Category Archives: Evolution

A new study shows that even short-tubed flowers can specialise on hawkmoths as pollinators

Of all of the “classical” pollination syndromes, flowers that are hawkmoth pollinated have one of the highest levels of predictability. If a flower is pale in colour, opens at night, is highly scented, and possesses a long tube at the bottom of which is a supply of nectar, there’s a very high likelihood that it’s pollinated by long-tongued hawkmoths (Sphingidae).

Indeed, one of the foundational stories about the development of our understanding of how pollination systems evolve, relates to Charles Darwin, the long-tubed orchid Angraecum sesquipedale and the hawkmoth Xanthopan morganii praedicta.

Fast forward 160 years and we now know that pollination syndromes are more complex than 19th and early 20th century scientists imagined – see my recent book Pollinators & Pollination: Nature and Society for a discussion of this topic. That’s not surprising because, as I point out, we probably have data on the interactions between plants and their pollinators for only about 10% of the estimated 352,000 species of flowering plants. There’s still much to be discovered!

As an example of how our understanding of specialised flower-hawkmoth interactions is developing, consider this recent study that I’ve just published with my Brazilian colleague Felipe Amorim and other collaborators. In it we have shown that, contrary to expectations, a species of Apocynaceae (Schubertia grandiflora) with a relatively short floral tube can specialise on hawkmoths with much longer tongues than we might predict.

The full reference with a link to the study is shown below, followed by the abstract. If you would like a PDF, please drop me a line via my Contact page:

Amorim, F.W., Marin, S., Sanz-Viega, P.A., Ollerton, J. & Oliveira, P.E. (2022) Short flowers for long tongues: functional specialization in a nocturnal pollination network of an asclepiad in long-tongued hawkmoths. Biotropica https://doi.org/10.1111/btp.13090

Abstract:

Since Darwin, very long and narrow floral tubes have been known to represent the main floral morphological feature for specialized long-tongued hawkmoth pollination. However, specialization may be driven by other contrivances instead of floral tube morphology. Asclepiads are plants with a complex floral morphology where primary hawkmoth pollination had never been described. We detailed here the intricate pollination mechanism of the South American asclepiad Schubertia grandiflora, where functional specialization on long-tongued hawkmoth pollinators occurs despite the short floral tube of this species. We studied two plant populations in the Brazilian Cerrado and recorded floral visitors using different approaches, such as light-trapped hawkmoths for pollen analysis, direct field observations, and IR motion-activated cameras. Finally, using a community-level approach we applied an ecological network analysis to identify the realized pollinator niche of S. grandiflora among the available niches in the pollinator community. Throughout a period of 17 years, long-tongued hawkmoths were consistently recorded as the main floral visitors and the only effective pollinators of S. grandiflora. Flowers rely on highly modified corona and gynostegium, and enlarged nectar chambers, to drive visitors and pollination mechanism. Despite its relative short-tube, network analysis placed S. grandiflora in the module including exclusively long-tongued hawkmoth pollinators and the most phenotypically specialized sphingophilous plants in the community. These results represent the first example of functional specialization in long-tongued hawkmoths in an asclepiad species. However, this specialization is uncoupled from the long floral tubes historically associated with the sphingophily syndrome.

Is the tropical epiphytic house plant Monolena primuliflora an “ant plant”?

I love going to botanic gardens and I keep a “life list” of those that I have visited. So on a visit to Lund University last week, to give a seminar and take part in an MSc defence, I was delighted to be able to add another one to that list. Lund University Botanical Garden is quite small, like many such urban gardens, and this is not the best time of the year to visit. But there was a good show of early spring plants in flowers, the sun was shining, and quite a number of people were enjoying the peace and calm in the middle of a city.

The glasshouses were especially busy, and they have a nice collection of cold-sensitive plants arranged by habitat and taxonomy, such as cacti and succulents, ferns, orchids, and so forth. One of the reasons why I enjoy botanic gardens so much is that I always, without exception, see plants that I have never previously encountered, often doing unexpected things.

Lund was no exception, and I was particularly intrigued by a plant called Monolena primuliflora which was being grown in a hanging basket, as is often the case with epiphytic plants. It’s a species of Melastomataceae, a family that I know well from tropical field work. But this one looked unlike any melastome that I’d ever seen. In particular, I was drawn to the large rhizome or caudex from which the leaves emerge:

This immediately reminded me of some of the epiphytic “ant plants” such as species of Myrmecodia and Hydophytum and especially ferns such as Lecanopteris. All of these myrmecophyte genera have evolved swollen stems or rhizomes which house colonies of ants. The ants in turn defend the plants against herbivores, in a mutualistically advantageous relationship.

Sure enough, when I searched online for information about Monolena primuliflora, it’s widely described in the house plant community as an “ant plant” – see here and here for example. After I tweeted about this, biologist Guillaume Chomicki (who has been researching these ant-plant interactions) was intrigued but asked about the evidence for it being a myrmecophyte:

That got me thinking, so I dug around in the botanical literature for the evidence and found…..nothing. The standard monograph on the genus by Warner (2002) doesn’t mention it and as far as I can tell (please someone will correct me if I am wrong) there’s no documented study of this species or genus having a myrmecophytic relationship with ants.

If I’m correct, how has the idea of Monolena primuliflora as an ant plant come about? This is a relatively new introduction to the houseplant trade and I suspect that plant sellers have made assumptions about the swollen rhizome (as I did!) to make the plant sound more interesting. There’s no doubt that the rhizome is fascinating and unusual in the family, but its function may be to store water (as found in many epiphytic orchids) rather than to house ants.

In my recent book Pollinators & Pollination: Nature and Society, and in this article last year in the magazine British Wildlife, I discussed how the world of plants (and pollinators) is full of myths and misunderstandings. This seems to be another one and by writing this blog post I’m hoping that we can clarify the situation with regard to Monolena primuliflora. So if you have any further information about it, please do comment below.

My thanks to everyone on Twitter who commented about the plant, especially Guillaume for asking the question!

Join me on Thursday for a free talk!

Join me this Thursday at a free online talk organised by Buglife where I’ll be giving an introduction to how flowers function and the ways in which their behaviour manipulates pollinators to ensure reproduction. I’ll be covering:

  • What are flowers and where did they come from?
  • How flowers function and reward pollinators.
  • Some case studies from my own research on flower and pollinator behaviour.
  • Why is it important that we understand floral biology?

Here’s the link to register for the event: https://www.buglife.org.uk/events/to-be-a-flower-with-professor-jeff-ollerton/

I look forward to seeing you there!

Leonard B. Thien (1938-2021) – botanist and pollination biologist

I was saddened to learn recently of the death of Professor Leonard B. Thien of Tulane University who passed away at the end of October after a long illness. Although I didn’t know Professor Thien personally, I knew of his work in floral ecology, pollination biology and plant evolution, topics on which he had worked for since obtaining his PhD in 1968. Over the course of his career he published more than 80 articles on a huge range of botanical subjects, including ground-breaking work on mosquito pollination of orchids (Thien 1969). The orchid species Alaticaulia thienii is named in his honour.

The studies Leonard Thien published that really inspired me when I was first starting out on my journey as a researcher, however, involved his work on “relictual” angiosperms, i.e. flowering plants that have very long evolutionary histories and deep phylogenetic roots back to the early Cretaceous period, for example Magnolia and Illicium. Papers with titles such as “Patterns of pollination in the primitive angiosperms” (Thien 1980) piqued my interest and motivated me to work on Australian Piperaceae for a short while following my PhD (Ollerton 1996). It was a topic that I struggled to gain further funding for, and later molecular systematic studies changed many of our ideas about what constitutes the most basal groups of extant flowering plants. But nonetheless, the questions that Leonard inspired in me, regarding the ecologies of these relictual taxa, and whether we can infer the reproductive ecology of the earliest flowering plants from studies of their surviving descendants, are ones that intrigue me to this day (van der Kooi and Ollerton 2020).

Leonard Thien kept up this interest even as new DNA technologies over turned old ideas, and he was the first to study the reproductive ecology of Amborella trichopoda on New Caledonia, a species now considered to be the earliest surviving clade of flowering plants (Thien et al. 2003). This is just one part of a legacy of work that current and future generations will build upon as we develop our understanding of the relationships between pollinators, plants, and evolutionary processes.

I’m grateful to Peter Bernhardt for prompting this post and for sending me a copy of the In Memoriam article that he and and David White will publish in the Plant Sciences Newsletter in March, and to Lorraine Thien for providing the photograph that accompanies this post.

References

Ollerton, J. (1996) Interactions between gall midges (Diptera: Cecidomyiidae) and inflorescences of Piper novae-hollandiae (Piperaceae) in Australia. The Entomologist 115: 181-184

Thien, L.B. 1969. Mosquito pollination of Habenaria obtusata (Orchidaceae). American Journal of Botany 56: 232-237.

Thien, L.B. 1980. Patterns of pollination in the primitive angiosperms. Biotropica 12: 1-14

Thien, L.B., Sage, T.L., Jaffre, T., Bernhardt, P., Pontieri, V., Wesston, P.H., Malloch, D., Azuma, H., Graham, S.W., McPherson, M.A., Hardeep, S.., Sage, R.S. & Dupre, J.-L. 2003. The population structure and floral biology of Amborella trichopoda (Amborellaceae). Annals of the Missouri Botanical Garden 90: 466-490

van der Kooi, C.J. & Ollerton, J. (2020) The origins of flowering plants and pollinators. Science 368: 1306-1308

A milkweed on the shore: tracking down an elusive Danish plant

Since arriving in Odsherred towards the end of August I’ve been looking out for one plant in particular on our bicycle rides and hikes around the region. Vincetoxicum hirundinaria is a widespread asclepiad or milkweed: a member of the family Apocynaceae, subfamily Asclepiadoideae. This is a group of plants on which I’ve published quite a few research papers and which feature heavily in my book Pollinators & Pollination: Nature and Society.

So far the species has proven elusive and a few Danish ecologists that I’d spoken with told me they had never seen it in the wild. The GBIF account of the species shows a few populations in this part of Denmark but I wasn’t sure if they were old records of populations that no longer exist. But as of yesterday I can confirm that at least one of those populations is extant!

We had cycled out to the small town of Klint about 13km west of us, to see the glacial moraine landscape for which the area is famous and which gives Odsherred UNESCO Geopark status. As we approached the small fishing harbour at Klint I let out an excited shout to Karin who was just ahead of me: in amongst the roadside vegetation I’d spotted the distinctive and immediately recognisable yellow of Vincetoxicum hirundinaria in its autumnal hues! In the photos that follow you can see how well that yellow stands out against the colours of the other plants in the community.

At this time of the year the plant has ceased flowering, but the occasional swollen green seed pod was evidence of successful pollination of their morphologically complex flowers.

I was surprised at just how close to the sea the plants were growing; they must get inundated by sea water during stormy tidal surges.

So what is pollinating these flowers on this exposed shoreline? That’s a question that I want to pursue in the coming years. The Pollinators of Apocynaceae Database has remarkably few records of pollinators in this species, given how widespread it is. Flies certainly pollinate it, but there’s also records of wasps and bees as visitors, including bumblebees on flowers of a plant that I had in cultivation in Northampton. There’s a couple of other research groups in Scandinavia and Europe who are looking at the pollination ecology of the species and I’m hoping that we can collaborate on a study of spatial variation in its reproduction. Vincetoxicum is quite a large genus (around 150 species) and only around 10% of the species have been studied in any detail. But these studies are revealing a complex diversity of pollinators, including most recently, cockroaches in the Chinese species Vincetoxicum hainanense. I’m sure this intriguing group of plants has more fascinating stories to tell us about the ecology and evolution of its pollination systems.

FIGURE 4 from Xiong et al. (2020) Specialized cockroach pollination in the rare and
endangered plant Vincetoxicum hainanense in China. American Journal of Botany 107:
1355–1365.

The largest West African flower: Pararistolochia goldieana!

Some years ago, browsing in a second hand bookshop, I happened across a copy of an old magazine from 1950 called Nigeria. Published by the then colonial government, it was a miscellaneous collection of articles about the culture, geography and natural history of that fascinating West African country. Although aspects of the contents are problematical by modern standards, I bought it because of a short article about a wild plant with enormous flowers and a remarkable pollination strategy. In particular, the spectacular photograph of a man holding a flower that’s the length of his forearm grabbed my attention: who couldn’t love a flower like that?!

The plant is Pararistolochia goldieana, a vine found in the forests of this region, as described in the introductory text:

These types of flowers are pollinated by flies, a common strategy in the Birthwort family (Aristolochiaceae) to which the plant belongs. This strategy of fly pollination in which flies are deceived into visiting the flowers by their stink and colour, and temporarily trapped in the enclosed chamber, is something that I explore in detail in my book Pollinators & Pollination: Nature and Society, particularly in the genus Ceropegia. Those plants show convergent evolution with the pollination systems of Aristolochiaceae, though they are unrelated.

Pararistolochia goldieana has a wide distribution across West Africa, including Cameroon, Equatorial Guinea, Nigeria, and Sierra Leone. The IUCN Red List categorises it as ‘Vulnerable’ due to habitat loss. The population where these photographs were taken is described on the final page of the article:

The city of Ibadan is one of the largest in Nigeria and has grown enormously, ‘from 40 km2 in the 1950s to 250 km2 in the 1990s‘. I wonder if this forest, and its botanical treasures, still exists?

During field work in Gabon in the 1990s I was fortunate enough to encounter a species of Pararistolochia in the rainforest of Lopé National Park. It was a different species to P. goldieana, with rather smaller but no less spectacular flowers, and it stank to high heaven! We knew it was there long before we saw it. I collected some flies from the flowers and had them identified, though I’ve never published the data: it’s available if anyone is working on a review of pollination in the family.

This 1950 article is anonymous, so I don’t know who to acknowledge for the amazing images. However the botanist R.W.J. Keay was working on a revision of the family for the Flora of West Tropical Africa project at the time, so it may have been written by him.

Online talks and training: here’s a selection of what I offer

Over the past few months I’ve done a large number of online talks for a variety of audiences, including natural history and gardening societies, beekeeping groups, private companies, university estates departments, and ecological consultancies. I thought it would be useful to provide a list of what I offer, with a short description. All talks are accessible and understandable to a broad audience, and can be tailored to the individual needs of the group:

Pollinators & Pollination: Nature and Society is an introduction to the importance of pollinators and the pollination services that they provide to both wild and crop plants. The name, of course, reflects that of my recent book.

The Politics of Pollination is an account of how society (governments, organisations and individuals) has responded to the current “pollination crisis” (if that’s what it actually is…)

Bees in Cities: an Introduction to Urban Pollinators focuses on the positive roles that urban environments can play for pollinators, and the potential threats of city living.

Pollinators in Gardens gives practical advice on how to make your garden “pollinator friendly”.

Pollinator Conservation: Threats and Opportunities describes how and why pollinators are declining and what we can do about it at the individual and societal level.

Habitat Creation and Management for Pollinators gives an introduction to how NGOs, estates departments, consultancies, and so forth, can effectively support pollinators in ways that go beyond just planting flowers and putting up a few “bee hotels”.

To Be a Flower is an introduction to how flowers function and the ways in which they manipulate the behaviour of their pollinators to ensure reproduction.

Darwin’s Unrequited Isle: a Personal Natural History of Tenerife describes some of the field work that we’ve been doing on this most fascinating of the Canary Islands.

Biodiversity: What Is It and Why Should We Care? gives a very general overview of the topic of biodiversity and ecosystem services.

Talks typically last for around 50 minutes, following which I’m happy to answer questions and discuss any issues that have arisen. I also offer a half- or full-day of training for those organisations that need more depth, for example ecological consultancies. Note that I charge for all of my talks and training. If you would like to enquire about any of this, please use the form on the Contact page.

How old are the flowering plants? A new study aims to reconcile the fossil and DNA evidence – but what does it mean for pollinators?

Yesterday I was contacted by a journalist to give a comment on a paper that’s just been published in Nature Ecology and Evolution:

Silvestro, D., Bacon, C.D., Ding, W. et al. (2021) Fossil data support a pre-Cretaceous origin of flowering plants. Nature Ecology and Evolution https://doi.org/10.1038/s41559-020-01387-8

I was happy to do so as it adds a fascinating twist to a long-standing interest of mine: when did the angiosperms evolve and what role did pollinators play in that evolution?

In the end they didn’t use the text that I sent back to them, so I thought that I’d share it on the blog:

The evolution of the angiosperms was arguably one of the most significant events in the history of life on Earth, but the timing of the origin of this group of plants remains a hotly debated topic, with conflicting evidence coming from the fossil record and molecular biology. This important new study has developed a novel statistical approach to reconcile these two lines of evidence, and comes down firmly on the side of the molecular evidence to conclude that angiosperms originated much earlier than the fossil record suggests. This will be sure to stir up further debate that can only be resolved by finding well preserved and accurately interpreted fossils of an appropriate age. In the future I would like to see Silvestro et al.’s technique applied to the major groups of pollinators such as bees and wasps (Hymenoptera) and butterflies and moths (Lepidoptera) where there is likewise a discrepancy between what the fossils and DNA are telling us. Pollinators have had a profound influence on angiosperm evolution and we might expect a close correlation between the origin and subsequent diversification of these different groups of organisms. This would certainly support the findings from Silvestro et al.’s study. It’s an exciting time for researchers in this field: a world without flowers and pollinators would look very different

Flowers can be assholes – quite literally!

2003-572 s G Bochum

WARNING: There’s a high yuck factor to this post, it’s not for the squeamish or easily offended!

One of my Twitter contacts, Traci Birge in Finland, has been reading Pollinators & Pollination: Nature and Society, and making some very nice comments about it. I had to laugh at this one in which she describes some plants as “assholes” because of the way in which they deceive pollinators into visiting their flowers but offer no reward in return:

If you follow that thread you can see that Traci was closer to the truth than perhaps she realised: there are some plants with flowers that appear to mimic the anuses of dead mammals, particularly in the families Apocynaceae and Araceae. By their smell, texture, colour and hairiness they are fooling flies into visiting the flowers, because assholes, like any mammalian orifice, provide an entry point for maggots of carrion-feeding flies. Sometimes the deception is so great that the flies lay their eggs on these blooms, though of course the maggots starve.

A great example of an anus-mimicking bloom is the Dead Horse Arum (Helicodiceros muscivorus). Check out the image above: if that doesn’t look like a horse’s ass, I don’t know what does!

Other examples might be found within the stapeliads, especially the genus Huernia which often have a thickened annulus to the centre of the flower. However that could also be interpreted as mimicking an open, inflamed wound on the side of an animal:

As I point out in the book, you might imagine that there would be strong natural selection against flies visiting these flowers if they lose fitness by laying eggs on such an unsuitable substrate. But the flowers are tapping into really deep-seated behaviours and clearly the flies can’t distinguish the flowers from the real thing.

This is flower pollination that is far removed from the deliciously perfumed, cute-and-cuddly, heart-warming world of bees and flowers. Isn’t nature wonderful?

All photos from Wikipedia, as follows:

Helicodiceros muscivorus: Göteborgs botaniska trädgård (photographer: Ingemar Johansson) – http://www.mynewsdesk.com/se/pressroom/goteborgs_botaniska_tradgard/image/view/dracunculus-muscivorus-128973, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=19265330

Huernia zebrina: Enzo^ – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=10963668

Huernia schneideriana: Juan Carlos Fonseca Mata – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=94705877

Finally, a physical copy of my book!

Yesterday I was delighted to finally receive an advance copy of my book Pollinators & Pollination: Nature and Society! It’s been over three years in the writing and production, much longer than I had anticipated. But, as I describe in its pages, the book is the culmination of >50 years of experience, study and research. So perhaps three years isn’t so bad…

If you’re interested in buying a copy you can order it direct from Pelagic Publishing and from most of the large online booksellers. Let me know what you think.