Interactions between flowering plants and the animals that pollinate them are known to be responsible for part of the tremendous diversity of the angiosperms, currently thought to number at least 350,000 species. But the diversity of different types of pollination system (bird, bee, moth, fly, etc.) is unknown for most large, related groups of plants (what systematists term “clades”) such as families and subfamilies. In addition we know little about how these interactions with pollinators have evolved over time and in different parts of the world. Only a handful of groups of flowering plants have been studied with respect to questions such as:
How much do we currently know about the diversity of pollination systems in large clades?
How is that diversity partitioned between the smaller clades (e.g. subfamilies, tribes, genera) of a family, and what are the evolutionary transitions between the major groups of pollinators?
Do these pollination systems vary biogeographically across the clade’s range?
These sorts of questions have been addressed for the massive, globally distributed Apocynaceae (one of the top 10 or 11 largest angiosperm families with more than 5,300 species) in a study just published using a new database of pollinators of the family. What’s more, the work is open access and anyone can download a copy for free. Here’s the citation with a link to the paper:
Ollerton, J., Liede-Schumann, S., Endress, M E., Meve, U. et al. [75 authors in all] (2019) The diversity and evolution of pollination systems in large plant clades: Apocynaceae as a case study. Annals of Botany 123: 311–325
In this study we have shown that (among other things):
- The family is characterised by an enormous diversity of pollination systems involving almost all of the major pollen vectors and some that are nearly unique to the Apocynaceae.
- Earlier diverging clades have a narrower range of pollination systems than those that evolved later.
- Transitions from one type of pollination system to another are evolutionarily constrained, and rarely or never occur, whereas others have taken place much more often, e.g. between wasp and beetle pollination.
- There is significant convergent evolution of pollination systems, especially fly and moth pollination, by geographically and phylogenetically distinct clades.
You’ll notice that there are 75 (!) authors on this paper. That’s because we’ve pulled together a huge amount of previously unpublished data and used some state of the art analyses to produce this work. It was a monumental effort, especially considering that my colleague Sigrid Liede-Schumann and I only decided to push ahead with this project about a year ago when we chatted at the International Botanical Congress that I posted about at the time. In truth however the origins of this paper go back over 20 years to 1997 when when Sigrid and I published a study of what was then known about pollination systems in the Asclepiadaceae (the asclepiads).
In that paper we said that the research “is intended to be ongoing…[we]…hope to re-review asclepiad pollination within the next decade”. At the time I didn’t think it would actually take more than 20 years! However over that period a lot has changed. For one thing the Asclepiadaceae no longer exists, broken up and subsumed within a much larger Apocynaceae. Also, I’ve done a lot of work in the field and in the herbarium on some of the smaller groups within the family, such as Ceropegia. Others, including many of my co-authors, have also been working on different groups in various parts of the world. Finally the level of sophistication of the analyses we are now able to do has increased beyond recognition compared to what we could achieve in the mid-1990s. All of this means that now is the right time to produce this study.
Having said all of that, this is still a work in progress. Our Pollinators of Apocynaceae Database contains a sample of just over 10% of the species in the family. So lots more data on plant-pollinator interactions needs to be collected before we say we fully understand how pollination systems have evolved in this most remarkable family. I’d be happy to talk with anyone who is interested in the family and being involved in future data collection.
The database will be freely available to anyone who wants to use it – lots more can be done with this information and, once again, I’m happy to chat with potential collaborators.
I was recently interviewed about the study, and about plant-pollinator interactions and the Apocynaceae more generally, for the In Defense of Plants podcast – here’s a link to that interview.
Finally, I’d like to express my sincerest thanks to my co-authors on this study – I really couldn’t have done it without you guys!