Category Archives: Evolution

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.

Why are bees like Bactrian camels? Because they both have two humps!

It was eminent bee biologist Charles Michener who first* pointed out that there was something odd about the global distribution of bees. In his 1979 paper Biogeography of the bees he writes:

“unlike many groups which abound in the tropics, bees attain their greatest abundance in warm temperate areas”

Think about that for a moment: in contrast to most other groups of insects, birds, mammals, flowering plants, fish, indeed the majority of the Earth’s biodiversity, bees are NOT generally at their most species rich in tropical areas. Rather, we have to move north and south of the equator to find them at their highest diversity. This is an odd pattern of distribution for such a successful (> 20,000 species), globally widespread and ecologically important group of organisms.

Some 15 years ago I was inspired by Michener’s comments when, together with colleagues Steve Johnson and Andrew Hingston, we wrote a chapter called Geographical variation in diversity and specificity of pollination systems for the 2006 Waser & Ollerton edited volume Plant-pollinator Interactions: from Specialization to Generalization. In that chapter we presented a rough analysis of how bee diversity per unit area in different countries changes with latitude. This, and a follow-up that appeared in my 2017 Annual Review of Ecology, Evolution and Systematics paper, confirmed Michener’s view that there’s an unusual relationship between bee diversity and latitude, with peak species richness outside of the tropics, in warm, dry environments.

What I really hoped over this time was that some serious bee biologists would follow up Michener’s insights and produce a full analysis of how bee diversity changes across the planet. Yesterday that hope was realised when Michael Orr, Alice Hughes, Douglas Chesters, John Pickering, Chao-Dong Zhu and John Ascher published the first analysis of bee diversity across the whole planet, and its underlying causes, in their open-access paper Global Patterns and Drivers of Bee Distribution.

Their analyses are based on a data set of >5,800,000 records of where bees occur and it’s been an incredible achievement to bring all of that together into a planet-wide view of where bees are found, and why. I highly recommend that you download and read it, it’s an impressive piece of work.

What have camels got to do with all of this? Well, as the authors show in their paper (from which the image above is taken), if you graph up the increase in bee species richness with latitude from the poles in each hemisphere, you get two humps at about 35 degrees north and south of the equator: like a Bactrian camel. In contrast, as I noted above, if you were to do the same for for most other species you’d get a single hump at the equator: like a dromedary camel.

One of the key drivers of this bimodal pattern seems to be the amount of rainfall in an environment – bees do not like it too wet, in contrast to their relatives the ants which do show the more typical tropical peak in diversity. As the authors put it:

“humidity may play a key role in limiting bee distribution, such as through spoilage of pollen resources”

One of the implications of this for the biogeography of plant-pollinator interactions is that we might expect there to be a greater diversity of different types of pollinators in areas where bees are not so abundant. And indeed that is exactly what we find: in that Ollerton, Johnson and Hingston book chapter I mentioned we showed that there’s a step-change in the diversity of functionally specialised pollination systems as one moves from the sub-tropics into the tropics. There could be many reason for that but I suspect that one is a relative lack of bees compared to the number of plants species; thus you get tropical “oddities” such as specialised cockroach pollination in some plants.

Orr et al.’s paper is a milestone in bee biogeography and opens up new opportunities for conserving these insects, and their vital relationships with the flowering plants. To give just one example: these analyses provide a framework for predicting bee diversity hotspots in parts of the world that have been poorly explored by bee taxonomists, but which are nevertheless severely threatened by habitat degradation and conversion to agriculture. It could also be used for predicting how climate change might affect future bee distributions, especially in parts of the world that are expected to become wetter. I’m looking forward to seeing how the team’s work develops in the future.

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*It’s always risky to state “first”, but Michener was certainly the first that I am aware of. Let me know if you’ve come across any precedents.

Recent pollinator and pollination related research that’s caught my eye

2020-07-30 16.25.26

As I near completion of the copy-editing phase of my forthcoming book it’s frustrating to see all of the great research that’s been produced in recent weeks that I probably won’t be able to cite!  Here’s a few things that caught my eye:

Damon Hall and Dino Martins have a short piece on Human dimensions of insect pollinator conservation in Current Opinion in Insect Science.  My favourite line is: “any call to ‘save the bees’ must be a call to stabilize agriculture”.  Amen to that.

In the journal New Phytologist, Rhiannon Dalrymple and colleagues, including Angela Moles who hosted me during my recent stay in Australia, have a great study entitled Macroecological patterns in flower colour are shaped by both biotic and abiotic factors.  The title pretty much sums it up: in order to fully understand how flowers evolve we need to consider more than just their interactions with pollinators.  It’s another demonstration of how we must look beyond simplistic ideas about pollination syndromes to fully understand the complexities of the relationship between flowering plants and pollinators…..

…..talking of which, again in New Phytologist, Agnes Dellinger asks: Pollination syndromes in the 21st century: where do we stand and where may we go?  It’s an insightful and far-reaching review of a topic that has intrigued me for more than 25 years.  There are still a lot of questions that need to be asked about a conceptual framework that, up until the 1990s, most people in ecology and biology accepted rather uncritically.  One of the main unanswered questions for me is how further study of largely unexplored floras will reveal the existence of new pollination systems/syndromes.  Which leads nicely to….

…..an amazing paper in Nature this week by Rodrigo Cámara-Leret et al. showing that New Guinea has the world’s richest island flora.  The described flora includes 13,634 plant species, 68% of which are endemic to New Guinea!  And the description of new species each year is not leveling off, there’s still more to be discovered.  A commentary on the paper by Vojtech Novotny and Kenneth Molem sets some wider context to the work, and quite a number of media outlets have covered the story.  Why is this relevant to pollinators and pollination?  Well, we actually know very little about this critical aspect of the ecology of the island: there’s only a handful of published studies of plant-pollinator interactions from New Guinea, mostly focused on figs, bird-flower interactions, and a couple of crops.  For such a biodiverse part of the world that’s a big gap in our understanding.

Finally, James Reilly, Rachael Winfree and colleagues have a paper in Proceedings of the Royal Society series B showing that: Crop production in the USA is frequently limited by a lack of pollinators.  Most significant findings to me were that of the seven crops studied, five of them have their yields limited by lack of pollinators, and that even in areas of highly intensive farming, wild bees provided as much pollination service as honeybees.

That’s a few of the things that I spotted this week; what have you seen that’s excited or intrigued you?  Feel free to comment.

 

Get a 30% discount if you pre-order my new book Pollinators & Pollination: Nature and Society

PollinatorsandPollination-frontcover

In the next few months my new book Pollinators & Pollination: Nature and Society will be published.  As you can imagine, I’m very excited! The book is currently available to pre-order: you can find full details here at the Pelagic Publishing website.  If you do pre-order it you can claim a 30% discount by using the pre-publication offer code POLLINATOR.

As with my blog, the book is aimed at a very broad audience including the interested public, gardeners, conservationists, and scientists working in the various sub-fields of pollinator and pollination research. The chapter titles are as follows:

Preface and Acknowledgements
1. The importance of pollinators and pollination
2. More than just bees: the diversity of pollinators
3. To be a flower
4. Fidelity and promiscuity in Darwin’s entangled bank
5. The evolution of pollination strategies
6. A matter of time: from daily cycles to climate change
7. Agricultural perspectives
8. Urban environments
9. The significance of gardens
10. Shifting fates of pollinators
11. New bees on the block
12. Managing, restoring and connecting habitats
13. The politics of pollination
14. Studying pollinators and pollination
References
Index

 

 

The evolution of insect pollination: a new essay just published

Science MagazineIn the latest issue of the journal Science you’ll find a commentary essay entitled: “The origins of flowering plants and pollinators“, written by Casper van der Kooi and myself.  It’s open access so do go and read it.

This commentary brings together some  recent findings in palaeontology, molecular phylogenetics, and pollinator sensory physiology and behaviour, to discuss the progress that’s been made in understanding the deep-time evolution of this most familiar and charismatic of ecological interactions.

The short version is that the old conceptual models are absolutely wrong.  Some version of “first came the gymnosperms and they were primitive and unsuccessful because they were wind pollinated.  Then, at the start of the Cretaceous, the angiosperms evolved and they were insect pollinated and advanced and so more successful” continues to appear in text books.  But we’ve known for a long time that many of the Jurassic gymnosperms were insect pollinated.  This may (or may not) predate insect pollination of angiosperms: there are huge disagreements between palaeobotanists and molecular phylogeneticists about when the first flowering plants evolved.  The graphic above comes from our essay and shows just how big the discrepancy is: molecular models suggest an origin for the angiosperms about 70 million years prior to the first confirmed fossils.  That’s about equivalent to the whole of the Jurassic period!  There are similar disagreements when it comes to the evolution of pollinating insects: for the Lepidoptera (butterflies and moths) the difference between the earlier molecular and later fossil evidence may be as much as 100 million years.

As we discuss, there are huge implications in these discrepancies for understanding not just how major elements within the Earth’s biodiversity evolved, but also for the origins of pollinator sensory physiology.  Insect behaviours linked to colour vision and odour reception may in turn influence effective crop and wild plant pollination.

The image accompanying our essay is by the very talented biologist, science communicator and graphic designer Elzemiek Zinkstok – follow that link and check out her work.