The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study

Background and Aims Large clades of angiosperms are often characterized by diverse interactions with pollinators, but how these pollination systems are structured phylogenetically and biogeographically is still uncertain for most families. Apocynaceae is a clade of >5300 species with a worldwide distribution. A database representing >10 % of species in the family was used to explore the diversity of pollinators and evolutionary shifts in pollination systems across major clades and regions. Methods The database was compiled from published and unpublished reports. Plants were categorized into broad pollination systems and then subdivided to include bimodal systems. These were mapped against the five major divisions of the family, and against the smaller clades. Finally, pollination systems were mapped onto a phylogenetic reconstruction that included those species for which sequence data are available, and transition rates between pollination systems were calculated. Key Results Most Apocynaceae are insect pollinated with few records of bird pollination. Almost three-quarters of species are pollinated by a single higher taxon (e.g. flies or moths); 7 % have bimodal pollination systems, whilst the remaining approx. 20 % are insect generalists. The less phenotypically specialized flowers of the Rauvolfioids are pollinated by a more restricted set of pollinators than are more complex flowers within the Apocynoids + Periplocoideae + Secamonoideae + Asclepiadoideae (APSA) clade. Certain combinations of bimodal pollination systems are more common than others. Some pollination systems are missing from particular regions, whilst others are over-represented. Conclusions Within Apocynaceae, interactions with pollinators are highly structured both phylogenetically and biogeographically. Variation in transition rates between pollination systems suggest constraints on their evolution, whereas regional differences point to environmental effects such as filtering of certain pollinators from habitats. This is the most extensive analysis of its type so far attempted and gives important insights into the diversity and evolution of pollination systems in large clades

Pitfall Flower Development and Organ Identity of Ceropegia sandersonii (Apocynaceae-Asclepiadoideae)

Deceptive Ceropegia pitfall flowers are an outstanding example of synorganized morphological complexity. Floral organs functionally synergise to trap fly-pollinators inside the fused corolla. Successful pollination requires precise positioning of flies headfirst into cavities at the gynostegium. These cavities are formed by the corona, a specialized organ of corolline and/or staminal origin. The interplay of floral organs to achieve pollination is well studied but their evolutionary origin is still unclear. We aimed to obtain more insight in the homology of the corona and therefore investigated floral anatomy, ontogeny, vascularization, and differential MADS-box gene expression in Ceropegia sandersonii using X-ray microtomography, Light and Scanning Electronic Microscopy, and RT-PCR. During 10 defined developmental phases, the corona appears in phase 7 at the base of the stamens and was not found to be vascularized. A floral reference transcriptome was generated and 14 MADS-box gene homologs, representing all major MADS-box gene classes, were identified. B- and C-class gene expression was found in mature coronas. Our results indicate staminal origin of the corona, and we propose a first ABCDE-model for floral organ identity in Ceropegia to lay the foundation for a better understanding of the molecular background of pitfall flower evolution in Apocynaceae

FIGURE 3. Ceropegia gilboaensis. A in Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa

FIGURE 3. Ceropegia gilboaensis. A, Gynostegium in dorsal view; B, Flower in dorsal view; C, Pollinarium; D, Half flower detail; E, Flower in lateral view; F, Gynostegium in dorso-lateral view; G, Habit with detached flowering shoot. Scale bar: A: 1 mm; B: 2.5 mm; C: 0.6 mm; D: 0.8 mm; E: 4 mm; F: 1.3 mm; G: 10 mm. Artist: Angela Beaumont.Published as part of <i>Heiduk, Annemarie, Crouch, Neil R. & Styles, David G.A., 2023, Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa, pp. 125-136 in Phytotaxa 591 (2)</i> on page 130, DOI: 10.11646/phytotaxa.591.2.4, <a href="http://zenodo.org/record/10121325">http://zenodo.org/record/10121325</a&gt

FIGURE 2 in Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa

FIGURE 2. Known distribution of Ceropegia gilboaensis (open triangle), C. modestantha (filled circle), C. pulchellior (open circle) and C. ngomensis (open diamond).Published as part of <i>Heiduk, Annemarie, Crouch, Neil R. & Styles, David G.A., 2023, Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa, pp. 125-136 in Phytotaxa 591 (2)</i> on page 128, DOI: 10.11646/phytotaxa.591.2.4, <a href="http://zenodo.org/record/10121325">http://zenodo.org/record/10121325</a&gt

FIGURE 5 in Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa

FIGURE 5. Gynostegial corona in lateral (left) and dorsal (centre) view, and pollinaria (right). A, Ceropegia gilboaensis, B, C. ngomensis; C, C. modestantha; D, C. pulchellior. Scale bars: 0.5 mm (gynostegia), 200 Μm (pollinaria). Photographs: Annemarie Heiduk.Published as part of <i>Heiduk, Annemarie, Crouch, Neil R. & Styles, David G.A., 2023, Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa, pp. 125-136 in Phytotaxa 591 (2)</i> on page 132, DOI: 10.11646/phytotaxa.591.2.4, <a href="http://zenodo.org/record/10121325">http://zenodo.org/record/10121325</a&gt

FIGURE 1 in Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa

FIGURE 1. Flowers of selected South African brood-site mimicking species of Ceropegia sect. Chamaesiphon. A–D, C. australis; E, C. bruceae; F, C. chlorozona; G, C. coddii; H, C. modestantha; I, C. ngomensis; J, C. petrophila; K, C. pulchellior; L, C. remota. Photographs: Annemarie Heiduk (A–C, I); David Styles (D–H, J–L).Published as part of <i>Heiduk, Annemarie, Crouch, Neil R. & Styles, David G.A., 2023, Ceropegia gilboaensis (Apocynaceae), a new species from the Midlands of KwaZulu-Natal, South Africa, pp. 125-136 in Phytotaxa 591 (2)</i> on page 126, DOI: 10.11646/phytotaxa.591.2.4, <a href="http://zenodo.org/record/10121325">http://zenodo.org/record/10121325</a&gt

Origin and early evolution of Ceropegieae (Apocynaceae-Asclepiadoideae)

<p>The first-branching lineages of the tribe Ceropegieae, Anisotominae, Leptadeniinae, and Heterostemminae, are the focus of the present study. In the ingroup we molecularly analysed 34 samples from southern and (north)eastern Africa and Asia for the nuclear internal transcribed spacer (ITS) region, and five plastid markers (<i>trn</i>T-L, trnL-F and <i>trn</i>H<i>-psb</i>A intergenic spacers, <i>trn</i>L, and <i>rps</i>16 introns). Maximum Parsimony and Bayesian analyses were conducted for phylogenetic reconstruction and Bayesian binary MCMC (BBM) analysis as implemented in RASP for testing biogeographic inference. Sister to the well-known hyperdiverse subtribe Stapeliinae (around 700 species) are the Anisotominae, an African subtribe of <i>c</i>. 30 species, with the tropical <i>Neoschumannia</i> in sister-group position to the remaining genera, <i>Anisotoma</i>, <i>Emplectanthus</i>, <i>Riocreuxia</i>, and <i>Sisyranthus</i>. <i>Emplectanthus</i> is sequenced in full for the first time, and its monophyly as sister to <i>Anisotoma</i> is documented. As in <i>Sisyranthus</i>, new sequences in <i>Riocreuxia</i>, especially in <i>Riocreuxia torulosa</i> s.l., reveal very low genetic variation pointing to an actively radiating and speciating group, possibly in adaptation to pollinator pressure. Molecular and morphological data necessitate the transfer of <i>Brachystelma natalense</i> to <i>Anisotoma</i>, and the new combination <i>Anisotoma natalensis</i> is proposed. Leptadeniinae are sister to the Stapeliinae–Anisotominae clade. The position of the strictly Asian, rheophytic <i>Pentasachme</i> could be resolved as sister to the remaining genera of Leptadeniinae, <i>Conomitra</i>, <i>Leptadenia</i>, and <i>Orthanthera</i>. The position of the S Asian/Australasian wet forest lianas of the genus <i>Heterostemma</i> as sister to the remaining Ceropegieae is confirmed, indicating a humid Asian origin for this tribe known for its arid-adapted African succulents.</p

Origin and early evolution of Ceropegieae (Apocynaceae-Asclepiadoideae)

<p>The first-branching lineages of the tribe Ceropegieae, Anisotominae, Leptadeniinae, and Heterostemminae, are the focus of the present study. In the ingroup we molecularly analysed 34 samples from southern and (north)eastern Africa and Asia for the nuclear internal transcribed spacer (ITS) region, and five plastid markers (<i>trn</i>T-L, trnL-F and <i>trn</i>H<i>-psb</i>A intergenic spacers, <i>trn</i>L, and <i>rps</i>16 introns). Maximum Parsimony and Bayesian analyses were conducted for phylogenetic reconstruction and Bayesian binary MCMC (BBM) analysis as implemented in RASP for testing biogeographic inference. Sister to the well-known hyperdiverse subtribe Stapeliinae (around 700 species) are the Anisotominae, an African subtribe of <i>c</i>. 30 species, with the tropical <i>Neoschumannia</i> in sister-group position to the remaining genera, <i>Anisotoma</i>, <i>Emplectanthus</i>, <i>Riocreuxia</i>, and <i>Sisyranthus</i>. <i>Emplectanthus</i> is sequenced in full for the first time, and its monophyly as sister to <i>Anisotoma</i> is documented. As in <i>Sisyranthus</i>, new sequences in <i>Riocreuxia</i>, especially in <i>Riocreuxia torulosa</i> s.l., reveal very low genetic variation pointing to an actively radiating and speciating group, possibly in adaptation to pollinator pressure. Molecular and morphological data necessitate the transfer of <i>Brachystelma natalense</i> to <i>Anisotoma</i>, and the new combination <i>Anisotoma natalensis</i> is proposed. Leptadeniinae are sister to the Stapeliinae–Anisotominae clade. The position of the strictly Asian, rheophytic <i>Pentasachme</i> could be resolved as sister to the remaining genera of Leptadeniinae, <i>Conomitra</i>, <i>Leptadenia</i>, and <i>Orthanthera</i>. The position of the S Asian/Australasian wet forest lianas of the genus <i>Heterostemma</i> as sister to the remaining Ceropegieae is confirmed, indicating a humid Asian origin for this tribe known for its arid-adapted African succulents.</p

Journal of Comparative Physiology A / Flower scent of Ceropegia stenantha : electrophysiological activity and synthesis of novel components

In specialized pollination systems, floral scents are crucial for flowerpollinator communication, but key volatiles that attract pollinators are unknown for most systems. Deceptive Ceropegia trap flowers are famous for their elaborate mechanisms to trap flies. Recent studies revealed species-specific floral chemistry suggesting highly specialized mimicry strategies. However, volatiles involved in fly attraction were until now identified in C. dolichophylla and C. sandersonii, only. We here present data on C. stenantha for which flower scent and pollinators were recently described, but volatiles involved in flowerfly communication stayed unknown. We performed electrophysiological measurements with scatopsid fly pollinators (Coboldia fuscipes) and identified 12 out of 13 biologically active floral components. Among these volatiles some were never described from any organism but C. stenantha. We synthesized these components, tested them on antennae of male and female flies, and confirmed their biological activity. Overall, our data show that half of the volatiles emitted from C. stenantha flowers are perceived by male and female fly pollinators and are potentially important for flowerfly communication in this pollination system. Further studies are needed to clarify the role of the electrophysiologically active components in the life of scatopsid fly pollinators, and to fully understand the pollination strategy of C. stenantha.(VLID)354646