 and 23). Fruits of Whether species like L. schultzei or C. imitans might suffer these two species showed no significant differences in seed from pollinator limitation remains to be tested since in this study numbers when pollinated naturally or visited by a single no xenogamous hand pollinations were performed. Generally, pollinator (Fig. 1A and B). C. denticulata on the other hand is a low seed to ovule ratios can also result from other factors like species with very high numbers of seeds per capsule (mean b1 nutrient shortages or represent random fluctuations around a 100) under natural conditions. Here, fruits that had been visited pollen-resource equilibrium (Ashman et al., 2004). However, by a single pollinator contained significantly fewer seeds than flowers blooming in Namaqualand probably compete for fruits that had been naturally pollinated (Fig. 1C). L. schultzei pollinators (Marloth, 1908; Moldenke, 1976; Cohen and was the only species where autogamy, geitonogamy and natural Shmida, 1993; Struck, 1994, 1995; Pufal et al., in press). Most pollination resulted in similar numbers of seeds (Fig. 1D) surprising was that the two Cheiridopsis species having solitary although the range of seed numbers per capsule for control fruits and terminated, cream or yellow flowers of comparable size (30 was much larger. A reason might be the remarkably low seed to 50 mm in diameter, unpublished data), with overlapping numbers in general (mean: 8). Under natural conditions on blooming periods following a steady state strategy (Proctor and average only 6% of the ovules get fertilized. In contrast, Yeo, 1996), have such different pollination success. Both species R. goodiae having slightly higher numbers of ovules but similar share the same pollinators but whether the low fertilization rate amounts of pollen (Table 1) had almost 30% of its ovules of C. imitans (10%) compared to C. denticulata (74%) results pollinated. But the two phylogenetically and morphologically from competition for visiting insects remains to be investigated. related Cheiridopsis species differed enormously in this respect: while only 10% of the ovaries of C. imitans were fertilized, Acknowledgements C. denticulata was notably “successful” with a fertilization rate of 74%. This is even more astounding since C. denticulata has This study was embedded in BIOTA Southern Africa (www. about 2/3 more ovaries than C. imitans but comparable numbers biota-africa.com) which is sponsored by the German Federal of pollen grains (Table 1). Ministry of Education and Research (Bmbf 01LC0024). Northern All examined Aizoaceae species showed extremely high Cape Nature Conservation Services kindly issued research pollen–ovule ratios. R. goodiae and C. imitans had statistically permits. Gesine Pufal acknowledges the financial support comparable ratios on average ranging up to 6000 and 10000. provided by the Hans Merensky Foundation. Anonymous For C. denticulata and L. schultzei on the other hand referees gave helpful comments to improve the manuscript. significantly lower proportions of mean 2000 and 3000 were determined (Table 1). References

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Edited by J Van Staden