1
|
McCarren S, Johnson SD, Theron GL, Coetzee A, Turner R, Midgley J. Flower orientation and corolla length as reproductive barriers in the pollinator-driven divergence of Erica shannonea and Erica ampullacea. Plant Biol J 2023; 25:1083-1090. [PMID: 37676744 DOI: 10.1111/plb.13575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 08/08/2023] [Indexed: 09/09/2023]
Abstract
A variety of reproductive barriers can enable reproductive isolation and stable coexistence of plant species. Differing floral traits might play an important role in reproductive isolation imposed by pollinators. Such shifts in pollinator use have been hypothesized to contribute to the radiation of Erica (Ericaceae) in the Cape Floristic Region, South Africa. The sister species Erica shannonea and Erica ampullacea co-occur and overlap in flowering phenology. Both have unscented long-tubed flowers consistent with adaptations for pollination by long-proboscid flies (LPFs), but differences in flower orientation and corolla tube length are indicative of a shift in pollinator species. We conducted controlled pollination experiments and pollinator observations to determine the breeding system and pollinators of the two species. Both species are self-incompatible and require pollinator visits for seed production, suggesting that pollinators could strongly influence flower evolution. The horizontally orientated flowers of E. shannonea were found to be pollinated by Philoliche rostrata (Tabanidae), which has a long, fixed forward-pointing proboscis, while the vertically upright orientated flowers of E. ampullacea were found to be pollinated by Prosoeca westermanni (Nemestrinidae), which has a shorter proboscis that can swivel downwards. The nemestrinid fly's proboscis is too short to access the nectar in the relative long-tubed flowers of E. shannonea and the tabanid fly's proboscis cannot swivel down to access the upright flowers of E. ampullacea. Consequently, these traits are likely to act as reproductive barriers between the two Erica species and thereby might have contributed to speciation and enable stable coexistence.
Collapse
Affiliation(s)
- S McCarren
- Department of Biological Sciences, University of Cape Town, Cape Town, South Africa
| | - S D Johnson
- Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa
| | - G L Theron
- Department of Natural Sciences, KwaZulu-Natal Museum, Pietermaritzburg, South Africa
| | - A Coetzee
- Nelson-Mandela University, George, South Africa
| | - R Turner
- Department of Biological Sciences, University of Cape Town, Cape Town, South Africa
| | - J Midgley
- Department of Biological Sciences, University of Cape Town, Cape Town, South Africa
| |
Collapse
|
2
|
Coetzee A, Spottiswoode CN, Seymour CL. Post-pollination barriers enable coexistence of pollinator-sharing ornithophilous Erica species. J Plant Res 2020; 133:873-881. [PMID: 32997284 DOI: 10.1007/s10265-020-01226-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2020] [Accepted: 09/23/2020] [Indexed: 06/11/2023]
Abstract
Some evolutionary radiations produce a number of closely-related species that continue to coexist. In such plant systems, when pre-pollination barriers are weak, relatively strong post-pollination reproductive barriers are required to maintain species boundaries. Even when post-pollination barriers are in place, however, reproductive interference and pollinator dependence may strengthen selection for pre-pollination barriers. We assessed whether coexistence of species from the unusually speciose Erica genus in the fynbos biome, South Africa, is enabled through pre-pollination or post-pollination barriers. We also tested for reproductive interference and pollinator dependence. We investigated this in natural populations of three bird-pollinated Erica species (Erica plukenetii, E. curviflora and E. coccinea), which form part of a large guild of congeneric species that co-flower and share a single pollinator species (Orange-breasted Sunbird Anthobaphes violacea). At least two of the three pre-pollination barriers assessed (distribution ranges, flowering phenology and flower morphology) were weak in each species pair. Hand-pollination experiments revealed that seed set from heterospecific pollination (average 8%) was significantly lower than seed set from outcross pollination (average 50%), supporting the hypothesis that species boundaries are maintained through post-pollination barriers. Reproductive interference, assessed in one population by applying outcross pollen three hours after applying heterospecific pollen, significantly reduced seed set compared to outcross pollen alone. This may drive selection for traits that enhance pre-pollination barriers, particularly given that two of the three species were self-sterile, and therefore pollinator dependent. This study suggests that post-pollination reproductive barriers could facilitate the coexistence of congeneric species, in a recent radiation with weak pre-pollination reproductive barriers.
Collapse
Affiliation(s)
- Anina Coetzee
- FitzPatrick Institute of African Ornithology, DSI-NRF Centre of Excellence, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa.
| | - Claire N Spottiswoode
- FitzPatrick Institute of African Ornithology, DSI-NRF Centre of Excellence, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa
- Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK
| | - Colleen L Seymour
- FitzPatrick Institute of African Ornithology, DSI-NRF Centre of Excellence, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa
- South African National Biodiversity Institute, Kirstenbosch Research Centre, Claremont, 7753, South Africa
| |
Collapse
|
3
|
Pirie MD, Kandziora M, Nürk NM, Le Maitre NC, Mugrabi de Kuppler A, Gehrke B, Oliver EGH, Bellstedt DU. Leaps and bounds: geographical and ecological distance constrained the colonisation of the Afrotemperate by Erica. BMC Evol Biol 2019; 19:222. [PMID: 31805850 PMCID: PMC6896773 DOI: 10.1186/s12862-019-1545-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 11/21/2019] [Indexed: 12/28/2022] Open
Abstract
Background The coincidence of long distance dispersal (LDD) and biome shift is assumed to be the result of a multifaceted interplay between geographical distance and ecological suitability of source and sink areas. Here, we test the influence of these factors on the dispersal history of the flowering plant genus Erica (Ericaceae) across the Afrotemperate. We quantify similarity of Erica climate niches per biogeographic area using direct observations of species, and test various colonisation scenarios while estimating ancestral areas for the Erica clade using parametric biogeographic model testing. Results We infer that the overall dispersal history of Erica across the Afrotemperate is the result of infrequent colonisation limited by geographic proximity and niche similarity. However, the Drakensberg Mountains represent a colonisation sink, rather than acting as a “stepping stone” between more distant and ecologically dissimilar Cape and Tropical African regions. Strikingly, the most dramatic examples of species radiations in Erica were the result of single unique dispersals over longer distances between ecologically dissimilar areas, contradicting the rule of phylogenetic biome conservatism. Conclusions These results highlight the roles of geographical and ecological distance in limiting LDD, but also the importance of rare biome shifts, in which a unique dispersal event fuels evolutionary radiation.
Collapse
Affiliation(s)
- Michael D Pirie
- Institut für Organismische und Molekulare Evolutionsbiologie, Johannes Gutenberg-Universität, Anselm-Franz-von-Bentzelweg 9a, 55099, Mainz, Germany. .,Department of Biochemistry, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa. .,Current address: University Museum, The University of Bergen, Postboks 7800, N-5020, Bergen, Norway.
| | - Martha Kandziora
- Institut für Organismische und Molekulare Evolutionsbiologie, Johannes Gutenberg-Universität, Anselm-Franz-von-Bentzelweg 9a, 55099, Mainz, Germany.,Life and Environmental Sciences, School of Natural Sciences, University of California, Merced, USA
| | - Nicolai M Nürk
- Department of Plant Systematics, Bayreuth Centre of Ecology and Environmental Research (BayCEER), University of Bayreuth, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Nicholas C Le Maitre
- Department of Biochemistry, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa.,Department of Plant Science, University of the Free State, QwaQwa, Bloemfontein, South Africa
| | - Ana Mugrabi de Kuppler
- INRES Pflanzenzüchtung, Rheinische Friedrich-Wilhelms-Universität Bonn, Katzenburgweg 5, 53115, Bonn, Germany
| | - Berit Gehrke
- Institut für Organismische und Molekulare Evolutionsbiologie, Johannes Gutenberg-Universität, Anselm-Franz-von-Bentzelweg 9a, 55099, Mainz, Germany.,Current address: University Museum, The University of Bergen, Postboks 7800, N-5020, Bergen, Norway
| | - Edward G H Oliver
- Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
| | - Dirk U Bellstedt
- Department of Biochemistry, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa
| |
Collapse
|
4
|
Theron GL, de Waal C, Barrett SCH, Anderson B. Geographic variation of reproductive traits and competition for pollinators in a bird-pollinated plant. Ecol Evol 2019; 9:10122-10134. [PMID: 31673331 PMCID: PMC6816071 DOI: 10.1002/ece3.5457] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Revised: 04/25/2019] [Accepted: 05/28/2019] [Indexed: 11/19/2022] Open
Abstract
Geographic variation in the reproductive traits of animal-pollinated plants can be shaped by spatially variable selection imposed by differences in the local pollination environment. We investigated this process in Babiana ringens (Iridaceae), an enigmatic species from the Western Cape region of South Africa. B. ringens has evolved a specialized perch facilitating cross-pollination by sunbirds and displays striking geographic variation in perch size and floral traits. Here, we investigate whether this variation can be explained by geographic differences in the pollinator communities. We measured floral and inflorescence traits, and abiotic variables (N, P, C, and rainfall) and made observations of sunbirds in populations spanning the range of B. ringens. In each population, we recorded sunbird species identity and measured visitation rates, interfloral pollen transfer, and whether the seed set of flowers was pollen limited. To evaluate whether competition from co-occurring sunbird-pollinated species might reduce visitation, we quantified nectar rewards in B. ringens and of other co-flowering bird-pollinated species in local communities in which populations occurred. Variation in abiotic variables was not associated with geographical variation of traits in B. ringens. Malachite sunbirds were the dominant visitor (97% of visits) and populations with larger-sized traits exhibited higher visitation rates, more between-flower pollen transfer and set more seed. No sunbirds were observed in four populations, all with smaller-sized traits. Sunbird visitation to B. ringens was not associated with local sunbird activity in communities, but sunbird visitation was negatively associated with the amount of B. ringens sugar relative to the availability of alternative nectar sources. Our study provides evidence that B. ringens populations with larger floral traits are visited more frequently by sunbirds, and we propose that visitation rates to B. ringens may be influenced, in part, by competition with other sunbird-pollinated species.
Collapse
Affiliation(s)
- Genevieve L. Theron
- Department of Botany and ZoologyStellenbosch UniversityMatielandSouth Africa
| | - Caroli de Waal
- Department of Botany and ZoologyStellenbosch UniversityMatielandSouth Africa
| | | | - Bruce Anderson
- Department of Botany and ZoologyStellenbosch UniversityMatielandSouth Africa
| |
Collapse
|
5
|
Stock WD, Wienand KT, Baker AC. Impacts of invading N 2-fixing Acacia species on patterns of nutrient cycling in two Cape ecosystems: evidence from soil incubation studies and 15N natural abundance values. Oecologia 1995; 101:375-382. [PMID: 28307060 DOI: 10.1007/bf00328825] [Citation(s) in RCA: 144] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/1994] [Accepted: 10/16/1994] [Indexed: 10/26/2022]
Abstract
This study examines the impacts of woody, N2-fixing invasive Acacia spp. on the patterns of nutrient cycling in two invaded ecosystems of differing nutrient status in the Cape floristic region. Patterns of soil nutrient mineralization were measured by a field incubation method while the significance of the fixation process in altering nutrient cycling was assessed by the δ15N natural abundance technique. The results confirm earlier reports that invasion by woody shrubs results in organic matter and nutrient enrichment of surface soils of both ecosystems. However, patterns of nutrient availability (phosphorus and nitrogen) were not necessarily enhanced. In the more fertile strandveld both phosphorus and nitrogen (significant at P<0.10) showed trends towards enhanced annual mineralization rates upon invasion, while in the low nutrient fynbos system only phosphorus followed this trend. It is unclear whether this differential response is a consequence of plant- or soil-derived feedbacks on the decomposition processes in each system. The δ15N values of the soils from the invaded sites of both ecosystems indicated a strong influence of the alien species on the soil nitrogen component. However, as with other studies of natural ecosystems, the contribution of nitrogen from fixation could not be readily quantified with the δ15N natural abundance method because of problems in selecting suitable non-N2-fixing reference plants. A technique of disrupting nodule structure and function, by fumigation with O2, to obtain the δ15N value of a non-N2-fixing speciment of the study species was tried and found to overcome some of the problems associated with the lack of suitable reference plants. With this technique it was possible to detect the almost total dependence of A. saligna on N2-fixation in the fynbos soils with their low nitrogen mineralization rates. In the strandveld ecosystem with much higher soil nitrogen release rates A. cyclops was only partly dependent on fixation (about half) for its nitrogen. The nutrient enrichment of both ecosystems and trends towards enhanced rates of nutrient mineralization could have profound implications on the long-term success of alien invader clearing operations and the restoration of the indigenous flora at these sites.
Collapse
Affiliation(s)
- W D Stock
- Department of Botany, University of Cape Town, 7700, Rondebosch, South Africa
| | - K T Wienand
- Department of Botany, University of Cape Town, 7700, Rondebosch, South Africa
| | - A C Baker
- Department of Botany, University of Cape Town, 7700, Rondebosch, South Africa
| |
Collapse
|
6
|
Abstract
Fynbos is the dominant vegetation type in the Cape floristic region. Periodic fires are a natural phenomenon in fynbos and fire-stimulated seed germination has been reported for a number of fynbos species. Amongst the factors proposed as being directly responsible for the effects of fire are: heat fracturing hard seed coats, heat stimulating seed embryos, high-temperature desiccation of seed coats, ethylene and ammonia in smoke stimulating seed germination, and unknown chemical factors in plant-derived smoke and smoke extracts stimulating germination. In this study 28 fynbos species were screened for a seed germination response to smoke and/or smoke extract treatments. Twelve of these species showed a statistically significant enhancement of germination in response to treatment. For the first time smoke per se has been shown to act as a seed germination cue for fynbos species in the Asteraceae, Ericaceae and Restionaceae, and for the first time smoke extracts have been shown to enhance germination in fynbos species of Proteaceae. The most marked response to both smoke and smoke extracts was shown by seed of Syncarpha vestita (syn. Helichrysum vestitum) (Asteraceae).
Collapse
Affiliation(s)
- N A C Brown
- Conservation Biology Research Unit, National Botanical Institute, Kirstenbosch, Private Bag X7, Claremont, 7735 South Africa
| |
Collapse
|