Category Archives: History of science

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.

The value of butterfly specimens for understanding species extinctions – a new study just published.

The Chequered Skipper Reintroduction Project has featured in several posts over the last few years – see here and here – and University of Northampton PhD researcher Jamie Wildman has been working hard to complete his thesis under the less-than-ideal conditions imposed by the COVID-19 pandemic. The first paper from the project has just been published and it deals with Jamie’s monumental efforts to bring together all of the scattered data relating to preserved Chequered Skipper specimens held in museums and private collections. An existing database contained just 266 records; Jamie’s efforts increased that by an order of magnitude, adding a further 3,533 new records that document where and when specimens were collected, and by whom.

This 1,328 % increase in data means that we now know much more about the historical distribution of this butterfly and how that changed over time.

The Chequered Skipper went extinct in England in 1976 and this enhanced database will allow us to understand why that extinction occurred. This initial paper documents the strategy used to find the additional records as a road map for how others might proceed in the future. The full reference with a link to the paper is here:

Wildman, J.P., Ollerton, J., Bourn, N.A.D., Brereton, T.M., Moore, J.L. & McCollin, D. (2022) The value of museum and other uncollated data in reconstructing the decline of the chequered skipper butterfly Carterocephalus palaemon (Pallas, 1771). Journal of Natural Science Collections 10: 31-44

This is the abstract:

The chequered skipper butterfly Carterocephalus palaemon (Pallas, 1771) was declared extinct in England in 1976 after suffering a precipitous decline in range and abundance during the 20th Century. By searching and collating museum and other records, we show how a deeper understanding of this decline can be achieved, thus furthering conservation objectives. A preexisting Butterflies for the New Millennium (BNM) database of United Kingdom butterfly species records, created by Butterfly Conservation in conjunction with the Biological Records Centre (BRC), contained 266 historic C. palaemon records from England. United Kingdom (UK) museums and natural history societies were contacted for specimen data, and these sources added 2175 new records to the BNM. Owners of private specimen collections were also contacted, and these collections accounted for a further 465 records. Specimens originating from UK museums, other institutions, and private collections represent 2640 (71%) of total new records. Other sources, such as personal accounts held in museums, published and unpublished texts produced an additional 894 records. A further 437 records from museums, private collections, and other sources were considered partial and omitted from the data due to limited or misleading date and/or locality information. In summary, data from UK museums and other sources has infilled English C. palaemon distribution prior to 1976, offering further insight into potential environmental and anthropogenic drivers of decline at key sites. The quality and quantity of data obtained using the method outlined in this study suggests similar work could be carried out for other extinct or declining butterfly species to improve our knowledge of habitat requirements and historical distribution via modelling, identify causes of decline, and provide valuable information for potential reintroductions.

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

Travelling July: a pilgrimage to the tomb of Sir Richard Francis and Lady Isabel Burton

The blog has been very quiet during June and July as it’s been quite a couple of months! At the very end of June the sale of our house was completed. Since then Karin and I have been staying with family and friends, doing some house-sitting and living in Air BnBs as we completed work commitments, and traveled around the country seeing people, prior to our departure to Denmark.

During a trip to London last week we managed to squeeze in a side trip to a place that I have longed to visit for over 30 years: the tomb of Captain Sir Richard Francis Burton and his wife Lady Isabel Burton. As I recounted in a post a few years ago, Burton’s life and exploits have long been a subject of fascination for me – see: Sex and drugs and the source of the Nile.

The couple’s burial place is in Mortlake – check out the Burtonia website for details. The mausoleum, designed by Lady Isabel, is in the form of an Arabian tent, and features both Christian and Islamic imagery – very fitting for a man who converted to Islam and was given Catholic last rights on his death bed at the insistence of his wife.

An unusual feature of the tomb is that there is a set of steel steps leading to a glass window at the rear, through which one can view the devoted couple’s coffins and grave goods. It’s a poignant and touching experience. Below are some photographs that we took on the day.

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

 

 

What exactly is a “pollination system”?

Pollination systems

This is a post I’ve been meaning to write for some time, but have never got round to.  What’s catalysed me is an email this morning from Casper van der Kooi asking me about how I define the term “pollination system”, as he’d had some discussions about its use with his colleagues in The Netherlands.

“Pollination system” is one of those terms that seems to mean different things to different people. The way I use it, and I think the way we meant it in the 1996 paper Generalization in pollination systems and why it matters, is that the pollination system = floral phenotype + pollinators.  That is to say, the colour, shape, size, odour, rewards, etc. produced by a flower (or an inflorescence functioning as a single reproductive unit) plus the animals that effectively transfer pollen.

To me this is distinct from a “pollination syndrome” which refers only to the floral phenotype, or “pollinator guild/functional group” which refers only to the flower visitors.  However I have seen “pollination syndrome” used to include floral phenotype + pollinators.  But to my mind they are distinct things.

I have also seen other authors use “pollination system” to mean the community of plants and pollinators in an area, or as analogous to the breeding system, but neither of those are the way that I use it.  I decided to look at the history of the term on Web of Science and the earliest use on there is a paper by Levin & Berube (1972): Phlox and Colias – efficiency of a pollination system.  There were a few other papers from the same decade and all were using pollination system in the way I described above, i.e. floral phenotype + pollinators.

To look for earlier usage of pollination system I searched the Google Ngram Viewer; as you can see in the image above, I found examples of the term back as far as the 1940s in which the pollination system of grasses is referred to as being “cross pollination” (i.e. what we would now refer to as the breeding system).  There’s also texts from the 1950s referring to artificial wind pollination of date palms as a “helicopter pollination system”.

Does it matter how “pollination system” is used, or that it varies in meaning according to the author?  Probably not as long as the meaning is defined in the text.  Ecology is replete with terminology that has slightly different usage according to the researcher (“biodiversity” being an obvious example) and I don’t get a sense that this has held back the field.  Or is that too optimistic a conclusion?  Do you use the term in a different way to me?  As always, your comments are welcomed.

A short history of ecology doctorates in the UK

UK ecology doctorates

Doctorate-level research qualifications (DSc, PhD, DPhil, etc.) do not have an especially long history, although as academics we take them for granted as the usual gateway drug qualification to professional research.  In the UK the first research doctorates were awarded only towards the end of the 19th century and took some time to become fully established in the university landscape.  The British Library’s EThOS site provides a searchable database of doctorates awarded by UK institutions.  Although it’s not complete, the 500,000 records it holds provides a fascinating resource for anyone curious about the history of doctoral education and in research trends in their own discipline.

I thought it would be interesting to look at the history of UK ecology doctorates and, using “ecology” as a search term discovered the following:

  • The earliest record for an ecology doctorate (actually a DSc) was for “An ecological survey of Natal: the Pietermaritzburg district” by J.W. Bews, awarded by the University of Edinburgh in 1912.
  • As far as I can tell from the names (which often give only the initials) the first woman to be awarded an ecology PhD was Mary Seaton for “A floristical and ecological survey of West Lothian” in 1927, again at the University of Edinburgh.
  • As you can see from the graph above, for the first half of the 20th century the number of ecology doctorates averaged only one or two a year, and in many years none were awarded.
  • From about 1950 onward there begins a steep rise in the number of awards.  I was expecting that this rise would be broadly exponential, in line with the widening of access to higher education and the increasing rate of scientific discovery.  However there are some interesting peaks and troughs in the observed pattern.
  •  The first bulge occurs in the early- to mid-1980s, with a second bulge from the mid-1990s until the early 2000s.  It would be interesting to speculate on what had caused those.
  • However it’s from 2010 onward that the really steep rise in ecology doctorates occurs: in the decade from 2010 to 2019 (which I have not graphed as the year has not yet ended) 3833 doctorates were awarded.  That compares to 4820 for the previous c. 100 years.
  • However, one must be careful about assigning any given thesis to the field of ecology as the word is increasingly used outside of the subject, e.g. in a thesis entitled “Understanding extra-judicial responses to young people’s offending : out of court disposals and ‘diversion’ in social context” (University of Bedfordshire 2019).
  • Possibly balancing that latter bias is the trend of using the word “biodiversity” rather than ecology; there are at least 700 such theses.  Some of these will be taxonomic rather than ecological, but by no means all.
  • I wonder whether we reached a peak in ecology doctorates in 2016 (when 506 were awarded).  As of June 2019 only 92 have been awarded so the downward trend seen in the last couple of years may be continuing.

There is no doubt much more that could be discovered by someone with an interest in the history of science and the time to dig further into the topic.  If anyone wants a copy of the raw data, drop me an email and I will happily send it.

When did the flowering plants evolve? Two new studies come to different conclusions

2019-04-23 17.42.40.jpg

The angiosperms (flowering plants) are far and away the most diverse group of plants ever to have evolved.  There are an estimated 350,000 to 370,000 species, more than all other groups of plants (ferns, conifers, cycads, mosses, etc.) combined, living and extinct.  The origin of the flowering plants was termed an “abominable mystery” by Charles Darwin – or perhaps it wasn’t: see this essay by Prof. Richard Buggs for an alternative view of what Darwin was describing, and this paper by Prof. William Friedman giving a different interpretation.

These disagreements about what Darwin meant are as nothing compared to disagreements about when the flowering plants actually evolved and how we interpret fossils and evidence from molecular phylogenies.  Two new studies illustrate this point: they use some of the same information to come to completely different conclusions.  I’ve copied the details and abstracts below, with links to the originals, and emphasised the areas of disagreement in bold text.  And I’m going to leave it at that; I don’t have a horse in this race and I have no idea which (if either) is correct.

There are, however, profound implications for understanding when and how relationships between flowering plants and their pollinators evolved, as I noted in my recent review of pollinator diversity.  If the much earlier, Triassic origin of the angiosperms is correct then perhaps the earliest flowering plants did not co-opt pollinators that were already servicing gymnosperms.  Perhaps the relationships between plants and pollinators originated with the (Triassic) angiosperms and the gymnosperms subsequently evolved to exploit this.  My feeling is that only more, better fossils will provide definitive answers.

Here’s the details of the studies:

Coiro et al. (2019) How deep is the conflict between molecular and fossil evidence on the age of angiosperms? New Phytologist

Abstract: The timing of the origin of angiosperms is a hotly debated topic in plant evolution. Molecular dating analyses that consistently retrieve pre‐Cretaceous ages for crown‐group angiosperms have eroded confidence in the fossil record, which indicates a radiation and possibly also origin in the Early Cretaceous. Here, we evaluate paleobotanical evidence on the age of the angiosperms, showing how fossils provide crucial data for clarifying the situation. Pollen floras document a Northern Gondwanan appearance of monosulcate angiosperms in the Valanginian and subsequent poleward spread of monosulcates and tricolpate eudicots, accelerating in the Albian. The sequence of pollen types agrees with molecular phylogenetic inferences on the course of pollen evolution, but it conflicts strongly with Triassic and early Jurassic molecular ages, and the discrepancy is difficult to explain by geographic or taphonomic biases. Critical scrutiny shows that supposed pre‐Cretaceous angiosperms either represent other plant groups or lack features that might confidently assign them to the angiosperms. However, the record may allow the Late Jurassic existence of ecologically restricted angiosperms, like those seen in the basal ANITA grade. Finally, we examine recently recognized biases in molecular dating and argue that a thoughtful integration of fossil and molecular evidence could help resolve these conflicts.

 

Li et al. (2019) Origin of angiosperms and the puzzle of the Jurassic gap. Nature Plants

Abstract: Angiosperms are by far the most species-rich clade of land plants, but their origin and early evolutionary history remain poorly understood. We reconstructed angiosperm phylogeny based on 80 genes from 2,881 plastid genomes representing 85% of extant families and all orders. With a well-resolved plastid tree and 62 fossil calibrations, we dated the origin of the crown angiosperms to the Upper Triassic, with major angiosperm radiations occurring in the Jurassic and Lower Cretaceous. This estimated crown age is substantially earlier than that of unequivocal angiosperm fossils, and the difference is here termed the ‘Jurassic angiosperm gap’. Our time-calibrated plastid phylogenomic tree provides a highly relevant framework for future comparative studies of flowering plant evolution.

 

Celebrating Conrad Gesner Day 2017 (and Spiral Sunday #27)!

Gessner house Zurich March 2008 018

Happy Conrad Gesner Day!  Who is he, you may ask?  And why does he have a day?  Conrad Gesner (sometimes spelled Konrad Gessner) was a Swiss naturalist and polymath, born on this day (26th March) in 1516; he lived much of his life in Zurich, where he died on 13 December 1565.  Gesner was an extremely important figure in Renaissance science and scholarship, and when I visited Zurich in 2008 to give a seminar at the university, a tour of the old town revealed a number of references to the great man, including the memorial stone above.

Gesner’s Historia animalium (“History of Animals”)  is considered one of the founding texts of modern zoology, and for that reason he is memorialised in the name Gesneria Hübner, 1825; this is a genus of moths in the family Crambidae.

However Gesner was also a botanist and wrote a couple of books on the subject, though his Historia plantarum was not published until two centuries after his death.  To celebrate Gesner’s botanical achievements Linnaeus erected the genus Gesneria L. for a group of flowering plants.  Sounds odd to have the same name for two very different types of organism, but this cross-kingdom duplication of genera is allowable under the various codes of taxonomic nomenclature.

Gesneria in turn is the type genus for the family Gesneriaceae.  It’s quite a big family (about 3,450 species in 152 genera) and is ecologically important in the tropics and subtropics, where species may be pollinated by insects and birds, and are often epiphytic on trees.  It’s not a particularly economically important family, though a number of genera are widely grown as ornamentals, and there are specialist gesneriad growers and collectors.  The more familiar plants include those mainstays of Mothering Sunday (which by coincidence is also today) African Violets (Saintpaulia), Cape Primroses (Streptocarpus) and gloxinias (Gloxinia):

Gloxinias 20170325_105735

As I was looking through my photographs from the trip to Zurich in 2008 I spotted the following image of some wrought ironwork from the old city which may well be contemporary with Gesner.  This seems a fitting way to celebrate both the great man and this week’s Spiral Sunday:

Spirals in Zurich March 2008 119.png Happy Birthday Dr Gesner!

Dispelling the myth that orchid species usually only have a single pollinator

Orchids at Kew 2014-02-24 15.30.32

The idea that members of the plant family Orchidaceae (the orchids) “typically have exclusive relationships with their pollinators“, such that each orchid has only one pollinator, is a persistent one.  Recently I’ve encountered it on horticultural websites (follow that last link), in grant proposals, and on Wikipedia.

The problem is that it’s not true: it’s a myth that is perpetuated by people (often botanists or horticulturalists) who may know a lot about orchids but don’t know as much as they think they know about pollination ecology.

Orchids certainly have some fascinating and often quite intricate floral mechanisms to ensure pollination, but these have not necessarily evolved to attract and exploit just one species of pollinator.  Even in the case of sexually deceptive orchids that fool their (male) pollinating insects into believing that they are mating with a female of the same species, it is sometimes the case that more than one insect species is involved.  For example, in the well studied genus Ophrysflowers are pollinated by a narrow taxonomic range of pollinators, from a single species to up to five closely related species“.  As the authors of that last paper state, this is not the same as the mythological “extreme case of one orchid/one pollinator”.

Likewise different species of orchid bees may pollinate the same orchid flowers as they visit to collect scent compounds; for example in the Brazilian species Dichaea pendula, species from at least two different bee genera act as pollinators (Nunes et al. 2016).

The fact that “one orchid/one pollinator” is a myth is not new knowledge, it’s been widely discussed in the pollination ecology literature for decades.  For example, in our 1996 paper “Generalization in Pollination Systems, and Why it Matters” we showed data from the late 19th/early 20th centuries that clearly indicated a range of specialization in European orchids (follow that link and look at  Figure 3B).  Even earlier than this, in his 1992 paper “Trends in the pollination ecology of the Orchidaceae: evolution and systematics” Raymond Tremblay showed that only about 62% of species for which he could find data had a single pollinator, and that this varied considerably between different subfamilies of Orchidaceae, with some subfamilies being more specialized than others.

More recently, in a chapter in the 2006 book I co-edited with Nick Waser entitled “Geographical Variation in Diversity and Specificity of Pollination Systems” Steve Johnson, Andrew Hingston and myself looked at data from southern African compared to North American and European orchids; here’s the figure from that assessment:

 

Ollerton et al Figure 7 - JPEG

Orchids  are more specialized in southern Africa compared to Europe and North America (as are a number of other plant groups including the asclepiads, which we’re comparing them with here).  But even in southern Africa, only about 65% of the orchids studied have a single pollinator species.  It’s worth pointing out, though, that many of the species included in this analysis, and in Raymond Tremblay’s paper, have been studied only at single sites and often in single years, meaning that we have no idea if there is any spatio-temporal variation in the pollinators a particular orchid species exploits.

Why does this myth persist?  I think it’s for the same reason that myths are retold from generation to generation: they are great stories that fascinate the teller and the audience.  Indeed, orchids are very special plants with some amazing floral and vegetative adaptations, fascinating relationships with fungi, and incredible diversity.  But we don’t have to mythologise their relationships with their pollinators to try to make orchids more special than they already are.